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Network Working Group                                            J. PolkRequest for Comments: 5432                                   S. DhesikanCategory: Standards Track                                  Cisco Systems                                                            G. Camarillo                                                                Ericsson                                                              March 2009Quality of Service (QoS) Mechanism Selectionin the Session Description Protocol (SDP)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Polk, et al.                Standards Track                     [Page 1]

RFC 5432             QoS Mechanism Selection in SDP           March 2009Abstract   The offer/answer model for the Session Description Protocol (SDP)   assumes that endpoints somehow establish the Quality of Service (QoS)   required for the media streams they establish.  Endpoints in closed   environments typically agree out-of-band (e.g., using configuration   information) regarding which QoS mechanism to use.  However, on the   Internet, there is more than one QoS service available.   Consequently, there is a need for a mechanism to negotiate which QoS   mechanism to use for a particular media stream.  This document   defines such a mechanism.Table of Contents1. Introduction ....................................................32. Terminology .....................................................33. SDP Attributes Definition .......................................34. Offer/Answer Behavior ...........................................44.1. Offerer Behavior ...........................................44.2. Answerer Behavior ..........................................44.3. Resource Reservation .......................................54.4. Subsequent Offer/Answer Exchanges ..........................55. Example .........................................................56. IANA Considerations .............................................66.1. Registration of the SDP 'qos-mech-send' Attribute ..........66.2. Registration of the SDP 'qos-mech-recv' Attribute ..........66.3. Registry for QoS Mechanism Tokens ..........................77. Security Considerations .........................................78. Acknowledgements ................................................79. References ......................................................89.1. Normative References .......................................89.2. Informative References .....................................8Polk, et al.                Standards Track                     [Page 2]

RFC 5432             QoS Mechanism Selection in SDP           March 20091.  Introduction   The offer/answer model [RFC3264] for SDP [RFC4566] does not provide   any mechanism for endpoints to negotiate the QoS mechanism to be used   for a particular media stream.  Even when QoS preconditions [RFC3312]   are used, the choice of the QoS mechanism is left unspecified and is   up to the endpoints.   Endpoints that support more than one QoS mechanism need a way to   negotiate which one to use for a particular media stream.  Examples   of QoS mechanisms are RSVP (Resource Reservation Protocol) [RFC2205]   and NSIS (Next Steps in Signaling) [QoS-NSLP].   This document defines a mechanism that allows endpoints to negotiate   the QoS mechanism to be used for a particular media stream.  However,   the fact that endpoints agree on a particular QoS mechanism does not   imply that that particular mechanism is supported by the network.   Discovering which QoS mechanisms are supported at the network layer   is out of the scope of this document.  In any case, the information   the endpoints exchange to negotiate QoS mechanisms, as defined in   this document, can be useful for a network operator to resolve a   subset of the QoS interoperability problem -- namely, to ensure that   a mechanism commonly acceptable to the endpoints is chosen and make   it possible to debug potential misconfiguration situations.2.  Terminology   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.  SDP Attributes Definition   This document defines the 'qos-mech-send' and 'qos-mech-recv' session   and media-level SDP [RFC4566] attributes.  The following is their   Augmented Backus-Naur Form (ABNF) [RFC5234] syntax, which is based on   the SDP [RFC4566] grammar:      attribute            =/ qos-mech-send-attr      attribute            =/ qos-mech-recv-attr      qos-mech-send-attr   = "qos-mech-send" ":"                             [[SP] qos-mech *(SP qos-mech)]      qos-mech-recv-attr   = "qos-mech-recv" ":"                             [[SP] qos-mech *(SP qos-mech)]      qos-mech             = "rsvp" / "nsis" / extension-mech      extension-mech       = tokenPolk, et al.                Standards Track                     [Page 3]

