MMUSIC                                                         S. Loreto
Internet-Draft                                              G. Camarillo
Intended status: Standards Track                                Ericsson
Expires: August 13, 2010                                February 9, 2010


Stream Control Transmission Protocol (SCTP)-Based Media Transport in the
                   Session Description Protocol (SDP)
                    draft-loreto-mmusic-sctp-sdp-05

Abstract

   SCTP (Stream Control Transmission Protocol) is a transport protocol
   used to establish associations between two endpoints.  This document
   describes how to express media transport over SCTP in SDP (Session
   Description Protocol).  This document defines the 'SCTP' and 'SCTP/
   DTLS' protocol identifiers for SDP.

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   This Internet-Draft will expire on August 13, 2010.

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Protocol Identifier . . . . . . . . . . . . . . . . . . . . . . 3
   4.  The Setup and Connection Attributes and Association
       Management  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Actpass/Passive . . . . . . . . . . . . . . . . . . . . . . 5
     6.2.  Existing Connection Reuse . . . . . . . . . . . . . . . . . 6
     6.3.  SDP description for DTLS Connection . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8


























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.  Introduction

   SDP (Session Description Protocol) [RFC4566] provides a general-
   purpose format for describing multimedia sessions in announcements or
   invitations.  RFC4145 [RFC4145] specifies a general mechanism for
   describing and establishing TCP (Transmission Control Protocol)
   streams.  RFC 4572 [RFC4572] extends RFC4145 [RFC4145] for describing
   TCP-based media streams that are protected using TLS (Transport Layer
   Security) [RFC4346].

   This document defines a new protocol identifier, 'SCTP', to describe
   SCTP-based [RFC4960] media streams.  Additionally, this document
   specifies the use of the 'setup' and 'connection' SDP attributes to
   establish SCTP associations.  These attributes were defined in
   RFC4145 [RFC4145] for TCP.  This document discusses their use with
   SCTP.

   Additionaly this document define a new protocol identifier, 'SCTP/
   DTLS', to establish secure SCTP-based media streams over DTLS
   (Datagram Transport Layer Security) [RFC4347], as specified in
   [I-D.ietf-tsvwg-dtls-for-sctp], using SDP.  The authentication
   certificates are interpreted and validated as defined in RFC4572
   [RFC4572].  Self-signed certificates can be used securely, provided
   that the integrity of the SDP description is assured as defined in
   RFC4572 [RFC4572].

   TLS is designed to run on top of a byte-stream oriented transport
   protocol providing a realible, in-sequence delivery like TCP.  Since
   no-one so far has implemented SCTP over TLS, due to some serious
   limitations described in [I-D.ietf-tsvwg-dtls-for-sctp], this
   document does not make use of TLS over SCTP as described in RFC3436
   [RFC3436].


.  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.


.  Protocol Identifier

   The following is the format for an 'm' line, as specified in RFC4566
   [RFC4566]:




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       m=<media> <port> <proto> <fmt> ...

   This document defines two new values for the 'proto' field: 'SCTP'
   and 'SCTP/DTLS'.

   The 'SCTP' protocol identifier is similar to both the 'UDP' and 'TCP'
   protocol identifiers in that it only describes the transport protocol
   and not the upper-layer protocol.  Media described using an 'm' line
   containing the 'SCTP' protocol identifier are carried using SCTP
   [RFC4960].

   The 'SCTP/DTLS' protocol identifier indicates that the media
   described will use the Datagram Transport Layer Security (DTLS)
   [RFC4347] over SCTP as specified in [I-D.ietf-tsvwg-dtls-for-sctp].

   An 'm' line that specifies 'SCTP' or 'SCTP/DTLS' MUST further qualify
   the application-layer protocol using an fmt identifier.

   An 'm' line that specifies 'SCTP/DTLS' MUST further provide a
   certificate fingerprint.  An SDP attribute (an 'a' line) is used to
   transport and exchange end point certificate.  The authentication
   certificates are interpreted and validated as defined in [RFC4572].


.  The Setup and Connection Attributes and Association Management

   The use of the 'setup' and 'connection' attributes in the context of
   an SCTP association is identical to the use of these attributes in
   the context of a TCP connection.  That is, SCTP endpoints MUST follow
   the rules in Sections 4 and 5 of RFC 4145 [RFC4145] when it comes to
   the use of the 'setup' and 'connection' attributes in offer/answer
   [RFC3264] exchanges.

   The management of an SCTP association is identical to the management
   of a TCP connection.  That is, SCTP endpoints MUST follow the rules
   in Section 6 of RFC 4145 [RFC4145] to manage SCTP associations.
   Whether to use the SCTP ordered or unordered delivery service is up
   to the applications using the SCTP association.


