This sets the interdigit timer used while collecting the called-party number, DNIS, via R2 signaling specifically when there is no digit map to otherwise determine when dialing is complete, restarting after each received digit and, on expiry, signaling that no more digits are coming. Without a digit map to know the expected number length in advance, this timer is the only mechanism the gateway has to decide dialing has finished, so setting it too short can truncate legitimately slower digit entry, while too long adds unnecessary delay to every call before routing begins. With this timer set to 4 seconds, if no new DNIS digit arrives for 4 seconds after the last one, the gateway concludes the dialed number is complete and proceeds to route the call with whatever digits it has collected.