Roaming

In wireless telecommunications, roaming is a general term that refers to the extending of the connectivity service in a location that is different from the home location where the service was registered. Roaming ensures that the wireless device keeps connected to the network, without losing the connection. The term "roaming" originates from the GSM (Global System for Mobile Communications) sphere; the term "roaming" can also be applied to the CDMA technology. Traditional GSM Roaming is defined (cf. GSM Association Permanent Reference Document AA.39) as the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network, by means of using a visited network. This can be done by using a communication terminal or else just by using the subscriber identity in the visited network. Roaming is technically supported by mobility management, authentication, authorization and billing procedures.

Roaming in general

Roaming is divided into "SIM-based roaming" and "Username/password-based roaming", whereby the technical term "roaming" also encompasses roaming between networks of different network standards, such as e.g. WLAN (Wireless Local Area Network) or GSM. Device equipment and functionality, such as SIM card capability, antenna and network interfaces, and power management, determine the access possibilities.

* SIM-based roaming: GSM subscriber roams onto a Public WLAN operated by:
o their GSM Operator, or
o another Operator who has a roaming agreement with their GSM Operator.

* Username/password based roaming: GSM subscriber roams onto a Public WLAN operated by o their GSM Operator, or
o another Operator who has a roaming agreement with their GSM Operator.

The roaming process

The details of the roaming process differ among types of cellular networks, but in general, the process resembles the following:

• When the mobile device is turned on or is transferred via a handover to the network, this new visited network sees the device, notices that it is not registered with its own system, and attempts to identify its home network. If there is no roaming agreement between the two networks, maintenance of service is impossible, and service is denied by the visited network.
• The visited network contacts the home network and requests service information (including whether or not the mobile should be allowed to roam) about the roaming device using the IMSI number.
• If successful, the visited network begins to maintain a temporary subscriber record for the device. Likewise, the home network updates its information to indicate that the mobile is on the host network so that any information sent to that device can be correctly routed.

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