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1.Introduction:
We must have an interface between the application programs and the protocol software in order to use network facilities. My seminar is on a model of an interface between application programs and TCP/IP protocols. The standard of TCP/IP protocol do not specify exactly how application programs interact with the protocol software. Thus the interface architecture is not standardized; its design lies outside of scope of the protocol suite. It is further should be noticed that it is inappropriate to tie the protocols to a particular interface because no single interface architecture works well on all systems. In particular, because protocol software resides in a computer’s operating system, interface details depend on the operating system.
In spite of lack of standards, a programmer must know about the such interfaces to be able to use TCP/IP. Although I have chosen UNIX operating system in order to explain the model, it has widely accepted and is used in many systems.
One thing more, the operations that I will list here, will have no standard in any sense.
2.UNIX I/O Paradigm And Network I/O:
Developed in the late 1960s and early 1970s, Unix was originally designed as a timesharing system for single processor computers. It is a process-oriented operating system in which each application program executes as a user level process. An application program interacts with the operating system by making system calls. From the programmer’s point of view, system calls look and behave exactly like other procedure calls. They take arguments and return one or more results. Arguments can be values or pointers to objects in the application program.
The UNIX input-output primitives follow a paradigm sometimes referred to as open-read-write-close. Before a user process can perform I/O operations, it calls open to specify the file or device to be used and obtains permission. The call to open returns a small integer file descriptor that process uses when performing I/O operations on the opened file or device. Once an object has been opened, the user process make one or more calls to read and write to transfer data. Read transfer the into the process; write transfers data from the user process to the file or device. Both read and write take three arguments that specify the file descriptor to use, the address of a buffer, and the number of bytes to transfer. After all transfer operations are complete, the user process calls close to inform the operating system that it has finished using the object. The operating system automatically closes all open descriptors if a process terminates without calling close.
Originally, UNIX designers cast all I/O operations in the open-read-write-close paradigm. The scheme included I/O for character-oriented devices like keyboards and block-oriented devices like disks and files. An early implementation of TCP/IP under UNIX also used the open-read-write-close paradigm with special file name:-
/dev/tcp
The group adding network protocols to UNIX decided that because network protocols are more complex than conventional I/O devices, interactions between user processes and network protocols must be more complex than interactions between user processes and conventional I/O facilities. In particular, the protocol interface must allow programmers to create both server code that awaits connections passively as well as client code that forms connections actively. Furthermore, application programs sending datagrams may wish to specify the destination address along with each datagram instead of binding destinations at the time they call open. To handle all these cases, the designers chose to abandon the traditional UNIX open-read-write-close paradigm, and added several new operating system calls as well as new library routines. Adding network protocols to UNIX increased the complexity of I/O interface substantially.
3.Sockets:
A socket is defined as an end point for communication .A pair of processes communicating over a network employs a pair of sockets-one for each process. A socket is made up of an IP address concatenated with a port number. In general sockets use client-server architecture. The waits for incoming client requests by listening to a specified port. Once a request is received, the server accepts a connection from the client socket to complete the connection.