[c-nsp] SLAs on a Gigabit Ethernet link

Adam Greene maillist at webjogger.net
Mon Sep 18 17:23:08 EDT 2006


Hi,

Perhaps this is asking a lot, but if anyone is able to point me in the right
direction or provide some good summary answers, I'd be grateful.

I need to generate a Service Level Agreement for a customer that we're going
to be providing a point-to-point link for. On either end of the link will be
a 3560G. The link will actually be wireless, via Gigabit radios, but that's
not so relevant. We'll be connecting two branches of a Radiology department.
They plan to pass large MRI files between the two locations.

First off, I am trying to figure out how to conceptualize the SLA. Network
availability is a no-brainer (the link passes traffic or it doesn't).
However, the customer wants to be sure that the link is always performing
well, and that the maximum bandwidth capacity of the link is always
available to him.

I'm thinking of making use of Cisco's IP SLAs functionality to monitor any
performance guarantees I may make to the customer.

Some questions:
-    do the 3560G's even support IP SLAs? According to CCO, all IOS supports
it (except for some obscure exceptions), but I don't find any reference to
it in the 3560 configuration guide, and when I grope around on a 3750 in the
lab, the switch seems not to support SLAs ("sh ip sla" is an unknown
command; "ip sla ..." is an unknown configuration command)
-    it seems that the UDP jitter operation could be a good way to get
information about packet loss and latency on the link. However, I'm not sure
that obtaining these values will necessarily enable me to provide the
customer with exactly what he needs. The customer needs to know that the
link supports up to 1Gbps of data traffic (minus any overhead) at all times;
if the customer himself is maxing out the link and I measure latency and
packet loss, the results could appear poor. On the contrary, though, the
link would be doing exactly what it is supposed to be doing: passing ~1Gbps
traffic.

Perhaps one way to approach monitoring of the SLA could be to continuously
graph the utilization of the link and then associate the utilization values
to the packet loss and latency at any given moment. But then it seems that I
would need an algorithm of some kind to determine what acceptable latency
and packet loss are on a 1Gbps link at varying traffic loads.

Does anyone have any tips about how to approach these issues?

Thanks,
Adam












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