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Help me better understand DLCI

Help me better understand DLCI

(OP)
I'm a voice guy that is learning the data side and have a question about frame relay DLCI numbers. I'm trying to determine without a doubt if the DLCI number stays the same along the path to the destination or if it changes/could change from node to node.

My logic and a basic understanding of what I read in numerous books and results of online searches tells me it stays the same for the duration of the virtual circuit being established. I do understand that each end in a 'conversation' uses its own designated DLCI, but I can't seem to find a definitive answer on whether this number stays the same all the way to the other end.

I find many references saying the identifier only has local significance. I just don't know if this means local to each link in the path or to each originating end. I appreciate any assistance in clearing this up for me.

RE: Help me better understand DLCI

As you say DLCI's are typically locally significant, i.e. Site A and Site B have a PVC built between them but Site A may use a different DLCI than Site B. Neither site cares what that the other's DLCI is. It only matters that the customer equipment (Frame Relay DTE) recognises and is configured for its own local DLCI.

The interconnecting Frame Relay swithces provide the necessary intelligence and are responsible for mapping DLCI's from one location to another to create a PVC between 2 sites.

It is possible (albeit it's not that widespread at all) to use Global Addressing. This is where each DLCI assigned to a site is unique across the entire Frame Relay network.

RE: Help me better understand DLCI

(OP)
Thanks KiscoKid.

Forgive my being a little stubborn but I want to make absolute sure I've got this part nailed down. It really does help me to feel more confident working on things when there is no ambiguity on my part as to what I'm doing or talking about.

Can I assume that when source A sends a frame to destination B, source A uses a DLCI of 123 (or whatever), each switch along the way will know what port/interface to send 123 out on when it sees that address?

I was uncertain if that was the case or perhaps when the first switch sees 123 it knows to send it out interface X but then changes the DLCI for whatever reason. The next hop along the way would know the new DLCI as intended to go out interface Y and may change the DLCI as well for whatever reason.

If the DLCI stays the same, then does LAPD or Q.933 inform each switch along the way what interface to send the frame out of so that the PVC can be established?

Thanks again for your time.

V

RE: Help me better understand DLCI

Quote:

Can I assume that when source A sends a frame to destination B, source A uses a DLCI of 123 (or whatever), each switch along the way will know what port/interface to send 123 out on when it sees that address?

The DLCI's are Locally significant, so no thats not correct, the DLCI locally refers to the PVC, which is the map between the 2 DTE devices... At the other end, a different dlci may map the same PVC

UnaBomber
ccnp mcse2k

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