Online Programz

The global IP Internet is the most famous and successful implementation of an internet. It has existed in one form or another since 1969. While the internal architecture of the Internet is complex and constantly changing, the organization of client-server applications has remained remarkably stable since the early 1980s.

Each Internet host runs software that implements the TCP/IP protocol (Transmission Control Protocol/Internet Protocol), which is supported by almost every modern computer system. Internet clients and servers communicate using a mix of sockets interface functions and Unix I/O functions.The sockets functions are typically implemented as system calls that trap into the kernel and call various kernel-mode functions in TCP/IP.

TCP/IP is actually a family of protocols, each of which contributes different capabilities. For example, the IP protocol provides the basic naming scheme and a delivery mechanism that can send packets, known as datagrams, from one Internet host to any another host. The IP mechanism is unreliable in the sense that it makes no effort to recover if datagrams are lost or duplicated in the network. UDP (Unreliable Datagram Protocol) extends IP slightly, so that packets can be transfered from process to process, rather than host to
host. TCP is a complex protocol that builds on IP to provide reliable full duplex (bidirectional) connections between processes. To simplify our discussion, we will treat TCP/IP as a single monolithic protocol. We
will not discuss its inner workings, and we will only discuss some of the basic capabilities that TCP and IP provide to application programs.