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Cisco GSR 12012

For those of you who didn't know, the 12012 is physically 12-slot chassis, however it was originally designed with a 15-slot chassis.

Packet memory carves special virtual queues for each slot to help avoid Head of Line Blocking (whereby the first packet holds up other packets due to destination limitations). This means that when packet memory is carved up during initialisation, it creates 15 virtual queues instead of 12. As it is only supports 12-slots, this leaves queues 13 to 15 unused. (Incidently, there is one additional queue (0), that is used for control packets like updates, keepalives etc).

So my question is:

- Why was the 12012 designed with a 15-slot chassis?

- Why did Cisco not re-design the chassis or 'code-out' the 3 extra virtual queues that are carved for Rx/Tx packet memory?

If you could enlighten me on this one, I would be grateful. Because I think

that it's just a waste of memory to leave them there unused. I can't

understand why Cisco would sell them like this?

Thanks!

D.

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