Routing Protocols of Ad Hoc Network

Routing Protocols of Ad Hoc Network

Introduction• What is Ad Hoc Network

• All nodes are mobile and can be connected dynamically in an arbitrary manner.

• No default router available• Potentially every node becomes a router: must be able to forward traffic on behalf of others

Two types of wireless networks • Infrastructured network:

A network with fixed and wired gateways. When A mobile unit goes out of range of one base station, it connects with new base station

• Infrastructureless (ad hoc) networks:All nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes.

Why is Ad Hoc hard

• Because of a constantly changing set of nodes. Routing!

• Security new vulnerabilities, nasty neighbors• Power running with batteries, little computing

power.

The Expected Properties of Protocols

1. A routing protocol should be distributed

2. Assume routes as unidirectional links

3. Power efficient

4. Consider its security

5. Hybrid protocols can be preferred

6. Be aware of Quality of Service

Three categories of Protocols

1. Table Driven Routing Protocols

Pro-active, learn the network’s topology before a forwarding request comes in

2. On-Demand Routing Protocols

Re-active, become active only when needed

3. Hybrid routing protocols

Use pro-active protocol in local zone, use re-active protocol between zones.

What is “on-demand”

• The routes are created when required

• The source has to discover a route to the destination

• The source and intermediate nodes have to maintain a route as long as it is used

• Routes have to be repaired in case of topology changes.

On-Demand Routing Protocols

1. Ad hoc On-demand Distance Vector Routing

2. Dynamic Source Routing Protocol

3. Temporally Ordered Routing Algorithm

4. Associativity Based Routing

5. Signal Stability Routing

Ad Hoc On-demand Distance Vector Routing

• AODV includes route discovery and route maintenance.

• AODV minimizes the number of broadcasts by creating routes on-demand

• AODV uses only symmetric links because the route reply packet follows the reverse path of route request packet.

• AODV uses hello messages to know its neighbors and to ensure symmetic links.

The node discards the packets having been seen

source

destination

The source broadcasts a route packetThe neighbors in turn broadcast the packet till it reaches the destination

Reply packet follows the reverse path of route request packet recorded in broadcast packet

RREQ

RREP

Route Maintenance

• If the source node moves, it reinitiate the route discovery.

• If intermediate node moves, its upstream node sends a RREP to the source. The source restarts the route discovery.

Dynamic Source Routing Protocol

• A node maintains route caches containing the routes it knows.

• Include route discovery and route maintenance.

Route discovery•The source sends a broadcast packet which contains source address, destination address, request id and path.

•If a host saw the packet before, discards it.

•Otherwise, the route looks up its route caches to look for a route to destination, If not find, appends its address into the packet, rebroadcast,

•If finds a route in its route cache, sends a route reply packet, which is sent to the source by route cache or the route discovery.

destination

source1

65

4

3

2

8

7

(1,4)

(1,2)

(1,3)

(1,3,5,6)(1,3,5)

(1,4,7)

source broadcasts a packet containing address of source and destination

The route looks up its route caches to look for a route to destinationIf not find, appends its address into the packet

The destination sends a reply packet to source.

The node discards the packets having been seen

How to send a reply packet

• If the destination has a route to the source in its route cache, use it

• Else if symmetric links are supported, use the reverse of route record

• Else if symmetric links are not supported, the destination initiate route discovery to source

Route maintenance

• Whenever a node transmits a data packet, a route reply, or a route error, it must verify that the next hop correctly receives the packet.

• If not, the node must send a route error to the node responsible for generating this route header

• The source restart the route discovery

Add entries into route cache

• The Source and destination in route discovery

• Intermediate hosts in route discovery

• The hosts receiving any broadcast

Temporally Order Routing Algorithm

• Creating Routes: query/reply• QRY packet is flooded through network

• UPD packet propagates back if route exist

• Maintaining Routes: link-reversal• UPD packets re-orient the route structure

• Erasing Routes• CLR packet is flooded through network to erase

invalid routes

a

fe

d

c

b

h

g

(-,-,-,-,d)

(-,-,-,-,b)

(-,-,-,-,c)

(-,-,-,-,f)(-,,-,-,-e)

Only the non-NULL node (destination) responds with a UPD packet.

