Session Description Protocol (SDP) Offer/Answer Procedures
For Stream Control Transmission Protocol (SCTP) over
Datagram Transport Layer Security (DTLS) Transport.
EricssonHirsalantie 1102420JorvasFinlandchrister.holmberg@ericsson.comTurboBridge4905 Del Ray Avenue, Suite 300BethesdaMD20814USA+1 (240) 292-6632rshpount@turbobridge.comEricssonHirsalantie 1102420JorvasFinlandSalvatore.Loreto@ericsson.comEricssonHirsalantie 1102420JorvasFinlandGonzalo.Camarillo@ericsson.com
RAI
MMUSICSCTP, SDP, DTLS
The Stream Control Transmission Protocol (SCTP) is a transport protocol
used to establish associations between two endpoints.
draft-ietf-tsvwg-sctp-dtls-encaps-09 specifies how SCTP can be used on
top of the Datagram Transport Layer Security (DTLS) protocol, referred to
as SCTP-over-DTLS.
This specification defines the following new Session Description Protocol (SDP)
protocol identifiers (proto values):'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. This
specification also specifies how to use the new proto values with the
SDP Offer/Answer mechanism for negotiating SCTP-over-DTLS associations.
SDP (Session Description Protocol) provides a
general-purpose format for describing multimedia sessions in announcements
or invitations. TCP-Based Media Transport in the Session Description Protocol
(SDP) specifies a general mechanism for describing and
establishing TCP streams.
Connection-Oriented Media Transport over the Transport Layer Security (TLS)
Protocol in SDP extends RFC4145 for
describing TCP-based media streams that are protected using TLS.
The Stream Control Transmission Protocol (SCTP) is a
reliable transport protocol used to transport data between two
endpoints using SCTP associations.
specifies how SCTP can be used on
top of the Datagram Transport Layer Security (DTLS) protocol, referred to
as SCTP-over-DTLS.
This specification defines the following new Session Description Protocol (SDP)
protocol identifiers (proto values):'UDP/DTLS/SCTP'
and 'TCP/DTLS/SCTP'. This specification also specifies how to use the new proto
values with the SDP Offer/Answer mechanism for negotiating
SCTP-over-DTLS associations.
NOTE: Due to the characteristics of TCP, while multiple SCTP streams can still
be used, usage of 'TCP/DTLS/SCTP' will always force ordered and reliable delivery
of the SCTP packets, which limits the usage of the SCTP options. Therefore, it is
RECOMMENDED that TCP is only used in situations where UDP traffic is blocked.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
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.
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-over-DTLS: SCTP used on top of DTLS, as specified in
.
This section defines the following new SDP Media Description (m-
line) protocol identifiers (proto values) for describing an SCTP
association: '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
:
The '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.
NOTE: When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are used,
the underlying transport protocol is respectively UDP and TCP; SCTP is
carried on top of DTLS which is on top of those transport-layer protocols.
The new proto values are defined as below:
The 'UDP/DTLS/SCTP' proto value describes an SCTP association on top of
a DTLS association on top of UDP, as defined in
.
The 'TCP/DTLS/SCTP' proto value describes an SCTP association on top of
a DTLS association on top of TCP, as defined in .
defines that specifications defining new proto values must
define the rules by which their media format (fmt) namespace is managed.
An m- line with a proto value of 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'
always describes 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.
When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values, the m- line fmt value,
identifying the application-layer protocol, MUST be registered by IANA.
defines the
IANA registry for the media format namespace.
NOTE: A mechanism on how to describe, and manage, individual SCTP streams within an
SCTP association, is outside the scope of this specification. defines
a mechanism for negotiating individual SCTP streams used to realize WebRTC
data channels .
This section defines the values that can be used within an
SDP media description ("m=" line) associated with an
SCTP-over-DTLS association.
This specification creates an IANA registry for 'association-usage' values.
NOTE: 'webrtc-datachannel' indicates the WebRTC Data Channel Establishment Protocol
defined in .
This section defines a new SDP media-level attribute, 'sctp-port'.
