draft-ietf-mmusic-file-transfer-mech-03.txt   draft-ietf-mmusic-file-transfer-mech-04.txt 
MMUSIC Working Group M. Garcia-Martin MMUSIC Working Group M. Garcia-Martin
Internet-Draft Nokia Siemens Networks Internet-Draft Nokia Siemens Networks
Intended status: Standards Track M. Isomaki Intended status: Standards Track M. Isomaki
Expires: December 7, 2007 Nokia Expires: April 26, 2008 Nokia
G. Camarillo G. Camarillo
S. Loreto S. Loreto
Ericsson Ericsson
June 5, 2007 October 24, 2007
A Session Description Protocol (SDP) Offer/Answer Mechanism to Enable A Session Description Protocol (SDP) Offer/Answer Mechanism to Enable
File Transfer File Transfer
draft-ietf-mmusic-file-transfer-mech-03.txt draft-ietf-mmusic-file-transfer-mech-04.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on December 7, 2007. This Internet-Draft will expire on April 26, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
This document provides a mechanism to negotiate the transfer of one This document provides a mechanism to negotiate the transfer of one
or more files between two endpoints by using the Session Description or more files between two endpoints by using the Session Description
Protocol (SDP) offer/answer model specified in RFC 3264. SDP is Protocol (SDP) offer/answer model specified in RFC 3264. SDP is
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Alternatives Considered . . . . . . . . . . . . . . . . . 5 1.1. Alternatives Considered . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7 4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
5. File selector . . . . . . . . . . . . . . . . . . . . . . . . 8 5. File selector . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Extensions to SDP . . . . . . . . . . . . . . . . . . . . . . 9 6. Extensions to SDP . . . . . . . . . . . . . . . . . . . . . . 9
7. File Disposition Types . . . . . . . . . . . . . . . . . . . . 14 7. File Disposition Types . . . . . . . . . . . . . . . . . . . . 15
8. Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 15 8. Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Offerer's Behavior . . . . . . . . . . . . . . . . . . . . 16 8.1. Offerer's Behavior . . . . . . . . . . . . . . . . . . . . 16
8.1.1. The Offerer is a File Sender . . . . . . . . . . . . . 16 8.1.1. The Offerer is a File Sender . . . . . . . . . . . . . 16
8.1.2. The Offerer is a File Receiver . . . . . . . . . . . . 17 8.1.2. The Offerer is a File Receiver . . . . . . . . . . . . 17
8.1.3. SDP Offer for Several Files . . . . . . . . . . . . . 18 8.1.3. SDP Offer for Several Files . . . . . . . . . . . . . 18
8.2. Answerer's Behavior . . . . . . . . . . . . . . . . . . . 18 8.2. Answerer's Behavior . . . . . . . . . . . . . . . . . . . 18
8.2.1. The Answerer is a File Receiver . . . . . . . . . . . 18 8.2.1. The Answerer is a File Receiver . . . . . . . . . . . 18
8.2.2. The Answerer is a File Sender . . . . . . . . . . . . 19 8.2.2. The Answerer is a File Sender . . . . . . . . . . . . 19
8.3. The 'file-transfer' attribute . . . . . . . . . . . . . . 20 8.3. The 'file-transfer-id' attribute . . . . . . . . . . . . . 20
8.4. Indicating File Transfer Offer/Answer Capability . . . . . 22 8.4. Indicating File Transfer Offer/Answer Capability . . . . . 22
8.5. Re-usage of Existing m= Lines in SDP . . . . . . . . . . . 22 8.5. Re-usage of Existing m= Lines in SDP . . . . . . . . . . . 23
8.6. MSRP Usage . . . . . . . . . . . . . . . . . . . . . . . . 23 8.6. MSRP Usage . . . . . . . . . . . . . . . . . . . . . . . . 23
8.7. Considerations about the 'file-icon' attribute . . . . . . 24 8.7. Considerations about the 'file-icon' attribute . . . . . . 24
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Offerer sends a file to the Answerer . . . . . . . . . . . 25 9.1. Offerer sends a file to the Answerer . . . . . . . . . . . 25
9.2. Offerer requests a file from the Answerer and second 9.2. Offerer requests a file from the Answerer and second
file transfer . . . . . . . . . . . . . . . . . . . . . . 29 file transfer . . . . . . . . . . . . . . . . . . . . . . 30
9.3. Example of a capability indication . . . . . . . . . . . . 36 9.3. Example of a capability indication . . . . . . . . . . . . 37
10. Security Considerations . . . . . . . . . . . . . . . . . . . 37 10. Security Considerations . . . . . . . . . . . . . . . . . . . 38
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
11.1. Registration of new SDP attributes . . . . . . . . . . . . 38 11.1. Registration of new SDP attributes . . . . . . . . . . . . 39
11.1.1. Registration of the file-selector attribute . . . . . 38 11.1.1. Registration of the file-selector attribute . . . . . 39
11.1.2. Registration of the file-transfer attribute . . . . . 38 11.1.2. Registration of the file-transfer-id attribute . . . . 40
11.1.3. Registration of the file-disposition attribute . . . . 38 11.1.3. Registration of the file-disposition attribute . . . . 40
11.1.4. Registration of the file-date attribute . . . . . . . 39 11.1.4. Registration of the file-date attribute . . . . . . . 40
11.1.5. Registration of the file-icon attribute . . . . . . . 39 11.1.5. Registration of the file-icon attribute . . . . . . . 41
11.1.6. Registration of the file-range attribute . . . . . . . 39 11.1.6. Registration of the file-range attribute . . . . . . . 41
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 39 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 41
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
13.1. Normative References . . . . . . . . . . . . . . . . . . . 40 13.1. Normative References . . . . . . . . . . . . . . . . . . . 41
13.2. Informational References . . . . . . . . . . . . . . . . . 41 13.2. Informational References . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
Intellectual Property and Copyright Statements . . . . . . . . . . 43 Intellectual Property and Copyright Statements . . . . . . . . . . 45
1. Introduction 1. Introduction
The Session Description Protocol (SDP) Offer/Answer [RFC3264] The Session Description Protocol (SDP) Offer/Answer [RFC3264]
provides a mechanism for two endpoints to arrive at a common view of provides a mechanism for two endpoints to arrive at a common view of
a multimedia session between them. These sessions often contain a multimedia session between them. These sessions often contain
real-time media streams such as voice and video, but are not limited real-time media streams such as voice and video, but are not limited
to that. Basically, any media component type can be supported, as to that. Basically, any media component type can be supported, as
long as there is a specification how to negotiate it within the SDP long as there is a specification how to negotiate it within the SDP
offer/answer exchange. offer/answer exchange.
The Message Session Relay Protocol (MSRP) The Message Session Relay Protocol (MSRP) [RFC4975] is a protocol for
[I-D.ietf-simple-message-sessions] is a protocol for transmitting transmitting instant messages (IM) in the context of a session. The
instant messages (IM) in the context of a session. The protocol protocol specification describes the usage of SDP for establishing a
specification includes a description how to use it with SDP. In MSRP sessions. In addition to plain text messages, MSRP is able to
addition to plain text messages, MSRP is able to carry arbitrary carry arbitrary (binary) Multipurpose Internet Mail Extensions (MIME)
(binary) Multipurpose Internet Mail Extensions (MIME) [RFC2045] [RFC2045] compliant content, such as images or video clips.
compliant content, such as images or video clips.
There are many cases where the endpoints involved in a multimedia There are many cases where the endpoints involved in a multimedia
session would like to exchange files within the context of that session would like to exchange files within the context of that
session. With MSRP it is possible to embed files as MIME objects session. With MSRP it is possible to embed files as MIME objects
inside the stream of instant messages. MSRP also has other features inside the stream of instant messages. MSRP also has other features
that are useful for file transfer. Message chunking enables the that are useful for file transfer. Message chunking enables the
sharing of the same transport connection between the transfer of a sharing of the same transport connection between the transfer of a
large file and interactive IM exchange without blocking the IM. MSRP large file and interactive IM exchange without blocking the IM. MSRP
relays [I-D.ietf-simple-msrp-relays] provide a mechanism for Network relays [RFC4976] provide a mechanism for Network Address Translator
Address Translator (NAT) traversal. Finally, Secure MIME (S/MIME) (NAT) traversal. Finally, Secure MIME (S/MIME) [RFC3851] can be used
[RFC3851] can be used for ensuring the integrity and confidentiality for ensuring the integrity and confidentiality of the transferred
of the transfered content. content.
However, the baseline MSRP does not readily meet all the requirements However, the baseline MSRP does not readily meet all the requirements
for file transfer services within multimedia sessions. There are for file transfer services within multimedia sessions. There are
four main missing features: four main missing features:
o The recipient MUST be able to distinguish "file transfer" from o The recipient must be able to distinguish "file transfer" from
"file attached to IM", allowing the recipient to treat the cases "file attached to IM", allowing the recipient to treat the cases
differently. differently.
o It MUST be possible for the sender to send the request for a file o It must be possible for the sender to send the request for a file
transfer. It MUST be possible for the recipient to accept or transfer. It must be possible for the recipient to accept or
decline it, using the meta information in the request. The actual decline it, using the meta information in the request. The actual
transfer MUST take place only after acceptance by the recipient. transfer must take place only after acceptance by the recipient.
o It MUST be possible for the sender to pass some meta information o It must be possible for the sender to pass some meta information
on the file before the actual transfer. This MUST be able to on the file before the actual transfer. This must be able to
include at least content type, size, hash and name of the file, as include at least content type, size, hash and name of the file, as
well as a short (human readable) description. well as a short (human readable) description.
o It MUST be possible for the recipient to request a file from the o It must be possible for the recipient to request a file from the
sender, providing meta information about the file. The sender sender, providing meta information about the file. The sender
MUST be able to decide whether to send a file matching the must be able to decide whether to send a file matching the
request. request.
The rest of this document is organized as follows. Section 3 defines The rest of this document is organized as follows. Section 3 defines
a few terms used in this document. Section 4 provides the overview a few terms used in this document. Section 4 provides the overview
of operation. Section 5 introduces the concept of the file selector. of operation. Section 5 introduces the concept of the file selector.
The detailed syntax and semantics of the new SDP attributes and The detailed syntax and semantics of the new SDP attributes and
conventions on how the existing ones are used is defined in conventions on how the existing ones are used is defined in
Section 6. Section 7 discusses the file disposition types. Section 6. Section 7 discusses the file disposition types.
Section 8 describes the protocol operation involving SDP and MSRP. Section 8 describes the protocol operation involving SDP and MSRP.
Section 8.4 describes the mechanism whereby a user can learn the Finally, some examples are given in Section 9.
support for the functionality described in this specification at a
remote endpoint. Finally, some examples are given in Section 9.
1.1. Alternatives Considered 1.1. Alternatives Considered
The requirements are related to the description and negotiation of The requirements are related to the description and negotiation of
the session, not to the actual file transfer mechanism. Thus, it is the session, not to the actual file transfer mechanism. Thus, it is
natural that in order to meet them it is enough to define attribute natural that in order to meet them it is enough to define attribute
extensions and usage conventions to SDP, while MSRP itself needs no extensions and usage conventions to SDP, while MSRP itself needs no
extensions and can be used as it is. This is effectively the extensions and can be used as it is. This is effectively the
approach taken in this specification. Another goal has been to approach taken in this specification. Another goal has been to
specify the SDP extensions in such a way that a regular MSRP endpoint specify the SDP extensions in such a way that a regular MSRP endpoint
which does not support them could still in some cases act as an which does not support them could still in some cases act as an
endpoint in a file transfer session, albeit with a somewhat reduced endpoint in a file transfer session, albeit with a somewhat reduced
functionality. functionality.
In some ways the aim of this specification is similar to the aim of In some ways the aim of this specification is similar to the aim of
content indirection mechanism in the Session Initiation Protocol content indirection mechanism in the Session Initiation Protocol
(SIP) [RFC4483]. Both mechanisms allow a user agent to decide (SIP) [RFC4483]. Both mechanisms allow a user agent to decide
whether or not to download a file based on information about the whether or not to download a file based on information about the
file. However, there are some differences. With content file. However, there are some differences. With content
indirection, it is not possible for the other endpoint to explicitly indirection, it is not possible for the other endpoint to explicitly
accpet or reject the file transfer. Also, it is not possible for an accept or reject the file transfer. Also, it is not possible for an
endpoint to request a file from another endpoint. Furthermore, endpoint to request a file from another endpoint. Furthermore,
content indirection is not tied to the context of a media session, content indirection is not tied to the context of a media session,
which is sometimes a desirable property. Finally, content which is sometimes a desirable property. Finally, content
indirection typically requires some server infrastructure, which may indirection typically requires some server infrastructure, which may
not always be available. (It is possible to use content indirection not always be available. It is possible to use content indirection
directly between the endpoints too, but in that case there is no directly between the endpoints too, but in that case there is no
definition for how it works for endpoints behind NATs.) definition for how it works for endpoints behind NATs. The level of
requirements in implementations decides which solution meets the
requirements.
Based on the argumentation above, this document defines the SDP Based on the argumentation above, this document defines the SDP
attribute extensions and usage conventions needed for meeting the attribute extensions and usage conventions needed for meeting the
requirements on file transfer services with the SDP offer/answer requirements on file transfer services with the SDP offer/answer
model, using MSRP as the transfer protocol within the session. model, using MSRP as the transfer protocol within the session.
In principle it is possible to use the SDP extensions defined here In principle it is possible to use the SDP extensions defined here
and replace MSRP with any other similar protocol that can carry and replace MSRP with any other similar protocol that can carry
MIME objects. This kind of specification can be written as a MIME objects. This kind of specification can be written as a
separate document if the need arises. separate document if the need arises. Essentially, such protocol
should be able to be negotiated on an SDP offer/answer exchange
(RFC 3264 [RFC3264]), be able to carry MIME objects between two
endpoints, and use a reliable transport protocol (e.g., TCP).
This specification defines a set of SDP attributes that describe a This specification defines a set of SDP attributes that describe a
file to be transfered between two endpoits. The information needed file to be transferred between two endpoints. The information needed
to describe a file could be potentially encoded in a few different to describe a file could be potentially encoded in a few different
ways. The MMUSIC working group considered a few alternative ways. The MMUSIC working group considered a few alternative
approaches before deciding to use the encoding described in approaches before deciding to use the encoding described in
Section 6. In particular, the working group looked at the MIME Section 6. In particular, the working group looked at the MIME
'external-body' type and the use of a single SDP attribute or 'external-body' type and the use of a single SDP attribute or
parameter. parameter.
