Hi Techies,

Let's start posting Windows Mobile application development based interview questions and answers in this thread.

Thanks

__________________
Prasanna Vignesh
MCPD | Web Developer

What is an IMEI?

The IMEI (International Mobile Equipment Identity) is a unique 15 or 17 digit code used to identify an individual mobile station to a GSM or UMTS network. The IMEI number facilitates an important function; it easily identifies a mobile phone being used on a GSM (Global System for Mobile Communications) network. The IMEI is a useful tool to stop a phone that is stolen from accessing a network and being used. Mobile phone owners that have their phones stolen can contact their mobile network provider and ask them to ban or shut off a phone using its IMEI number. With an IMEI number, the phone can be banned from the network quickly and easily. It is important to note that swapping a SIM card will not stop a phone from being banned.

An IMEI device is only used to identify the device and does not usually relate to a specific individual or organization. Other numbers such as ESN (Electronic Serial Numbers) and MEID (Mobile Equipment Identifiers) can link an individual to a phone. Usually, an IMSI number stored on a SIM card can identify the subscriber on a network.

There are a few ways in which you can locate your mobile phone's IMEI number, it can usually be found on the handset, beneath the battery, sometimes printed on a small white label. Another way to easily locate your IMEI phone is to dial the following sequence of numbers into the handset: *#06#. If you have a Sony Ericsson mobile phone, you can retrieve the IMEI by pressing the following key sequence: right,*, left, left,*, left, *, left.

The Structure of an IMEI Number

IMEI numbers either come in a 15 digit or 17 digit sequences of numbers. These numbers can identify a handset. Currently the format of the IMEI is AA-BBBBBB-CCCCCC-D.

* These two digits are for the Reporting Body Identifier, indicating the GSMA approved group that allocated the TAC (Type Allocation Code).
* BBBBBB- The Remainder of the TAC
* CCCCCC- Serial Sequence of the Model
* D- Luhn Check Digit of the entire model or 0 (This is an algorithm that validates the ID number)

How can I find my IMEI?

The IMEI (International Mobile Equipment Identity) number can be displayed on most phones by dialing the code *# 06 #.

The IMEI is also usually printed on the compliance plate under the battery.

What is a Subscriber Identity Module (SIM)?

The Subscriber Identity Module (SIM) is a small smart card which contains both programming and information.

The A3 and A8 algorithms are implemented in the Subscriber Identity Module (SIM).

Subscriber information, such as the IMSI (International Mobile Subscriber Identity), is stored in the Subscriber Identity Module (SIM).

The Subscriber Identity Module (SIM) can be used to store user-defined information such as phonebook entries.

One of the advantages of the GSM architecture is that the SIM may be moved from one Mobile Station to another. This makes upgrades very simple for the GSM telephone user.

What is an IMSI?

The IMSI (International Mobile Subscriber Identity) is a unique 15-digit code used to identify an individual user on a GSM network.

The IMSI consists of three components:

* Mobile Country Code (MCC)
* Mobile Network Code (MNC)
* Mobile Subscriber Identity Number (MSIN)

The IMSI is stored in the Subscriber Identity Module (SIM).

What are the components of a GSM network?

Subscriber Equipment

Mobile Station (MS) - The mobile telephone.

The Switching System (SS)

Home Location Register (HLR) - A database which stores data about GSM subscribers, including the Individual Subscriber Authentication Key (Ki) for each Subscriber Identity Module (SIM).

Mobile Services Switching Center (MSC) - The network element which performs the telephony switching functions of the GSM network. The MSC is responsible for toll ticketing, network interfacing, common channel signaling.

Visitor Location Register (VLR) - A database which stores temporary information about roaming GSM subscribers.

Authentication Center (AUC) - A database which contains the International Mobile Subscriber Identity (IMSI) the Subscriber Authentication key (Ki), and the defined algorithms for encryption.

Equipment Identity Register (EIR) - A database which contains information about the identity of mobile equipment in order to prevent calls from stolen, unauthorized, or defective mobile stations.

The Base Station System (BSS)

Base Station Controller (BSC) - The network element which provides all the control functions and physical links between the MSC and BTS. The BSC provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in Base Transceiver Stations.

Base Transceiver Station (BTS) - The network element which handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network.

The Operation and Support System (OSS)

Message Center (MXE) - A network element which provides Short Message Service (SMS), voice mail, fax mail, email, and paging.

Mobile Service Node (MSN) - A network element which provides mobile intelligent network (IN) services.

Gateway Mobile Services Switching Center (GMSC) - A network element used to interconnect two GSM networks.

GSM Interworking Unit (GIWU) - The network element which interfaces to various data networks.

What is a TIMSI?

The TIMSI (Temporary IMSI) is a pseudo-random number generated from the IMSI (International Mobile Subscriber Identity) number.

The TIMSI is utilized in order to remove the need to transmit the IMSI over-the-air. This helps to keep the IMSI more secure.

To track a GSM user via the IMSI/TIMSI, an eavesdropper must intercept the GSM network communication where the TIMSI is initially negotiated.

In addition, because the TIMSI is periodically renegotiated, the eavesdropper must intercept each additional TIMSI re-negotiation session.

What are the PIN and PUK?

PIN (Personal Identity Number) is a 4-8 digit access code which can be used to secure your telephone from use.

PIN2 (Personal Identity Number 2) is a 4-8 digit access code which can be used to access the priority number memory and cost of calls.

The PUK (Personal Unblocking Key) and PUK2 are used to unlock the PIN and PIN 2 codes respectively if your SIM card is blocked.

How do I change my PIN and PUK?
Change SIM Card PIN ** 04 * old PIN * new PIN * new PIN #
Change SIM Card PIN2 ** 042 * old PIN2 * new PIN2 *new PIN2 #
Change SIM Card PUK ** 05 * old PUK * new PUK * new PUK #
Change SIM Card PUK2 ** 052 * old PUK2 * new PUK2 * new PUK2 #

Note: These codes only work on some mobile stations offered by some providers.