draft-ietf-mmusic-sctp-sdp-02.txt   draft-ietf-mmusic-sctp-sdp-03.txt 
MMUSIC S. Loreto MMUSIC S. Loreto
Internet-Draft G. Camarillo Internet-Draft G. Camarillo
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: April 25, 2013 October 22, 2012 Expires: July 25, 2013 January 21, 2013
Stream Control Transmission Protocol (SCTP)-Based Media Transport in the Stream Control Transmission Protocol (SCTP)-Based Media Transport in the
Session Description Protocol (SDP) Session Description Protocol (SDP)
draft-ietf-mmusic-sctp-sdp-02 draft-ietf-mmusic-sctp-sdp-03
Abstract Abstract
SCTP (Stream Control Transmission Protocol) is a transport protocol SCTP (Stream Control Transmission Protocol) is a transport protocol
used to establish associations between two endpoints. This document used to establish associations between two endpoints. This document
describes how to express media transport over SCTP in SDP (Session describes how to express media transport over SCTP in SDP (Session
Description Protocol). This document defines the 'SCTP', 'SCTP/DTLS' Description Protocol). This document defines the 'SCTP', 'SCTP/DTLS'
and 'DTLS/SCTP' protocol identifiers for SDP. and 'DTLS/SCTP' protocol identifiers for SDP.
Status of this Memo Status of this Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2013. This Internet-Draft will expire on July 25, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 4
4. Media Formats . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Media Formats . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. data channels and m-line . . . . . . . . . . . . . . . . . 5 4.1. datachannels and m-line . . . . . . . . . . . . . . . . . 5
5. Streams Attribute . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Media Descriptions . . . . . . . . . . . . . . . . . . . . 5
6. Datachannel Attribute . . . . . . . . . . . . . . . . . . . . 6 4.3. Predefinition of Data Channels . . . . . . . . . . . . . . 6
7. The Setup and Connection Attributes and Association 5. Media attributes . . . . . . . . . . . . . . . . . . . . . . . 7
Management . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. sctpmap Attribute . . . . . . . . . . . . . . . . . . . . 7
8. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. stream Attribute . . . . . . . . . . . . . . . . . . . . . 7
9. Network Address Translation (NAT) Considerations . . . . . . . 8 5.3. label Attribute . . . . . . . . . . . . . . . . . . . . . 8
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.4. subprotocol Attribute . . . . . . . . . . . . . . . . . . 8
10.1. Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 8 5.5. max_retr Attribute . . . . . . . . . . . . . . . . . . . . 8
10.2. Existing Connection Reuse . . . . . . . . . . . . . . . . 9 5.6. max_time Attribute . . . . . . . . . . . . . . . . . . . . 8
10.3. SDP description for DTLS Connection . . . . . . . . . . . 10 5.7. unordered Attribute . . . . . . . . . . . . . . . . . . . 9
11. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. The Setup and Connection Attributes and Association
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 Management . . . . . . . . . . . . . . . . . . . . . . . . . . 9
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 9
13.1. Normative References . . . . . . . . . . . . . . . . . . . 11 8. Network Address Translation (NAT) Considerations . . . . . . . 10
13.2. Informative References . . . . . . . . . . . . . . . . . . 12 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 10
9.2. Existing Connection Reuse . . . . . . . . . . . . . . . . 11
9.3. SDP description for DTLS Connection . . . . . . . . . . . 12
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
SDP (Session Description Protocol) [RFC4566] provides a general- SDP (Session Description Protocol) [RFC4566] provides a general-
purpose format for describing multimedia sessions in announcements or purpose format for describing multimedia sessions in announcements or
invitations. RFC4145 [RFC4145] specifies a general mechanism for invitations. RFC4145 [RFC4145] specifies a general mechanism for
describing and establishing TCP (Transmission Control Protocol) describing and establishing TCP (Transmission Control Protocol)
streams. RFC 4572 [RFC4572] extends RFC4145 [RFC4145] for describing streams. RFC 4572 [RFC4572] extends RFC4145 [RFC4145] for describing
TCP-based media streams that are protected using TLS (Transport Layer TCP-based media streams that are protected using TLS (Transport Layer
Security) [RFC5246]. Security) [RFC5246].