A MIME 'external-body' could potentially be used to describe the file A MIME 'external-body' could potentially be used to describe the file
to be transfered. In fact, many of the SDP parameters this to be transferred. In fact, many of the SDP parameters this
specification defines are also supported by 'external-body' body specification defines are also supported by 'external-body' body
parts. The MMUSIC working group decided not to use 'external-body' parts. The MMUSIC working group decided not to use 'external-body'
body parts because a number of existing offer/answer implementations body parts because a number of existing offer/answer implementations
do not support multipart bodies. do not support multipart bodies.
The information carried in the SDP attributes defined in Section 6 The information carried in the SDP attributes defined in Section 6
could potentially be encoded in a single SDP attribute. The MMUSIC could potentially be encoded in a single SDP attribute. The MMUSIC
working group decided not to follow this approach because it is working group decided not to follow this approach because it is
expected that implementations support only a subset of the parameters expected that implementations support only a subset of the parameters
defined in Section 6. Those implementations will be able to use defined in Section 6. Those implementations will be able to use
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role of the file sender. role of the file sender.
4. Overview of Operation 4. Overview of Operation
An SDP offerer creates an SDP body that contains the description of An SDP offerer creates an SDP body that contains the description of
one or more files that the offerer wants to send or receive. The one or more files that the offerer wants to send or receive. The
offerer sends the SDP offer to the remote endpoint. The SDP answerer offerer sends the SDP offer to the remote endpoint. The SDP answerer
can accept or reject the transfer of each of those files. can accept or reject the transfer of each of those files.
The actual file transfer is carried out using the Message Session The actual file transfer is carried out using the Message Session
Relay Protocol (MSRP) [I-D.ietf-simple-message-sessions]. Each SDP Relay Protocol (MSRP) [RFC4975]. Each SDP "m=" line describes an
"m=" line describes an MSRP media stream used to transfer a single MSRP media stream used to transfer a single file at a time. That is,
file. That is, the transfer of multiple simultaneous files requires the transfer of multiple simultaneous files requires multiple "m="
multiple "m=" lines and corresponding MSRP media streams. It should lines and corresponding MSRP media streams. It should be noted that
be noted that multiple MSRP media streams can share a single multiple MSRP media streams can share a single transport layer
transport layer connection, so this mechanism will not lead to connection, so this mechanism will not lead to excessive use of
excessive use of transport resources. transport resources.
Each "m=" line for an MSRP media stream is accompanied with a few Each "m=" line for an MSRP media stream is accompanied with a few
attributes describing the file to be transferred. If the file sender attributes describing the file to be transferred. If the file sender
generates the SDP offer, the attributes describe a local file to be generates the SDP offer, the attributes describe a local file to be
sent (push), and the file receiver can use this information to either sent (push), and the file receiver can use this information to either
accept or reject the transfer. However, if the SDP offer is accept or reject the transfer. However, if the SDP offer is
generated by the file receiver, the attributes are intended to generated by the file receiver, the attributes are intended to
characterize a particular file that the file receiver is willing to characterize a particular file that the file receiver is willing to
get (pull) from the file sender. It is possible that the file sender get (pull) from the file sender. It is possible that the file sender
does not have a matching file or does not want to send the file, in does not have a matching file or does not want to send the file, in
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The attributes describing each file are provided in SDP by a set of The attributes describing each file are provided in SDP by a set of
new SDP attributes, most of which have been directly borrowed from new SDP attributes, most of which have been directly borrowed from
MIME. This way, user agents can decide whether or not to accept a MIME. This way, user agents can decide whether or not to accept a
given file transfer based on the file's name, size, description, given file transfer based on the file's name, size, description,
hash, icon (e.g., if the file is a picture), etc. hash, icon (e.g., if the file is a picture), etc.
SDP direction attributes (e.g., 'sendonly', 'recvonly') are used to SDP direction attributes (e.g., 'sendonly', 'recvonly') are used to
indicate the direction of the transfer, i.e., whether the SDP offerer indicate the direction of the transfer, i.e., whether the SDP offerer
is willing to send of receive the file. Assuming that the answerer is willing to send of receive the file. Assuming that the answerer
accepts the file transfer, the actual transfer of the files takes accepts the file transfer, the actual transfer of the files takes
place with ordinary MSRP. place with ordinary MSRP. Note that the 'sendonly' and 'recvonly'
attributes refer to the direction of MSRP SEND requests and do not
preclude other protocol elements (such as 200 responses, REPORT
requests, etc.).
In principle the file transfer can work even with an endpoint In principle the file transfer can work even with an endpoint
supporting only regular MSRP without understanding the extensions supporting only regular MSRP without understanding the extensions
defined herein, in a special case where that endpoint is the defined herein, in a special case where that endpoint is the
recipient of the file. The regular MSRP endpoint answers the recipient of the file. The regular MSRP endpoint answers the
offer as it would answer any ordinary MSRP offer without paying offer as it would answer any ordinary MSRP offer without paying
attention to the extension attributes. In such a scenario the attention to the extension attributes. In such a scenario the
user experience would however be reduced, as the recipient would user experience would however be reduced, as the recipient would
not know (by any protocol means) the reason for the session and not know (by any protocol means) the reason for the session and
would not be able to accept/reject it based on the file would not be able to accept/reject it based on the file
attributes. attributes.
5. File selector 5. File selector
Specially in case the SDP offer is generated by the file receiver, Specially in case the SDP offer is generated by the file receiver,
the offer needs a mechanism to unambiguously identify the requested the offer needs a mechanism to unambiguously identify the requested
file. For this purpose, the file transfer mechanism introduces the file. For this purpose, the file transfer mechanism introduces the
concept of a file selector, which is defined as the combination of notion of a file selector, which is defined as the combination of the
the 4-tuple composed of the name, size, type, and hash of the file. 4-tuple composed of the name, size, type, and hash of the file. We
We call each of these individual items a selector. The file selector call each of these individual items a selector. The file selector
can be composed of any number of selectors, so, it does not require can be composed of any number of selectors, so, it does not require
that all four selectors are present at the same time. that all four selectors are present at the same time.
The purpose of the file selector is to provide enough information The purpose of the file selector is to provide enough information
that characterizes a file to the remote entity, so that both the that characterizes a file to the remote entity, so that both the
local and the remote entity can refer to the same file. The file local and the remote entity can refer to the same file. The file
selector is encoded in a 'file-selector' media attribute in SDP. The selector is encoded in a 'file-selector' media attribute in SDP. The
formal syntax of the 'file-selector' media attribute is described in formal syntax of the 'file-selector' media attribute is described in
Figure 1. Figure 1.
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file selector can point to zero, one, or more files, depending on the file selector can point to zero, one, or more files, depending on the
presence of the mentioned selectors in the SDP and depending on the presence of the mentioned selectors in the SDP and depending on the
available files in a host. The file transfer mechanism specified in available files in a host. The file transfer mechanism specified in
this document requires that a file selector eventually results at this document requires that a file selector eventually results at
most in a single file to be chosen. Typically, if the hash selector most in a single file to be chosen. Typically, if the hash selector
is known, it is enough to produce a file selector that points to is known, it is enough to produce a file selector that points to
exactly zero or one file. However, a file selector that selects a exactly zero or one file. However, a file selector that selects a
unique file is not always known by the offerer. Sometimes only the unique file is not always known by the offerer. Sometimes only the
name, size or type of file are known, so the file selector may result name, size or type of file are known, so the file selector may result
in selecting more than one file, which is an undesired case. The in selecting more than one file, which is an undesired case. The
opposite is also true: if the file selector contains a hash and a opposite is also true: if the file selector contains a hash selector
name selectors, there is a risk that the remote host has renamed the and a name selector, there is a risk that the remote host has renamed
file, in which case, although a file whose computed hash equals the the file, in which case, although a file whose computed hash equals
hash selector exists, the file name does not match that of the name the hash selector exists, the file name does not match that of the
selector, thus, the file selection process will result in the name selector, thus, the file selection process will result in the
selection of zero files. selection of zero files.
Since there are several hashing algorithms, such as SHA-1 [RFC3174], This specification uses the Secure Hash Algorithm 1, SHA-1 [RFC3174].
SHA-256, SHA-384, SHA-512 [RFC4634], etc., a file selector MAY If future needs require adding support for different hashing
contain several hashes, each one describing the hash of the file with algorithms, they will be specified as extensions to this document.
a different hashing algorithm. Implementations that make use of the
hash SHOULD select one among the supported hashes before selecting a
file. So, when several hashes are present in the SDP, the file
selector consists of the union of the name, size, type, and any of
the supported hash algorithms.
Implementations according to this specification MUST implement the Implementations according to this specification MUST implement the
'file-selector' attribute and MAY implement any of the other 'file-selector' attribute and MAY implement any of the other
attributes specified in this specification. SDP offers and answers attributes specified in this specification. SDP offers and answers
for file transfer MUST contain a 'file-selector' media attribute that for file transfer MUST contain a 'file-selector' media attribute that
selects the file to be transferred and MAY contain any of the other selects the file to be transferred and MAY contain any of the other
attributes specified in this specification. attributes specified in this specification.
The 'file-selector' media attribute is also useful when learning the The 'file-selector' media attribute is also useful when learning the
support of the file transfer offer/answer capability that this support of the file transfer offer/answer capability that this
document specifies. This is further explained in Section 8.4. document specifies. This is further explained in Section 8.4.
6. Extensions to SDP 6. Extensions to SDP
We define a number of new SDP [RFC4566] attributes that provide the We define a number of new SDP [RFC4566] attributes that provide the
required information to describe the transfer of a file with MSRP. required information to describe the transfer of a file with MSRP.
These are all media level only attributes in SDP. The following is These are all media level only attributes in SDP. The following is
the formal ABNF syntax [RFC4234] of these new attributes. It is the formal ABNF syntax [RFC4234] of these new attributes. It is
built above the SDP [RFC4566] grammar, RFC 2045 [RFC2045], RFC 2183 built above the SDP [RFC4566] grammar, RFC 2045 [RFC2045], RFC 2183
[RFC2183], and RFC 2392 [RFC2392]. [RFC2183], RFC 2392 [RFC2392], and RFC 2822 [RFC2822].
attribute = file-selector-attr / file-disp-attr / attribute = file-selector-attr / file-disp-attr /
file-date-attr / file-icon-attr / file-tr-id-attr / file-date-attr /
file-range-attr file-icon-attr / file-range-attr
;attribute is defined in RFC 4566 ;attribute is defined in RFC 4566
file-selector-attr = "file-selector" [":" selector *(SP selector)] file-selector-attr = "file-selector" [":" selector *(SP selector)]
selector = filename-selector / filesize-selector / selector = filename-selector / filesize-selector /
filetype-selector / hash-selector filetype-selector / hash-selector
filename-selector = "name:" DQUOTE filename-string DQUOTE filename-selector = "name:" DQUOTE filename-string DQUOTE
; DQUOTE defined in RFC 4234 ; DQUOTE defined in RFC 4234
filename-string = 1*(%x01-09/%x0B-0C/%x0E-21/%x23-FF) filename-string = 1*(filename-char/percent-encoded)
;any byte except NUL, CR, LF, or double quotes filename-char = %x01-09/%x0B-0C/%x0E-21/%x23-24/%26-FF)
;any byte except NUL, CR, LF,
;double quotes, or percent
percent-encoded = "%" HEXDIG HEXDIG
; HEXDIG defined in RFC 4234
filesize-selector = "size:" filesize-value filesize-selector = "size:" filesize-value
filesize-value = integer ;integer defined in RFC 4566 filesize-value = integer ;integer defined in RFC 4566
filetype-selector = "type:" type "/" subtype *(";"parameter) filetype-selector = "type:" type "/" subtype *(";"parameter)
; parameter defined in RFC 2045 ; parameter defined in RFC 2045
type = token type = token ; token defined in RFC 4566
subtype = token subtype = token
hash-selector = "hash:" hash-algorithm ":" hash-value hash-selector = "hash:" hash-algorithm ":" hash-value
hash-algorithm = token ;see IANA Hash Function hash-algorithm = token ;see IANA Hash Function
;Textual Names registry ;Textual Names registry
hash-value = 2UHEX *(":" 2UHEX) ;only "sha-1" currently supported
hash-value = 2HEXDIG *(":" 2HEXDIG)
; Each byte in upper-case hex, separated ; Each byte in upper-case hex, separated
; by colons. ; by colons.
; HEXDIG defined in RFC 4234
file-transfer = "file-transfer:" file-transfer-value file-tr-id-attr = "file-transfer-id:" file-transfer-id-value
file-transfer-value = "new" / "existing" / token file-transfer-value = token
file-disp-attr = "file-disposition:" file-disp-value file-disp-attr = "file-disposition:" file-disp-value
file-disp-value = token file-disp-value = token
file-date = "file-date:" date-param *(SP date-param) file-date-attr = "file-date:" date-param *(SP date-param)
date-param = c-date-param / m-date-param / r-date-param date-param = c-date-param / m-date-param / r-date-param
c-date-param = "creation:" DQUOTE date-time DQUOTE c-date-param = "creation:" DQUOTE date-time DQUOTE
m-date-param = "modification:" DQUOTE date-time DQUOTE m-date-param = "modification:" DQUOTE date-time DQUOTE
r-date-param = "read:" DQUOTE date-time DQUOTE r-date-param = "read:" DQUOTE date-time DQUOTE
; date-time is defined in RFC 2822 ; date-time is defined in RFC 2822
; numeric timezones (+HHMM or -HHMM) ; numeric timezones (+HHMM or -HHMM)
; must be used ; must be used
; DQUOTE defined in RFC 4234 ; DQUOTE defined in RFC 4234 files.
file-icon-attr = "file-icon:" file-icon-value file-icon-attr = "file-icon:" file-icon-value
file-icon-value = cid-url ;cid-url defined in RFC 2392 file-icon-value = cid-url ;cid-url defined in RFC 2392
file-range-attr = "file-range:" start-range "-" end-range
start-range = integer ;integer defined in RFC 4566
end-range = integer / "*"
file-range-attr = "file-range:" integer "-" integer
;integer defined in RFC 4566
Figure 1: Syntax of the SDP extension Figure 1: Syntax of the SDP extension
When used for capability query (see Section 8.4), the 'file-selector' When used for capability query (see Section 8.4), the 'file-selector'
attribute MUST NOT not contain any selector, because its presence attribute MUST NOT contain any selector, because its presence merely
merely indicates compliance to this specification. indicates compliance to this specification.