The attribute can be associated with an SDP media description (m- line)
with a 'UDP/DTLS/SCTP' or a 'TCP/DTLS/SCTP' proto value. In that case
the m- line port value indicates the port of the underlying transport layer
protocol (UDP or TCP), and the 'sctp-port' value indicates the SCTP port.
No default value is defined for the SDP sctp-port attribute. Therefore, if
the attribute is not present, the associated m- line MUST be considered invalid.
NOTE: This specification only defines the usage of the SDP 'sctp-port'
attribute when associated with an m- line containing one of the following proto
values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'. Usage of the attribute with other
proto values needs to be defined
in a separate specification.
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
The definition of the SDP 'sctp-port' attribute is:
The mux category for
the SDP 'sctp-port' attribute is CAUTION.
As the usage of multiple SCTP associations on top of a single
DTLS association is outside the scope of this specification,
no mux rules are specified for the 'UDP/DTLS/SCTP' and
'TCP/DTLS/SCTP' proto values. Future extensions, that define
how to negotiate multiplexing of multiple SCTP associations of top of
a single DTLS association, need to also define the mux rules for the
attribute.
This section defines a new SDP media-level attribute, 'max-message-size'.
The attribute can be associated with an m- line to indicate the maximum
SCTP user message size (indicated in bytes) that an SCTP endpoint is willing to
receive on the SCTP association associated with the m- line. Different
attribute values can be used in each direction.
An SCTP endpoint MUST NOT send a SCTP user message with a message size
that is larger than the maximum size indicated by the peer, as it
cannot be assumed that the peer would accept such message.
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.
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
values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'.
Usage of the attribute with other proto values needs to be defined
in a separate specification.
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
The definition of the SDP 'max-message-size' attribute is:
The mux category for the SDP 'max-message-size' attribute
is CAUTION.
As the usage of multiple SCTP associations on top of a single
DTLS association is outside the scope of this specification,
no mux rules are specified for the 'UDP/DTLS/SCTP' and
'TCP/DTLS/SCTP' proto values.
The UDP/DTLS/SCTP transport is realized as described below:
SCTP on top of DTLS is realized according to the procedures
defined in ; and
DTLS on top of UDP is realized according to the procedures in
defined in .
NOTE: While allows
multiple SCTP associations on top of a single DTLS association,
the procedures in this specification only support the negotiation of a single
SCTP association on top of any given DTLS association.
The TCP/DTLS/SCTP transport is realized as described below:
SCTP on top of DTLS is realized according to the procedures
defined in ; and
DTLS on top of TCP is realized using the framing method defined in
, with DTLS packets being sent and received
instead of RTP/RTCP packets using the shim defined in ,
so that length field defined in
precedes each DTLS message, and SDP signaling according to the procedures
defined in this specification.
NOTE: TLS on top of TCP, without using the framing method defined in
is outside the scope of this specification.
A separate proto value would need to be registered for such transport realization.
This section describes how to manage an SCTP association, DTLS association
and TCP connection using SDP attributes.
The SCTP association, the DTLS association and the TCP connection are managed independently
from each other. Each can be established and closed without impacting others.
The detailed SDP Offer/Answer procedures for the SDP attributes
are described in .
This specification does not define semantics for the SDP direction
attributes . Unless semantics of these
attributes for an SCTP association usage have been defined, SDP direction
attributes MUST be ignored if present.
When an SCTP association is established, both SCTP endpoints
MUST initiate the SCTP association (i.e. both SCTP endpoints take the 'active'
role), and MUST use the same SCTP port as client port and server port (in order to
prevent two separate SCTP associations from being established).
As both SCTP endpoints take the 'active' role, the SDP 'setup'
attribute does not apply to SCTP association
establishment. However the 'setup' attribute does apply to establishment
of the underlying DTLS association and TCP connection.
NOTE: The procedure above is different from TCP, where one endpoint takes the 'active'
role, the other endpoint takes the 'passive' role, and only the 'active' endpoint initiates
the TCP connection .
