A socket is essentially a “door” between an application process and end-to-end transport protocol:

2 socket types for 2 transport services:

• UDP - unreliable datagram

  • no handshake before sending data
  • sender explicitly attaches IP destination address and port number to each packet
  • receiver extracts sender IP address and received packet
  • transmitted data may be lost or received out-of-order

  

  • see sample code in slides

• TCP - connection-oriented, reliable, byte-oriented

  • client must contact server → server process must be running and have created socket that welcomes client contact

  • client creates TCP socket and specifies IP address + port number of server process

  • client TCP establishes connection to server TCP

  • server TCP creates new socket for server process to communicate with particular client

    • server may talk to multiple clients
    • source port numbers are used to distinguish clients

    

  • see sample code in slides