When used in an SDP offer or answer, the 'file-selector' attribute When used in an SDP offer or answer, the 'file-selector' attribute
MUST contain at least one selector. Selectors parametrize the file MUST contain at least one selector. Selectors characterize the file
to be transferred. There are four selectors in this attribute: to be transferred. There are four selectors in this attribute:
'name', 'size', 'type', and 'hash'. 'name', 'size', 'type', and 'hash'.
The 'name' selector in the 'file-selector' attribute contains the The 'name' selector in the 'file-selector' attribute contains the
filename of the content enclosed in double quotes. The filename is filename of the content enclosed in double quotes. The filename is
encoded in UTF-8 [RFC3629]. Its value SHOULD be the same as the encoded in UTF-8 [RFC3629]. Its value SHOULD be the same as the
'filename' parameter of the Content-Disposition header field 'filename' parameter of the Content-Disposition header field
[RFC2183] that could be signalled by the actual file transfer. If a [RFC2183] that would be signaled by the actual file transfer. If a
file name contains double quotes, they MUST be percent-encoded. The file name contains double quotes or any other character that the
'name' selector MUST not contain characters that can be interpreted syntax does not allow in the 'name' selector, they MUST be percent-
as directory structure by the local operating system. If such encoded. The 'name' selector MUST not contain characters that can be
characters are present in the file name, they MUST be percent- interpreted as directory structure by the local operating system. If
such characters are present in the file name, they MUST be percent-
encoded. encoded.
Note that the 'name' selector might still contain characters that, Note that the 'name' selector might still contain characters that,
although not meaningful for the local operating system, might although not meaningful for the local operating system, might
still be meaningful to the remote operating system (e.g., '\', still be meaningful to the remote operating system (e.g., '\',
'/', ':'). Therefore, implementations are responsible for '/', ':'). Therefore, implementations are responsible for
sanitizing the input received from the remote endpoint before sanitizing the input received from the remote endpoint before
doing a local operation, such as the creation of a local file. doing a local operation in the local file system, such as the
Among other things, implementations can percent-encode characters creation of a local file. Among other things, implementations can
that are meaningful to the local operating system before doing percent-encode characters that are meaningful to the local
file system local calls. operating system before doing file system local calls.
The 'size' selector in the 'file-selector' attribute indicates the The 'size' selector in the 'file-selector' attribute indicates the
size of the file in octets. The value of this attribute SHOULD be size of the file in octets. The value of this attribute SHOULD be
the same as the 'size' parameter of the Content-Disposition header the same as the 'size' parameter of the Content-Disposition header
field [RFC2183] that could be signalled by the actual file transfer. field [RFC2183] that would be signaled by the actual file transfer.
Note that the 'size' selector merely includes the file size, and does Note that the 'size' selector merely includes the file size, and does
not include any potential overhead added by a wrapper, such as not include any potential overhead added by a wrapper, such as
message/cpim. message/cpim [RFC3862].
The 'type' selector in the 'file-selector' attribute contains the The 'type' selector in the 'file-selector' attribute contains the
MIME media type of the content. In general, anything that can be MIME media and submedia types of the content. In general, anything
expressed in a Content-Type header field (see RFC 2045 [RFC2045]) can that can be expressed in a Content-Type header field (see RFC 2045
also be expressed with the 'type' selectors. Possible MIME Media [RFC2045]) can also be expressed with the 'type' selectors. Possible
Type values are the ones listed in the IANA registry for MIME Media MIME Media Type values are the ones listed in the IANA registry for
Types [1]. Zero or more parameters can follow. The syntax of MIME Media Types [1]. Zero or more parameters can follow. The
'parameter' is specified in RFC 2045 [RFC2045] . syntax of 'parameter' is specified in RFC 2045 [RFC2045] .
The 'hash' selector in the 'file-selector' attribute provides a hash The 'hash' selector in the 'file-selector' attribute provides a hash
computation of the file to be transferred. This is commonly used by computation of the file to be transferred. This is commonly used by
file transfer protocols. For example, FLUTE file transfer protocols. For example, FLUTE
[I-D.ietf-rmt-flute-revised] uses hashes (called message digests) to [I-D.ietf-rmt-flute-revised] uses hashes (called message digests) to
verify the contents of the transfer. The purpose of the 'hash' verify the contents of the transfer. The purpose of the 'hash'
selector is two-fold: On one side, in pull operations, it allows the selector is two-fold: On one side, in pull operations, it allows the
file receiver to identify a remote file by its hash rather than by file receiver to identify a remote file by its hash rather than by
its file name, providing that the file receiver has learned the hash its file name, providing that the file receiver has learned the hash
of the remote file by some out-of-band mechanism. On the other side, of the remote file by some out-of-band mechanism. On the other side,
in either push or pull operations, it allows the file sender to in either push or pull operations, it allows the file receiver to
provide the hash of the file to be transmitted, which can be used by verify the contents of the received file, or even avoid unnecessary
the file receiver for verification of its contents or to avoid the transmission of an existing file.
unnecessary transmission of a file that already exists.
The 'file-transfer' attribute provides a mechanism for distinguishing The address space of the SHA-1 algorithm is big enough to avoid
new file transfers from existing ones. A new file transfer is one any collision in hash computations in between two endpoints. When
that, in case of acceptance, will provoke the transfer of a file. transferring files, the actual file transfer protocol should
This is typically the case of new INVITE requests. On the contrary, provide reliable transmission of data, so verifications of
an existing file transfer is one that is declared in the SDP, but received files should always succeed. However, if endpoints need
does not lead to any file to be transferred, potentially because the to protect the integrity of a file, they should use some other
file transfer is still going on or because it has already finished. mechanism than the 'hash' selector specified in this memo.
This is the case of a re-INVITE request, which can be due to a number
of reasons (session timer, addition/removal of other media types in
the SDP, update in SDP due to changes in other session parameters,
etc.). Implementations according to this specification MUST include
a 'file-transfer' attribute in SDP answers and offers. The 'file-
transfer' attribute can take any of two values: "new" or "existing".
The "new" value indicates that a file transfer will start once the
SDP negotiation is successfully concluded. The "existing" value
indicates that the file transfer MUST NOT start at the end of the SDP
negotiation. Section 8 and Section 8.3 provide further details.
The 'hash' selector includes the hash algorithm and its value. In The 'hash' selector includes the hash algorithm and its value.
fact, since there are several hashing algorithms, the 'file-selector' Possible hash algorithms are those defined in the IANA registry of
attribute in SDP MAY contain several 'hash' selectors with different Hash Function Textual Names [2]. Implementations according to this
algorithms. Possible hash algorithms are those defined in the IANA specification MUST support the US Secure Hash Algorithm 1 (SHA1)
registry of Hash Function Textual Names [2]. Implementations [RFC3174]. If need arises, extensions can be drafted to support
according to this specification MUST support the US Secure Hash several hashing algorithms. Therefore, implementations according to
Algorithm 1 (SHA1) [RFC3174] and MAY support other hashing this specification MUST be prepared to receive SDP containing more
algorithms. The value is the byte string resulting of applying the than a single 'hash' selector in the 'file-selector' attribute.
hash algorithm to the content of the whole file.
The value of the 'hash' selector is the byte string resulting of
applying the hash algorithm to the content of the whole file, even
when the file transfer is limited to a number of octets (i.e., the
'file-range' attribute is indicated).
The 'file-transfer-id' attribute provides a unique identification to
the actual file transfer. It is used to distinguish a new file
transfer request from a repetition of the SDP (or the fraction of the
SDP that deals with the file description). This attribute is
described in much greater detail in Section 8.3.
The 'file-disposition' attribute provides a suggestion to the other The 'file-disposition' attribute provides a suggestion to the other
endpoint about the intended disposition of the file. Section 7 endpoint about the intended disposition of the file. Section 7
provides further discussion of the possible values. The value of provides further discussion of the possible values. The value of
this attribute SHOULD be the same of the disposition type parameter this attribute SHOULD be the same as the disposition type parameter
of the Content-Disposition header field [RFC2183] that could be of the Content-Disposition header field [RFC2183] that would be
signalled by the actual file transfer protocol. signaled by the actual file transfer protocol.
The 'file-date' attribute indicates the dates at which the file was The 'file-date' attribute indicates the dates at which the file was
created, modified, or last read. This attribute MAY contain a created, modified, or last read. This attribute MAY contain a
combination of the 'creation', 'modification', and 'read' parameters. combination of the 'creation', 'modification', and 'read' parameters,
Only one parameter of each type (creation, modification, or read) but MUST NOT contain more than one of each type .
MUST be present in a 'file-date' attribute.
The 'creation' parameter indicates the date at which the file was The 'creation' parameter indicates the date at which the file was
created. The value MUST be a quoted string which contains a created. The value MUST be a quoted string which contains a
representation of the creation date of the file in RFC 2822 [RFC2822] representation of the creation date of the file in RFC 2822 [RFC2822]
'date-time' format. Numeric timezones (+HHMM or -HHMM) MUST be used. 'date-time' format. Numeric timezones (+HHMM or -HHMM) MUST be used.
The value of this parameter SHOULD be the same as the 'creation-date' The value of this parameter SHOULD be the same as the 'creation-date'
parameter of the Content-Disposition header field [RFC2183] that parameter of the Content-Disposition header field [RFC2183] that
could be signalled by the actual file transfer protocol. would be signaled by the actual file transfer protocol.
The 'modification' parameter indicates the date at which the file was The 'modification' parameter indicates the date at which the file was
last modified. The value MUST be a quoted string which contains a last modified. The value MUST be a quoted string which contains a
representation of the last modification date to the file in RFC 2822 representation of the last modification date to the file in RFC 2822
[RFC2822] 'date-time' format. Numeric timezones (+HHMM or -HHMM) [RFC2822] 'date-time' format. Numeric timezones (+HHMM or -HHMM)
MUST be used. The value of this parameter SHOULD be the same as the MUST be used. The value of this parameter SHOULD be the same as the
'modification-date' parameter of the Content-Disposition header field 'modification-date' parameter of the Content-Disposition header field
[RFC2183] that could be signalled by the actual file transfer [RFC2183] that would be signaled by the actual file transfer
protocol. protocol.
The 'read' parameter indicates the date at which the file was last The 'read' parameter indicates the date at which the file was last
read. The value MUST be a quoted string which contains a read. The value MUST be a quoted string which contains a
representation of the last date the file was read in RFC 2822 representation of the last date the file was read in RFC 2822
[RFC2822] 'date-time' format. Numeric timezones (+HHMM or -HHMM) [RFC2822] 'date-time' format. Numeric timezones (+HHMM or -HHMM)
MUST be used. The value of this parameter SHOULD be the same as the MUST be used. The value of this parameter SHOULD be the same as the
'read-date' parameter of the Content-Disposition header field 'read-date' parameter of the Content-Disposition header field
[RFC2183] that could be signalled by the actual file transfer [RFC2183] that would be signaled by the actual file transfer
protocol. protocol.
The 'file-icon' attribute can be useful with certain file types such The 'file-icon' attribute can be useful with certain file types such
as images. It allows the sender to include a pointer to a body that as images. It allows the file sender to include a pointer to a body
includes a small preview icon representing the contents of the file that includes a small preview icon representing the contents of the
to be transferred. This allows the sender to include the icon as file to be transferred, which the file receiver can use to determine
another body accompanying the SDP, and to the recipient to get the whether it wants to receive such file. The 'file-icon' attribute
icon of the file to be transferred. The 'file-icon' attribute
contains a Content-ID URL, which is specified in RFC 2392 [RFC2392]. contains a Content-ID URL, which is specified in RFC 2392 [RFC2392].
Section 8.7 contains further considerations about the 'file-icon' Section 8.7 contains further considerations about the 'file-icon'
attribute. attribute.
The 'file-range' attribute provides a mechanism to signal a chunk of The 'file-range' attribute provides a mechanism to signal a chunk of
a file rather than the complete file. This enable use cases where a a file rather than the complete file. This enable use cases where a
file transfer can be interrupted, resumed, even perhaps changing one file transfer can be interrupted, resumed, even perhaps changing one
of the endpoints. The 'file-range' attribute is composed to two of the endpoints. The 'file-range' attribute contains the start
integer values separated by a dash "-". The first integer value range and end range of the file, separated by a dash "-". The start
refers to the first byte of the file to be transferred. The second range value refers to the position of the file where the file
integer value refers to the last byte of the file to be transferred. transfer should start. The first byte of a file gets the ordinal
The first byte of a file is indicated with "1". The absence of this number "1". The end range value refers position of the file where
attribute indicates a complete file, i.e., like if the 'file-range' the file transfer should stop. The end range value MAY contain a "*"
attribute would have been present with values 1-<size_of_file>. The if the total size of the file is not known in advance. The absence
of this attribute indicates a complete file, i.e., as if the 'file-
range' attribute would have been present with a value 1-*. The
'file-range' attribute must not be confused with the Byte-Range 'file-range' attribute must not be confused with the Byte-Range
header in MSRP. The former indicates the portion of a file that the header in MSRP. The former indicates the portion of a file that the
application would read and pass onto the MSRP stack for application would read and pass onto the MSRP stack for
transportation. From the point of view of MSRP, the portion of the transportation. From the point of view of MSRP, the portion of the
file is viewed as a whole message. The latter indicates the number file is viewed as a whole message. The latter indicates the number
of bytes of that message that are carried in a chunk and the total of bytes of that message that are carried in a chunk and the total
size of the message. Therefore, MSRP starts counting the delivered size of the message. Therefore, MSRP starts counting the delivered
message at byte number 1, independently of position of that byte in message at byte number 1, independently of position of that byte in
the file. the file.
skipping to change at page 14, line 35 skipping to change at page 14, line 40
t=0 0 t=0 0
m=message 7654 TCP/MSRP * m=message 7654 TCP/MSRP *
i=This is my latest picture i=This is my latest picture
a=sendonly a=sendonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://atlanta.example.com:7654/jshA7we;tcp a=path:msrp://atlanta.example.com:7654/jshA7we;tcp
a=file-selector:name:"My cool picture.jpg" type:image/jpeg a=file-selector:name:"My cool picture.jpg" type:image/jpeg
size:32349 hash:sha-1: size:32349 hash:sha-1:
72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E 72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
a=file-transfer:new a=file-transfer-id:vBnG916bdberum2fFEABR1FR3ExZMUrd
a=file-disposition:not-render a=file-disposition:attachment
a=file-date:creation:"Mon, 15 May 2006 15:01:31 +03:00" a=file-date:creation:"Mon, 15 May 2006 15:01:31 +0300"
a=file-icon:cid:id2@alicepc.example.com a=file-icon:cid:id2@alicepc.example.com
a=file-range:1-32349 a=file-range:1-32349
Figure 2: Example of SDP describing a file transfer Figure 2: Example of SDP describing a file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The 'file-selector' attribute in the above figure is split
in three lines for formatting purposes. Real implementations will in three lines for formatting purposes. Real implementations will
encode it in a single line. encode it in a single line.
