A , B , C , D , E , F , G , H , I , J , K , L , M , N , O , P , Q , R , S , T , U , V , W , X , Y , Z
For example, an IAP may purchase a T1 link (1.544Mb/s) and resell that bandwidth in chunks consisting of ISDN (64Kb/s, 128Kb/s) and analog modems (14.4Kb/s, 28.8Kb/s). The IAP's customer base is likely to include both businesses and individuals. Individual customers usually connect to the IAP via a modem and telephone line to a (preferably local) point of presence.
An IAP may also be an Internet Service Provider.
ISDN was first published as one of the 1984 ITU-T {Red Book} recommendations. The 1988 {Blue Book} recommendations added many new features. ISDN uses mostly existing {Public Switched Telephone Network} (PSTN) switches and wiring, upgraded so that the basic "call" is a 64 kilobits per second, all-digital end-to-end channel. {Packet} and {frame} modes are also provided in some places.
There are different kinds of ISDN connection of varying bandwidth (see {DS level}):
| DS0 | = | 1 channel PCM at | 64 kbps |
| T1 or DS1 | = | 24 channels PCM at | 1.54 Mbps |
| T1C or DS1C | = | 48 channels PCM at | 3.15 Mbps |
| T2 or DS2 | = | 96 channels PCM at | 6.31 Mbps |
| T3 or DS3 | = | 672 channels PCM at | 44.736 Mbps |
| T4 or DS4 | = | 4032 channels PCM at | 274.1Mbps |
A {Basic Rate Interface} (BRI) is two 64K "bearer" channels and a single "delta" channel ("2B+D"). A {Primary Rate Interface} (PRI) in North America and Japan consists of 24 channels, usually 23 B + 1 D channel with the same physical interface as T1. Elsewhere the PRI usually has 30 B + 1 D channel and an {E1} or DS1interface.
A {Terminal Adaptor} (TA) can be used to connect ISDN channels to existing interfaces such as {RS-232} and {V.35}.
Different services may be requested by specifying different values in the "Bearer Capability" field in the call setup message. One ISDN service is "telephony" (i.e. voice), which can be provided using less than the full 64 kbps bandwidth (64 kbps would provide for 8192 eight bit samples per second) but will require the same special processing or {bit diddling} as ordinary PSTN calls. Data calls have a Bearer Capability of "64 kbps unrestricted".
ISDN is offered by local telephone companies, but most readily in Australia, France, Japan and Singapore, with the UK somewhat behind and availability in the USA rather spotty.
(In March 1994) ISDN deployment in Germany is quite impressive, although (or perhaps, because) they use a specifically German signalling specification, called {1.TR.6}. The French {Numeris} also uses a non-standard protocol (called {VN4}; the 4th version), but the popularity of ISDN in France is probably lower than in Germany, given the ludicrous pricing. There is also a specifically-Belgian V1 experimental system. The whole of Europe is now phasing in {Euro-ISDN}.
See also {Frame Relay}, {Network Termination}, {SAPI}.
A {FAQ}
is available by {(ftp://src.doc.ic.ac.uk/usenet/news-info/comp.dcom.isdn/)}.
newsgroup: {news:comp.dcom.isdnnews:comp.dcom.isdn}.
(06 Dec 1994)
Liste des ISP en France : http://www.imaginet.fr/ime/fourniss.htm.