GSM SoftModem on Linux a Direct Radio Link Protocol Interface
Christian Olrog · 1999
As more and more organizations realize the benefits of dynamic data distribution over the internet, the need for being able to retrieve this information at any time and place increases. The widespread deployment of the Global System for Mobile communications (GSM) throughout Europe and other parts of the world provides a common infrastructure which provides a travelling, or rather non-stationary, user with suitable gear near ubiquitous access to this information. The idea is to use a device driver implementing the Radio Link Protocol, and making a transparent virtual serial port under Linux, which may be connected to PPP and TCP/IP, thus facilitating data communications over a GSM cellular telephone without the need for additional hardware, except for a cable. Basics of GSM are discussed, and some of the issues regarding the real-time demands on operating systems in general and Linux in particular are discussed. This paper is the result of a thesis project carried out at Ericsson Research for a little more than 6 months, as a final part of the authors Master of Science degree from the Royal Technical institute of Technology (KTH) of Stockholm, Sweden.