7. File Disposition Types 7. File Disposition Types
The SDP Offer/Answer for file transfer allows the file sender to The SDP Offer/Answer for file transfer allows the file sender to
indicate a preferred disposition of the file to be transferred in a indicate a preferred disposition of the file to be transferred in a
new 'file-disposition' attribute. In principle, any value listed in new 'file-disposition' attribute. In principle, any value listed in
the IANA registry for Mail Content Disposition Values [3] is the IANA registry for Mail Content Disposition Values [3] is
skipping to change at page 15, line 30 skipping to change at page 15, line 38
the new 'file-disposition' attribute in SDP. To indicate that a file the new 'file-disposition' attribute in SDP. To indicate that a file
should not be automatically rendered, this memo users the existing should not be automatically rendered, this memo users the existing
'attachment' value of the Content-Disposition type in the new 'file- 'attachment' value of the Content-Disposition type in the new 'file-
disposition' attribute in SDP. The default value is 'render', i.e., disposition' attribute in SDP. The default value is 'render', i.e.,
the absence of a 'file-disposition' attribute in the SDP has the same the absence of a 'file-disposition' attribute in the SDP has the same
semantics as 'render'. semantics as 'render'.
The disposition value 'attachment' is specified in RFC 2183 The disposition value 'attachment' is specified in RFC 2183
[RFC2183] with the following definition: [RFC2183] with the following definition:
"Bodyparts can be designated 'attachment' to indicate that they "Body parts can be designated 'attachment' to indicate that
are separate from the main body of the mail message, and that they are separate from the main body of the mail message, and
their display should not be automatic, but contingent upon some that their display should not be automatic, but contingent upon
further action of the user." some further action of the user."
In the case of this specification, the 'attachment' disposition In the case of this specification, the 'attachment' disposition
type is used o indicate that the display of the file should not be type is used to indicate that the display of the file should not
automatic, but contingent upon some further action of the user. be automatic, but contingent upon some further action of the user.
8. Protocol Operation 8. Protocol Operation
This Section discusses how to use the parameters defined in Section 6 This Section discusses how to use the parameters defined in Section 6
in the context of an offer/answer [RFC3264] exchange. Additionally, in the context of an offer/answer [RFC3264] exchange. Additionally,
this section also discusses the behavior of the endpoints using MSRP. this section also discusses the behavior of the endpoints using MSRP.
Usually the file transfer session is initiated when the offerer sends Usually the file transfer session is initiated when the offerer sends
an SDP offer to the answerer. The answerer either accepts or rejects an SDP offer to the answerer. The answerer either accepts or rejects
the file transfer session and sends an SDP answer to the offerer. the file transfer session and sends an SDP answer to the offerer.
skipping to change at page 16, line 22 skipping to change at page 16, line 30
file sender. In this case the SDP offer contains a session or file sender. In this case the SDP offer contains a session or
media 'recvonly' attribute, and accordingly the SDP answer media 'recvonly' attribute, and accordingly the SDP answer
contains a session or media 'sendonly' attribute. contains a session or media 'sendonly' attribute.
8.1. Offerer's Behavior 8.1. Offerer's Behavior
An offerer that wishes to send or receive one or more files to or An offerer that wishes to send or receive one or more files to or
from an answerer MUST build an SDP [RFC4566] description of a session from an answerer MUST build an SDP [RFC4566] description of a session
containing one or more "m=" lines, each one describing an MSRP containing one or more "m=" lines, each one describing an MSRP
session (and thus, one file transfer operation), according to the session (and thus, one file transfer operation), according to the
MSRP [I-D.ietf-simple-message-sessions] procedures. All the media MSRP [RFC4975] procedures. All the media line attributes specified
line attributes specified and required by MSRP and required by MSRP [RFC4975] (e.g., "a=path", "a=accept-types",
[I-D.ietf-simple-message-sessions] (e.g., "a=path", "a=accept-types",
etc.) MUST be included as well. For each file to be transferred etc.) MUST be included as well. For each file to be transferred
there MUST be a separate "m=" line. there MUST be a separate "m=" line.
8.1.1. The Offerer is a File Sender 8.1.1. The Offerer is a File Sender
In a push operation, the file sender creates and SDP offer describing In a push operation, the file sender creates and SDP offer describing
the file to be sent. The file sender MUST add a 'file-selector' the file to be sent. The file sender MUST add a 'file-selector'
attribute media line containing at least one of the 'type', 'size', attribute media line containing at least one of the 'type', 'size',
'hash' selectors in indicating the type, size, or hash of the file, 'hash' selectors in indicating the type, size, or hash of the file,
respectively. If the file sender is able to compute the hash of the respectively. The file sender MUST add a 'file-transfer-id'
file with different hashing algorithms, it MAY add several 'hash' attribute containing a new identifier value, i.e., not used within
selectors, each one referring to a different hashing algorithm. The the current session. Additionally, the file sender MUST add a
file sender MUST add a 'file-transfer' attribute with a value that session or media 'sendonly' attribute to the SDP offer. Then the
indicates whether a new file transfer should start ("new" value), or file sender sends the SDP offer to the file receiver.
whether the SDP merely indicates an existing file transfer
("existing" value), in which case a new file transfer should not
start. Additionally, the file sender MUST add a session or media
'sendonly' attribute to the SDP offer. Then the file sender sends
the SDP offer to the file receiver.
Not all the selectors in the 'file-selector' attribute might be Not all the selectors in the 'file-selector' attribute might be
known when the file sender creates the SDP offer, for example, known when the file sender creates the SDP offer, for example,
because the host is still processing the file. because the host is still processing the file.
The 'hash' selector in the 'file-selector' attribute contains The 'hash' selector in the 'file-selector' attribute contains
valuable information to the file receiver to identify whether the valuable information to the file receiver to identify whether the
file is already available and need not be transmitted. If the file is already available and need not be transmitted.
sender supports several hashing algorithms, then several 'hash'
selector can be included.
The file sender MAY also add a 'name' selector in the 'file-selector' The file sender MAY also add a 'name' selector in the 'file-selector'
attribute, and a 'file-icon', 'file-disposition', and 'file-date' attribute, and a 'file-icon', 'file-disposition', and 'file-date'
attributes further describing the file to be transferred. The 'file- attributes further describing the file to be transferred. The 'file-
disposition' attribute provides a presentation suggestion, (for disposition' attribute provides a presentation suggestion, (for
example: the file sender would like the file receiver to render the example: the file sender would like the file receiver to render the
file or not). The three date attributes provide the answerer with an file or not). The three date attributes provide the answerer with an
indication of the age of the file. The file sender MAY also add a indication of the age of the file. The file sender MAY also add a
'file-range' attribute indicating the start and stop offset of the 'file-range' attribute indicating the start and stop offsets of the
file transfer. file.
When the file sender receives the SDP answer, if the port number of
the answer for a file request is non-zero, the file sender starts the
transfer of the file according to the negotiated parameters in SDP.
8.1.2. The Offerer is a File Receiver 8.1.2. The Offerer is a File Receiver
In a pull operation, the file receiver creates the SDP offer and In a pull operation, the file receiver creates the SDP offer and
sends it to the file sender. The file receiver MUST include a 'file- sends it to the file sender. The file receiver MUST include a 'file-
selector' attribute and SHOULD add, at least, one of the selector selector' attribute and SHOULD add, at least, one of the selector
defined for that attribute (i.e., 'name', 'type', 'size', or 'hash'). defined for that attribute (i.e., 'name', 'type', 'size', or 'hash').
Several 'hash' selectors MAY be included if each 'hash' selector is In many cases, if the hash of the file is known, that is enough to
computed with a different hashing algorithm. In many cases, if the identify the file, therefore, the offerer can include only a 'hash'
hash of the file is known, that is enough to identify the file, selector. However, specially in cases where the hash of the file is
therefore, the offerer can include only a 'hash' selector. However, unknown, the file name, size, and type can provide a description of
specially in cases where the hash of the file is unknown, the file the file to be fetched. The file receiver MUST also add a 'file-
name, size, and type can provide a description of the file to be transfer-id' attribute with a newly created random value (new within
fetched. The file receiver MUST also add a 'file-transfer' attribute the current session). The file receiver MAY also add a 'file-range'
with a value that indicates whether a new file transfer should start attribute indicating the start and stop offsets of the file. There
("new" value), or whether the SDP merely indicates an existing file is no need to for the file receiver to include further file
transfer ("existing" value), in which case a new file transfer should attributes in the SDP offer, thus it is RECOMMENDED that SDP offerers
not start. There is no need to for the file offerer to include do not include any other file attribute defined by this specification
further file attributes in the SDP offer, thus it is RECOMMENDED that (other than the mandatory ones). Additionally, the file receiver
SDP offerers do not include any other file attribute defined by this MUST create an SDP offer that contains a session or media 'recvonly'
specification (other than the mandatory ones). Additionally, the attribute.
file receiver MUST create an SDP offer that contains a session or
media 'recvonly' attribute.
The file receiver MAY also add a 'file-range' attribute indicating
the start and stop offset of the file transfer.
When the file receiver receives the SDP answer, if the port number of When the file receiver receives the SDP answer, if the port number of
the answer for a file request is non-zero and if the 'file-transfer' the answer for a file request is non-zero, then the file receiver
attribute is set to "new", then the file receiver should receive the should receive the file using the protocol indicated in the m= line.
file using the protocol indicated in the m= line. If the SDP answer If the SDP answer contains a supported hashing algorithm in the
contains a supported hashing algorithm in the 'hash' selectors of the 'hash' selectors of the 'file-selector' attribute, then the file
'file-selector' attribute, then the file receiver SHOULD compute the receiver SHOULD compute the hash of the file after its reception and
hash of the file after receipt and check against the hash received in check it against the hash received in the answer. In case the
the answer. In case the computed hash does not match the one computed hash does not match the one contained in the SDP answer, the
contained in the SDP answer, the file receiver SHOULD consider that file receiver SHOULD consider that the file transfer failed and
the file transfer failed and SHOULD inform the user. SHOULD inform the user.
8.1.3. SDP Offer for Several Files 8.1.3. SDP Offer for Several Files
An offerer that wishes to send or receive more than one file An offerer that wishes to send or receive more than one file
generates an "m=" line per file along with the file attributes generates an "m=" line per file along with the file attributes
described in this specification. This way, the answerer can reject described in this specification. This way, the answerer can reject
individual files by setting the port number of their associated "m=" individual files by setting the port number of their associated "m="
lines to zero, as per regular SDP [RFC4566] procedures. lines to zero, as per regular SDP [RFC4566] procedures. Each file
has its own file transfer identifier, which uniquely identifies each
file transfer.
Using an "m=" line per file implies that different files are Using an "m=" line per file implies that different files are
transferred using different MSRP sessions. However, all those MSRP transferred using different MSRP sessions. However, all those MSRP
sessions can be set up to run over a single TCP connection, as sessions can be set up to run over a single TCP connection, as
described in Section 8.1 of [I-D.ietf-simple-message-sessions]. described in Section 8.1 of RFC 4975 [RFC4975].
8.2. Answerer's Behavior 8.2. Answerer's Behavior
If the answerer wishes to reject a file offered by the offerer, it If the answerer wishes to reject a file offered by the offerer, it
sets the port number of the "m=" line associated with the file to sets the port number of the "m=" line associated with the file to
zero, as per regular SDP [RFC4566] procedures and MUST set the 'file- zero, as per regular SDP [RFC4566] procedures. The rejected answer
transfer' attribute that mirrors the value received in the SDP offer. MUST contained a 'file-selector' and 'file-transfer-id' attributes
whose values mirror the corresponding values of the SDP offer.
If the answerer decides to accept the file, it proceeds as per If the answerer decides to accept the file, it proceeds as per
regular MSRP [I-D.ietf-simple-message-sessions] and SDP [RFC4566] regular MSRP [RFC4975] and SDP [RFC4566] procedures.
procedures.
8.2.1. The Answerer is a File Receiver 8.2.1. The Answerer is a File Receiver
In a push operation the answerer is the file receiver. When the file In a push operation the SDP answerer is the file receiver. When the
receiver gets the SDP offer, it extracts the attributes and file receiver gets the SDP offer, it extracts the attributes and
parameters that describe the file and typically requests permission parameters that describe the file and typically requests permission
to the user to accept or reject the reception of the file. If the from the user to accept or reject the reception of the file. If the
file transfer operation is accepted, the file receiver MUST create an file transfer operation is accepted, the file receiver MUST create an
SDP answer according to the procedures specified in RFC 3264 SDP answer according to the procedures specified in RFC 3264
[RFC3264]. If the offer contains 'name', 'type', 'size' selectors in [RFC3264]. If the offer contains 'name', 'type', 'size' selectors in
the 'file-selector' attribute, the answerer MUST copy them into the the 'file-selector' attribute, the answerer MUST copy them into the
answer. If the offer contains one ore more 'hash' selectors in the answer. The file receiver copies the value of the 'file-transfer-id'
'file-selector' attribute, the answerer discards those with non- attribute to the SDP answer. Then the file receiver MUST add a
supported hashing algorithms and MUST copy the remaining (if any) to session or media 'recvonly' attribute according to the procedures
the 'file-selector' attribute of the answer. This informs the specified in RFC 3264 [RFC3264]. The file receiver MUST NOT include
offerer that the answerer supports this specification. The file 'file-icon', 'file-disposition', or 'file-date' attributes in the SDP
receiver then adds a 'file-transfer' attribute with an appropriate answer.
value. Then the file receiver MUST add a session or media 'recvonly'
attribute according to the procedures specified in RFC 3264
[RFC3264]. The file receiver MUST NOT include 'file-icon', 'file-
disposition', or 'file-date' attributes in the SDP answer.
If the SDP offer contains one or more 'hash' selectors in the 'file- The file receiver can use the hash to find out if a local file with
selector' attribute, the answerer discards those with unsupported the same hash is already available, in which case, this could imply
hashing algorithms. The file receiver can use the remaining hashes the reception of a duplicated file. It is up to the answerer to
to find out if a local file with the same hash is already available, determine whether the file transfer is accepted or not in case of a
in which case, this could imply the reception of a duplicated file. duplicated file.
