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Ask Slashdot: What Is an Acceptable Broadband Latency?
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?"
I used to work for AT&T Uverse and over 200ms was enough to get a tech onsite to look at the problem.
First pos... Dammit!
...of the broadband wars. All consumers really seem to care about is faster download speeds, so networks offer it - by munging up their network so much that latency is measured in seconds. With the death of the network engineer, people just aren't educated enough to realize that part of the whole broadband experience is getting your packets sent and received fast, not just your GET or retrieve request getting all the data it asked for quickly. If you have to wait more than a second or two for your requests to even get there, then most people are gonna give up and try somewhere else.
If there isn't a perfectly linear tube filled(emptied?) with hard vacuum between their GBIC and my GBIC, providing the lowest possible roundtrip time(that fiber crap can slow your photons by 30-50%), the connection isn't good enough.
Just where exactly are these 'test servers' in relation to you? What, exactly, was this 'test'? This seems a bit of a worthless test. It's entirely possible your DSL has less than 100 ms latency, but the delay is on the server end or the links in between. This is too vague a scenario to comment on.
My feelings about 'acceptable' latency depend on how much I am paying for it, at what bandwidth, with what level of SLA, and for what purpose.
When you say the word "latency" most tech-savvy folks think about the propagation speed of the technology (e.g. electricity in copper, or light in fiber), and thus assume it's basically proportional to distance.
However, latency comes from other things as well. Serialization delay adds latency, and the lower the symbol speed the more it adds. Multiaccess media adds latency while waiting to transit. Multiplexing anything adds a small amount of latency looking for a time slot.
The biggest culprit? Bufferbloat. This is a term that has been coined to describe the fact that many networking devices have entirely too much buffer. In the best case someone has sized the buffer for the max line rate that device may see (perhaps 25Mbps for your DSL modem, when your link is only 10Mbps), in the worst some misguided engineer thought "more == better" when figuring out how much to buffer, or just didn't care. There are a number of efforts to try and fix this poor situation, http://www.bufferbloat.net/ is the place to start. Basically buffers add latency. A small amount of buffering increases throughput, but beyond that it does nothing but increase latency and generally make the user experience crappy. When the link is full you need to drop packets _quickly_, because that's the signal to TCP to back off. Packet loss is a _good_ thing on a full link.
Try running ICSI's Netalyzr (http://netalyzr.icsi.berkeley.edu/) which will attempt to estimate your uplink and downlink buffering. If you have a "router" in front of your DSL modem it may have some tuning, or "QoS rate shaping" that will help. If it's a device provided by your service provider you may not have access to the settings, and it may simply be configured wrong. With some vendors asking for a different model of device may help, with others, you may be screwed.
The technologies involved should deliver 20ms latencies if properly configured. You should absolutely expect that, but getting them to acknowledge a problem may take latencies over 50ms. If your service provider thinks 300ms is normal, you need to escalate or move to a different provider.
I consider anything past 80ms to be slow for my cable connection (to 8.8.8.8).
I just tested 19,17,18,18
I previous test had a 60 something thrown in. This is via a boring home VPN router, shared connection, but under a dozen, and all light users.
13 hops to 8.8.8.8 from here.
33,34,33,63 to /.
300 is what I get on hotel wifi, or my cellphone (to be fair, on my cell phone it goes up to 1000), as can hotel wifi become unusable, I swear most hotels must have 300+ rooms sharing a T1 line.
Wow, sent an e-mail as suggested when clicking on "use classic" banner, and got a fast response that addressed my msg
Generally 1ms or less.
Pinging one of my servers in co-lo on the other side of London and traversing my moderate-speed (~4Mbps/1Mbps) ASDL only takes just over 14ms round-trip.
Pinging my server in the US gives ~110ms.
Singapore: ~270ms.
Sydney, Australia: ~310ms.
So I can get right round the globe and back in about 300ms, *starting* the trip over ADSL.
Rgds
Damon
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http://m.earth.org.uk/
Pinging DamonHD [794830] with 32 bytes of data:
Rgds
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