What is ISDN?

Recent technological developments in the DOT have laid a firm foundation for the provision of new and modern services by means of Integrated Services Digital Network (ISDN). As a consequence, DOT is now poised to offer a range of powerful services that are of significance for both the business and residential subscribers.

Who Can Avail This Service?

The service will be offered initially in Delhi, Bombay, Calcutta, Madras, Bangalore and Ahmedabad followed by Jaipur, Ranchi and Hyderabad. ISDN will be offered through the new technology imported exchanges.

Is ISDN Different from the Existing Analog Phones?

Intergrated Services Digital Network (ISDN) has emerged as a powerful tool worldwide, for provisioning of different services—voice, data and image—by means of the existing telephone network. ISDN is being viewed as a logical extension of the digitalisation of the network and most developing countries are in different stages of implementing ISDN. In ISDN even subscriber voice is sent in the digital form and so the phone is called a digital phone.

An ISDN subscriber can establish at least two simultaneous independent calls on the existing pair of telephone line (Basic Rate ISDN), whereas only one call is possible at present. The two simultaneous calls in ISDN can be of any type—speech, data, image or video.

The call setup time for a call between two ISDN subscribers will be very short, of the order of 1 to 2 seconds.

ISDN will also support a whole new set of additional facilities, called supplementary services. (see Figure)

From the ISDN Line Can I Call Other Analog Subscribers?

The ISDN subscriber will have full connectivity both nationally and internationally to other telephone subscribers.

What Equipment Can be Connected to the ISDN Line?

In the ISDN, the telephone line is terminated on a common box, called the network termination, provided at the subscriber's premises. Beyond this box, on the internal wiring in the subscriber's premises, upto 8 ISDN terminals can be connected. These ISDN terminals can be of several types, for example, ISDN telephone, personal computer (PC), video phone, video conferencing equipment, etc. In addition, existing terminals such as rotary and push button telephones, FAX machines and modems can also be connected to the internal wiring with suitable adaptors.

What Are the Services offered by ISDN?

A wide range of services catering to the needs of residential and business subscribers will be offered.

Data files between PCs will be transmitted at a high rate of 64,000 bits/s. This is more than 6 times the typical speeds possible at present.

An attractive service of ISDN being offered to DOT customers is video conferencing which has potential of curtailing travelling requirements of business executives. Video conferencing can be achieved between any two ISDN customers on dial-up basis on existing telephone lines. Two types of video conferencing are being offered. For high quality video (384 kb/s), three ISDN lines will be required by the customer. In this case in addition to video image of the participants, still pictures of documents and drawings can also be transmitted. For ordinary video conferencing (128 kb/s), a single ISDN line will be sufficient.

ISDN Customer Premises Installation [Figure]

Can I Get the `Phone Plus' Facilities Offered Now?

ISDN will also support a whole new set of additional facilities, called supplementary services for speech calls. The following services will be available for calls made between ISDN subscribers:

Calling Line Identification Presentation (CLIP): 

When an ISDN subscriber receives a call,the calling subscriber number will be displayed on his ISDN telephone before the called subscriber answers the call. (The ISDN phone has a small LCD display resembling those available in calculators). Thus, the subscriber knows the telephone number of caller from the very beginning, even before answering the call. For example, when the subscriber is already in conversation, he may choose to attend the second incoming call depending on the caller's number displayed. This service will be provided free of cost to all ISDN subscribers.

Calling Line Identification Restriction (CLIR): This service may be provided on subscription by one time payment. By means of this service, the calling subscriber will be able to prevent the presentation of his number to the called subscriber (Prevention of CLIP). However, this service will be overridden by certain agencies such as police and fire services, since they may need to know the identity of the caller in all cases.

Advice of Charge (AOC): The amount charged for a call, in terms of call units, will be displayed on the calling subscriber's ISDN phone. In case of long distance calls, it is possible to see the count of metering pulses incremented for this call. This will be continuously updated as the call is in progress.

Multiple Subscriber Number (MSN): As upto 8 terminals can be connected in parallel on the subscriber premises wiring, to call a specific terminal (PC to call a PC, and phone to call a phone), separate number can be allotted to each terminal. This will be particularly useful when the call is received from a normal (analog) subscriber. In case call is received from an ISDN subscriber, the terminal selection will be automatically made.

