1. SOCKET
PROGRAMMING
Presented By :
Divya Sharma

2. Overview What are sockets ? What is file descriptor ? Protocols
Client – Server paradigm
Socket API
TCP(Transmission Control Protocol)
UDP(User Datagram Protocol)

3. What are Sockets ? A socket is defined as an endpoint of communication
Service access point of TCP/IP protocol stack
• between Application layer and Transport layer
A file descriptor that lets an application read/write data from/to the network
Once configured the application can
• Send data to the socket
• Receive data from the socket

4. What is file descriptor ?
Text Terminal
Keyboard
#x sock
#stdin
Program
Internet
#1stdout
Display
#2stden
E.g. cout writes data to stdout #(1)
cin read data from stdin #(0)

5. A socket is a file descriptor that lets an application read/write from/to the network
int fd; /*socket descriptor*/
if ((fd = socket(AF_INET, SOCK-STREAM, 0)) < 0) }
fd = socket(AF_INET,
SOCK_STREAM, 0)) < 0) }
perror(“socket”);
exit(1);
socket returns an integer(socket descriptor)
fd < 0} indicates that an error occurred
Socket descriptor s are similar to file descriptors
AF_INET: associates a socket with the internet protocol family
SOCK_STREAM: selects the TCP protocol
SOCK_DGRAM: selects the UDP protocol

6. Protocols
A protocol is a set of rules of communication. Protocols are the building blocks of a network architecture.
Each protocol object has two different interfaces:
service interface: operations on this protocol
peer-to-peer interface: messages exchanged with peer
Term “protocol” is overloaded
specification of peer-to-peer interface
module that implements this interface

7. Client - Server paradigm
Server waits for client to request a connection.
Client contacts server to establish a connection.
Client sends request.
Server sends reply.
Client and/or server terminate connection.

8. Socket API
Server and client exchange messages over the network through a common Socket API
CLIENTS
SERVER
User space
PORTS
TCP/UDP
TCP/UDP
Kernel space
SOCKET API IP IP
Ethernet
Adapter
Ethernet
Adapter
Hardw-are

9. Example TCP applications
Transmission Control Protocol (TCP)
TCP
Reliable - guarantee delivery
Byte stream - in - order delivery
Connection - oriented - single socket per connection
Setup connection followed by data transfer
Telephone call
Guaranteed delivery
In order delivery
Connection oriented
Setup connection followed by conversation
Example TCP applications
Web, , Telnet

10. Review: TCP Client - server interaction
TCP Server
socket( )
bind( )
TCP Client
listen( )
socket( )
accept( )
Connection establishment
connect( )
Data request
write( )
read( )
Data reply
write( )
read( )
read()
close( )
end – of - file notification
close()

11. User Datagram Protocol (UDP)
Single socket to receive messages
No guarantee of delivery
Not necessarily in – order delivery
Datagram - independent packets
Must address each packet
Post Mail
Single mail box to receive letters
Unreliable
Not necessarily in - order delivery
Letters send independently
Must address each reply
Example UDP applications
Multimedia, voice over IP

12. blocks until datagram received from a client
Review: UDP Client – server interaction
UDP Server
socket( )
UDP client
bind( )
socket( )
sendto( )
recvfrom( )
data request
blocks until datagram received from a client
data reply
sendto()
recvfrom( )
close( )
close( )

13. TCP vs. UDP Transmission Control Protocol (TCP)
One - to - one
Connection - oriented
Reliable
In order delivery
Transmission after connect
User Datagram Protocol (UDP)
One to one or many
Connectionless
Unreliable
Unordered delivery
Transmission with destination address

14. Final thoughts
Make sure to #include the header files that defines used functions
Check man – pages and web – site for additional information

15. Thank You