Introduction

    Electronic comunication has become essential for every organisation. The use of the Internet and his components, the e-mail and the World Wide Web, has become a necessity companies, non-gouvernamental organisations, educational or official organisations. The Internet offers new ways of communicating like Voice over IP, Video over IP and Instant Messaging It also allows a company to join the local networks of his branches in a big corporate network, by using VPN (Virtual Private Network), so that all the members of the company have access to the same resources and applications installed on the companies central servers.
    But all this network dependent applications are efficient only if the network is functioning well, which usually means that it has a small reply time and a high bandwidth. In most cases, an organisation has a single Internet link shared by all the users, as well as by the servers hosted in the local network. The traffic generated by the users from their workstations, by using programs like chat, Instant Messaging or web browsers, has the tendancy to grow rapidly up to the limit of the Internet channel contracted with the ISP and as a result, the network parameters are degrading to values that make almost impossible the normal functioning of those applications that are supposed to generate profit.