---

[attachment=7535]

---

Introduction
Importance of networking
Computer network – system for communication between computers (fixed, temporary)
History starts with Advanced Research Projects Agency (ARPA) in 1962
1969 the beginning of ARPANet which connected University of LA, SRI, University of California at Santa Barbara, and the University of Utah
Mobile Ad-hoc Network
Self-configuring network of mobile routers (and associated hosts) connected by wireless links
This union forms a random topology
Routers move randomly free
Topology changes rapidly and unpredictably
Standalone fashion or connected to the larger Internet
Suitable for emergency situations like natural or human-induced disasters, military conflicts, emergency medical situations, etc.
Mobile Ad-hoc Network
Ad-hoc network versus Mobile Ad-hoc network
Increase of mobile applications
Additional challenges
Changes to the network topology
Need of extreme network flexibility
Answer = Mobile Ad-hoc Network
While MANETs are self contained, they can also be tied to an IP-based global or local network – Hybrid MANETs
Hybrid Mobile Ad-hoc Network
Hybrid Mobile Ad-hoc Network
Hybrid Mobile Ad-hoc Network
Hybrid Mobile Ad-hoc Network
Hybrid Mobile Ad-hoc Network
History of MANETs
Earliest MANETs were called “packet radio” networks, sponsored by DARPA (1970)
These packet radio systems predated the Internet and were part of motivation of the original IP suite
Later DARPA experiments included the Survivable Radio Network (SURAN) project (1980s)
1990s – the advent of inexpensive 802.11 radio cards for personal computer
Current MANETs are designed primary for military utility; examples include JTRS (Joint Tactical Radio System) and NTDR (Near-Term Digital Radio).
Routing Protocols for MANETs
Two types of routing protocols:
Table-Driven Routing Protocols
Destination-Sequenced Distance-Vector Routing (DSDV)
Clusterhead Gateway Switch Routing (CGSR)
The Wireless Routing Protocol (WRP)
Source-Initiated On-Demand Routing Protocols
Ad-Hoc On-Demand Distance Vector Routing (AODV)
Dynamic Source Routing (DSR)
Temporally-Ordered Routing Algorithm (TORA)
Associativity-Based Routing (ABR)
Signal Stability Routing (SSR)
Routing Protocols for MANETs
Destination-Sequenced Distance-Vector Routing (DSDV)
Table-driven algorithm based on the classical Bellman-Ford routing mechanism
Improvements – freedom of loops in routing tables
Routing is achieved by using routing tables maintained by each node
The main complexity in DSDV is in generating and maintaining these routing tables
Clusterhead Gateway Switch Routing (CGSR)
Uses DSDV as an underlying protocol and Least Cluster Change (LCC) clustering algorithm
A clusterhead is able to control a group of ad-hoc hosts
Each node maintains 2 tables:
A cluster member table, containing the cluster head for each destination node
A DV-routing table, containing the next hop to the destination
The routing principle:
Lookup of the clusterhead of the destination node
Lookup of next hop
Packet send to destination
Destination clusterhead delivers packet

Clusterhead Gateway Switch Routing (CGSR)
Clusterhead Gateway Switch Routing (CGSR)
Drawbacks: too frequent cluster head selection can be an overhead and cluster nodes and Gateway can be a bottleneck
The Wireless Routing Protocol (WRP)
Table-based protocol with the goal of maintaining routing information among all nodes in the network
Each node is responsible for four tables:
Distance table
Routing table
Link-cost table
Message retransmission list (MRL) table
Link exchanges are propagated using update messages sent between neighboring nodes
Hello messages are periodically exchanged between neighbors
This protocol avoids count-to-infinity problem by forcing each node to check predecessor information
Drawbacks: 4 tables requires a large amount of memory and periodic hello message consumes power and bandwidth
Source-Initiated On-Demand Routing Protocols
Ad-Hoc On-Demand Distance Vector Routing (AODV)
Builds on DSDV algorithm and the improvement is on minimising the number of required broadcasts by creating routes on an on-demand basis (not maintaining a complete list of routes)
Broadcast is used for route request
Advantages: uses bandwidth efficiently, is responsive to changes in topology, is scalable and ensures loop free routing
Drawbacks: nodes use the routing caches to reply to route queries. Result: “uncontrolled” replies and repetitive updates in hosts’ caches yet early queries cannot stop the propagation of all query messages which are flooded all over the network

Dynamic Source Routing (DSR)
Based on the concept of source routing
Mobile nodes are required to maintain route caches that contain the source routes of which the mobile is aware
2 major phases:
Route discovery – uses route request and route reply packets
Route maintenance – uses route error packets and acknowledgments
Advantages: No periodic hello message and fast recovery - cache can store multiple paths to a destination
Drawbacks: the packets may be forwarded along stale cached routes. It has a major scalability problem due to the nature of source routing. Same as AODV, nodes use the routing caches to reply to route queries
Temporally-Ordered Routing Algorithm (TORA)
Highly adaptive, loop-free, distributed routing algorithm based on the concept of page link reversal
Proposed to operate in a highly dynamic mobile networking environment
It is source initiated and provides multiple routes for any desired source/ destination pair
This algorithm requires the need for synchronized clocks
Temporally-Ordered Routing Algorithm (TORA)
3 basic functions:
Route creation
Route maintenance
Route erasure
Advantages: provides loop free paths at all instants and multiple routes so that if one path is not available, other is readily available. It establishes routes quickly so that they may be used before the topology changes.
Drawbacks: exhibits instability behavior similar to "count-to-infinity" problem in distance vector routing protocols.
Associativity-Based Routing (ABR)
Free from loops, deadlock, and packet duplicates, and defines a new routing metric for ad-hoc mobile networks
Each node generates periodic beacons (hello messages) to signify its existence to the neighbors
These beacons are used to update the associativity table of each node
With the temporal stability and the associativity table the nodes are able to classify each neighbor page link as stable or unstable
Associativity-Based Routing (ABR)
ABR consists of 3 phases:
Route Discovery
Route Repair/Reconstruction
Route Delete
If node A has in his Route Cache a route to the destination E, this route is immediately used. If not, the Route Discovery protocol is started
Associativity-Based Routing (ABR)
Associativity-Based Routing (ABR)
Advantages: free from duplicate packets
Drawbacks: Short beaconing interval to reflect association degree precisely
Signal Stability Routing (SSR)
descendent of ABR and ABR predates SSR
it selects routes based on signal strength between nodes and on a node’s location stability thus offers little novelty
SSR route selection criteria has effect of choosing routes that have ‘stronger’ connectivity and it can be divided into:
Dynamic Routing Protocol (DRP) or
Static Routing Protocol (SRP)
Signal Stability Routing (SSR)
DRP is responsible for maintenance of signal stability table and routing table
SRP processes packets by passing the packets up the stack if it is the intended receiver and forwarding the packet if it is not
Advantages: to select strong connection leads to fewer route reconstruction
Drawbacks: long delay since intermediate nodes can’t answer the path (unlike AODV, DSR)