MMUSIC C. Holmberg
Internet-Draft S. Loreto
Intended status: Standards Track G. Camarillo
Expires: June 22, 2015 Ericsson
December 19, 2014
Stream Control Transmission Protocol (SCTP)-Based Media Transport in the
Session Description Protocol (SDP)
draft-ietf-mmusic-sctp-sdp-10
Abstract
SCTP (Stream Control Transmission Protocol) is a transport protocol
used to establish associations between two endpoints.
This specification describes how to describe SCTP associations using
the Session Description Protocol (SDP), and defines the following new
SDP Media Description protocol identifiers (proto values):'SCTP',
'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'.
The specification also describes how to use the new proto values
together with the SDP Offer/Answer mechanism in order to negotiate
and establish SCTP associations, and how to indicate the SCTP
application usage.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 22, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SCTP Terminology . . . . . . . . . . . . . . . . . . . . . . 4
4. SDP Media Descriptions . . . . . . . . . . . . . . . . . . . 4
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Protocol Identifiers . . . . . . . . . . . . . . . . . . 5
4.3. Media Format Management . . . . . . . . . . . . . . . . . 5
4.4. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. SDP 'sctp-port' Attribute . . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. SDP 'max-message-size' Attribute . . . . . . . . . . . . . . 7
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. SDP 'fmtp' Attribute . . . . . . . . . . . . . . . . . . . . 7
7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. UDP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 8
9. TCP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 8
10. SCTP Association Management . . . . . . . . . . . . . . . . . 8
10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 8
10.2. SDP sendrecv/sendonly/sendrecv/inactive Attribute . . . 9
10.3. SDP setup Attribute . . . . . . . . . . . . . . . . . . 9
10.3.1. General . . . . . . . . . . . . . . . . . . . . . . 9
10.3.2. SCTP Association Initiation . . . . . . . . . . . . 9
10.3.3. TLS Role Determination . . . . . . . . . . . . . . . 9
10.4. SDP connection Attribute . . . . . . . . . . . . . . . . 10
11. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 10
11.1. General . . . . . . . . . . . . . . . . . . . . . . . . 10
11.2. Generating the Initial SDP Offer . . . . . . . . . . . . 11
11.3. Generating the SDP Answer . . . . . . . . . . . . . . . 11
11.4. Offerer Processing of the SDP Answer . . . . . . . . . . 12
11.5. Modifying the Session . . . . . . . . . . . . . . . . . 13
12. Multihoming Considerations . . . . . . . . . . . . . . . . . 13
13. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 14
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13.1. General . . . . . . . . . . . . . . . . . . . . . . . . 14
13.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 14
14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14
15. Security Considerations . . . . . . . . . . . . . . . . . . . 14
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
16.1. New SDP proto values . . . . . . . . . . . . . . . . . . 14
16.2. New SDP Attribute . . . . . . . . . . . . . . . . . . . 15
16.3. association-usage Name Registry . . . . . . . . . . . . 15
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
18. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 16
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
19.1. Normative References . . . . . . . . . . . . . . . . . . 17
19.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
SDP (Session Description Protocol) [RFC4566] provides a general-
purpose format for describing multimedia sessions in announcements or
invitations. TCP-Based Media Transport in the Session Description
Protocol (SDP) [RFC4145] specifies a general mechanism for describing
and establishing TCP (Transmission Control Protocol) [RFC5246]
streams. Connection-Oriented Media Transport over the Transport
Layer Security (TLS) Protocol in the Session Description Protocol
(SDP) [RFC4572] extends RFC4145 [RFC4145] for describing TCP-based
media streams that are protected using TLS.
SCTP (Stream Control Transmission Protocol) is a transport protocol
used to establish associations between two endpoints.
This specification describes how to describe SCTP associations using
the Session Description Protocol (SDP) [RFC4566], and defines the
following new SDP Media Description [RFC4566] protocol identifiers
(proto values):'SCTP', 'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/
SCTP'.
The specification also describes how to use the new proto values
together with the SDP Offer/Answer mechanism [RFC3264] in order to
negotiate and establish SCTP associations, and how to indicate the
SCTP application usage.
