It is accessed by the network during registration to check whether the equipment has been reported as stolen. As this is included in the SIM, and it means that by moving the SIM card from one mobile to another, the user could easily change mobiles.
The ease of changing mobiles whilst keeping the same number meant that people would regularly upgrade, thereby creating a further revenue stream for network providers and helping to increase the overall financial success of GSM. It must be noted that as the number of BS increases with the scaling of the subscriber population some of the maintenance tasks are transferred to the BTS, allowing savings in the cost of ownership of the system.
The 2G GSM network architecture follows a logical method of operation. It is far simpler than current mobile phone network architectures which use software defined entities to enable very flexible operation. However the 2G GSM architecture does show the voice and operational basic functions that are needed and how they fit together. As the GSM system was all digital, the network was a data network. A base station antenna carrying 2G GSM signals GSM network architecture elements In order that the GSM system operates together as a complete system, the overall network architecture brings together a series of data network identities, each with several elements.
A basic diagram of the overall system architecture for the 2G GSM mobile communications system includes four major elements which are shown below: Simplified GSM Network Architecture Diagram Within this diagram the different network areas can be seen - they are grouped into the four areas that provide different functionality, but all operate to enable reliable mobile communications to be achieved.
These include registration, authentication, call location, inter-MSC handovers and call routing to a mobile subscriber. It also provides an interface to the PSTN so that the mobile communications calls can be routed from the mobile network to a phone connected to a landline.
Interfaces to other MSCs are provided to enable calls to be made to mobiles on different networks. Home Location Register HLR : This database contains all the administrative information about each subscriber along with their last known location.
When a user switches on their phone, the phone registers with the network and from this it is possible to determine which BTS it communicates with so that incoming calls can be routed appropriately.
Even when the phone is not active but switched on it re-registers periodically to ensure that the network HLR is aware of its latest position. There is one HLR per network, although it may be distributed across various sub-centres to for operational reasons.
The VLR can be implemented as a separate entity, but it is commonly realised as an integral part of the MSC, rather than a separate entity. In this way access is made faster and more convenient. Each mobile equipment has a number known as the International Mobile Equipment Identity. This number, as mentioned above, is installed in the equipment and is checked by the network during registration. In an offnet local call the call originating operator pays the call terminating operator.
Whereas, in the offnet international call the call originator pays the carrier, who then pays to call terminating operator. As we are here to generate revenue and increase the income, the rates for international calls are much higher than the local calls.
The payment is done on the predefined currency. Every operator and carrier has a contract which defines the rate at which they will pay to each other. Normally, the payment is done in relation to the duration of the calls travelled from the operator to the carrier and vice versa.
The CDR primarily contains: a. Anumber- Calling Party b. Bnumber- Called Party c. Timestamp — At what time did the call originate d. Duration — How long did the call last for There are various other fields are also generated but the above 4 fields are very important to help in generation of bill for postpaid or deducting balance for prepaid in OCS- Online Charging System. It is used to control and monitor the system and various network elements. It facilitates the maintenance activities that are required for a GSM network.
It provides the following: a. Provide network overview and support maintenance b. Once the phone is switched on, the message is sent to it. The HLR is a database used for storage and management of subscriptions.
The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription in the form of SIM, then all the information about this subscription is registered in the HLR of that operator. The MSC performs the switching of calls between the mobile and other fixed or mobile network users, as well as the management of mobile services such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber.
It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others.
The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time. The Authentication Center is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and ciphering of the radio channel.
The AUC protects network operators from different types of fraud found in today's cellular world. An IMEI is marked as invalid if it has been reported stolen or is not type approved. The OSS is the functional entity from which the network operator monitors and controls the system.
The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network.
An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations. It is also known as the air interface or the radio link.
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