oversubscription in ethernet fabric: latency and bandwidth degradation
What levels of oversubscription are common in ethernet fabric backbones in a LAN setup? Let's say each of my Nexus5000 switch ports supports 10 Gbps; does that mean the switch-to-switch interconnect has to be specified to be "number- of-switch-ports" x 10Gbps? I suspect not, but what are the common reduction factors people use?
Also, naively I assume that worst-case I'd get an effective bandwidth of
[ backbone / number-of-switch-ports ]
Is this a reasonable approximation? In this case though, does the switch communicate to the ports and ask them to "talk" slower than 1Gbps? If it didn't then this might mean dropped packets since the switch-to-switch fabric was already full (assuming the switch doesn't have infinite buffers)?
Finally, how does one apply a similar calculation to predicting the latency degradation? If a best-case, tiny-packet end-to-end latency is x usecs how do I predict what it will be after a certain amount of oversubscription in the switch-to-switch backbone?
[sorry for the crosspost; I tried comp.os.networking before but didn't get any leads there!] --
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