Version 7.2 653 Mediant 500L Gateway & E-SBC
User's Manual 29. SBC Overview
The allowed coders are configured in the Allowed Audio Coders Groups table. For more
information, see ''Configuring Allowed Audio Coder Groups'' on page 434.
29.5.4 Prioritizing Coder List in SDP Offer
In addition to restricting the use of coders using Allowed Audio Coders Groups (see
''Configuring Allowed Audio Coder Groups'' on page 434), you can also prioritize the coders
listed in the SDP offer. This feature is referred to as Coder Preference and applies to both
SBC legs:
Incoming SDP offer: The device arranges the coder list in the incoming SDP offer
according to the order of appearance of the Allowed Audio Coders Group that is
associated with the incoming dialog. The coders listed higher up in the group take
preference over ones listed lower down. To configure this, configure the 'Allowed
Coders Mode' parameter (IpProfile_SBCAllowedCodersMode) in the associated IP
Profile to Preference or Restriction and Preference. If you configure the parameter
to to Preference, the coders in the SDP offer that also appear in the Allowed Audio
Coders Group are listed first in the SDP offer, and the coders in the SDP offer that do
not appear in the Allowed Audio Coders Group are listed after the Allowed coders in
the SDP offer. Therefore, this setting does not restrict coder use to Allowed coders,
but uses (prefers) the Allowed coders whenever possible.
Outgoing SDP offer: If only Allowed coders are used, the device arranges the coders
in the SDP offer as described above.
29.5.5 Multiple RTP Media Streams per Call Session
The device's SBC application supports multiple RTP media streams per SBC call session.
It supports the negotiation of up to five media streams ('m=' line) in the SDP offer/answer
model per session. The media can include a combination of any of the following types:
Audio, indicated in the SDP as 'm=audio'
Video, indicated in the SDP as 'm=video'
Text, indicated in the SDP as 'm=text'
Fax, indicated in the SDP as 'm=image'
Binary Floor Control Protocol (BFCP), indicated in the SDP as 'm=application <port>
UDP/BFCP'
The device transparently forwards Binary Floor Control Protocol (BFCP) signaling over
UDP between IP entities (RFC 4582). BFCP is a signaling protocol used by some third-
party conferencing servers to share content (such as video conferencing, presentations or
documents) between conference participants (SIP clients supporting BFCP). The SDP
offer/answer exchange model is used to establish (negotiate) BFCP streams between
clients. The BFCP stream is identified in the SDP as 'm=application <port> UDP/BFCP' and
a dedicated UDP port is used for the BFCP streams.
29.5.6 Interworking Miscellaneous Media Handling
This section describes various interworking features relating to media handling.
29.5.6.1 Interworking RTP Redundancy
The device supports interworking of RTP redundancy (according to RFC 2198) between
SIP entities. Employing IP Profiles, you can configure RTP redundancy handling per SIP
entity:
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