(0,0,0,0,h)

(-,-,-,-,a)

The source broadcasts a QRY packet with height(D)=0, all others NULL

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e) (0,0,0,2,f)

(0,0,0,2,d)(0,0,0,3,a)

source

Dest.

A node receiving a UPD sets its height to one more than UPD

Source receives a UPD with less height

UPD

QRY

QRYQRY

(-,-,-,-,g)(0,0,0,1,g)

TORA: Height metric

• Each node contains a quintuple• Logical time of a link failure

• Unique ID of the node that defined the new reference level

• Reflection indicator bit

• A propagation ordering parameter, height

• Unique ID of the node

Route Maintenance and Erasing• No reaction necessary if all nodes still have downstream

links.

• A new reference level is defined if a node loses its last downstream link.

• Synchronized clock is important, accomplished via GPS or algorithm such as Network Time Protocol.

• CLR packet to be flooded to clear the invalid packet.

a

fe

d

c

b

h

g

(0,0,0,0,h)

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e)(0,0,0,2,f)

(0,0,0,2,d)(0,0,0,3,a)

Dest.

(0,0,0,1,g)

Link failure with no reaction

fe

d

c

b

h

g

(0,0,0,0,h)

(0,0,0,4,b)

(0,0,0,4,c)

(0,0,0,3,e)(0,0,0,2,f)

(0,0,0,2,d)(0,0,0,4,s)

Dest.

(0,0,0,1,g)

Re-establishing route after link failure

(1,d,0,0,d)

A new reference level is defined

UDPas

UDP

(0,0,0,3,a)(1,d,0,-1,a)(1,d,0,-2,s)

Associativity Based Routing

• Each route keeps a associativity table

• A high value of associativity tick indicates a low state of node mobility

• A route is selected based on associativity states of nodes, finds the high value of associativity tick (low mobility routes)

Associativity table

• All nodes generate periodic beacons

• When a neighbor node receives a beacon, it increases its associativity tick with respect to the sending node in associativity table

• Associativity ticks are reset when the neighbors of a node or the node itself move out of proximity

Route Discovery

• The source broadcast a QRY message

• Each intermediate node appends its address and associativity ticks to QRY,

• The destination can examine the associativity ticks to select route. If the multiple paths have the same overall degree of stability, select the minimum number of hops

S1

6

5

3

2

8

7

D

Route Re-construction

LQ

Node broadcasts a LQ packet

LQ9

RN

Node times out, sends RN packet to upstream node to erase invalid node and invoke LQ

If the D receives the LQ, it replies.

If the LQ process backtracking >1/2 path, new discovery from source.

Route Erasing

• If the the route is no longer desired, the source may not be aware of any route node changes because partial reconstruction.

• The source node initiates a route delete (RD) broadcast to erase the invalid route.

Signal Stability Routing

• Selects route based on the signal strength between nodes and a node’s location stability

• Comprise two protocols:• Dynamic Routing Protocol (DRP)

• Static Routing Protocol (SRP)

Dynamic Routing Protocol

• DRP maintains the signal strength of neighboring nodes by periodic beacon from neighbor

• Signal strength is recorded as a strong or weak channel

• After the updating, DRP passes the packet to the SRP

• SRP processes the route search

source1

65

4

3

2

8

7

The source broadcast a QRY packet

Weak channelStrong channel

The QRY packets are forwarded only if they are received over strong channel. No packet can be sent over weak channel

destination

• The problem is if there are only weak links can reach the destination. What happen?

source

1

65

4

3

2

8

7

The source times out, it changes the PREF field in the headerWeak channel are acceptable

