4. Mobile network services

• In the 1980s, a group of European experts defined a digital cellular network capable of accommodating several million users (GSM). The specifications produced by this group are public and managed by ETSI.

GSM services can be divided into two groups: voice services and data services (text, image, fax and file transmission). Data transmission can be synchronous or asynchronous, and transparent or non-transparent.

• In transparent mode, the link is managed entirely by the terminals, with no end-to-end control.

• In the non-transparent mode, more suitable for asynchronous transfers, network equipment performs certain functions, such as error correction, on network sections, without terminal intervention. It uses the Radio Link Protocol...