Socket programming
- 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 #x sock Keyboard #std in s td #1 Display ut o Program Internet #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 User space SERVER PORTS TCP/UDP TCP/UDP IP Ethernet Adapter SOCKET API IP Ethernet Adapter Kernel space Hardw -are
- 9. Transmission Control Protocol (TCP) TCP Telephone call • Reliable - guarantee delivery • Guaranteed delivery • Byte stream - in - order delivery • In order delivery • Connection oriented • Setup connection followed by conversation • Connection - oriented single socket per connection • Setup connection followed by data transfer Example TCP applications Web, E-mail, Telnet
- 10. Review: TCP Client - server interaction TCP Server socket( ) bind( ) TCP Client listen( ) socket( ) connect( ) write( ) Connection establishment Data request accept( ) read( ) Data reply write( ) read( ) close( ) end – of - f ile read() notification close()
- 11. User Datagram Protocol (UDP) UDP • • • • • Post Mail Single socket to receive messages No guarantee of delivery Not necessarily in – order delivery Datagram - independent packets Must address each packet • • • • • 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. Review: UDP Client – server interaction UDP Server socket( ) UDP client bind( ) socket( ) sendto( ) recvfrom( ) close( ) data requ est data reply recvfrom( ) blocks until datagram received from a client sendto() 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
Editor's Notes
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