Polycom RMX 1500 Administrator's Manual page 591

Direct Dial-in to Endpoints or DMA VMR using Automatically
Generated Destination Numbers
ISDN/PSTN participants can call the destination endpoints without
interaction with the IVR of the gateway. This dialing method is enabled
when the administrator configures the Gateway Profile to automatically
generate the dial string of the destination endpoint or Meeting Room on
the DMA by truncating the dial in string and replacing the truncated
digits by other digits that can be used as the destination number.
For a detailed description of the call flow when dialing the DMA using
this method, see "Calling a DMA Direct with Automatically Generated
Destination Dial Strings" on page 17-27.
Calling an IP Endpoint via Gateway
If the call destination is an IP endpoint, the endpoints must be registered
to the same gatekeeper to which the RMX is registered. There should be a
mapping between the dial-in numbers in the range defined for the ISDN
Network Service and also assigned to the Gateway Profile and the IP
endpoints, in such a way that the alias of each endpoint is the number that
will be appended to the ISDN prefix.
When the call arrives to the gateway, this prefix is truncated and replaced
by digits that correspond to the MCU prefix in the gatekeeper and the call
is forwarded to the destination endpoint.
Figure 18 Call Flow from ISDN Endpoint to H.323 Endpoint with Automatically
Generated Forwarded Dial String
Chapter 17-Gateway Calls
17-11