STD Code Numbering Logic of Indian Telephone System


There is indeed some sense in the the apparently random numbering system. I tried to make sense out of this chaos many years ago (way back in 1990s and I have thrown away the original paper). So, here goes .......
  1. The major metro towns have two digit codes and also act as area co-ordinators (or primary gateways/hubs) e.g. 11 for Delhi (North India), 22 for Bombay (West India), 33 for Calcutta (East India), and 44 for Madras (South India). This was OK initially but soon these exchanges could not bear the load.
  2. Other major centers came up, but these had 3-digit codes. They are usually the district HQ or cities large enough to warrant 3 digits.

    5xx is UP area, 6xx is Orissa, 7xx is MP, 8xx is Karnataka. Other identifications exist for various areas of India e.g. 1xx covers parts of Rajasthan, Haryana, Chandigarh, HP, J&K, and parts of Uttranchal (see Dehradun code), 2xx covers Maharashtra, Gujrat, some parts of MP and South Rajasthan and so on.

  3. The number of digits in the code gives you an idea of the distance from the area/regional hubs -- longer the number, more the distance plus it is more difficult to get through as communication moves through Satellite, Microwave to ground-based cables. Also, the number of digits in the STD code indicate the capacity of the exchange -- larger the STD code smaller is the exchange. You can also approximately guess the path hops that you will take to reach the desired number by looking at the STD code.
I hope this sheds some light on this obscure system which is based on international standards (CCITT or ITU ?). If you take a map of India and use different colors for the first digit of the STD codes, you will see the pattern emerging and it does seem to make sense. Please be tolerant of some having 4-digit phones and some 7-digit ones. Note that the STD code plus the phone number should be 8-10 digits. Be aware that this is as per the international norms of STD coding. India is still in transition -- change of Bangalore code from 812 to 80, Hyderabad changing its code to a 2-digit number (40) and Pune changing its code also to a 2-digit (20), indicates that they now has similar capacity exchanges that the other metro towns have.

(Author of this article is unknown -- this appeared in soc.culture.indian newsgroup in 1993)

Well, if you carefully study the telephone arrangements in India , you would find a sort of hierarchy. P&T had divided telephone operations in following form and according to level and expected exchage capacity they have assigned the STD code for that city or district. Also, for national dialling there is requeirement of subscriber having to dial minimum of 8 digits or maximum of 10 digits. I hope this answers why there is variable length STD code.

Sometimes you may find in a city of having telephone numbers of different length, this is due to capacity of exchange serving that particular area. For example in Bombay you may find 6 or 7 digit numbering. As demand rises, they would install newer exchage or upgrade it for larger capacity. In that situation they change the exchage code from 2 digits to 3 hence it becomes 7-digit number.

I guess we follow the number scheme suggested by CCITT which works under ITU.

		The HIERARCHY


                     O  Primary Center (Example Delhi, 2 digit)
                     |
		     |
       o ---------------------------o
       |                            |
     Regional Center               Regional Center (Example Shimla, 3 digit)
                                    I
                    .---------------.
                    |               |          
               District Off         District Office (Example Kullu, 4 digit)
                                    |
                          .----------------------.
                          |                      |
                        Tehsil Office           Tehsil Office (5 digit)

If you see in above example, Delhi STD code is 11, Shimla its 177 and Kullu (17**). In all these cases first digit i.e. 1 represents the primary center. If you take estern part first digit would be 3 as Calcutta being primary center (33).
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Updated : October 20, 2005
Created : August 14, 1997