In the<font color=#00334D> implementation
</font>of the proposed system certain wireless communication protocols are used. The protocols are of predefined standards. The communication process makes the system more desirable and understandable in a better way. For the demo version it is easier more even to show the system working in a better way. The two wireless communication protocols are the part of the proposed system. They are
i. GSM communication protocol
ii. RF communication protocol
6.1 GSM communication protocol
The GSM divides the infrastructure into the following three parts
i. Network Switching Subsystems (NSS)
ii. Base Station Subsystem (BSS)
iii. Network Management Subsystem (NMS)
6.1.1 Network Switching Subsystem (NSS)
Fundamentally, the network and switching subsystems (NSS) is responsible for call connection, supervision and release operations between calling and called stations, where one or both of them are mobile stations (MS). Other functions include:
i. Handling short messages and packet data (email, fax and a variety of notifications)
ii. Providing âbearerâ channel for data communications
iii. Maintaining database of its own users as well as visitors
iv. Variety of authentication and encryption
v. Gateway to PSTN, other mobile networks and data networks including the Internet
6.1.1.1 Home Location Register
The home location register (HLR) is a database used for storing and managing subscriptions. Generally a PLMN (Public Land Mobile Network) consists of several HLRs. The first two digits of the mobile directory number (e.g. 0171 2620757) are the number of the HLR where the mobile subscriber is stored. The data includes permanent data on subscribers (such as subscriber's service profile) as well as dynamic data (such as current location and activity status). When an individual buys a subscription from one of the GSM operators, he or she is registered in the HLR of that operator.
Data Elements (Subscriber) Examples
i. Mobile Stationâs Identities
a. IMSI (International Mobile Subscriber Identity) (the primary Key),
b. Current TMSI (Temporary IMSI)
c. IMEI (International Mobile Equipment Identity)
ii. Mobile Stationâs Telephone number
a. MSISDN (Mobile Stations ISDN number)
b. Current MSRN (Mobile Station Roaming Number), if assigned
iii. Name and address of the subscriber
iv. Current service subscription profile
v. Current location (MSC/VRL address)
vi. Authentication and encryption keys
a. Individual Subscriber Authentication Key (KI)
vii. Mobile Country Code (MCC) and MNC (Mobile Network Code)
viii. List of MSC/VLR that belongs to this HLR
6.1.1.2 Mobile Switching Center and Visitor Location Register
The mobile switching center (MSC) performs the telephony switching function. A mobile station must be attached to a single MSC at a time (either homed or visitor), if it is currently active (not switched off). The visitor location register (VLR) is a database attached to an MSC to contain information about its currently associated mobile stations (not just for visitors). However, it is not designed to include visitors since a visitor has telephone number that does not belong to this switch. That is why a separate VLR is needed.
An MSC, with the help of the HLR, allocates a visitor a âlocalâ telephone number (the MSRN), which is not currently allocated to anyone. This allocation is temporary (like visitor ID card). The VLR stores the MSRN as mobile stationâs telephone number (along with other information). However, VLR also stores some information like âsecurity tripleâ (authentication and encryption information) for each mobile station that are currently attached to the MSC. A VLR stores such information not only for its visitors but also for the homed mobile stations. From this perspective VLR is for homed mobile stations as well. It contains the following data,
i. Information of currently attached mobile stations
a. IMSI/TMSI numbers
b. MSISDN/MSRN numbers
c. Security triple (authentication and encryption information)
d. Location Area Identity (where the mobile station is currently located)
ii. List of base stations that belong to this MSC/VLR (by their BSIC or Base Station Identity Code)
iii. List of location areas that belong to this MSC/VLR (by their LAI or Location Area Identity code)
6.1.1.3 Authentication Center
The authentication center (AUC) provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world. The GSM has standard encryption and authentication algorithm which are used to dynamically compute challenge keys and encryptions keys for a call.
6.1.1.4 Equipment Identity Register
The equipment identity register (EIR) is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR can be implemented as stand-alone nodes or as a combined AUC/EIR node.
6.1.1.5 GSM Interworking Unit/Function
The GSM Interworking (IW) function or Unit (GIWF/U) is for data communication (such as the Internet access) support. Though the basic function of MSC is voice traffic switching the MSC has additional capability to forward data between the mobile station and GIWF/U
