Difference between H245 Signal and H245 Alphanumaric

H245 Signal and H245 Alphanumaric are two DTMF relay methods for h.323 dial peers. They are both out of band DTMF relay methods.

H245 Signal transmits two events, the start and the stop when holding the key and releasing the key. In another word, it records the duration. It is useful in calling card scenario.

H245 Alphanumaric only sends one event, and it has the default during period for 200ms.

The Cisco recommended DTMF relay method is H245 Alphanumaric.