Ask Slashdot: What Is an Acceptable Broadband Latency? 396
holmedog writes "A simple question with a lot of answers (I hope). I recently had issues with my DSL broadband at home, and after a month of no resolution, I was told 300ms latency (to their test servers) was the acceptable range for Centurylink 10.0Mbps. This got a shocked reaction out of me to say the least. I would think anything over 125ms to be in the unacceptable range. So, I have come to you to ask: What do you consider to be acceptable broadband latency and why?"
Re:Latency (Score:5, Interesting)
What exactly would he do? Latency is a function of all the hops between you and the other machine. I doubt they're going to reconfigure their network topology for a single user.
Some measurements (Score:2, Interesting)
I do have a 10 Mbps DSL at home with the following ping time statistics:
First hop to ISP over DSL line in Finland: 22 ms
City 500 km away within the same ISP network: 33 ms
International connection to 10 hops and about 2500 km away: 50 ms
International connection over some European countries and over Atlantic to New York (~8000 km): 125 ms
Continuing journey from New York to Tokyo, Japan (lots of kilometers): 300 ms
How far is their test server anyway?
Re:Latency (Score:4, Interesting)
I had AT&T's DSL and did some gaming. I live in Ohio, and the servers were west coast. I typically had 75-100ms latency when the TimeWarner users were complaining about server lag and 500-1500mls latency. When they were down to 150-200ms (good for them), I typically hovered around 50-60ms.
This was 7-8 years ago.
IMHO, 300ms is unacceptable.
My current cable gives me around 100ms average latency with SW:TOR.
To me, "acceptable latency" comes with the type of service, and the distance to the target. This covers my views with servers in the continental US:
With my previous DSL experience, I would be pissed with a DSL service that had 100ms or more latency except at the busy hours
With cable, I expect upwards of 200ms, but the average should be closer to 100-150ms.
With WiFi in the equation, I'd add a bit more, and be surprised if it were less than +50ms, but would still be pissed if it were more than +100ms.
Mind you though, this is from anecdotal experience, YMMV.
How are you measuring latency? (Score:4, Interesting)
The first question I'd have about high latency numbers is how you're measuring them. Lots of devices are pretty slow about responding to pings and traceroutes. (Big routers, in particular, tend to make that a much lower priority than routing packets or doing other useful work, and the ping response comes from the CPU. while the actual packet routing happens in ASICs.) On the other hand, doing a traceroute to some distant site can let you see a bunch of dubious measurements, and the smallest numbers tell you a lot because they're a ceiling on the latency of everything up to that point. I've also seen throughput measurement tools that think sending 18000-byte pings is a good idea, and they're not only hopelessly broken for measuring throughput, they get really entertaining latency results as well. The quick and dirty test is "ping 8.8.8.8" followed by "traceroute 8.8.8.8", which points you to Google's anycasted DNS servers.
Traceroute also gives you some hints about routing - if you're in San Francisco, and your route to google.com is going by way of New York, something's weird with your ISP's peering. (I've seen that kind of thing happen - the user's ISP in Denver had recently moved, so their upstream link to the Tier 1 the user's headquarters used was down for a couple of months until they got a bigger access line built to the new site, and their ISP's other Tier 1 upstream didn't peer with the first Tier1 in Denver, and the San Francisco peering was overloaded back then so they were getting routed somewhere awkwardly far away.) But even so, it's really hard to burn more than an extra 120ms with bad routing unless you cross an ocean. (That's two extra round-trips across North America, or dancing around Europe; Asian users can occasionally get weird routes.)
The next thing to do is be sure you're really really not running anything else while running your latency tests. Jim Gettys's "Bufferbloat" paper is really insightful, and you need to read it (but don't measure your latency while you're downloading it :-) A typical latency problem is that you're trying to download more bandwidth than something on your access line can support (such as your wifi router), so the device buffers traffic, and what you're really seeing is that bittorrent or big http transfer is filling up your wifi to maximize throughput, which is trashing your latency. Or alternatively, you've got something hogging your upstream, making it difficult for ACKs on downstream traffic to get through.
Re:Latency (Score:5, Interesting)
Hi! Thanks for the reply. To put some perspective - I've been troubleshooting this particular issue for ~1.5 months and have done the traceroute to make sure it is their issue and not mine. The 3rd hop hits one of their centers in a major city near me and that is the turning point.
I didn't include this in the original story as I figured it was far to specific to my case.
Re:Latency (Score:5, Interesting)
Hi! Thanks for the reply. To put some perspective - I've been troubleshooting this particular issue for ~1.5 months and have done the traceroute to make sure it is their issue and not mine. The 3rd hop hits one of their centers in a major city near me and that is the turning point.
I didn't include this in the original story as I figured it was far to specific to my case.
Have you tried IM'ing CTL_Joey at the dslreports.com forums? I used to have CenturyLink, and there were always connectivity issues cropping up. He was usually able to have my issues resolved, or at least explain what was going on.