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Rokk

@unitedgrain.ca

DSL and Cable Latency

I have read that latency is based on physical distance but some people also say that there can be other factors like connection tuning that can help bad latency? I just want to gather peoples thoughts on this. I get a 42ms first hop with my ADSL connection and am getting a 29ms first hop with my cable connection. I would like to know if there are any remedies for this before I seriously start talking to the ISP providers. I have called a couple times now but I'm just getting 'Level 1' support. I mean the guy asked me what Linux was. If it can't be fixed I'll drop it but if there is a chance to get it better I'll keep pushing til I get someone who knows what they are talking about. Thanks I appreciate any info I can get on this.

James


drslash
Goya Asma
Premium
join:2002-02-18
Marion, IA
Who is your DSL provider? As of now, some DSL providers use interleaving. Interleaving adds a base time delay that cannot be overcome. For example, Qwest has a 32ms interleave, so no matter what, there is a 32ms of latency in addition to the other factors that add to latency. In either case of your DSL or cable, the providers are going to say that the latency is in the acceptable range. On the other hand, that does nothing for your gaming performance, if that's what your doing.
--
Save water...drink beer!


Rokk

@unitedgrain.ca
reply to Rokk
I use Telus for ADSL and Shaw for cable. On the Telus I have a Counter Strike server going otherwise it wouldn't be too much of an issue. Though it is still irritating


PetePuma
How many lumps do you want
Premium,MVM
join:2002-06-13
Arlington, VA
reply to Rokk
You talk about getting something fixed, but frankly those latencies, while not great, are not bad.

Latency could be caused by interference at your end:
»/faq/5322

However, given that your pings aren't that high, my guess is that you are just seeing the physical limits of your connections between you and your ISPs backbone.


drslash
Goya Asma
Premium
join:2002-02-18
Marion, IA
reply to Rokk
A search over in the Telus forum on the word 'interleave' produced not matches. It is safe to assume that Telus does not use interleave on their connections.

By the nature of your question and the not too bad latency figures, I pegged you as an online gamer. I am not a gamer but I understand the gamer's mantra "You can never have enough lack of lag"
--
Save water...drink beer!


Rokk

@unitedgrain.ca
Ya but its frustrating to see that the first hop is more than all the other hops in the route combined. I can get to another server in 65ms and 10 hops and 42ms of that is my first hop. It just seems wrong but if that is how it works. That is how it works. Most the people I talk to are in that 8 to 14ms first hop and all of them are under 20ms. Which makes me wonder if there are other issues besides my distance from the CO. Most importantly can there be other issues? Lines? frequency? That is mostly what I am looking for.

James

grapeape69ca

join:2001-12-12
Winchester, ON
reply to Rokk
I used to have a telus connection. I was getting similar first hop latency to yours. I kept pestering telus until they got me in touch with someone who actually knew what was going on. It took him 2 minutes with me on phone to 'dial in' the connection (frequency adjustment from the switching station???) and my latency dropped from ~40 to ~15.

There are many factors that can affect your latency, but I'd keep pestering telus until they at least test your connection from their end, and hopefully by a knowlegable tech.


Rokk

@unitedgrain.ca
reply to Rokk
BTW, thanks I really appreciate the help. If you want to take a peek the domain is wolverine.burninghusk.com

James


whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9
reply to Rokk


Picaso

join:2003-01-23
Beverly Hills, CA

1 edit
reply to Rokk
Distance to the CO has nothing to do with Latency. If the assumption here is that the time it takes DSL signal (electricity) to travel is going to be noticable between 5,000' and 12,000'..there are some serious misconceptions.

Latency is a measure of processing time over a device(router/DSLAM/Switch/Bridge/etc), simply how long it takes for a device to transfer incoming electrical/optical signals from one interface to another. A router is simply a specialized PC. What happens when a PC has to many things going on? It slows down...

Your issues revolves around your first Hop, the first hop is the accumulated delay between "YOU" and the next layer 3(IP)device. What does your latency look like when there is no activity from outside sources (Gamers)? The delay itself could simply stem from your PC's inability to process ethernet frames. Now I am not saying that is the issue, it however is often the most overlooked culprit.

"You can tell if interleaving is active on your line by measuring the first hop ping. If it is under 20ms, interleaving is disabled. If it is above 45ms, interleaving is enabled."

BS-- Interleaving is variable setting, depending on the amount of error correction needed. True most manufacturers have a default setting but it is defenantly configurable. So if your provider is using a low level of interleaving it may only add 1 or 2 ms at best and do very little to stabalize your line. Also 45ms to the first hop does not mean interleaving.. it means there is delay from some factor, interleaving is just one possibility.

Good luck...


