In our age, Internet is the biggest information network in the world; it consists of a set of heterogeneous networks from over 100 countries displaying huge amounts of virtual resources; it provides facilities such as email, file transmission protocol (ftp), workgroups discussion or chat,...

In our age, Internet is the biggest information network in the world; it consists of a set of heterogeneous networks from over 100 countries displaying huge amounts of virtual resources; it provides facilities such as email, file transmission protocol (ftp), workgroups discussion or chat,...