Roaming
Encyclopedia
In wireless
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

 telecommunications, roaming is a general term referring to the extension of connectivity service in a location that is different from the home location where the service was registered. Roaming ensures that the wireless device is kept connected to the network, without losing the connection. The term "roaming" originates from the GSM (Global System for Mobile Communications)
Global System for Mobile Communications
GSM , is a standard set developed by the European Telecommunications Standards Institute to describe technologies for second generation digital cellular networks...

 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
Cellular network
A cellular network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area...

 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
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

, 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
Authentication
Authentication is the act of confirming the truth of an attribute of a datum or entity...

, authorization
Authorization
Authorization is the function of specifying access rights to resources, which is related to information security and computer security in general and to access control in particular. More formally, "to authorize" is to define access policy...

 and bill
Bill (payment)
A bill or invoice is a document requesting payment for an order previously supplied. Presentation of a bill is common practice on the part of credit card companies, utilities, and other service providers...

ing 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)
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...

 or GSM. Device equipment and functionality, such as SIM card
Subscriber Identity Module
A subscriber identity module or subscriber identification module is an integrated circuit that securely stores the International Mobile Subscriber Identity and the related key used to identify and authenticate subscriber on mobile telephony devices .A SIM is held on a removable SIM card, which...

 capability, antenna and network interfaces, and power management
Power management
Power management is a feature of some electrical appliances, especially copiers, computers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built...

, 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 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
    Intranet
    An intranet is a computer network that uses Internet Protocol technology to securely share any part of an organization's information or network operating system within that organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network...

     services;
  • Access to operator walled garden
    Walled garden (media)
    A walled garden is an analogy used in various senses in information technology. In the telecommunications and media industries, a "walled garden" refers to a carrier or service provider's control over applications, content, and media on platforms and restriction of convenient access to...

     services; and
  • Access to public Internet
    Internet
    The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

    .

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.
this is tested by all the mobile phones are working in roaming condition

Roaming agreements

The legal roaming business aspects negotiated between the roaming partners for billing of the services obtained are usually stipulated in so called roaming agreements. The GSM Association broadly outlines the content of such roaming agreements in standardized form for its members. For the legal aspects of authentication, authorization and billing of the visiting subscriber, the roaming agreements typically can comprise minimal safety standards, as e.g. location update procedures or financial security or warranty procedures.

The roaming process

The details of the roaming process differ among types of cellular networks, but in general, the process resembles the following:
  1. 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.
  2. 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.
  3. 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.


If a call is made to a roaming mobile, the public telephone network routes
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...

 the call to the phone's registered service provider, who then must route it to the visited network. That network must then provide an internal temporary phone number to the mobile. Once this number is defined, the home network forwards the incoming call to the temporary phone number, which terminates at the host network and is forwarded to the mobile.

In order that a subscriber is able to "latch" on to a visited network, a roaming agreement needs to be in place between the visited network and the home network. This agreement is established after a series of testing processes called IREG (International Roaming Expert Group) and TADIG (Transferred Account Data Interchange Group). While the IREG testing is to test the proper functioning of the established communication links, the TADIG testing is to check the billability of the calls.

The usage by a subscriber in a visited network is captured in a file called the TAP (Transferred Account Procedure) for GSM / CIBER (Cellular Intercarrier Billing Exchange Record) for CDMA, AMPS etc... file and is transferred to the home network. A TAP/CIBER file contains details of the calls made by the subscriber viz. location, calling party, called party, time of call and duration, etc. The TAP/CIBER files are rated as per the tariffs charged by the visited operator. The home operator then bills these calls to its subscribers and may charge a mark-up/tax applicable locally.
As recently many carriers launched own retail rate plans and bundles for Roaming, TAP records are generally used for wholesale Inter-Operators settlements only.

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 both United States and India 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
Flagfall
Flagfall or flag fall is common Australian expression for a fixed start fee, especially in the haulage and railroad industry. From the Australia mobile phone industry, the expression has recently begun to spread to other English language countries, as business jargon for an initial fixed fee for...

charge.

Roaming in Europe

In the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

, the Regulation on roaming charges has been in force since 30 June 2007, forcing service providers to lower their roaming fees across the 27-member bloc. It later also included EEA
European Economic Area
The European Economic Area was established on 1 January 1994 following an agreement between the member states of the European Free Trade Association and the European Community, later the European Union . Specifically, it allows Iceland, Liechtenstein and Norway to participate in the EU's Internal...

 member states. The regulation sets a price cap of €0.39 (€0.49 in 2007, €0.46 in 2008, €0.43 in 2009) per minute for outgoing calls, and €0.15 (€0.24 in 2007, €0.22 in 2008, €0.19 in 2009) per minute for incoming calls - excluding tax. If the Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....

 is satisfied that competition will continue to keep prices at this level, or lower, the regulation will expire in mid 2012. Since mid 2009 there is also an €0.11 (excluding tax) maximum price for SMS text message included into this regulation.

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
T-Mobile USA
T-Mobile USA, Inc. is an American mobile-network operator, headquartered in Bellevue, Washington, that provides wireless voice, messaging and data services in the United States, Puerto Rico and the U.S. Virgin Islands. The company is the fourth-largest wireless carrier in the U.S. market with 33.73...