Weak channelStrong channel

destination

Route Maintenance

• The intermediate node sends an error message to the source if link fails

• The source initiates another route-search process to find a new path to the destination

• The source also send an erase message to erase the invalid node

Conclusion

Comparison based on routing overhead

• DSR has lower routing load than AODV

Because AODV has to depend on route discovery more often, DSR limits the overhead by using route cache

• TORA is higher because its overhead is the sum of neighbor discovery plus routing creating and maintenance

Comparison on the basis of packet delivery ratio

Packet delivery ratio in different source number in TORA

• DSR and AODV perform well than TORA, delivering over 95% packet regardless of mobility rate.

• TORA is lower because the link-reversal process fails in the routing maintenance.

• TORA has a better performance in the less sources.

Comparison of throughput

Because sometimes stale routes are selected in DSR

Comparison on the basis of delay

• AODV has less delay than DSR

• AODV replies to first RREQ, so it chooses the least congested route.

• The overhead of TORA is worst. It has a better delivery ratio in less sources.

• DSR is good at all mobility rate and movement speed. Its performance is poor in a higher load.

• AODV performs almost as well as DST at all mobility rates and movement. It depends more on route discovery which may increase overhead in network

Advantage and Disadvantage

On-Demand AODV DSR TORA ABR SSR Overall complexity

Medium Medium High High High

Overhead Low Medium Medium High High Loop-free Yes Yes Yes Yes Yes Beaconing requirements

No No No Yes Yes

Multiple route support

No Yes Yes No No

Routes maintained in

Route table Route cache Route table Route table Route table

Route reconfiguration methodology

Erase route; notify source


Link reversal; route repair

Localized broadcast query


Routing metric

Freshest and shortest path

Shortest path Shortest path Associativity and shortest path and others

Associativity and stability

Overview

Pro-active Ad-hoc Routing Protocols

• DSDV 1994

– Destination Sequenced Distance-Vector

• WRP 1996 – Wireless Routing Protocol

• Fisheye 1999 – Fisheye State Routing


• DSDV 1994




DSDV

DSDV is based on idea of classical Bellman-Ford Routing Algorithm

Each node maintains a routing table listing all available destinations. The attributes of each destination are the next hop, the number of hops to reach to the destination, and a sequence number, which is originated by the destination node.

Both periodic and triggered routing updates to maintain table

Problems of Distance Vector

Pro-active routing based on Distance Vector

• Topology changes are slowly propagated• Count-to-infinity problem

• Moving nodes create confusion:• they carry connectivity data which are wrong at new

place

• Table exchange eats bandwidth

DSDV

How DSDV addresses the problems?

• Tagging of distance information:• The destination issues increasing sequence number

• Other nodes can discard old/duplicate updates

• Changes are not immediately propagated• Wait some setting time

• Incremental updates instead of full table exchange

DSDV

v

( metric, sequence #)

(infinity, odd number)

When a node receives a infinity metric with a later sequence number, it will trigger a route update broadcast to the disseminate the news.


• DSDV 1994




Wireless Routing Protocol

• Each node maintains a distance table, a routing table, a link-cost table and a message retransmission list.

• Distance table of node i: (matrix)For each destination j and each neighbor of i(k)

• Distance to j


• Routing table of node i is a vector:• The destination’s identifier

• The distance to the destination

• The predecessor and successor of the chosen shortest path


• Link-cost Table:• The cost of relaying information through each

neighbor

• Message retransmission list: • One or more retransmission entries


• Information Exchanged among nodes:(routing table update messages )

• Identifier of the sending node• A sequence number assigned by the sending

node• An update list of updates or ACKs to update

message • A response list of nodes that should send an

ACK to the update message


J

K

IB

(0, J)

(2, K)

(2, K)

(1, K)

X1110

1

5

10

(, K)

(10, B)

(10, I)

(11, B)


• Each node will communicate with its neighbors reporting any changes in the system

• Each node will keep track of which node should send an acknowledgement

• Nodes will keep track of the changes in the system by periodic transmission of ‘hello’ messages

• This protocol will force nodes to do consistent check of their predecessor hence avoiding count-to-infinity problem.


