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.
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:
- The mobile notices that it can no longer maintain a connection to a base station within your service provider's network. It begins to search for other networks that it can communicate with.
- Once a good network has been identified, the mobile identifies itself to the new network.
- This new "host" 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. It may refuse service at this point if it determines that it does not have a roaming agreement with the home network.
- The host network contacts the home network and requests information about the roaming mobile. This includes the mobile's telephone number, subscribed services, and whether or not the mobile should be allowed to roam.
- If successful, the host network then 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.
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.
Due to the transactions, infrastructure changes, and politics involved in roaming, it is generally not feasible to maintain an active telephone call between unassociated networks, resulting in dropped calls. Moreover, if there is no roaming agreement between the two networks, maintenance of call is completely impossible, as service is then denied by the new network.
Calls, of course, can and should be maintainable between base stations on the same network. This process is known as handoff and is not related to roaming.
Some companies have shared antenna agreements between each other that allow for free roaming from one network to another. However, although the mobile will not notice that it is roaming, it technically is, and may still be prone to dropped calls as a result of the change in network.
See also
