Cable Modem Sleep/Standby Power Requirements

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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


Re: Cable Modem Sleep/Standby Power Requirements wrote:
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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: /

Warren H.

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Re: Cable Modem Sleep/Standby Power Requirements

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.

Re: Cable Modem Sleep/Standby Power Requirements

daveoman wrote:

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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

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

Re: Cable Modem Sleep/Standby Power Requirements

$Bill wrote:
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A couple of less LEDs flickering....

Re: Cable Modem Sleep/Standby Power Requirements

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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.

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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


Re: Cable Modem Sleep/Standby Power Requirements

Gary wrote:

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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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Re: Cable Modem Sleep/Standby Power Requirements wrote:
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Ron Hunter

Re: Cable Modem Sleep/Standby Power Requirements writes:
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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.

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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.

Re: Cable Modem Sleep/Standby Power Requirements

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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