Mobile phone network registration
a summary or tutorial about the way in which a mobile phone achieves
registration onto a cellular telecommunications system or network.
On any cellular telecommunications system the way in which
registration and call set-up occur needs to be carefully managed. Not only does
the cellular telecommunications network need to provide quick and efficient
service for its rightful customers, but it also needs to be able to offer high
levels of security for the user and the network.
There are many different cellular telecommunications systems
in use around the globe. Older ones are being phased out, and newer cellular
systems are being introduced. Accordingly there is no single way in which
registration and call set up are managed. However there are some general
principles that are used, and these are illustrated here.
Basic requirements
When the mobile phone is turned on it needs to be able to communicate with the
cellular telecommunications network. However the phone does not have an
allocated channel, time slot or chip code (dependent upon the type of access
method used). It is therefore necessary for there to be some methods or
allocated means within the cellular telecommunications network, whereby a newly
switched on mobile can communicate with the network and set up the standard
communication.
Even if a call is not to be made instantly, the network needs
to be able to communicate with the mobile to know where it is. In this way the
network can route any calls through the relevant base station as the network
would be soon overloaded if the notification of an incoming call had to be sent
via several base stations.
Registration
There are a variety of tasks that need to be undertaken when a phone is turned
on. This can eb seen by the fact that it takes a few seconds from switching the
phone on before it is ready for use. Part of this process is the software
start-up for the phone, but the majority comes from the registration process
with the cellular network. There are several aspects to the regristration. The
first is to make contact with the base station, and next the mobile has to
register to allow it to have access to and use the network.
In order to make contact with the base station the mobile
uses a paging or control channel. The name of this channel, and the exact way in
which it works will vary from one cellular standard to the next, but it is a
channel that is used that the mobile can access to indicate its presence. The
message sent is often called the "attach" message. Once this has been achieved
it is necessary for the mobile to register with the cellular network, and to be
accepted onto it.
Network elements
It is necessary to have a register or database of users allowed to register with
a given network. With mobiles often being able to access the all the channels
available in a country, methods of ensuring the mobile registers with the
correct network, and to ensure the account is valid are required. Additionally
it is required for billing purposes. To achieve this, an entity on the network
often known as the Authentication Centre (AuC) is used. The network and the
mobile communicate and numbers giving the identity of the subscriber. Here the
user information is checked to provide authentication and encryption parameters
that verify the user's identity and ensure the confidentiality of each call
protecting users and network operators from fraud.
Once accepted onto the network two further registers are
normally required. These are the Home Location Register (HLR) and the Visitors
Location Register (VLR). These two registers are required to keep track of the
mobile so that the network knows where it is at any time so that calls can be
routed to the correct base station or general area of the network. These
registers are used to store the last known location of the mobile. Thus at
registration the register is updated and then periodically the mobile updates
its position. Even when the mobile is in what is termed its idle mode it will
periodically communicate with the network to update its position and status.
When the mobile is switched off it sends a detach message.
This informs the network that it is switching off, and enables the network to
update the last known position for the mobile.
Home and abroad
The two registers are required, one for mobiles for which the network is the
home network, i.e. the one with whom the contract exists, and the other for
visitors. If there was only one register then every time the mobile sent any
message to the foreign network, this would need to be relayed back to the home
network and this would require international signalling. The approach which is
adopted is to send a message back to the HLR when the mobile first enters the
new country saying that the mobile is in a different network and that any calls
for that mobile should be forwarded to the foreign visited network.
Summary
By undergoing a registration procedure when the mobile is turned on, the
cellular network is able to communicate correctly with it, provide access for
outgoing calls, and also route any incoming calls to it in the most efficient
manner. Registration also only allows those mobiles that have permission to
access the network to communicate with it.
|
