Acme Packet SBC and Configuring “Comfort Noise Generation”11 Jun 2016
Comfort Noise (RFC 3389) is the
sound played in an RTP stream to prevent a user form hearing total silence on the connection.
Not all telephony systems have the ability to play music while a party is on hold. Without Comfort Noise (CN) the party on hold may think the connection dropped unless there is an indicator letting know the call has not been dropped..
ECZ-7.4.0 the Acme Packet SBC has the ability to
inject Comfort Noise into an RTP stream by analyzing the SDP Offer and SDP Answer from both SIP endpoints.
CN interworking is triggered on a per realm basis.
In the example below the
calling party (Skype for Business) SDP Offer contains CN and is traversing a realm called
core which has
enabled. The SBC forwards SDP to the
called party. If the called party SDP Answer contains CN the SBC does not do anything because both endpoints support Comfort Noise. If CN is
not present in the PSTN’s SDP Answer the SBC
adds CN to the egress SDP Answer (towards Skype for Business) and will take responsibility for injecting CN into the RTP stream.
Example SBC configuration:
sbc# config t sbc(configure)# media-manager sbc(media-manager)# realm-config sbc(realm-config)# spl-option +comfort-noise-generate sbc(realm-config)# done media-manager realm-config identifier core addr-prefix 10.24.124.0/24 network-interface s1p0 mm-in-realm enabled spl-options comfort-noise-generate