Does the cable modem really need to be unplugged for 30 seconds?
I think Pompomtom is on the right track. Certainly CMOS circuits can remain powered by capacitors for 2 or 3 seconds. Thirty seconds seems excessive for that. It is more likely that the long power-off period is so that the modem back at the cable company can detect the dropped connection and reset itself. When some types of modems connect, they have a handshake protocol in which they select modes and train for optimal speed. Perhaps they want to restart the training protocol and that requires 30 seconds for detection and initialization on the other end.
Cable modems are reasonably low power devices. They are also connected to TWO infrastructures, the cable/internet and the power grid. Resetting/reacquiring IP takes many seconds, and if the modem went off line every time that the power grid got a hiccup, you’d be highly inconvenienced. There is very likely an intentional design feature to bridge short term power interruptions, and the likely nature of this is capacitors. Since the modems are reasonably low power, in order to actually have the modem enter its ‘power up reset’ phase, it first has to run out of power. Where I am, I have a my PC backed up with a UPS. I do not have my cable modem backed up. I get power hits all the time that make my UPS squeak, but never lose my ISP connection. Often, I get several hits in succesion. Never do I lose my connection. QED. On the power up reset, there are several ways of providing this signal. The simplest is a series cap and resistor to V+. When the power is first connected, the node between t
Back in the day when my cable stopped working on a weekly basis, I’d call the cable co. and would be told to hold the modem reset button for 5 seconds…or 10 seconds….or anything up to a minute. Basically different people told me different crap. I suppose it’s a good way of keeping the user on the line without having to talk much, and since the help-desk people get paid by the hour… My cable company has gotten much better, usually the modem stops responding once every few months, at which point I press the reset button as quickly as possible and that does the trick. Of course, like others said it my depend on your modem. Why not try doing an increasing time interval to see how long it takes to make it start working?
I would say it’s bunk as I’ve never waited thirty seconds to power cycle my cable modem. I will pull out the cord and plug it right back in and it works everytime. There’s a couple of reason they might tell you to do this: They are first-level support people who generally have less knowledge of how computers, networking and electronics work than the average cable-modem customer. Newer computer systems have all kinds of nifty power-handling features. On most modern desktops you have to press and hold the power button for five second to get a machine to power off. This is by design, and perhaps they think it’s necessary for everything electronic? In other words, when you call your cable company’s tech support, you’re not usually dealing with the brightest bulbs in the electrical department. Since most problems that come into a first-level queue are generally caused by the keyboard-to-chair interface, they have a script that was written by some management comittee and they follow it exact
