About SIM [Under GSM]
Main functions of SIM are: Store various subscriber data, Execute
authentication related algorithms. These data are simply stored in
files in an organised way as specified by standards. The data
include IMSI, Address book, Authentication/Ciphering data,
Network/Operator information, mobile number, SIM capability
information (Service Table) etc.
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SIM-ME interface - 11.11 «
There is also an advanced feature called SIM Application Toolkit
(SAT) with which the applications in SIM can interact with user
through ME. Popular example is operator specific "Menu" in ME. The
menu contain items like "Weather", "Flight schedule" etc. The menu
items are shown by ME to user as per instructions from SIM. When
user selects an item, ME informs this to SIM (using SAT). SIM (or
application in SIM) processes it and uses SAT for further action.
The further action could be show next level of menu or send SMS or
make a call. Yes, with SAT, SIM can instruct ME to send SMS or
make a call. This part of SAT is known as "proactive SIM".
Another interesting feature of SAT is "Call control by SIM". With this feature, SIM can stop the call made by user or modify the parameters of call (like called number) etc. Similar is "MO Short message control by SIM" for SMS control.
Note that ME need to support SAT features for it to work.
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SAT - 11.14 «
In addition to GSM standards, few of the operators have come out with standardised usage of common features like Voice Mail waiting indication, Network operator name etc. This is known as Common PCN Handset Specification (CPHS). Most of these features are SIM specific like an additional file for storing Voice Mail Waiting Indication - that would be updated by ME as mentioned in CPHS document. Some of these features are being made part of 3GPP specification.
Below is picture of plug-in SIM that is used in handheld GSM mobile phones.
ME and SIM are collectively called MS (Mobile Subscriber).
We will continue with GSM interfaces and protocol layers in next article.
References: GSM book by Mouly and Pautet, GSM Networks book by Heine
© Copyright Samir Amberkar 2010
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