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ISDN Line Simulator User’s Manual
40-400-00012, Rev. E 6
devices, particularly those that support video conferencing or LAN
adaptation, need both B Channels for a single call.
If your communications device requests any of these services, the Simulator
provides the necessary processing and resources. A special case, which
uses the D Channel and X.25 packet data transmission is also supported and
may occur while both B Channels are connected. To enable this service, see
Chapter 3 section on D Channel X.25 Packet Handling Function.
Some limitations apply to all ISDN-BRI communications, however. For
example, if two devices are connected to a single line and you establish a
call between them, both B Channels at that line are allocated to connect the
call. In other words, both B Channels are “busy” during one connected call.
Consequently, any device that uses two B Channels for a single call, such as
a video conferencing application, cannot connect to another device on the
same line.
Another limitation occurs when attempting to place a call to a device that
does not support the requested call type. For example, a call placed from an
ISDN data terminal to an ISDN voice telephone will be rejected by the
telephone.
In some cases, the call type and number of channels are satisfied and the
called device answers the call, but the calling application is not compatible
with the called application. For example, not all video conferencing
applications use the same data encoding. Or, a Terminal Adaptor that
converts ISDN to RS-232 may answer a data call that is carrying FAX
information. A well-designed application determines that it cannot process
the data and releases the call. Otherwise the user must hang up.
What To Read Next
For a technical review of ISDN-BRI operation, including physical layer
indications, data link packet protocol, and call control signaling, read Chapter
2.
For a comprehensive review of Simulator provisioning, read Chapter 3.
For more details about Simulator operation, read Chapter 4.
For troubleshooting guidelines, technical references, read Chapter 5.