Does the codec preference on a dial-peer make a major impact? We have a 3rd party recording server which is able to record calls when the codec specified in the dial-peer is G.729r8. When we force the dial-peer to use G.711ulaw, the recording server is unable to record the calls. This is happening for calls from the PSTN cloud which matches this dial-peer. Any ideas?
Well you have to check that with the recording vendor. Cisco can support any type of codec, g729 slighly degrades the voice quality so it is not the common choice for voice on a LAN.
Are you referring to the voice codec configuration on a voip dial-peer? If so for-instance setting the dial-peer to voice codec g711ulaw tells the dial-peer to only allow calls to use g711ulaw.
If you use the "voice-class codec X", list codecs in preference order and then apply the voice-class codec X to the dial-peer you allow the dial-peer to negotiate codec.
For the PSTN the codec will be g711 so if the voice recorder cannot record in g711 you will need an MTP and transcoder resources allocated to allow this to work.
I am assuming you have voice-class codec defined on your dialpeer to negotiate either codec, well only one codec is always negotiate based on the order in the class, so if g729 is the negotiated codec between the endpoints but your app only works with g711 then you need to change the order of codecs in the class to make it work.