AVT A. Begen Internet-Draft Cisco Updates: 5760 (if approved) April 3, 2010 Intended status: Standards Track Expires: October 5, 2010 RTP Control Protocol (RTCP) Port for Multicast Sessions draft-begen-avt-rtcp-port-for-ssm-01 Abstract The Session Description Protocol (SDP) has an attribute that allows RTP applications to specify an address and a port associated with the RTP Control Protocol (RTCP) traffic. In RTP-based source-specific multicast (SSM) sessions, the same attribute is used to designate the address and the RTCP port of the Feedback Target in the SDP description. However, the RTCP port associated with the SSM session itself cannot be specified by the same attribute to avoid ambiguity, and thus, is required to be derived from the "m=" line of the media description. Similarly, in any-source multicast (ASM) sessions, there is no explicit way to specify the destination RTCP port. Deriving the RTCP port from the "m=" line imposes an unnecessary restriction. This document removes this restriction by introducing a new SDP attribute. 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 October 5, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. Begen Expires October 5, 2010 [Page 1]
Internet-Draft RTCP Port for Multicast Sessions April 2010 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3 3. The 'multicast-rtcp' Attribute . . . . . . . . . . . . . . . . 3 3.1. SDP Example . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Registration of SDP Attributes . . . . . . . . . . . . . . 6 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Begen Expires October 5, 2010 [Page 2]
Internet-Draft RTCP Port for Multicast Sessions April 2010 1. Introduction The Session Description Protocol (SDP) [RFC4566] has an attribute that allows RTP applications [RFC3550] to specify an address and a port associated with the RTP Control Protocol (RTCP) traffic [RFC3605]. This attribute is called 'rtcp'. Now consider a network where one or more media senders send RTP packets to a distribution source, which then multicasts these RTP packets to multicast receivers using a source-specific multicast (SSM) arrangement [RFC5760]. The distribution source also multicasts the forward RTCP traffic (i.e., RTCP Sender Reports and Receiver Reports or their summaries) to the receivers in the same SSM session. In RTP-based SSM sessions, the 'rtcp' attribute is used to designate the address and the RTCP port of the Feedback Target in the SDP description [RFC5760]. However, the RTCP port associated with the SSM session itself cannot be specified by the same attribute since it could potentially cause ambiguity. Thus, the multicast RTCP port is required to be derived from the "m=" line of the media description (See Section 10.2 of [RFC5760]) by following the +1 rule. However, [RFC3550] lifted the requirement for the +1 rule since it imposed an unnecessary restriction on RTCP port selection. In this specification, we introduce a new SDP attribute to remove this restriction. The new attribute allows the multicast sender to use its desired port in the RTCP session. Similar to SSM sessions, in any-source multicast (ASM) sessions, there is no explicit way to specify the destination RTCP port, either, and the new SDP attribute is equally applicable in ASM sessions as well. If approved, this document intends to update [RFC5760]. 2. Requirements Notation 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. The 'multicast-rtcp' Attribute In RTP-based SSM sessions, the distribution source may use different multicast RTP and RTCP ports to send the RTP and RTCP packets, respectively. Alternatively, the distribution source may use RTP/ RTCP port muxing [I-D.ietf-avt-rtp-and-rtcp-mux], in which case the RTP and RTCP packets are sent to the same destination port in the SSM Begen Expires October 5, 2010 [Page 3]
Internet-Draft RTCP Port for Multicast Sessions April 2010 session. For the former case, this document defines a new SDP attribute, called 'multicast-rtcp'. By using this attribute, the distribution source MAY use a desired port for the SSM RTCP session. The formal description of the 'multicast-rtcp' attribute is defined by the following ABNF [RFC5234] syntax: rtcp-attribute = "a=multicast-rtcp:" port CRLF Figure 1: ABNF syntax for the 'multicast-rtcp' attribute Here, the 'port' token is defined as specified in Section 9 of [RFC4566]. The 'multicast-rtcp' attribute MAY be used as a media-level attribute; it MUST NOT be used as a session-level attribute. 3.1. SDP Example In the SDP description shown in Figure 2, a source stream is multicast from a distribution source (with a source IP address of 198.51.100.1) to the multicast destination address of 233.252.0.2 and port 41000. The forward RTCP traffic is multicast in the same multicast group but to port 42000 as specified by the "a=multicast- rtcp:42000" line. A feedback target with an address of 192.0.2.1 and port of 43000 is specified by the 'rtcp' attribute. Begen Expires October 5, 2010 [Page 4]
Internet-Draft RTCP Port for Multicast Sessions April 2010 v=0 o=ali 1122334455 1122334466 IN IP4 ssm.example.com s='multicast-rtcp' Example t=0 0 a=rtcp-unicast:rsi m=video 41000 RTP/AVPF 98 i=Multicast Stream c=IN IP4 233.252.0.2/255 a=source-filter:incl IN IP4 233.252.0.2 198.51.100.1 a=rtpmap:98 MP2T/90000 a=multicast-rtcp:42000 a=rtcp:43000 IN IP4 192.0.2.1 a=mid:1 Figure 2: Example SDP showing the use of the 'multicast-rtcp' attribute 4. Security Considerations The 'multicast-rtcp' attribute is not believed to introduce any significant security risk to multimedia applications. A malevolent third party could use this attribute to redirect the RTCP traffic, but this requires intercepting and rewriting the packets carrying the SDP description; and if an interceptor can do that, many more attacks are possible, including a wholesale change of the addresses and port numbers at which the media will be sent. Therefore, as usual adequate security measures are RECOMMENDED to ensure the integrity and authenticity of the SDP descriptions so that transport addresses of the media senders, distribution sources, feedback targets as well as other session-specific information can be authenticated. 5. IANA Considerations The following contact information shall be used for all registrations in this document: Ali Begen abegen@cisco.com 170 West Tasman Drive San Jose, CA 95134 USA Begen Expires October 5, 2010 [Page 5]
Internet-Draft RTCP Port for Multicast Sessions April 2010 5.1. Registration of SDP Attributes This document registers a new attribute name in SDP. SDP Attribute ("att-field"): Attribute name: multicast-rtcp Long form: Port in the multicast RTCP session Type of name: att-field Type of attribute: Media level Subject to charset: No Purpose: See this document Reference: This document Values: See this document 6. Acknowledgments Thanks to Colin Perkins amd Magnus Westerlund for suggesting the name for the 'multicast-rtcp' attribute. Some parts of this specification are based on [RFC3605] and [RFC5760]. So, thanks to those who contributed to those specifications, too. 7. References 7.1. Normative References [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, October 2003. [RFC5760] Ott, J., Chesterfield, J., and E. Schooler, "RTP Control Protocol (RTCP) Extensions for Single-Source Multicast Sessions with Unicast Feedback", RFC 5760, February 2010. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. Begen Expires October 5, 2010 [Page 6]
Internet-Draft RTCP Port for Multicast Sessions April 2010 7.2. Informative References [I-D.ietf-avt-rtp-and-rtcp-mux] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", draft-ietf-avt-rtp-and-rtcp-mux-07 (work in progress), August 2007. Author's Address Ali Begen Cisco 170 West Tasman Drive San Jose, CA 95134 USA Email: abegen@cisco.com Begen Expires October 5, 2010 [Page 7]