Quick Question: We just installed a T3 from our 7204 to a major backbone provider and I'm seeing 20 ms between us and them when I ping right from our router to theirs. I also see it consistanly for that hop on traceroutes to and from us. That seems to be rather a lot of latency for that line. The thing that bothers me is that it's a consistant 20 ms when the line isn't loaded. Any thoughts? Chuck Scott cscott@gaslightmedia.com
What distance is it running ? On Sat, 17 Feb 2001, Charles Scott wrote: | | | Quick Question: | We just installed a T3 from our 7204 to a major backbone provider and | I'm seeing 20 ms between us and them when I ping right from our router to | theirs. I also see it consistanly for that hop on traceroutes to and from | us. That seems to be rather a lot of latency for that line. The thing that | bothers me is that it's a consistant 20 ms when the line isn't loaded. Any | thoughts? | | Chuck Scott | cscott@gaslightmedia.com | | | | --- Rev. Chris Cappuccio -=- http://www.dqc.org/~chris/ "If you don't turn on to politics, politics will turn on you" - Ralph Nader
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.
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 /////////////////////////////////////////////////////////////////////////////////////////////////////////// A little nonsense now and then is relished by the wisest men. -- Willie Wonka \ 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.
On Sat, Feb 17, 2001 at 11:00:33AM -0500, Paul Bradford wrote:
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
That is an important thing by itself. While throughput is nice too, latency, and to the same extent jitter control, are important to many real time application users (e.g. gamers are a big category right now). David Reed put it nicely when he said: http://www.contextmag.com/archives/199907/TheGreatLie.asp John
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