Source Description RTCP Packets (SDES)

  A SDES packet consists of a SDES header and a variable number of chunks for the described sources. Each chunk in turn consists of a SSRC/CSRC identifier and a collection of SDES items. SDES items themselves consists of a SDES item type code (8 bits), a length field (8 bits) and as much text octets as the length field indicates.

SDES Header

 0               1               2               3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|    SC   |  PT=SDES=202  |            length L           |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
|                          SSRC/CSRC_1                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           SDES items                          |
|                              ...                              |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
|                          SSRC/CSRC_2                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           SDES items                          |
|                              ...                              |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

V, P, PT, L:

As described for SR packets, with the packet type code set to 202.

SC:

5 bits
The number of SSRC/CSRC chunks contained in this SDES packet.

The different SDES items are encoded according to a type-length-value scheme. Currently, CNAME, NAME, EMAIL, PHONE, LOC, TOOL, NOTE, and PRIV items are defined in [RFC1889].
The CNAME item is mandatory in every SDES packet, which in turn is mandatory part of every compound RTCP packet.
Like the SSRC identifier, a CNAME must differ from the CNAMEs of every other session participants. But instead of choosing the CNAME identifier randomly, the CNAME should allow both a person or a program to locate the source by means of the CNAME contents.

 0               1               2               3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    CNAME=1    |     length    | user and domain name         ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+