It is up to the answerer to determine whether the file transfer is
accepted or not in case of a duplicated file.
If the SDP offer contains a 'file-range' attribute and the file If the SDP offer contains a 'file-range' attribute and the file
receiver accepts to receive the range of bytes declared in there, the receiver accepts to receive the range of bytes declared in there, the
file receiver MUST include a 'file-range' attribute in the SDP answer file receiver MUST include a 'file-range' attribute in the SDP answer
with the same range of values. If the file receiver does not accept with the same range of values. If the file receiver does not accept
the reception of that range of bytes, it SHOULD reject the transfer the reception of that range of bytes, it SHOULD reject the transfer
of the file. of the file.
8.2.2. The Answerer is a File Sender 8.2.2. The Answerer is a File Sender
In a pull operation the answerer is a file sender. In this case, the In a pull operation the answerer is the file sender. In this case,
file sender MUST first inspect the received SDP offer and apply the the file sender MUST first inspect the value of the
file selector. The file selector is encoded in the 'file-selector' 'file-transfer-id' attribute. If the has not been previously been
media attribute line in SDP. First, if the file selector contains used throughout the session, then acceptance of the file MUST provoke
several hashes, the file sender MUST select one of them which the transfer of the file over the negotiated protocol. However, if
contains a supported hashing algorithm and discard the rest. Then the value has been previously used by another file transfer operation
the file sender applies the file selector, which implies selecting within the session, then the file sender MUST NOT alert the user and
those files that match one by one with the 'name', 'type', 'size', MUST NOT start a new transfer of the file. No matter whether an
and 'hash' selectors of the 'file-selector' attribute line (if they actual file transfer is initiated or not, the file sender MUST create
are present). The file selector identifies zero or more candidate a proper SDP answer that contains the 'file-transfer-id' attribute
files to be sent. If the file selector is unable to identify any with the same value received in the SDP offer, and then it MUST
file, then the answerer MUST reject the MSRP stream for file transfer continue processing the SDP answer.
by setting the port number to zero, and then the file sender SHOULD
also reject the SDP as per procedures in RFC 3264 [RFC3264], if this The file sender MUST always create an SDP answer according to the SDP
is the only stream described in the SDP offer. offer/answer procedures specified in RFC 3264 [RFC3264]. The file
sender inspects the file selector of the received SDP offer, which is
encoded in the 'file-selector' media attribute line. Then the file
sender applies the file selector, which implies selecting those files
that match one by one with the 'name', 'type', 'size', and 'hash'
selectors of the 'file-selector' attribute line (if they are
present). The file selector identifies zero or more candidate files
to be sent. If the file selector is unable to identify any file,
then the answerer MUST reject the MSRP stream for file transfer by
setting the port number to zero, and then the file sender SHOULD also
reject the SDP as per procedures in RFC 3264 [RFC3264], if this is
the only stream described in the SDP offer.
If the file selector points to a single file and the file sender If the file selector points to a single file and the file sender
decides to accept the file transfer, the file sender MUST create an decides to accept the file transfer, the file sender MUST create an
SDP answer that contains a 'sendonly' attribute, according to the SDP answer that contains a 'sendonly' attribute, according to the
procedures described RFC 3264 [RFC3264]. The file sender SHOULD add procedures described RFC 3264 [RFC3264]. The file sender SHOULD add
one or more 'hash' selectors in the answer, with algorithms supported a 'hash' selector in the answer with the locally computed SHA-1 hash
by the file sender and values locally computed by the file sender, over the complete file. If a hash value computed by the file sender
and SHOULD include at least one with a hash algorithm selected among differs from that specified by the file receiver, the file sender can
those present in the offer. The file sender MUST NOT include a either send the file without that hash value or reject the request by
'hash' selector with an algorithm that was present in the offer and a setting the port in the media stream to zero. The file sender MAY
value that differs from what was in the offer. If a hash value also include a 'type' selector in the 'file-selector' attribute line
computed by the file sender differs from that specified by the file of the SDP answer. The answerer MAY also include a 'file-icon' and
receiver, the file sender can either send the file without that hash 'file-disposition' attributes to further describe the file. Although
value or reject the request by setting the port in the media stream the answerer MAY also include a 'name' and 'size' selectors in the
to zero. The file sender MAY also include a 'type' selector in the 'file-selector' attribute, and a 'file-date' attribute, it is
'file-selector' attribute line of the SDP answer. The file sender RECOMMENDED not to include them in the SDP answer if the actual file
MUST add a 'file-transfer' attribute with the appropriate value. The transfer protocol (e.g., MSRP [RFC4975]) can accommodate a Content-
answerer MAY also include a 'file-icon' and 'file-disposition' Disposition header field [RFC2183] with the equivalent parameters.
attributes to further describe the file. Although the answerer MAY
also include a 'name' and 'size' selectors in the 'file-selector'
attribute, and a 'file-date' attribute, it is RECOMMENDED not to
include them in the SDP answer if the actual file transfer protocol
(e.g., MSRP [I-D.ietf-simple-message-sessions]) can accommodate a
Content-Disposition header field [RFC2183] with the equivalent
parameters.
The whole idea of adding file descriptors to SDP is to provide a The whole idea of adding file descriptors to SDP is to provide a
mechanism where a file transfer can be accepted prior to its mechanism where a file transfer can be accepted prior to its
start. Adding any SDP attributes that are otherwise signalled start. Adding any SDP attributes that are otherwise signaled
later in the file transfer protocol would just duplicate the later in the file transfer protocol would just duplicate the
information, but will not provide any information to the offerer information, but will not provide any information to the offerer
to accept or reject the file transfer (note that the offerer is to accept or reject the file transfer (note that the offerer is
requesting a file). requesting a file).
Last, if the file selector points to multiple candidate files, the Last, if the file selector points to multiple candidate files, the
answerer MAY use some local policy, e.g. consulting the user, to answerer MAY use some local policy, e.g. consulting the user, to
choose one of them to be defined in the SDP answer. If that choise choose one of them to be defined in the SDP answer. If that choice
cannot be done, the answere SHOULD reject the MSRP media stream for cannot be done, the answerer SHOULD reject the MSRP media stream for
file transfer (by setting the port number to zero). file transfer (by setting the port number to zero).
If the need arises, future specifications can provide a suitable If the need arises, future specifications can provide a suitable
mechanism that allows to either select multiple files or, e.g., mechanism that allows to either select multiple files or, e.g.,
resolve ambiguities by returning a list of files that match the resolve ambiguities by returning a list of files that match the
file selector. file selector.
If the SDP offer contains a 'file-range' attribute and the file If the SDP offer contains a 'file-range' attribute and the file
sender accepts to send the range of bytes declared in there, the file sender accepts to send the range of bytes declared in there, the file
sender MUST include a 'file-range' attribute in the SDP answer with sender MUST include a 'file-range' attribute in the SDP answer with
the same range of values. If the file sender does not accept sending the same range of values. If the file sender does not accept sending
that range of bytes, it SHOULD reject the transfer of the file. that range of bytes, it SHOULD reject the transfer of the file.
8.3. The 'file-transfer' attribute 8.3. The 'file-transfer-id' attribute
This specification creates an extension to the SDP Offer/Answer Model This specification creates an extension to the SDP Offer/Answer Model
[RFC3264], and because of that, it is assumed that the existing SDP [RFC3264], and because of that, it is assumed that the existing SDP
behaviour is kept intact. The SDP behaviour requires, for example, behavior is kept intact. The SDP behavior requires, for example,
that SDP is sent again to the remote party in situations where the that SDP is sent again to the remote party in situations where the
media description or perhaps other SDP parameters have not changed media description or perhaps other SDP parameters have not changed
with respect a previous offer/answer exchange. Let's consider the with respect a previous offer/answer exchange. Let's consider the
SIP Session Timer (RFC 4028) [RFC4028], which uses re-INVITEs to SIP Session Timer (RFC 4028) [RFC4028], which uses re-INVITE requests
refresh sessions. RFC 4028 recommends to send unmodified SDP in a to refresh sessions. RFC 4028 recommends to send unmodified SDP in a
re-INVITE to refresh the session. Should this re-INVITE contain SDP re-INVITE to refresh the session. Should this re-INVITE contain SDP
describing a file transfer operation and occur while the file describing a file transfer operation and occur while the file
transfer was still going on, there would be no means to detect transfer was still going on, there would be no means to detect
whether the SDP creator wanted to abort the current file transfer whether the SDP creator wanted to abort the current file transfer
operation and initiate a new one or the SDP file description was operation and initiate a new one or the SDP file description was
included in the SDP due to other reasons (e.g., session timer included in the SDP due to other reasons (e.g., session timer
refresh). refresh).
A similar scenario occurs when two endpoints have successfully agreed A similar scenario occurs when two endpoints have successfully agreed
on a file transfer, which is currently taking place when one of the on a file transfer, which is currently taking place when one of the
skipping to change at page 21, line 26 skipping to change at page 21, line 23
the current ongoing file transfer and add the new media descriptions. the current ongoing file transfer and add the new media descriptions.
The problem is that, the other endpoint is not able to determine if a The problem is that, the other endpoint is not able to determine if a
new file transfer is requested or not. new file transfer is requested or not.
In other cases, a file transfer was successfully completed. Then, if In other cases, a file transfer was successfully completed. Then, if
an endpoint re-sends the SDP offer with the media stream for the file an endpoint re-sends the SDP offer with the media stream for the file
transfer, then the other endpoint wouldn't be able to determine transfer, then the other endpoint wouldn't be able to determine
whether a new file transfer should start or not. whether a new file transfer should start or not.
To address these scenarios this specification defines the 'file- To address these scenarios this specification defines the 'file-
transfer' attribute, which can take any of two values: "new" or transfer-id' attribute which contains a unique file transfer
"existing". A "new" value in the 'file-transfer' attribute indicates identifier. The file transfer identifier helps both endpoints to
that the endpoint wants to create a new file transfer. This is the determine whether the SDP offer is requesting a new file transfer or
case of initial offer/answer exchanges, or in cases where an endpoint it is a repetition of the SDP. A new file transfer is one that, in
wants to abort the existing file transfer an re-start the file case of acceptance, will provoke the actual transfer of a file. This
transfer once more. An "existing" value in the 'file-transfer' is typically the case of new offer/answer exchanges, or in cases
attribute indicates that the endpoint is already involved or has where an endpoint wants to abort the existing file transfer and re-
concluded the actual file transfer, consequently, a new additional start the file transfer once more. On the other hand, the repetition
file transfer MUST NOT start. of the SDP does not lead to any actual file to be transferred,
potentially because the file transfer is still going on or because it
has already finished. This is the case of a repeated offer/answer
exchanges, which can be due to a number of reasons (session timer,
addition/removal of other media types in the SDP, update in SDP due
to changes in other session parameters, etc.).
Endpoints MUST include a 'file-transfer' attribute in any SDP offer Implementations according to this specification MUST include a 'file-
or answer that defines a file transfer operation, according to this transfer-id' attribute in SDP offers and answers. The SDP offerer
specification. An SDP answer that MUST not downgrade the offered MUST select a file transfer identifier according to the syntax and
'file-transfer' value. Table 1 shows the possible combination of add it to the 'file-transfer-id' attribute. The SDP answerer MUST
'file-transfer' values in SDP offers and answers both for pull and copy the value of the 'file-transfer-id' attribute in the SDP answer.
push file transfer operations.
+----------+----------------+ The file transfer identifier MUST be unique within the current
| Offerer | Answerer | session (never used before in this session), and it is RECOMMENDED to
+----------+----------------+ be unique across different sessions. It is RECOMMENDED to select a
| new | new | relatively big random identifier (e.g., 32 characters) to avoid
| existing | new / existing | duplications. The SDP answerer MUST keep track of the proposed file
+----------+----------------+ transfer identifiers in each session and copy the value of the
received file transfer identifier in the SDP answer.
If a file transfer is suspended and resumed at a later time, the
resumption is considered a new file transfer (even when the file to
be transferred is the same), therefore, the SDP offerer MUST choose a
new file transfer identifier.
Table 1: 'file-transfer' attribute values
If an endpoint sets the port number to zero in the media description If an endpoint sets the port number to zero in the media description
of a file transfer, for example because it wants to reject the file of a file transfer, for example because it wants to reject the file
transfer operation, then the SDP answer should mirror the value of transfer operation, then the SDP answer should mirror the value of
the 'file-transfer' attribute included in the SDP offer. This the 'file-transfer-id' attribute included in the SDP offer. This
effectively means that setting a media stream to zero has higher effectively means that setting a media stream to zero has higher
precedence than any value that the 'file-transfer' attribute can precedence than any value that the 'file-transfer-id' attribute can
take. take.
As a side effect, the 'file-transfer' attribute can be used for As a side effect, the 'file-transfer-id' attribute can be used for
aborting and restarting again an ongoing file transfer. Assume that aborting and restarting again an ongoing file transfer. Assume that
two endpoints agree on a file transfer and the actual transfer of the two endpoints agree on a file transfer and the actual transfer of the
file is taking place. At some point in time in the middle of the file is taking place. At some point in time in the middle of the
file transfer, one endpoint sends a new SDP offer, equal to the file transfer, one endpoint sends a new SDP offer, equal to the
initial one, where the 'file-transfer' attribute is set to "new". initial one, except for the value of the 'file-transfer-id'
This indicates that the offerer wants to abort the existing transfer attribute, which is a new value within the session. This indicates
and start a new one, according to the SDP parameters. The SDP that the offerer wants to abort the existing transfer and start a new
answerer SHOULD abort the ongoing file transfer, according to the one, according to the SDP parameters. The SDP answerer SHOULD abort
procedures of the file transfer protocol (e.g., MSRP), and start the ongoing file transfer, according to the procedures of the file
sending file once more from the initial requested octet. transfer protocol (e.g., MSRP), and start sending file once more from
the initial requested octet.
In another scenario, an endpoint that has successfully transferred a In another scenario, an endpoint that has successfully transferred a
file wants to send an SDP due to other reasons than the transfer of a file wants to send an SDP due to other reasons than the transfer of a
file. The SDP offerer creates an SDP file that maintains the media file. The SDP offerer creates an SDP file description that maintains
description line corresponding to the file transfer. The SDP offerer the media description line corresponding to the file transfer. The
MUST then set the port number to zero and MUST set the 'file- SDP offerer MUST then set the port number to zero and MUST keep the
transfer' attribute to "existing" to indicate that the media stream same value of the 'file-transfer-id' attribute that the initial file
is offered but must not be used. transfer got.
