Cisco TelePresence ISDN Gateway

DTMF fails to work through the ISDN Gateway from an IP endpoint

Why does DTMF fail to work through the Cisco TelePresence ISDN GW from an IP endpoint?

The Cisco TelePresence ISDN Gateway does not transcode out-of-band DTMF to in-band DTMF for video calls.

In Cisco TelePresence ISDN Gateway versions earlier than release 1.4 the gateway advertised out-of-band DTMF for video calls. Most IP endpoints chose to use out-of-band DTMF in preference to in-band DTMF and therefore DTMF would work with the gateway auto-attendant but would not be detected by endpoints on the ISDN side of the network.

In release 1.4 and later, the Cisco TelePresence ISDN Gateway no longer advertises out-of-band DTMF for video calls. IP endpoints should therefore use in-band DTMF as audio tones, which the gateway will forward to the ISDN endpoint. However, note that some IP endpoints may still try to send out-of-band DTMF (which will not be forwarded over ISDN).

This article applies to the following products:

  • Cisco TelePresence ISDN GW 3200 and 3241 / MSE 8310 and 8321 ISDN blades

July 6th, 2011TAA_KB_431