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Controlling Your LAN
users can remotely wake up the nodes on their network,
run a certain process and put them to sleep all of this by
Wake on LAN technology.
networked environment is more powerful than ever. This makes
the network administrator's job more complex. As an administrator,
you can't take full advantage of the networked environment
unless it is effectively managed.
Consider the following situation: you have upgraded all the
PCs that needed more memory, disk or processing power on your
network. Now you're ready to install the software.
There are three options that you can consider here:
Request all users to install the software themselves.
Send numerous messages asking all the users to leave their
PCs switched on overnight and send the technician around
do a manual install on each PC during the night.
Write a script that runs during off-hours, remotely turns
on each PC, installs the application and turns the machine
The first option cannot ensure that all users have upgraded.
Also in the process it would affect productivity of the end
user. If you adopt the second, it takes care of the two issues
quoted above but involves a huge amount work for the technical
staff. To avoid disrupting users and overwhelming the network
during prime work hours, you would like to have your technicians
install it automatically at night. Ideally, adopting option
three can reduce your network management headaches, raising
productivity in the process.
You can achieve this by using a technology called Wake on
LAN. It is one of the most powerful desktop management technologies
that a network administrator can employ.
Remote wake-up feature, combined with other remote management
capabilities, gives network administrators the ability to
switch machines on remotely and automatically during off-hours,
to perform any remote management activities. The system can
be automatically powered on from a fully powered off state
over the network. Once the system is awake, it can be directed
to run utilities such as virus scan or disk backup, or install
software upgrades, and then return to a sleep state. The combination
of off-hours wake-up and remote access allows network administrators
save time on automated software installations and upgrades,
in the process increasing end-user productivity by avoiding
disruptions during work hours.
Wake Over Network
Remote Wake up, also known as Wake on LAN technology, was
a result of the need for better management of power on PCs.
Earlier; PCs never had any power management built-in. A PC
could only be powered ON or OFF manually by the user. As a
result, remote management of PCs was difficult.
If a network administrator wants to remotely manage PCs during
off-hours, then users have to keep their PC switched on in
anticipation of maintenance. This resulted in lot of power
wastage. As a result of this, PC vendors and OS vendors came
out with technologies such as Advanced Power Management (APM)
and Advanced Configuration and Power Management Interface
(ACPI), where a PC can detect a state of inactivity and can
be put in to a low power state where it consumes very less
power. Or even the PCs could be shutdown when not in use.
Then came the question of how to turn on these PCs to full
power mode remotely, when required for some remote management
activity. The result of this requirement is Remote Wake up
or Wake on LAN technology.
This allows a network administrator to start a system remotely
using a LAN signal from a management console. It is achieved
through ACPI where a system can wake from a low power mode
in response to a specified network packet. When the system
is turned off, the managed adapter continuously monitors the
network and watches for a wake-up packet. When it receives
that packet, it alerts the system, which then comes to full
power-state and stands ready for any remote management tasks.
Wake On LAN Technology works?
Wake on LAN technology involves a Network Interface Card (NIC)/
Modem that waits for a wake-up trigger from the network. When
it receives the trigger it initiates system power up.
The trigger to wake-up the target machine can be recognized
in multiple ways.
Wake on LAN originally used a technology known as Magic Packet,
which sends a data packet directly to a system. This packet
consists of data that has 16 repetitions of the system's media
access control (MAC) layer address. The MAC address is unique
to the network adapter in the system. So the Magic Packet
wakes only the system targeted for start-up. 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 the system. This is BIOS level
Byte Matching (PMB) Or Packet filtering Technology
In a magic packet the wake-up packet is predefined and depends
on the MAC address of the target machine. Hence, for waking
up each individual machine on
the network, a separate packet, containing its MAC
address needs to be sent. As an alternative, if an
administrator can configure his own set of packets for which
a group of PCs can respond and wake up, it is advantageous
to wake up a group of PCs with one single packet. This is
achieved in Pattern Byte Matching or Packet filtering. PBM
provides the wake-up packet for systems that support ACPI.
The system downloads a series of patterns, configured by the
administrator, to the network adapter, which in turn monitors
for the arrival of these patterns in a packet. If it finds
these patterns, the network adapter generates a PME signal
to wake up the system. In other words the system filters a
defined set of data trigger packets from the network and takes
action. This is more flexible than Magic Packet. In contrast
to Magic Packet, which is a BIOS level control, this is an
Operating System (OS) level control and hence can be much
more flexible in its utilization.
(WOR) Wake-up Technology
Wake-on-Ring makes it is possible to wake up your desktop
PC remotely when the modem attached to it detects a telephone
ring. After the modem detects the ring, the PC restores itself
to full power. With this convenient feature, it is also possible
to use your PC as a fax machine, telephone answering machine
or remote data server.
Wake-on-link is a new wake-up technology designed for energy
management under ACPI. All network clients on an Ethernet
network depend on link state changes, or heartbeat pulses,
to ensure continuous connection to the LAN. If the link is
down or there is a break in network, the heartbeat pulse is
interrupted. Under control of future ACPI-compatible operating
systems, the absence of a heartbeat pulse can signal a sleeping
network client to go into a deeper sleep state to conserve
Re-establishing the network link state signals the client
to transition to a lighter sleep state. These adjustments
are designed to yield budget savings in large corporate networks.
Today, many Wake on LAN-enabled network adapters support both
wake-on-link and wake-up by Magic Packet.
