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TOPIC: Difference between circuit swicthing and PVC

Difference between circuit swicthing and PVC 6 years 8 months ago #33383

  • freakhead
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Circuit switching is switching the hardware and dedicating the line through out, where as packet switching is no dedicated hardware.
I think I am missing the basic concept here.
I understand PVC apples for Frame relays for packet switching.
But technically speaking how do they vary? Is it like dedicating a virtual line forever??
But the PVC format goes like DSLAM/SLOT/CARD/PORT right? so how is this virtual? its same as dedicating the whole in right?
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Re: Difference between circuit swicthing and PVC 6 years 8 months ago #33384

  • S0lo
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Good question. PVC (Private Virtual Circuit) looks (acts) like a dedicated circuit (line) to the router/DTE devices at both ends. But it's actually implemented using a packet switched network internally. This is where the word "virtual" comes from. So the bandwidth of the network is really shared.

Now you might ask, "If it's actually a shared packet switched, then where is the dedication part?". In-fact, frame-relay kind of simulates a dedicated line by some thing called a Committed Information Rate (CIR). When you buy a PVC, the ISP/vendor promises you a certain CIR (like 1Mbps or 4Mbps, according to the package that you payed for). Frame-relay packet switching has capabilities that can insure you (almost) always get a bandwidth not less than the CIR, possibly more. When there is a congestion in the network, some packets from subscribers that are exceeding their CIR are dropped. At normal or low load times, frame relay tends to allow more than the CIR.
Studying CCNP...

Ammar Muqaddas
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Re: Difference between circuit swicthing and PVC 6 years 8 months ago #33386

  • freakhead
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I think I understood what you said.
The connection from ISP to the router is fixed (DSLAM/SL/CARD/PR). but from here on its not.
In terms of a telco, the E3/E1 links between DSLAM s and aggregators implement the packet form , where multiple O/P ports from DSLAM are connected to same Aggregator port. hence a control can be imposed here over the data flow.
Thanks for that. :)
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