Extract From RFC 3550 11. RTP over Network and Transport Protocols
This section describes issues specific to carrying RTP packets within particular network and transport protocols. The following rules apply unless superseded by protocol-specific definitions outside this specification. RTP relies on the underlying protocol(s) to provide demultiplexing of RTP data and RTCP control streams. For UDP and similar protocols, RTP SHOULD use an even destination port number and the corresponding RTCP stream SHOULD use the next higher (odd) destination port number. For applications that take a single port number as a parameter and derive the RTP and RTCP port pair from that number, if an odd number is supplied then the application SHOULD replace that number with the next lower (even) number to use as the base of the port pair. For applications in which the RTP and RTCP destination port numbers are specified via explicit, separate parameters (using a signaling protocol or other means), the application MAY disregard the restrictions that the port numbers be even/odd and consecutive although the use of an even/odd port pair is still encouraged. The RTP and RTCP port numbers MUST NOT be the same since RTP relies on the port numbers to demultiplex the RTP data and RTCP control streams. Although I am not sure why you say odd port RTP is for Fax Call? My understanding from the above extract is that the signalling protocol gets the last word, and with NAT and firewall traversal considerations I would think applications need to be tolerant. Regards Paul From: discussion-boun...@sipforum.org [mailto:discussion-boun...@sipforum.org] On Behalf Of NK Sent: Saturday, 11 January 2014 5:08 a.m. To: sip-implement...@cs.columbia.edu Cc: sip-implementors@lists.cs.columbia.edu Subject: [SIPForum-discussion] Even Port number for RTP in SDP Dear All, Can you please help me on one issue, where one of client is complaining that they need RTP even port in SDP not the ODD. Which is Fax Call. Although I checked the RFC 2327 & 4566 for SDP. In RFC 2327 its clearly mentioned that we should use even port for RTP compliance, whereas in RFC 4566 Its not clearing that is it MANDATORY or not. Can you please help me on this. >From RFC2327 m=<media> <port> <transport> <fmt list> A session description may contain a number of media descriptions. Each media description starts with an "m=" field, and is terminated by either the next "m=" field or by the end of the session description.A media field also has several sub-fields: o The first sub-field is the media type. Currently defined media are "audio", "video", "application", "data" and "control", though this list may be extended as new communication modalities emerge (e.g.,telepresense).The difference between "application" and "data" is that the former is a media flow such as whiteboard information, and the latter is bulk-data transfer such as multicasting of program executables which will not typically be displayed to the user. "control" is used to specify an additional conference control channel for the session. o The second sub-field is the transport port to which the media stream will be sent. The meaning of the transport port depends on the network being used as specified in the relevant "c" field and on the transport protocol defined in the third sub-field. Other ports used by the media application (such as the RTCP port, see [2]) should be derived algorithmically from the base media port. Note: For transports based on UDP, the value should be in the range 1024 to 65535 inclusive. For RTP compliance it should be an even number. Regards, Nitin Kapoor _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
