Fast Path ADSL/ADSL2

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Forky
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Fast Path ADSL/ADSL2

Post by Forky » Tue Jul 14, 2009 5:51 am

Apologies in advance if this has already been discussed, i searched and found nothing.

As University break set in at the start of July and my next semester will only be part-time, I have started playing my beloved Quake 3 and now Quake Live once again. I think we have briefly touched on this topic in a previous post of mine, but it was more of a side track then a good discussion.

Quake 3 has no hitscan what so ever, and thus you must aim in front of players to hit them. Obviously a difference between interleaved and fast path ADSL is incredibly noticeable here, so......

Lets look at Quake Live (thus, hitscan style games):

Now, I don't really mind what anyone thinks, but I do notice an incredible difference between 50 ping and 90 ping in the ability of the software to predict what has hit and what hasn't. I think it is absolutely no coincidence that my accuracy is ALWAYS lower on a West Australian server even though Quake Live has hitscan style netcode. Thus, I believe there will be a noticeable difference between 9ms and 40ms (the difference in ping I got when moving from Powertel to Optus DSLAM).

I often see people asking how they can lower their ping, the answer is almost always; change to Internode, and I find that disturbing because i know just how much of a ripoff they are. However I have no argument to suggest they move to Exetel. If, this customer is with Internode, then people always tell them they have the option to get on an ADSL1 fast path profile if they raise a ticket with internode (this is if they are on an Optus DSLAM). Obviously, if they are on an Agile DSLAM with Internode then they can change to fast path ADSL2+ without any worries.

So, my question is, does Exetel also have this option to move a customer on an Optus DSLAM to an ADSL1 fast path profile? (obviously an ADSL2+ fast path would be far superior such as what i had on the powertel equipment, but beggars can't be choosers). I think it would be beneficial to Exetel if they can provide fast path options for gamers.

ForumAdmin
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Re: Fast Path ADSL/ADSL2

Post by ForumAdmin » Tue Jul 14, 2009 1:56 pm

I've asked someone knowledgeable to reply.

JasonM

Re: Fast Path ADSL/ADSL2

Post by JasonM » Tue Jul 14, 2009 1:59 pm

Optus profiles do not allow for a "Fast" mode profile, all profiles are "Interleaved" to reduce drop outs.

paulp
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Re: Fast Path ADSL/ADSL2

Post by paulp » Tue Jul 14, 2009 2:08 pm

Hi Forky,

For Optus DSLAM's, all profile's by default are interleaved for stability reasons - however I am checking to see if any possible alternatives can be done

Forky
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Re: Fast Path ADSL/ADSL2

Post by Forky » Tue Jul 14, 2009 3:53 pm

That would be great. I already recommend Exetel to lots of people (in fact I decided to become a lite agent to take full advantage of it) it would be nice if I could add gamers to my list. :)

paulp
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Re: Fast Path ADSL/ADSL2

Post by paulp » Mon Jul 20, 2009 1:23 pm

Hi,

Confirming my original post this option is not available, however from what I have been told, layer 3 would be more of a direct cause to latency issues than layer 2 issues. Below recommends the following as per our supplier's advice;



"Some service providers often asks for Layer 2 services from us (i.e. switched services which can be a variety of deployments - ethernet, fibre, dark fibre... etc.) The main advantage of having these services is that they have low latency because it only involves 2 layers (at the most) on each hop the data goes through. This means less processing = less delay. While this does not affect the bandwidth/throughput, these are important concepts to consider when establishing the needs of a customer, speed wise. I think of these layers as ladders to climb up and down every time it passes a network element. On a layer 2 service, devices involved on the delivery of these services (that may add on to latency) will be a layer 2 device at the most (eg: a switch). Routers generally are slower than a switch (by a few microseconds) but generally have more filtering and smarter capabilities interconnecting networks together.

Going back to the initial enquiry, if we start putting services into fast path instead of interleaving, the data transmissions will be then submitted to errors without any capability of detecting or correcting them somehow. This in turn may result to more delays because the packet will have to time out - if the application even does (dependent on how the application is designed - might just hang), then perhaps get a retransmission done to complete the pending operation, i.e. more delays than that of what we are trying to get rid of. The difference between the 2 is very minimal... and negligible. Personally, I'd rather have a stable service."

- So there you have it, which I have to agree with. I recommend doing a traceroute to see if there is something else we can detect from a layer 3 perspective. Fast-path or not, the changes would be very small, not to mention sacrificing a good deal of stability for miniscule gains in latency(assuming error free transmission in the process).

Forky
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Location: Newcastle

Re: Fast Path ADSL/ADSL2

Post by Forky » Tue Jul 28, 2009 2:48 pm

I have to completely disagree with the above reply made to you.

It is almost non-existent that an application is made to hang upon a packet being lost. Packets are lost with or without interleaving generally along some other path through some other router over the infinite amounts of paths a packet can take over the internet. As an example, I am currently at the parents place, here to install Exetel VoiP in the old man's office, their home connection is 1.5mbit ADSL on a fast path profile (default for 1.5mbit ADSL supplied through telstra DSLAMs). Packets are being lost every now and then, yet, no program I am using here is even the slightest bit affected by the process, no speed is lost (always 160KB/sec) and my ping in Quake Live is completely stable.

This is the same experience i had with Powertel DSLAMs when i was on ADSL2+ fast path. My latency was incredible (9-11ms in game) and my speeds where actually faster than on the optus equipment (thanks to being able to use a 7dB margin). People on this forum always argue that there is almost no difference between the two, which is true for MOST people. However, for a very small minority (i understand that my argument is fruitless since we are such a small minority) the difference is real, and noticeable. As i said above, internode caters to us, however, i would really wish Exetel to do the same, but again, beggars can't be choosers.

