問題文
The two SIP legs of a call on a border element carry preference lists that differ, and a supplementary service changes the codec in mid-call. What does the guide say about the transcoding resource?
選択肢
- It is held for the whole life of the call, since a change of codec across the two legs has to be met out of the resource reserved and held at setup.
- It is barred once the call has come up, since a change of codec across the two legs is settled out of the preference list and the codec of the leg that answers.
- It is moved across to the other leg, since a change of codec across the two legs is carried out of the resource and list of the leg that offers.
- It is put in or taken out while the call runs, since a change of codec across the two legs is what calls for that resource in the first place.