Bandwidth
Bandwidth refers to the rate at which data is transferred over the communication link. The
underlying carrier technology depends on the bandwidth available. A difference exists
between bandwidth points in the North American (T-carrier) speci?¬?cation and the European
(E-carrier) system. Both of these systems are based on the plesiochronous digital hierarchy
(PDH) supported in their networks. Optical networks use a different bandwidth hierarchy,
which again differs between North America and Europe. In the United States, the Optical
Carrier (OC) de?¬?nes the bandwidth points, and in Europe, the Synchronous Digital
Hierarchy (SDH) de?¬?nes the bandwidth points.
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Service Provider
Network
384 Chapter 5: WAN Connections
In North America, the bandwidth is usually expressed as a digital service level number
(DS0, DS1, and so forth) that technically refers to the rate and format of the signal. The
most fundamental line speed is 64 kbps, or DS0, which is the bandwidth required for an
uncompressed, digitized phone call.
Serial connection bandwidths can be incrementally increased to accommodate the need for
faster transmission. For example, 24 DS0s can be bundled to get a DS1 line (also called a
T1 line) with a speed of 1.
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