8.4. Indicating File Transfer Offer/Answer Capability 8.4. Indicating File Transfer Offer/Answer Capability
The SDP Offer/Answer Model [RFC3264] provides provisions for The SDP Offer/Answer Model [RFC3264] provides provisions for
indicating a capability to another endpoint (see Section 9 of RFC indicating a capability to another endpoint (see Section 9 of RFC
3264 [RFC3264]). The mechanism assumes a high-level protocol, such 3264 [RFC3264]). The mechanism assumes a high-level protocol, such
as SIP [RFC3261], that provides a capability query (such as a SIP as SIP [RFC3261], that provides a capability query (such as a SIP
OPTIONS request). RFC 3264 [RFC3264] indicates how to build the SDP OPTIONS request). RFC 3264 [RFC3264] indicates how to build the SDP
that is included in the response to such request. As such, RFC 3264 that is included in the response to such request. As such, RFC 3264
indicates that and endpoint builds an SDP body that contains an "m=" indicates that and endpoint builds an SDP body that contains an "m="
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8.5. Re-usage of Existing m= Lines in SDP 8.5. Re-usage of Existing m= Lines in SDP
The SDP Offer/Answer Model [RFC3264] provides rules that allow SDP The SDP Offer/Answer Model [RFC3264] provides rules that allow SDP
offerers and answerers to modify an existing media line, i.e., re-use offerers and answerers to modify an existing media line, i.e., re-use
an existing media line with different attributes. The same is also an existing media line with different attributes. The same is also
possible when SDP signals a file transfer operation according to the possible when SDP signals a file transfer operation according to the
rules of this memo. Therefore, the procedures defined in RFC 3264 rules of this memo. Therefore, the procedures defined in RFC 3264
[RFC3264], in particular those defined in Section 8.3, MUST apply for [RFC3264], in particular those defined in Section 8.3, MUST apply for
file transfer operations. An endpoint that wants to re-use an file transfer operations. An endpoint that wants to re-use an
existing m= line to start the file transfer of another file creates a existing m= line to start the file transfer of another file creates a
different 'file-selector' attribute and sends the 'file-transfer' to different 'file-selector' attribute and a different value of the
the value "new". 'file-transfer-id' attribute.
If the file offerer re-sends an SDP offer with a port different than If the file offerer re-sends an SDP offer with a port different than
zero, then the 'file-transfer' attribute determines whether a new zero, then the 'file-transfer-id' attribute determines whether a new
file transfer will start or whether the file transfer does not need file transfer will start or whether the file transfer does not need
to start. If the SDP answerer accepts the SDP, then file transfer to start. If the SDP answerer accepts the SDP, then file transfer
starts from the indicated byte (if a 'file-range' attribute is starts from the indicated byte (if a 'file-range' attribute is
present). present).
8.6. MSRP Usage 8.6. MSRP Usage
The file transfer service specified in this document uses "m=" lines The file transfer service specified in this document uses "m=" lines
to describe the unidirectional transfer of a file. Consequently, to describe the unidirectional transfer of a file. Consequently,
each MSRP session established following the procedures in Section 8.1 each MSRP session established following the procedures in Section 8.1
skipping to change at page 23, line 44 skipping to change at page 23, line 50
request; each of these portions of the complete message is called a request; each of these portions of the complete message is called a
"chunk". So, it is still valid to send a file in several chunks, but "chunk". So, it is still valid to send a file in several chunks, but
from the MSRP point of view, all the chunks together form an MSRP from the MSRP point of view, all the chunks together form an MSRP
message: the CPIM message that wraps the file. When chunking, notice message: the CPIM message that wraps the file. When chunking, notice
that MSRP does not require to wait for a 200-class response for a that MSRP does not require to wait for a 200-class response for a
chunk before sending the following one. Therefore, it is valid to chunk before sending the following one. Therefore, it is valid to
send pipelined MSRP SEND requests containing chunks of the same MSRP send pipelined MSRP SEND requests containing chunks of the same MSRP
message (the file). Section 9.1 contains an example of a file message (the file). Section 9.1 contains an example of a file
transfer using pipelined MSRP requests. transfer using pipelined MSRP requests.
The MSRP specification [I-D.ietf-simple-message-sessions] defines a The MSRP specification [RFC4975] defines a 'max-size' SDP attribute.
'max-size' SDP attribute. This attribute specifies the maximum This attribute specifies the maximum number of octets of an MSRP
number of octets of an MSRP message that the creator of the SDP is message that the creator of the SDP is willing to receive (notice
willing to receive (notice once more the definition of "MSRP once more the definition of "MSRP message"). File receivers MAY add
message"). File receivers MAY add a 'max-size' attribute to the MSRP a 'max-size' attribute to the MSRP m= line that specifies the file,
m= line that specifies the file, indicating the maximum number of indicating the maximum number of octets of an MSRP message. File
octets of an MSRP message. File senders MUST NOT exceed the 'max- senders MUST NOT exceed the 'max-size' limit for any message sent in
size' limit for any message sent in the resulting session. the resulting session.
In the absence of a 'file-range' attribute in the SDP, the MSRP file In the absence of a 'file-range' attribute in the SDP, the MSRP file
transfer MUST start with the first byte of the file and end with the transfer MUST start with the first byte of the file and end with the
last byte (i.e., the whole file is transferred). If a 'file-range' last byte (i.e., the whole file is transferred). If a 'file-range'
attribute is present in SDP, the file sender application MUST extract attribute is present in SDP, the file sender application MUST extract
the indicated range of bytes from the file (start and stop bytes). the indicated range of bytes from the file (start and stop bytes).
Then the file sender application SHOULD wrap those bytes in an Then the file sender application MAY wrap those bytes in an
appropriate wrapper, such as message/cpim. Last, the file sender appropriate wrapper. MSRP mandates implementations to implement the
application delivers the message/cpim to MSRP for transportation. message/cpim wrapper [RFC3862]. Usage of a wrapper is negotiated in
MSRP will consider the message/cpim as a whole message, and will the SDP (see Section 8.6 in RFC 4975 [RFC4975]). Last, the file
start numbering bytes at number 1. sender application delivers the content (e.g., the message/cpim body)
to MSRP for transportation. MSRP will consider the delivered content
as a whole message, and will start numbering bytes with the number 1.
Note that the default content disposition of MSRP bodies is 'render'. Note that the default content disposition of MSRP bodies is 'render'.
When MSRP is used to transfer files, the MSRP Content-Disposition When MSRP is used to transfer files, the MSRP Content-Disposition
header can also take the value 'attachment' as indicated in header can also take the value 'attachment' as indicated in
Section 7. Section 7.
Once the file transfer is completed, the file sender SHOULD close the Once the file transfer is completed, the file sender SHOULD close the
MSRP session, and MUST behave according to the MSRP MSRP session, and MUST behave according to the MSRP [RFC4975]
[I-D.ietf-simple-message-sessions] procedures with respect closing procedures with respect closing MSRP sessions.
MSRP sessions.
8.7. Considerations about the 'file-icon' attribute 8.7. Considerations about the 'file-icon' attribute
This specification allows a file sender to include a small preview of This specification allows a file sender to include a small preview of
an image file: an icon. A 'file-icon' attribute contains a CID URL an image file: an icon. A 'file-icon' attribute contains a CID URL
[RFC2392] that points to an additional body that contains the actual [RFC2392] that points to an additional body that contains the actual
icon. Since the icon is sent as a separate body along the SDP body, icon. Since the icon is sent as a separate body along the SDP body,
the file sender has to use a MIME multipart/mixed body that contains the file sender MUST wrap the SDP body and the icon bodies in a MIME
an SDP body part and the icon body part. Therefore, implementations multipart/related body. Therefore, implementations according to this
according to this specification MUST implement the multipart/mix MIME specification MUST implement the multipart/related MIME type
type [RFC2046]. [RFC2387]. When creating a multipart/related MIME wrapper, the SDP
body MUST be the root body, which according to RFC 2387 [RFC2387] is
identified as the first body in the multipart/related MIME wrapper or
explicitly identified by the 'start' parameter. According to RFC
2387 [RFC2387], the 'type' parameter MUST be present and point to the
root body, i.e., the SDP body.
However, if the file sender sends a request that contains a Assume that an endpoint behaving according to this specification
multipart/mix MIME body that includes an SDP body part and an icon tries to send a file to a remote endpoint that neither implements
body part, and the file receiver does not support multipart MIME this specification nor implements multipart MIME bodies. The file
types, then the file receiver will reject, via a higher protocol sender sends an SDP offer that contains a multipart/related MIME body
mechanism (e.g., SIP), the request. In this case, it is RECOMMENDED that includes an SDP body part and an icon body part. The file
that the file sender removes the icon body part, creates a single SDP receiver, not supporting multipart MIME types, will reject the SDP
body (i.e., without multipart MIME) and re-tries the request again. offer, via a higher protocol mechanism (e.g., SIP). In this case, it
This increases the chances of getting the SDP accepted at the file is RECOMMENDED that the file sender removes the icon body part,
receiver (albeit the file receiver will not implement this creates a single SDP body (i.e., without multipart MIME) and re-sends
specification, which mandates the implementation of multipart MIME the SDP offer again. This provides some backwards compatibility with
bodies). file receives that do not implement this specification and increases
the chances of getting the SDP accepted at the file receiver.
Since the icon is sent as part of the signalling, it is recommended Since the icon is sent as part of the signaling, it is recommended to
to keep icons restricted to the minimum number of bytes that provide keep icons restricted to the minimum number of bytes that provide
significance. significance.
9. Examples 9. Examples
9.1. Offerer sends a file to the Answerer 9.1. Offerer sends a file to the Answerer
This section shows an example flow for a file transfer scenario. The This section shows an example flow for a file transfer scenario. The
example assumes that SIP [RFC3261] is used to transport the SDP example assumes that SIP [RFC3261] is used to transport the SDP
offer/answer exchange, although the SIP details are briefly shown in offer/answer exchange, although the SIP details are briefly shown in
the sake of brevity. the sake of brevity.
skipping to change at page 26, line 13 skipping to change at page 27, line 13
attaches it to a SIP INVITE request addressed to Bob. attaches it to a SIP INVITE request addressed to Bob.
INVITE sip:bob@example.com SIP/2.0 INVITE sip:bob@example.com SIP/2.0
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.com>;tag=1928301774 From: Alice <sip:alice@example.com>;tag=1928301774
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 1 INVITE CSeq: 1 INVITE
Max-Forwards: 70 Max-Forwards: 70
Date: Sun, 21 May 2006 13:02:03 GMT Date: Sun, 21 May 2006 13:02:03 GMT
Contact: <sip:alice@alicepc.example.com> Contact: <sip:alice@alicepc.example.com>
Content-Type: multipart/mixed; boundary="boundary71" Content-Type: multipart/related; type="application/sdp";
boundary="boundary71"
Content-Length: [length] Content-Length: [length]
--boundary71 --boundary71
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: [length of SDP] Content-Length: [length of SDP]
v=0 v=0
o=alice 2890844526 2890844526 IN IP4 alicepc.example.com o=alice 2890844526 2890844526 IN IP4 alicepc.example.com
s= s=
c=IN IP4 alicepc.example.com c=IN IP4 alicepc.example.com
t=0 0 t=0 0
m=message 7654 TCP/MSRP * m=message 7654 TCP/MSRP *
i=This is my latest picture i=This is my latest picture
a=sendonly a=sendonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://alicepc.example.com:7654/jshA7we;tcp a=path:msrp://alicepc.example.com:7654/jshA7we;tcp
a=file-selector:name:"My cool picture.jpg" type:image/jpeg a=file-selector:name:"My cool picture.jpg" type:image/jpeg
size:4092 hash:sha-1: size:4092 hash:sha-1:
72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E 72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
a=file-transfer:new a=file-transfer-id:Q6LMoGymJdh0IKIgD6wD0jkcfgva4xvE
a=file-disposition:render a=file-disposition:render
a=file-date:creation:"Mon, 15 May 2006 15:01:31 +03:00" a=file-date:creation:"Mon, 15 May 2006 15:01:31 +0300"
a=file-icon:cid:id2@alicepc.example.com a=file-icon:cid:id2@alicepc.example.com
--boundary71 --boundary71
Content-Type: image/jpeg Content-Type: image/jpeg
Content-Transfer-Encoding: binary Content-Transfer-Encoding: binary
Content-ID: <id2@alicepc.example.com> Content-ID: <id2@alicepc.example.com>
Content-Length: [length of image] Content-Length: [length of image]
Content-Disposition: icon Content-Disposition: icon
[...small preview icon of the file...] [...small preview icon of the file...]
--boundary71-- --boundary71--
Figure 4: INVITE request containing an SDP offer for file transfer Figure 4: INVITE request containing an SDP offer for file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The Content-Type header field and the 'file-selector'
in three lines for formatting purposes. Real implementations will attribute in the above figure are split in several lines for
encode it in a single line. formatting purposes. Real implementations will encode it in a
single line.
From now on we omit the SIP details for the sake of brevity. From now on we omit the SIP details for the sake of brevity.
F2: Bob receives the INVITE request, inspects the SDP offer and F2: Bob receives the INVITE request, inspects the SDP offer and
extracts the icon body, checks the creation date and file size, and extracts the icon body, checks the creation date and file size, and
decides to accept the file transfer. So Bob creates the following decides to accept the file transfer. So Bob creates the following
SDP answer: SDP answer:
v=0 v=0
o=bob 2890844656 2890844656 IN IP4 bobpc.example.com o=bob 2890844656 2890844656 IN IP4 bobpc.example.com
skipping to change at page 27, line 28 skipping to change at page 28, line 29
c=IN IP4 bobpc.example.com c=IN IP4 bobpc.example.com
t=0 0 t=0 0
m=message 8888 TCP/MSRP * m=message 8888 TCP/MSRP *
a=recvonly a=recvonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://bobpc.example.com:8888/9di4ea;tcp a=path:msrp://bobpc.example.com:8888/9di4ea;tcp
a=file-selector:name:"My cool picture.jpg" type:image/jpeg a=file-selector:name:"My cool picture.jpg" type:image/jpeg
size:4092 hash:sha-1: size:4092 hash:sha-1:
72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E 72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
a=file-transfer:new a=file-transfer-id:Q6LMoGymJdh0IKIgD6wD0jkcfgva4xvE
Figure 5: SDP answer accepting the SDP offer for file transfer Figure 5: SDP answer accepting the SDP offer for file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The 'file-selector' attribute in the above figure is split
in three lines for formatting purposes. Real implementations will in three lines for formatting purposes. Real implementations will
encode it in a single line. encode it in a single line.
