integrated services digital network

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integrated services digital network - Free On-line Dictionary of Computing (26 May 2007) :

  Integrated Services Digital Network
  IDSN
  ISDN
  
     <communications> (ISDN) A set of communications standards
     allowing a single wire or optical fibre to carry voice,
     digital network services and video.  ISDN is intended to
     eventually replace the plain old telephone system.
  
     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 274.1   Mbps
  
     Each channel here is equivalent to one voice channel.  DS0 is
     the lowest level of the circuit.  T1C, T2 and T4 are rarely
     used, except maybe for T2 over microwave links.  For some
     reason 64 kbps is never called "T0".
  
     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 interface.
  
     A Terminal Adaptor (TA) can be used to connect ISDN channels
     to existing interfaces such as EIA-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.
  
     FAQ (ftp://src.doc.ic.ac.uk/usenet/news-info/comp.dcom.isdn/)
     .
  
     Usenet newsgroup: news:comp.dcom.isdn.
  
     (1998-03-29)