Definition

• UNIX likes to make all I/O look like file I/O

  • You use read() and write() to communicate with remote computers over the network

  • A file descriptor use for network communications is called a socket

  • Just like files

    • Your program can have multiple network channels open at once
    • You need to pass a file descriptor to read() and write() to let the OS know which network channel to use
    • The system have a file descriptor table

    

• Types of Sockets

  • Stream sockets
    • For connection-oriented, point-to-point, reliable byte streams
      • Using TCP, SCTP, or other stream transports
  • Datagram sockets
    • For connection-less, one-to-many, unreliable packets
      • Using UDP or other packet transports
  • Raw sockets
    • raw IP packet manipulation

Stream Sockets

Typically used for client-server communications

• Client
  • an application that establishes a connection to a from clients
• Server
  • an application that receives connections from clients
• Can also be used for other forms of communication like peer-to-peer

Datagram Sockets

Often used as a building block

• no flow control, ordering, or reliability, so used less frequently
• e.g. streaming media application or DNS lookups