NOTE: When the SCTP association is established it is assumed that any NAT traversal
procedures for the underlying transport protocol (UDP or TCP) have successfully been
performed.
The SDP 'connection' attribute does not apply to the SCTP
association. In order to trigger the closure of an existing SCTP association, and
establishment of a new SCTP association, the SDP 'sctp-port' attribute []
is used to indicate a new (different than the ones currently used) SCTP port. The existing
SCTP association is closed, and the new SCTP association is established, if one or both
endpoints signal a new SCTP port. The 'connection' attribute does apply to establishment
of underlying TCP connections.
Alternatively, an SCTP association can be closed using the SDP 'sctp-port' attribute
with a zero attribute value. Later, a new SCTP association can be established using the
procedures in this section for establishing an SCTP association.
SCTP associations might be closed without SDP signalling, e.g, in case of a failure.
The procedures in this section MUST be followed to establish a new
SCTP association. This requires a new SDP Offer/Answer exchange.
New (different than the ones currently used) SCTP ports MUST be used by both
endpoints.
NOTE: Closing and establishing a new SCTP association using the SDP
'sctp-port' attribute will not affect the state of the underlying
DTLS association.
A DTLS association is managed according to the procedures in .
Hence, the SDP 'setup' attribute is used to negotiate the (D)TLS roles ('client' and 'server')
.
NOTE: The SDP 'setup' attribute is used to negotiate both the DTLS roles and the
TCP roles ().
NOTE: As described in , if the Interactive Connectivity
Establishment (ICE) mechanism is used, all ICE
candidates associated with a DTLS association are considered part of the same DTLS association.
Thus, a switch from one candidate pair to another candidate pair will not trigger the establishment
of a new DTLS association.
The TCP connection is managed according to the procedures in . Hence,
the SDP 'setup' attribute is used to negotiate the TCP roles ('active' and 'passive'), and
the SDP 'connection' attribute is used to indicate whether to use an existing TCP connection,
or create a new one. The SDP 'setup' attribute 'holdconn' value MUST NOT be used.
NOTE: A change of the TCP roles will also trigger a closure of the DTLS association, and
establishment of a new DTLS association, according to the procedures in .
NOTE: As specified in , usage of the SDP 'setup' attribute
'holdconn' value is not allowed. Therefore this specification also forbids usage of the attribute
value for TCP, as DTLS is transported on top of TCP.
This section defines the SDP Offer/Answer
procedures for negotiating and establishing an SCTP-over-DTLS association.
Unless explicitly stated, the procedures apply to both the
'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' m- line proto values.
Each endpoint MUST associate one or more certificate fingerprints, using
the SDP 'fingerprint' attribute with the m- line, following the procedures
in .
The authentication certificates are interpreted and validated as
defined in . Self-signed
certificates can be used securely, provided that the integrity of the
SDP description is assured as defined in .
Each endpoint MUST associate an SDP 'tls-id' attribute with the m- line,
following the procedures in .
When the offerer creates an initial offer, the offerer:
MUST associate an SDP setup attribute with the m- line;
MUST associate an SDP 'sctp-port' attribute with the m- line;
MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection'
attribute, with a 'new' attribute value, with the m- line; and
MAY associate an SDP 'max-message-size' attribute
[] with the m- line.
When the answerer receives an offer, which contains an m- line describing
an SCTP-over-DTLS association, if the answerer accepts the association,
the answerer:
MUST insert a corresponding m- line in the answer, with an m- line
proto value identical to the value in
the offer;
MUST associate an SDP 'setup' attribute with the m- line;
MUST associate an SDP 'sctp-port' attribute with the m- line. If the
offer contained a new (different than the one currently used) SCTP
port value the answerer MUST also associate a new SCTP port value. If
the offer contained a zero SCTP port value, or if the answerer does not
accept the SCTP association, the answerer MUST also associate a zero
SCTP port value; and
MAY associate an SDP 'max-message-size' attribute
[] with the m- line. The
attribute value in the answer is independent from the value
(if present) in the corresponding m- line of the offer.