Call Forwarding Services (CF): The call to a subscriber can be forwarded to another number under different circumstances like, subscriber being busy or no answer. Calls can be forwarded unconditionally also (CFB, CFNR, CFU).

Call Forwarding Busy (CFB): If the called subscriber is busy, the incoming calls to his number can be diverted to another number specified by him.

Call Forwading Unconditional (CFU): All the incoming calls to a subscriber can be diverted to another number specified by him. The ring directly goes to the diverted number in this case.

Terminal Portability (TP):In the subscriber's premises upto 8 terminals can be connected to a single ISDN line. These terminals can be in different rooms and also can be on different floors. The internal wiring in the subscriber's premises is terminated on sockets. During conversation it is possible to transfer the call from one terminal to another or even remove the terminal and connect it to another socket at a different location. This facility is available for calling as well as called subscriber.

Call Hold: During conversation, it is possible to hold at least two more calls. The subscriber can switch between these calls.

Closed User Group (CUG): Companies with offices in different cities can have their ISDN number in a closed user group. The subscribers can call each other using short numbers as if they are connected to a PABX. This group enjoys certain calling privileges like selective call barring and additional level of security.

ISDN Phone

This terminal, in addition to having a handsent and dialing key pad, also has an LCD display, additional key for storing frequently dialed numbers and other function keys.

(i) Display:The ISDN phone has an LCD display resembling those available in calculators. The number dialed is displayed, so that the caller can leisurely enter the digits without mistake. This reduces wrong calling.In case of CLIP service, the calling number is displayed. In case of AOC, the number of call units charged is displayed. This is also used for programming of MSN, CF, etc. In addition to providing tones on the status of the call (dial tone, busy tone, ringing tone, routing tone, etc.) the status is also displayed. This combined with speaker phone facility provides true hands free operation.

(ii) Logging: The logging facility provides for automatic storing of calling subscriber number, when the call could not be answered. The calling number can be recalled using the log.

Other facilities like redialing, memory dialing and speaker phone are also available. The phone is also called a digital phone, since signals are transmitted and received in digital form. So the phone provides clear and noise-free conversation. In ISDN, the line condition is always checked continuously, so that any fault in the line is immediately detected.

Terminal Adaptor

The existing terminals like rotary telephone, pushbutton telephone, modems, personal computers and FAX machines can be connected. This is a quick solution to the problem of availing many ISDN facilities with the existing terminals. Only a terminal adaptor needs to be procured. The terminal adaptor provides connectivity to ISDN line on one side. On the other side a number of connectors are possible.

(i) Analog connector: Rotc telephones, push button telephones (pulse type or tone type), modems, FAX, answering machines, cordless phones, etc., can be connected.

(ii) Data port: Any PC with RS232C connection (serial port of the PC) can be connected to this port. Data transfer using standard software packages like Xtalk or Procomm is possible upto 9600 bps. A modem is not required.

PC Add-on ISDN Card

This card can be fitted in standard personal computers and can be used for data transfer at 64 kb/s. This card fits into vacant slot of any standard 386/486 PC. A software is also provided which can be installed in the PC. The connector from the PC is connected to the ISDN line. Using the software, files from the PC can be transmitted or received at 64 kb/s. For example, the complete information on a 2 Mbyte floppy can be transmitted in 4 minutes. Using both the channels, it is possible to send the data at 128 kb/s.

Video Conferencing Equipment

This equipment consists of a computer, TV monitor, camera and other control units. This is a professional equipment owned by DOT. Users utilise this facility paying DOT on the usage basis.

This equipment can be connected to the network using 3 ISDN lines. The equipment establishes connection to a similar equipment on the other side, by dialing through the network. Moving video images of the conference participants can be sent as well as received along with their conversation. It is possible to send diagrams and photographs by a still picture camera. Data transfer can also be done simultaneously. The equipment works at 384 kb/s.

In addition, video images can be sent or received on an auxiliary equipment like VCR.

Using the control panel, the video camera can be moved or zoomed on the required participants of the conference. The transmitted picture can be viewed along with the received picture.

Desk Top Video Conferencing

This is a compact version of the video conferencing equipment, usually PC based. The PC is upgradedby one or two add-on cards. A camera is provided which can be appropriately placed. Only 128 kbits/s of transmission capacity is required and, therefore, a single basic access ISDN line is sufficient. In many models, it is also possible to transfer files and jointly edit documents.