Internet is built upon a collection of networks that covers the world. These networks contain differnt types of computers, and somehow, something must hold the whole thing togather. That something is TCP/IP. TCP/IP is the common name of over 100 protocols that are used to connect computers and networks. The actual name TCP/IP comes from TCP ( Transmission Control Protocol) and IP ( Internet Protocol ). Within the Internet, data is broken into small packets called fragments. For example, say that you send a long mail on the other side of the country. TCP will divide the message into packets. Each packet is marked with a sequence number. Each host on the Internet is assigned a unique 32-bit (For IP version 4) IP address. Data are carried out in the form of packets which contain source and destination IP addresses. Internet routers maintain a view of the network topology in the form of routing tables. These tables are consulted when making packet routing decisions. The process of routing involves inspecting the destination address contained in the packet and based on the contents of the routing table, determining the next hop router to which the packet should be relayed. Each router along the source and the destination nodes repeat this process until the packet is finally delivered to the destination host.