RFC 5432             QoS Mechanism Selection in SDP           March 2009   The 'qos-mech' token identifies a QoS mechanism that is supported by   the entity generating the session description.  A token that appears   in a 'qos-mech-send' attribute identifies a QoS mechanism that can be   used to reserve resources for traffic sent by the entity generating   the session description.  A token that appears in a 'qos-mech-recv'   attribute identifies a QoS mechanism that can be used to reserve   resources for traffic received by the entity generating the session   description.   The 'qos-mech-send' and 'qos-mech-recv' attributes are not   interdependent; one can be used without the other.   The following is an example of an 'm' line with 'qos-mech-send' and   'qos-mech-recv' attributes:      m=audio 50000 RTP/AVP 0      a=qos-mech-send: rsvp nsis      a=qos-mech-recv: rsvp nsis4.  Offer/Answer Behavior   Through the use of the 'qos-mech-send' and 'qos-mech-recv'   attributes, an offer/answer exchange allows endpoints to come up with   a list of common QoS mechanisms sorted by preference.  However, note   that endpoints negotiate in which direction QoS is needed using other   mechanisms, such as preconditions [RFC3312].  Endpoints may also use   other mechanisms to negotiate, if needed, the parameters to use with   a given QoS mechanism (e.g., bandwidth to be reserved).4.1.  Offerer Behavior   Offerers include a 'qos-mech-send' attribute with the tokens   corresponding to the QoS mechanisms (in order of preference) that are   supported in the send direction.  Similarly, offerers include a   'qos-mech-recv' attribute with the tokens corresponding to the QoS   mechanisms (in order of preference) that are supported in the receive   direction.4.2.  Answerer Behavior   On receiving an offer with a set of tokens in a 'qos-mech-send'   attribute, the answerer takes those tokens corresponding to QoS   mechanisms that it supports in the receive direction and includes   them, in order of preference, in a 'qos-mech-recv' attribute in the   answer.  On receiving an offer with a set of tokens in a 'qos-mech-   recv' attribute, the answerer takes those tokens corresponding to QoS   mechanisms that it supports in the send direction and includes them,   in order of preference, in a 'qos-mech-send' attribute in the answer.Polk, et al.                Standards Track                     [Page 4]

RFC 5432             QoS Mechanism Selection in SDP           March 2009   When ordering the tokens in a 'qos-mech-send' or a 'qos-mech-recv'   attribute by preference, the answerer may take into account its own   preferences and those expressed in the offer.  However, the exact   algorithm to be used to order such token lists is outside the scope   of this specification.   Note that if the answerer does not have any QoS mechanism in common   with the offerer, it will return empty 'qos-mech-send' and 'qos-mech-   recv' attributes.4.3.  Resource Reservation   Once the offer/answer exchange completes, both offerer and answerer   use the token lists in the 'qos-mech-send' and 'qos-mech-recv'   attributes of the answer to perform resource reservations.  Offerers   and answerers SHOULD attempt to use the QoS mechanism with highest   priority in each direction first.  If an endpoint (the offerer or the   answerer) does not succeed in using the mechanism with highest   priority in a given direction, it SHOULD attempt to use the next QoS   mechanism in order of priority in that direction, and so on.   If an endpoint unsuccessfully tries all the common QoS mechanisms for   a given direction, the endpoint MAY attempt to use additional QoS   mechanisms not supported by the remote endpoint.  This is because   there may be network entities out of the endpoint's control (e.g., an   RSVP proxy) that make those mechanisms work.4.4.  Subsequent Offer/Answer Exchanges   If, during an established session for which the QoS mechanism to be   used for a given direction was agreed upon using the mechanism   defined in this specification, an endpoint receives a subsequent   offer that does not contain the QoS selection attribute corresponding   to that direction (i.e., the 'qos-mech-send' or 'qos-mech-recv'   attribute is missing), the endpoints SHOULD continue using the same   QoS mechanism used up to that moment.5.  Example   The following is an offer/answer exchange between two endpoints using   the 'qos-mech-send' and 'qos-mech-recv' attributes.  Parts of the   session descriptions are omitted for clarity purposes.   The offerer generates the following session description, listing both   RSVP and NSIS for both directions.  The offerer would prefer to use   RSVP and, thus, includes it before NSIS.Polk, et al.                Standards Track                     [Page 5]

