The term roaming (English " wandering " for " stray " or " roam " ) or channeling is originally from the area of ​​the GSM radio network. Traditional GSM Roaming is the ability of a mobile network operator to automatically receive in another foreign network than its home network or to make calls, to send and receive data, or to have access to other cellular network services. Roaming capabilities have then, for example, for a participant meaning when it moves out of range, which is covered by its home network. The operational readiness of the devices outside of their own radio network is technically supported by authentication, authorization, and accounting procedures ( billing ).

Distinction between

From the term " roaming " (also called " Macro Mobility " ) are to be distinguished handover and cell change (also called " micro- mobility" ). These terms refer to the change of the radio cell during a call or an ongoing data connection. Herein, if the network ( PLMN) change, it is called InterPLMN handover or InterPLMN -cell -change.

Both functions can be used, for example, when sister companies internationally active mobile phone companies so interconnect their directly neighboring national networks, the services can be shared across borders without interruption.

These functions also took O ₂ when changing from its own network in the network of T -Mobile in rural areas not requiring O2 network. These two companies had a national roaming realized. Technically, this is - apart from the Neighbourhood RF cell planning - the same as roaming between international partners. National roaming is in principle - just like normal roaming - also possible without having to take place handover, what with limited regional networks (eg in India or the U.S.) is useful.

International Roaming ( abbreviated as IR ) is used as differentiation from national roaming and denotes a connection from a mobile network abroad.

Outbound Roaming refers to the use of another network (for example: use of a foreign mobile network on holiday).

Inbound Roaming refers to the use of its own network by a foreign participant (example: foreign mobile subscriber to visit).

Note: Outbound and Inbound always depend on the perspective of the network operator. A subscriber of network A, which is located in the network B, is from the perspective of his home network A is an outbound roamer. From the perspective of the visited network B it is an inbound roamer.

Roaming general

Roaming is a distinction between "SIM -based roaming " and " Username-/Password-basiertem roaming ", where also the roaming networks in different network standards such as WLAN ( Wireless Local Area Network) and GSM, under the technical term roaming falls. Features and functionality of the device, such as SIM card capability, antennas and network interface and energy management, determine the ways to access.

Using the example of WLAN / GSM roaming, the following scenarios can be distinguished ( cf. GSM Association Permanent Reference Document AA.39 ):

  • SIM -based roaming: A GSM user moves ( in slang: " roaming " ) in a public Wi-Fi, by: its own GSM network operator is operated or
  • Another network operator, operating a related agreement ( "roaming agreement" ) owns the home network operator.
  • Its own GSM network operator is operated or
  • Another network operator is operating and has a corresponding agreement with the home operator.

The above-mentioned roaming scenarios are intended bidirectional, that is, they include both the roaming of a GSM network to a WLAN as well as a WLAN in a GSM network. Traditional roaming in networks same standards, for example, from a WLAN to a WLAN or GSM network in a GSM network has already been described above, and also defined by the strangeness of the network, based on the type of subscriber entry in the home user directory.

Regarding the possible scenarios for the authorization of a user, is often sought by the mobile service providers that the participant gets access to the same services and services regardless of the type of access network standard or network. However, other scenarios with a differentiation of shared services for networks and network standards also exist, eg for prepaid method. The access scenarios may include a wide range of services, including:

  • Access to shared intranet services;
  • Access to specific services of the service provider (so-called operator Walled Garden Services, see the article " Walled Garden "); and
  • Access to the public Internet.

The uninterrupted ( seamless ) Access (English seamless access) to these services regardless of the type of access and the network standard is one of the goals in merging the different network standards. It also of session continuity is ( English for " resistant session " or " persistent / permanent connection " ) spoken.