NOTE: TLS is designed to run on top of a byte-stream oriented
transport protocol providing a reliable, in-sequence delivery like
TCP. [RFC6083] presents serious limitations with transporting SCTP
on top of TLS. Therefore, defining a mechanism to negotiate media
streams transported using SCTP on top of TLS is outside the scope of
this specification.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
levels for compliant implementations.
3. SCTP Terminology
SCTP Association: A protocol relationship between SCTP endpoints,
composed of the two SCTP endpoints and protocol state information
including Verification Tags and the currently active set of
Transmission Sequence Numbers (TSNs), etc. An association can be
uniquely identified by the transport addresses used by the endpoints
in the association. Two SCTP endpoints MUST NOT have more than one
SCTP association between them at any given time.
SCTP Stream: A unidirectional logical channel established from one to
another associated SCTP endpoint, within which all user messages are
delivered in sequence except for those submitted to the unordered
delivery service.
SCTP Transport address: A transport address is traditionally defined
by a network-layer address, a transport-layer protocol, and a
transport-layer port number. In the case of SCTP running over IP, a
transport address is defined by the combination of an IP address and
an SCTP port number (where SCTP is the transport protocol).
4. SDP Media Descriptions
4.1. General
This section defines the following new SDP Media Description (m-
line) protocol identifiers (proto values) for describing an SCTP
association: 'SCTP', 'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/
SCTP'. The section also describes how an m- line, associated with
the proto values, is created.
The following is the format for an 'm' line, as specified in RFC4566
[RFC4566]:
m=<media> <port> <proto> <fmt> ...
The 'SCTP', 'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto
values are similar to both the 'UDP' and 'TCP' proto values in that
they only describe the transport-layer protocol and not the upper-
layer protocol.
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NOTE: When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are
used, the underlying transport protocol is either UDP or TCP, SCTP is
carried on top of either of those transport-layer protocols.
The m- line fmt value, identifying the application-layer protocol,
MUST be registered by IANA.
4.2. Protocol Identifiers
The new proto values are defined as below:
o The 'SCTP' proto value describes an SCTP association, as defined
in [RFC4960].
o The 'SCTP/DTLS' proto value describes a Datagram Transport Layer
Security (DTLS) [RFC6347] connection on top of an SCTP
association, as defined in [RFC6083].
o The 'UDP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS connection on top of UDP, as defined in Section 8.
o The 'TCP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS connection on top of TCP, as defined in Section 9.
4.3. Media Format Management
[RFC4566] defines that specifications defining new proto values must
define the rules by which their media format (fmt) namespace is
managed. Use of an existing MIME subtype for the format is
encouraged. If no MIME subtype exists, it is recommended that a
suitable one is registered through the IETF process [RFC6838]
[RFC4289] by production of, or reference to, a standards-track RFC
that defines the transport protocol for the format.
An m- line with a proto value of 'SCTP', 'SCTP/DTLS', 'UDP/DTLS/SCTP'
or 'TCP/DTLS/SCTP' always describe a single SCTP association.
In addition, such m- line MUST further indicate the application-layer
protocol using an 'fmt' identifier. There MUST be exactly one 'fmt'
value per m- line associated with the proto values defined in this
specification. The "fmt" namespace associated with those proto
values describes the generic application usage of the entire SCTP
association, including the associated SCTP streams.
NOTE: A mechanism on how to describe, and manage, individual SCTP
streams within an SCTP association, is outside the scope of this
specification.
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4.4. Syntax
sctp-m-line = %x6d "="
("application" SP sctp-port SP "SCTP" SP sctp-fmt CRLF) /
("application" SP sctp-port SP "SCTP/DTLS" SP sctp-fmt CRLF) /
("application" SP udp-port SP "UDP/DTLS/SCTP" SP sctp-fmt CRLF) /
("application" SP udp-port SP "TCP/DTLS/SCTP" SP sctp-fmt CRLF)
sctp-port = port
udp-port = port
sctp-fmt = association-usage
association-usage = token
4.5. Example
m=application 12345 UDP/DTLS/SCTP webrtc-datachannel
a=max-message-size: 100000
5. SDP 'sctp-port' Attribute
5.1. General
This section defines a new SDP media-level attribute, 'sctp-port'.
