| Computer network has been growing explosively. Two decades ago, few people had access to a network. Now, computer communication has become an essential part of our infrastructure. Networking is used in every aspect of business, including advertising, production, shipping, planning, billing, and accounting. Consequently, many corporations have multiple networks. In short, computer networks are everywhere. Continued growth of the global Internet is one of the most interesting and exciting phenomena in networking. Two decades ago, the Internet was a research project that involved a few dozen sites. Today, the Internet has grown into a production communication system that reaches millions of people in eighty-two countries on all continents around the world.Computer networking is a complex subject. Many technologies exist, and each technology has features that distinguish it from the others. Multiple organizations have created networking standers independently, which are not all compatible. Many companies have created commercial networking products and services that use the technologies in unconventional ways. Finally, networking is complex because multiple technologies exist that can be used to interconnect two or more networks. As a result, many combinations of network are possible.Protocols are the standards that specify how data are represented when being transferred from one machine to another. They specify how the transfer occurs, how errors are detected, and how acknowledgements are passed. To simplify protocol design and implementation, communication problems are segregated into sub problems that can be solved independently. Each sub problem is assigned a separate protocol. The idea of layering is fundamental because it provides a conceptual framework for protocol design. In a layered model, each layer handles one part of the communication problem and usually corresponds to one protocol. Protocols follow the layering principle, which states that the software implementing layer n on the destination machine receives exactly what the software implementing layer n on the source machine sends. The two most famous models are the ISO's Reference Model of Open System Interconnection, often referred to as the ISO model, which contains 7 conceptual layers, and the TCP/IP Internet Layering Model, which is organized into 4 conceptual layers that are built on a fifth layer of hardware. TCP/IP protocol suit is the most widely implemented networking protocol suit, and the global Internet used today was build upon it.The Internet protocol, the protocol that corresponds to the upper third layer---Internet layer in the TCP/IP protocol suit is the most important protocol in the model. The Internet layer handles communication from one machine to another. It accepts a request to send a packet from the transport layer along with an identification of the machine to which the packet should be sent. It encapsulates the packet in an IP datagram, fills in the datagram header, and uses the routing algorithm to determine to the appropriate network interface for transmission. The Internet layer also handles incoming datagrams, checking their validity, and uses the routing algorithm to decide whether the datagram should be processed locally or forwarded. For datagram addressed to the local machine, software in the Internet layer deletes the datagram header, and chooses from among several transport protocol the one that will handle the packet. Finally, the Internet layer sends ICMP error and control messages as needed and handles all incoming ICMP message.Though the current version of IP has been extremely successful, neither the global Internet nor the TCP/IP protocol is static. The stimulus for change occurs as increases in load and size force improvements needed to maintain service, as new applications demand more from the underlying technology, and as new technologies make it possible to provide new services. An effort to define the next generation of Internet Protocol (IPng) has produced much discussion and several pr... |
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