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Aging Cable Modem Causes Performance Decline

I got my current iMac a couple of weeks before the release of Mac OS X 10.7 Lion last year — in fact, Lion was the reason I decided to upgrade from my 2007 model iMac. As a registered Apple developer, I was eligible to download the golden master candidate of Lion a couple of weeks before release, and as someone who writes about technology I felt it was important to learn as much as I could about it as soon as I could. I also knew that my old iMac was reaching the end of its supported life, and that a number of Lion features (such as AirDrop) would not be implemented on it. So I migrated my Snow Leopard installation from my old iMac to the new one, and then downloaded Lion and installed it over Snow Leopard.

As with any migration and upgrade, some things felt snappier, and some didn’t. Overall, though, the performance of the new software on my new iMac was pretty good, but, at that time, I wasn’t so much interested in performance tests and specs as in learning the various new features and exploring the interesting idiosyncrasies of Lion. But gradually I began to notice a certain sluggishness. Web pages took just a little longer to load; videos seemed to buffer more often than before; Dropbox files seemed to take just a little longer to sync. It wasn’t so much as to be alarming, just a little annoying.

At the time, I chalked it up to the early version of Lion not being fully optimized, coupled with various digital detritus that had made its way onto my new iMac from my old one. I made a note that I would, when I had the time, take a look into Joe Kissell’s “Take Control of Speeding Up Your Mac” and see if I could track down what was making my shiny new iMac behave like it had a mild case of arthritis.

Of course, when it comes to dealing with housekeeping chores like that, there is usually something more urgent, or more interesting, to do. So I just kept putting off any serious attempt to fix things, especially since things weren’t really broken, just sluggish.

The slowness problem got worse. But it did so gradually enough not to make me take action. When I did think about it at all, I thought maybe it was my ISP being overloaded: I had noticed a steady lengthening of my AirPort menu as more and more neighbors activated more and more wireless access points around me, and I knew that cable modem connections were apt to show slowdowns as local usage and congestion increased. Besides, I had articles to do, as well as books to write and edit and help produce.

Then came the first TidBITS Presents event (see “Watch Joe Kissell and Adam Engst in TidBITS Presents: Adieu MobileMe,” 16 June 2012). Adam had asked me to lurk in the background and monitor the presentation, notifying him via a separate chat window if I spotted any problems. I was unable to do so: my link to the presentation kept losing sync, or freezing, or just being dropped. Finally, it was time to do some real investigation into my slowdown issues, about the same time Adam was experiencing his own bandwidth-related problems (see “Are You Getting the Bandwidth You’re Paying For?,” 11 July 2012).

The first thing I did was fiddle with the Wi-Fi channel my base station was using: I figured that with so many base stations sprouting up around me, maybe I should move to a non-default Wi-Fi channel where I might expect less congestion or interference. Doing that seemed to make things snappier when I restarted everything, at first, but the slowness soon (and by soon, I mean within hours) recurred.

Then I powered everything off, disconnected my base station, and connected my cable modem directly to my old iMac: the Ethernet cable wouldn’t reach to my new iMac, and besides, I wanted to see if it was the Lion installation that was the issue (my old iMac was still running Snow Leopard). Again, the slowness was somewhat alleviated, but only temporarily, just like it had been when I fiddled with Wi-Fi channels. I reconnected my base station and went back to my Lion-equipped iMac.

On my iMac, I went to, ran the test, and saw that I was getting roughly 1.5 Mbps on downloads: about twice what I used to get with DSL years earlier, but well below what I was paying my ISP for. Finally, I made the phone call to my ISP to complain.

Over the phone, the technician ran a test or two and claimed that the cable modem seemed to be working fine. He instructed me to disconnect my base station, and to connect via Ethernet directly. I told him I had done that and didn’t want to crawl beneath my desk and fiddle with cables again. He said he really couldn’t help me, since the problem was probably at my end, but, after I complained more insistently, he reluctantly scheduled a service appointment for me for later in the week.

When the next technician arrived, he took one look at my cable modem and said, “I’ve seen this before.” According to him, the ISP had been delivering this particular model of cable modem to customers along with a power supply (a typical wall-wart-type transformer) that delivered just slightly more voltage than the modem required. This power supply apparently caused those modems to generate slightly more heat in operation than was optimal, and it caused the modems to fail gradually over time as internal components began to emit extra radio frequency noise — static, in short — that caused packets to drop and be resent. It all sounded somewhat specious to me, but it did seem to explain the gradual performance decay. What’s more, when he swapped out my old modem and power supply with a different modem, I suddenly had ten times the downstream bandwidth that I had been getting earlier.

To this day, I don’t know if it was indeed overheating or something else that caused my old cable modem’s performance to degrade slowly, but the cable modem, for whatever reason, really was the cause of my bandwidth woes.

I learned several things from this:

  • Deal with technical problems as soon as you notice them, since they seldom, if ever, heal themselves, and the longer you wait, the harder it can be to remember salient details.

  • Don’t assume it’s software causing the problem: it often is, but not always — hardware can fail, too, and sometimes not so catastrophically as to be obvious.

  • And, in the case of network issues, don’t be afraid to call your ISP and be firm with them — sometimes a simple phone call can resolve a seemingly intransigent problem.


