ILGIN KAVAKLIOGULLARI Computer Science And Engineering Student @ Techical University of Sofia

1. SOCKET PROGRAMMING
DISTRIBUTED SYSTEMS AND COMPUTER COMMUNICATIONS
ILGIN KAVAKLIOĞULLARI
CSE - 273213005

2. WHAT IS SOCKET?
A network socket is an endpoint of a connection in a
computer network. In Internet Protocol (IP) networks,
these are often called Internet sockets. It is a handle
(abstract reference) that a program can pass to the
networking application programming interface (API) to
use the connection for receiving and sending data.
Sockets are often represented internally as integers.

3. WHAT IS SOCKET?
A socket API is an application programming interface,
usually provided by the operating system, that allows
application programs to control and use network sockets.
Internet socket APIs are usually based on the Berkeley
sockets standard. In the Berkeley sockets standard, sockets
are a form of file descriptor (a file handle), due to the Unix
philosophy that "everything is a file", and the analogies
between sockets and files. Both have functions to read,
write, open, and close.

4. WHAT IS SOCKET?
A socket address is the combination of an IP address and a
port number, much like one end of a telephone connection is
the combination of a phone number and a particular
extension. Sockets need not have an address, for example,
for only sending data, but if a program binds a socket to an
address, the socket can be used to receive data sent to that
address. Based on this address, Internet sockets deliver
incoming data packets to the appropriate application process
or thread.

5. DEFINITION
An Internet socket is characterized by at least the following:
• Local socket address, consisting of the local IP address
and a port number
• Protocol: A transport protocol, e.g., TCP, UDP, raw IP. This
means that TCP port 53 and UDP port 53 are distinct
sockets.
A socket that has been connected to another socket, e.g.,
during the establishment of a TCP connection, also has a
remote socket address.
TCP: Transmission Control Protocol / UDP: User Datagram
Protocol

6. DEFINITION
Client Server

7. DEFINITION
Within the operating system and the application that
created a socket, a socket is referred to by a unique
integer value called a socket descriptor. The operating
system forwards the payload of incoming IP packets to
the corresponding application by extracting the socket
address information from the IP and transport protocol
headers and stripping the headers from the application
data.

8. DEFINITION
In IETF Request for Comments, Internet Standards, in many
textbooks, as well as in this article, the term socket refers to an
entity that is uniquely identified by the socket number. In other
textbooks, the term socket refers to a local socket address, i.e. a
"combination of an IP address and a port number". In the original
definition of socket given in RFC 147, as it was related to the ARPA
network in 1971, "the socket is specified as a 32 bit number with
even sockets identifying receiving sockets and odd sockets
identifying sending sockets." Today, however, socket
communications are bidirectional.
On Unix-like operating systems and Microsoft Windows, the
command line tools netstat and ss are used to list established
sockets and related information.
IETF: Internet Engineering Task Force / ARPA: Advanced Research Projects Agency

9. TYPES OF SOCKETS
Several types of Internet socket are available:
• Stream sockets, also known as connection-oriented sockets,
which use Transmission Control Protocol (TCP), Stream Control
Transmission Protocol (SCTP) or Datagram Congestion Control
Protocol (DCCP).
App
socket
3 2 1
Dest.

10. TYPES OF SOCKETS
• Datagram sockets, also known as connectionless
sockets, which use User Datagram Protocol (UDP).
App
socket
3 2 1
D1
D3
D2

11. TYPES OF SOCKETS
• Raw sockets (or Raw IP sockets), typically available
in routers and other network equipment. Here the
transport layer is bypassed, and the packet headers
are made accessible to the application.
• Other socket types are implemented over other
transport protocols, such as Systems Network
Architecture (SNA).

12. SOCKET STATES IN THE CLIENT-
SERVER MODEL
Computer processes that provide application services are referred
to as servers, and create sockets on start up that are in listening
state. These sockets are waiting for initiatives from client
programs.
A TCP server may serve several clients concurrently, by creating a
child process for each client and establishing a TCP connection
between the child process and the client. Unique dedicated
sockets are created for each connection. These are in established
state when a socket-to-socket virtual connection or virtual circuit
(VC), also known as a TCP session, is established with the remote
socket, providing a duplex byte stream.

13. SOCKET STATES IN THE CLIENT-
SERVER MODEL
A server may create several concurrently established TCP
sockets with the same local port number and local IP
address, each mapped to its own server-child process,
serving its own client process. They are treated as different
sockets by the operating system, since the remote socket
address (the client IP address and/or port number) are
different; i.e. since they have different socket pair tuples.

14. SOCKET STATES IN THE CLIENT-
SERVER MODEL
A UDP socket cannot be in an established state, since UDP
is connectionless. Therefore, netstat does not show the state
of a UDP socket. A UDP server does not create new child
processes for every concurrently served client, but the same
process handles incoming data packets from all remote
clients sequentially through the same socket. It implies that
UDP sockets are not identified by the remote address, but
only by the local address, although each message has an
associated remote address.

15. SOCKET PAIRS
Communicating local and remote sockets are called socket
pairs. Each socket pair is described by a unique 4-tuple
consisting of source and destination IP addresses and port
numbers, i.e. of local and remote socket addresses. As seen
in the discussion above, in the TCP case, each unique
socket pair 4-tuple is assigned a socket number, while in the
UDP case, each unique local socket address is assigned a
socket number.

16. IMPLEMENTATIONS
Sockets are usually implemented by an application
programming interface (API) library. Most implementations
are based on Berkeley sockets, for example Winsock
introduced in 1991. Other API implementations exist, such
as the STREAMS-based Transport Layer Interface (TLI).
Development of application programs that utilize this API is
called socket programming or network programming.

17. IMPLEMENTATIONS
• In 1983, Berkeley sockets, also known as the BSD socket API,
originated with the 4.2BSD Unix operating system (released in
1983) as an API. Only in 1989, however, could UC Berkeley
release versions of its operating system and networking library
free from the licensing constraints of AT&T's copyright-protected
Unix.
• In 1987, the Transport Layer Interface (TLI) was the networking
application programming interface provided by AT&T UNIX
System V Release 3 (SVR3). and continued into Release 4
(SVR4).
• Other early implementations were written for TOPS-20, MVS,
VM, IBM-DOS (PCIP).

18. MY SOCKET CHAT APPLICATION
My application consists of two parts.
• Server
• Client
Explanations are in the codes.
This program coded with C# language.

19. SERVER
Libraries

21. CLIENT
Libraries

23. OUTPUT OF CODES