The attribute can be associated with an SDP media descriptor (m-
line) with a 'UDP/DTLS/SCTP' or a 'TCP/DTLS/SCTP' proto value, in
which case the m- line port value indicates the port of the
transport-layer protocol (UDP or TCP), on which SCTP is carried.
If the SDP sctp-port attribute is not present, the m- line MUST be
discarded.
Usage of the SDP sctp-port attribute with other proto values is not
specified, and MUST be discarded if received.
5.2. Syntax
sctp-port-attr = "a=sctp-port:" port
port = 1*DIGIT
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6. SDP 'max-message-size' Attribute
6.1. General
The SDP 'max-message-size' attribute can be associated with an m-
line to indicate the maximum message size that an SCTP endpoint is
willing to receive on the SCTP association associated with the m-
line.
The remote peer MUST assume that larger messages will be rejected by
the SCTP endpoint. SCTP endpoints need to decide on appropriate
behavior in case a message that exceeds the maximum size needs to be
sent.
If the SDP 'max-message-size' attribute contains a maximum message
size value of zero, it indicates the SCTP endpoint will handle
messages of any size, subject to memory capacity etc.
If the SDP 'max-message-size' attribute is not present, the default
value is 64K.
6.2. Syntax
max-message-size-attr = "a=max-message-size:" max-message-size
max-message-size = 1*DIGIT
7. SDP 'fmtp' Attribute
7.1. General
The SDP 'fmtp' attribute can be used with an m- line, associated with
an SCTP association, to indicate the maximum message size that an
SCTP endpoint is willing to receive, for a particular SCTP
association usage, on that SCTP association.
The remote peer MUST assume that larger messages will be rejected by
the SCTP endpoint. SCTP endpoints need to decide on appropriate
behavior in case a message that exceeds the maximum size needs to be
sent.
If the SDP 'fmtp' attribute contains a maximum message size value of
zero, it indicates the SCTP endpoint will handle messages of any
size, subject to memory capacity etc.
If the SDP 'fmtp' attribute is not present, the default value is 64K.
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NOTE: This specification only defines the usage of the SDP 'max-
message-size' attribute when associated with an m- line containing
one of the following proto field values: 'SCTP', 'SCTP/DTLS',
'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'. Usage of the attribute with
other proto values needs to be defined in a separate specification.
7.2. Syntax
sctpmap-attr = "a=fmtp:" association-usage [max-message-size]
max-message-size = "max-message-size" EQUALS 1*DIGIT
8. UDP/DTLS/SCTP Transport Realization
The UDP/DTLS/SCTP transport is realized as described below:
o SCTP on top of DTLS is realized according to the procedures
defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and
o DTLS on top of UDP is realized according to the procedures in
defined in [RFC6347].
9. TCP/DTLS/SCTP Transport Realization
The TCP/DTLS/SCTP transport is realized as described below:
o SCTP on top of DTLS is realized according to the procedures
defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and
o DTLS on top of TCP is realized using the framing method defined in
[RFC4571].
NOTE: DTLS on top of TCP, without using the framing method defined in
[RFC4571] is outside the scope of this specification. A separate
proto value would need to be registered for such transport
realization.
10. SCTP Association Management
10.1. General
The management of an SCTP association is identical to the management
of a TCP connection. An SCTP endpoints MUST follow the rules in
Section 6 of [RFC4145] to manage SCTP associations. Whether to use
the SCTP ordered or unordered delivery service is up to the
applications using the SCTP association, and this specification does
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not define a mechanism to indicate the type of delivery service using
SDP.
10.2. SDP sendrecv/sendonly/sendrecv/inactive Attribute
This specification does not define semantics for the SDP direction
attributes [RFC4566]. Specifications for an individual SCTP
association usage MAY define how the attributes can be used with that
usage. Unless semantics of these attributes for an SCTP association
usage have been defined, SDP direction attributes MUST be discarded
if present.
10.3. SDP setup Attribute
10.3.1. General
The SDP setup attribute is used to determine the 'active/passive'
status of the endpoints, following the procedures for TCP in
[RFC4145].
10.3.2. SCTP Association Initiation
Both the 'active' and 'passive' endpoint MUST initiate the SCTP
association, and MUST use the same SCTP port as client port and
server port (in order to prevent two separate SCTP associations from
being established).
