The Digital Network
Roger L. Freeman · 2002
Abstract The objective of this chapter is provide realizable performance objectives of the digital network as well as the impairments that can be expected and how to limit their impact on those performance objectives. The chapter also covers network synchronization without which that network would become inoperable or very badly degraded with excessive slips. The digital network to which we refer is the underlying network supporting the PSTN. In industrialized countries the PSTN is completely digital; in emerging nations it is rapidly becoming so. The PSTN is a network open to public correspondence which supports the communication of voice, data, and video. There are also private and industrial networks. In many situations these private networks are backed up by the PSTN in case of dramatic failure or catastrophe. It is just for this reason we recommend private and industrial networks to follow PSTN practice (in most respects) so that there is a viable interface when the need arises. It is assumed that the digital network is based on 8‐bit PCM using either A‐law or μ‐law companding discussed earlier. In North America there is not one singular network, but many networks under different ownerships. With the divestiture of the Bell System, seven regional Bell operating companies came into being. The long‐distance network consists of several or many competing carriers or IXCs depending on how one wishes to define a long‐distance carrier. Those with their own facilities with thousands of miles of transmission facilities and multiple switches may amount to six or seven, while others just resell service. The fact there are many interconnecting digital networks poses some difficult interfacing issues for the network designer, particularly multiple clock problems, where each of these networks has its own master clock.