CUCM: Expected Digits And Num Digits

In this blog post I expose the following two features in CUCM: Expected Digits and Num Digits.

Expected digits is a feature that allows CUCM to know how many digits it should receive from PSTN or a gateway. This feature is useful in overlapped dialing.

Overlapped dialing is when CUCM receives the dialed number of an inbound call digit by digit.

Suppose we have an analog gateway such as the VG202, equipped with one FXS port set as POTS, in port type. This port connects to a POTS phone. And when the phone sends the dialed digits, the gateway (and CUCM behind it) could not know how many digits to expect. So it is useful to set the Expected Digits value.

Num Digits is more powerful than Expected Digits. It is the number of digits that CUCM needs to extract from the called number of an inbound call, in order to make  a routing decision. the digits in Num digits are taken from right to left. For example, if you set Num Digits to 4, and the called number of an inbound call is 9441523, then CUCM will extract 5123 and give it to the call routing component.

Both Expected Digits and Num Digits are found only with POTS type of ports, on FXS ports.

CUCM Expected Digits and Num Digits configuration

Here is a sample analog voice gateway setting. A VG202 that has two FXS ports.


Let’s choose the first FXS port and set its type to Loop Start:


If you scroll down the page, you won’t find neither Expected digits, nor Num Digits.


Now, we go back in the menu and set the type to POTS:


And here you find Expected Digits and Num Digits


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