Once the answerer has sent the answer the answerer:
MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not yet
been established, or if an existing TCP connection is to be
closed and replaced by a new TCP connection, follow the procedures
in for closing and establishing a TCP connection;
MUST, if a DTLS association has not yet been established, or if
an existing DTLS association is to be closed and replaced by a
new DTLS association, follow the procedures in
for closing the currently used, and establishing a new, DTLS association; and
MUST, if an SCTP association has not yet been established, or if an
existing SCTP association is to be closed and replaced by a new
SCTP association, initiate the closing of the existing
SCTP association (if applicable) and establishment of the SCTP association.
If the SDP 'sctp-port' attribute in the answer contains a zero attribute
value, the answerer MUST NOT establish an SCTP association. If an SCTP
association exists, the offerer MUST close it.
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, following the
procedures in . In addition, the answerer MUST NOT
initiate the establishment of a TCP connection, a DTLS association or a
DTLS association associated with the m- line.
Once the offerer has received the answer the offerer:
MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not yet
been established, or if an existing TCP connection is to be
closed and replaced by a new TCP connection, follow the procedures
in for closing and establishing a TCP connection;
MUST, if a DTLS association has not yet been established, or if
an existing DTLS association is to be closed and replaced by a
new DTLS association, follow the procedures in
for closing and establishing a DTLS association; and
MUST, if an SCTP association has not yet been established, or if an
existing SCTP association is to be closed and replaced by a new
SCTP association, initiate the closing of the existing
SCTP association (if applicable) and establishment of the SCTP association.
If the SDP 'sctp-port' attribute in the answer contains a zero attribute
value, the offerer MUST NOT establish an SCTP association. If an SCTP
association exists in that case, the offerer MUST close it.
If the m- line in the answer contains a zero port value, the offerer
MUST NOT initiate the establishment a TCP connection, a DTLS association
or an SCTP association associated with the m- line. If a TCP connection,
or a DTLS association or an SCTP association exists in that case, the offerer MUST close it.
When an offerer sends an updated offer, in order to modify a previously established
SCTP association, it follows the procedures in ,
with the following exceptions:
If the offerer wants to close an SCTP association, and immediately establish a new SCTP association,
the offerer MUST associate an SDP 'sctp-port' attribute with a new (different than the
one currently used) attribute value. This will not impact the underlying
DTLS association (and TCP connection in case of TCP/DTLS/SCTP).
If the offerer wants to close an SCTP association, without immediately establishing a new
SCTP association, the offerer MUST associate an SDP 'sctp-port' attribute with a zero attribute
value. This will not impact the underlying DTLS association (and TCP connection
in case of TCP/DTLS/SCTP).
If the offerer wants to establish an SCTP association, and another SCTP association
was previously closed, the offerer MUST associate an SDP 'sctp-port' attribute with
a new attribute value (different than the value associated with the previous SCTP association).
If the previous SCTP association was closed successfully following use of an SDP 'sctp-port' attribute with a zero
attribute value, the offerer MAY use the same attribute value for the new SCTP association
that was used with the previous SCTP association before it was closed. This will not impact
the underlying DTLS association (and TCP connection in case of TCP/DTLS/SCTP).
If the offerer wants to close an existing SCTP association, and the
underlying DTLS association (and the underlying TCP connection in case of
TCP/DTLS/SCTP) it MUST assign a zero port value to the m- line associated with the
SCTP and DTLS associations (and TCP connection in case of TCP/DTLS/SCTP),
following the procedures in .
NOTE: This specification does not define a mechanism for explicitly closing a DTLS
association while maintaining the overlying SCTP association. However, if a DTLS
association is closed and replaced with a new DTLS association, as a result of some other action
, the state of the SCTP association is not affected.
The offer follows the procedures in regarding
the DTLS association impacts when modifying a session.
In the case of TCP/DTLS/SCTP, the offerer follows the procedures in
regarding the TCP connection impacts when
modifying a session.
