CHAPTER19 Coders and Profiles
Mediant 800 Gateway & E-SBC | User's Manual
Parameter Description
For multiplexing, the initial SDP offer must include the
"a=rtcp-mux" attribute to request multiplexing of RTP and
RTCP onto a single port. If the SDP answer wishes to
multiplex RTP and RTCP, it must also include the "a=rtcp-
mux" attribute. If the answer does not include the attribute,
the offerer must not multiplex RTP and RTCP packets. If
both ICE and multiplexed RTP-RTCP are used, the initial
SDP offer must also include the "a=candidate:" attribute for
both RTP and RTCP along with the "a=rtcp:" attribute,
indicating a fallback port for RTCP in case the answerer
does not support RTP and RTCP multiplexing.
■ [0] Not Supported = (Default) RTP and RTCP packets
use different ports.
■ [1] Supported = Device multiplexes RTP and RTCP
packets onto a single port.
Note: As RTP multiplexing has been defined by the
WebRTC standard as mandatory, the support is important
for deployments implementing WebRTC. For more
information on WebRTC, see WebRTC.
'RTCP Feedback'
sbc-rtcp-feedback
[IPProfile_
SBCRTCPFeedback]
Enables RTCP-based feedback indication in outgoing
SDPs sent to the SIP entity associated with the IP Profile.
The parameter supports indication of RTCP-based
feedback, according to RFC 5124, during RTP profile
negotiation between two communicating SIP entities. RFC
5124 defines an RTP profile (S)AVPF for (secure) real-time
communications to provide timely feedback from the
receivers to a sender. For more information on RFC 5124,
see http://tools.ietf.org/html/rfc5124.
Some SIP entities may require RTP secure-profile
feedback negotiation (AVPF/SAVPF) in the SDP
offer/answer exchange, while other SIP entities may not
support it. The device indicates whether or not feedback is
supported on behalf of the SIP entity. It does this by adding
an "F" or removing the "F" from the SDP media line ('m=')
for AVP and SAVP. For example, the following shows
"AVP" appended with an "F", indicating that the SIP entity
is capable of receiving feedback
m=audio 49170 RTP/SAVPF 0 96
■ [0] Feedback Off = (Default) The device does not send
the feedback flag ("F") in SDP offers/answers that are
sent to the SIP entity. If the SDP 'm=' attribute of an
incoming message that is destined to the SIP entity
includes the feedback flag, the device removes it
before sending the message to the SIP entity.
■ [1] Feedback On = The device includes the feedback
flag ("F") in the SDP offer sent to the SIP entity. The
device includes the feedback flag in the SDP answer
sent to the SIP entity only if it was present in the SDP
offer received from the other SIP entity.
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