What is Switching? – Definition from Trenovision

Switching

Switching is the process of providing a temporary connection between and incoming line and a particular outgoing line.

  • Electronic switches interpret the dialed number and make the necessary connection.
    • The numbering scheme is hierarchical
    • Ex: 91 – 80 – 2555 – 1234 
  • Most switches in PSTN local exchanges are designed to handle 10000 lines.

Types of switching

  • Circuit switching: Mainly used for voice communication
  • Packet switching: Preferred for data communication
    • Datagram packet switching
    • Virtual Circuit (VC) packet switching
      • Switched Virtual Circuit (SVC)
      • Permanent Virtual Circuit (PVC)

Circuit Switching

Circuit Switching 

  • An end-to-end connection (circuit) is established before communication can begin.
  • The circuit is dedicated for that connection till it is disconnected.
  • Not suitable for data transmission, since data is generally bursty.
    • The circuit utilization will be very low.
    • One has to wait for the circuit to be set up.
  • Therefore data transmission normally uses packet switching.

Packet switching

  • Packet switching does not provide a dedicated connection.
  • Messages are divided into fixed-size packets.
  • Each packet has information about the destination (and sender) in its header.
  • No set-up time needed.
  • Adopts a store-and-forward technique for the transmission.
  • Delay is mainly due to the waiting and processing time at the nodes (routers).
  • Delay depends on the network traffic along the path taken by a packet.
  • Charges are based on the number of packets sent.
  • Network lines are utilization optimally.

Datagram Packet switching

  • The packets of a particular message, going from A to B, may take different routes, depending on the traffic condition when they are being transmitted.
    • Flexibility in taking the best route.
  • There is a possibility of the packets reaching the destination in a different order.
  • Sequence numbers are used to help re-order them at the receiver side.

Datagram Packet switching​

 

Virtual-circuit Packet switching

  • All the packets of a particular message take the same route, which is determined in the beginning.
  • This route is called the Virtual Circuit.
  • The packets always arrive in the correct order.
  • The routing is simpler at the intermediate routers.

Virtual-circuit Packet switching