ISDN Has emerged as a powerful tool worldwide for provisioning of different services like voice, data and image transmission over the telephone line through the telephone network. ISDN is being viewed as the logical extension of the digitalization of telecommunication network and most developed countries are in different stages of implementing ISDN.

An ISDN subscriber can establish two simultaneous independent calls (except when the terminal equipment is such that it occupies two 'B' channels for one call itself like in video conferencing etc.) on existing pair of wires of the telephone line (Basic rate ISDN) where as only one call is possible at present on the analog line /telephone connection. The two simultaneous calls in ISDN can be of any type like speech, data, image etc. The call setup time for a call between two ISDN subscribers is very short, of the order of 1 to 2 seconds. ISDN also supports a whole new set of additional facilities, called Supplementary Services.


The ISDN subscriber will have full connectivity, nationally, to other analog telephone subscribers. At present ISDN services are available to and from India for the following countries:
  • Australia
  • Austria Belgium
  • Canada
  • Denmark
  • France
  • Germany
  • Ireland
  • Italy
  • Israel
  • Japan
  • Malaysia
  • Netherland
  • Norway
  • Phillipines
  • Singapore
  • Switzerland
  • Thailand
  • U.A.E
  • U.S.A

Services Offered By ISDN

  • Normal Telephone & Fax (G3)
  • Digital Telephone -with a facility to identify the calling subscriber number and other facilities.
  • G4 Fax
  • Data Transmission at 64 Kbps with ISDN controller card
  • Video Conferencing at 128 Kbps
  • Video Conferencing at 384 Kbps (Possible with 3 ISDN lines)
  • ATM (Asynchronous Transfer Mode) or PVC (Permanent Virtual Circuit)

List of ISDN stations of BSNL in India

Variety of supplementary Services supported by ISDN.

  • Calling Line Identification Presentation(CLIP)
  • Calling Line Identification Restriction(CLIR)
  • Multiple Subscriber Number(MSN)
  • Terminal Portability(TP)
  • Call Hold(CH)
  • Call Waiting(CW)
  • User to User Signaling (UUSI)

Types of Accesses

There are two types of "accesses" (connections) for ISDN.
Basic Rate Access(BRA): 2B+D
  • 2 Channels of 64 Kbps for Speech And Data.
  • 1 Channel of 16 Kbps for Signalling

Primary Rate Access (PRA): 30 B+D
  • 30 Channels of 64 Kbps for speech and data.
  • 1 Channel of 64 Kbps for signalling.