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GPRS Cellular Network

Availability of subscribers

GPRS is a service within the world-wide cellular network GSM for data transmission. As a rule, the GPRS network provider acts at the same time as Internet service provider and offers access to the world-wide web for the GPRS devices. Data traffic is usually performed between a mobile field device with a GPRS connection and the company headquarters via GPRS network and Internet.

green arrow: connection establishment authorized
red arrow: connection establishment denied

Security at the cost of availability
  • Connection establishment from GPRS participant to the Internet always possible
  • Connection establishment from the Internet to the GPRS participant blocked to avoid interferences from the Internet (hacking)
  • Permanent availability for cellular terminal devices, e.g. by permanent fix IP addresses and communication in a protected private IP network with mdex-fixed IP or "always on" with VPN


An internet connection supposes mobile devices to meet two requirements:

  1. Protection of the terminal device against active interferences from the Internet (hacking)
  2. Limiting the - compared with standard Internet - relatively expensive bandwidth on the transmission path to desired data traffic


The standard solution of most GPRS providers is a restriction of your changeover to Internet to a connection established by the GPRS terminal device itself. Any connecting requests from "outside" are denied. Thus, standard applications such as web surfing or e-mailing may be run in a safe and unimpeded way.


As a rule, this kind of insular routing is also used between GPRS devices and rounded off by attributing dynamic and private IP addresses to the terminal devices.

Note: In some countries also GPRS accesses without these restrictions are offered. You should use these only in case both, an external security concept as well as a protection against extremely high costs due to undesired internet traffic, may be installed.


The safe standard configuration of GPRS networks is an effective prevention of undesired as well as desired connections:

  • Establishing a connection from a control station to the field device is impossible (polling)
  • A field device with a web configuration is not addressable (mobile server)
  • Field devices cannot connect to each other


Since connectivity is subject to routing rules, no harm may be done even if an external caller should happen to know your present IP address (e.g. through a service like dynDNS).

Security and Accessibility

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.

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