Waking the dead

Before I made the enthusiastic jump to broadband, I was the proud owner of a standalone PC with a regular dial-up Internet connection. Every now and again, I'd come home after a hard day's networking to find my Windows XP machine up and running, even though I had suspended it the night before.

Odd, eh? I investigated further by consulting the Event logs - these revealed when the machine had decided to come alive. The odd thing was that they were always times when the house was empty. The penny then dropped and I picked up the phone on my modem line and dialled the number for call retrieval. Sure enough, the time of the last call coincided with my PC waking from its deep slumbers.

So it was the modem that was waking up the PC. My ABIT motherboard supported a feature called Wake On Modem - AKA Wake On Ring. A quick tweak of my BIOS setup turned this feature off and my home PC never mysteriously woke from its slumbers ever again.

Wake on Modem is a direct descendant of Wake On LAN, or WOL, a technique that allows a PC to be roused remotely. Unlike Wake On Modem, which doesn't require any special software, WOL requires a program that sends a signal to the network card to make it work.

You might think that WOL is a techie feature reserved purely for network administrators and you'd be almost right. But it's also relevant to the home user. If you have several PCs and still use Internet Connection Sharing, you might want to be able to turn on the host computer from one of the clients, saving you a trip down the corridor.

Or, maybe, if you're accessing your home PC from work, or your work PC from home, you might want to turn it on remotely to get to your files and then shut it down when you're done. So maybe you do need WOL after all (WOL can be turned on easily on most PC cards, see here)..

Magic packets

A magic packet lies at the heart of WOL - a specifically formatted packet that's sent over a network to every network card. The content of the packet allows it to identify that the magic packet is intended for it. If the packet is correctly formatted, the network interface card (NIC) tells the PC to wake up.

There are various formats of magic packet, but the classic AMD version simply consists of the network card's media access control (MAC) address repeated 16 times. The MAC address is unique to the network adapter in the system.

So the Magic Packet wakes only the system targeted for startup. When the network adapter receives and decodes this packet, it sends a power management event (PME) signal to the system that brings it back to full power and boots it up. This is BIOS-level control.

WOL aware of that

Early WOL implementations didn't require an OS that was WOL-aware. However, they did require a computer that was equipped with a feature named Advanced Power Management (APM). APM provided BIOS-based power control.

All current PCs feature the more sophisticated ACPI (Advanced Configuration and Power Interface), which extends the APM concept to allow the OS to selectively control power by individual components. ACPI supports a variety of power states. Each state represents a different level of power, from fully powered up to completely powered down, with partial levels of power in each intermediate state. They are:

S0 On and fully operational S1 System is in low-power mode (aka sleep mode). The CPU clock is stopped, but RAM is powered on and being refreshed S2 Similar to S1, but power is removed from the CPU S3 Suspend to RAM (aka standby mode). Most components are shutdown except RAM S4 Suspend to disk (aka hibernate mode). The memory contents are swapped to the disk drive, and then reloaded into RAM when the system is awakened S5 Power off

ACPI-aware operating systems, such as Windows 98, Me, 2000 and XP, all support remote wake-up. However, they don't support wake from S5 state, only from stand­by or hibernation. In some ACPI-capable computers, though, the BIOS may have a setting that allows you to wake from an S5 state anyway.

A NIC in time

You must have an ATX 2.01-compliant power supply or better, one that provides a 5V standby current, which must be at least 800mA, and an ATX motherboard with a WOL connector. This is to accommodate older WOL NICs that use a tiny cable to wake up the system. Most current motherboards support the PCI 2.2 bus standard which gets round the need for a special cable with the right NIC. Here the wake-up signal is routed through the PCI bus.

Some motherboards can be picky and will only permit resumption from the powered-off state if the NIC is in a particular PCI slot. Finally, the BIOS must support remote power control and the Wake On LAN feature. And, of course, you'll need a NIC which is Wake On LAN-enabled. If your network socket still shows a green status LED after you've shut down computer, it probably supports Wake On LAN.

There are two things to do in order to configure a PC so that it can be awoken remotely: WOL needs to be turned on in the BIOS and on the NIC. To configure your BIOS, you'll need to enter your BIOS Setup. In both APM and ACPI computers, you may find settings for Wake On LAN, generally under the Power Control area and titled "Wake On LAN" and/or "Wake On PME" for WOL commands sent via cable or the PCI bus respectively.

In ACPI computers, if you are using an ACPI-aware OS - such as Windows 2000 or XP - and wish to be able to power up the system from a powered-off state, look for an ACPI specific setting such as "Wake On LAN from S5" and choose to enable it.

To configure your NIC, double-click the Network icon in Control Panel, or right-click on your Network Neighborhood icon and select Properties. Choose your WOL-compliant network adapter from the list, click Configure, and click the Power Management tab.

Check the "allow this device to bring the computer out of standby" tick box. Alternatively, you may find that your NIC already comes with some utility software such as 3Com's NIC Doctor or Intel's PROset, which will let you turn on WOL support.


In order to wake a properly configured computer with WOL, you need a program that can send the proper packets over your network. You can use a number of programs to do this including LANDesk Client Manager, v3.10 or later, by Intel.

This software comes with most WOL-compliant motherboards - at long last you have a use for it. See www.intel.com/support/motherboards/desktop/sb/cs-009032.htm for more details. An alternative is AMD's Magic Packet software. This software is a free download from AMD at www.amd.com/us-en/assets/content_type/utilities/magic_pkt.exe.

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Roger Gann

PC World
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