NOTE: The procedure above is different from TCP, where only the
'active' endpoint initiates the TCP connection [RFC4145].
If the m- line proto value is 'TCP/DTLS/SCTP', only the 'active'
endpoint will initiate the TCP connection, following the procedures
in [RFC4145]. Both endpoints will still initiate the SCTP
association on top of the TCP connection.
10.3.3. TLS Role Determination
If the m- line proto value is 'SCTP/DTLS', 'UDP/DTLS/SCTP' or
'TCP/DTLS/SCTP', the 'active/passive' status is used to determine the
TLS roles of the endpoints. Following the procedures in [RFC4572],
the 'active' endpoint will take the TLS client role.
Once a DTLS connection has been established, if the 'active/passive'
status of the endpoints change (as result of an offer/answer
transaction) during a session, a new DTLS connection MUST be
established. Therefore, endpoints SHOULD NOT change the 'active/
passive' status during a session, unless they want to establish a new
DTLS connection.
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If the transport parameters or the key fingerprints change, the
endpoints MUST establish a new DTLS connection. In such case the
'active/passive' status of the endpoints will again be determined
following the procedures in [RFC4145], and the new status will be
used to determine the TLS roles of the endpoints associated with the
new DTLS connection.
NOTE: The procedure above is identical to the one defined for SRTP-
DTLS in [RFC5763].
10.4. SDP connection Attribute
The SDP connection attribute is used following the procedures in
[RFC4145], with the additional SCTP specific considerations described
in this section.
If the m- line proto value is 'TCP/DTLS/SCTP', an SDP connection
attribute associated with that m- line applies to both the SCTP
association and the TCP connection. Therefore, an attribute 'new'
value indicates that both a new SCTP association, and a new TCP
connection, have to be established, following the procedures in
[RFC4145].
NOTE: This specification does not define a mechanism which allows re-
establishing of a new SCTP association, while maintaining the TCP
connection.
The SDP connection attribute value does not automatically impact an
existing DTLS connection. Section 10.3.3 describes in which cases a
new DTLS connections will be established.
NOTE: If the m- line proto value is 'SCTP/DTLS', and if the SCTP
association is re-established, the DTLS connection also needs to be
re-established.
11. SDP Offer/Answer Procedures
11.1. General
This section defines the SDP Offer/Answer [RFC3264] procedures for
negotiating and establishing an SCTP association. Unless explicitly
stated, the procedures apply to all m- line proto values ('SCTP',
'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP') defined in this
specification.
If the m- line proto value is 'SCTP/DTLS', 'UDP/DTLS/SCTP' or
'TCP/DTLS/SCTP', each endpoint MUST provide a certificate
fingerprint, using the SDP 'fingerprint' attribute [RFC4145], if the
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endpoint supports, and is willing to use, a cipher suite with an
associated certificate.
The authentication certificates are interpreted and validated as
defined in [RFC4572]. Self-signed certificates can be used securely,
provided that the integrity of the SDP description is assured as
defined in [RFC4572].
NOTE: The procedures apply to a specific m- line describing an SCTP
association. If an offer or answer contains multiple m- lines
describing SCTP associations, the procedures are applied separately
to each m- line.
11.2. Generating the Initial SDP Offer
When the offerer creates an initial offer, the offerer:
o MUST, if the m- line proto value is 'SCTP/DTLS', 'UDP/DTLS/SCTP'
or 'TCP/DTLS/SCTP', associate an SDP setup attribute
[Section 10.3], with an 'actpass' value, with the m- line;
o MUST, if the m- line proto is 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP',
associate an SDP 'sctp-port' attribute [Section 5] with the m-
line;
o MUST associate an SDP 'connection' attribute [Section 10.4], with
a 'new' value, with the m- line; and
o MAY associate an SDP 'max-message-size' attribute [Section 7] with
the m- line.
11.3. Generating the SDP Answer
When the answerer receives an offer, which contains an m- line
describing an SCTP association, if the answerer accepts the m- line
it:
o MUST insert a corresponding m- line in the answer, with an
identical m- line proto value [RFC3264];
o MUST, if the m- line proto value is 'SCTP/DTLS', 'UDP/DTLS/SCTP'
or 'TCP/DTLS/SCTP', associate an SDP 'setup' attribute
[Section 10.3], with an 'active' or 'passive' value, with the m-
line;
o MUST, if the m- line proto is 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP',
associate an SDP 'sctp-port' attribute[Section 5] with the m-
line; and
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o MAY associate an SDP 'max-message-size' attribute [Section 7] with
the m- line.