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[I-D.tuexen-tsvwg-sctp-dtls-encaps], using SDP. SCTP over DTLS is [I-D.tuexen-tsvwg-sctp-dtls-encaps], using SDP. SCTP over DTLS is
used by the RTCWeb protocol suite for transporting non- media data used by the RTCWeb protocol suite for transporting non- media data
between browsers. between browsers.
The authentication certificates are interpreted and validated as The authentication certificates are interpreted and validated as
defined in RFC4572 [RFC4572]. Self-signed certificates can be used defined in RFC4572 [RFC4572]. Self-signed certificates can be used
securely, provided that the integrity of the SDP description is securely, provided that the integrity of the SDP description is
assured as defined in RFC4572 [RFC4572]. assured as defined in RFC4572 [RFC4572].
TLS is designed to run on top of a byte-stream oriented transport TLS is designed to run on top of a byte-stream oriented transport
protocol providing a realible, in-sequence delivery like TCP. Since protocol providing a reliable, in-sequence delivery like TCP. Since
no-one so far has implemented SCTP over TLS, due to some serious no-one so far has implemented SCTP over TLS, due to some serious
limitations described in [RFC6083], this document does not make use limitations described in [RFC6083], this document does not make use
of TLS over SCTP as described in RFC3436 [RFC3436]. of TLS over SCTP as described in RFC3436 [RFC3436].
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119] and indicate requirement described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
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The SDP specification, [RFC4566], states that specifications defining The SDP specification, [RFC4566], states that specifications defining
new proto values, like the SCTP, SCTP/DTLS and DTLS/SCTP proto values new proto values, like the SCTP, SCTP/DTLS and DTLS/SCTP proto values
defined in this RFC, must define the rules by which their media defined in this RFC, must define the rules by which their media
format (fmt) namespace is managed. Use of an existing MIME subtype format (fmt) namespace is managed. Use of an existing MIME subtype
for the format is encouraged. If no MIME subtype exists, it is for the format is encouraged. If no MIME subtype exists, it is
RECOMMENDED that a suitable one is registered through the IETF RECOMMENDED that a suitable one is registered through the IETF
process [RFC4288] [RFC4289] by production of, or reference to, a process [RFC4288] [RFC4289] by production of, or reference to, a
standards-track RFC that defines the transport protocol for the standards-track RFC that defines the transport protocol for the
format. format.
4.1. data channels and m-line 4.1. datachannels and m-line
SCTP defines a stream as an unidirectional logical channel existing SCTP defines a stream as an unidirectional logical channel existing
within an SCTP association one to another SCTP endpoint. The streams within an SCTP association one to another SCTP endpoint. The streams
are used to provide the notion of in-sequence delivery. Each user are used to provide the notion of in-sequence delivery. Each user
message is sent on a particular stream, either order or unordered. message is sent on a particular stream, either order or unordered.
Ordering is preserved only for all ordered messages sent on the same Ordering is preserved only for all ordered messages sent on the same
stream. stream.
A datachannel may be: A Data Channel may be:
unidirectional: formed by one single incoming or outgoing SCTP unidirectional: formed by one single incoming or outgoing SCTP
stream stream
bidirectional: a pair of one incoming stream and one outgoing SCTP bidirectional: a pair of one incoming stream and one outgoing SCTP
stream stream
Using the format part of the m line for negotiating datachannel Using the format part of the m line for negotiating datachannel
allows the intermediaries nodes to become aware of the kind of allows the intermediaries nodes to become aware of the kind of
traffic actually exchanged on each datachannel, as well as of the traffic actually exchanged on the datachannels, as well as the
number of datachannels established within the association. initial set of datachannels established within the association.
If the <port> sub-field is 'SCTP' or 'SCTP/DTLS' or 'DTLS/SCTP' the This document allows only one media format on top of an association.