Multihoming is not supported when sending SCTP on top of DTLS,
as DTLS does not expose address management of the underlying
transport protocols (UDP or TCP) to its upper layer.
When SCTP-over-DTLS is used in NAT environment, it relies on the NAT
traversal procedures for the underlying transport protocol (UDP or TCP).
When SCTP-over-DTLS is used with UDP based ICE candidates
then the procedures for UDP/DTLS/SCTP [] are used.
When SCTP-over-DTLS is used with TCP based ICE candidates
then the procedures for TCP/DTLS/SCTP [] are used.
In ICE environments, during the nomination process, endpoints go through multiple
ICE candidate pairs, until the most preferred candidate pair is found. During
the nomination process, data can be sent as soon as the first working candidate
pair is found, but the nomination process still continues and selected candidate pairs
can still change while data is sent. Furthermore, if endpoints roam between networks,
for instance when mobile endpoint switches from mobile connection to WiFi, endpoints will
initiate an ICE restart, which will trigger a new nomination process between the new set
of candidates and likely result in the new nominated candidate pair.
Implementations MUST treat all ICE candidate pairs associated with
an SCTP association on top of a DTLS association as part of the same
DTLS association. Thus, there will only be one SCTP handshake and one DTLS
handshake even if there are multiple valid candidate pairs, and shifting from one candidate
pair to another, including switching between UDP to TCP candidate pairs, will not impact
the SCTP or DTLS associations. If new candidates are added, they will also be part of the
same SCTP and DTLS associations. When transitioning between candidate pairs, different
candidate pairs can be currently active in different directions and implementations MUST
be ready to receive data on any of the candidates, even if this means sending and receiving
data using UDP/DTLS/SCTP and TCP/DTLS/SCTP at the same time in different directions.
In order to maximize the likelihood of interoperability between the endpoints, all
ICE enabled SCTP-over-DTLS endpoints SHOULD implement support for UDP/DTLS/SCTP.
When an SDP offer or answer is sent with multiple ICE candidates during initial connection
negotiation or after ICE restart, UDP based candidates SHOULD be included and default
candidate SHOULD be chosen from one of those UDP candidates. The proto value MUST match
the transport protocol associated with the default candidate. If UDP transport is used
for the default candidate, then 'UDP/DTLS/SCTP' proto value MUST be used. If TCP transport
is used for the default candidate, then 'TCP/DTLS/SCTP' proto value MUST be used.
Note that under normal circumstances the proto value for offers and answers sent during ICE
nomination SHOULD be 'UDP/DTLS/SCTP'.
When a subsequent SDP offer or answer is sent after ICE nomination is complete, and does not
initiate ICE restart, it will contain only the nominated ICE candidate pair.
In this case, the proto value MUST match the transport protocol associated with the
nominated ICE candidate pair. If UDP transport is used for the nominated pair,
then 'UDP/DTLS/SCTP' proto value MUST be used. If TCP transport is used for the
nominated pair, then 'TCP/DTLS/SCTP' proto value MUST be used. Please note that if an endpoint
switches between TCP-based and UDP-based candidates during the nomination process the endpoint
is not required to send an SDP offer for the sole purpose of keeping the proto value of the
associated m- line in sync.
NOTE: The text in the paragraph above only applies when the usage of ICE
has been negotiated. If ICE is not used, the proto value MUST always reflect
the transport protocol used at any given time.
defines general SDP security considerations, while
, and
define security considerations when using the SDP offer/answer mechanism
to negotiate media streams.
defines general SCTP security considerations
and defines security
considerations when using SCTP on top of DTLS.
This specification does not introduce new security considerations in addition
to those defined in the specifications listed above.
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this document.]
This document updates the "Session Description Protocol (SDP) Parameters" registry,
following the procedures in ,
by adding the following values to the table in the SDP "proto" field registry:
TypeSDP NameReferenceprotoUDP/DTLS/SCTP[RFCXXXX]protoTCP/DTLS/SCTP[RFCXXXX]
This document defines a new SDP media-level attribute,'sctp-port'. The
details of the attribute are defined in .
