AudioCodes Mediant 800 User Manual page 796

CHAPTER 30 SBC Overview
1. On the inbound leg for the incoming SDP offer: The device allows and keeps the coders in the
SDP that also appear in the Allowed Audio Coders Group for coder restriction (i.e., G.711 and
G.729). It changes the order of listed coders in the SDP so that G.711 is listed first. The device
removes the coders (i.e., G.723) from the SDP that do not appear in the Allowed Audio Coders
Group for coder restriction.
m=audio 6050 RTP/AVP 0 8 18 96
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=fmtp:4 annexa=no
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=ptime:20
a=sendrecv
2. On the outbound leg for the outgoing SDP offer: The SDP offer now includes only the G.711
and G.729 coders due to the coder restriction process on the incoming SDP offer (see Step 1).
a. The device adds the extension coder to the SDP offer and therefore, the SDP offer now
includes the G.711, G.729 and G.726 coders.
m=audio 6050 RTP/AVP 0 8 18 96 96
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000
a=rtpmap:96 G726-32/8000
a=fmtp:4 annexa=no
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=ptime:20
a=sendrecv
b. The device applies coder restriction to the SDP offer. As the Allowed Audio Coders Group
for coder restriction includes the G.723, G.726, and G.729 coders, the device allows and
keeps the G.729 and G.726, but removes the G.711 coder as it does not appear in the
Allowed Audio Coders Group for coder restriction.
m=audio 6050 RTP/AVP 18 96 96
a=rtpmap:18 G729/8000
a=rtpmap:96 G726-32/8000
a=fmtp:4 annexa=no
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=ptime:20
a=sendrecv
3. The device includes only the G.729 and G.726 coders in the SDP offer that it sends from the
outgoing leg to the outbound SIP entity. The G.729 is listed first as the Allowed Audio Coders
Group for coder restriction takes precedence over the extension coder.
➢
To configure coder transcoding:
1. In the Coder Groups table, configure a Coders Group for extension coders. For more
information, see
2. In the IP Profiles table, configure the IP Profile associated with the SIP entity:
Configuring Coder Groups.
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Mediant 800 Gateway & E-SBC | User's Manual