Data Communications Systems : Internet

The Internet is a public data network that interconnects private and government computers. The Internet transfers data from point-to-point by packets that use Internet protocol (IP). Each transmitted packet in the Internet finds its way through the network switching through nodes (computers). Each node in the Internet forwards received packets to another location (another node) that is closer to its destination. Each node contains routing tables that provide packet-forwarding information. The Internet was designed to allow continuous data communication in the event some parts of the network were disabled. The world wide web (WWW) is an application on the Internet that allows users to graphically navigate through computers that are connected to the Internet.

The Internet is a network of networks. Although these networks communicate with each other using many different languages (protocols), they all agree to transport data within their network according to a common Internet communication language called transmission control protocol/Internet protocol (TCP/IP). TCP/IP is a set of protocols developed by the U.S. Department of Defense (US DOC) that facilitate the interconnection of dissimilar computer systems across networks. The TCP protocol coordinates the overall flow of data during a data communication session between points (nodes) in the Internet.

IP is an addressing structure that allows packets of data to be routed (re-directed) as they migrate through different networks to reach their ultimate destination. Each network receives packets of data in a format that is compatible with the Internet (IP address followed by control and data information) and they encapsulate (place the whole Internet data message into their own data packet format (including the IP address and control information). This allows IP data packets (called “datagrams”) to be sent through the network regardless of their actual length or format.

Figure 1 shows that the Internet is the network of networks and it communicates using the universal protocol language TCP/IP. This diagram shows a user who is sending email through the Internet. In this diagram, the application is email. The data from the email is divided into packets and given sequence number by TCP protocol. The destination address is appended to each packet by the IP layer. The IP packets are then sent through an Ethernet LAN by encapsulating the IP datagram within the Ethernet data packet. When the data packet is extracted from the Ethernet, it is placed on the E1 transmission line. When the IP data packet reaches the ATM network, it is subdivided into very small 53 byte data packets that travel through the ATM network. When the ATM packets reach their destination in the ATM network, the original IP datagram is recreated and transferred via the T1 communication line. The T1 communication line interfaces to another Ethernet data network. This Ethernet data network encapsulates the IP datagram and forwards it on to the NIC of the receiving computer. The NIC of the receiving computer removes the IP address and reassembles the IP data packets to form the original email message.


Figure 1: Internet Data Routing