sip trunk to asterisk

Cisco Netwerk (C-NSP)

If the call is terminating on the 2800 ( ie ip to tdm) there is no need to transcode….

It would just be a standard sip offer/answer dialog.

As long as one codec matches it would be fine.

 

If you have 2 ip legs you should look into cisco border element configs as an SBC.

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book.html

 

You can then decide how to work the codec selection and how the cisco interacts( interferes may be a better term) with the media session between the 2 legs Transcoding would only be necessary if you have two IP legs and each leg needs to use a different codec.

Leg 1 g711a and leg2 g729 for example.

The 2800 can do this

http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-border-element/100480-cube-transcode.html