This is also required of a stationary mobile that reselects coverage from a cell in a different location area, because of signal fade.
Thus, a subscriber has reliable access to the network and may be reached with a call, while enjoying the freedom of mobility within the whole coverage area.
In the least-precise case, TMSI is randomly assigned by the VLR to every mobile in the area, the moment it is switched on, in order to support identity confidentiality.
At that point, the global "international mobile subscriber identity" (IMSI) must be sent to the network.
Every cellular system has a broadcast mechanism to distribute such information to a plurality of mobiles.
Roaming is defined[2] 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.
Roaming is technically supported by a mobility management, authentication, authorization and billing procedures.
This is due to the fact that every paging request has to be broadcast to every base station in the location area.
Ultimately, this wastes bandwidth and power on mobile devices by requiring them to listen for broadcast messages too often.
It is also known as GSM-IP ("Internet Protocol") because it will connect users directly to Internet Service Providers The bursty nature of packet traffic means that more paging messages are expected per mobile, and so it is worth knowing the location of the mobile more accurately than it would be with traditional circuit-switched traffic.
The main differences are that the "Serving GPRS Support Node" (SGSN) is the element involved.
This can avoid signaling peaks in some conditions: for instance, the UEs of passengers of a train may not perform tracking area updates simultaneously.
On the network side, the involved element is the Mobility Management Entity (MME).