Re: T3 Latency

[Paul Bradford <pbradford () adelphia net>]

Charles,
   One thing I have a hard time explaining to some customers is that
latency is one thing....  what does it tell me... it tells me that from
one hop to another things are a bit slow.... the real important thing is
how are you're throughput speeds... I started a thread a while back asking
a similar question... is ping/traceroute a good measurement of throughput
on the link?  the unanimous response was use pathchar or mtr or ttcp which
all give you a better guestimate of how your link is doing performance
wise..

Thanks,
Paul

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Paul A. Bradford CCNA                           Adelphia High Speed Data
Voice: (814)274-6663                            Network Engineer II
Fax: (814)274-0780                              paul () adelphia net
ICQ #6054021                                    pbradford () adelphia net

On Sat, 17 Feb 2001, Charles Scott wrote:

> In response to all the questions below...
>
>   The distance is from Northern Michigan to Chicago, apparently via
> Detroit, which is about 500 Miles without knowing which way the fiber
> really goes. There are I believe more than one SONET ring involved in the
> transport. Also something like 13 cross connects, but no other routers in
> that path.
>   When asked, the provider suggested that the latency was due to the
> router I'm hitting being fairly busy. However, the latency is that same
> when I ping it as when I go through it and it's always 20 ms, nothing
> less. I'd think that if it's a matter of a low priority response issue,
> that the latency would be variable and not be a fixed addition to the path
> times going past the router.
>   OK, here's the funny thing, I have an account on anohter system here in
> town that's also connected via a T3, but is 7 hops to the router that is
> my first hop. When I ping the router that's my first hop from that system
> I get about 22ms for all 7 hops while I get 20ms for just the first hop.
>   I've been looking for any system that would have low latency response on
> the other side of that router, but so far nothing on the other side of it
> is anything less than 20ms.
>   I guess the other question is how much of a marketing liability is this
> going to be for my service. We're spending the money on this line to get
> us the best connectivity we can from up here. Something tells me that some
> dedicated or co-location customer is going to ask me about this latency
> issue.
>
> Still wondering...
>
> Chuck Scott
>
>
>
>
>
> --From Chris
>
> > What distance is it running ?
>
> --From Jeff
>
> You may want to check with the carrier of the circuit and make sure
> that it's taking the path you expect. If it's on someting like a SONET
> ring, it may be riding a much longer path that you would expect.
>
> --From Brian
>
> keep in mind you are pinging/tracerouteing that is aimed at the router.
> ICMP is very low on the routers priority
> list. The major providor's aggrigate router is prob pushing a few loaded
> links. Better test is ping to a idle host nearby off their router.
>
>
> --From Jonathan
>
> With certain routers if they have enough stress, the RTT to the router
> will be larger then though the router.  This has to do with caching
> algorithms the router uses.  Also, some large providers do not have you
> connect directly into a rotuer, but into a switch that acts as a MUX, and
> then they have an OC48 link up to the router.  If that OC48 has been
> oversubscribed you might see latency, though I would hope not that
> consistent.
>
> What does your ISP's install engineer say?  For a T3 that is going less
> then 100 miles, the latency really should be 10percent of what you are
> seeing.