• DSDV 1994




Fisheye State Routing

For each node i one list , four tables are maintained:• A neighbor list

• A set of nodes adjacent to node i

• A topology table• Link state information reported by node j• timestamp

• A next hop table• Next hop to forward the msg along the shortest path

• A distance table• Distance of shortest path from i to j


It is an implicit hierarchical routing protocol.

Link state packets are not flooded. Node maintain a link list table based on the up-to-date information received from neighbor nodes, periodically exchange it with their local neighbors only




Comparison and AnalysisNotation:• N- number of nodes in network• D- Maximum hop distance• d – degree of node connectivity• I – routing update interval• ni – average number of nodes in scope i

• wi – damping factor of update frequency for level i


Line Overhead: the aggregate volume of control bytes exchanged by a node per unit time

• O( ni* d/ wi)/I

* Global State Routing: O(N*d/I)

Converge Time:

• O(D*I)

Scaling ProblemsCommon Assumption of current ad-hoc research:

Small networks with less than 100 nodes

How to scale this to 1000 and more nodes?

- routing hierarchy

- Create logical cells(partition into clusters)- Use one protocol inside a cluster

- Designate a cluster-head or gateway

- Two-level Routing- Direct routing inside a cluster

- Inter-cluster routing from cluster-heads

- Add more levels if needed

Clustering Routing Protocols

• HSR – Hierarchical State Routing

• ZRP – Zone Routing Protocol

• CEDAR – Core extraction distributed ad-hoc Routing





Hierarchical RoutingThe network contains two kinds of nodes: endpoints and

switched. Only endpoints can be sources and destinations for user data traffic, only switches can perform routing functions.

To form the lowest level partition in the hierarchy, endpoints choose the most convenient switched, they will group themselves around the switches.

The switch will organize themselves hierarchically into clusters. Lower level cluster heads organize to form the higher level clusters.

As nodes move, clusters may split or merge, altering cluster membership.

Hierarchical State Routing

Based on link state• Quick response to topology changes

• Flooding overhead

partitioning and clustering

Hierarchical Routing

• Reduce the routing table storage and processing overhead

• Mobility and location management

Comparisons

Simulation:

100 mobile hosts in 1000m*1000m

Radio transmission range : 120m

Data rate: 2Mb/sFSR: 2-level scoping; Radius is 2 hops; refresh rate ratio is

1:3

HSR: 2 levels

On-Demand: differ routing entry timeout A(3 secs) B(6secs)





Zone Routing Protocol

• Routing Zone:• Defined for each each node and includes the

nodes whose distance is at most some predefined number

Each node is required to know the topology of the network within its routing zone only and nodes are updated about topology changes only within its routing zone. (using proactive algorithm)



• Trade-off between the cost and latency of the ZRP route discovery protocol

• ZRP path is more stable than full path.

• The behavior of ZRP can be adjusted by changing the value of diameter.

Comparison

• Flat-routed (peer to peer connections restricted only by the propagation condition)

• A two-tiered: on the lower tier , at least one node serve as gateway.

Although the routing between nodes that belong to the same tier is peer-to-peer routing, routing between two tiers is throught the gateway node.

Flat-Routed

Two-Tier





CEDAR

CEDAR dynamically establishes a core of the network, and then incrementally propagates the link state of stable high bandwidth links to the nodes of the core. Route computation is on demand, and is performed by core nodes using only local state.

We propose CEDAR as a QoS routing algorithm for small to medium size ad hoc networks

CEDAR

A dominating set S is a set such that every node in V is either in S or is a neighbor of a node in S. a dominating set with minimum cardinality is called a minimum dominating set.

