of channels it offers.
has a maximum throughput of 64 kbps. B channels can carry encoded pulse code modulation
(PCM) digital voice, video, or data. B channels are used mainly for circuit-switched data
communications such as High-Level Data Link Control (HDLC) and Point-to-Point
Protocol (PPP). However, they can also carry packet-switched data communications.
In essence, it provides a local loop to the telephone company's central office. The router
uses the D channel to dial destination phone numbers. It has a bandwidth of 16 kbps for
BRI or 64 kbps for PRI. Although the D channel is used mainly for signaling, it too can
also carry packet-switched data (X.25, Frame Relay, and so on).
rate connection consists of two bearer (B) channels and a single (D) channel. When both B
channels are active, the aggregate bandwidth becomes 128,000 bps.
two B channels. Implementations of one B channel provide cost reduction, and zero B channel
implementations enable another technology (such as X.25) to be run across the D channel. In
this book, we do not discuss the deployment of zero B channel deployments because such
implementations are not typical in most internetworks. Figure 6-2 depicts the typical 2B+D
model.
unshielded twisted-pair (UTP) cable at your site. The telco runs the cable to a location within
your premises (usually a telephone room). Many times, the base installation charge covers only
bringing the line into your premises. In that case, you must decide if you want to extend the
cable into your wiring closet or server room. Usually it is well worth the negligible additional
charge to enable the telco installer to extend it to a point that is easy to reach from the router
with another cable.
B channel 2 = 64 kbps