Communication Manager supports the transition of an existing SIP audio call to a fax call.
During a SIP audio call, when Communication Manager receives a reINVITE message with the audio and image stream, Communication Manager performs one of the following operations:
If T.38 is administered, Communication Manager accepts the image stream and rejects the audio stream.
If T.38 is not administered, Communication Manager accepts the audio stream and rejects the image stream.
The gateway at the near end converts the analog fax streams into T.38-defined data packets. The gateway at the far end converts the T.38-defined signals into analog fax streams and transmits the streams to the receiving analog device.
Communication Manager uses the T.38 protocol for fax transmission only if the protocol can be successfully negotiated with the peer SIP entity. Otherwise, Communication Manager falls back to G.711 for fax transmission if the G.711 codec is administered.
