- Ad hoc networks:
- Ad Hoc network = a dynamic network whose links between neighboring nodes are formed in an "ad hoc" ("haphazard") fashion.
- Mobile Adhoc Network (MANET):
- Mobile ad hoc network (MANET) = a dynamically self-configuring network of mobile devices connected by wireless links.
Characteristics of a MANET:
- Each device in a
MANET is
free to move independently
in any direction
- Devices will
make and break
connections to
other devices
dynamically and
frequently !!!
- Each (mobile) device
can (and must)
forward messages
from/to other mobile devices:
- Each (mobile) device operates like a mini router.
- MANET example: (dotted lines means
nodes are able to communicate
with each other)
- At time
t1:
- At a later time
t2:
- At time
t1:
- Fact:
- Due to
power capability difference:
- A wireless link between 2 (wireless) mobile nodes is unidirectional (= asymmetric !!!)
Example:
- Consider these 2 nodes:
- A can send to B
- but B cannot send to A
- Due to
power capability difference:
- $64,000 problem:
- How to equip each mobile device with information to route messages to the desired destination ???
- Important facts:
- The network topology in
a MANET is
ever changing !!!
- Routing failures
is a frequent occurence
- The routing protocol must handle route failures efficiently !!!
- MANET nodes must discover/re-dicover the network topology from time to time....
- The network topology in
a MANET is
ever changing !!!
- Basic idea in MANET
routing:
- A new node
(that joins the
MANET) must:
- Announce its
presence to
other nodes
- Listen for (and record/maintain)
announcement broadcasted
by its neighbors
- Announce its
presence to
other nodes
- Each node can:
- Learn (and maintain)
the identity of
it neighbors
- Learn (and maintain)
the identity of
it neighbors
- Recursive learning:
- A node can
learn from
its neighbor nodes:
- Nodes that are
2 hops away
and how to reach them,
- Nodes that are
2 hops away
- And so on... (nodes 3 hops away, 4 hops away, .....)
- A node can
learn from
its neighbor nodes:
- A new node
(that joins the
MANET) must:
- Categories of
MANET routing algorithms:
- Pro-active
- This type of protocols maintains
up-to-date
lists of destinations
and
their routes
by periodically
distributing routing tables
throughout the network.
- This type of algorithm adapts the link state algorithm or the distance vector algorithm
- This type of protocols maintains
up-to-date
lists of destinations
and
their routes
by periodically
distributing routing tables
throughout the network.
- Reactive (on-demand)
- This type of protocols
will find a route
only when a node has a
packet to transmit.
The on demand route discovery algorithm searches for a route by flooding the network with Route Request (RReq) packets.
- This type of protocols
will find a route
only when a node has a
packet to transmit.
- Hybrid:
- A comibination of pro-active and on-demand
- Pro-active
- Dicdactical note:
- I will discuss (for time sake)
- one of the on-demand algorithm (called Dynamic Source Routing)
because they are so different from the algorithms that we discussed.
(The pro-active algorithms are very similar to the link state (flooding) or the distance vector algorithms)
- The material on
DSR is
not found in the
text book.
- I made my notes from this publication: click here
- I will discuss (for time sake)