Internet services (or network services) are a form of distributed applications in which software components running on networked hosts coordinate via ubiquitous communication protocols on the Internet. The components that accept and handle requests are often referred to as server and the components that issue requests to and receive responses from servers are clients. Both client and server are essentially userlevel processes, which may be run in the same host or different hosts on the Internet. Most of the network services are organized in a server/client model, in which servers and clients are running on different hosts. There are recent ﬁle sharing services in a peer-to-peer model, in which each host assumes both server and client roles. The communication protocols in network services must be open and published. They can either be standardized or industry de facto standards. The Hypertext Transfer Protocol (HTTP) is the most popular standard protocol endorsed by the WWW Consortium (W3C) for communication between Web servers and clients like Microsoft IE and Mozilla Firefox.