What does unplugging my DSL modem do?

Question

My Internet connection routinely becomes slow. It still works, but it feels "clogged", and even the maximum speed it intermittently reaches is only 1/10th of the normal maximum speed. speedtest.net actually reports lower download speeds than upload speeds, when it should be the opposite. Verizon tells me to unplug the DSL modem for 30 seconds and plug it back in, and my connection is restored to normal. Chat support said "There is some connection issue from the central office" and couldn't give me any more details.

So what does unplugging the modem actually do? Why does it fix the problem? Is there some other way to trigger the same effect? It seems to me that something must be poorly designed if it requires this, either the modem itself or something at the central office. What kind of network problems might cause issues like this?

(My modem, specifically, is a Westell Wirespeed 2100 (B90-210015-04), which the Internet says is "simply a bridge modem. It does not have a web interface, routing functions, or built in PPPoE. That means you will have to use a PPPoE client from somewhere else.")

Answer 1

What is happening here, is that your modem is slowly desynchronizing from the ISP. This desynchronization causes packets you are sending and receiving to become corrupt, requiring them to be resent, and thus, lowering your speed.

To fix this issue easier, I suggest a simple solution. Get one of those outlet timers that people use for when they go on vacation and want to have lights turned on. Then set it to power the router from, say, 4:16am to 4:15am, so that it is powercycled during a time you're not going to be using it in the first place.

Answer 2

Unplugging the modem forces a refresh from the main server, basically. There's more to it than that, but you are resetting the modem, which causes it to update it's settings from the ISP. The network issues are all going to be on the ISP end, and in that case there is very little you can do as the end user to fix it.

ISP support people are notorious for the modem reset, as well as resetting routers. Also, don't tell them you have a router if you can avoid it (if you do) since they will unconditionally blame the router for the issue. The classic line is "Our signal looks good to the modem, so it must be an issue on your end."

The short answer is, it's an ISP issue and the fix is to get a new ISP. You may have an issue with the actual modem, but it will be hard to convince them to replace it for you.

Answer 3

From Tefus FAQ, section "Some network basics about internet service" :

if Telus has oversubscribed your trunk cable (has too many customers with ADSL on the set of cables going from your place to your ADSL port), then there will be interference between your set of telephone wires carrying your ADSL signal and the signal on the telephone wires of the person next to you in the cable bundle. When this happens, BOTH your ADSL modem and the other ADSL modem slow down until the bit-error-rate decays to an acceptable level. This is completely automatic - you have NO control over this. Now, extend this over multiple connections. As the load on the system imposed by users increases (time-of-day) the amount of interference increases. ALL the modems then start to throttle - quite correctly - so that everyone gets at least as much of the pie as they can get without robbing their neighbour.

Another thing - the higher the maximum ADSL transfer rate, the LOWER the number of ADSL pairs that are allowed in a cable bundle because the higher-frequency-signals used to achieve the higher ADSL transfer rate spread further from your pair than the lower-frequency-signals used for a lower ADSL transfer rate.

So, the result of the above is that if Telus offers high-speed ADSL to everyone - and a cable that has been working fine with an ADSL-pair-density originally set for 1.5Mb/s is suddenly faced with a lot of those people upgrading to 3MB or 6Mb/s, guess what happens? The higher interference caused by the higher-transfer-rate signals causes EVERYONE to slow down, because there are more EXISTING ADSL pairs in that cable than the enhanced or extreme-speed-service can support. And it only gets worse for every customer Telus upgrades from standard to enhanced or extreme service.

Now, please note that this trunk-cable-interference occurs on the Telus side of the demarc. You have NO control over this - trunk-cable ADSL density is a function of decisions made by Telus sales. IMO, from the results being shown, both enhanced and extreme service is massively oversubscribed - and a whole bunch of enhanced and extreme users should be downgraded back to 1.5Mb/s to allow the system to recover stability at that rate.

So it seems like your ISP simply has too many high-speed subscribers on your cable bundle. My guess is that by resetting the router you are restarting the line at its normal speed, then again sliding down the hill as the interference from the other lines starts biting in.