Prioritizing Coder List In Sdp Offer - AudioCodes Mediant 800B User Manual

User's Manual
3. Adding to the example, assume the following:

For the outgoing leg, the device selects the common coders G.711 and G.729
(explained in the example above).

Outgoing leg includes the Extended coder G.726.

Outgoing leg includes the following Allowed coders: G.723, G.726, and G.729.
As a result, the device selects the common coders, i.e., G.729 and G.726 (coder
priority did not change Extension coder order).
If the Allowed coders policy on the SDP incoming leg returns an empty coders list, the
device rejects the call (SIP 488 or ACK and BYE). If both Extension coders and Allowed
coders policies on SDP (in this order) returns an empty coders list, the outgoing leg rejects
the call (SIP 488, or ACK and BYE).
Below is an example, assuming that Allowed Coders list (ordered) includes G711A-law
(PCMA), G729, and G711U-law (PCMU), and Extension Coder is G729.
1. SDP offer - original offer:
m=audio 6050 RTP/AVP 0 8 4 96
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:4 G723/8000
a=fmtp:4 annexa=no
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=ptime:20
a=sendrecv
2. SDP offer - after manipulation:
m=audio 6010 RTP/AVP 8 0 96 18
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=ptime:20
a=sendrecv
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
In the SDP, the "m=audio 6010 RTP/AVP 8 0 96 18" line shows that the coder priority has
changed - G.711A-law ("8") and then G.711U-law ("0") - and that the Extension coder
G.729 ("18") has been added. The G.723 coder ("4) in the original offer was removed as it
was not defined in the Allowed Coders list (i.e., a restricted coder).

To configure Extension coders:
1. In the Coders Group table (see 'Configuring Coder Groups' on page 240), configure a
Coders Group for extension coders.
2. In the IP Profile table, select this Coders Group in the 'Extension Coders Group ID'
parameter.
3. In the IP Profile table, enable this feature by setting the 'Allowed Coders Mode'
parameter to Restriction or Restriction and Preference.

27.4.7 Prioritizing Coder List in SDP Offer

In addition to restricting the use of coders with Allowed coders, the device can prioritize the
coders listed in the SDP offer. This feature is referred to as Coder Preference. This is done
on both SBC legs:
Version 6.6 433
‎ 2 7. SBC Overview
Mediant 800B GW & E-SBC