Generally we can distinguish between two types of mobility:
-
Terminal mobility: A mobile terminal can move around the network without disrupting the service;
-
Personal mobility (nomadicity): A user can move to different terminals and networks and still be connected.
Terminal mobility requires a wireless connection, while personal mobility can be implemented without necessarily having wireless connections. What is available now on the Internet could be called personal mobility or portability; one can move to different places, connect to the Internet and check e-mails etc. Through their advanced services, mobile operators are attempting to provide terminal mobility.
Mobility can be implemented at different levels:
-
At link layer
-
At application layer
-
At IP layer
When it comes to e-mail application, the mobility (nomadic use) is implemented at the application level. This type of mobility is highly relevant for the VoIP. The VoIP service can be offered like e-mail, i.e. so that the only precondition for service accessibility is the availability of an IP connection. Here it is extremely complex to determine the location of the caller, which creates regulatory problems for emergency calls, discussed in the section about VoIP.