ISDN Services

What is ISDN ?

Integrated Services Digital Network (ISDN) is a state-of-the-art Public Switched Digital Network for provisioning of different services�voice, data & image transmission over the telephone line through the telephone network.


Types of ISDN:-

I) BRI or BRA having TWO chl. With total speed @128 kbps
 ii) PRI or PRA having 30 chls with total speed @ 2mbps.


The following services are offered on a dial-up basis between two ISDN subscribers:
(i) Desktop Video Conferencing on using three ISDN lines at 64/128 kbps.
(ii) High quality video conferencing by using three ISDN lines at 384 kbps 
(iii) Video Telephony.
(iv) Teleconferencing which facilitates the transmission of pictures, documents and drawings etc. apart from voice and images of the participants.
(v) High speed data transmission at 64/128 kbps.
(vi) High speed facsimile at 64/128 kbps with G4 Fax terminal.
(vii) Access to Internet with a higher bandwidth of 64/128 kbps giving significantly improved response time and quality of service.


ISDN, being a Value Added Service, offers many supplementary features/services:
(1) Calling Line Identification Presentation
(2) Advice of Charge
(3) Line Hunting
(4) Closed User Group
(5) User to User Signalling
(6) Call Waiting
(7) Call forwarding
On No Reply
On Busy
(8) Multiple Subscriber Number


The ISDN telephone line is terminated on a common box called the Network Termination (NT) at the subscriber�s premises. The Network Termination unit along with accessories will be provided by the MTNL or can be procured by the subscriber. The terminal equipment has to be procured by the subscriber himself from the open market. The terminal equipment should be TEC approved for the satisfactory working of ISDN.


(a) ISDN feature phone: this is a simplest type of ISDN phone which has an LCD display and some additional keys.
(b) Terminal adapter
(c) PC add-on ISDN card
(d) Video phone
(e) G4 fax
(f) G4 fax

Benefits of ISDN

Single connection can support both voice and data.

High quality services being digital right from subs, premises (end to end).

Eight terminals can be connected on a single line.

High speed data transfer from PC to PC is possible  64 Kbps against existing 9.6 Kbps (6 times faster).

Two calls can be established simultaneously on a single pair of wires.

The call set time is very short (1-2 seconds).

A number of supplementary services are supported like in pots.

Calling Line Identification, Call Forwarding, Call Forwarding on busy signal, Call Forwarding on no reply, Call Forwarding unconditional, Advice of Charge, Terminal Portability, Multiple Subscriber Number, Closed User Group.

Benefits of ISDN for Network Operators

Avoidance of separate networks for different services.

Economical use of the equipment of the digitalized telephone network, especially the copper pair of the subscriber line.

Reduction in costs due to simplified operation and maintenance procedures.

How is ISDN line superior to the phone line ?

    • The signal on the ISDN line voice or data, is sent in digital mode.
    • The signal level at subscriber's terminal equipment is independent of
      line length.
    • An ISDN subscriber can establish two simultaneous independent calls
      which could be voice, data, image or combination of any two whereas
      only one call is possible on ordinary telephone lines.
The call set-up time between two ISDN subscribers is extremely short.