Frame Relay <what is it?>

coldbug

LOL..i passed Net+ and still dont understand the meaning of it.
ok..i am studying for MCP and come across on this Frame Relay thing again on Chapter 12 of Sybex, Understanding Remote Access Security

WAN's connection include:
1. T- lines
2. DSL
3. Cable
4. Frame Relay

Frame Relay is a virtual circuit-based switching protocol used to connect devices on a WAN.
It is commonly used with a permanent virtual circuit.

I have searched on the net, but still dont get the picture of it in my head. Can someone explain to me with a good example. What is a permanent virtual circuit?

seuss_ssues

This should do the trick:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm

EdTheLad

coldbug wrote:

Frame Relay is a virtual circuit-based switching protocol used to connect devices on a WAN.
It is commonly used with a permanent virtual circuit.

I have searched on the net, but still dont get the picture of it in my head. Can someone explain to me with a good example. What is a permanent virtual circuit?

A permanent virtual circuit is exactly how it is named, permanent and virtual
The circuit is pre provisioned before data can be sent.FR uses datalink connection identifiers(dlci's), these are effectively numbers used in the FR header to differentiate between different flows of data.So if my router has an ip address mapped to a dlci it means my router will send all information destined for that ip address out the FR interface with the configured dlci. A FR network consists of FR switches, when a FR switch receives a FR frame it looks at the header,reads the dlci and then checks its local database to match the incoming port/dlci with an outgoing port/dlci.So if you want end to end connectivity between 2 routers across a FR switching core you must tell the switches where to send the data, this is done by pre provisioning all the switches along the path with the correct port/dlci pair, the data can now be switched along the same path from router1 to router2 everytime.This path is called a virtual circuit, because you have manually configured it, you must also manually delete it, so it is permanent until you remove it.So it is a permanent virtual circuit.
There is another type of circuit called a switched virtual circuit SVC, this is created from signaling messages between the routers and FR switches, this connection gets established dynamically when data needs to pass between the routers and it can be torn down dynamically when the required data has been transferred.

coldbug

virtual circuit has nothing to do with CSMA/CD or CSMA/CA..is that correct?
are those twos involve in routing issues or just on IEEE standards?

Paul Boz

CSMA/CD is the method which ethernet uses to detect and prevent collisions on a segment.