draft-ietf-mmusic-sctp-sdp-06.txt   draft-ietf-mmusic-sctp-sdp-07.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: August 17, 2014 February 13, 2014 Expires: January 5, 2015 July 4, 2014
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-06 draft-ietf-mmusic-sctp-sdp-07
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
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 17, 2014. This Internet-Draft will expire on January 5, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 3
4. Media Formats . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Media Formats . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Media Descriptions . . . . . . . . . . . . . . . . . . . . 5 4.1. Media Descriptions . . . . . . . . . . . . . . . . . . . 5
5. Media attributes . . . . . . . . . . . . . . . . . . . . . . . 6 4.1.1. sctp-port . . . . . . . . . . . . . . . . . . . . . . 6
5.1. sctpmap Attribute . . . . . . . . . . . . . . . . . . . . 6 4.1.2. max-message-size . . . . . . . . . . . . . . . . . . 6
6. The Setup and Connection Attributes and Association 5. The Setup and Connection Attributes and Association
Management . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Management . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Network Address Translation (NAT) Considerations . . . . . . . 8 7. Network Address Translation (NAT) Considerations . . . . . . 8
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9 8.1. Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 8
9.2. Existing Connection Reuse . . . . . . . . . . . . . . . . 9 8.2. Existing Connection Reuse . . . . . . . . . . . . . . . . 9
9.3. SDP description for SCTP over DTLS Connection . . . . . . 10 8.3. SDP description for SCTP over DTLS Connection . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8.4. SDP description for SCTP over DTLS Connection using
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 default values . . . . . . . . . . . . . . . . . . . . . 10
11.1. sctpmap attribute . . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10.1. sctp-port attribute . . . . . . . . . . . . . . . . . . 12
13.1. Normative References . . . . . . . . . . . . . . . . . . . 12 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
13.2. Informative References . . . . . . . . . . . . . . . . . . 13 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 12.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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. TCP-Based Media Transport in the Session Description invitations. TCP-Based Media Transport in the Session Description
Protocol (SDP) [RFC4145] specifies a general mechanism for describing Protocol (SDP) [RFC4145] specifies a general mechanism for describing
and establishing TCP (Transmission Control Protocol) streams. and establishing TCP (Transmission Control Protocol) streams.
Connection-Oriented Media Transport over the Transport Layer Security Connection-Oriented Media Transport over the Transport Layer Security
(TLS) Protocol in the Session Description Protocol (SDP) [RFC4572] (TLS) Protocol in the Session Description Protocol (SDP) [RFC4572]
skipping to change at page 3, line 29 skipping to change at page 3, line 13
SCTP : to describe SCTP-based [RFC4960] media streams. SCTP : to describe SCTP-based [RFC4960] media streams.
SCTP/DTLS : to describe media streams transported using the Datagram SCTP/DTLS : to describe media streams transported using the Datagram
Transport Layer Security (DTLS) [RFC4347] protocol over SCTP, as Transport Layer Security (DTLS) [RFC4347] protocol over SCTP, as
specified in [RFC6083]. DTLS over SCTP provides communications specified in [RFC6083]. DTLS over SCTP provides communications
privacy for applications that use SCTP as their transport privacy for applications that use SCTP as their transport
protocol. protocol.
DTLS/SCTP : to describe media streams transported using SCTP on top DTLS/SCTP : to describe media streams transported using SCTP on top
of the Datagram Transport Layer Security (DTLS) protocol, as of the Datagram Transport Layer Security (DTLS) protocol, as
defined in [I-D.tuexen-tsvwg-sctp-dtls-encaps]. defined in [I-D.ietf-tsvwg-sctp-dtls-encaps].
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 reliable, 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
skipping to change at page 4, line 32 skipping to change at page 4, line 15
Media described using an 'm' line containing the 'SCTP' protocol Media described using an 'm' line containing the 'SCTP' protocol
identifier are carried using SCTP [RFC4960]. identifier are carried using SCTP [RFC4960].
