Thomas Haug, who, after all, chaired both the NMT and the GSM groups, points out that the two systems had great similarities. This may not be obvious to users because the technology is different, but the system architecture is basically the same and the facilities offered are largely similar.
“You can see immediately that the NMT designers had a great impact on GSM. And that is not particularly far-fetched because these were the people who wrote the GSM mandate,” Haug says.
He lists the features shared by NMT and GSM:
• Automatic connection irrespective of the position of the caller or the number called
• Automatic location of the subscriber called
• Equally usable in every country in which the system had been established
• A system of numbers adapted to the fixed network
• Unrestricted use across national borders
• A system of numbers that provides unambiguous identification of subscribers
• The “tromboning” principle for call-forwarding
• Handheld phones as in NMT
• Same call procedures as in the fixed networks (apart from dialing before initiating the call)
• Transfer between base stations during calls.
Among the similarities that users cannot see directly are:
• Databases for continual registration of the position of mobile subscribers
• No major alterations to the fixed network
• Modern signaling systems for communication between exchanges.
The two most important differences can be found in the stringent security mechanisms that have been incorporated (above all, SIM cards, which enable powerful encryption, theft protection and so on). This was not developed for NMT until its later versions of the 1990s.
“The digital transmission of speech in GSM, which makes powerful encryption possible but leads to somewhat worse speech quality and some delay, is hardly something that a user will notice,” Haug says.
Author: Svenolof Karlsson & Anders Lugn