Nortel BCM 3.7, Manual

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Welcome to ISDN 859
Programming Operations Guide
ISDN Layers
ISDN layers refer to the standards established to guide the manufacturers of ISDN equipment and
are based on the OSI (Open Systems Interconnection) model. The layers include both physical
connections, such as wiring, and logical connections, which are programmed in computer
software.
When equipment is designed to the ISDN standard for one of the layers, it works with equipment
for the layers above and below it. There are three layers at work in ISDN for Business
Communications Manager. To support ISDN service, all three layers must be working properly.
• Layer 1: A physical connection that supports fundamental signaling passed between the ISDN
network (your service provider) and the Business Communications Manager system. When
the LED on a BRI S/T Media Bay Module configured as BRI is lit, your layer 1 is functioning.
• Layer 2: A logical connection between the central office or the far end and the Business
Communications Manager system. Business Communications Manager has one or two of
these connections for each BRI link, and one for each PRI link. Without Layer 2, call
processing is not possible and there is no dial tone.
• Layer 3: Also a logical connection between the ISDN network (your service provider) and the
Business Communications Manager system. For BRI lines, layer 3 is where call processing
and service profile identifier (SPID) information is exchanged. This controls which central
office services are available to the connection. For example, a network connection can be
programmed to carry data calls.
Note: Throughout this chapter, references are made to Service profile identifiers (SPIDs).
SPIDs are a part of the BRI National ISDN standard. SPIDs are not used in the ETSI BRI
standard or on PRI.
The system of layers is important when you are installing, maintaining, and troubleshooting an
ISDN system. For information about troubleshooting ISDN, see the
System Management User
Guide .
ISDN bearer capability
Bearer capability describes the transmission standard used by the BRI or PRI line so that it can
work within a larger ISDN hardware and software network.
The bearer capability for BRI and PRI is voice/speech, 3.1 kHz audio, and data (unrestricted 64
kbps, restricted 64 kbps, or 56 kbps).