The 'SCTP/DTLS' protocol identifier indicates that the media The 'SCTP/DTLS' protocol identifier indicates that the media
described will use the Datagram Transport Layer Security (DTLS) described will use the Datagram Transport Layer Security (DTLS)
[RFC4347] over SCTP as specified in [RFC6083]. [RFC4347] over SCTP as specified in [RFC6083].
The 'DTLS/SCTP' protocol identifier indicates that the media The 'DTLS/SCTP' protocol identifier indicates that the media
described will use SCTP on top of the Datagram Transport Layer described will use SCTP on top of the Datagram Transport Layer
Security (DTLS) protocol as specified in Security (DTLS) protocol as specified in
[I-D.tuexen-tsvwg-sctp-dtls-encaps]. The actual layer below DTLS can [I-D.ietf-tsvwg-sctp-dtls-encaps]. The actual layer below DTLS can
be plain UDP or what ICE agrees on (in the case ICE is used to be plain UDP or what ICE agrees on (in the case ICE is used to
negotiate the actual transport flow). The lower layer used is negotiate the actual transport flow). The lower layer used is
identified from the elements present inside the m= line block. identified from the elements present inside the m= line block.
An 'm' line that specifies 'SCTP' or 'SCTP/DTLS' or 'DTLS/SCTP' MUST An 'm' line that specifies 'SCTP' or 'SCTP/DTLS' or 'DTLS/SCTP' MUST
further qualify the application-layer protocol using an fmt further qualify the application-layer protocol using an fmt
identifier. identifier.
An 'm' line that specifies 'SCTP/DTLS' or 'DTLS/SCTP' MUST provide a An 'm' line that specifies 'SCTP/DTLS' or 'DTLS/SCTP' MUST provide a
certificate fingerprint only if the endpoint supports, and is willing certificate fingerprint only if the endpoint supports, and is willing
skipping to change at page 5, line 17 skipping to change at page 4, line 43
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. Media Descriptions An m-line with <proto> of 'SCTP', 'SCTP/DTLS' or 'DTLS/SCTP' always
describe a single SCTP association.
The media description change slightly depending on the actual An 'm' line that specifies 'SCTP', 'SCTP/DTLS' or 'DTLS/SCTP' MUST
<proto>. further qualify the application-layer protocol using an 'fmt'
identifier.
If the <proto> sub-field is 'SCTP' or 'SCTP/DTLS' The 'fmtp' attribute should be used to map from the 'association-
usage' (as used in an "m=" line) to the max-message-size parameter
indicating the maximum message size, in bytes, the endpoint is
willing to accept.
the <port> is the SCTP transport port and follows the same active/ The sctp-port attribute specifies the actual sctp port.
passive offer/answer model described in Section 4.1 of [RFC4145];
the <fmt> sub-field carries the same port number value specified m=application 12345 DTLS/SCTP webrtc-datachannel
in the <port> and the mandatory SDP "sctpmap" attribute contains a=fmtp:webrtc-datachannel max-message-size=100000
the actual media format within the protocol parameter. a=sctp-port 4060
m=application 54111 SCTP/DTLS 54111 4.1. Media Descriptions
a=sctpmap:54111 t38 1
Running SCTP over DTLS make possible to have multiple SCTP An 'm' line containing the 'SCTP', 'SCTP/DTLS' or 'DTLS/SCTP'
associations on top of the same DTLS connection; each SCTP protocol identifier has the following syntax:
association make use of a distinct port number that is mainly used to
demultiplex the associations.
If the <proto> sub-field is 'DTLS/SCTP' sctp-m-line = %x6d "="
("application" space sctp-port space "SCTP" space sctp-fmt CRLF) /
("application" space sctp-port space "SCTP/DTLS" space sctp-fmt CRLF) /
("application" space udp-port space "DTLS/SCTP" space sctp-fmt CRLF)
the <port> is the UDP transport port; sctp-port = port
the <fmt> sub-field carries the SCTP port number and the mandatory udp-port = port
SDP "sctpmap" attribute contains the actual media format within
the protocol parameter. The SCTP port number is the UA chosen
port to use on the DTLS channel.