 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 common. Following the merger of Orange UK
Orange UK
Orange is a mobile network operator and internet service provider in the United Kingdom, which launched in 1994. It was once a constituent of the FTSE 100 Index but was purchased by France Télécom in 2000, which then adopted the Orange brand for all its other mobile communications activities...

 and T-Mobile UK on 1 July 2010, national roaming has been possible between these two networks since 5 October 2010 at no additional cost pending the technical merging of the two networks.
  • 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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 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
    Mobile Signature Roaming
    The concept of Mobile signature Roaming is: an Access point should be able to get a Mobile Signature from any enduser, even if the AP and the enduser have not contracted a commercial relationship with the same MSSP. Otherwise, an AP would have to build commercial terms with as many MSSPs as...

    :

Mobile signature Roaming allows an access point
Wireless access point
In computer networking, a wireless access point is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards...

 to get a Mobile Signature
Mobile signature
A mobile signature is a digital signature generated either on a mobile phone or on a SIM card.-Origins of the term:mSignThe term first appeared in articles introducing mSign . It was founded in 1999 and comprised 35 member companies...

 from any end-user, even if the AP and the end-user have not contracted a commercial relationship with the same MSSP
Service switching point
In telephony, a service switching point is the telephone exchange that initially responds, when a telephone caller dials a number, by sending a query to a central database called a service control point so that the call can be handled...

. 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(reference).
Network elements belonging to the same Operator but located in different areas (a typical situation where assignment of local licenses is a common practice)pair depends on the switch and its location.Hence, software changes and a greater processing capability are required, but furthermore this situation could introduce the fairly new concept of roaming on a per MSC basis instead of per Operator basis. But this is actually a burden, so it is avoided.
  • Permanent Roaming:

This type of roaming refers to customers who purchase service with a mobile phone operator intending to permanently roaming, or be off-network. This becomes possible because of the increasing popularity and availability of "free roaming" service plan, where there is no cost difference between on and off network usage. The benefits of getting service from a mobile phone operator that isn't local to you can include cheaper rates, or features and phones that aren't available on your local mobile phone operator, or to get to a particular mobile phone operator's network to get free calls to other customers of that mobile phone operator through a free unlimited mobile to mobile feature. To accidentally become a permanent roaming customer does not usually happen. Most mobile phone operators will require the customer's living or billing address be inside their coverage area or less often inside the government issued radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 license of the mobile phone operator, this is usually determined by a computer estimate because it it's impossible to guarantee coverage. If a potential customer's address is not within the requirements of that mobile phone operator, they will be denied service. In order to permanently roam customers may use a false address and online billing
Electronic billing
Electronic billing is the electronic delivery of invoices and related information by a company to its customers. Electronic billing is referred to by a variety of terms,including the following:*Electronic bill payment...

, or a relative or friends address which is in the required area, and a 3rd party billing option.

Most mobile phone operator discourage or prohibit permanent roaming since they must pay per minute rates to the network operator their customer is roaming onto to, while they can not pass that extra cost onto customers ("free roaming").
  • Trombone roaming:

Roaming calls within a local tariff area, when at least one of the phones belong outside that area. Usually implemented with trombone routing also known as tromboning

The routing of trombone roaming.

See also

  • IEEE 802.11
    IEEE 802.11
    IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...

    • IEEE 802.11f
    • IEEE 802.11r
      IEEE 802.11r
      IEEE 802.11r-2008 or fast BSS transition is an amendment to the IEEE 802.11 standard to permit continuous connectivity aboard wireless devices in motion, with fast and secure handoffs from one base station to another managed in a seamless manner...

  • Home Location Register
  • Handoff
  • Mobile IP
    Mobile IP
    Mobile IP is an Internet Engineering Task Force standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address. Mobile IP for IPv4 is described in IETF RFC 5944, and extensions are defined in IETF RFC 4721...

  • Mobile phone
    Mobile phone
    A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

  • Mobile phones on aircraft
    Mobile phones on aircraft
    As of 2011, most airlines do not allow the use of mobile phones on aircraft, because it is thought they could adversely affect the navigational instruments in the cockpit...

  • Mobility management
    Mobility management
    Mobility management is one of the major functions of a GSM ora UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be delivered to them....

  • Regulation on roaming charges in the European Union
  • Roaming sim
    Roaming SIM
    Roaming SIMs can be defined as mobile phone SIM cards that operate on more than one network within their home country. They currently have two main applications, least cost call routing for roaming mobile calls and machine to machine....

  • GSM frequency bands
  • UMTS frequency bands
    UMTS frequency bands
    The UMTS frequency bands are radio frequencies used by third generation wireless Universal Mobile Telecommunications System networks.They were allocated by delegates to the World Administrative Radio Conference held in Málaga-Torremolinos, Spain between February 3, 1992 and March 3, 1992...

  • Vertical handoff
    Vertical handoff
    Vertical handover or vertical handoff refers to a network node changing the type of connectivity it uses to access a supporting infrastructure, usually to support node mobility. For example, a suitably equipped laptop might be able to use both a high speed wireless LAN and a cellular technology for...

  • Visitor Location Register

Standardisation Organizations

  • ETSI website, European Telecommunications Standards Institute.
  • Direct access to ETSI standards publications.
  • GSM website, Global System for Mobile communications by the GSM Association (GSMA)

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK