  Recently, the mobile industry has experienced an extreme increment in number
of its users. The GSM network with the greatest worldwide number of users
succumbs to several security vulnerabilities. Although some of its security
problems are addressed in its upper generations, there are still many operators
using 2G systems. This paper briefly presents the most important security flaws
of the GSM network and its transport channels. It also provides some practical
solutions to improve the security of currently available 2G systems.