I am a Telecommunication Engineering student (only have two maths courses to go... who likes maths?), i do have very limited experience and by no means am i an expert, but i feel that the above reply is a bit of an insult to both yours and my intelligence, or perhaps, understanding on the matter. It seems to be aimed at a year 10 student, and although mostly correct in that context, we all know there is a lot more to it.

Interleaving adds a certain amount of delay (depending on settings) as it waits for, lets say, 25ms worth of packets to come in, and then uses the forward error correction parts of the packets to correct the stream (which i believe is convolutional error correction?). By waiting for more packets, it has more error correction code to use over the stream, please correct me if am wrong, i have pulled this from distant memory.

So to say that interleaving does not add delay is very silly, as that is exactly what makes it tick. In my case it increased my latency to the exchange and thus to Sydney by over 300%.

Sorry for the trouble,
Johnno

EDIT: Just found my notes, and the packets are interleaved before transmission (thus 25ms worth of packets are interleaved together then sent). If burst errors occur during transmission, when de-interleaved there is hopefully only a few bits in each packet that are corrupt and the forward error correction can deal with it. - For anyone who cares.

Dazzled
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Re: Fast Path ADSL/ADSL2

Post by Dazzled » Tue Jul 28, 2009 3:41 pm

I like maths....what (apart from n-dimensional statistics) could be more fun than signal processing in several dimensions of Monsieur Fourier's domain? (I suspect CoreyPlover likes maths too). You are right though, properly written systems are not killed by the odd transmission error, but is it worth dropping interleaving specially for a few quick-reflexed gamers?

Forky
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Re: Fast Path ADSL/ADSL2

Post by Forky » Tue Jul 28, 2009 5:45 pm

Well, that is the question isn't it. Does Exetel want a larger share of the gamer internet market, or not? As i said, i recommend Exetel to anyone i can, i would like to have argument to fight the fast path ADSL internode provides. I make the trade off between ping and price/features, but a lot gamers arn't interested,they just want the lowest ping they can get.

As for maths, i very much do enjoy the Engineering which involves the maths, i do not like doing the maths subjects themselves that never really deal with anything real, and are extremely abstract. I skipped them and learnt the maths as i was doing the engineering subjects which was a lot more useful imo. :)

Dazzled
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Re: Fast Path ADSL/ADSL2

Post by Dazzled » Tue Jul 28, 2009 6:26 pm

You will come to realise that the maths alone are real.

CoreyPlover
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Re: Fast Path ADSL/ADSL2

Post by CoreyPlover » Tue Jul 28, 2009 7:08 pm

Dazzled wrote:You will come to realise that the maths alone are real.
Reminds me of http://xkcd.com/435/

Interleaved vs Fast is not about packets being lost, but rather more robust protection from noise bursts. Meaning that, in some circumstances, and especially at the higher frequencies of ADSL2+ vs ADSL, data transmission is higher (at the sacrifice of latency) under interleaved paths compared to fast paths.

But, that is all academic as Optus doesn't offer fast path services. I reckon that Exetel's target audience are those wishing for low $/GB quotas and low cost VOIP capable services, meaning that Interleaved services cater very well for the overwhelming majority of users. It is a pity though, because as you say Fast path would have catered to those gamers desiring low latency services.

Forky
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Location: Newcastle

Re: Fast Path ADSL/ADSL2

Post by Forky » Tue Jul 28, 2009 9:11 pm

Indeed it is a shame optus do not provide these services to Exetel. The Internode site specifically says they can put people on an ADSL1 fast path profile on Optus DSLAMs, so i dunno whats going on there.

I do feel that Optus is very over conservative with their ADSL2+ setups.

1) you can only connect at 12dB margins which is well above what is generally accepted as stable (being 6 or 7dB)

2) Interleaving connections has the same kind of effect as the above. Both, together, is almost overkill.

jingt
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Re: Fast Path ADSL/ADSL2

Post by jingt » Wed Jul 29, 2009 4:41 pm

ADSL systems support two latency paths for data transmission, the interleaved path and the fast path.
Interleaving uses more overhead for more error correction code, to get more reliability, less errors, less drop outs and less packet loss.
Fast mode has less error correction code in each packet, of course it is more efficienct, but it sacrifices reliability.

I think the reason why optus does not use fast mode is because they are worried about the issue of poor telephone line, long distance to CO, line interference etc. They want to privide reliable service to customer.

Powertel does allow fast mode but Optus only uses interleaving.

Forky
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Re: Fast Path ADSL/ADSL2

Post by Forky » Thu Oct 29, 2009 3:22 am

Sorry to dig up a reletively old thread, but didn't wanna post a new one since this is still related to this thread.

I have finally gotten tired of having an interleaved ping, and being on optus infrastructure... Currently Newcastle users are seeing a 20+ms rise in ping times (55ms), god knows what is going on there, but it happened all through september, was fine during October (32ms) till a few days ago where it has now started again.
jingt wrote:Powertel does allow fast mode but Optus only uses interleaving.
So if i was to move back to a BYO plan (where i had fast path ADSL) and for some reason my connection is interleaved, i can request it to be changed to fast path?

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Re: Fast Path ADSL/ADSL2

Post by NetworkAdmin » Thu Oct 29, 2009 11:46 am

I will see if we get any movement from Optus on the issue.

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