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Roaming is a general term in wireless telecommunications that refers to the extending of connectivity service in a location that is different from the home location where the service was registered. The term "roaming" originates from the GSM (Global System for Mobile Communications) sphere. 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.
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: 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.
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 terms of user service scenarios, the user can have access to the same set of services, irrespective of access type. However, differentiation also exists.
Service scenarios may include access to a range of different services, including:
* Access to corporate Intranet services;
* Access to operator walled garden services; and
* Access to public Internet.
In the case of session continuity, seamless access to these services across different access types is provided.
Home and visited networks
The differentiation between home network and visited network is technically given by the type of subscriber entry in a specific network. If a subscriber has no entry in the home subscriber register of the network (e.g. Home Location Register (HLR) in GSM networks or local customer database in WLANs), the required subscriber data must first be requested by the visited network e.g. from the subscriber's home network in order that the subscriber can be authenticated and any authorization for using the network services can be checked. The "visiting" subscriber acquires an entry in a user database of the visited network (e.g. Visited Location Register (VLR)) and the authorized network services are enabled. For the roaming procedure in practice, the possibility of assigning the subscriber data is always indispensable in order that authentication, authorization and billing of the subscriber can be performed in the corresponding network. Thus, the term roaming is not linked to a specific network standard, but rather to the type of subscriber entry in the home subscriber register of the mobile radio network. If a subscriber can use his personal service profile, which he uses in the home network, in the visited network as well, this is also referred to as Global Service Roaming Capability.
Tariffs
Roaming fees are traditionally charged on a per-minute basis and they are typically determined by the service provider's pricing plan. Several carriers in the United States have eliminated these fees in their nationwide pricing plans. All of the major carriers now offer pricing plans that allow consumers to purchase nationwide roaming-free minutes. However, carriers define "nationwide" in different ways. For example, some carriers define "nationwide" as anywhere in the U.S., whereas others define it as anywhere within the carrier's network.
An operator intending to provide roaming services to visitors publishes the tariffs that would be charged in his network at least sixty days prior to its implementation under normal situations. The visited operator tariffs may include tax, discounts etc. and would be based on duration in case of voice calls. For data calls, the charging may be based on the data volume sent and received. Some operators also charge a separate fee for call setup i.e. for the establishment of a call. This charge is called a Flagfall charge.
Additional notions and types of roaming
* Regional roaming:
This type of roaming refers to the ability of moving from one region to another region inside national coverage of the mobile operator. Initially, operators may have provide commercial offers restricted to a region (sometimes to a town). Due to the success of GSM and the decrease in cost, regional roaming is rarely offered to clients except in nations with wide geographic areas like the USA, Russia, India, etc., in which there are a number of regional operators.
* National roaming:
This type of roaming refers to the ability to move from one mobile operator to another in the same country. For example, a subscriber of T-Mobile USA who is allowed to roam on AT&T Mobility's service would have national roaming rights. For commercial and license reasons, this type of roaming is not allowed unless under very specific circumstances and under regulatory scrutiny. This has often taken place when a new company is assigned a mobile telephony license, to create a more competitive market by allowing the new entrant to offer coverage comparable to that of established operators (by requiring the existing operators to allow roaming while the new entrant has time to build up its own network). In a country like India, where the number of regional operators is high and the country is divided into circles, this type of roaming is altogether too common[citation needed].
* International roaming:
This type of roaming refers to the ability to move to a foreign service provider's network. It is, consequently, of particular interest to international tourists and business travellers.
Broadly speaking, international roaming is easiest using the GSM standard, as it is used by over 80% of the world's mobile operators. However, even then, there may be problems, since countries have allocated different frequency bands for GSM communications (there are two groups of countries: most GSM countries use 900/1800 MHz, but the United States and some other countries in the Americas have allocated 850/1900 MHz): for a phone to work in a country with a different frequency allocation, it must support one or both of that country's frequencies, and thus be tri or quad band.
* Inter-standards roaming:
This type of roaming refers to the ability to move seamlessly between mobile networks of different technologies.
Since mobile communication technologies have evolved independently across continents, there is significant challenge in achieving seamless roaming across these technologies. Typically, these technologies were implemented in accordance with technological standards laid down by different industry bodies and hence the name.
A number of the standards making industry bodies have come together to define and achieve interoperability between the technologies as a means to achieve inter-standards roaming. This is currently an ongoing effort.
* Mobile Signature Roaming:
The concept of Mobile signature Roaming is: an access point should be able to get a Mobile Signature from any end-user, even if the AP and the end-user have not contracted a commercial relationship with the same MSSP. Otherwise, an AP would have to build commercial terms with as many MSSPs as possible, and this might be a cost burden. This means that a Mobile Signature transaction issued by an Application Provider should be able to reach the appropriate MSSP, and this should be transparent for the AP
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