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ISDN FAQ
by Technical Staff, VSNL Mumbai

1) What is ISDN ?

ISDN (Integerated Services Digital Network) is a digital telephone service that provides fast accurate data transmission over exisiting telephone wiring.

2) Is special cabling required for ISDN ?

No,ISDN line is provided over exisiting copper wires used in standard telephone connection.

3)In the context of ISDN,they keep referring to terms like BRI ,2B+D , PRI etc ? What are they ?

There are two types of connections for ISDN . One is called the Basic Rate ISDN (BRI) or 2B+D in which two 64Kbps channels are available to ISDN subscriber.The other is Primary Rate Interface (PRI) or 30B+D. This is useful mainly for large business etc . At present MTNL/DOT is offering only BRI.

4) Can the ISDN line user call another analog telphone user ?

The ISDN user will have full connectivity,both nationally and internationally ,to other analog telphone users.

5) How is the ISDN line different from existing analog telephone line ?

An ISDN line is a telephone line from a new technology exchange in which user's voice ,data, or images or a combination thereof are sent and received in digital format right from user's premises.An ISDN user can establish two simulateous independent calls on existing pair of wires of the telephone line where as only one call is possible at prsent on the analog line telephone connection.

6) What are its application ?

ISDN offers the quality and speed which was only available to people who bought expensive point to point leased line. The popular usage are :

  • higher speed internet access
  • backup for leased line
  • Videoconferencing
  • Telecommuting etc.
7) How fast is ISDN compared to analog modems ?

The speed of transmission using a regular telephone line and standard V.34 modem is generally 28.8 Kbps ,with ISDN line the line speed can go as high as 128 kbps with out compression ..almost 4 times faster !!!

8) What is the benefit to use ISDN line to access Internet?

As internet become more and more information intensive with video graphics, sound and multimedia , your ability to take advantage of these new resources depends on speed of your internet of your internet connection . ISDN internet access offers follwoing additional feature:

  • subsecond connection time.
  • faster access at 64 kbps or 128 kbps
  • more efficient and economical
9) Who gives ISDN connection ?

ISDN line is provided by MTNL/DOT

10) What are the charges I have to pay MTNL/DOT ?

The usage charges for ISDN calls are same as for PSTN subject to minimum charges of Rs 5000/- per month per subscriber. There are additional monthly rental and one time installation charges.

11) What do I need to connect to internet using ISDN ?

There are three basic componets required :

  • 1) ISDN phone line from MTNL/DOT
  • 2) ISDN hardware
  • 3) ISDN Internet access provider
12) What type of Computer System do users need ?

Windows users should have following minimum configuration :

  • pentium 100 or higher windows based computer.
  • Windows 95 or Windows NT
  • 16 MB RAM (Extra RAM will really speed up your web browsing on graphically oriented sites )
  • 15 MB free hard disk space
  • 16550 UART
  • Com. port 1 or 2
13) Can one use existing analog modem with ISDN line ?

No , for Internet access over ISDN line user need to have terminal adaptor or ISDN card etc.

14) What type of ISDN equipment should on buy ?

List of VSNL tested ISDN terminal adaptor and card is given in hardware requirement.

15) Where is ISDN internet access available ?

Our ISDN internet access is available at present in Mumbai and very soon we wil start the services in Delhi, Chennai, Calcutta ,Pune , banglore .

16) How much does ISDN internet access cost ?

See tariff section for this .

17) Is ISDN internet access for business or consumers ?

ISDN access is primarly for consumers and small to medium size business. How ever many larger business use ISDN internet access for remote access and telecommuting application.

18) Do you support 2-B (128Kbps) connections ?

Yes , you will need to setup your equipment configuration for a 2-B connection.Your ability to use 2-B channel simulataneously is dependent on type of ISDN terminal adapter you have purchased.

19) What is Multilink PPP ?

The Multilink point to point (MPP) bundles multiple B channels for data rates over 64 Kbps .It allows dynamic bandwidth allocation.We support the Multilink PPP protocal.

20) What is dynamic bandwidth allocation ?

Dynamic bandwidth allocation is the ability for a device to drop and add channels as needed. True dynamic bandwidth would allow a terminal adapter to allocate a second channel if the load on the first one becomes too heavy.

21) Why VSNL is offering an ISDN TA solution instead of router solution ?

We will be offering LAN ISDN services soon .

21) Where can one learn more about isdn ?

The following are few of the interesting isdn sites :



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