F4: Alice opens a TCP connection to Bob and creates an MSRP SEND F4: Alice opens a TCP connection to Bob and creates an MSRP SEND
request. This SEND request contains the first chunk of the file. request. This SEND request contains the first chunk of the file.
skipping to change at page 28, line 16 skipping to change at page 29, line 16
To-Path: msrp://bobpc.example.com:8888/9di4ea;tcp To-Path: msrp://bobpc.example.com:8888/9di4ea;tcp
From-Path: msrp://alicepc.example.com:7654/iau39;tcp From-Path: msrp://alicepc.example.com:7654/iau39;tcp
Message-ID: 12339sdqwer Message-ID: 12339sdqwer
Byte-Range: 1-2048/4385 Byte-Range: 1-2048/4385
Content-Type: message/cpim Content-Type: message/cpim
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.com> From: Alice <sip:alice@example.com>
DateTime: 2006-05-15T15:02:31-03:00 DateTime: 2006-05-15T15:02:31-03:00
Content-Disposition: render; filename="My cool picture.jpg"; Content-Disposition: render; filename="My cool picture.jpg";
creation-date="Mon, 15 May 2006 15:01:31 +03:00"; creation-date="Mon, 15 May 2006 15:01:31 +0300";
size=4092 size=4092
Content-Type: image/jpeg Content-Type: image/jpeg
... first set of bytes of the JPEG image ... ... first set of bytes of the JPEG image ...
-------d93kswow+ -------d93kswow+
Figure 6: MSRP SEND request containing the first chunk of actual file Figure 6: MSRP SEND request containing the first chunk of actual file
F5: Alice sends the second and last chunk. Note that MSRP allows to F5: Alice sends the second and last chunk. Note that MSRP allows to
send pipelined chunks, so there is no need to wait for the 200 (OK) send pipelined chunks, so there is no need to wait for the 200 (OK)
skipping to change at page 29, line 33 skipping to change at page 30, line 33
In this example Alice, the SDP offerer, first wishes to fetch a file In this example Alice, the SDP offerer, first wishes to fetch a file
from Bob, the SDP answerer. Alice knows that Bob has a specific file from Bob, the SDP answerer. Alice knows that Bob has a specific file
she wants to download. She has learned the hash of the file by some she wants to download. She has learned the hash of the file by some
out-of-band mechanism. The hash selector is enough to produce a file out-of-band mechanism. The hash selector is enough to produce a file
selector that points to the specific file. So, Alice creates an SDP selector that points to the specific file. So, Alice creates an SDP
offer that contains the file descriptor. Bob accepts the offer that contains the file descriptor. Bob accepts the
transmission and sends the file to Alice. When Alice has completely transmission and sends the file to Alice. When Alice has completely
received Bob's file, she intends to send a new image file to Bob. received Bob's file, she intends to send a new image file to Bob.
Therefore Alice re-uses the existing SDP media line with different Therefore Alice re-uses the existing SDP media line with different
attributes and updates the description of the new file she wants to attributes and updates the description of the new file she wants to
send to Bob's User Agent Server (UAS). Figure 10 shows the sequence send to Bob's User Agent Server (UAS). In particular, Alice creates
flow. a new file transfer identifier since this is a new file transfer
operation. Figure 10 shows the sequence flow.
Alice's UAC Bob's UAS Alice's UAC Bob's UAS
| | | |
|(1) (SIP) INVITE | |(1) (SIP) INVITE |
|----------------------->| |----------------------->|
|(2) (SIP) 200 OK | |(2) (SIP) 200 OK |
|<-----------------------| |<-----------------------|
|(3) (SIP) ACK | |(3) (SIP) ACK |
|----------------------->| |----------------------->|
| | | |
skipping to change at page 31, line 24 skipping to change at page 32, line 24
Content-Length: [length of SDP] Content-Length: [length of SDP]
v=0 v=0
o=alice 2890844526 2890844526 IN IP4 alicepc.example.com o=alice 2890844526 2890844526 IN IP4 alicepc.example.com
s= s=
c=IN IP4 alicepc.example.com c=IN IP4 alicepc.example.com
t=0 0 t=0 0
m=message 7654 TCP/MSRP * m=message 7654 TCP/MSRP *
a=recvonly a=recvonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:image/jpeg a=accept-wrapped-types:*
a=path:msrp://alicepc.example.com:7654/jshA7we;tcp a=path:msrp://alicepc.example.com:7654/jshA7we;tcp
a=file-selector:hash:sha-1: a=file-selector:hash:sha-1:
72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E 72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
a=file-transfer:new a=file-transfer-id:aCQYuBRVoUPGVsFZkCK98vzcX2FXDIk2
Figure 11: INVITE request containing an SDP offer for file transfer Figure 11: INVITE request containing an SDP offer for file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The 'file-selector' attribute in the above figure is split
in two lines for formatting purposes. Real implementations will in two lines for formatting purposes. Real implementations will
encode it in a single line. encode it in a single line.
From now on we omit the SIP details for the sake of brevity. From now on we omit the SIP details for the sake of brevity.
F2: Bob receives the INVITE request, inspects the SDP offer, computes F2: Bob receives the INVITE request, inspects the SDP offer, computes
skipping to change at page 32, line 17 skipping to change at page 33, line 17
s= s=
c=IN IP4 bobpc.example.com c=IN IP4 bobpc.example.com
t=0 0 t=0 0
m=message 8888 TCP/MSRP * m=message 8888 TCP/MSRP *
a=sendonly a=sendonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://bobpc.example.com:8888/9di4ea;tcp a=path:msrp://bobpc.example.com:8888/9di4ea;tcp
a=file-selector:type:image/jpeg hash:sha-1: a=file-selector:type:image/jpeg hash:sha-1:
72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E 72:24:5F:E8:65:3D:DA:F3:71:36:2F:86:D4:71:91:3E:E4:A2:CE:2E
a=file-transfer:new a=file-transfer-id:aCQYuBRVoUPGVsFZkCK98vzcX2FXDIk2
Figure 12: SDP answer accepting the SDP offer for file transfer Figure 12: SDP answer accepting the SDP offer for file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The 'file-selector' attribute in the above figure is split
in two lines for formatting purposes. Real implementations will in two lines for formatting purposes. Real implementations will
encode it in a single line. encode it in a single line.
F4: Alice opens a TCP connection to Bob. Bob then creates an MSRP F4: Alice opens a TCP connection to Bob. Bob then creates an MSRP
SEND request that contains the file. SEND request that contains the file.
skipping to change at page 32, line 39 skipping to change at page 33, line 39
To-Path: msrp://alicepc.example.com:7654/iau39;tcp To-Path: msrp://alicepc.example.com:7654/iau39;tcp
From-Path: msrp://bobpc.example.com:8888/9di4ea;tcp From-Path: msrp://bobpc.example.com:8888/9di4ea;tcp
Message-ID: 12339sdqwer Message-ID: 12339sdqwer
Byte-Range: 1-2027/2027 Byte-Range: 1-2027/2027
Content-Type: message/cpim Content-Type: message/cpim
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.com> From: Alice <sip:alice@example.com>
DateTime: 2006-05-15T15:02:31-03:00 DateTime: 2006-05-15T15:02:31-03:00
Content-Disposition: render; filename="My cool photo.jpg"; Content-Disposition: render; filename="My cool photo.jpg";
creation-date="Mon, 15 May 2006 15:01:31 +03:00"; creation-date="Mon, 15 May 2006 15:01:31 +0300";
modification-date="Mon, 15 May 2006 16:04:53 +03:00"; modification-date="Mon, 15 May 2006 16:04:53 +0300";
read-date="Mon, 16 May 2006 09:12:27 +03:00"; read-date="Mon, 16 May 2006 09:12:27 +0300";
size=1931 size=1931
Content-Type: image/jpeg Content-Type: image/jpeg
...binary JPEG image... ...binary JPEG image...
-------d93kswow$ -------d93kswow$
Figure 13: MSRP SEND request containing the actual file Figure 13: MSRP SEND request containing the actual file
F5: Alice acknowledges the reception of the SEND request. F5: Alice acknowledges the reception of the SEND request.
skipping to change at page 34, line 13 skipping to change at page 35, line 13
request addressed to Bob. request addressed to Bob.
INVITE sip:bob@example.com SIP/2.0 INVITE sip:bob@example.com SIP/2.0
To: Bob <sip:bob@example.com>;tag=1928323431 To: Bob <sip:bob@example.com>;tag=1928323431
From: Alice <sip:alice@example.com>;tag=1928301774 From: Alice <sip:alice@example.com>;tag=1928301774
Call-ID: a84b4c76e66710 Call-ID: a84b4c76e66710
CSeq: 2 INVITE CSeq: 2 INVITE
Max-Forwards: 70 Max-Forwards: 70
Date: Sun, 21 May 2006 13:02:33 GMT Date: Sun, 21 May 2006 13:02:33 GMT
Contact: <sip:alice@alicepc.example.com> Contact: <sip:alice@alicepc.example.com>
Content-Type: multipart/mixed; boundary="boundary71" Content-Type: multipart/related; type="application/sdp";
boundary="boundary71"
Content-Length: [length of multipart] Content-Length: [length of multipart]
--boundary71 --boundary71
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: [length of SDP] Content-Length: [length of SDP]
v=0 v=0
o=alice 2890844526 2890844527 IN IP4 alicepc.example.com o=alice 2890844526 2890844527 IN IP4 alicepc.example.com
s= s=
c=IN IP4 alicepc.example.com c=IN IP4 alicepc.example.com
t=0 0 t=0 0
m=message 5670 TCP/MSRP * m=message 5670 TCP/MSRP *
i=This is my latest picture i=This is my latest picture
a=sendonly a=sendonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://alicepc.example.com:5670/iau39;tcp a=path:msrp://alicepc.example.com:5670/iau39;tcp
a=file-selector:name:"sunset.jpg" type:image/jpeg a=file-selector:name:"sunset.jpg" type:image/jpeg
size:4096 hash:sha-1: size:4096 hash:sha-1:
58:23:1F:E8:65:3B:BC:F3:71:36:2F:86:D4:71:91:3E:E4:B1:DF:2F 58:23:1F:E8:65:3B:BC:F3:71:36:2F:86:D4:71:91:3E:E4:B1:DF:2F
a=file-transfer:new a=file-transfer-id:ZVE8MfI9mhAdZ8GyiNMzNN5dpqgzQlCO
a=file-disposition:render a=file-disposition:render
a=file-date:creation:"Sun, 21 May 2006 13:02:15 +03:00" a=file-date:creation:"Sun, 21 May 2006 13:02:15 +0300"
a=file-icon:cid:id3@alicepc.example.com a=file-icon:cid:id3@alicepc.example.com
--boundary71 --boundary71
Content-Type: image/jpeg Content-Type: image/jpeg
Content-Transfer-Encoding: binary Content-Transfer-Encoding: binary
Content-ID: <id3@alicepc.example.com> Content-ID: <id3@alicepc.example.com>
Content-Length: [length of image] Content-Length: [length of image]
Content-Disposition: icon Content-Disposition: icon
[..small preview icon...] [..small preview icon...]
--boundary71-- --boundary71--
Figure 15: Reuse of the SDP in a second file transfer Figure 15: Reuse of the SDP in a second file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The Content-Type header field and the 'file-selector'
in three lines for formatting purposes. Real implementations will attribute in the above figure are split in several lines for
encode it in a single line. formatting purposes. Real implementations will encode it in a
single line.
F7: Bob receives the re-INVITE request, inspects the SDP offer and F7: Bob receives the re-INVITE request, inspects the SDP offer and
extracts the icon body, checks the creation date and file size, and extracts the icon body, checks the creation date and file size, and
decides to accept the file transfer. So Bob creates the following decides to accept the file transfer. So Bob creates the following
SDP answer: SDP answer:
v=0 v=0
o=bob 2890844656 2890855440 IN IP4 bobpc.example.com o=bob 2890844656 2890855440 IN IP4 bobpc.example.com
s= s=
c=IN IP4 bobpc.example.com c=IN IP4 bobpc.example.com
t=0 0 t=0 0
m=message 9999 TCP/MSRP * m=message 9999 TCP/MSRP *
a=recvonly a=recvonly
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:* a=accept-wrapped-types:*
a=path:msrp://bobpc.example.com:9999/9an4ea;tcp a=path:msrp://bobpc.example.com:9999/9an4ea;tcp
a=file-selector:name:"sunset.jpg" type:image/jpeg a=file-selector:name:"sunset.jpg" type:image/jpeg
size:4096 hash:sha-1: size:4096 hash:sha-1:
58:23:1F:E8:65:3B:BC:F3:71:36:2F:86:D4:71:91:3E:E4:B1:DF:2F 58:23:1F:E8:65:3B:BC:F3:71:36:2F:86:D4:71:91:3E:E4:B1:DF:2F
a=file-transfer:new a=file-transfer-id:ZVE8MfI9mhAdZ8GyiNMzNN5dpqgzQlCO
a=file-disposition:render a=file-disposition:render
Figure 16: SDP answer accepting the SDP offer for file transfer Figure 16: SDP answer accepting the SDP offer for file transfer
NOTE: The 'file-selector' attribute in the above figure is split NOTE: The 'file-selector' attribute in the above figure is split
in three lines for formatting purposes. Real implementations will in three lines for formatting purposes. Real implementations will
encode it in a single line. encode it in a single line.
F9: Alice opens a new TCP connection to Bob and creates an MSRP SEND F9: Alice opens a new TCP connection to Bob and creates an MSRP SEND
request that contains the file. request that contains the file.
skipping to change at page 36, line 16 skipping to change at page 37, line 16
To-Path: msrp://bobpc.example.com:9999/9an4ea;tcp To-Path: msrp://bobpc.example.com:9999/9an4ea;tcp
From-Path: msrp://alicepc.example.com:5670/iau39;tcp From-Path: msrp://alicepc.example.com:5670/iau39;tcp
Message-ID: 13449sdqwer Message-ID: 13449sdqwer
Byte-Range: 1-2027/2027 Byte-Range: 1-2027/2027
Content-Type: message/cpim Content-Type: message/cpim
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.com> From: Alice <sip:alice@example.com>
DateTime: 2006-05-21T13:02:15-03:00 DateTime: 2006-05-21T13:02:15-03:00
Content-Disposition: render; filename="Sunset.jpg"; Content-Disposition: render; filename="Sunset.jpg";
creation-date="Sun, 21 May 2006 13:02:15"; creation-date="Sun, 21 May 2006 13:02:15 -0300";
size=1931 size=1931
Content-Type: image/jpeg Content-Type: image/jpeg
...binary JPEG image... ...binary JPEG image...
