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Gsm
networks |
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The basic structure of GSM networks is a large and
seemingly complicated affair when looked at from the end users point of
view. All that the consumer wants to see is service bars on their
mobile phone when they come to use it. How those bars get there, and
what exactly it is that makes the bar count rise or fall is largely
unimportant to the consumer. Only at times when the network coverage
fails does the end user really start to wonder just what on Earth may
be going on with their service. As with most things in life, there is
not always a need to know what is going on, but for those who want
to understand a GSM and its many components, there is some basic
information to understand.
The structure of a GSM network is large, but in order to break things
down into bite size chunks, there are a few main sections into which
all the aspects of a GSM service can fall. It all starts with the base
stations and controllers. This is known as the Base Station Subsystem.
These are radio transmitters that connect a mobile phone to a cellular
network. Base stations are all connected, so whenever you move out of
range of one, your are "handed over" to
the next one. This is to ensure
that you do not lose a connection.
The handset and the SIM card inside will have a digital signature,
which asks a network for permission to use it. This will be the
subscribers' network of choice. This signature is sent to a Base
Station Controller that then passes on the request to a Mobile
Switching Centre. It is the Mobile Switching Centre that relays all
calls to, or from you, whether it is from fixed line networks or other
mobile network providers. The Home Location Register, as part of the
Mobile Switching Centre will have details of your subscription, and if
granted, it will send a message to your mobile phone, via the Base
Station Controller and its network that you can use their network. The
result of all this, which only takes a couple of seconds, is seeing the
network name appear on your handset's screen. You have been given
permission and can use the network.
A lot of the work on GSM networks is done in the Mobile Switching
Centre, as it will also check to see what aspects of a service you are
subscribed to. So if you are trying to make an international call, but
do not have those privileges, then you will not be connected. Similarly
if you are not available, then the call will be directed to a mailbox
if activated. During the "handing over" of one Base Station to another,
the Home Location Register will be updated. This is so that the network
will know where to route your calls through once you move into the
domain of another Base Station. SMS messages operate on a different
frequency within GSM networks to that of calls, so the two never get in
the way of one another. These digital features of GSM is why is it is
seen as the most popular and efficient mobile phone communications
standard across Europe and the world.
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