MMUSIC C. Holmberg
Internet-Draft Ericsson
Intended status: Standards Track R. Shpount
Expires: April 10, 2017 TurboBridge
S. Loreto
G. Camarillo
Ericsson
October 7, 2016
Session Description Protocol (SDP) Offer/Answer Procedures For Stream
Control Transmission Protocol (SCTP) over Datagram Transport Layer
Security (DTLS) Transport.
draft-ietf-mmusic-sctp-sdp-18
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 10, 2017.
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Copyright Notice
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document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 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
4.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 6
4.4.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . 6
4.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. SDP 'sctp-port' Attribute . . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 7
6. SDP 'max-message-size' Attribute . . . . . . . . . . . . . . 7
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 8
7. UDP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 8
8. TCP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 9
9. Association And Connection Management . . . . . . . . . . . . 9
9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute . . . . 9
9.3. SCTP Association . . . . . . . . . . . . . . . . . . . . 9
9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) . . . 10
9.5. TCP Connection (TCP/DTLS/SCTP) . . . . . . . . . . . . . 11
10. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 11
10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 11
10.2. Generating the Initial SDP Offer . . . . . . . . . . . . 11
10.3. Generating the SDP Answer . . . . . . . . . . . . . . . 12
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10.4. Offerer Processing of the SDP Answer . . . . . . . . . . 13
10.5. Modifying the Session . . . . . . . . . . . . . . . . . 13
11. Multihoming Considerations . . . . . . . . . . . . . . . . . 14
12. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 14
12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 14
12.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 14
13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. Establishment of UDP/DTLS/SCTP association . . . . . . . 15
14. Security Considerations . . . . . . . . . . . . . . . . . . . 16
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
15.1. New SDP proto values . . . . . . . . . . . . . . . . . . 17
15.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 17
15.2.1. sctp-port . . . . . . . . . . . . . . . . . . . . . 17
15.2.2. max-message-size . . . . . . . . . . . . . . . . . . 18
15.3. association-usage Name Registry . . . . . . . . . . . . 18
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
18.1. Normative References . . . . . . . . . . . . . . . . . . 21
18.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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 [RFC0793] streams. Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol in SDP
[RFC4572] extends RFC4145 [RFC4145] for describing TCP-based media
streams that are protected using TLS.
The Stream Control Transmission Protocol (SCTP) [RFC4960] is a
transport protocol used to establish associations between two
endpoints.
The Stream Control Transmission Protocol (SCTP) [RFC4960] is a
transport protocol used to establish associations between two
endpoints. [I-D.ietf-tsvwg-sctp-dtls-encaps] 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) [RFC4566] 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 [RFC3264] for negotiating SCTP-over-DTLS associations.
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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 TLS on
top of SCTP. Therefore, defining a mechanism to negotiate media
streams transported using TLS on top of SCTP, i.e., 'SCTP/TLS', is
outside the scope of this specification. In addition, defining a
mechanism to negotiate non-protected SCTP associations is also
outside the scope of this specification.
2. Conventions
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 [RFC2119].
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.
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).
SCTP-over-DTLS: SCTP used on top of DTLS, as specified in
[I-D.ietf-tsvwg-sctp-dtls-encaps].
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: UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. The section also
describes how an m- line, associated with the proto values, is
created.
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The following is the format for an 'm' line, as specified in RFC4566
[RFC4566]:
m=<media> <port> <proto> <fmt> ...
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 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 'UDP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS association on top of UDP, as defined in Section 7.
o The 'TCP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS association on top of TCP, as defined in Section 8.
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 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.
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NOTE: A mechanism on how to describe, and manage, individual SCTP
streams within an SCTP association, is outside the scope of this
specification.
4.4. Syntax
4.4.1. General
This section defines the ABNF [RFC5234] for the SDP media description
when associated with any of the proto values defined in this
document.
This specification creates an IANA registry for 'association-usage'
values.
4.4.2. ABNF
sctp-m-line = %x6d "="
("application" SP udp-port SP "UDP/DTLS/SCTP" SP fmt CRLF) /
("application" SP tcp-port SP "TCP/DTLS/SCTP" SP fmt CRLF)
udp-port = port
tcp-port = port
fmt = association-usage
association-usage = token
token and port as defined in RFC4566
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 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.
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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.
Usage of the SDP 'sctp-port' attribute with other proto values is not
specified, and MUST be discarded if received.
5.2. Syntax
The ABNF for the SDP 'sctp-port' attribute is:
sctp-port-attr = "a=sctp-port:" port
port = (1*5)DIGIT
The SCTP port range is between 0 and 65535 (both included).
Leading zeroes MUST NOT be used.
5.3. Mux Category
The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the SDP
sctp-port' attribute is SPECIAL. Usage of the attribute is only
applicable when associated with 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'
proto value m- lines.
