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Global
System for Mobile Communications (GSM)
GSM
network is designed by using digital wireless technology. It
offers compatible wireless services to all mobile users in all
over the world. The basic requirements for GSM are following:
Services:
The
services, which are provided by the system, should be potable to
all Mobile Stations or Mobile Phones so that it can b used in
all over the world.
Quality of services
and security:
The
quality of both voice and data services of GSM should be good.
The voice data is encoded in digital form by using a modulation
technique i.e.Gussian Minimum Shift Keying (GMSK).The security
features should be provided by the system to protect the network
against unauthorized users.
Radio frequency
utilization:
The system should use the
available band of frequencies (For uplink: 890-915MHz & For
downlink: 935-960MHz) efficiently.
Network:
Network designers manage the identification and numbering plans
while switching and mobility management based upon signaling
system i.e. Signaling System Number 7(SS7).
GSM Architecture
The
main component groups of GSM architecture are:
Mobile Stations (MSs):
The
Mobile Station (MS) consist of two operational parts.
Mobile Equipment (ME):
This is the hard ware used by the subscriber to access the
network and it has a unique identity number known as
International Mobile Equipment Identity (IMEI).
Subscriber Identity Module (SIM):
This is a type of electronic card that is plugs into ME and
contains detailed information about the mobile subscriber.
Base
Station System (BSS):
BSS
is central equipment, which is located at the cell site. It
provides the link between MS and NSS. The BSS consists of two
operational parts.
Base
Transceiver Station (BTS):
BTS
consists of transmitting and receiving antennas and signaling
equipment that provide air interface for a cell to route the
call. BTS communicates with the MS.A single BTS can support one
or more cells.
Base
Station Controller (BSC):
All
switching functions, which are performed in MSC, are controlled
by BSC. It also supports handoff strategies and allocate or
release temporary channels for those users whose needed handoff.
Several BTSs can be controlled by a single BSC and one MSC can
serve many BSCs
Network Switching Subsystem (NSS)
It
is the main switching center of GSM network. NSS includes the
following:
Mobile Switching Center (MSC):
It
is the basic unit of NSS, which supports call-switching or
routing functions. Its purpose is the same as that of telephone
exchange but due to advanced wireless technology, its working is
much better than that of exchange. Each MSC provides coverage to
a defined geographic area only.
Home
Location Register (HLR):
For subscriber its a reference data base. Current location of
MS, identification numbers and various addresses are maintained
in it.
Visitor Location Register (VLR):
It’s also a type of database. When an MS moves from home
location to a visited location then its location is registered
as a visitor in the VLR of visited system and this information
is also updated in HLR of MS, by the VLR.
Equipment Identity Register (EIR):
Its again a type of database, which contains information about
MS equipment and check and identify its international validity
of hardware and software to work properly.
Authentication center (AUC):
Its a processing center and is normally worked together with
HLR.Like HLR its also require to continuously access or update
subscribers data. Its main purpose is to provide data security
features to authenticate the subscriber.
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