Reference Guide for the Model RT210/RT211 ISDN Routers
C-2 Ordering ISDN Lines
National ISDN is a series of standards designed to make it easier to order ISDN services from your
telephone company. The National ISDN (NI) standards published by Bellcore are known as NI-1,
NI-2, and NI-3. The NI-2 standard, which includes NI-1, is the one that most telephone companies
have now implemented. Switches from AT&T, Northern Telecom, and Siemens account for almost
all of the switches on the North American Market. These switches all support NI and because of
that, most telephone companies offer National ISDN in their networks. However, a significant
number of proprietary ISDN line provisions still exist, particularly in AT&T-equipped central
offices.
When you order lines from your telephone company, we recommend that you ask for National
ISDN.
Directory Numbers and SPIDs
In North America the technique of subadressing is not used. Instead, a device is identified by the
switch in the telephone company’s central office by a Service Profile Identifier (SPID). When your
telephone company notifies you of the directory number(s) assigned to your line, they provide you
with a SPID (Service Profile Identifier). The SPID is a code that must be sent to the switch at the
telephone company by your terminal each time it is started. The code is a signal to the switch that
says the device is available and lists what the capabilities are. Your equipment is not able to make
or receive calls until this SPID negotiation process has taken place. Since the SPID acts like a
password, it is very important not to make a mistake when you configure it into your router.
When only one device is attached to a line, known as point-to-point networking, it is not necessary
to identify separate devices. During point-to-point networking, the SPID is not used.
SPIDs are normally based on their corresponding seven-digit Directory Numbers. In addition to
the DN, there is a prefix and a suffix. The exact format of a SPID varies from telephone company
to telephone company, and between switch types. The prefix is frequently the area code or, with
AT&T switches, it can be 01. The suffix can be from one to four digits long. Sometimes you must
assign the final two digits (called a TID, or Terminal Identifier, which must be in the range 00 to
62). It is important to check with your telephone company to find out what the format of the SPID
should be.
For National ISDN, the telephone companies are introducing a scheme that is uniform across the
country and the same for all switch types. For a single device on a line, the default SPID is
[area code][directory number][01][01]. The second [01] represents the TID. This scheme is
expected to be in place nationwide by the end of 1996.
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