This document defines a new SDP media-level attribute,'max-message-size'. The
details of the attribute are defined in .
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this document.]
This specification creates a new IANA registry, following the procedures in
, for the namespace associated with the
'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.
NOTE: Usage indication of individual SCTP streams is outside the scope of this
specification.
The fmt value, "association-usage", used with these "proto" values is required.
It is defined in .
As part of this registry, IANA maintains the following information:
The identifier of the
subprotocol, as will be used as the fmt value.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.
The authors wish to thank Harald Alvestrand, Randell Jesup, Paul Kyzivat,
Michael Tuexen, Juergen Stoetzer-Bradler, Flemming Andreasen and Ari Keranen for
their comments and useful feedback. Ben Campbell provided comments as part
of his AD review. Brian Carpenter performed the Gen-ART review.
[RFC EDITOR NOTE: Please remove this section when publishing]Changes from draft-ietf-mmusic-sctp-sdp-25
SDP 'dtls-id' attribute re-named to 'tls-id'.Changes from draft-ietf-mmusic-sctp-sdp-24
Minor editorial fix by Roman.Changes from draft-ietf-mmusic-sctp-sdp-23
Changes based on IESG review.- Proto value clarifications.Changes from draft-ietf-mmusic-sctp-sdp-22
Changes based on Gen-ART review by Brian Carpenter.Changes from draft-ietf-mmusic-sctp-sdp-21
Changes based on AD review by Ben Campbell.Changes from draft-ietf-mmusic-sctp-sdp-20
Informative reference to draft-ietf-rtcweb-data-protocol added.Changes from draft-ietf-mmusic-sctp-sdp-19
Changes based on WG chair comments from Flemming Andreasen.Changes from draft-ietf-mmusic-sctp-sdp-18
Changes based on WGLC comments from Paul Kyzivat.Changes from draft-ietf-mmusic-sctp-sdp-17
Removal of 'SCTP'.Document title changed.Disallow usage of SDP 'setup' attribute 'holdconn' value.Roman Shpount added as co-editor.Changes from draft-ietf-mmusic-sctp-sdp-15
Chapter about SCTP, DTLS and TCP association/connection management modified.Removal of SCTP/DTLS.Changes from draft-ietf-mmusic-sctp-sdp-14
Changes based on WGLC comments from Magnus Westerlund.- ABNF clarification that token and port are defined in RFC4566.- Specify 40 as maximum digit character length for the SDP max-message-size value.- Editorial clarification.Changes based on discussions at IETF#92.- Specify that all ICE candidate pairs belong to the same DTLS association.Changes from draft-ietf-mmusic-sctp-sdp-13
Changes based on comments from Paul Kyzivat.- Text preventing usage of well-known ports removed.- Editorial clarification.Changes from draft-ietf-mmusic-sctp-sdp-12
Mux category rules added for new SDP attributes.Reference to draft-ietf-mmusic-sdp-mux-attributes added.Changes based on comments from Roman Shpount:- Specify that fingerprint or setup roles must not be modified,
unless underlying transport protocol is also modified.Changes based on comments from Ari Keranen:- Editorial corrections.Changes based on comments from Flemming Andreasen:- Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used,
the DTLS association is established before the SCTP association.- Clarify that max-message-size value is given in bytes, and
that different values can be used per direction.- Section on fmtp attribute removed.- Editorial corrections.Changes from draft-ietf-mmusic-sctp-sdp-11
Example added.Changes from draft-ietf-mmusic-sctp-sdp-10
SDP max-message-size attribute added to IANA considerations.Changes based on comments from Paul Kyzivat:- Text about max message size removed from fmtp attribute section.Changes from draft-ietf-mmusic-sctp-sdp-09
'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP transports added.Changes from draft-ietf-mmusic-sctp-sdp-08
Default SCTP port removed:- Usage of SDP sctp-port attribute mandatory.SDP max-message-size attribute defined:- Attribute definition.- SDP Offer/Answer procedures.Text about SDP direction attributes added.Text about TLS role determination added.