Avaya BCM50 Konfigurationsanleitung PDF herunterladen (Seite 536)

536 Appendix C ISDN overview

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Analog versus ISDN

ISDN offers significantly higher bandwidth and speed than analog transmission because of its

end-to-end digital connectivity on all transmission circuits. Being digital allows ISDN lines to

provide better quality signaling than analog POTS lines, and ISDN out-of band data channel

signaling offers faster call set up and tear down.

While an analog line carries only a single transmission at a time, an ISDN line can carry one or

more voice, data, fax, and video transmissions simultaneously.

An analog modem operating at 14.4K takes about 4.5 minutes to transfer a 1MB data file and a

28.8K modem takes about half that time. Using one channel of an ISDN line, the transfer time is

reduced to only 1 minute and if two ISDN channels are used, transfer time is just 30 seconds.

When transmitting data, the connect time for an average ISDN call is about three seconds per call,

compared to about 21 seconds for the average analog modem call.

Types of ISDN service

Two types of ISDN services (lines) are available: Basic Rate Interface (BRI) and Primary Rate

Interface (PRI). Each line is made up of separate channels known as B and D channels which

transmit information simultaneously.

• BRI is known as 2B+D because it consists of two B-channels and one D-channel.

• PRI is known as 23B+D(in North America) or as 30B+D (in Europe). In North America,

23B+D consists of 23 B-channels and one D-channel (T1 carrier). In Europe, 30B+D consists

of 30 B-channels and one D-channel (E1 carrier).

B channels: B channels are the bearer channel and are used to carry voice or data information and

have speeds of 64 kbps. Since each ISDN link (BRI or PRI) has more than one B-channel, a user

can perform more than one transmission at the same time, using a single ISDN link.

D channels: The standard signaling protocol is transmitted over a dedicated data channel called

the D-channel. The D-channel carries call setup and feature activation information to the

destination and has speeds of 16 kbps (BRI) and 64 kbps PRI. Data information consists of control

and signal information and for BRI only, packet-switched data such as credit card verification.

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. Three layers are at work in ISDN for BCM. To support ISDN

service, all three layers must be working properly.

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Avaya BCM50 Konfigurationsanleitung Seite 536