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IMSI Vs MSISDN

+2 votes
9,783 views

IMSI and MSISDN are used to denote the mobile in some sense i.e. Sim Identification or User identification. My question is why we have two numbers, is there any relation between these i.e. can we deduce IMSI from MSISDN or vice versa. Is it necessary to have both numbers or there can be cases when only one number is available or applicable.

posted Jul 4, 2013 by Salil Agrawal

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3 Answers

+3 votes
 
Best answer

Both serves different purpose -

IMSI - International Mobile Subscriber Identity
MSISDN - Mobile Directory Number

One is used to identify a subscriber by operator. Other is used to route the call. A subscriber becomes customer of an operator by buying the SIM card of the operator. At this point the subscriber is allocated an IMSI and an MSISDN. IMSI is used to identify a subscriber by the operator. But MSISDN is the number which is used for dialing. So when you call your friend/a mobile, you call the MSISDN number of the mobile, not the IMSI.

For Eg: Consider 2 subscriber's A & B. And assume the values given below;

IMSI (A) : 987123111111111
IMSI (B) : 987124111111111

MSISDN (A) : 9448012121
MSISDN (B) : 9448121212

So when A would like to call B, A dials the MSISDN number of B, i.e, 9448121212. And same is true for vice-versa.

Now coming to need of IMSI, when a mobile is switched on, it needs to identify and authenticate the subscriber with the network. Only then the mobile will be able to use the network services. So to identify the user in this scenario, the IMSI of the subscriber is used. In fact the IMSI is burned in the SIM card, which will be used while authenticating with network. MSISDN will not be stored in the SIM.

answer Jul 4, 2013 by Kevin Peterson
Hi Kevin, that was explained well. However, I have a doubt with MNP can we still retain the same IMSI? and as per my knowledge there is something called as ICCID that is burned into the sim which is unique per sim card. what is the difference between ICCID and IMSI?
In case of MNP IMSI remains same, MSISDN is the once which is used to route the call. ICCID is a card identifier (physically) where as IMSI is the subscriber identifier. Let me put some details about ICCID -

The ICCID (Integrated Circuit Card Identifier) identifies each SIM internationally. A full ICCID is 19 or 20 characters. It is possible to extract the ICCID by using the 'AT!ICCID?' modem command.
The format of the ICCID is: MMCC IINN NNNN NNNN NN C x
MM = Constant (ISO 7812 Major Industry Identifier, = 89 for "Telecommunications administrations and private operating agencies")
CC = Country Code (i.e. 61 = Australia, 86 = China)
II = Issuer Identifier (AAPT = 14, EZI-PhoneCard = 88, Hutchison = 06, Optus = 02/12/21/23, Telstra = 01, Telstra Business = 00/61/62, Vodafone = 03)
N{12} = Account ID ("SIM number")
C = Checksum calculated from the other 19 digits using the Luhn algorithm.
x = An extra 20th digit is returned by the 'AT!ICCID?' command, but doesn't seem to be an official part of the ICCID.

However you can post a saperate question for difference between ICCID and IMSI.
What is the difference between ICCID and IMSI?
+2 votes

Consider this, if your mobile phone gets stolen or you lost your mobile phone, you can still keep your MSISDN by using a new SIM. MSISDN is only tied to the IMSI at the point when the account is active in the system, and the IMSI can be changed as and when required, whereas the MSISDN is tied to the customer.

answer Jul 5, 2013 by anonymous
+2 votes

@Kevin,
That was a comprehensive answer. But would beg to defer from your statement for the question raised by @Pavithra:

In case of MNP IMSI remains same.

I would say its not the case, because IMSI is a combination of MCC(mobile country code), MNC(mobile network code) and MSIN( mobile subscription identification number).

The MNC contains information about the operator. So the IMSI will definitely change during MNP. Its only the MSISDN that would remain same(of course, the sole purpose of MNP). A new pairing of IMSI/MSISDN would happen on the new operator's network.
Cheers!

answer Jul 9, 2013 by Ranjeeth K Rao
Looks that Kevin has reversed the IMSI and MSISDN for the MNP case.
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M2M devices and data cards without voice services may not need an MSISDN, how are such records maintained on the HLR? Is it mandatory to have an MSISDN associated with every IMSI record on the HLR? If yes, can we just have a dummy/fake MSISDN associated in such a case so to avoid consuming/wasting a real MSISDN?


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