Wake on LAN
Wake on LAN ( WOL for short ) is a standard published by AMD in 1995 in cooperation with Hewlett-Packard for starting a computer that is switched off via the built-in network card.
System requirements
To be able to use Wake on LAN (WOL), the main board , network card and BIOS APM (Advanced Power Management) or Advanced Configuration and Power Interface (ACPI) must support the WOL standard. Computers that support ACPI usually offer more options for using WOL than those with the older APM standard. A general requirement for WOL is that the network card continues to be supplied with power via the standby branch of the power supply unit, even when the computer is switched off.
Magic Packet
The network card waits for a so-called Magic Packet (trademark of AMD), upon receipt of which the computer is switched on.
The data packet is either addressed directly to the network card or is sent as a broadcast . It contains the hexadecimal value FF six times in a row ; Immediately thereafter, the MAC address of the network card of the respective target system is repeated 16 times without interruption . This content can be packaged in any package (e.g. IP , IPX ). There are many software tools (e.g. etherwake for Unix-like operating systems ) that can send such packets.
Other WOL methods
Depending on the network card, BIOS, operating system and network card driver, other methods are also offered to wake up a computer. With a link change , a computer wakes up when the physical network connection is established or disconnected (for example, when the network cable is plugged in). The Pattern Match method reacts to various data packets sent to the computer (including via ping ) and usually ensures that the computer wakes up very frequently. In addition to the quasi-standard Magic Packet, there are other (older) data formats for the WOL packet.
Configure WOL
The ACPI specification stipulates that WOL should wake up a computer from the idle states S3 (Suspend-to-RAM - STR), S4 (Suspend-to-Disk - STD) and S5 (Soft-Off). In addition, appropriate options in the power management of the BIOS and the network card must be activated so that WOL can function at all.
cabling
Initially, a three-pole cable had to be connected between the network card and the mainboard for WOL communication. Its pin assignment is:
| Pin code | Surname | function | colour |
|---|---|---|---|
| 1 | + 5VSB | 5 V standby voltage | red |
| 2 | GND | Dimensions | black |
| 3 | WOL | Wake-on-LAN signal | green or yellow |
While the plug connection on the motherboard side is standardized, there are also different connections on network cards. With current systems, this cable is no longer necessary, since the power management events were introduced with PCI version 2.2 . The WOL signal and the power supply when the systems are switched off now go directly through the PCI slot. Right from the start, no additional cable was required for PCI Express . However, the mainboard and network adapter must still explicitly support WOL if this function is to be used.
Web links
- AMD: Magic Packet Technology Whitepaper Rev. A (1995) (English, PDF; 37 kB)