Wake-on-link has limited functionality and is not expected
to be widely adopted for several reasons. First, implementing
wake-on-link in hardware is difficult and implementations
can vary significantly. Second, wake-on-link yields marginal
energy savings over current OS directed sleep states, because
such a small percentage of network clients never lose their
Is Required To Make It Work?
You need the following hardware:
PCs: Choose a PC, which is designed for remote power control
and the Wake on LAN feature.
Adapters: Choose a network adapter, based on the type of network
(Ethernet or Token Ring) you use, which is Wake on LAN enabled.
Then, when the user turns off the PC, an auxiliary power supply
keeps the adapter active on the Ethernet or token ring network.
The sequences of events are as follows:
The Network administrator programs/ schedules a wake-up
request from a management console at a specific time for
a set of target PCs. Typically, the wake-up request is
scheduled for after hours or weekends, times when demands
on the bandwidth are low.
The program, which runs at scheduled time from Management
Console, sends a wake-up request packet over the Ethernet
or token ring network to all Wake on LAN-enabled target
The network adapter on the Wake On LAN enabled PC intercepts
the wake-up frame and signals it to power up. The PC powers
up and goes through its normal startup sequence.
In integration with any system management software, powered-up
PC initiates the work that has been scheduled for it,
like software installation.
Powered-up PC completes the work and waits for a period
of inactivity and then goes into hibernation or sleep
mode or can be remotely shutdown.
What Do LAN Wake-up Frames Do?
In the auxiliary-powered state, the adapters monitor LAN
traffic for valid LAN wake-up frames. Token ring wake-up frames
follow the industry-standard Magic Packet specifications,
which means that their destination addresses can be one of
these three types:
Broadcast: The destination address is all 1s and goes
to all nodes on the network.
Multicast: The first bit of the address is 1, which identifies
a group address for a group of workstations. Higher layer
functions determine the group of workstations being addressed.
Individual: The destination address is the unique address
of a node on the network.
The wake-up frame for a Wake on LAN-enabled adapter can have
a broadcast, multicast or an individual destination address.
Each wake-up frame contains a unique data field, one that
is not expected in typical LAN traffic. It contains an individual
MAC address, the address of the Wake on LAN adapter in the
target PC, which ensures that the frame is sent only to the
PC at that address.
The wake-up frame format consists of these required contiguous
six bytes of F (XX'FF') followed by a 48-bit target address
repeated at least eight times.
sequences can appear anywhere within the wake-up frame, and
you can modify any frames being sent over the respective networks
to include them. When the micro code in the adapter detects
these sequences, it sends a signal to the PC. The PC then
turns on, just as if you turned it on using the On/Off switch.
Consider a large organization with a huge number of desktops.
Each evening when these businesses close, the desktops are
powered down by users.
With the right PCs and network adapters, each workstation
could be automatically booted up just when the employees arrive
for work next morning and check in by integrating Wake on
LAN technology with appropriate desktop management application.
As a result of this:
No one would need to come in early to do that.
No one would have to wait during the power-up sequences.
No one would have to ask a customer to wait till his/her
A little increased productivity here, a little increased productivity
there it all adds up.
Consider a sales person who covers the globe from Tokyo to
Lisbon, from Nice to Venice, from Moscow to Jinzhou. Think
what they could accomplish if they could access their workstations
remotely. For example, by logging onto the Internet through
their laptops, salespeople could start up their workstations
each night to compile the inventory database for the next
Then, they could upload the results and have them the next
morning. For accomplishing this they need not keep their laptop
always powered ON when they are travelling. They can start
up their laptop only when required to complete their work
remotely and then shut it down remotely. This is possible
through Wake on LAN technology.
Consider situations such as these:
You rarely use a thermal wax printer, but you'd like it
to be turned on and ready to use in 15 minutes.
You had 17 remote servers in 17 remote locations shut
down in the last half hour. You need to restart them.
You have to turn on the print and file servers each morning,
but they're scattered over several floors of an office
suite. It typically takes you 45 minutes to get to all
And the list grows. All these can be achieved with appropriate
use of Wake on LAN technology.
Some of the benefits this technology can offer are:
A remote wake-up technology that enables you to remotely power
systems "on" for off-hours maintenance. This technology,
when used with appropriate Desktop Management application,
helps save time on automated software installations, upgrades,
disk backups, virus scans and such other scheduled remote
management tasks. Equally important, it increases end-user
productivity by moving such planned disruptions to off-hours.
By remotely initiating long routines such as inventory and
asset management after hours and on weekends.
By analyzing and resolving support problems remotely.
By saving the time it takes to turn on all of the computers
manually when you want to install the latest release of software
on multiple machines.
By eliminating delays in or interruptions of users' "real"
By using Wake on LAN technology today, you can:
Power up your PC or multiple PCs from a remote location.
Manage networks more efficiently.
Save bandwidth during the day by transmitting large files
Help your company save on its energy bill.
Eliminate trips back to work to troubleshoot a problem.
Be on the leading edge when new applications for Wake
on LAN technology become available.
Once you begin thinking about the scope for today's applications
for Wake on LAN technology, implement them and start reaping
the benefits, a whole lot of new application areas are bound
to come up bringing in immense productivity benefits to the
wake-up enables network
administrators to switch machines on remotely and automatically
to perform remote
off-hours wake-up and remote access allows network administrators
save time on automated software installations and upgrades,
and increases end-user
productivity by avoiding disruptions during
using Wake on
today, you can save bandwidth during the day by transmitting
large files at night
S Rajashekhar, Software Development Manager, Network Management
Technologies group, Novell, Bangalore. He can be reached at