lecture 7

Wireless Ad Hoc and Sensor Networks CSE 5109

Sajeeb SahaAssistant ProfessorDept. of CSE, JnU

Wireless Ad Hoc Routing Protocols

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What is Routing?

– The process of moving a packet of data from source to destination.

– Routing is usually performed by a dedicated device called a router.

– Each intermediary computer performs routing by passing along the message to the next computer.

– Part of this process involves analyzing a routing table to determine the best path.

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Common objective: Route packets along the optimal path

– Routing protocols adapt to changing network conditions and by definition offers multi-hop paths

– Routing protocols differ in route table construction maintenance update

Next-hop routing protocols can be categorized as:– Link-state– Distance-vector

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Purpose of Routing

– [Dijkstra 1959 and McQuillan+ 1980]– Traditional link-state protocols may not be suitable– Closer to centralized version of shortest-path algorithm– Each node maintains a view of network topology with a cost for each link– Link costs are broadcast periodically to keep the views consistent– Each node updates its view and applies a shortest-path algorithm to find its

next hop for each destination– Routing loops may occur due to propagation delays, partitioned networks, and

so on– Alternative link-state routing approaches may not require all nodes to have the

identical link-state information and route selection algorithms and may find routes on demand

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Link State Routing

Distributed database problem

– [Ford+ 1962 and Leiner+ 1987]– Based on shortest-path routing algorithms i.e., Distributed Bellman-

Ford– DBF algorithms are also known as Distance-Vector (DV)– Routers exchange their distances to known destinations; – a router uses the distance vectors received from its neighbors to

compute its own distances. – For each destination, the node stores a single route table entry along

with next-hop neighbor– Route table entry for destination contains metric which is distance

from node to the destination and also the next-hop (vector) towards destination

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Distance Vector Routing

Distributed computation problem

• Mobility– Induced route changes

– Induced packet losses

– frequent network partitions

• Error-Prone Shared Broadcast Radio Channel– Hidden/Exposed terminal problem

– Packet losses due to transmission errors

• Bandwidth Constraint– Less data rate

– Minimum Control Information 7

Challenges in Wireless Ad Hoc Routing

• Resource Constraint– Battery Life

– Processing Power

• Security Hazard– Ease of snooping on wireless transmissions

– Ease of denial-of-service attack

– Misbehaving nodes difficult to identify

– Nodes can be easily compromised

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Challenges in Wireless Ad Hoc Routing

1. The routing protocol should be Distributed.

2. It must be adaptive to frequent topology changes.

3. Route computation and maintenance must involve a minimum number of nodes.

4. It must be Localized.

5. The routes must be loop-free and stale-free.

6. The number of packet collisions must be kept to a minimum.

7. It must converge to a optimal route.

8. It must optimally use scarce resources such as bandwidth, computing power, memory, and battery power.

9. It should be able to provide a certain level of quality of service (QoS)

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Wireless Ad Hoc Routing Requirements

Ad-Hoc Mobile Routing

Protocols

Table Driven / Proactive Hybrid

On-Demand-Driven / Reactive

DSDV

GSRFSR

HSR

ZHLS

CGSR

WRPAODVDSRTORACBRPABR

SSR

ZRP

Cluster

OLSR10

Wireless Ad Hoc Unicast Routing Protocols

Table Driven Routing Protocol

– proactive!!– continuously evaluate the routes– attempt to maintain consistent, up-to-date routing

information• when a route is needed, one may be ready

immediately– when the network topology changes

• the protocol responds by propagating updates throughout the network to maintain a consistent view

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• Proactive: maintain routing information independently of need for communication

• Update messages send throughout the network periodically or when network topology changes.

• Low latency, suitable for real-time traffic• Bandwidth might get wasted due to periodic

updates• They maintain O(N) state per node, N = #nodes

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• DSDV – Destination-Sequenced Distance Vector

• WRP – Wireless Routing Protocol• GSR – Global State Routing• FSR – Fisheye State Routing• HSR – Hierarchical State Routing• ZHLS – Zone-based Hierarchical Link State

Routing Protocol• CGSR – Clusterhead Gateway Switch Routing

Protocol


– reactive!!– on-demand style: create routes only when it is

desired by the source node• route discovery: invoke a route-determination

procedure• the procedure is terminated when

– a route has been found– no route is found after all route permutations

are examined – longer delay: sometimes a route may not be ready

for use immediately when data packets come

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On Demand Routing Protocol

• Reactive: discover route only when you need it• Saves energy and bandwidth during inactivity• Can be bursty -> congestion during high activity• Significant delay might occur as a result of route

discovery• Good for light loads, collapse in large loads

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• AODV – Ad Hoc On-demand Distance Vector Routing

• DSR – Dynamic Source Routing• TORA – Temporally Ordered Routing

Algorithm• CBRP – Cluster Based Routing Protocols• ABR – Associativity Based Routing• SSR – Signal Stability Routing


Hybrid Routing Protocols

• Proactive for neighborhood, Reactive for far away (Zone Routing Protocol, Haas group)

• Proactive for long distance, Reactive for neighborhood (Safari)

• Attempts to strike balance between the two

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Hierarchical Routing

• Nodes are organized in clusters• Cluster head “controls” cluster• Trade off

– Overhead and confusion for leader election– Scalability: intra-cluster vs intercluster

• One or Multiple levels of hierarchy

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Geographical Routing

• Nodes know their geo coordinates (GPS)• Route to move packet closer to end point• Protocols DREAM, GPSR, LAR• Propagate geo info by flooding (decrease

frequency for long distances)19

Ad Hoc Wireless Networks: Architectures and Protocols

• Chapter 7

Suggested Reading

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THANK YOU

lecture 7

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