-------d95ksxox+ -------d95ksxox+
Figure 17: MSRP SEND request containing the actual file Figure 17: MSRP SEND request containing the actual file
F10: Bob acknowledges the reception of the SEND request. F10: Bob acknowledges the reception of the SEND request.
skipping to change at page 36, line 46 skipping to change at page 37, line 46
request. request.
F12: Alice acknowledges the reception of the BYE request and sends a F12: Alice acknowledges the reception of the BYE request and sends a
200 (OK) response. 200 (OK) response.
9.3. Example of a capability indication 9.3. Example of a capability indication
Alice sends an OPTIONS request to Bob (this request does not contain Alice sends an OPTIONS request to Bob (this request does not contain
SDP). Bob answers with a 200 (OK) response that contain the SDP SDP). Bob answers with a 200 (OK) response that contain the SDP
shown in Figure 20. The SDP indicates support for CPIM messages that shown in Figure 20. The SDP indicates support for CPIM messages that
can contain other few MIME types. The maximum MSRP message size that can contain other MIME types. The maximum MSRP message size that the
the endpoint can receive is 20000 octets. The presence of the 'file- endpoint can receive is 20000 octets. The presence of the 'file-
selector' attribute indicates support for the file transfer offer/ selector' attribute indicates support for the file transfer offer/
answer mechanism. answer mechanism.
Alice's UAC Bob's UAS Alice's UAC Bob's UAS
| | | |
|(1) (SIP) OPTIONS | |(1) (SIP) OPTIONS |
|----------------------->| |----------------------->|
|(2) (SIP) 200 OK | |(2) (SIP) 200 OK |
| with SDP | | with SDP |
|<-----------------------| |<-----------------------|
skipping to change at page 37, line 24 skipping to change at page 38, line 24
Figure 19: Flow diagram of a capability request Figure 19: Flow diagram of a capability request
v=0 v=0
o=bob 2890844656 2890855439 IN IP4 bobpc.example.com o=bob 2890844656 2890855439 IN IP4 bobpc.example.com
s=- s=-
c=IN IP4 bobpc.example.com c=IN IP4 bobpc.example.com
t=0 0 t=0 0
m=message 0 TCP/MSRP * m=message 0 TCP/MSRP *
a=accept-types:message/cpim a=accept-types:message/cpim
a=accept-wrapped-types:text/plain text/html image/jpeg image/gif a=accept-wrapped-types:*
a=max-size:20000 a=max-size:20000
a=file-selector a=file-selector
Figure 20: SDP of the 200 (OK) response to an OPTIONS request Figure 20: SDP of the 200 (OK) response to an OPTIONS request
10. Security Considerations 10. Security Considerations
The SDP attributed defined in this specification identify a file to The SDP attributed defined in this specification identify a file to
be transfered between two endpoints. An endpoint can offer to send be transferred between two endpoints. An endpoint can offer to send
the file to the other endpoint or request to receive the file from the file to the other endpoint or request to receive the file from
the other endpoint. In the former case, an attacker modifying those the other endpoint. In the former case, an attacker modifying those
SDP attributes could cheat the receiver making it think that the file SDP attributes could cheat the receiver making it think that the file
to be transfered was a different one. In the latter case, the to be transferred was a different one. In the latter case, the
attacker could make the sender send a different file than the one attacker could make the sender send a different file than the one
requested by the receiver. Consequently, it is RECOMMENDED that requested by the receiver. Consequently, it is RECOMMENDED that
integrity protection be applied to the SDP session descriptions integrity protection be applied to the SDP session descriptions
carrying the attributes specified in this specification. carrying the attributes specified in this specification.
The descriptions of the files being transfered between endpoints may The descriptions of the files being transferred between endpoints may
reveal information the endpoints may consider confidential. reveal information the endpoints may consider confidential.
Therefore, it is RECOMMENDED that SDP session descriptions carrying Therefore, it is RECOMMENDED that SDP session descriptions carrying
the attributes specified in this specification be encrypted. the attributes specified in this specification be encrypted.
TLS and S/MIME are the natural choices to provide offer/answer TLS and S/MIME are the natural choices to provide offer/answer
exchanges with integrity protection and confidentiality. exchanges with integrity protection and confidentiality.
It is possible that a malicious or misbehaving implementation tries
to exhaust the resources of the remote endpoint, e.g., the internal
memory or the file system, by sending very large files. To protect
from this attack an SDP answer SHOULD first verify the identity of
the SDP offerer, and perhaps, only accept file transfers from trusted
sources. Mechanisms to verify the identity of the file sender depend
on the high-level protocol that carries the SDP, for example, SIP
[RFC3261] and MSRP [RFC4975].
It is also RECOMMENDED that implementations take measurements to
avoid attacks on resource exhaustion, for example, by limiting the
size of receive files, verifying that there is enough space in the
file system to store the file prior to its reception, or limiting the
number of simultaneous file transfers.
File receivers MUST also sanitize all input, such as the local file
name, prior to making calls to the local file system to store a file.
This is to prevent the existence of meaningful characters to the
local operating system that could damage it.
Once a file has been transferred the file receiver must take care
with it. Typically file transfer is a commonly used mechanism for
transmitting computer virus, spyware, and other types of malware.
File recipients should apply all possible security technologies
(e.g., antivirus, antispaware, etc.) to dismiss the risk of damage at
their host.
11. IANA Considerations 11. IANA Considerations
This document instructs IANA to register a number of SDP attributes This document instructs IANA to register a number of SDP attributes
according to the following: according to the following:
11.1. Registration of new SDP attributes 11.1. Registration of new SDP attributes
This memo provides instructions to IANA to register a number of media This memo provides instructions to IANA to register a number of media
level only attributes in the Session Description Protocol Parameters level only attributes in the Session Description Protocol Parameters
registry [4]. The registration data, according to RFC 4566 [RFC4566] registry [4]. The registration data, according to RFC 4566 [RFC4566]
follows. follows.
Note to the RFC Editor: replace "RFC XXXX" with the RFC number of Note to the RFC Editor: replace "RFC XXXX" with the RFC number of
this specification. this specification.
11.1.1. Registration of the file-selector attribute 11.1.1. Registration of the file-selector attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-selector Attribute name: file-selector
Long-form attribute name: File Selector Long-form attribute name: File Selector
Type of attribute: media level only Type of attribute: media level only
This attribute is subject to the charset attribute This attribute is subject to the charset attribute
Description: This attribute unambiguously identify a file by Description: This attribute unambiguously identify a file by
indicating a combination of the 4-tuple composed of the name, indicating a combination of the 4-tuple composed of the name,
size, type, and hash of the file. size, type, and hash of the file.
Specification: RFC XXXX Specification: RFC XXXX
11.1.2. Registration of the file-transfer attribute 11.1.2. Registration of the file-transfer-id attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-transfer Attribute name: file-transfer-id
Long-form attribute name: File Transfer Long-form attribute name: File Transfer Identifier
Type of attribute: media level only Type of attribute: media level only
This attribute is subject to the charset attribute This attribute is subject to the charset attribute
Description: This attribute indicates whether the SDP requests a Description: This attribute contains a unique identifier of the
new file transfer or indicates an existing file transfer. file transfer operation within the session.
Specification: RFC XXXX Specification: RFC XXXX
11.1.3. Registration of the file-disposition attribute 11.1.3. Registration of the file-disposition attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-disposition Attribute name: file-disposition
Long-form attribute name: File Disposition Long-form attribute name: File Disposition
Type of attribute: media level only Type of attribute: media level only
This attribute is not subject to the charset attribute This attribute is not subject to the charset attribute
Description: This attribute provides a suggestion to the other Description: This attribute provides a suggestion to the other
endpoint about the intended disposition of the file endpoint about the intended disposition of the file
Specification: RFC XXXX Specification: RFC XXXX
11.1.4. Registration of the file-date attribute 11.1.4. Registration of the file-date attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-date Attribute name: file-date
Long-form attribute name: Long-form attribute name:
Type of attribute: media level only Type of attribute: media level only
This attribute is not subject to the charset attribute This attribute is not subject to the charset attribute
Description: This attribute indicates the dates at which the file Description: This attribute indicates the dates at which the file
was created, modified, or last read. was created, modified, or last read.
Specification: RFC XXXX Specification: RFC XXXX
11.1.5. Registration of the file-icon attribute 11.1.5. Registration of the file-icon attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-icon Attribute name: file-icon
Long-form attribute name: File Icon Long-form attribute name: File Icon
Type of attribute: media level only Type of attribute: media level only
This attribute is not subject to the charset attribute This attribute is not subject to the charset attribute
Description: For image files, this attribute contains a pointer to Description: For image files, this attribute contains a pointer to
a body that includes a small preview icon representing the a body that includes a small preview icon representing the
contents of the file to be transferred contents of the file to be transferred
Specification: RFC XXXX Specification: RFC XXXX
11.1.6. Registration of the file-range attribute 11.1.6. Registration of the file-range attribute
Contact: Miguel Garcia <miguel.garcia@nsn.com> Contact: Miguel Garcia <miguel.garcia@nsn.com>
Phone: +358 71800 8000 Phone: +358 71400 4000
Attribute name: file-range Attribute name: file-range
Long-form attribute name: File Range Long-form attribute name: File Range
Type of attribute: media level only Type of attribute: media level only
This attribute is not subject to the charset attribute This attribute is not subject to the charset attribute
Description: it contains the range of transferred bytes of the Description: it contains the range of transferred bytes of the
file file
Specification: RFC XXXX Specification: RFC XXXX
12. Acknowledgements 12. Acknowledgements
The authors would like to thank Mats Stille, Nancy Greene, Adamu The authors would like to thank Mats Stille, Nancy Greene, Adamu
Haruna, and Arto Leppisaari for discussing initial concepts described Haruna, and Arto Leppisaari for discussing initial concepts described
in this memo. Thanks to Pekka Kuure for reviewing initial versions in this memo. Thanks to Pekka Kuure for reviewing initial versions
this document and providing helpful comments. Joerg Ott, Jiwey Wang, this document and providing helpful comments. Joerg Ott, Jiwey Wang,
Amitkumar Goel, Sudha Vs, Dan Wing, Juuso Lehtinen, Remi Denis- Amitkumar Goel, Sudha Vs, Dan Wing, Juuso Lehtinen, Remi Denis-
Courmont, Colin Perkins, Paul Kyzivat, and Sudhakar An discussed and Courmont, Colin Perkins, Paul Kyzivat, Sudhakar An, Peter Saint-
provided comments and improvements to this document. Andre, Jonathan Rosenberg, and Eric Rescorla discussed and provided
comments and improvements to this document.
13. References 13. References
13.1. Normative References 13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating
Presentation Information in Internet Messages: The Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, August 1997. Content-Disposition Header Field", RFC 2183, August 1997.
[RFC2387] Levinson, E., "The MIME Multipart/Related Content-type",
RFC 2387, August 1998.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource [RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998. Locators", RFC 2392, August 1998.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, [RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001. April 2001.
[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001. (SHA1)", RFC 3174, September 2001.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
June 2002. June 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC3851] Ramsdell, B., "Secure/Multipurpose Internet Mail [RFC3851] Ramsdell, B., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification", Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, July 2004. RFC 3851, July 2004.
[RFC3862] Klyne, G. and D. Atkins, "Common Presence and Instant
Messaging (CPIM): Message Format", RFC 3862, August 2004.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[I-D.ietf-simple-message-sessions] [RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Campbell, B., "The Message Session Relay Protocol", Session Relay Protocol (MSRP)", RFC 4975, September 2007.
draft-ietf-simple-message-sessions-19 (work in progress),
February 2007.
13.2. Informational References 13.2. Informational References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC4028] Donovan, S. and J. Rosenberg, "Session Timers in the [RFC4028] Donovan, S. and J. Rosenberg, "Session Timers in the
Session Initiation Protocol (SIP)", RFC 4028, April 2005. Session Initiation Protocol (SIP)", RFC 4028, April 2005.
[RFC4483] Burger, E., "A Mechanism for Content Indirection in [RFC4483] Burger, E., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483, Session Initiation Protocol (SIP) Messages", RFC 4483,
May 2006. May 2006.
[RFC4634] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms [RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
(SHA and HMAC-SHA)", RFC 4634, August 2006. for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
[I-D.ietf-simple-msrp-relays]
Jennings, C., "Relay Extensions for the Message Sessions
Relay Protocol (MSRP)", draft-ietf-simple-msrp-relays-10
(work in progress), December 2006.
[I-D.ietf-rmt-flute-revised] [I-D.ietf-rmt-flute-revised]
Paila, T., "FLUTE - File Delivery over Unidirectional Paila, T., "FLUTE - File Delivery over Unidirectional
Transport", draft-ietf-rmt-flute-revised-03 (work in Transport", draft-ietf-rmt-flute-revised-04 (work in
progress), January 2007. progress), October 2007.
URIs URIs
[1] <http://www.iana.org/assignments/media-types/> [1] <http://www.iana.org/assignments/media-types/>
[2] <http://www.iana.org/assignments/hash-function-text-names> [2] <http://www.iana.org/assignments/hash-function-text-names>
[3] <http://www.iana.org/assignments/mail-cont-disp> [3] <http://www.iana.org/assignments/mail-cont-disp>
[4] <http://www.iana.org/assignments/sdp-parameters> [4] <http://www.iana.org/assignments/sdp-parameters>
Authors' Addresses Authors' Addresses
Miguel A. Garcia-Martin Miguel A. Garcia-Martin
Nokia Siemens Networks Nokia Siemens Networks
P.O.Box 6 P.O.Box 6
Nokia Siemens Networks, FIN 02022 Nokia Siemens Networks, FIN 02022
Finland Finland
Phone: +358-71400-4000
Email: miguel.garcia@nsn.com Email: miguel.garcia@nsn.com
Markus Isomaki Markus Isomaki
Nokia Nokia
Keilalahdentie 2-4 Keilalahdentie 2-4
Espoo 02150 Espoo 02150
Finland Finland
Email: markus.isomaki@nokia.com Email: markus.isomaki@nokia.com
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com Email: Gonzalo.Camarillo@ericsson.com
Salvatore Loreto Salvatore Loreto
Ericsson Ericsson
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