Once the answerer has sent the answer, the answerer:
o MUST, if an SCTP association associated with the m- line has yet
not been established, or if an existing SCTP association is to be
re-established, initiate the establishing of the SCTP association;
and
o MUST, if the answerer is the 'active' endpoint, and if an DTLS
connection associated with the m- line is to be established (or
re-established), initiate the establishing of the DTLS connection
(by sending a ClientHello message).
If the answerer does not accept the m- line in the offer, it MUST
assign a zero port value to the corresponding m- line in the answer.
In addition, the answerer MUST NOT establish an SCTP association, or
a DTLS connection, associated with the m- line.
11.4. Offerer Processing of the SDP Answer
When the offerer receives an answer, which contains an m- line with a
non-zero port value, describing an SCTP association, the offerer:
o MUST, if the offerer is the 'active' endpoint, if the m- line
proto is 'TCP/DTLS/SCTP', and if a TCP connection used to carry
the SCTP association has yet not been established (or if an
existing TCP connection is to be re-established), initiate the
establishing of the TCP connection;
o MUST, if an SCTP association associated with the m- line has yet
not been established (or if an existing SCTP association is to be
re-established), initiate the establishing of the SCTP
association; and
o MUST, if the offerer is the 'active' endpoint, and if an DTLS
connection associated with the m- line is to be established (or if
an existing DTLS connection is to be re-established), initiate the
establishing of the DTLS connection (by sending a ClientHello
message).
If the m- line in the answer contains a zero port value, the offerer
MUST NOT establish a TCP connection, an SCTP association, or a DTLS
connection, associated with the m- line.
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11.5. Modifying the Session
When an offerer sends an updated offer, in order to modify a
previously established SCTP association, it follows the procedures in
Section 11.2, with the following exceptions:
o Unless the offerer wants to re-establish an existing SCTP
association, the offerer MUST associate an SDP connection
attribute, with an 'existing' value, with the m- line; and
o If the offerer wants to disable a previously established SCTP
association, it MUST assign a zero port value to the m- line
associated with the SCTP association, following the procedures in
[RFC3264].
NOTE: Different SCTP association usages might define protocol
procedures etc that need to be performed before an SCTP association
is terminated. Such procedures are outside the scope of this
specification.
12. Multihoming Considerations
SCTP supports multihoming. An SCTP endpoint is considered multihomed
if it has more than one IP address on which SCTP can be used. An
SCTP endpoint inform the remote peer about its IP addresses using the
address parameters in the INIT/INIT-ACK chunk. Therefore, when SDP
is used to describe an SCTP association, while the "c=" line contains
the address which was used to negotiate the SCTP association,
multihomed SCTP endpoints might end up using other IP addresses.
If an endpoint removes the IP address [RFC5061] that it offered in
the SDP "c=" line associated with the SCTP association, it MUST send
a new Offer, in which the "c=" line contains an IP address with is
valid within the SCTP association.
NOTE: In some network environments, intermediaries performing gate-
and firewall control use the address information in the SDP "c=" and
"m=" lines to authorize media, and will not pass media sent using
other addresses. In such network environment, if an SCTP endpoints
wants to change the address information on which media is sent and
received, it needs to send an updated Offer, in which the SDP "c="
and "m=" lines contain the new address information.
Multihoming is not supported when sending SCTP on top of DTLS, as
DTLS does not expose address management to its upper layer.
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13. NAT Considerations
13.1. General
SCTP features not present in UDP or TCP, including the checksum
(CRC32c) value calculated on the whole packet (rather than just the
header), and multihoming, introduce new challenges for NAT traversal.
[I-D.ietf-behave-sctpnat] defines an SCTP specific variant of NAT,
which provides similar features of Network Address and Port
Translation (NAPT).
Current NATs typically do not support SCTP. [RFC6951] defines a
mechanism for sending SCTP on top of UDP, which makes it possible to
use SCTP with NATs and firewalls that do not support SCTP.