.  Multihoming

   An SCTP endpoint, unlike a TCP endpoint, can be multihomed.  An SCTP
   endpoint is considered to be multihomed if it has more than one IP
   address.  A multihomed SCTP endpoint informs a remote SCTP endpoint
   about all its IP addresses using the address parameters of the INIT
   or the INIT-ACK chunk (depending on whether or not the multihomed
   endpoint is the one initiating the establishment of the association).



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   Therefore, once the address provided in the 'c' line has been used to
   establish the SCTP association (i.e., to send the INIT chunk),
   address management is performed using SCTP.  This means that two SCTP
   endpoints can use addresses that were not listed in the 'c' line but
   that were negotiated using SCTP mechanisms.

   Some intermediaries performing firewall control use the addresses in
   offer/answer exchanges to perform media authorization.  That is, they
   will not let media through unless it is sent to the address in the
   'c' line.  Therefore, it is RECOMMENDED that SCTP endpoints use a
   main address all the time (e.g., they do not send retransmissions to
   a backup address) and that they send a re-INVITE every time they
   change that address.


.  Examples

   The following examples show the use of the 'setup' and 'connection'
   SDP attributes.  As discussed in Section 4, the use of this
   attributes with an SCTP association is identical to their use with a
   TCP connection.  For the purpose of brevity, the main portion of the
   session description is omitted in the examples, which only show 'm'
   lines and their attributes (including 'c' lines).

6.1.  Actpass/Passive

   An offerer at 192.0.2.2 signals its availability for an SCTP
   association at SCTP port 54111.  Additionally, this offerer is also
   willing to initiate the SCTP association:

              m=image 54111 SCTP *
              c=IN IP4 192.0.2.2
              a=setup:actpass
              a=connection:new

   The endpoint at 192.0.2.1 responds with the following description:

              m=image 54321 SCTP *
              c=IN IP4 192.0.2.1
              a=setup:passive
              a=connection:new

   This will cause the offerer (at 192.0.2.2) to initiate an SCTP
   association to port 54321 at 192.0.2.1.







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6.2.  Existing Connection Reuse

   Subsequent to the exchange in Section 6.1, another offer/answer
   exchange is initiated in the opposite direction.  The endpoint at
   192.0.2.1, which now acts as the offerer, wishes to continue using
   the existing association:

              m=application 54321 SCTP *
              c=IN IP4 192.0.2.1
              a=setup:passive
              a=connection:new

                                 Figure 1

   The endpoint at 192.0.2.2 also wishes to use the existing SCTP
   association and responds with the following description:

              m=application 9 SCTP *
              c=IN IP4 192.0.2.2
              a=setup:active
              a=connection:new

                                 Figure 2

   The existing SCTP association between 192.0.2.2 and 192.0.2.1 will be
   reused.

6.3.  SDP description for DTLS Connection

   An offerer at 192.0.2.2 signals the availability of a T.38 fax
   session over SCTP/DTLS.

           m=image 54111 SCTP/DTLS t38
           c=IN IP4 192.0.2.2
           a=setup:actpass
           a=connection:new
           a=fingerprint:SHA-1 \
                  4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB


.  Security Considerations

   See RFC 4566 [RFC4566] for security considerations on the use of SDP
   in general.  See RFC 3264 [RFC3264], RFC 4145 [RFC4145] and RFC 4572
   [RFC4572] for security considerations on establishing media streams
   using offer/answer exchanges.  See RFC 4960 [RFC4960] for security
   considerations on SCTP in general and [I-D.ietf-tsvwg-dtls-for-sctp]
   for security consideration using DTLS on top of SCTP.  This



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   specification does not introduce any new security consideration in
   addition to the ones discussed in those specifications.


.  IANA Considerations

   This document defines a new proto value: SCTP.  Its format is defined
   in Section 3.  This proto value should be registered by the IANA
   under "Session Description Protocol (SDP) Parameters" under "proto".

   The SDP specification, [RFC4566], states that specifications defining
   new proto values, like the SCTP and SCTP/DTLS proto values defined in
   this RFC, must define the rules by which their media format (fmt)
   namespace is managed.  For the SCTP protocol, new formats SHOULD have
   an associated MIME registration.  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 [RFC2048] by production of, or reference to, a standards-
   track RFC that defines the transport protocol for the format.


.  Normative References

   [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [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.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

   [RFC3436]  Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
              Layer Security over Stream Control Transmission Protocol",
              RFC 3436, December 2002.




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   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, 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.

   [I-D.ietf-tsvwg-dtls-for-sctp]
              Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
              Transport Layer Security for Stream Control Transmission
              Protocol", draft-ietf-tsvwg-dtls-for-sctp-02 (work in
              progress), October 2009.


Authors' Addresses

   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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