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Configuring Dial Services

2-2

ISDN is primarily a dial service that uses switched connections as circuits. This

means that you can use channels and services on an as-needed basis instead of

having a connection up all the time, regardless of need. This choice ensures a cost-

effective use of phone lines as well as bandwidth efﬁciency.

ISDN Standards

The ITU-T (formerly CCITT) has deﬁned a set of standards to ensure universal

implementation of ISDN technology. The next sections detail the following ISDN

standards:

• Basic Rate Interface (BRI)

• Primary Rate Interface (PRI)

• The B Channel

• The D Channel

Basic Rate Interface

The basic rate interface (BRI) transmits data at a rate of 64 Kb/s over each of two

bearer channels, also called B channels, which are dedicated to data transmission.

Along with the two B channels, BRI uses one data channel called the D channel.

The D channel handles all signaling information such as call setup requests. It

transmits this information at a rate of 16 Kb/s.

The networking industry also refers to BRI service as 2B + D, to denote the

combination of the two B channels and one D channel. These three channels are

combined into one physical, twisted-pair line that terminates at your premises and

that provides a total of 144 Kb/s bandwidth (Figure 2-2).

Figure 2-2. Conceptual Drawing of BRI

2B + D

B channel

D channel

64 Kb/s

16 Kb/s

144 Kb/s

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Avaya Configuring Dial Services Manual do Utilizador Página 44