13.2. ICE Considerations
At the time of writing this specification, no procedures have been
defined for using ICE (Interactive Connectivity Establishment)
[RFC5768] together with SCTP. Such procedures, including the
associated SDP Offer/Answer procedures, are outside the scope of this
specification, and might be defined in a future specification.
14. Examples
TODO: ADD EXAMPLES HERE
15. Security Considerations
[RFC4566] defines general SDP security considerations, while
[RFC3264], [RFC4145] and [RFC4572] define security considerations
when using the SDP offer/answer mechanism to negotiate media streams.
[RFC4960] defines general SCTP security considerations. security
considerations on SCTP in general, while [RFC6083] defines security
considerations when using DTLS on top of SCTP.
This specification does not introduce new security considerations in
addition to those defined in the specifications listed above.
16. IANA Considerations
16.1. New SDP proto values
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
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This document updates the "Session Description Protocol (SDP)
Parameters" registry, following the procedures in [RFC4566], by
adding the following values to the table in the SDP "proto" field
registry:
+---------------+---------------+-----------+
| Type | SDP Name | Reference |
+---------------+---------------+-----------+
| proto | SCTP | [RFCXXXX] |
| proto | SCTP/DTLS | [RFCXXXX] |
| proto | UDP/DTLS/SCTP | [RFCXXXX] |
| TCP/DTLS/SCTP | [RFCXXXX] |
+---------------+---------------+-----------+
Table 1: SDP "proto" field values
16.2. New SDP Attribute
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
This document defines a new SDP media-level attribute,'sctp-port', as
follows:
Attribute name: sctp-port
Type of attribute: media
Subject to charset: No
Purpose: Indicate the SCTP port value associated
with the SDP Media Description.
Appropriate values: Integer
Contact name: Christer Holmberg
Contact e-mail: christer.holmberg@ericsson.com
Reference: RFCXXXX
16.3. association-usage Name Registry
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
This specification creates a new IANA registry, following the
procedures in [RFC5226], for the "fmt" namespace associated with the
'SCTP', 'SCTP/DTLS', 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' protocol
identifiers. Each "fmt" value describes the usage of an entire SCTP
association, including all SCTP streams associated with the SCTP
association.
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NOTE: Usage indication of individual SCTP streams is outside the
scope of this specification.
The "fmt" value, "association-usage", used with these "proto" is
required. It is defined in [Section 4].
As part of this registry, IANA maintains the following information:
association-usage Name: .The identifier of the subprotocol, as will
be used in the <sctp-fmtp> subfield.
association-usage reference: A reference to the document in which
the association usage is defined.
association-usage names are to be subject to the "First Come First
Served" IANA registration policy [RFC5226].
IANA is asked to add initial values to the registry.
| name | Reference |
-+--------------------+-------------------------------------+
| webrtc-datachannel | draft-ietf-rtcweb-data-protocol-xx |
-+----------------------------------------------------------|
Figure 1
17. Acknowledgments
The authors wish to thank Harald Alvestrand, Randell Jesup, Paul
Kyzivat, Michael Tuexen for their comments and useful feedback.
18. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-sctp-sdp-09
o 'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'
o Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP
transports added.
Changes from draft-ietf-mmusic-sctp-sdp-08
o Default SCTP port removed:
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o - Usage of SDP sctp-port attribute mandatory.
o SDP max-message-size attribute defined:
o - Attribute definition.
o - SDP Offer/Answer procedures.
o Text about SDP direction attributes added.
o Text about TLS role determination added.
19. References
19.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
[RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures", BCP
13, RFC 4289, December 2005.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, July 2006.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
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[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061, September
2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, RFC
6838, January 2013.
[I-D.ietf-tsvwg-sctp-dtls-encaps]
Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
dtls-encaps-06 (work in progress), November 2014.
19.2. Informative References
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, May 2010.
[RFC5768] Rosenberg, J., "Indicating Support for Interactive
Connectivity Establishment (ICE) in the Session Initiation
Protocol (SIP)", RFC 5768, April 2010.
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083, January 2011.
[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, May 2013.
[I-D.ietf-behave-sctpnat]
Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
Transmission Protocol (SCTP) Network Address Translation",
draft-ietf-behave-sctpnat-09 (work in progress), September
2013.
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Authors' Addresses
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
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