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RMcQ

How do ISP's set your download speeds?

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I'm with Centurylink that sells me 6Mbps ADSL broadband. They say that is all they can provide since I am rural (only 2.5 miles from the central office).  My question is how do they cap the limit by subscriber? I consistently get only 5 out of the 6Mbps that I pay for.

 

Recently their service messed up and Centurylink was briefly giving me an erratic 12-22Mbps download speed so I don't think the old copper lines are an issue. I'm also using the Westell 7500 modem that they gave me years ago. Would the old modem be stealing some speed and keeping me from the 6 that I pay for? How is the speed limit capped? Mechanical? Software?

 

I'm mainly interested in how the speeds are capped.  Thanks...

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Interesting question. There are several ways to do it. Each has less or more merit depending on the goal. Given that an ISP's goal is the  managing speed limits on a per customer basis, and the fact they tend to discuss (and sell) "speed" in terms of bits-per-second, my guess would be they are throttling at the signalling level versus measuring and capping a "byte flow" inside their switching gear. If I am right about that (and that's a big if) then the modem at their end, that your modem talks to, would set the max transmission speed.

I really don't think it would be practical for them to do otherwise.

That's my $0.02

 

 

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12 hours ago, rebrecs said:

Interesting question. There are several ways to do it. Each has less or more merit depending on the goal. Given that an ISP's goal is the  managing speed limits on a per customer basis, and the fact they tend to discuss (and sell) "speed" in terms of bits-per-second, my guess would be they are throttling at the signalling level versus measuring and capping a "byte flow" inside their switching gear. If I am right about that (and that's a big if) then the modem at their end, that your modem talks to, would set the max transmission speed.

I really don't think it would be practical for them to do otherwise.

That's my $0.02

 

 

Throttling at the "signalling level" as you suggest seems to be a pretty good guess going by the graph that I attached.  This is typical of what I get. I just wish they would throttle at what I'm paying for.  It's like buying something that costs $9.50 total, giving them $10.00 and not getting my change back.

 

I have only recently discovered TestMy.net. It's a fantastic service that's being provided and has explained my irritation with Centurylink over the years. It is only recently that the service has become stable where I live (west central Missouri) so I guess they're doing something to improve with the exception of providing faster speeds.  Every Mbps counts in a rural setting.

2019-12-10.png

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RMcQ, yes, TestMy.Net is a great resource. I never see any ads so no telling how they get paid. Possibly selling the test results. Or maybe collecting from the ISPs for a better service resource than they have :-) Who knows.

Anyway, back to the topic, does centurylink have a speed test of their own ? If so, it is likely an Ookla based test. The results of those have to be used carefully, but they can provide an interesting data point. I ask, because you have a 5% middle variance. I spent some time fighting middle variance and it was the ISP Ookla speed test that gave me the hints I needed to finally fix it. When my TMN tests were indicating a high middle variance the ISP test was also bursty. The ISP speed test always returned perfect numbers (i.e. the full paid-for speed) but on its meter I could see the traffic stopping ans starting in bursts, which agreed with the middle variance result on my TMN speed test. My variance may have been greater than 5, and the notes are not handy. I don't know how bad the variance has to be before the bursts can be seen on Ookla. But, i WOULD LIKE TO

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know what happens when you run the ISP test, if you are so inclined. By the way, fixing the middle variance did make a big difference in my overall TMN results, especially on the upload side.

 

sorry for two posts, I hit the wrong button or something while trying to undo the caps lock

 

 

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rebrecs, Centurylink uses Ookla. It looks like they connect me to a server in Kansas City, Mo. to run the speed check which is only 45 miles away. The upload/download results are very close to TMN's but nowhere near as informative. I don't see a spike at the beginning of the downloads by just looking at the speed dial and I don't know what the 2ms "jitter" is that Ookla reports.

 

 

 

2019-12-12 08_30_27-Internet Speed Test CenturyLink.png

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In this context, jitter is a statement of deviation. In fact, engineers/techs who only work on tcp/ip networks will also use the word synonymous with "late packet arrival."

