Socket Programming

goal: learn how to build client/server applications that communicate using sockets

socket: door between applications process and end-end-transport protocol

Two socket types for two transport services:

• UDP: unreliable datagram
• TCP: reliable, byte stream-oriented

Socket programming with UDP

UDP: no “connection” between client and server:

• no handshaking before sending data
• sender explicitly attaches IP destination address and port # to each packet
• receiver extracts sender IP address and port# from received packet

UDP: transmitted data may be lost or received out-of-order

Application viewpoint:

• UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server processes

Socket programming with TCP

Client must contact server

• server process must first be running
• server must have created socket (door) that welcomes client’s contact

Client contacts server by:

• Creating TCP socket, specifying IP address, port number of server process
• when client creates socket: client TCP establishes connection to server TCP
• when contacted by client, server TCP creates new socket for server process to communicate with that particular client
  • allows server to talk with multiple clients
  • source port numbers used to distinguish clients (more in Chap 3)

Application viewpoint

TCP provides reliable, in-order byte-stream transfer (“pipe”) between client and server processes.