Quick Start Manual

Reference Guide for the Model XM128 ISDN Digital Modem
6-8 ISDN Overview
If you want the Model XM128 modem to answer inbound calls using all possible protocols, refer
to Table 6-4 for the commands used to set the best-effort call answering bit.
Ambiguity Resolution Switch for Voice Calls
For a speech or voice-band-data call, if the &ZI number assignment can tell which of the analog
adapters is being addressed, then the call is delivered to the proper destination. Sometimes,
however, ambiguity of address matching may exist. This ambiguity may exist if the &ZIn numbers
of the various protocols are either unassigned or not matched or the address information is absent
in the incoming setup message. In this case, users may want to set answering priority to an analog
port. The AT&Ln command sets the address ambiguity resolution flag as follows:
• AT&L0
The analog adapter 1 has the higher priority to answer a voice or voice-band-analog-data call.
If the analog adapter 1 is busy, the call is routed to the analog adapter, PHONE 2.
• AT&L1
The analog adapter 2 has the higher priority to answer a voice or voice-band-analog-data call.
If the analog adapter 2 is busy, the call is routed to the analog adapter, PHONE 1.
Multi Auto-Answering of Data Calls
When an ISDN data call comes in, the Model XM128 modem can determine the protocol to be
used in one of two ways.
One is way is through the information conveyed by the setup message. For DSS1, this information
includes the bearer capability, low-layer compatibility, or high-layer compatibility information
elements; for 1TR6, it includes the Service Indicator as well as an Additional Octet of the Service
Indicator.
The other way is by the Multi Auto-answering process. The Model XM128 modem determines
the protocol by monitoring the B channel signal sent by the calling site.
With either method, the data call can be identified by the modem to be X.75, V.110, V.120,
or PPP, MPPP Async-to-Sync conversion.
Table 6-4. Best-effort call answering bit commands
Command Function
ATS119.3=0 Answer call only when number matched (by default)
ATS119.3=1 Best-effort call answering