The Internet and the World Wide Web are based on TCP/IP. The term "TCP/IP" refers to not only the TCP (transmission control protocol) and IP (Internet protocol), but also includes other protocols, applications, and even the network medium. These protocols include UDP, ARP, and ICMP. These applications include telnet, FTP, Secure Shell, NFS,Web browsers and servers, and the many items collectively called the Web services. This chapter is an encyclopedic survey of these topics starting from the seven-layer OSI model to recent improvements in the implementations of the protocol stack and firewalls.
A computer system communicates with another system by sending a stream of bytes. A byte is a sequence of 8 bits. A checksum is the arithmetic sum of a sequence of numbers used to detect errors that may have altered some of the numbers in the sequence. The communication is actually between a process running on one system with one running on the other system.
The two processes communicate information in a pre-agreed form known as protocol. That is, the two processes agree on the meaning of specific byte values occurring in specific positions in the stream.
This chapter describes the core protocols known as IP and TCP, and a few application protocols based on these. The details of IP and TCP are not directly experienced by the ordinary user unless a network sniffer is used. Nevertheless, it is crucial to understand these before attempting to understand the application protocols. In each protocol, there is a stream of bytes known as a frame, a datagram, a packet or a segment depending on the "level".

Specifies the format of packets, or datagrams, and the addressing scheme they use.

User Datagram Protocol establishes a more efficient way to send and receive information. It is used mostly for streaming music or video, where real time performance is important.

Transmission Control Protocol establishes a virtual connection between a destination and a source.

Hypertext Transfer Protocol transfers information from World Wide Web servers to browsers.

FTP is used to send files over the Internet.

Higher level protocols and custom protocols meet discrete connection requirements.