1. 1 Computer Networks Switching Technologies

2. 2 Switched Network Long distance transmission typically done over a network of switched nodes End devices are stations –Computer, terminal, phone, etc. A collection of nodes and connections is a communications network Data routed by being switched from node to node

3. 3 A Switched Network

4. 4 Switching Nodes Node to node links usually multiplexed Two different switching technologies –Circuit switching –Packet switching Datagram Virtual Circuits

5. 5 Circuit Switching A Circuit is a dedicated (for the duration of the call) communication path between two stations. Circuit switching requires three phases namely circuit establishment, data transfer and circuit termination Must have intelligence for routing Once connected, transfer is transparent Developed for voice traffic (Telephony)

6. 6 Circuit Switching

7. 7 Connection-less (Datagram) Packet Switching Each packet treated independently Packets can take any practical route Packets may arrive out of order Packets may be lost (dropped) Up to receiver to re-order packets

8. 8 Connection-Less Packet Switching

9. 9 Virtual Circuit Switching A virtual connection (not a dedicated path) is established before any packets are sent Call request and call accept packets establish connection (handshake) Each packet contains a virtual circuit identifier instead of destination address No routing decisions required for each packet Clear request to drop virtual connection

10. 10 Switched Virtual Circuit (Cont.)

11. 11 Switched Virtual Circuit (Cont.)

12. 12 Timing Diagrams

13. 13 Virtual Circuit v.s. Datagram Virtual circuits –Packets are forwarded more quickly No routing decisions to make –Less reliable Loss of a node looses all circuits through that node Datagram –No call setup phase Better if few packets –More flexible Routing can be used to avoid congested parts of the network

14. 14 Circuit v.s. Packet Switching