Matrix Telecom SIMADO GBR42 System Manual page 91

• A single PRI connection is usually much less expensive than
obtaining the equivalent number of B-channels through multiple
BRI connections
• Primary benefit of PRI is that the bandwidth can be dynamically
allocated among applications. E.g. certain channels can be
allocated for voice calls, but as those calls are terminated, the
unused B-channels can be reallocated to such high-bandwidth
applications as video conferencing. This is usually accomplished
via a PBX or a server capable of distributing the E1 bandwidth on a
PRI link.
The ISDN Terminology
Various new terms used in context of ISDN are explained below.
ISDN functional devices and reference points:
The ISDN standards define several different types of devices. Each
device type has certain functions and responsibilities but may not
represent an actual physical piece of equipment. Hence these are
called functional devices. The LE, NT1, NT2, TE1, TE2 and TA are
examples of the functional devices.
Since functional devices do not work in isolation, there are several
device-to-device interfaces, each requiring a communications
protocol. Each of these device interfaces is called a reference point.
The functional devices and reference points are explained below in
detail.
Network Termination Type1 (NT1)
This functional device represents the termination of the physical
connection between the customer site and the Local Exchange (LE).
The NT1's responsibilities include line performance monitoring,
timing, physical signaling protocol conversion, power transfer and the
multiplexing of the B-Channel and D-Channel.
Network Termination Type2 (NT2)
These functional devices refer to those devices that provide customer
site switching, multiplexing, and concentration. This includes PBXs,
LANs, mainframe computers, terminal controllers and other CPE for
voice and data switching. NT2 is generally absent in some ISDN
environments, such as residential or Centrex ISDN service.
SIMADO GBR42 V1 System Manual
Matrix
91