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Table Of Contents  CertiGuide to Network+
 9  Chapter 0111: Wide Area Networking
      9  III  Individual Dial Up Remote Access

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ISDN
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PRI ISDN
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BRI ISDN

BRI ISDN (Basic Rate Interface Integrated Digital Subscriber Network) Uses an existing copper pair and is most often installed in the home or SOHO (Small Office Home Office) site. This type of ISDN can be used to setup two different phone numbers, with each being known as bearer channels or ‘B’ channels for short. Each of the two B channels can carry 64Kb/sec of data. A third channel is known as the Data channel or D line.

This is a slower 16Kb/sec channel that is used for signaling and control of the B lines.

The B channels can be used separately over one pair of copper for one as a voice or other analog line, and the other as a digital line. The alternative is to ‘bond’ the two B lines that create a 128Kb/sec connection. When the two B lines are bonded, it is frequently possible to have an incoming or outgoing call on the analog side drop off to handle the analog request, dropping the connection to 64Kb/sec. After the call terminates, the bond is re-joined and the connection returns to 128Kb/sec.

Figure 58: Analog Signal

 


Figure 59: Digital Signal

 


BRI ISDN can run at 128Kb/sec and drop down to 64Kb/sec for an analog connection. It automatically reconnects at 128Kb/sec upon termination of the analog call.

As an individual, if you order ISDN, a BRI line is almost always what you’ll get from the phone company.

To complete an installation of an ISDN line, a NT1 (Network Termination) is installed at the customer site to protect the phone company network from damage. The NT1 device has a TE (Terminal Equipment) port as well as a TA (Terminal Adapter) port. The TE is for digitally based ISDN compatible devices, while the TA is for analog based devices such as fax or telephones.

ISDN needs repeaters

ISDN
is a digital signal. Since digital signals do not degrade with grace, they are distance limited from the customer site to the CO (Central Office), without repeaters installed by the RBOC (phone co.).



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ISDN
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PRI ISDN
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