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Comments about Aging Cable Modem Causes Performance Decline
(Comments are closed.)

Adam Bell  2012-08-19 18:59
I have shared this experience. In my case, I took the modem into my ISP's local office and asked if there was anything wrong with it. There was -- it was too old. I traded it in on the spot and my problem with slowdown were solved.
Alan Forkosh  An apple icon for a TidBITS Supporter 2012-08-19 20:44
Good one. Excellent advice. I'll look into mine now. It is also a good idea to upgrade one's wireless router periodically if one is used.
The same issue happened to me few years ago. It too was running too hot. I forgot the brand of the modem. It wasn't Motorola.
George Chase  2012-08-19 23:51
Those symptoms are awful similar to my experience that turned out to be my HP drivers on 10.8. When I unplugged the printer from the iMac, all was fine again.
heavyboots  2012-08-20 14:41
As to point 1, dealing with technical problems as soon as they occur, cable modem degradation is one of those ones where I'd almost disagree—you have to wait for it to get bad enough that the service tech who comes out can truly acknowledge that there *is* a problem.

If he doesn't, some cable co's will charge you for the visit and/or you can develop a reputation for crying wolf with them.
Michael E. Cohen  An apple icon for a TidBITS Staffer 2012-08-20 14:46
In my particular case, the technician didn't even have to run a test. He had seen problems with that same type of modem many times before. And, when he did run his test, he saw an incredibly low signal-to-noise ratio. I suspect he would've seen a low signal-to-noise ratio even a year earlier, about the time I began to notice the slowdown.
Glantz  2012-08-20 20:20
I may have the same problem. What brand modem was faulty?
Michael E. Cohen  An apple icon for a TidBITS Staffer 2012-08-20 23:41
To be honest, I don't recall. Sorry. It's whatever Time Warner was handing out in Santa Monica a few years ago.
Adam Engst  An apple icon for a TidBITS Staffer 2012-08-21 08:53
My experience is that the cable companies use a variety of different brands all the time, sometimes to enable different service packages, and sometimes just because it's what they have around. Apart from asking for a DOCSIS 3 modem, I've never heard of people worrying too much about the particular brand. If you have an old modem and aren't getting the bandwidth you're promised, just call and ask for a new one.
I have a DOCSIS 2 cable modem. I researched into the difference between it and DOCSIS 3. I was sur-prised that the new DOCSIS 3 standard does not necessarily help increase speed unless your provider supports what DOSCSIS 3 does AND you need more upload speed. Otherwise, the difference between 2 and 3 is basically nothing.
So those that gained speed from 2 to 3 did so because of the service their provider offers that works with 3. Dumb luck.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2012-08-25 12:07
There's another factor, which is that some DOCSIS 2 modems have slow processors or don't do a very efficient job. In some cases, switching to DOCSIS 3, which includes backwards compatibility, can increase performance.
Michael E. Cohen  An apple icon for a TidBITS Staffer 2012-08-21 10:02
Perhaps as an oblique homage to the nearby Leo Carillo State Beach, Time Warner in Santa Monica replaced my old modem with a Cisco. ("Oh, Pancho!")
Dave Price  2012-08-20 22:02
Ever since I upgraded to a DOCSIS 3 modem my speeds have exceeded what I'm paying for. The old DOCSIS 2 modem didn't have what it takes.
If you are running a DOCSIS 2 modem, you really should upgrade to DOCSIS 3 with channel bonding. A call to your cable operator or a google search will fill in the details.
Norman Stoehr  2012-08-21 08:22
Time Warner Desert Cities sent a technician out after trading modems did not solve the problem. He found mucked up cable wiring in my house, which he had also seen before. It took him an hour to fix it, and it's been wonderful since.
MaxumJohn  2012-08-21 10:02
As a support person for an Internet server (Rumpus FTP), I can verify that this is a very common problem, and isn't restricted to one brand of cable modem. I've seen diminishing performance and steadily worsening network problems with a variety of cable modems, hubs, routers, Ethernet adapters and even cables. It would seem that a network device would either fail or work reliably, but they can steadily deteriorate and I've seen it dozens of times. If you are having problems, check each component of your network, one device at a time, even your cables.
Hank Roberts  2012-08-21 21:12
Yup. Happened to me with a router, and with a DSL modem. Both known failures with age.

Someone told me long ago that most problems with semiconductors aren't sudden complete failure but slow creep out of spec -- the "semi" part drifting toward either the "conductor" end or the dead rock end of the scale, where all the various parts are specified to have their "semiconductor" behavior change in a known narrow range.
Robert Bononi  2012-08-27 15:57
This article is confirmation of what I recently went through in upgrading my router. I am a Verizon customer and my router was the original model Actiontec that was installed about 6 or 7 years ago. I guess that I complained enough to customer service that they sent me the newest "GigE" model Actiontec router. The computer that is hard-wired into this router is lightning fast but my Netflix streaming (a few rooms away) via my wireless Blu-ray player isn't all that much faster than it was before. My next step will be to hard-wire the Blu-ray in an attempt to capture some of the newfound speed. You can bet I won't wait another seven years to upgrade my router.