RFC 5432             QoS Mechanism Selection in SDP           March 2009      m=audio 50000 RTP/AVP 0      a=qos-mech-send: rsvp nsis      a=qos-mech-recv: rsvp nsis   The answerer supports NSIS in both directions, but not RSVP.   Consequently, it returns the following session description:      m=audio 55000 RTP/AVP 0      a=qos-mech-send: nsis      a=qos-mech-recv: nsis6.  IANA Considerations   This specification registers two new SDP attributes and creates a new   registry for QoS mechanisms.6.1.  Registration of the SDP 'qos-mech-send' Attribute   IANA has registered the following SDP att-field under the Session   Description Protocol (SDP) Parameters registry:   Contact name:   Gonzalo.Camarillo@ericsson.com   Attribute name:   qos-mech-send   Long-form attribute name:   QoS Mechanism for the Send Direction   Type of attribute:   Session and Media levels   Subject to charset:   No   Purpose of attribute:   To list QoS mechanisms supported in the send                           direction   Allowed attribute values:   IANA Registered Tokens6.2.  Registration of the SDP 'qos-mech-recv' Attribute   IANA has registered the following SDP att-field under the Session   Description Protocol (SDP) Parameters registry:   Contact name:   Gonzalo.Camarillo@ericsson.com   Attribute name:   qos-mech-recv   Long-form attribute name:   QoS Mechanism for the Receive Direction   Type of attribute:   Session and Media levelsPolk, et al.                Standards Track                     [Page 6]

RFC 5432             QoS Mechanism Selection in SDP           March 2009   Subject to charset:   No   Purpose of attribute:   To list QoS mechanisms supported in the                           receive direction   Allowed attribute values:   IANA Registered Tokens6.3.  Registry for QoS Mechanism Tokens   The IANA has created a subregistry for QoS mechanism token values to   be used in the 'qos-mech-send' and 'qos-mech-recv' attributes under   the Session Description Protocol (SDP) Parameters registry.  The   initial values for the subregistry are as follows:      QoS Mechanism                Reference      ---------------------------- ---------      rsvpRFC 5432      nsisRFC 5432   As per the terminology in [RFC5226], the registration policy for new   QoS mechanism token values shall be 'Specification Required'.7.  Security Considerations   An attacker may attempt to add, modify, or remove 'qos-mech-send' and   'qos-mech-recv' attributes from a session description.  This could   result in an application behaving in a non-desirable way.  For   example, the endpoints under attack may not be able to find a common   QoS mechanism to use.   Consequently, it is strongly RECOMMENDED that integrity and   authenticity protection be applied to SDP session descriptions   carrying these attributes.  For session descriptions carried in SIP   [RFC3261], S/MIME [RFC3851] is the natural choice to provide such   end-to-end integrity protection, as described in [RFC3261].  Other   applications MAY use a different form of integrity protection.8.  Acknowledgements   Dave Oran helped form this effort.  Flemming Andreasen and Magnus   Westerlund provided useful comments on this specification.Polk, et al.                Standards Track                     [Page 7]

RFC 5432             QoS Mechanism Selection in SDP           March 20099.  References9.1.  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.   [RFC3851]  Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail              Extensions (S/MIME) Version 3.1 Message Specification",RFC 3851, July 2004.   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session              Description Protocol",RFC 4566, July 2006.   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 5226,              May 2008.   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for              Syntax Specifications: ABNF", STD 68,RFC 5234, January              2008.9.2.  Informative References   [QoS-NSLP] Manner, J., Karagiannis, G., and A. McDonald, "NSLP for              Quality-of-Service Signaling", Work in Progress, February              2008.   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1              Functional Specification",RFC 2205, September 1997.   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,              A., Peterson, J., Sparks, R., Handley, M., and E.              Schooler, "SIP: Session Initiation Protocol",RFC 3261,              June 2002.   [RFC3312]  Camarillo, G., Ed., Marshall, W., Ed., and J. Rosenberg,              "Integration of Resource Management and Session Initiation              Protocol (SIP)",RFC 3312, October 2002.Polk, et al.                Standards Track                     [Page 8]

RFC 5432             QoS Mechanism Selection in SDP           March 2009Authors' Addresses   James Polk   Cisco Systems   3913 Treemont Circle   Colleyville, Texas  76034   USA   Phone: +1-817-271-3552   EMail: jmpolk@cisco.com   Subha Dhesikan   Cisco Systems   170 W. Tasman Drive   San Jose, CA  95134   USA   EMail: sdhesika@cisco.com   Gonzalo Camarillo   Ericsson   Hirsalantie 11   Jorvas  02420   Finland   EMail: Gonzalo.Camarillo@ericsson.comPolk, et al.                Standards Track                     [Page 9]