To circuit or to packet

[keith5]

Cisco teaches that packet switching contrast from circuit switching in that one meathod establishes a dedicated circuit before communicating and the other is implied to splits data into packets routed over a shared network with multiple routes without the initial dedicated ciruit establishment. Further reading seems to show more similarity and overlaps in function. What happens within Circuit Switching networks after the initial dedicated circuit is established, and are there more definitive differences between the two types of switched networks and their functionality?

[Richard Burts]

Brian

Perhaps a slightly different way to look at this is that with circuit switching you have a dedicated infrastructure while with packet switching you have a shared infrastructure. With circuit switching your data, and only your data goes over that circuit, while with packet switching your packets share the infrastructure. And that also means that with circuit switching you pay for 100% of the infrastructure (you pay for it while you are using it and you pay for it while you are not using it) while with packet switching you basically are paying only for the part that you use.

HTH

Rick

[keith5]

Rick,

Thanks for the reply, that really helps. It just seems that if the providor is using Time-division Multiplexing with circuit switching that it takes away from availability of a dedicated network the customer is paying for.

Brian

[Joseph W. Doherty]

As the names imply, packet switching networks switch packets, circuit switching network switch circuits. What's often confusing is how we might run data packets on both but what really matters is what the network topology switches.

Circuit switching networks guarantee bandwidth end-to-end. They also indicate, as you note, when the circuit is established, where packet switched networks just make a best effort attempt. Examples of switched networks include POTS (analog), switched-56 and ISDN. An example of a packet switched network is the Internet.

Because of the critical difference that circuit switching guarantees bandwidth when a circuit is established, while packet switching doesn't, and a bandwidth guarantee can be critically important, packet switching, or similar switching technologies, sometimes layers this onto their networks. Examples might include RSVP and SVCs on both frame-relay and ATM. (PVCs would be equivalent of leased lines, i.e. no dynamic switching.)