<fmt> sub-fields contain datachannel number identifiers. When a list That means that all the datachannels must use the same media format.
of datachannel number identifiers is given, this implies that all of
these datachannel MUST be used in the association. For the payload
type assignments the "a=datachannel:" attribute (see Section 6)
SHOULD be used to map from a datachannel number to a media encoding
name that identifies the payload format transported by the
datachannel.
[NOTE] The datachannel number identifier does not necessarily map [NOTE] The exact definition of datachannel depends on the actual
directly with the number of the stream used to form the channel. media type using it.
[OPEN ISSUE 1]do we need a stream attribute for it? 4.2. Media Descriptions
[NOTE] The exact definition of datachannel depends from the actual The media description change slightly depending on the actual
media type in use it can be a unidirectional channel formed by a <proto>.
unidirectional stream of an SCTP association or a bidirectional
channel consisting of two SCTP streams one for each side of the
association.
[OPEN ISSUE 2] do we need to register the "RTCWeb" media type in If the <proto> sub-field is 'SCTP' or 'SCTP/DTLS'
accordance with the requirements of RFC 4288 here or in the
Datachannel draft?.
[OPEN ISSUE 3] do we need also an attribute to specify the SCTP port the <port> is the SCTP transport port and follows the same active/
number for the SCTP over DTLS scenario? that can be useful in the passive offer/answer model described in Section 4.1 of [RFC4145];
case where multiple association are running on top of the same DTLS
session.
An example of a datachannel payload type assignment is RTCWeb used the <fmt> sub-field carries the same port number value specified
only in certain defined datachannel of the SCTP association. in the <port> and the mandatory "a=sctpmap:" attribute contains
the actual media format within the protocol parameter.
m=application 54111 DTLS/SCTP 0 1 2 m=application 54111 SCTP/DTLS 54111
a=streams=3 a=sctpmap:54111 t38 1
a=datachannel:0 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:1 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:2 RTCWeb label=xxxx;options="dictionary string"
5. Streams Attribute Running SCTP over DTLS make possible to have multiple SCTP
associations on top of the same DTLS connection; each SCTP
association make use of a distinct port number that is mainly used to
demultiplex the associations.
The 'streams' attribute indicates the number of streams to be If the <proto> sub-field is 'DTLS/SCTP'
supported by the association. If this attribute is not present, the
implementation should provide a default, with a suggested value of
16.
streams-attr = "a=streams=" streamsnumbers the <port> is the UDP transport port;
streamsnumbers = 1*DIGIT
6. Datachannel Attribute the <fmt> sub-field carries the SCTP port number and the mandatory
"a=sctpmap:" attribute contains the actual media format within the
protocol parameter.
This attribute maps from a datachannel number (as used in an "m=" When a list of port number identifiers is given, this implies that
line) to an encoding name denoting the payload format to be used. all of these associations MUST run on top of the same DTLS
connection. For the payload type assignments the "a=sctpmap:"
attribute (see Section 5.1) SHOULD be used to map from a port number
to a media encoding name that identifies the payload format
transported by the association or the actual application protocol
running on top of it.
datachannel-attr = "a=datachannel:" datachannel-number m=application 54111 DTLS/SCTP 5000 5001 5002
datachannel-number = 1*DIGIT c=IN IP4 79.97.215.79
a=sctpmap:5000 webrtc-datachannel 16
a=sctpmap:5001 bfcp 2
a=sctpmap:5002 t38 1
7. The Setup and Connection Attributes and Association Management 4.3. Predefinition of Data Channels
An 'm' line that specifies 'SCTP' or 'SCTP/DTLS' or 'DTLS/SCTP' MAY
further provide the definition of channels running within the
association. When provided the channel definition MUST include the
"a=stream:" attribute (see Section 5.2) indicating the stream number
used to form the channel, the "a=label:" attribute (see Section 5.3)
indicating the name of the channel and the "a=subprotocol:" attribute
(see Section 5.4) indicating which protocol the client would like to
speak on the channel.
By default a channel is defined as 'reliable', however it is possible
specify a channel as Partial Reliable indicating that the messages
will not be retransmitted more times than specified in the
"a=max_retr:" attribute (see Section 5.5) or indicating messages
might not be transmitted or retransmitted after a specified life-time
given in milli-seconds in the "a=max_time:" attribute (see
Section 5.6).
