green zone: all connections authorized
red arrow: connection establishment denied
Security and availability may be realised at the same time if the GPRS provider or a service provider allows for an alternative configuration of the router to the Internet.
The service mdex fixed.IP creates for each customer a closed-circuit user group consisting of mobile devices and protected external accesses via Internet. The devices identify themselves during login and get always the same IP addresses. The alternative routing rules enable a free communication establishment among each other: mobile server, connections between mobile devices and polling from the master control are possible without restrictions.
The restrictive security rules as in the general GPRS network still apply for devices, which do not belong to the own user group.
An additional advantage of closed-circuit user groups is that they do without additional protocols - this service is provided within the TCP/IP standard, thus avoiding any adaptation of terminal devices.
Service providers for closed-circuit user groups also go by the name of Virtual Mobile Operator (VMO), meaning to point out the fact that these providers use the radio network of a GPRS provider, but forward the data independently from it.