The status ahd evolution of ISDN in the united states

ISDN is being rapidly deployed in the United States. Each of the Regional Bell Operating Companies as well as several independent telephone companies currently offer ISDN commer cial service through use of the basic rate interface. AT&T has been leading the way for interexchange carrier implementation of ISDN by providing primary-rate-interface-based services via direct connections to theAT&Tservice node. The major interex change carriers have also deployed Signaling System No 7 throughout their networks. Equoment for ISDN implementation ispredominandy supplied byAT&Tandfflorthern Telecom; how ever, European and Japanese vendors are also active in the United States market. The localexchangecarrier'sprimary, motivationfor central office based ISDN has been to provide business services which are competitive with digital PBXs. There are several impedi ments to residential ISDIV which make it unlikely that it will be common in the United States for several years. One of the most c am m on configu ra tions for deploy ing c en tra I offi c e bas ed ISDN is the use of remote vehicles. Remoting strategies have reduced cost through pair gain and, in some installations, the ability so use T(ratherthan relatively expensive Q) line cardsandeliminate NTI's. One of the largest drawbacksfor ISDN Centrex today is that it exists in islands where end-to-end ISDN functionality is only available to subscribers on the same switch. Increasing deployment of Signaling @System No. 7 by the local exchange carriers and interconnection with interexchange carrier S87 networks should remedy this situation. Interexchange carriers are deplqy@ng the ISDNprimary rate interface toprovide more attractive service offeringsfor custom erswhoconnectdirectlytotheirservicenode. Customerdemand fortheAT&Tprimapyrateinterfacchasbeenverystrong. The single most sought after function on the primary rate has been delivery of calling party number which is usedpredominantly in telemarketing applications Other functions such as more effi cient trunk usage, the use ofswitched HO and H11 channels and message associated user to user information are also drawing increasing attention. PBXvendors areplacing initial emphasis on theprimary rate interface in order to gain access to the nationwide ISDN capa bilities offered by AT&T There has been less emphasis on the basic rate because PBXs already support sophisticated voice telephone fimcdonahiy via proprietary interfaces. These pro prietary solutions are generally lower cost than basic rate and support a wide range of supplementary services. However, these proprietary interfaces do not currently support eitherpassive bus or D-channel data functionality. There is a very limited availa bility oflSDN trunk arrangements, all of which are based on the primary rate, by which PBX's can access the local exchange carrier ISDN networks.