By default a channel is defined as 'ordered' (i.e. within a stream,
an endpoint MUST deliver DATA chunks received to the upper layer
according to the order of their Stream Sequence Number), however it
is possible specify a channel as Unordered using the "a=unordered"
attribute (see Section 5.7).
m=application 54111 DTLS/SCTP 5000 5001 5002
c=IN IP4 79.97.215.79
a=sctpmap:5000 webrtc-DataChannel 2
a=sctpmap:5001 bfcp 1
a=sctpmap:5002 t38 1
a=webrtc-DataChannel:5000 stream=1;label="channel 1";subprotocol="chat";
a=webrtc-DataChannel:5000 stream=2;label="channel 2";subprotocol="file transfer";max_retr=3
5. Media attributes
5.1. sctpmap Attribute
The sctpmap attribute maps from a port number (as used in an "m="
line) to an encoding name denoting the payload format to be used on
top of the SCTP association or the actual protocol running on top of
it. It also can provide the number of streams to be supported by the
association. If this attribute is not present, the implementation
should provide a default, with a suggested value of 16.
sctpmap-attr = "a=sctpmap:" sctpmap-number protocol [streams]
sctpmap-number = 1*DIGIT
protocol = labelstring
labelstring = text
text = byte-string
streams = 1*DIGIT
5.2. stream Attribute
The 'stream' attribute indicates the actual stream number within the
association used to form the channel.
stream-attr = "a=stream=" streamnumber
streamnumber = 1*DIGIT
5.3. label Attribute
The 'label' attribute indicates the name of the channel. It
represents a label that can be used to distinguish, in the context of
the WebRTC API, an RTCDataChannel object from other RTCDataChannel
objects.
label-attr = "a=label=" labelstring
labelstring = text
text = byte-string
5.4. subprotocol Attribute
The 'subprotocol' attribute indicates which protocol the client would
like to speak on the channel.
subprotocol-attr = "a=subprotocol=" labelstring
labelstring = text
text = byte-string
5.5. max_retr Attribute
The 'max_retr' attribute indicates the max times an user message will
be retransmitted.
maxretr-attr = "a=maxretr=" maxretrvalue
maxretrvalue = 1*DIGIT
5.6. max_time Attribute
An user messages might not be transmitted or retransmitted after a
specified life-time given in milli-seconds in the 'max_time'
attribute.
maxtime-attr = "a=maxtime=" maxtimevalue
maxtimevalue = 1*DIGIT
5.7. unordered Attribute
The 'unordered' attribute indicates that DATA chunks in the channel
MUST be dispatched to the upper layer by the receiver without any
attempt to reorder.
6. The Setup and Connection Attributes and Association Management
The use of the 'setup' and 'connection' attributes in the context of The use of the 'setup' and 'connection' attributes in the context of
an SCTP association is identical to the use of these attributes in an SCTP association is identical to the use of these attributes in
the context of a TCP connection. That is, SCTP endpoints MUST follow the context of a TCP connection. That is, SCTP endpoints MUST follow
the rules in Sections 4 and 5 of RFC 4145 [RFC4145] when it comes to the rules in Sections 4 and 5 of RFC 4145 [RFC4145] when it comes to
the use of the 'setup' and 'connection' attributes in offer/answer the use of the 'setup' and 'connection' attributes in offer/answer
[RFC3264] exchanges. [RFC3264] exchanges.
The management of an SCTP association is identical to the management The management of an SCTP association is identical to the management
of a TCP connection. That is, SCTP endpoints MUST follow the rules of a TCP connection. That is, SCTP endpoints MUST follow the rules
in Section 6 of RFC 4145 [RFC4145] to manage SCTP associations. in Section 6 of RFC 4145 [RFC4145] to manage SCTP associations.
Whether to use the SCTP ordered or unordered delivery service is up Whether to use the SCTP ordered or unordered delivery service is up
to the applications using the SCTP association. to the applications using the SCTP association.
