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Chapter 8
Troubleshooting ISDN
ISDN problems may be divided into three general categories: misconfig-
ured routers, physical wiring and ISDN protocol issues, and misconfigured
switches. You will learn about each type of problem in this section.
Misconfigured Routers
The router configuration is one of many areas that can require attention when
researching ISDN problems. Misconfiguration issues can happen due to a variety
of reasons, including typographical errors, erroneous information from service
providers, and failure to correctly configure the router itself.
Service Profile Identifiers (SPIDs)
The
Service Profile Identifiers
, or SPIDs, are analogous to phone numbers in the
analog phone environment. The numbers usually include the telephone number
with area code and, occasionally, extra digits used by the switch. This results in
a SPID of
41555512340101
, for example, which corresponds to number
415-555-1234, with additional parameters of
0101
. The local service provider
should document these numbers for the administrator.
ISDN is unique in that the local device must learn its identifying number.
This is contrasted with analog phones, which remain unaware of their actual
phone number--relying on a switch to trigger the ringer.
SPIDs are used only in North America, and the integration of the phone num-
ber into the SPID is most applicable for public ISDN installations. Private ISDN
networks usually use SPIDs without a phone number.
It is surprisingly common for administrators to assign IP addresses within two
different subnets on ISDN interfaces that connect to each other. It is important
to consider each end of an ISDN DDR connection to be part of a single subnet.
From a Layer 3 perspective, they are the same as any other point-to-point
WAN connection.
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