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Why does my internet connection slow down sometimes?


Intermittently, my internet connection becomes really slow. The download
speed seems to be OK (650 -700 kbps) but I periodically show a latency period
as high as >3600 ms. My ISP says that is normal but I don’t think they know
what they are talking about.

I used to be with your ISP (the original question called out the ISP by
name), and, well … let’s just say I’m no longer with them.

There are several reasons that internet speeds can vary, but in general I
wouldn’t expect latency (the time it takes for a response to arrive) of over
3.5 seconds.

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Off the top of my head, here are some reasons you might be seeing those
performance characteristics:

  • Activity on your own machine. I suspect this is not the case, but I do have
    to call it out since it could be a biggie. Basically anything else you’re doing
    on your machine that accesses the internet could be adversely impacting the
    speed tests that you’re running. Of particular note are viruses that may have
    planted a spam-bot on your machine. They’ll periodically start sending big
    batches of spam which could certainly affect your apparent internet speed.

  • The quality of your phone line. I ran into this myself some
    years ago. Turned out I had a noisy phone line, that was impacted by water
    seeping into the wires underground. Once the telephone company came out,
    discovered and fixed that, life was good. Even with my more recent T-1
    installation, the technicians had to switch the wires used because of the poor
    signal quality of the originally selected pair.

  • ISP Traffic. Even though your DSL connection to your ISP is dedicated only
    to you, at some point “upstream” it is aggregated with the internet traffic of
    others. Cable users see this most frequently, since their bandwidth is
    not dedicated, but rather shared with their immediate neighbors. If
    there’s something happening to use up all resources after your connection is
    aggregated with others, the impact might well be reduced performance.

  • Traffic at “the other end”. I’m going to assume that you’re seeing a general
    problem across all of your internet connections, but if it’s a problem with one
    particular site or service, the issue could easily be at their end.

  • A poor quality or dying DSL modem. I experienced this as well. Rather than
    just fail outright, I have seen DSL modems die a slow death, and performance is
    often one of the early warning signs.

  • Problems with your own network card or equipment. This needs to be included
    for completeness. One of the things that most ISP technical support people will
    tell you to do is to disconnect everything but one computer from your
    connection, and test it that way. It’s annoying, but there’s a reason: this
    eliminates all of your other equipment, such as routers, switches and other
    computers, from impacting the results. In your case, it would be interesting to do
    exactly that, and then see if the result change if you use a different

Unfortunately, as you can see, there are many places to potentially point the
finger. A good ISP will help you diagnose at least somewhat, or perhaps put you
in contact with the data side of your local telephone company that actually
provides the physical connection into your home. (As an aside, even though your
ISP and your telephone company might share a name that does not mean
that they are the same company, or that even if they are that the two divisions
work well together. Often, it’s just the opposite.)

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15 comments on “Why does my internet connection slow down sometimes?”

  1. Can you say bittorrent? :)

    Perhaps – that really depends on your ISP’s capacity.

    The other scenario we keep hearing about is if you are using bittorrent, your ISP may be throttling you. (In which case I’d switch ISP’s, myself.)


  2. I don’t think it exactly matches the case described here; but, my ISP’s DNS servers were often incredibly slow to respond or failed to respond at all. I switched my router to point to OpenDNS and my web experience is quicker overall.

  3. My internet connection is really slow but I think it is my computer that is doing it. I have Windows 98 and a 100.00 MBPS ethernet connection.
    I must upgrade I think.

  4. Your answer to slow internet experience has helped me with my problem with ATT&T. My DSL slowness is turtleish. My problem is with my lack of knowledge and their support considers me a nut when they try to help me and I do not understand. Keep up the good work, I’m learning.

  5. I’ve just recently changed my ISP but I’m with Betty in that the technicians I speak with don’t seem to understand what I’m saying….maybe it is because I can’t understand their gutteral accents…but what is the solution…???I guess you learn to live with it since changing ISP’s presents another problem???

  6. what did you mean by ISP’s throttling you for using bittorrent? How does that work? I have had an exceptionally good connection until recently when I downloaded a torrent. I know it wasn’t a virus and I haven’t checked the router, but it’s fairly new. Could they be throttling my connection speed because of that download?

    Two things: one, using bittorrent uses bandwidth of course, so everything else you’re doing that also requires internet bandwidth will appear slower while bittorrent is running.

    ISPs are starting to watch for bittorrent usage (they can look at the packets of information being transferred and it’s often clear that they are bittorrent), and will penalize people who use it by intentionally slowing down their internet connection – throttling it.

    – Leo
  7. I have this problem with a workhorse Netgear router. Paying for 20megs from Virgin: get 3.5megs on average. Called Virgin, engineer came round. He said it could ‘be anything’ on MY system…and BTW, Virgin ‘STRANGLES’ the connection speed because they don’t have the capacity to provide the service. (verbatim).

  8. hello, I’m having some issues with brighthouse lately. It seems as if the internet connection is very unstable because every time I ping google, the internet response times varies every packet. A technician came and supposedly “fixed” my issue, but it’s still continueing. (P.S. sometimes the internet’s super fast)

  9. 600 to 700kbps i amazing to me in australia the best Internet connection I’ve ever had is when i signed up on a 1gps which by the time it reaches ‘my PC it’s only 100kbps
    what going on?

  10. Everytime oir son comes to visit and uses his laptop on our wireless cable network – the network stops working. I’ve asked him several time if he is downloading something or playing games etc but he is denying it (not sure if I believe him). It never fails that when he is here our network will stop working several times a day. I’m really curious on WHY and WHAT is he doing or what does he have on his computer that does that to out network.

  11. Hi,
    I am sharing connection with the landlord, but everytime I share, connection slows down, and if I ask him or his sons about this,then they say the connection is ok. I am unable to understand. They have a wireless connection. I do not know what should I do? The connection signal on my computer will always show excellent. Please suggest what could be the reason.

  12. Hello! I have read your article, and, I have to say, I have had the same problems, but I am not sure it is any of the above. I use fiber optics cable and internet, and usually get about 16-18 Mbps. Lately, it has periods of times where it literally slows down to almost 12kbps for up to an hour. My computer shows that there is no problem, and the modem is brand new. We are gamers, and usually have 3 PCs going at once, but before recently, that has NEVER been an issue. And it affects everyone, so we know it isn’t just one computer. We have called our ISP, they have come out several times, but it still seems to persist after a few days.

    It usually happens the same time every night, but I experienced it today after lunch. Apparently our ISP doesn’t know how to fix it, so I am trying to find someone who can shed some light on this.

    If you have any ideas, excellent. If not, I completely understand.


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