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Roaming helps ensure that a traveling wireless device (typically a cell phone) is kept connected to a network without breaking the connection. In wireless telecommunications, Traditional Roaming is a general term referring to 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. For example; should you travel beyond your cell phone company's transmitter range, your cell phone would automatically hop onto another phone company's service, if available. Using another phone company's service can be done by using the subscriber identity in the visited network. Roaming is technically supported by mobility management, authentication, authorization and accounting billing procedures (known as AAA or 'triple A'). The term "roaming" originates from the GSM (Global System for Mobile Communications) standard used by mobile phones, which is the de facto global standard for mobile communications with over 80% market share. The term "roaming" can also be applied to the CDMA technology, (a channel access method that includes 3G, etc.). == 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, 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. Using the example of WLAN/GSM roaming, the following scenarios can be differentiated (cf. GSM Association Permanent Reference Document AA.39): * SIM-based (roaming): GSM subscriber roams onto a Public WLAN operated by: * * their GSM Operator, or * * another Operator who has a roaming agreement with their GSM Operator. * Username/password based roaming: GSM subscriber roams onto a Public WLAN operated by: * * their GSM Operator, or * * another Operator who has a roaming agreement with their GSM Operator. Although these user/network scenarios focus on roaming from GSM Network Operator's network(s), clearly roaming can be bi-directional, i.e. from Public WLAN Operators to GSM Networks. Traditional roaming in networks of the same standard, e.g. from a WLAN to a WLAN or a GSM network to a GSM network, has already been described above and is likewise defined by the foreignness of the network based on the type of subscriber entry in the home subscriber register. In the case of session continuity, seamless access to these services across different access types is provided. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「roaming」の詳細全文を読む スポンサード リンク
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