External GSM phone calls now made simpler

On 2 July, the IT/CS Telecom Service introduced a new service making external calls from CERN GSM phones easier. A specific prefix is no longer needed for calls outside CERN.

The Telecom Section of the IT/CS Group is introducing a new system that will make life easier for GSM users. It is no longer necessary to use a special prefix (333) to call an external number from the CERN GSM network. Simply dial the number directly like any other Swiss GSM customer.

CERN currently has its own private GSM network with the Swiss mobile operator, Sunrise, covering the whole of Switzerland. This network was initially intended exclusively for calls between CERN numbers (replacing the old beeper system). A special system was later introduced for external calls, allowing them to pass through the CERN telephone exchanges. Users first dialled the 333 prefix to obtain a dial tone from the telephone exchanges then, after a short wait, they dialled an external connection prefix (0, 20, 20 or 21) and finally the number they wanted to call.

The advantage of this special routing system is that it allows CERN to keep costs under control. Depending on the number dialled, the telephone exchange automatically selects the cheapest operator to handle the call. The system also makes it possible for each GSM user to be allocated very precise external calling rights, allowing CERN to make substantial savings on its GSM bill. However, the system is also very restrictive. "Users could not take advantage of the automatic call-back function if they missed a call, the handling of numbers in the phone book was complicated and, in general, the whole system took quite a bit of getting used to", explains Frédéric Chapron, Head of the Telecom Section.

The new system, which has been in operation since 2 July 2007, masks CERN’s specific routing procedure. External calls are routed through gateways that simulate calls with the 333 prefix, directing them towards the telephone exchanges. This solution simplifies the process but allows the technical and financial advantages of the old system to be retained. For those who can’t bear to say goodbye to the 333 prefix, it will remain in use, acting as a safety net in case of problems with the automatic routing system.