6
"*#06#" on the keyboard. The IMEI code will be changed when displace new main board. It is necessary to
refresh new symbol for the equipment.
4.2 SIM card
：
1
）
Brief introduction of SIM card
SIM is the abbreviation of Subscriber Identity Model (customer recognition module). SIM card is also
called smart card, ID card of user. The GSM digital mobile phone can be used when inserting this card only.
There are three kind of materials in the SIM card: Surface metallic circuit board, IC integrated circuit, black
protective hard glue. The work of surface metallic circuit board is transmitting information between IC and the
mobile phone. The black protective hard glue purely for protects IC. And IC is the important part in SIM card.
IC saved user's information, encryption key and other information in the SIM card. It identify user for GSM
network and encrypte voice information for user during the call. The work of the six blocks on the metallic
circuit is record input information, voice, instruction of network operation business respectively and so on. The
using of SIM card prevent simultaneous calling and wire tapping. Facture of SIM card is according to GSM
international standard and criterion strictly. It ensure common communication for user reliably. The using of
SIM card divides card and mobile phone in the GSM system. One SIM card marks one user. SIM card can be
inserted in every GSM mobile phone, and the fee of communication can be recorded to the marked account of
the user. SIM card contain personal data of accessing GSM service that must be needed, they are:
International mobile subscriber recognition
Temporarily mobile subscriber recognition
Main system
Registration service
The PIN reconciliation locks the code
The call limits the code
The user stores individual data. For instance, the short news, the fixed digit dialing, shrink the position
digit dialing, the performance parameter, the speech spends the register and so on
Will access the net the numeral mobile phone, otherwise will have the possibility to cause the card to
receive the damage.
2
）
Security function
There is mobile phone SIM card lock function to prevent other people use the SIM card random. To
unblocking it, just input PIN code easily. The PIN code (personal Identity Number) is called individual
identification code. It is 4digit long, established by user himself. It belongs to the password of SIM card that
protect security of SIM card. Its original estate is not activating. After its starting up, GSM system will identify
the mobile phone automatically after turn on the phone every time. It will estimate validity of the SIM card, in
other words, it will check password with mobile phone. It provides services to user after approving by the
system only. There are 3 times of opportunities for input PIN code. It will lock automatically if the 3 times of
opportunities failed all. The way of unblocking it is input PUK only. PUK (PIN Unblocking Key) is the master key
for unblock the PIN code. Every SIM card has its corresponding PUK code. It is 8digit long, managed by user
himself. It is controlled by network operation business too. At present, the domestic motion bureau has opened
PUK inquire service that user could manage PUK code by themselves. There are 10 times of opportunities for
input PUK code. The SIM card will start up self-destruction program automatically if the 10 of opportunities
failed all. Then invalidate the SIM card. In this case, it is necessary to transact a new SIM card. Therefore,
please do not decode without correct PUK code
Setting calling restriction is another way of protect the SIM card. The calling restriction is away of restrict
call in and call out through establishing password. User could establish or cancel every kind of restriction of the
mobile phone at will, preventing call out by mistake, stealing call, especially international long distance call,
avoiding unnecessary loss. The password of calling restriction is 4digit long which the original estate is 0000.
The user who transacts this service should modify the original password, for improving the security. The calling
restriction could be set according to both file way and coding way. These two ways of setting have the same
effect. It is noticed that this kind of service is for user only who use international long distance service, and it
can not be used with calling diversion service at the same time
5. Introduction of GSM System
：
5.1
：
The history and development of GSM
：
1981 Analogue cellular introduced
Franco-German study of digital pan-European cellular system
1987 MoU signed by over 18 countries
Summary of Contents for W420
Page 1: ...Voxtel Repair Manual Item W420 ...
Page 23: ...23 3 LDO circuit ...
