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A service profile identifier (SPID) is a
number provided by the ISDN carrier to identify the line
configuration of the BRI service. SPIDs allow multiple ISDN devices,
such as voice and data, to share the local loop. SPIDs are required
by DMS-100 and National ISDN-1 switches. Depending on the software
version it runs, an AT&T 5ESS switch might require SPIDs as
well.
Each SPID points to line setup and
configuration information. When a device attempts to connect to the
ISDN network, it performs a D channel Layer 2 initialization process
that causes a TEI to be assigned to the device. The device then
attempts D channel Layer 3 initialization. If SPIDs are necessary
but not configured or configured incorrectly on the device, the
Layer 3 initialization fails, and the ISDN services cannot be used.
The AT&T 5ESS switch supports up
to eight SPIDs per BRI. Because multiple SPIDs can be applied to a
single B channel, multiple services can be supported simultaneously.
For example, the first B channel can be configured for data, and the
second B channel can be configured for both voice (using an ISDN
telephone) and data.
DMS-100 and National ISDN-1 switches
support only two SPIDs per BRI: one SPID for each B channel. If both
B channels will be used for data only, configure the router for both
SPIDs (one for each B channel). You cannot run data and voice over
the same B channel simultaneously. The absence or presence of a
channel's SPID in the router's configuration dictates whether the
second B channel can be used for data or voice.
How Are SPID Numbers Chosen?
To keep SPID numbers simple (an oxymoron, it seems), most telcos use
part of the ISDN phone number in the SPID naming system. Therefore, SPIDs are often the ISDN phone number with some optional numbers. For example, the SPID for the phone number
(888) 555-1212 could be 888555121200.
A local directory number (LDN) might also be necessary if the router is to answer calls made to the second directory number.
The commands to set SPIDs and LDNs on both B channels are as follows:
Router(config-if)#isdn spid1 spid-number [ldn]
Router(config-if)#isdn spid2 spid-number [ldn]
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