When a list of SCTP port number identifiers is given, this implies sctp-fmt = association-usage
that 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.
m=application 54111 DTLS/SCTP 5000 association-usage = token
c=IN IP4 79.97.215.79
a=sctpmap:5000 webrtc-datachannel max-message-size=100000 streams=16
5. Media attributes The media description change slightly depending on the actual
<proto>.
5.1. sctpmap Attribute If the <proto> sub-field is 'SCTP' or 'SCTP/DTLS', the <port> is
the SCTP transport port (sctp-port) and follows the same active/
passive offer/answer model described in Section 4.1 of [RFC4145].
The sctpmap attribute maps from a port number (as used in an "m=" If the <proto> sub-field is 'DTLS/SCTP', the <port> is the UDP
line) to an encoding name denoting the payload format to be used on transport port (udp-port).
top of the SCTP association or the actual protocol running on top of
it.
The sctpmap MUST include the app parameter indicating the application The <fmt> sub-field carries the parameter indicating the conventional
running on top of the association. usage of an entire sctp association (association-usage).
The sctpmap line should also contain the max-message-size parameter association-usage:
indicating the maximum message size, in bytes, the endpoint is The association-usage token indicates the conventional usage of an
willing to accept. entire sctp association including its streams (e.g. the pairing of
certain streams, the protocol carried over certain streams, etc).
The peer should assume that larger message will be rejected by the This parameter is a required parameter. [TBD a value for the
endpoint, though it is up to the endpoint decide the appropriate generic usage as defined in RFC 4960 [RFC4960]].
behaviour.
A parameter with value of '0' will signal a best effort attempt, Any offered association MAY be rejected in the answer, for any
subject to the current endpoint memory capacity, to handle reason. If an association offer is rejected, the offerer and
messages of any size. answerer MUST NOT establish an SCTP association for it. To reject an
SCTP association, the <port> in the answer MUST be set to zero.
If the parameter is not present, the implementation should provide 4.1.1. sctp-port
a default, with a suggested value of 64K.
It may also provide the stream parameter to specify the initial sctp-port-attr = "a=sctp-port=" portnumber
number of incoming streams to be supported by each side of the port-number = port
association.
If this parameter is not present, the implementation should The sctp-port attribute specifies the actual sctp port. This
provide a default, with a suggested value of 16. attribute is optional and is only meaningful and required if the the
<proto> sub-field is 'DTLS/SCTP'. If the attribute is not present,
the default value is 5000.
sctpmap-attr = "a=sctpmap:" sctpmap-number 4.1.2. max-message-size
app [max-message-size] [streams]
sctpmap-number = 1*DIGIT
app = token
max-message-size = "max-message-size" EQUALS 1*DIGIT
streams = "streams" EQUALS 1*DIGIT"
For the "a=sctpmap:" attribute line in the offer, there MUST be a sctpmap-attr = "a=fmtp:" association-usage [max-message-size]
corresponding "a=sctpmap:" attribute line in the answer. max-message-size = "max-message-size" EQUALS 1*DIGIT
Any offered association MAY be rejected in the answer, for any The 'fmtp' attribute may be used to map from the 'association-usage'
reason. If an association offer is rejected, the offerer and (as used in an "m=" line) to the max-message-size parameter
answerer MUST NOT establish an SCTP association for it. To reject an indicating the maximum message size, in bytes, the endpoint is
SCTP association, the SCTP port number in the "a=sctpmap:" attribute willing to accept.
line in the answer MUST be set to zero.
Any offered association with an "a=sctpmap:" attribute line providing The max-message-size parameter indicates the maximum message size, in
an incoming stream number of zero or larger than 65535 MUST be bytes, the endpoint is willing to accept. The peer should assume
rejected in the answer. An offered association answered with an that larger message will be rejected by the endpoint, though it is up
"a=sctpmap:" attribute line providing an incoming stream number of to the endpoint decide the appropriate behaviour. A parameter with
zero or larger than 65535 MUST NOT be established. value of '0' will signal a best effort attempt, subject to the
current endpoint memory capacity, to handle messages of any size. If
the parameter is not present, the implementation should provide a
default, with a suggested value of 64K.
