Wake On LAN

Wake on LAN ( WOL short ) is a 1995 by AMD in collaboration with Hewlett -Packard published standard to start off a computer via the built-in network card.

System

To be able to wake on LAN ( WOL) use, motherboard, network card and BIOS APM ( Advanced Power Management ) or Advanced Configuration and Power Interface ( ACPI) must support the WOL standard. Computer that supports ACPI, usually provide more opportunities for the use of WOL than those with the older standard APM. The general requirement is for WOL that the network card is still powered by the standby current leg of the power supply with power even when the computer is off.

Magic Packet

The NIC waits for a so-called Magic Packet ( trademark of AMD), the receipt of which the computer is turned on.

The data packet is addressed either directly to the network card or is sent as a broadcast. It contains six times in a row, the hexadecimal value FF; immediately followed by a continuous 16- fold repetition of the MAC address of the network card appears. This content can be packaged in any packet (eg, IP, IPX). There are many software tools (eg etherwake for unix -like operating systems) that can send such packets.

Other WOL methods

Depending on your network card, BIOS, operating system and network card drivers, other methods for waking up a computer are available. For a link Change awakens a computer when the physical network connection is connected or disconnected ( so for example if the network cable is plugged in). The method Pattern Match responds to various directed to the computer data packets ( inter alia by ping) and usually provides that the computer very often awakened. There is also next to the quasi-standard Magic Packet other (older) data formats for the WOL packet.

Configuring WOL

In the ACPI specification is set that WOL a computer from the states S3 (Suspend -to-RAM - STR ) - should wake up and S5 ( Soft-Off), S4 (STD Suspend -to-Disk ). Furthermore, some specific options in the power management of the BIOS and the network card must be enabled in order for WOL can function at all.

Cabling

Initially, a three-pole cable was to connect to WOL communication between network card and motherboard. Its pin assignment is:

In current systems, this cable is no longer necessary, as with PCI version 2.2, the power management events were introduced. The WOL signal and the power supply when disconnected systems go now directly via the PCI slot. For PCI Express was needed from the start, no additional cable. However motherboard and network adapters must continue to support explicitly WOL when this function is to be used.