Roaming
Roaming is a general term in
wireless telecommunications that refers to the
extending of connectivity service in a network
that is different than the network with which a
station is registered.
The canonical example of "roaming" is for
cellular phones, when you take your phone to an
area where your service provider does not have
coverage (eg, another country).
In order for a mobile device to roam to another
network, a number of processes need to be
performed. The very first necessity for
inter-network roaming is that your service
provider must have a roaming agreement with the
network to which you have moved.
The details of the roaming process differ among
types of wireless networks, but in general, the
process resembles the following:
When the mobile is turned on or is transferred
via a handover to the network, this new
"visited" network sees the mobile, notices that
it is not a mobile registered with its own
system, and attempts to identify the home
network of the mobile. If there is no roaming
agreement between the two networks, maintenance
of call is completely impossible, as service is
then denied by the visited network.
The visited network contacts the home network
and requests information about the roaming
mobile. This includes the mobile's IMSI number,
subscribed services, and whether or not the
mobile should be allowed to roam.
If successful, the visited network begins to
maintain a temporary subscriber record for the
mobile. Likewise, the home network updates its
information to indicate that the mobile is on
the host network so that any calls made to that
mobile can be correctly routed.
When a call is made to a roaming mobile, the
public telephone network will route the call to
your service provider's network, since that is
where your phone number terminates. Your home
network is then responsible for re-routing the
call to the host network. This will require the
host network to provide a temporary phone number
on its network that it will route to the mobile.
Once this number is defined, the home network
re-routes the incoming call to the temporary
phone number, which terminates at the host
network. The host network then routes that call
to the mobile.
In 802.11 roaming can also mean subscriber
mobility or handover within the same network.
External Links
-
GSM Roaming (http://www.gsmworld.com/roaming/index.shtml)
- International GSM Association
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