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.
6. SDP 'max-message-size' Attribute
6.1. General
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 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.
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.
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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.
6.2. Syntax
The ABNF for the SDP 'max-message-size' attribute is:
max-message-size-attr = "a=max-message-size:" max-message-size
max-message-size = 1*40DIGIT
Leading zeroes MUST NOT be used.
6.3. Mux Category
The mux category for the SDP 'max-message-size' attribute is SPECIAL.
The mux rules depends on the proto value of the associated m- line.
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.
7. 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].
NOTE: While [I-D.ietf-tsvwg-sctp-dtls-encaps] allows multiple SCTP
associations on top of a single DTLS association, the procedures in
this specification only supports the negotiation of a single SCTP
association on top of any given DTLS association.
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8. 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], with DTLS packets being sent instead of RTP/RTCP
packets, and SDP signaling according to the procedures defined in
this specification.
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.
9. Association And Connection Management
9.1. General
This section describes how to mange an SCTP association, DTLS
association and TCP connection using SDP attributes.
In case of UDP/DTLS/SCTP and TCP/DTLS/SCTP the SCTP association, DTLS
association and TCP connection are managed independently for each
other. An association/connection can be re-established without
impacting other associations/connections.
The detailed SDP Offer/Answer [RFC3264] procedures for the SDP
attributes are described in (Section 10).
9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute
This specification does not define semantics for the SDP direction
attributes [RFC4566]. Unless semantics of these attributes for an
SCTP association usage have been defined, SDP direction attributes
MUST be discarded if present.
9.3. SCTP Association
When an SCTP association is established/re-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).
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As both SCTP endpoints take the 'active' role, this specification
does not define usage of the SDP 'setup' attribute [RFC4145] for
SCTP.
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
[RFC4145].
NOTE: In case of SCTP-over-DTLS, when the SCTP association is
established it is assumed that any NAT traversal procedures for the
underlying transport protocol (UDP or TCP) has successfully been
performed.
Usage of the SDP 'connection' attribute [RFC4145] is not defined for
SCTP. In order to trigger the closure and re-establishment of an
SCTP association, the SDP 'sctp-port' attribute (Section 5) is used
to indicate a new (different than the ones currently used) SCTP port.
Alternatively, an SCTP association can be closed using the SDP 'sctp-
port' attribute with a zero attribute value. Later, the SCTP
association can be re-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. When such SCTP association is re-established the
SCTP endpoints MUST use the procedures in this section for
establishing an SCTP association. New (different than the ones
currently used) SCTP ports MUST be used.
NOTE: Closing and re-establishing the SCTP association using the SDP
'sctp-port' attribute will not impact the underlying DTLS
association.
9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP)
An DTLS association is managed according to the procedures in
[I-D.ietf-mmusic-dtls-sdp]. Hence, the SDP 'setup' attribute is used
to negotiate the (D)TLS roles ('client' and 'server') [RFC4572].
NOTE: The SDP 'setup' attribute is used both to negotiate both the
DTLS roles and the TCP roles (Section 9.5).
NOTE: As described in [RFC5245], if the Interactive Connectivity
Establishment (ICE) mechanism [RFC5245] is used, all ICE candidates
associated with an DTLS association as considered part of the same
DTLS association. Thus, a switch from one candidate pair to another
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candidate pair will not trigger the establishment of a new DTLS
association.
9.5. TCP Connection (TCP/DTLS/SCTP)
The TCP connection is managed according to the procedures in
[RFC4145]. 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 re-establishment
of the DTLS association, according to the procedures in
[I-D.ietf-mmusic-dtls-sdp].
NOTE: As specified in [I-D.ietf-mmusic-dtls-sdp], 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.
10. SDP Offer/Answer Procedures
10.1. General
This section defines the SDP Offer/Answer [RFC3264] 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 [RFC4572] and [I-D.ietf-mmusic-4572-update].
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].
Each endpoint MUST associate an SDP 'dtls-id' attribute with the m-
line, following the procedures in [I-D.ietf-mmusic-dtls-sdp].
10.2. Generating the Initial SDP Offer
When the offerer creates an initial offer, the offerer:
o MUST associate an SDP setup attribute, with an 'actpass' value,
with the m- line;
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o MUST associate an SDP 'sctp-port' attribute with the m- line;
o MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection'
attribute, with a 'new' attribute value, with the m- line; and
o MAY associate an SDP 'max-message-size' attribute (Section 6) with
the m- line.
