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