1.1 What is the Internet What is the Internet? The Internet is a shared media (coaxial cable, copper wire, fiber optics, and radio spectrum) communication network between millions of hosts or end systems (computers, PDA's, TVs, cell phones, home electrical and security systems, etc) throughout the world A Nuts - and - Bolts Description Hosts or end systems are connected together via communication links, which are made up of different types of media (such as coaxial cable, copper wire, fiber optics, and radio spectrum), and routers. Different communication links can transmit data at different rates, with the transmission rate of a link measured in bits per second. COMPUTER NETWORKING (A TOP DOWN APPROACH FEATURING THE INTERNET)

The need to share the media for the communication links between the hosts or end systems has created the necessity to use a technique called packet switching. Packet switching enables multiple communicating hosts or end systems to share a path or parts of a path at the same time. Hosts or end systems access the Internet through Internet Service Providers (ISP's). ISP's provide a variety of types of network access to the hosts or end systems, including 56Kbps dial-up modem access, residential broadband access such as cable modem or DSL, high-speed LAN access and wireless access. ISP's also provide Internet access to content providers, connecting websites directly to the Internet. For the Hosts or end systems to use shared paths or parts of a path at the same time, Protocols must be established The Transmission Control Protocol (TCP) and the Internet Protocol (IP) are two of the most important protocols in the Internet. The Internet's principal protocols are collectively known as TCP/IP.

The IP protocol specifies the format of the packets that are sent and received among routers and hosts or end systems. TCP provides to an application reliable transport, flow control, and congestion control. The U.S. DoD required reliable data transmission to any destination on the network under any circumstances. The creation of the TCP/IP model helped to solve this difficult design problem. The TCP/IP model has since become the standard on which the Internet is based. Given the importance of protocols to the Internet, it's important that every one agree on what each and every protocol does. This is where standards come into play.

Internet standards are developed by the Internet Engineering Task Force (IETF). The IETF standards documents are called Requests For Comments (RFC's). RFC's started out as general requests for comments (hence the name) to resolve architecture problems that faced the precursor to the Internet. RFC's tend to be quite technical and detailed. They define protocols such as TCP, IP, HTTP (for the web), and SMTP {Single Mail Transfer Protocol (for open-standards )}. The IETF has also standardized what protocols must run by an Internet host or end system and an Internet router. There are more than 3500 RFC's. Other bodies also specify standards for network components, most notably for network links. The IEEE 802 LAN/MAN Standards Committee, for example, specifies the Ethernet and Wireless Wi-Fi standards.

1.1.2 A Service Description The Internet allows distributed applications running on its hosts or end systems to exchange data with each other. These applications include web surfing, instant messaging, audio and video streaming, Internet telephony, distributed games, peer - to - peer (P2P) file sharing, remote login, electronic mail, and much, much more. It is worth emphasizing that the web is not a separate network but rather just one of many distributed applications that use the communication services provided by the Internet. The Internet provides two services to its distributed applications: a connection - oriented reliable service and a connectionless - unreliable service. The connection - oriented reliable service guarantees that data transmitted from as sender to a receiver will eventually be delivered to the receiver in order and in its entirety. The connectionless - unreliable service does not make any guarantees about eventual delivery. Typically, a distributed application makes use of one or the other (but not both) of these two services.

1.1.3 What Is a Protocol? The protocols in human communication are separate rules about appearance, speaking, listening and understanding. They work together to help people successfully communicate. The need for protocols also applies to telecommunications, computing and network devices. Computers have no way of learning protocols, so network engineers have written rules for communication that must be strictly followed for successful host-to-host communication. These rules apply to different layers of sophistication such as which physical connections (media) to use, how hosts listen, how to interrupt, how to say good-bye, and in short how to communicate, what language to use and many others. Protocols may include signaling, authentication and error detection and correction capabilities. These rules, or protocols, that work together to ensure successful communication are grouped into what is known as a protocol suite. Protocols may be implemented by hardware, software, or a combination of the two.

TCP/IP refers to a collection (a "protocol suite") of its most used protocols. Most of the Internet's communication protocols are described in the Requests For Comments (RFC) documents of the Internet Engineering Task Force (IETF). As an example of a computer network protocol with which you are probably familiar, consider what happens when you make a request to a Web server, that is, when you type the URL of a Web page into your Web browser. First, your computer will send a connection request message to the Web server and wait for a reply. The Web server will eventually receive your connection request message and return a connection reply message. Knowing that it is now OK to request the Web document, your computer then sends the name of the Web page it wants to fetch from that Web server in a GET message. Finally, the Web server returns the Web page (file) to your computer.