Cable Modem Sleep/Standby Power Requirements

I'm trying to find some information about sleep/standby modes of ANY cable modems (DOCSYS 1.1 at least). I'd like to set up a system that has a minimum of power consumption. From what I've been able to determine, I can't find any modem that has some sort of sleepy mode on the cable network side of the world. They are always "on" and synced up on that WAN side (I assume so they can always respond to some sort of ping of the DOCSYS network.)

I've seen standby modes advertised, but that seems to only apply to some filtering of packets on the PC side.

In my perfect world, the modem would be asleep, drawing minimal power. It would wake up when addressed uniquely from the network head end, establish its connection, and then be available at full power mode. When done with a session, it would then go back to sleep.

Does anybody know of any modems out there capable of this kind of scheme?


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Well, first off, you'd probably find a lot more information if you spelled the acronym correctly. It's DOCSIS, Data Over Cable Systems Interface Specifications. (Last I checked, Interface is spelled with an I, not a Y.) And what you're describing would seem to violate the standard. But more power to you if you can invent something, get it's method of operation accepted into the standards, and then actually get providers to support such an extension of the standards.

If your goal is simply power conservation, you're not likely to raise much interest. Your clock radio is likely drawing more power than a cablemodem in standby mode. I'd put your chance of having something like that adopted at slim to none.

You can start here:

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Thanks for the rysponse.

You mentioned cablemodem in standby mode. Do you happen to know how much power is typically drawn in this mode? I didn't find any mention of this in the standards, so would guess it's manufacturer dependent? I did find mention of standby mode on a couple of cablemodems, but further investigation led to only the filtering of data on the Ethernet/USB side of the device; probably not much a power reduction mode at all.

I'm sure I'm going to have to break down and buy a modem or two and measure the power. Hopefully it just jumps during transmit and is small enough during receive mode.

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SB5100 :

Nominal power consumption for the SB5100 is 9 watts - not something I'd worry about.

Standby mode : There is a button on top of the SB5100 that says "Standby". If you press this button, the modem stops functioning, and is in standby mode. It won't transmit an internet connection anymore. This basically shuts it off without having to disconnect the unit to restart it. If you had pulled the power, the unit would have to go through it's startup procedure all over again when plugging it back in. By putting it in "Standby" you avoid those extra steps.

Note: I doubt standby mode changes the power consumption much (if at all).

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A couple of less LEDs flickering....

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L Alpert


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Ron Hunter

I should have noted that I copied that off a Googled SB5100 page writeup. I can't attest to anything that was said by that provider about standby mode and I should have quoted it. The 'stops functioning' is a poor description I would guess. ;)

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Thanks for the info.

It would be a private network, and communications would originate from both ends. I would also hopefully have control over the frequency of the ARP like packets. Guess that depends on the head end (CMTS?)

Hopefully the transmit and receive functionality can be split up to shrink the power requirements. I doubtful that provides much though.

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Agreed! To answer another poster's questions, DOCSIS 1.x/2.0 say nothing about power consumption. A modem could pull 1,000W and still pass DOCSIS

2.0 certification.

Actually, the standby button the SB5100 doesn't shut it off. It shuts off packet transfers over the LAN interface (Ethernet or USB) and some LEDs. The cable interface remains active and the modem continues to communicate with the CMTS.

The intent of standby mode is to give users a way to "disconnect" from the internet. This way, users can feel comfortable that no malware on their LAN can communicate with the internet. Standby mode may save a few mW of power, but nothing significant.

Now, I haven't seen DOCSIS 3.0 yet, but I wouldn't be surprised if low power modes are in there. With cable companies getting very interested in VoIP, low power is important to manage phone service uptimes during mains power outages.


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ISTR seeing a cable modem PCI card advertised a few months ago. Presumably if your computer went to sleep, the cable modem PCI card would, too.

That description sounds like a rather special case situation, not the typical home user:

1) Requests typically originate from the home user's side, not from the network side. 2) If you're using a dynamic IP address, then a DHCP negotiation will be required to obtain an IP address if you've been off the air long enough, or if the network has decided to reclaim your address for whatever reason. The customer end initiates that, and if you don't have an IP address assigned, the outside world isn't going to be able to address packets to your system. 3) Your system may need to respond to ARP packets from the headend. These aren't "addressed [to you] uniquely", they're broadcast to all sites on the subnet.

Your description sounds more like you want to set up a server with a static IP address to receive data from remote sites. If you're thinking of running an email or web server over a residential cable service, check the cable company's AUP/TOS: some don't allow servers.

Even if all that's not a problem, I think powering down when idle is unlikely to be of much benefit. Between virus and worm probes, spam, pings, ARP broadcasts, and other background "noise" directed at all the addresses in the broadband service address blocks, I suspect the cable modem would be awake most of the time anyway. -WBE

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