Internet Engineering Task Force (IETF) A. Begen
Request for Comments: 6128 Cisco
Updates: 5760 February 2011
Category: Standards Track
ISSN: 2070-1721
Internet Engineering Task Force (IETF) A. Begen
Request for Comments: 6128 Cisco
Updates: 5760 February 2011
Category: Standards Track
ISSN: 2070-1721
RTP Control Protocol (RTCP) Port for Source-Specific Multicast (SSM) Sessions
源特定多播（SSM）会话的RTP控制协议（RTCP）端口
Abstract
摘要
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. Deriving the RTCP port from the "m=" line imposes an unnecessary restriction. This document removes this restriction by introducing a new SDP attribute.
会话描述协议（SDP）具有一个属性，允许RTP应用程序指定与RTP控制协议（RTCP）通信量关联的地址和端口。在基于RTP的源特定多播（SSM）会话中，相同的属性用于指定SDP描述中反馈目标的地址和RTCP端口。但是，与SSM会话本身关联的RTCP端口不能由同一属性指定，以避免歧义，因此需要从媒体描述的“m=”行派生。从“m=”行派生RTCP端口会施加不必要的限制。本文档通过引入新的SDP属性来消除此限制。
Status of This Memo
关于下段备忘
This is an Internet Standards Track document.
这是一份互联网标准跟踪文件。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。有关互联网标准的更多信息，请参见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6128.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6128.
Copyright Notice
版权公告
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2011 IETF信托基金和确定为文件作者的人员。版权所有。
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.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................2
2. The 'multicast-rtcp' Attribute ..................................3
3. SDP Example .....................................................3
4. Security Considerations .........................................4
5. IANA Considerations .............................................4
5.1. Registration of SDP Attributes .............................5
6. Acknowledgments .................................................5
7. References ......................................................5
7.1. Normative References .......................................5
7.2. Informative References .....................................5
1. Introduction ....................................................2
2. The 'multicast-rtcp' Attribute ..................................3
3. SDP Example .....................................................3
4. Security Considerations .........................................4
5. IANA Considerations .............................................4
5.1. Registration of SDP Attributes .............................5
6. Acknowledgments .................................................5
7. References ......................................................5
7.1. Normative References .......................................5
7.2. Informative References .....................................5
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'.
会话描述协议（SDP）[RFC4566]具有一个属性，该属性允许RTP应用程序[RFC3550]指定与RTP控制协议（RTCP）通信量[RFC3605]关联的地址和端口。此属性称为“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.
现在考虑一个网络，其中一个或多个媒体发送者将RTP分组发送到分发源，然后使用源特定组播（SSM）安排[RTC560]将这些RTP分组多路广播到多播接收器。分发源还将转发RTCP通信（即RTCP发送方报告和接收方报告或其摘要）多播到同一SSM会话中的接收方。
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
在基于RTP的SSM会话中，“rtcp”属性用于指定SDP描述[RFC5760]中反馈目标的地址和rtcp端口。但是，与SSM会话本身关联的RTCP端口不能由同一属性指定，因为它可能导致歧义。因此，需要从媒体描述的“m=”行派生多播RTCP端口
(see Section 10.2 of [RFC5760]) by following the +1 rule (see Section 11 of [RFC3550]). However, [RFC3550] lifted the requirement for the +1 rule since it imposed an unnecessary restriction on RTCP port selection.
（参见[RFC5760]第10.2节）遵循+1规则（参见[RFC3550]第11节）。但是，[RFC3550]取消了+1规则的要求，因为它对RTCP端口选择施加了不必要的限制。
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. This document updates [RFC5760].
在本规范中，我们引入了一个新的SDP属性来删除此限制。新属性允许多播发送方在RTCP会话中使用其所需的端口。本文件更新了[RFC5760]。
In RTP-based SSM sessions, the distribution source can use different multicast RTP and RTCP ports to send the RTP and RTCP packets, respectively. Alternatively, the distribution source can use RTP/ RTCP port muxing [RFC5761], in which case the RTP and RTCP packets are sent to the same destination port in the SSM session.
在基于RTP的SSM会话中，分发源可以使用不同的多播RTP和RTCP端口分别发送RTP和RTCP数据包。或者，分发源可以使用RTP/RTCP端口复用[RFC5761]，在这种情况下，RTP和RTCP数据包被发送到SSM会话中的同一目标端口。
For the cases when the distribution source does not want to use the one higher port for the RTCP traffic, this document defines a new SDP attribute, called 'multicast-rtcp'. By using this attribute, the distribution source uses a desired port for the SSM RTCP session. In the absence of the 'multicast-rtcp' attribute, the +1 rule applies following [RFC5760].
对于分发源不希望将一个更高的端口用于RTCP通信的情况，本文档定义了一个新的SDP属性，称为“multicast RTCP”。通过使用此属性，分发源为SSM RTCP会话使用所需的端口。在缺少“多播rtcp”属性的情况下，+1规则适用于以下[RFC5760]。
The following ABNF [RFC5234] syntax formally describes the 'multicast-rtcp' attribute:
以下ABNF[RFC5234]语法正式描述了“多播rtcp”属性：
rtcp-attribute = "a=multicast-rtcp:" port CRLF
rtcp-attribute = "a=multicast-rtcp:" port CRLF
Figure 1: ABNF syntax for the 'multicast-rtcp' attribute
图1:multicast rtcp属性的ABNF语法
Here, the 'port' token is defined as specified in Section 9 of [RFC4566].