10.3. Generating the SDP Answer
When the answerer receives an offer, which contains an m- line
describing an SCTP-over-DTLS association, if the answerer accepts the
association line it:
o MUST insert a corresponding m- line in the answer, with an
identical m- line proto value [RFC3264];
o MUST associate an SDP 'setup' attribute, with an 'active' or
'passive' value, with the m- line;
o 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 the answerer
MUST also associate a zero SCTP port value; and
o MAY associate an SDP 'max-message-size' attribute (Section 6)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, if an SCTP
association has yet not been established, or if an existing SCTP
association is to be re-established, initiate the establishment of
the SCTP association.
The answerer follows the procedures in [I-D.ietf-mmusic-dtls-sdp]
regarding the establishment/re-establishment of the DTLS association.
In the case of TCP/DTLS/SCTP, the answerer follows the procedures in
[RFC4145] regarding the establishment/re-establishment of the TCP
connection association.
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 [RFC3264]. In addition, the answerer
MUST NOT initiate the establishment of an SCTP association, or a DTLS
association, associated with the m- line.
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10.4. Offerer Processing of the SDP Answer
Once the offerer has received the answer, which contains an m- line
with a non-zero port value, the offerer MUST, if an SCTP association
has yet not been established, or if an existing SCTP association is
to be re-established, initiate the 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, the offerer MUST close it.
The offerer follows the procedures in [I-D.ietf-mmusic-dtls-sdp]
regarding the establishment/re-establishment of the DTLS association.
In the case of TCP/DTLS/SCTP, the offerer follows the procedures in
[RFC4145] regarding the establishment/re-establishment of the TCP
connection association.
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
association, associated with the m- line. If an SCTP association,
DTLS association and/or TCP connection exists, the offerer MUST close
it.
10.5. 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 10.2, with the following exceptions:
o If the offerer wants to close and immediately re-establish an
existing 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).
o If the offerer wants to close, but not re-establish an existing
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).
o If the offerer wants to re-establish a previously closed SCTP
association, the offerer MUST associate an SDP 'sctp-port'
attribute with a new (different than the one currently used)
attribute value. If the SCTP association was previously closed
using an SDP 'sctp-port' attribute with a zero attribute value,
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the offerer MAY use the same attribute value that was used prior
to the SCTP association was closed. This will not impact the
underlying DTLS association (and TCP connection in case of
TCP/DTLS/SCTP).
o 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
[RFC3264].
o NOTE: This specification does not define a mechanism for
explicitly closing an DTLS association while maintaining the
overlying SCTP association. However, if a DTLS association is re-
established as a result of some other action
[I-D.ietf-mmusic-dtls-sdp] the SCTP association is not affected.
The offer follows the procedures in [I-D.ietf-mmusic-dtls-sdp]
regarding the DTLS association impacts when modifying a session.
In the case of TCP/DTLS/SCTP, the offer follows the procedures in
[RFC4145] regarding the TCP connection impacts when modifying a
session;
11. Multihoming Considerations
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.
12. NAT Considerations
12.1. General
When SCTP-over-DTLS is used in NAT environment, it relies on the NAT
traversal procedures for the underlying transport protocol (UDP or
TCP).
12.2. ICE Considerations
When SCTP-over-DTLS is used with UDP based ICE candidates as defined
in [RFC5245] procedures for UDP/DTLS/SCTP, as defined in Section 7
are used.
When SCTP-over-DTLS is used with TCP based ICE candidates as defined
in [RFC6544] procedures for TCP/DTLS/SCTP, as defined in Section 8
are used.
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Implementations MUST treat all ICE candidate pairs associated with a
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 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.
When an SDP offer or answer is sent, the proto value MUST match the
transport protocol associated with the default candidate. Hence, if
UDP transport is used for the default candidate the 'UDP/DTLS/SCTP'
proto value MUST be used. If TCP transport is used for the default
candidate the 'TCP/DTLS/SCTP' proto value MUST be used. However, if
an endpoint switch between TCP-based and UDP-based candidates during
a session the endpoint is not required to send an SDP offer in order
to modify that proto value of the associated m- line.
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.
13. Examples
13.1. Establishment of UDP/DTLS/SCTP association
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SDP Offer:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.1
a=dtls-id:abc3dl
a=setup:actpass
a=sctp-port:5000
a=max-message-size:100000
- The offerer indicates that the usage of the
UDP/DTLS/SCTP association will be as defined
for the 'webrtc-datachannel' format value.
- The offerer UDP port value is 54111.
- The offerer SCTP port value is 5000.
- The offerer indicates that it can take either the
client or the server DTLS role.
SDP Answer:
m=application 64300 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP4 192.0.2.2
a=dtls-id:ggr4rd
a=setup:passive
a=sctp-port:6000
a=max-message-size:100000
- The answerer UDP port value is 64300.
- The answerer SCTP port value is 6000.
- The answerer takes the server DTLS role.
14. 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 and
[I-D.ietf-tsvwg-sctp-dtls-encaps] 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.