8. Multihoming 7. Multihoming
An SCTP endpoint, unlike a TCP endpoint, can be multihomed. An SCTP An SCTP endpoint, unlike a TCP endpoint, can be multihomed. An SCTP
endpoint is considered to be multihomed if it has more than one IP endpoint is considered to be multihomed if it has more than one IP
address. A multihomed SCTP endpoint informs a remote SCTP endpoint address. A multihomed SCTP endpoint informs a remote SCTP endpoint
about all its IP addresses using the address parameters of the INIT about all its IP addresses using the address parameters of the INIT
or the INIT-ACK chunk (depending on whether the multihomed endpoint or the INIT-ACK chunk (depending on whether the multihomed endpoint
is the one initiating the establishment of the association). is the one initiating the establishment of the association).
Therefore, once the address provided in the 'c' line has been used to Therefore, once the address provided in the 'c' line has been used to
establish the SCTP association (i.e., to send the INIT chunk), establish the SCTP association (i.e., to send the INIT chunk),
address management is performed using SCTP. This means that two SCTP address management is performed using SCTP. This means that two SCTP
endpoints can use addresses that were not listed in the 'c' line but endpoints can use addresses that were not listed in the 'c' line but
that were negotiated using SCTP mechanisms. that were negotiated using SCTP mechanisms.
During the lifetime of an SCTP association, the endpoints can add and During the lifetime of an SCTP association, the endpoints can add and
remove new addresses from the association at any point [RFC5061]. If remove new addresses from the association at any point [RFC5061]. If
an endpoint removes the IP address listed in its 'c' line from the an endpoint removes the IP address listed in its 'c' line from the
SCTP association, the endpoint MUST update the 'c' line (e.g., by SCTP association, the endpoint SHOULD update the 'c' line (e.g., by
sending a re-INVITE with a new offer) so that it contains an IP sending a re-INVITE with a new offer) so that it contains an IP
address that is valid within the SCTP association. address that is valid within the SCTP association.
In some environments, intermediaries performing firewall control use In some environments, intermediaries performing firewall control use
the addresses in offer/answer exchanges to perform media the addresses in offer/answer exchanges to perform media
authorization. That is, policy-enforcement network elements do not authorization. That is, policy-enforcement network elements do not
let media through unless it is sent to the address in the 'c' line. let media through unless it is sent to the address in the 'c' line.
In such network environments, the SCTP endpoints can only exchange In such network environments, the SCTP endpoints can only exchange
media using the IP addresses listed in their 'c' lines. In these media using the IP addresses listed in their 'c' lines. In these
environments, an endpoint wishing to use a different address needs to environments, an endpoint wishing to use a different address needs to
update its 'c' line (e.g., by sending a re-INVITE with a new offer) update its 'c' line (e.g., by sending a re-INVITE with a new offer)
so that it contains the new IP address. so that it contains the new IP address.
It is worth to underline that when using SCTP on top of DTLS, only It is worth to underline that when using SCTP on top of DTLS, only
single homed SCTP associations can be used, since DTLS does not single homed SCTP associations can be used, since DTLS does not
expose any address management to its upper layer. expose any address management to its upper layer.
9. Network Address Translation (NAT) Considerations 8. Network Address Translation (NAT) Considerations
SCTP specific features (not present in UDP/TCP), such as the checksum SCTP specific features (not present in UDP/TCP), such as the checksum
(CRC32c) value calculated on the whole packet (not just the header) (CRC32c) value calculated on the whole packet (not just the header)
or its multihoming capabilities, present new challenges for NAT or its multihoming capabilities, present new challenges for NAT
traversal. [I-D.ietf-behave-sctpnat] describes an SCTP specific traversal. [I-D.ietf-behave-sctpnat] describes an SCTP specific
variant of NAT, which provides similar features of Network Address variant of NAT, which provides similar features of Network Address
and Port Translation (NAPT). and Port Translation (NAPT).
