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2.5 | WAN Link Options |
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2.5.8 | Describe ISDN |
Telephone companies developed ISDN with the intention of creating a totally digital network. ISDN devices include the following:
As shown in Figure
There are two ISDN services: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). ISDN BRI operates mostly over the copper twisted-pair telephone wiring in place today. ISDN BRI delivers a total bandwidth of a 144 kbps line into three separate channels. Two of the channels, called B (bearer) channels, operate at 64 kbps and are used to carry voice or data traffic. The third channel, the D (delta) channel, is a 16-kbps signaling channel used to carry instructions that tell the telephone network how to handle each of the B channels. ISDN BRI often is referred to as 2B+D. ISDN provides great flexibility to the
network designer because of its capability to use each of the B
channels for separate voice or data applications. For example, one
ISDN 64-kbps B channel can download a long document from the corporate
network while the other B channel browses a Web page. When you're
designing a WAN, you should be careful to select equipment that has
the right feature to take advantage of ISDN's flexibility.
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