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Integrated Services Digital Network:


       ISDN carries voice and data at the same time. Before the advent of ISDN, Internet gets disconnected while making call. You can either  make call or browse internet.

       To overcome this problem, ISDN is created.

       Now, due to broadband (ADSL) and Mobile internet is offering high speed internet, ISDN lost popularity.

       Bharat Sanchar Nigam Limited, Reliance Communications andBharti Airtel are the largest communication service providers, and offer both ISDN BRI and PRI services across the country.

       ISDN continues to be an important backup network for point-to-point leased line customers such as banks, Eseva Centers,Life Insurance Corporation of India, and SBI ATMs. 


ISDN channels
ISDN channels



ISDN modemISDN modem



    B channel abbreviated as Bearer channel is used to carry Voice and data (similar to Traffic channel in Cellular)

    D channel abbreviated as Delta channel (similar to signalling channel in cellular) is used to carry control and signalling information.

     Signalling channel carries information such as Call setup, call termination, billing



    One Bearer channel carries 64 Kbps, two Bearer channel carries 128 Kbps and so on.


Speed and services by ISDN in India:

   Ref: BSNL website


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.

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