05-06-2013, 03:23 PM
Ad hoc Networks
Ad hoc Networks.pptx (Size: 349.72 KB / Downloads: 17)
Ad Hoc Network
Collection of mobile wireless nodes forming a network without the aid of any infrastructure or centralized administration
Nodes have limited transmission range
Nodes act as a routers
Characteristics of Ad hoc Networks
Dynamic topologies
Limited channel bandwidth
Variable capacity links
Energy-constrained operation
Limited physical security
Challenges
Limited wireless transmission range
Broadcast nature of the wireless medium
Packet losses due to transmission errors
Mobility-induced route changes
Mobility-induced packet losses
Battery constraints
Potentially frequent network partitions
Ease of snooping on wireless transmissions (security hazard)
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
Cluster-head Gateway Switch Routing (CGSR)
Uses DSDV as an underlying protocol and
Least Cluster Change (LCC) clustering algorithm
A cluster-head 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 cluster-head of the destination node
Lookup of next hop
Packet send to destination
Destination cluster-
head delivers packet
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
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
Ad hoc Networks.pptx (Size: 349.72 KB / Downloads: 17)
Ad Hoc Network
Collection of mobile wireless nodes forming a network without the aid of any infrastructure or centralized administration
Nodes have limited transmission range
Nodes act as a routers
Characteristics of Ad hoc Networks
Dynamic topologies
Limited channel bandwidth
Variable capacity links
Energy-constrained operation
Limited physical security
Challenges
Limited wireless transmission range
Broadcast nature of the wireless medium
Packet losses due to transmission errors
Mobility-induced route changes
Mobility-induced packet losses
Battery constraints
Potentially frequent network partitions
Ease of snooping on wireless transmissions (security hazard)
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
Cluster-head Gateway Switch Routing (CGSR)
Uses DSDV as an underlying protocol and
Least Cluster Change (LCC) clustering algorithm
A cluster-head 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 cluster-head of the destination node
Lookup of next hop
Packet send to destination
Destination cluster-
head delivers packet
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
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