### Routing in Wireless (Mobile) "Ad Hoc" networks ---- introduction

 Ad Hoc network = a dynamic network whose links between neighboring nodes are formed in an "ad hoc" ("haphazard") fashion.

• 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:

• Uni-directional and bi-directional wireless links

• 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

• A challenging problem in a MANET

• \$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....

• MANET Routing Algorithms )

• 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

• Each node can:

• 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,

• And so on... (nodes 3 hops away, 4 hops away, .....)

• Types of MANET routing algorithms

• 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

• 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.

• Hybrid:

 A comibination of pro-active and on-demand

• Coverage of MANET routing

• 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.