Home and foreign networks

The " strangeness " of the network ( " visited network ") is defined by the type of subscriber entry in the network. If a user has no entry in the home directory of the network (eg, HLR ( Home Location Register) in GSM networks or local Customer Database WLANs ), the necessary subscriber data, for example, the home network of the subscriber from the visited network must first are required so that the subscriber is authenticated and authorized to use any of the network services can be examined. The "foreign" participant receives an entry in a user database of the visited network (eg, Visitor Location Register, VLR ) and the authorized network services are enabled. In the concrete process of roaming the option of assigning the subscriber data in each case is essential to ensure the appropriate network authentication, authorization and billing of the subscriber can be made. The concept of roaming is thus not tied to a specific network standard, but the type of subscriber entry in the home directory of the mobile network. Can use his personal service profile, which he also used in the home network is a participant in the foreign network, also referred to as so-called Global Service Roaming Capability.

Roaming agreements

The legal roaming terms and conditions, which are negotiated between the roaming partners for the settlement of the related services are usually held in so-called roaming agreements. The GSM Association provides its members the content of such roaming agreements broadly standardized ago. Roaming agreements can contribute to the legal implementation of the authentication, authorization, and billing for the net foreign participants typically include agreed minimum safety standard methods, such as location update process or financial hedging and warranty procedures.


From the perspective of the participating networks roaming is an exchange- technical feature. Main functionality is to access the mobile switching systems of the visited network to a home network user database, such as a subscriber register (HLR ) of the home network of the customer. It is checked whether the subscriber in question is not blocked, and the necessary authorization to use the service has ( in general or for roaming in particular).

For roaming prepaid cards may vary by card either not possible ( that is, the card works abroad at all), to a limited extent (for example, incoming calls are forwarded to the foreign network, and SMS can be sent as usual and be received) or be possible without restriction, or outgoing calls are only in the call-back method possible, at which the user is requesting a call back on his home network operator via a USSD code and this connects to the desired party. Since using this method, the number of countries in which users of prepaid cards can active call, multiplied.

The transfer of data roaming is realized by so-called clearing houses, whose task is the worldwide transmission of telephony data from the different network provider. In addition to the pure transmission of such data also provide services such as data consistency checks, tariff review and bill payment are paid by the clearing houses. There are only a few network providers who take on these tasks nor even the world.

End users maximum charges in the EU

The high transit fees of European mobile operators have been repeatedly criticized in recent years, including by the competent EU Telecoms Commissioner Viviane Reding. In March 2007, a maximum limit of European transit fees was proposed. On 7 June 2007 the EU Council of Ministers approved the Regulation, which established the fees for outgoing calls in other EU countries to a maximum of 49 cents per minute for calls received to a maximum of 24 cents plus the applicable VAT. Since August 30, 2008 was again lowered the ceiling price of 46 cents for outgoing and 22 cents for incoming calls - each plus the applicable VAT. On 1 July 2011, a further reduction of price limits came into force. These now be 35 cents to 11 cents for active and passive calls plus VAT. Next, an upper limit for SMS in the amount of 11 cents plus VAT has been introduced. In addition, mobile operators need 1 July 2009 to settle the exact second for passive roaming calls. For active calls, a minimum charging period of 30 seconds is allowed. This means that active conversations that take 30 seconds or longer, must be billed to the second in each case. This price ceiling was lowered continuously until 2014 on 1 July. Until December 15, 2015, are prohibited and thus abolished all EU-wide roaming charges.

Due to the repeatedly occurring error in the connection data transmission and computation billing error rate is very high. The network operators are now trying through the introduction of so-called zones of a simplified billing to "force". The client is thereby suggests a price certainty and a price cut. In reality there will be increased by up to 800%. Roaming accounting controls an error rate of around 40 % was found.

Since July 1, 2010 shall apply throughout the EU rule to limit the costs for the use of mobile Internet in other EU countries to a maximum of 800 euros per GB ( plus VAT). Since local data access is already available for 1 € per GB, there are just warnings to citizens in the law, the requirement that a user must be notified that he should come too 80 % of the cost cap of 50 euro per month. Unless otherwise requested by the user, the Internet connection is interrupted after reaching the upper cost limit.

Legal basis:

  • June 2007-June 2012: Council Regulation ( EC) No 717/ 2007 of the European Parliament and of the Council of 29 June 2007
  • Since July 1, 2012: Regulation ( EC) No 531/ 2012 of the European Parliament and of the Council of June 13, 2012