6. The Setup and Connection Attributes and Association Management 5. 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.
7. Multihoming 6. 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 SHOULD update the 'c' line (e.g., by SCTP association, the endpoint SHOULD update the 'c' line (e.g., by
skipping to change at page 8, line 33 skipping to change at page 8, line 5
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.
8. Network Address Translation (NAT) Considerations 7. 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 [RFC6951] design SCTP specific NATs, Encapsulating SCTP into UDP [RFC6951]
makes it possible to use SCTP in networks with legacy NAT and makes it possible to use SCTP in networks with legacy NAT and
firewalls not supporting SCTP. firewalls not supporting SCTP.
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 establish and maintain SCTP
in SDP or how to establish and maintain SCTP associations using ICE. associations using ICE. Should this feature be specified for SCTP in
Should these features be specified for SCTP in the future, there will the future, there will be a need to specify how to use them in an SDP
be a need to specify how to use them in an SDP environment as well. environment as well.
9. Examples 8. 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 6, the use of these SDP attributes. As discussed in Section 5, 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).
9.1. Actpass/Passive 8.1. 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 54111 m=application 54111 SCTP t38
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=sctpmap:54111 t38 1
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=application 54321 SCTP 54321 m=application 54321 SCTP t38
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=sctpmap:t54321 t38 1
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.
9.2. Existing Connection Reuse 8.2. Existing Connection Reuse
Subsequent to the exchange in Section 9.1, another offer/answer Subsequent to the exchange in Section 8.1, 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
The endpoint at 192.0.2.2 also wishes to use the existing SCTP The endpoint at 192.0.2.2 also wishes to use the existing SCTP
association and responds with the following description: association and responds with the following description:
m=application 54111 SCTP * m=application 54111 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.
9.3. SDP description for SCTP over DTLS Connection 8.3. SDP description for SCTP over DTLS Connection
This example shows the usage of SCTP over DTLS. This example shows the usage of SCTP over DTLS.
An offerer at 192.0.2.2 signals the availability of a webrtc- An offerer at 192.0.2.2 signals the availability of a webrtc-
DataChannel session over SCTP/DTLS. The DTLS connection runs on top DataChannel session over SCTP/DTLS. The DTLS connection runs on top
of port 54111. of port 54111. The sctp association runs on port 5000 (i.e. sctp-
port) over DTLS. The maximum message size, in bytes, the endpoint is
willing to accept is 100000 (i.e. max-message-size).
m=application 54111 DTLS/SCTP 5000 m=application 54111 DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.2 a=fmtp:webrtc-datachannel max-message-size=100000
a=setup:actpass a=sctp-port 5000
a=connection:new c=IN IP4 192.0.2.2
a=fingerprint:SHA-1 \ a=setup:actpass
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB a=connection:new
a=sctpmap:5000 webrtc-DataChannel max-message-size=100000 streams=16 a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 5 Figure 5
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=application 62442 DTLS/SCTP 5001 m=application 62442 DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1 a=fmtp:webrtc-datachannel max-message-size=100000
a=setup:actpass a=sctp-port 5000
a=connection:new c=IN IP4 192.0.2.1
a=fingerprint:SHA-1 \ a=setup:actpass
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB a=connection:new
a=sctpmap:5001 webrtc-DataChannel max-message-size=100000 streams=16 a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 6 Figure 6
10. Security Considerations 8.4. SDP description for SCTP over DTLS Connection using default values
This example shows the usage of SCTP over DTLS when default values
are used.
An offerer at 192.0.2.2 signals the availability of a webrtc-
DataChannel session over SCTP/DTLS. The DTLS connection runs on top
of port 54111. As the sctp association runs on the default sct-port
number 5000 over DTLS ant the maximum message size, in bytes, the
endpoint is willing to accept is equal to the default value of 64K
both the parameters may be omitted.
Note that as the sctp association is meant to be used to transport
webrtc data channel, the association-usage parameter is present with
the webrtc-datachannel value.
m=application 54111 DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.2
a=setup:actpass
a=connection:new
a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 7
The endpoint at 192.0.2.1 responds with the following description,
with default value for the sctp-port and max-message-size parameters:
m=application 62442 DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1
a=setup:actpass
a=connection:new
a=fingerprint:SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
Figure 8
9. 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.
11. IANA Considerations 10. 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".
11.1. sctpmap attribute The "fmt" value, "association-usage", used with these "proto" is
required. It is defined in section Section 4.1.
This document defines a new SDP session and media-level attribute:
'sctpmap'. Its format is defined in Section 5.1. This attribute
should be registered by IANA under "Session Description Protocol
(SDP) Parameters" under "att-field" (both session and media
level)".
The 'sctpmap' attribute also
'sctpmap'. Its format is defined in Section 5.1. This attribute
should be registered by IANA under "Session Description Protocol
(SDP) Parameters" under "att-field" (both session and media
level)".
The sctpmap also specifies tree parameters:
The mandatory 'app' parameter indicating the application running
on top of the association.
The optional max-message-size parameter indicating the maximum
message size, in bytes, the endpoint is willing to accept.
The optional streams parameter indicating the maximum message [Note] TBD whether a new registry is necessary to register the
size, in bytes, the endpoint is willing to accept. different possible "association-usage" values.
The 'stream' attribute indicating the initial number of incoming 10.1. sctp-port attribute
streams supported by each side of the association.
sctpmap-attr = "a=sctpmap:" sctpmap-number This document defines a new SDP session and media-level attribute:
app [max-message-size] [streams]
sctpmap-number = 1*DIGIT
app = token
max-message-size = "max-message-size" EQUALS 1*DIGIT
streams = "streams" EQUALS 1*DIGIT"
[Open Issue] This specification has to creats a new IANA registry sctp-port: Its format is define in section Section 4.1.This
named "SCTP Application" to register all the possible values of the attribute should be registered by IANA under "Session Description
'app' parameter and register as first value "webrtc-datachannel" for Protocol (SDP) Parameters" under "att-field" (both session and
draft-ietf-rtcweb-data-channel. media level)".
12. Acknowledgments 11. Acknowledgments
The authors wish to thank Harald Alvestrand, Randell Jesup, Paul The authors wish to thank Harald Alvestrand, Randell Jesup, Paul
Kyzivat, Michael Tuexen for their comments and useful feedback. Kyzivat, Michael Tuexen for their comments and useful feedback.
13. References 12. 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
June 2002. 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,
September 2005. September 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", RFC 4288, December 2005. Registration Procedures", RFC 4288, December 2005.
[RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures", Extensions (MIME) Part Four: Registration Procedures", BCP
BCP 13, RFC 4289, December 2005. 13, RFC 4289, December 2005.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006. Security", RFC 4347, April 2006.
[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.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, July 2006. Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
RFC 4960, September 2007. 4960, September 2007.
[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP) Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061, Dynamic Address Reconfiguration", RFC 5061, September
September 2007. 2007.
[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.ietf-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets for RTCWEB", Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress), dtls-encaps-04 (work in progress), May 2014.
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
Connectivity Establishment (ICE) in the Session Initiation Connectivity Establishment (ICE) in the Session Initiation
Protocol (SIP)", RFC 5768, April 2010. Protocol (SIP)", RFC 5768, April 2010.
[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream [RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, May 2013. to End-Host Communication", RFC 6951, May 2013.
[I-D.ietf-behave-sctpnat] [I-D.ietf-behave-sctpnat]
Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
Transmission Protocol (SCTP) Network Address Translation", Transmission Protocol (SCTP) Network Address Translation",
draft-ietf-behave-sctpnat-08 (work in progress), draft-ietf-behave-sctpnat-09 (work in progress), September
February 2013. 2013.
Authors' Addresses Authors' Addresses
Salvatore Loreto Salvatore Loreto
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Salvatore.Loreto@ericsson.com Email: Salvatore.Loreto@ericsson.com
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
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