Polycom MGC Administrator Administrator's Manual page 422

Chapter 7 - Configuring the Gateway
7-14
Figure 7-8: IP-to-ISDN System Configuration Using Address Book
For example, when the H.323 endpoint dials 8341#30 (step 1 in Figure 7-9,
"IP-to-ISDN Call Flow Using Address Book"), the MCU Network Service
prefix (as registered with Gatekeeper) is sent to the gatekeeper where the
digits 83 are identified as the gateway prefix (step 2 in Figure 7-9) and the
digits 41 as the Session Profile. The gatekeeper translates the prefix to the IP
address of the gateway (step 3 in Figure 7-9). The call is transferred to the
gateway with the digits 41and #30 (step 4 in Figure 7-9).