Current NATs do not typically support SCTP. As an alternative to Current NATs do not typically support SCTP. As an alternative to
design SCTP specific NATs, Encapsulating SCTP into UDP design SCTP specific NATs, Encapsulating SCTP into UDP
skipping to change at page 8, line 32 skipping to change at page 10, line 38
At the time of writing, the work on NAT traversal for SCTP is still At the time of writing, the work on NAT traversal for SCTP is still
work in progress. Additionally, no extension has been defined to work in progress. Additionally, no extension has been defined to
integrate ICE (Interactive Connectivity Establishment) [RFC5768] with integrate ICE (Interactive Connectivity Establishment) [RFC5768] with
SCTP and its multihoming capabilities either. Therefore, this SCTP and its multihoming capabilities either. Therefore, this
specification does not define how to describe SCTP-over-UDP streams specification does not define how to describe SCTP-over-UDP streams
in SDP or how to establish and maintain SCTP associations using ICE. in SDP or how to establish and maintain SCTP associations using ICE.
Should these features be specified for SCTP in the future, there will Should these features be specified for SCTP in the future, there will
be a need to specify how to use them in an SDP environment as well. be a need to specify how to use them in an SDP environment as well.
10. Examples 9. Examples
The following examples show the use of the 'setup' and 'connection' The following examples show the use of the 'setup' and 'connection'
SDP attributes. As discussed in Section 7, the use of these SDP attributes. As discussed in Section 6, the use of these
attributes with an SCTP association is identical to their use with a attributes with an SCTP association is identical to their use with a
TCP connection. For the purpose of brevity, the main portion of the TCP connection. For the purpose of brevity, the main portion of the
session description is omitted in the examples, which only show 'm' session description is omitted in the examples, which only show 'm'
lines and their attributes (including 'c' lines). lines and their attributes (including 'c' lines).
10.1. Actpass/Passive 9.1. Actpass/Passive
An offerer at 192.0.2.2 signals its availability for an SCTP An offerer at 192.0.2.2 signals its availability for an SCTP
association at SCTP port 54111. Additionally, this offerer is also association at SCTP port 54111. Additionally, this offerer is also
willing to initiate the SCTP association: willing to initiate the SCTP association:
m=application 54111 SCTP 0 1 2 m=application 54111 SCTP 54111
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=setup:actpass a=setup:actpass
a=connection:new a=connection:new
a=streams=3 a=sctpmap:54111 t38 1
a=datachannel:0 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:1 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:2 RTCWeb label=xxxx;options="dictionary string"
Figure 1 Figure 1
The endpoint at 192.0.2.1 responds with the following description: The endpoint at 192.0.2.1 responds with the following description:
m=image 54321 SCTP 0 1 2 m=image 54321 SCTP 54321
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=setup:passive a=setup:passive
a=connection:new a=connection:new
a=streams=3 a=sctpmap:t54321 t38 1
a=datachannel:0 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:1 RTCWeb label=xxxx;options="dictionary string"
a=datachannel:2 RTCWeb label=xxxx;options="dictionary string"
Figure 2 Figure 2
This will cause the offerer (at 192.0.2.2) to initiate an SCTP This will cause the offerer (at 192.0.2.2) to initiate an SCTP
association to port 54321 at 192.0.2.1. association to port 54321 at 192.0.2.1.
10.2. Existing Connection Reuse 9.2. Existing Connection Reuse
Subsequent to the exchange in Section 10.1, another offer/answer Subsequent to the exchange in Section 9.1, another offer/answer
exchange is initiated in the opposite direction. The endpoint at exchange is initiated in the opposite direction. The endpoint at
192.0.2.1, which now acts as the offerer, wishes to continue using 192.0.2.1, which now acts as the offerer, wishes to continue using
the existing association: the existing association:
m=application 54321 SCTP * m=application 54321 SCTP *
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=setup:passive a=setup:passive
a=connection:existing a=connection:existing
Figure 3 Figure 3
skipping to change at page 10, line 15 skipping to change at page 12, line 6
m=application 9 SCTP * m=application 9 SCTP *
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=setup:active a=setup:active
a=connection:existing a=connection:existing
Figure 4 Figure 4
The existing SCTP association between 192.0.2.2 and 192.0.2.1 will be The existing SCTP association between 192.0.2.2 and 192.0.2.1 will be
reused. reused.
