[c-nsp] ASR9k Bundle QoS in 6.0.1

Adam Vitkovsky Adam.Vitkovsky at gamma.co.uk
Wed Jun 8 08:13:29 EDT 2016

> Saku Ytti [mailto:saku at ytti.fi]
> Sent: Wednesday, June 08, 2016 12:49 PM
> On 8 June 2016 at 14:14, Adam Vitkovsky <Adam.Vitkovsky at gamma.co.uk>
> wrote:
> >> But is that really so? Why can't we do this with 100% separated
> >> fabrics with distributed arbiters? The linecard could resend fabric
> >> request if it does not receive reply in n microseconds, to handle
> >> failover with no loss?
> >>
> > We are actually talking nanoseconds here.
> The chassis delay for non-congested packets are in several microseonds,
> perhaps like 10us or bit less. For non-fabric, single NPU boxes can be under
> 5us. But how is this 10us budget distributed amongst lookup, fabric, copying
> etc. No clue.
I think that most of this 10us budget is consumed on r/w from/to memories and then a tiny bit for lookup (if you are doing just pure IP lookup).
If the fabric is meant to be non-blocking the arbitration(fabric routing) has to be negligible (buzz term: line-rate) that is within one tick of the fabric clock-rate the maximal solution has to be found and crossbar programed (I actually think the programing is done hand in hand with each found match) and data transmitted.


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
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