I have never looked at what exactly the n% means but lower is better and I think 2% is probably ok.I saw something about it on Wikipedia, but It gives me a headache to think about it simply due to my objection to the word being used in this context at all. In all other areas of engineering it describes a deviation from a fixed expected rate. I would love to hear somebody tell me how a packet switching network has or ever claimed to have a fixed expected rate. but anyway, that's just me. It likely means 2% of the time, packets arrived later significantly later than the mean. (taking aspirins and guessing)

 

I still think chasing down that middle variance may get you closer to your 6Mbps. Especially since both tests are about 1Mbps off. If you fix it, I bet your upload will jump up too. I'm only saying that because it made such a difference for me.

There are people on here that legitimately know a lot more about this than I do. I'm hoping one of them in particular will come to the rescue.

What kind of router do you use ?

 

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5 hours ago, rebrecs said:

What kind of router do you use ?

 

Westell A90-750022-07 ADSL2+.  It's a 4 port Ethernet/wireless. I have both computers connected by Ethernet. Been using it for years and have the manual in PDF format.  I get the same test results when using wireless, firewalls on or off and making sure nothing else is trying to grab some bandwidth while running a speed test.

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Interesting. So, if their own "blessed test" is a meg off, I think you already have a case to present. I don't know whether you already have <?>

Are you mandated by CenturyLink to use that specific router? I am really not happy to suggest spending money, who the heck wants to do that. But, an ISP only believes one configuration is legitimate when discussing your issues - and that is for your systems to be attached directly to a modem. In your case, you cannot do that since it is all built into one integrated entity. If you were inclined to separate the modem from the switching and Wifi gear, someday, it might be in your interest to do so.

The ISP techs, the kind that come to your house, have a gadget they use to hook to the modem. I would be interested (if it were me) to see what reading that thing produced.

Those gadgets produce all sorts of results, including REAL jitter (not network jitter) based on the clocks in the data stream. They also produce results regarding signal level (usually in db) and they produce results in Mbps !! The thing we want. If you don't have a discrete modem, then having a tech run the gadget is a good idea.

 

In your original post you asked whether your modem could be slowing you down. Maybe. But I think more than likely, if the culprit lies anywhere in the a90-7500, my bet would go on the switch/router settings. I say that because if the modem part of the box were getting transmission errors, they would see it at their end too, and your log would be filling up.

So, service call for tech+gadget, and check all the logfiles.

That's my $0.02

 

 

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If you're 2.5 miles from the "home office" (typically an MDF/IDF - main / intermediary data facility), you are outside the "sweet-zone" of ADSL.

 

Typically, (A)DSL sees maximum throughput at 2 miles or less from a MDF/IDF. Basically, the distance between your demarcation point (modem) and your ISP's closet.

 

You're only half-a-mile outside the sweet-zone, so I would still expect you to see reasonable speeds. That said, you might never see a stable 6Mbps, due to ADSL typically using older, buried phone / Cat3 lines. (Unless CenturyLink ran shielded coax/twinax copper or fiber, which I highly, highly doubt.)

 

The burst you see with TMN is likely because the lines are cool, so there's no electromagnetic field around them. Because ADSL is typically Cat3, it's often minimally (if at all) twisted, unshielded, and poor-cabling, so it's easy for the cabling to build an electromagnetic field that interferes with signal transmission. This field won't exist at an idle, it will only exist when data is being transmitted. Once the field has built up (often as quick as 50-2500ns) it starts creating cross-talk and signaling interference, slowing the throughput you can achieve. (Basically, error-rates go up, and as a result more of your bandwidth is spent on handling those errors.)

 

Unfortunately, without replacing the cabling, your speeds probably can't be improved much.

 

All that said, does CenturyLink offer 5Mbps? If so, I would downgrade to that and run some more testing. If their signaling is wonky, you'll see a similar drop (I would expect either 1Mbps or 833kbps drop when you switch if they have a signaling calculation incorrect). If you don't see a drop, save yourself the money and keep the 5Mbps connection. If you see a drop, document it (now, the 5 vs. 6, and then, the x vs. 5). If you still have a drop, call CenturyLink and explain the situation. I have no idea how well they'll assist you, but they should be able to make other accommodations (provide 6Mbps but bill at 5Mbps, for example).

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16 hours ago, nanobot said:

If you're 2.5 miles from the "home office" (typically an MDF/IDF - main / intermediary data facility), you are outside the "sweet-zone" of ADSL.