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15. IANA Considerations
15.1. New SDP proto values
[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 [RFC4566], by
adding the following values to the table in the SDP "proto" field
registry:
+-------+---------------+-----------+
| Type | SDP Name | Reference |
+-------+---------------+-----------+
| proto | UDP/DTLS/SCTP | [RFCXXXX] |
| proto | TCP/DTLS/SCTP | [RFCXXXX] |
+-------+---------------+-----------+
Table 1: SDP "proto" field values
15.2. New SDP Attributes
15.2.1. sctp-port
[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
Mux category: SPECIAL
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
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15.2.2. max-message-size
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
This document defines a new SDP media-level attribute,'max-message-
size', as follows:
Attribute name: max-message-size
Type of attribute: media
Mux category: SPECIAL
Subject to charset: No
Purpose: Indicate the maximum message size that
an SCTP endpoint is willing to receive
on the SCTP association associated
with the SDP Media Description.
Appropriate values: Integer
Contact name: Christer Holmberg
Contact e-mail: christer.holmberg@ericsson.com
Reference: RFCXXXX
15.3. 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
'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" 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 as the "fmt" value.
association-usage reference: A reference to the document in which
the association-usage is defined.
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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 |
|----------------------------------------------------------|
[RFC EDITOR NOTE: Please hold the publication of this draft
until draft-ietf-rtcweb-data-protocol has been published as an RFC.
Then, replace the reference to draft-ietf-rtcweb-data-protocol
with the RFC number.]
Figure 1
16. Acknowledgments
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.
17.
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-sctp-sdp-17
o Removal of 'SCTP'.
o Document title changed.
o Disallow usage of SDP 'setup' attribute 'holdconn' value.
o Roman Shpount added as co-editor.
Changes from draft-ietf-mmusic-sctp-sdp-15
o Chapter about SCTP, DTLS and TCP association/connection management
modified.
o Removal of SCTP/DTLS.
Changes from draft-ietf-mmusic-sctp-sdp-14
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o Changes based on WGLC comments from Magnus Westerlund.
o - ABNF clarification that token and port are defined in RFC4566.
o - Specify 40 as maximum digit character length for the SDP max-
message-size value.
o - Editorial clarification.
o Changes based on discussions at IETF#92.
o - Specify that all ICE candidate pairs belong to the same DTLS
association.
Changes from draft-ietf-mmusic-sctp-sdp-13
o Changes based on comments from Paul Kyzivat.
o - Text preventing usage of well-known ports removed.
o - Editorial clarification.
Changes from draft-ietf-mmusic-sctp-sdp-12
o Mux category rules added for new SDP attributes.
o Reference to draft-ietf-mmusic-sdp-mux-attributes added.
o Changes based on comments from Roman Shpount:
o - Specify that fingerprint or setup roles must not be modified,
unless underlying transport protocol is also modified.
o Changes based on comments from Ari Keranen:
o - Editorial corrections.
o Changes based on comments from Flemming Andreasen:
o - Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used, the
DTLS association is established before the SCTP association.
o - Clarify that max-message-size value is given in bytes, and that
different values can be used per direction.
o - Section on fmtp attribute removed.
o - Editorial corrections.
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Changes from draft-ietf-mmusic-sctp-sdp-11
o Example added.
Changes from draft-ietf-mmusic-sctp-sdp-10
o SDP max-message-size attribute added to IANA considerations.
o Changes based on comments from Paul Kyzivat:
o - Text about max message size removed from fmtp attribute section.
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:
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.
18. References
18.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
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[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005,
<http://www.rfc-editor.org/info/rfc4145>.
[RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures",
BCP 13, RFC 4289, DOI 10.17487/RFC4289, December 2005,
<http://www.rfc-editor.org/info/rfc4289>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
2006, <http://www.rfc-editor.org/info/rfc4571>.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572,
DOI 10.17487/RFC4572, July 2006,
<http://www.rfc-editor.org/info/rfc4572>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
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[I-D.ietf-mmusic-4572-update]
Holmberg, C., "SDP Fingerprint Attribute Usage
Clarifications", draft-ietf-mmusic-4572-update-07 (work in
progress), September 2016.
[I-D.ietf-mmusic-dtls-sdp]
Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer
Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-14 (work
in progress), July 2016.
[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-09 (work in progress), January 2015.
[I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-13
(work in progress), June 2016.
18.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083,
DOI 10.17487/RFC6083, January 2011,
<http://www.rfc-editor.org/info/rfc6083>.
[RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
"TCP Candidates with Interactive Connectivity
Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
March 2012, <http://www.rfc-editor.org/info/rfc6544>.
Authors' Addresses
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Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Roman Shpount
TurboBridge
4905 Del Ray Avenue, Suite 300
Bethesda, MD 20814
USA
Phone: +1 (240) 292-6632
Email: rshpount@turbobridge.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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