What is GSM and GSM Architecture?
GSM stands for Global System for Mobile Communication. GSM is an advance technology which is based on digital communication and is used for transmitting data as well as voice services. Any people living in Europe or Asia will definitely be having access to GSM.
To create a common European mobile telephone standard, the cellular network concept comes from Bell laboratories in 1970 and was established in 1982. GSM is based on the circuit switching concept in which the 200 KHz frequency is divided into 8 slots with each 25 KHz frequency. The working frequency of GSM is about 900 Hz to 1800 Hz but in US it is 850 Hz to 1900 Hz frequency. As it is a circuit switched network it uses narrowband TDMA technique. It can have the data rate speed of about 64 kbps to 120 Mbps.
GSM provides good and improved spectrum efficiency along with international roaming. It results in High quality speech and data services. It offers roaming services and is compatible with ISDN i.e. Integrated Services Digital Network.
Coming to the GSM Architecture it have different functional units. It has different division like:
- The Mobile Station (MS)
- The Base Station Subsystem (BSS)
- The Network Switching Subsystem (NSS)
- The Operation Support Subsystem (OSS)
There are some major sub division for these four divisions. These are:
- Home Location Register (HLR)
- Visitor Location Register (VLR)
- Equipment Identity Register (EIR)
- Authentication Center (AuC)
- SMS Serving Center (SMS SC)
- Gateway MSC (GMSC)
- Chargeback Center (CBC)
- Transcoder and Adaptation Unit (TRAU)
The BSS called Base Station Subsystem, its function is to manage the radio communication between the mobile station and mobile switching center also known as MSC. That is why BSS is also known as radio subsystem. Each BSS consists of many BSCs which connects MS to the NSS via MSC. The next is NSS called Network and switching subsystem, its function is to handle the switching of calls between external networks and and the BSCs in BSS. Also its function is to provide external excess to customers databases.
The next is OSS called Operation support subsystem. Its function is to support operation maintenance center and these operation maintenance centers are used to to monitor and maintain the performances of MS, BS, BSC, BTS, MSC.
Next comes the interfaces. In GSM architecture there are many interfaces, first is Abis Interface, it carries the traffic and maintains the data.
There is a microwave link between the BSCs and MSCs through which these are connected and these microwave links are known as A- interface. Thus A interface connects BSCs to the MSCs. Also the A interface uses SS7 protocol that is signaling correction control part (SCCP) which supports the communication.
Some basic terminology we use in GSM technology are:
Cell: Cell are the units which makes the whole telecom network effective. The cells are in the shape of hexagonal structure because it covers the most of the area. Each cell has one BTS and one Cell Global Identity I.e. CGI.
Frequency Reuse: Frequency reuse is the practice if using the same frequency in different cell at a particular required minimum distance. This offers the use of less range of frequency for more customers in telecom industry.
We will discuss more terminologies in detail in our new posts about GSM Architecture.
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