Rokk

@shawcable.net
reply to Rokk
Thanks I may need that good luck. With the latency issues the CS server is up but not being used so it is 'sleeping'. It has over the last 6 months been in that 39-44 ms range though the first tests were done on an XP system and this one is Linux. I'm not sure if there is a difference. I'm not using a router on this box but in my other network I have a router and it was usually adding 1 to 2 ms when I check with and without it. I do know I don't know enough about how the process works to know if there can be an improvement. Maybe Grapeape69ca is right and I keep pestering them until they prove to me that it can't be improved. Its just a lot of tedious whining if it turns out that there isn't much they can do. So I thought this would be the place to ask. It sounds like my first hops is at the high end of tolerable but I sure know quite a few people that are quite a bit better than I am and I sure would like to be among that group. I read the latency vs bandwidth thread and traceroute might not be the best way to check latency(??). Is there a better way? Thanks again guys.

James


Rokk

@shawcable.net
reply to Rokk
Sorry I got the traceroute thing out of a thread from "what pings to expect"


whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9
reply to Rokk
quote:
You can tell if interleaving is active on your line by measuring the first hop ping. If it is under 20ms, interleaving is disabled. If it is above 45ms, interleaving is enabled.
As Picaso so poignantly pointed out, blanket statements like this are simply wrong. Latency is the total result of interleaving, processing delays, and physical distance. Of course, the differences in physical distance delays whether we are talking about 1000 or 20000 feet, are both negligible. (The physical delay over a dsl connection of 20,000 feet is approximately 0.02ms.)

The physical delay is only really noticeable when you look at transcontinental, transoceanic or satellite link ping times. For example, going coast to coast in the US will add about 16ms of latency due to the physical distance alone. The up and down physical delay through a geosynchronous satellite will add a minimum of 242ms to the latency.

So, for all intensive purposes, the physical delay from your DSL or cable modem to the CO (central office) or DSLAM will have no bearing on the first hop latency. The real factors then, in your first hop latency are merely processing time, and interleaver depth.

Note of course that interleaver depths can add a lot of latency to your connection. Depending on the interleaver depths, the interleaving process can add anywhere from 0.15ms to 40ms or more to your latency. With HFC (hybrid fiber coaxial) cable internet, interleaving may add 0.22ms to 4.0ms of delay to your first hop latency. See this link for a chart from the DOCSIS RF specifications with exact interleaving depth vs. latency specifications for HFC cable internet systems: »[DSL] Changing Interleave to Fast-Track .

As far as interleaving depth vs. latency specifications go for ADSL, the exact delays are different in the various implementations (G.Lite, DMT, etc.), and for varying sizes of interleaver depth & block size. Typically when a carrier sets up a DSLAM, they set a parameter called 'maximum interleave delay' for each of the upstream and downstream paths. The modem and DSLAM then set the interleaver depth and block size according to other parameters, but in a way so that the maximum delay is not exceeded. IOW, the carrier sets the amount of delay. Likewise, the carrier may set the equipment up for 'fast' or 'fast-path' mode, meaning no interleaving is used for forward error correction. In general, carriers set the maximum delay somewhere between 20ms and 40ms. The interleaving induced delay, of course, is added to the variable processing latency to determine the total latency of the first-hop.

I found a good explanation of ADSL interleaving vs. latency from: »www.dslforum.org/aboutdsl/tech_faqs.html
quote:
The latency between the customers ADSL modem at the ADSL line card in the CO depends on the line coding technique and the interleaving depth of the error correction scheme. The interleaving depth can programmable up to latency of the order of 60 ms but is typically set to around 20 ms. This offers greater protection against impulsive noise and thus improved BER. Hence there is a latency/interactivity versus error performance trade-off. With the interleaver turned off the residual latency of standard ADSL is 2 ms. Some other modulation schemes can achieve less than this. Other parts of the system and ADSL above the physical layer must also be accounted for, e.g., ATM SAR function, router throughput, etc. ADSL delay time is variable and depends on the interleaving that is programmed. It varies from 2 - 20 msec each way. Hence worse case round trip delay added [due to interleaving] would be 2 x 20 msec = 40 msec.
If latency is your primary concern, you can ask the carrier to turn off interleaving for your ADSL circuit. Sometimes the proper terminology to use is to put you on 'fast-path'. Realize however, by doing so you will lose most of your ability to correct any bit errors due to impulse noise. This will result in a lower data rate, and more packet re-transmits. Worst case, for example if you are at the extreme end of serviceable distance (18,000 feet or so), your bit-error-rate may be so high that your ADSL connection may not work at all. It is possible that your carrier will not accept your request if this is likely to be the case. If you are not a gamer where latency is crucial, there is nothing to gain by doing so. In fact you would be doing yourself a disservice, because you are will only lower your data rate.