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Virtual Roaming Overview
 

Easy roaming is one of the advantages, which made the GSM standard prevail over other standards during the past few years. Customers often think that they can go anywhere and use their services to call, SMS or MMS any mobile in the world, as well as having their data services or Visio 3G. In reality, this is still far from being true.


Virtual Roaming: being able to use one’s phone everywhere, even if there is no bilateral agreement between the ‘home network’ and the ‘visited network’. This is thanks to the use of a ‘third party’, which has agreements with both and does the invoice clearing as well as the necessary signalling modification, so that this novel arrangement is almost transparent to the two parties concerned. The term ‘Open Connectivity’ was introduced by the GSM association in 2005 as an equivalent to ‘Virtual Roaming’. It covers two services: allowing a (typically small) network to have its subscribers roam in any network (‘outbound subscribers virtual roaming’), and allowing a (typically small) network to receive and invoice visitors from other countries. The demand for these services is mostly from the smaller networks, rather than from the larger operators that already have a roaming partner in most countries, as this represents only additional business.


Virtual roaming is a very comprehensive application of MAP, CAMEL, TCAP, SCCP and GTP, which allows these various topics to be put into a common perspective that is very useful for consolidating a detailed understanding.


Virtual Roaming is the objective and it has been ongoing since 1999; starting with SMS then MMS interworking. As it is big business, many suppliers have entered these two markets, but several implementations are very poor as they lack the Quality of Service which can only be provided by the SS7 signalling transparency. It is the aim of this book to explain a full Roaming Hub solution, including principles for bridging between the two main standards, GSM and IS 41, and the full provision of all existing mobile services in a virtual roaming situation, in the soon to arrive reality of an all IP network.


‘Open Connectivity’ is a term which emerged in 2006 as an equivalent to ‘Virtual Roaming’. There were about 800 GSM networks worldwide in 2008 and 1200 mobile networks in total (TDMA, CDMA, etc.). The number of bilateral agreements that need to have total service connectivity is therefore very high and the idea arose to replace many bilateral agreements (N×N-1)/2 by agreements with a number M of aggregating ‘virtual roaming suppliers’.


The ‘virtual Roaming Hub’ is a system which provides all the roaming services between two mobile networks A and B which do not have direct roaming agreements.

These services include:

all voice services (making and receiving calls);
all Visio 3G services;
all SMS services (sending and receiving);
transparent CAMEL prepaid charging scheme (T - CSI, O - CSI, SMS - CSI, GPRS - CSI, … );
GPRS data services (2.5G and 3G) (these will become even more important in the future);
location - based services;
VMS ‘anti - tromboning’ ;
stolen equipment checking.


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