System Requirements - Pc Compatible; How Wol Works; Magic Packet - Advantech ARK-3440 Series User Manual

C.2.2

System Requirements - PC Compatible

Wake on LAN (WoL) support is implemented on the motherboard of a computer.
Most modern motherboards with an embedded Ethernet controller support WoL with-
out the need for an external cable. Older motherboards must have a WAKEUP-LINK
header onboard and connected to the network card via a special 3-pin cable; how-
ever, systems supporting the PCI 2.2 standard coupled with a PCI 2.2 compliant net-
work adapter typically do not require a WoL cable as the required standby power is
relayed through the PCI bus.
PCI version 2.2 has PME (Power Management Events). What this means is that PCI
cards can send and receive PME via the PCI socket directly, without the need for a
WOL cable.
Laptops powered by the Intel 3945 chipset or newer (with explicit BIOS support)
allow waking up the machine using wireless (802.11 protocol). This is called Wake on
Wireless LAN (WoWLAN).
Wake on LAN must be enabled in the Power Management section of the mother-
board's BIOS. It may also be necessary to configure the computer to reserve power
for the network card when the system is shutdown.
In addition, in order to get WoL to work it is sometimes required to enable this feature
on the card. This can be done in Microsoft Windows from the properties of the net-
work card in the device manager, on the "Power Management" tab. Check "Allow this
device to bring the computer out of standby" and then "Only allow management sta-
tions to bring the computer out of standby" to make sure it does not wake up on all
network activity.
C.2.3

How WoL Works

Wake-on-LAN is not restricted to LAN (Local area network) traffic.
The general process of waking a computer up remotely over a network connection
can be explained thusly:
The target computer is shut down (Sleeping, Hibernating or Soft Off, i.e. ACPI state
G1 or G2), with power reserved for the network card. The network card listens for a
specific packet, called the "Magic Packet." The Magic Packet is broadcast on the
broadcast address for that particular subnet (or an entire LAN, though this requires
special hardware and/or configuration). When the listening computer receives this
packet, the network card checks the packet for the correct information. If the Magic
Packet is valid, the network card turns on the computer to full power and boots the
operating system.
The magic packet is sent on the data link or OSI-2 layer and broadcast to all NICs
(within the network of the broadcast address). Therefore, it does not matter whether
the remote host has a fixed or dynamic IP-address (OSI-3 layer).
In order for Wake on LAN to work, parts of the network interface need to stay on. This
increases the standby power used by the computer. If Wake on LAN is not needed,
turning it off may reduce power consumption while the computer is off but still
plugged in.
C.2.4

Magic Packet

The Magic Packet is a broadcast frame containing anywhere within its payload 6
bytes of ones (resulting in hexadecimal FF FF FF FF FF FF) followed by sixteen rep-
etitions of the target computer's MAC address.
Since the Magic Packet is only scanned for the string above, and not actually parsed
by a full protocol stack, it may be sent as a broadcast packet of any network- and
transport-layer protocol. It is typically sent as a UDP datagram to port 0, 7 or 9, or, in
former times, as an IPX packet.
53 ARK-3440 User Manual