Subject: [NEXTEL-1] IT Coach: MOBILE AD HOC NETWORKS (MANETs)

From: Marcel <[email-masked]>
Date: Sun, 30 Mar 2003 23:33:21 -0500

IT Coach: MOBILE AD HOC NETWORKS (MANETs)
ACW Team, 24-Mar-2003

Mobile Ad Hoc Networks (MANETs) is an alternative to the typical
mobile/access point or cellular structure for building a wireless
network.

Instead of having access points or base stations that control the
units in its vicinity, all the units within a MANET communicate with
each other.

If the final destination is another terminal on the network, the
information flow may be channelled directly to that terminal or
using several other terminals.

When the final destination is a wired network, the information will
be routed through as many terminals as necessary to reach one
that is connected to the wired network.

Such a setup is different from a traditional cell-based network in
which all terminals send information to a central access point or
base that would route information into the wired network or through
to other terminals.

The advantages

One of the advantages of MANETs is the relatively low cost of
deployment because the mobile devices become relay stations,
reducing or almost eliminating the need for infrastructure.

Another major advantage is the efficient use of radio spectrum.
Data will be transmitted over shorter distances, tying up less
spectrum per transmission.

The data will be routed through areas where traffic is less
concentrated, thus using spectrum in a more efficient manner
through spatial distribution.

In addition, higher data rates might be possible with MANETs.
Potentially smaller transmission distances and fewer obstructions
could increase data rates due to the higher power margin over
interference.

Obstacles to adoption

Despite these merits of MANETs, the technology has to overcome
a few obstacles.

Some of the drawbacks include the need for each device to be able
to track the location and data transmissions of the other units to
route the information to its final destination. Thus increasing
processing complexity and memory requirements.

There must also be enough units close by in the field for the unit to
route information through them.

Though the performance in terms of data rate might improve as the
number of deployed units is increased, system latency will
degrade because the data must be routed through a large number
of units.

Battery life is another problem. Though advocates of MANETs
claim the use of the technology would result in battery life
improvements, it is not clear whether this advantage is balanced
by the increased number of transmissions each unit must perform
to route data from other devices in the field.

Battery life in portable units is dominated by fixed power sources
such as a digital signal processor and receiver power when
transmissions are not near maximum power. These sources do
not vary with the transmission RF power.

Security issues pose a huge challenge to wider use of MANETs.
The collaborative and self-organising nature of MANETs could
open the network to security attacks that can disrupt the routing
protocol and disable communications.

Several protocols have been proposed to secure the route
discovery process in MANET, but they are designed to perform
route discovery only when a source node needs to route packets to
a destination. In other words, they are reactive rather than proactive
protocols.

But in many cases, proactive discovery of topology is more efficient.
For instance, in networks with low-to-medium mobility, or with high
connection rates and frequent communications with a large portion
of the network nodes.

In terms of standardisation efforts, the IETF (The Internet
Engineering Task Force) has formed a working committee to
develop standards for mesh networks since the late 1990s. The
working group had coined the acronym MANETs to describe the
mesh type networks and has published a series of protocols used
to describe the data transfer through these networks.

IT vendors such as MeshNetworks and Nokia have also developed
such technologies. MeshNetworks’ system is aimed towards
public access systems while Nokia’s Rooftop system operates in
the 2.4GHz spectrum.

Source: PwC, School Of Electrical And Computer Engineering,
Cornell University
http://www.cmpnetasia.com/ViewArt.cfm?Artid=19077&Catid=5&subcat=48

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