Typically, (A)DSL sees maximum throughput at 2 miles or less from a MDF/IDF. Basically, the distance between your demarcation point (modem) and your ISP's closet.

You're only half-a-mile outside the sweet-zone, so I would still expect you to see reasonable speeds. That said, you might never see a stable 6Mbps, due to ADSL typically using older, buried phone / Cat3 lines. (Unless CenturyLink ran shielded coax/twinax copper or fiber, which I highly, highly doubt.)

 

The burst you see with TMN is likely because the lines are cool, so there's no electromagnetic field around them. Because ADSL is typically Cat3, it's often minimally (if at all) twisted, unshielded, and poor-cabling, so it's easy for the cabling to build an electromagnetic field that interferes with signal transmission. This field won't exist at an idle, it will only exist when data is being transmitted. Once the field has built up (often as quick as 50-2500ns) it starts creating cross-talk and signaling interference, slowing the throughput you can achieve. (Basically, error-rates go up, and as a result more of your bandwidth is spent on handling those errors.)

 

Thank you for your explanation. It certainly describes what I am seeing and the possible reasons why. When DSL was first made available at my address they offed three packages; 3/6/10Mbps. 10Mbps is no longer offered. Centurylink customer service keeps saying I should NOT expect to see what I'm paying for due to routing issues which they cannot control, the age of the infrastructure and that I'm very close to the speed that I'm paying for consistently. Then they say upgrades are coming for my area in 2020.

 

If I go into the modem it reports the "DSL signal" that it is seeing. Currently it is 5.8Mbps. I saw 7Mbps once but it's almost always 5.8 and I don't know how often the modem refreshes itself to report the current signal.

 

My original question was to see if I could find out how the speeds are set by Centurylink or any other provider on a customer by customer basis. Now that I have more knowledge regarding this I probably shouldn't be complaining. People that get far less than what they pay for are on more solid ground complaining about it.

 

Thanks again!

 

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On 12/10/2019 at 5:44 PM, rebrecs said:

my guess would be they are throttling at the signalling level versus measuring and capping a "byte flow" inside their switching gear. If I am right about that (and that's a big if) then the modem at their end, that your modem talks to, would set the max transmission speed.

I may need to revise that remark. Lately I am seeing instances of data points on my results graphs that are much faster than the ISP speed limit for my account. What tends to happen it is a bit of oscillation above and below the speed limit, finally  converging on a more or less steady set of data points, and indicating a lot of middle variance. I have not changed anything. This is new. But, it the speed limit was set by setting fixed modem clocks, data would not be able to go faster than the modem speed. Thus, I remain open to the idea the ISP is measuring something else. (queue length/time, or packets / time <?>)

 

I think I will remain open also to the notion that this could be a side effect of the test, or the browsers, or the time-stamping on the systems under test.

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On 12/16/2019 at 9:33 AM, RMcQ said:

 

Thank you for your explanation. It certainly describes what I am seeing and the possible reasons why. When DSL was first made available at my address they offed three packages; 3/6/10Mbps. 10Mbps is no longer offered. Centurylink customer service keeps saying I should NOT expect to see what I'm paying for due to routing issues which they cannot control, the age of the infrastructure and that I'm very close to the speed that I'm paying for consistently. Then they say upgrades are coming for my area in 2020.

 

If I go into the modem it reports the "DSL signal" that it is seeing. Currently it is 5.8Mbps. I saw 7Mbps once but it's almost always 5.8 and I don't know how often the modem refreshes itself to report the current signal.

 

My original question was to see if I could find out how the speeds are set by Centurylink or any other provider on a customer by customer basis. Now that I have more knowledge regarding this I probably shouldn't be complaining. People that get far less than what they pay for are on more solid ground complaining about it.

 

Thanks again!

 

 

When I worked for one of the Tier-1 ISP's (think backbone's backbone) we set speeds by literally establishing a link timing variance.

 

Basically, 6Mbps means we can set the clock-rate on the link to 6Mhz assuming 1 bit per cycle. If we had a technology (like DOCSIS) which could transmit N signals per second, we set the clock rate to desired speed / symbol count.

 

Very basic, very easy to test, guarantees both sides understand what to do.

 

I don't know if that's what CenturyLink is doing, but it's highly likely.

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