RFC 3556 (rfc3556) - Page 2 of 8
Session Description Protocol (SDP) Bandwidth Modifiers for RTP Control Protocol (RTCP) Bandwidth
Alternative Format: Original Text Document
RFC 3556 SDP Bandwidth Modifiers for RTCP Bandwidth July 2003
The RTP specification allows a profile to specify that the RTCP
bandwidth may be divided into two separate session parameters for
those participants which are active data senders and those which are
not. Using two parameters allows RTCP reception reports to be turned
off entirely for a particular session by setting the RTCP bandwidth
for non-data-senders to zero while keeping the RTCP bandwidth for
data senders non-zero so that sender reports can still be sent for
inter-media synchronization. Turning off RTCP reception reports is
not recommended because they are needed for the functions listed in
the RTP specification, particularly reception quality feedback and
congestion control. However, doing so may be appropriate for systems
operating on unidirectional links or for sessions that do not require
feedback on the quality of reception or liveness of receivers and
that have other means to avoid congestion.
This memo defines an extension to the Session Description Protocol
(SDP) [3] to specify RTCP bandwidth for senders and non-senders
(receivers).
2. SDP Extensions
The Session Description Protocol includes an optional bandwidth
attribute with the following syntax:
b=:
where is a single alphanumeric word giving the meaning of
the bandwidth figure, and where the default units for are kilobits per second. This attribute specifies the
proposed bandwidth to be used by the session or media.
A typical use is with the modifier "AS" (for Application Specific
Maximum) which may be used to specify the total bandwidth for a
single media stream from one site (source).
This memo defines two additional bandwidth modifiers:
b=RS:
b=RR:
where "RS" indicates the RTCP bandwidth allocated to active data
senders (as defined by the RTP spec) and "RR" indicates the RTCP
bandwidth allocated to other participants in the RTP session (i.e.,
receivers). The exact behavior induced by specifying these bandwidth
modifiers depends upon the algorithm used to calculate the RTCP
reporting interval. Different algorithms may be specified by
different RTP profiles.
Casner Standards Track