Network Programming with Sockets

Sockets appeared in Berkeley Unix (BSD = Berkeley Software Distribution) for the first time. For that reason, they are also called Berkeley Sockets. Since Berkely Sockets were implemented in Unix Systems originally, they have a long history connected with Unix history. In the meantime, the BSD Sockets idea proofed to be good enough for other operating systems as well and so they are also available on other popular systems like Windows.

The term Socket has two meanings.

• A Socket - when refered to as Network Socket - is the information tupel (IP Adress, Port Number ). IP Address is provided by the UP Protocol, Port Number is stored in TCP or UDP - not in IP as many people believe! Please have a look at the Literature section below.
• In Unix a Socket is an internal data structure, that can be connected to a communication endpoint. The type of connection can be various and depends on the Unix implementation and Kernel configuration. On a typical Unix flavoured System you have support for IP (Internet Protocol), TCP (Transmission Control Program), UDP (User Datagram Protocol) and Unix Domain Sockets - a Unix IPC (Interprocess Communication), a very fast Communication channel soley found on Unix based systems. One might find support for many other protocols like X.25, RUDP (Reliable UDP), ...

For the application programmer, the socket is "visible" as a File Descriptor. The Programmer can treat a socket similar to a file and apply read(), write(), ioctl(), ... on it. This is the strength of the concept, but on the other hand a TCP connection is not a file and this difference maks socket Programming a bit tricky. It is not too hard to get something to work in reasonable time (please see also the Examples section), but to achieve ~ 100% reliability one needs a little bit of experience.

Socket Library

Network Programming is calling for a framework that addresses all the lower level issues so the application programmer can focus on the higher level problems. C++ World have developed their own C++ socket library, you can learn more about it here.

Literature

Richard Stevens "Unix Network Programming" has been a classic for many years. "Could you borrow me your Stevens, please?" is a phrase you hear quite often in developer labs. The book is good for Windows developers as well - not only because you can use Cygwin and "bypass" the Unix API - but also because lots of the System calls are industry standard (IEEE, POSIX). The book covers Berkely sockets, System V Transport Layer Interface (TLI), many protocols and their implementation (RPC, telnet, rlogin, rmt, lpr)
Comer and Stevens wrote a series of three books on "Internetworking with TCP/IP". I am using Volume II and Volume III. Volume II (Design, Implmentation and Internals) tells about the concept of TCP/IP protocols. It gives details about the TCP finite state machine as well as about SNMP, multicasting, urgent data, ospf (routing protocol). This is not a real programmers book, it is exaplaining conceptually how network programming works, from client and server perspective and also from the operating systems perspective. A very good book. Volume III is more programming oriented. All aspects of client/server computing are covered with lots of details and examples and pracatical hints. It is a good follow up of Volume II. I assume Volume I is good as well, but I have not read it.
Again Richard Stevens. TCP/IP Illustrated Vol 1. shows detailed message charts and state transition charts of many network protocols. IP, UDP, TCP, NFS, FTP, TFTP, BOOTP, DNS, SMTP, Telnet, Rlogin Protocols are explained in detail. Broadcasting, multicasting, message flows etc are also covered.