[j-nsp] QFX10002 as P Router

[Adam Vitkovsky]

> Doug Hanks [mailto:dhanks at gmail.com]
> Sent: Wednesday, April 20, 2016 11:41 PM
>
> MX isn’t a VoQ system. It actually buffers on both ingress and egress
> chipsets. The QFX10K is a VoQ system and buffers on ingress chip. QFX10K
> has 384K VoQs per PFE. In the case of the QFX10002-72Q that would be a
> system total of 2.3M.
>
Well if the only difference between VOQ system and non VOQ system would be buffering on ingress vs buffering on both ingress and egress we wouldn't get far would we.

My understanding is that:
The "VOQ" on ingress module represents BW* capacity of an egress entity**.
And for the above to hold true the system has to run arbitration - and that in turn results in implicit*** back-pressure.


*in correct implementations it should actually represent processing capacity per egress entity which then results in BW capacity as at the end of the day we still need to transport the whole packet body across the system.
**the egress entity could be: a queue, a BW entity (e.g. a 10Gbps entity on a 100GE int with a 10GE breakout cable), a port, a PFE/NPU, a LC.
***implicit back-pressure means the back-pressure is realized as a result of granting access only for what can be processed(and transmitted) per the egress entity.



adam










        Adam Vitkovsky
        IP Engineer

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