For proper ISDN operation, it is
important that the correct switch type is configured on the ISDN
device. The most common type in the United States is AT&T's 5ESS
and Nortel's DMS-100. The most common type in Japan is NTT. U.K.'s
most common types are Net3 and Net5. ISDN service providers use a variety of switch types for their
ISDN services. Services offered by carriers vary considerably from
nation to nation and region to region. Just like modems, each switch
type operates slightly differently and has a specific set of call
setup requirements. As a result, before you can connect a router to an
ISDN service, you must be aware of the switch types used at the CO.
You specify this information during router configuration so the router
can place ISDN network-level calls and send data.
In addition to learning about the
switch type your service provider uses, you also need to know what
Service Profile Identifiers (SPIDs) are assigned to your connection.
The ISDN carrier provides a SPID to identify the line configuration of
the ISDN service. SPIDs are a series of characters (that can look like
phone numbers) that identify you to the switch at the CO. After you're
identified, the switch links the services you ordered to the
connection.
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