此处，“端口”令牌的定义如[RFC4566]第9节所述。
The 'multicast-rtcp' attribute is defined as both a media-level and session-level attribute. Except where stated otherwise in this document, the rules of [RFC3550] apply.
“多播rtcp”属性定义为媒体级和会话级属性。除非本文件另有规定，[RFC3550]的规则适用。
In the session 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.
在图2所示的会话描述中，源流是从分发源（源IP地址为198.51.100.1）到多播目标地址233.252.0.2和端口41000的多播。转发RTCP流量在同一个多播组中进行多播，但发送到“a=多播RTCP:42000”行指定的端口42000。地址为192.0.2.1、端口为43000的反馈目标由“rtcp”属性指定。
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
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
图2：显示“multicast rtcp”属性使用的示例SDP
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.
“多播rtcp”属性被认为不会给多媒体应用程序带来任何重大安全风险。恶意的第三方可以使用此属性重定向RTCP流量，但这需要截获并重写带有SDP描述的数据包；如果拦截器能够做到这一点，就有可能发生更多的攻击，包括彻底改变媒体发送的地址和端口号。
In order to avoid attacks of this sort, the SDP description needs to be integrity protected and provided with source authentication. This can, for example, be achieved on an end-to-end basis using S/MIME [RFC5652] [RFC5751] when SDP is used in a signaling packet using MIME types (application/sdp). Alternatively, HTTPS [RFC2818] or the authentication method in the Session Announcement Protocol (SAP) [RFC2974] could be used as well.
为了避免此类攻击，SDP描述需要完整性保护并提供源身份验证。例如，当在使用MIME类型（应用程序/SDP）的信令分组中使用SDP时，这可以使用S/MIME[RFC5652][RFC5751]在端到端的基础上实现。或者，也可以使用HTTPS[RFC2818]或会话公告协议（SAP）[RFC2974]中的身份验证方法。
The following contact information shall be used for all registrations in this document:
本文件中的所有注册均应使用以下联系信息：
Ali Begen abegen@cisco.com
阿里出生abegen@cisco.com
This document registers a new attribute name in SDP.
此文档在SDP中注册一个新的属性名称。
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 or session level Subject to charset: No Purpose: Specifies the port for the SSM RTCP session Reference: [RFC6128] Values: See [RFC6128]
SDP属性（“att字段”）：属性名称：多播rtcp长格式：多播rtcp会话中的端口名称类型：att字段属性类型：媒体或会话级别取决于字符集：无用途：指定SSM rtcp会话引用的端口：[RFC6128]值：请参阅[RFC6128]
Thanks to Colin Perkins and Magnus Westerlund for suggesting the name for the 'multicast-rtcp' attribute and providing text for portions of this specification. Some parts of this specification are based on [RFC3605] and [RFC5760]. So, also thanks to those who contributed to those specifications.
感谢Colin Perkins和Magnus Westerlund为“multicast rtcp”属性提供了名称，并为本规范的部分内容提供了文本。本规范的某些部分基于[RFC3605]和[RFC5760]。所以，也要感谢那些为这些规范做出贡献的人。
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003.
[RFC3550]Schulzrinne，H.，Casner，S.，Frederick，R.，和V.Jacobson，“RTP：实时应用的传输协议”，STD 64，RFC 35502003年7月。
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC4566]Handley，M.，Jacobson，V.，和C.Perkins，“SDP：会话描述协议”，RFC4566，2006年7月。
[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.
[RFC5760]Ott，J.，Chesterfield，J.，和E.Schooler，“具有单播反馈的单源多播会话的RTP控制协议（RTCP）扩展”，RFC 57602010年2月。
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5234]Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，STD 68，RFC 5234，2008年1月。
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)", RFC 3605, October 2003.
[RFC3605]Huitema，C.，“会话描述协议（SDP）中的实时控制协议（RTCP）属性”，RFC3605，2003年10月。
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and Control Packets on a Single Port", RFC 5761, April 2010.
[RFC5761]Perkins，C.和M.Westerlund，“在单个端口上多路传输RTP数据和控制数据包”，RFC 5761，2010年4月。
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, September 2009.
[RFC5652]Housley，R.，“加密消息语法（CMS）”，STD 70，RFC 56522009年9月。
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2818]Rescorla，E.，“TLS上的HTTP”，RFC2818，2000年5月。
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000.
[RFC2974]Handley，M.，Perkins，C.，和E.Whelan，“会话公告协议”，RFC 2974，2000年10月。
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010.
[RFC5751]Ramsdell，B.和S.Turner，“安全/多用途Internet邮件扩展（S/MIME）版本3.2消息规范”，RFC 57512010年1月。
Author's Address
作者地址
Ali Begen Cisco 181 Bay Street Toronto, ON M5J 2T3 Canada
Ali Begen Cisco位于加拿大多伦多湾街181号M5J 2T3
EMail: abegen@cisco.com
EMail: abegen@cisco.com