10.3. SDP description for DTLS Connection 9.3. SDP description for DTLS Connection
An offerer at 192.0.2.2 signals the availability of a T.38 fax An offerer at 192.0.2.2 signals the availability of a T.38 fax
session over SCTP/DTLS. session over SCTP/DTLS.
m=image 54111 SCTP/DTLS 0 m=image 54111 DTLS/SCTP 5000
c=IN IP4 192.0.2.2 c=IN IP4 192.0.2.2
a=setup:actpass a=setup:actpass
a=connection:new a=connection:new
a=fingerprint:SHA-1 \ a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=fmtp:datachannel streams=1 a=sctpmap:5000 webrtc-DataChannel 16
a=datachannel:0 t38 label=xxxx;options="dictionary string" a=webrtc-DataChannel:5000 stream=1;label="channel 1";subprotocol="chat";
a=webrtc-DataChannel:5000 stream=2;label="channel 2";subprotocol="file transfer"
Figure 5 Figure 5
11. Security Considerations 10. Security Considerations
See RFC 4566 [RFC4566] for security considerations on the use of SDP See RFC 4566 [RFC4566] for security considerations on the use of SDP
in general. See RFC 3264 [RFC3264], RFC 4145 [RFC4145] and RFC 4572 in general. See RFC 3264 [RFC3264], RFC 4145 [RFC4145] and RFC 4572
[RFC4572] for security considerations on establishing media streams [RFC4572] for security considerations on establishing media streams
using offer/answer exchanges. See RFC 4960 [RFC4960] for security using offer/answer exchanges. See RFC 4960 [RFC4960] for security
considerations on SCTP in general and [RFC6083] for security considerations on SCTP in general and [RFC6083] for security
consideration using DTLS on top of SCTP. This specification does not consideration using DTLS on top of SCTP. This specification does not
introduce any new security consideration in addition to the ones introduce any new security consideration in addition to the ones
discussed in those specifications. discussed in those specifications.
12. IANA Considerations 11. IANA Considerations
This document defines three new proto values: 'SCTP', 'SCTP/DTLS' and This document defines three new proto values: 'SCTP', 'SCTP/DTLS' and
'DTLS/SCTP'. Their formats are defined in Section 3. These proto 'DTLS/SCTP'. Their formats are defined in Section 3. These proto
values should be registered by the IANA under "Session Description values should be registered by the IANA under "Session Description
Protocol (SDP) Parameters" under "proto". Protocol (SDP) Parameters" under "proto".
This document defines two SDP session and media-level attributes: This document defines two SDP session and media-level attributes:
'streams'. Its format is defined in Section 5. This attribute 'sctpmap'. Its format is defined in Section 5.1. This attribute
should be registered by IANA under "Session Description Protocol should be registered by IANA under "Session Description Protocol
(SDP) Parameters" under "att-field" (both session and media (SDP) Parameters" under "att-field" (both session and media
level)". level)".
'datachannel'. Its format is defined in Section 6. This 12. References
attribute should be registered by IANA under "Session Description
Protocol (SDP) Parameters" under "att-field" (both session and
media level)".
13. References
13.1. Normative References 12.1. 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.
[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.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145, the Session Description Protocol (SDP)", RFC 4145,
skipping to change at page 12, line 16 skipping to change at page 14, line 5
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[I-D.tuexen-tsvwg-sctp-dtls-encaps] [I-D.tuexen-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS
Encapsulation of SCTP Packets for RTCWEB", Encapsulation of SCTP Packets for RTCWEB",
draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress), draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress),
July 2012. July 2012.
13.2. Informative References 12.2. Informative References
[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol", Layer Security over Stream Control Transmission Protocol",
RFC 3436, December 2002. RFC 3436, December 2002.
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083, January 2011. Transmission Protocol (SCTP)", RFC 6083, January 2011.
[RFC5768] Rosenberg, J., "Indicating Support for Interactive [RFC5768] Rosenberg, J., "Indicating Support for Interactive
 End of changes. 43 change blocks. 
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