When a caller wishes to access an interactive menu, using digits to select the desired option, it is necessary to send the digit information to the far end. The CS 1000 refers to this as End-to-End Signaling.

With many TDM resources, this is possible using direct media through the audio path. A PRI call using 64 Kbps in E1 countries or using 56 kbps in T1 countries for 3.1 KHz audio provides a reliable media path for digit transmission.

However, IP is a lossy medium where packets can be lost and are subject to data compression which means the exact frequencies can be lost. Sending DTMF over G.729 for digit menus will fail. Therefore, End to End Signaling relies on DSPs in the MGC and in the UNIStim endpoints detecting the digits and using RFC 2833 transmission of digit packets. These indicate start a digit x, continue a digit x and end of digit x reliably.

The packets indicating the digit are detected and the tone reconstituted at the receiving end. Therefore, the digit is transmitted cleanly. Both CS 1000 and Communication Manager use RFC 2833 to provide reliable digit transmission. As the Device Adapter is entirely IP based, this suffices for End to End Signaling in the Device Adapter.