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Measuring your DSL speed is not easy. There are a number of speed test applications on the web (our contribution is here), and your ISP may suggest you try a single FTP download, or multiple FTP downloads.

What to do?

First, no single test is enough to determine the speed
of your line
. The internet has weather, as does your ISP, and the server you are downloading from. Weather can delay delivery, as any postman will tell you!

Once you have concluded, perhaps by comparing others' results, that your speed is not what it should be, here is a check list of things to worry about if you have a DSL line. For cable users, we have an excellent cable FAQ that may help you identify coax noise that could be slowing you down. cable tech faq.

    •Line quality test. If you have not done so already, try one of the two different line quality tests we offer on our tools page. Smokeping is open to all users, the line quality test is open to registered users. Both will show up a noisy line - one that is suffering from packet loss that can interfere with the smooth transfer of data.

    •ISP Weather. Your ISP may be suffering a "brown-out" at the time you tested. Only once consistent slow results, or a pattern, can be established, can you rule out temporary brownouts by your ISP.

    •Internet weather. More rarely, the internet as a whole, at key choke points, can become slow. Perhaps there is a fiber cut, or some router failure. Internet storms such as these rarely last long if they are big. But smaller, more local storms, may be more persistent.

    •ISP Routing. Larger ISPs have many options to route you onto the net, and at times they may be sub-optimal for you or your area. Normally this goes hand in hand with much higher than expected latency than you should expect.

    •Backhaul. Backhaul is the path of your data between you, and your first visible hop. To get to your first hop, your data may have to travel from CO to CO and even be carried across country to get to your ISP. All of this is invisible to you, but poor backhaul routing does result in high latency to your first hop, or worse.

    •DSL Interference. DSL operates across a wide frequency spectrum, and particular ADSL and G.lite, can vary speed downwards in response to noise on the line. There are often no user visible statistics on whether this is happening, and the only symptom is poor performance. Checking around the house for possible sources can sometimes reap rewards of immediate speed gain. Things such as poor house wiring, long home phone cable runs (rather than locating the DSL modem as close to the entry point of the line as possible), or in the case of ADSL, micro-filters of insufficient quality, or being installed backwards, older fax machines, or poor quality phone extension handsets. Even cordless phones and floro lights should be regarded with suspicion. By a process of elimination though, you can determine which if any of these possible problems is the cause of your persistent poor speed.
    One of our users adds: "Using an older NAT box (e.g. a linksys older than 2 years) can dramatically shrink throughput. In my case, direct connect averages around 9Mb while through the linksys I peak around 3Mb"

    •Home alarm systems, installed "in-series" to your phone line, can ruin an ADSL signal. placing them on another run with a filter should be a top priority.

    •Slow computer, USB modems.. CPU can be a factor in speed tests, particular java driven ones. Anything less than a pentium 100mhz CPU, and anything less than windows 98 cannot be trusted with more user-friendly speed tests. Even a basic computer, using command prompt FTP, should be able to outrun even fast DSL lines though. USB modems, particularly ones entirely software (driver) designed, consume CPU, and should also be considered as possible sources of slowdown.

    •Poor or dubious quality ethernet card. Even though the ethernet card is the most simple and proven part of the whole DSL setup, some no-brand type ether cards, especially when paired with doubtful or older ether drivers, can cause an interesting array of performance or other weird problems.. things such as web pages being viewable, but uploading failing, for example, has more than once been traced to a dodgy ethernet card.

    •Card conflicts. Especially with internet DSL modems, interrupt/slot related difficulties with windows and drivers can cause problems that are solved by re-arrangement of cards, or by removal of cards that are not needed. Stripping a PC down to the minimum when testing may quickly identify this as the source of any frustrating problems.

    • Home alarm systems, installed "in-series" to your phone line, can ruin an ADSL signal. Placing them on another run with a filter should be a top priority. This comment is actually the way it's designed to work. It's called 'seizure' - the process of ensuring 100% access to the phone line in the case of an alarm condition. The ideal scenario is to use a POTS splitter so that the phone and internet service is SPLIT before it gets to the demarcation block. This ensures that the alarm is connected to the PHONE side of the line without affecting the MODEM side (connected to the ADSL modem) of the line. This will allow an alarm to still have 'seizure' and also 'share' an ADSL line with an alarm system on the phones, WITHOUT FILTERs. Filters are generally poor quality and fail on occasion, but a pots splitter has much less likeliness of failure or accidental removal. Moving an alarm to an 'extension' defeats the 'seizure' of the telco line invalidating any assurances of reliable transmission. (This bullet point suggested by Jeruvy See Profile)


Feedback received on this FAQ entry:
  • I'm in an apartment block after complaining about slow Internet I'm on a 7 by .5 Mbps contract the internet provider told me all was well up to the junction box at the bottom of the block. In an attempt to prove them wrong I went downstrairs ripped out the wires from the box and hooked up a modem right there and to my surprise I got my 7/0.5. Finally in the apartment I started moving the modem to different a location and found a spot where it performed ok. The problem appears to be have been the location close to the mains fuse box.

    2011-10-08 03:22:46

  • I was having a lot of speed problems with zoomtown so I formated my drive and it worked fine until I installed shockwave flash then dropped like a rock. I use IE and Firefox. IE installed full version of shockwave and that is when my problems came up. I uninstalled shockwave flash and put only the plugin into firefox and my speed went up by a meg on download and has worked great. Maybe this will help someone else. suggested by Corby

    2011-03-11 12:26:19

  • I recently had a slow dsl connection (less than 100kbs when it should have been pver 300kbs) and the ISP kept saying the fault was with my system. I tried all the possible solutions and finally after two weeks called the ISP and complained. They still insisted their susytm was fine (all by remote checks) but when i threatened to leave the phone company sent a rep to my house and he exploned that the port connection at the phone company exchange had cause the problem. He went to the exchange, changed the port connection and everything was back to normal. So don't assume it is your computer when the phone company says the system is fine. Please pass the on - everyone should know about this!

    2008-12-19 15:49:56



Expand got feedback?

edited by KeysCapt See Profile
last modified: 2008-05-04 10:50:06


Also read About DSL for lots more information