CEDAR

Undirected graph G(V,E)

• Ni`(x) - ith deleted neighborhood , set of nodes whose distance from x is not greater than I, except node x itself

• Ni(x) – ith neighborhood , Ni`(x) U {x}

Given an MDS Vc of G, define a core of graph

C = (Vc, Ec) where Ec = {[u,v] | v Vc, u N3’(v)}

CEDAR

CEDAR

The following is a brief description of the three key components of CEDAR:

Core extraction: A set of nodes is distributed and dynamically elected to form the core of the network by approximating a minimum dominating set of the ad hoc network using only local computation and local state. Each core node maintains the local topology of the nodes in its domain, and also performs route computation on behalf of

these nodes.

CEDAR

Link state propagation:

QoS routing in CEDAR is achieved by propagating the bandwidth availability information of stable links in the core known to nodes far away in the network, while information about dynamic links or low bandwidth links is kept local. Slow-moving increase-waves and fast moving decrease-waves, which denote corresponding changes in available bandwidths on links, are used to propagate non-local information over core nodes.

CEDAR

Route computation: Route computation first establishes a core-path from the dominator of the source to the dominator of the destination. The core path provides the directionality of the route from the source to the destination. Using this directional information, CEDAR iteratively tries to find a partial route from the source to the domain of the furthest possible node in the core path (which then becomes the source for the next iteration)

satisfying the requested bandwidth, using only local information. Effectively, the computed route is a shortest widest furthest path using the core path as the guideline.

Conclusion

Reference1. Routing Protocols for Ad Hoc Mobile Wireless Networt by Padmini Misra,

ftp://ftp.netlab.ohio-state.edu/pub/jain/courses/cis788-99/adhoc_routing/index.html#CBRP2. A Comparison of On-Demand and Table Driven Routing for Ad-Hoc Wireless

Networks, by Jyoti Raju and J.J. Garcia-Luna-Aceves, http://www.soe.ucsc.edu/~jyoti/paper2/

3. A New Routing Protocol for the Reconfigurable Wireless Networks, Zygmunt J Hass4. Caching strategies in on-demand routing protocols for wireless ad hoc networks, by

Yih-chun hu and Divid B. Johnson, http://monarch.cs.cmu.edu5. Highly Dynamic Destination-Sequenced Distance-Vector Routing for Mobile

Computers, Pravin Bhagwat, Charles E. Perkins6. Dynamic source routing in ad hoc wireless networks, by David B. Johnson and David

A. Maltz, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/johnson-dsr.pdf7. A Performace Comparison of Multi-Hop Wireless Ad Hoc Network Routing

Protocols, Josh Broch etc8. An Efficient Routing Protocol for Wireless Netwrok, Shree Murthy etc9. Temporally-Ordered Routing Algorithm (TORA) Version 1 Funtional

Specification, by V. Park, S. Corson, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/corson-draft-ietf-manet-tora-spec-00.txt

10. Ad Hoc On Demand Distance Vector (AODV) Routing, by Charles Perkins, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/perkins-draft-ietf-manet-aodv-00.txt

Reference (cont.)7. An Introduction to Mobile Ad Hoc Network, by Ming Yu Jiang,

http://kiki.ee.ntu.edu.tw/mmnet1/adhoc/8. Scalable Routing Strategies for Ad hoc Wireless Network, by Atsushi Iwata , Ching-

Chuan Chiang etc.9. A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing

Protocols, by Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, Jorjeta Jetcheva, http://www1.ics.uci.edu/~atm/adhoc/paper-collection/johnson-performance-comparison-mobicom98.pdf

10. Fisheye State Routing: A Routing Schema for Ad Hoc Wireless Networks, by guangyu Pei, Mario Gerla, Tsi-Wei Chen

11. A review of current Routing protocols for ad-hoc Mobile Wireless Networks, by Elizabeth M. Royer and C-K Toh http://www.cs.ucsb.edu/~vigna/courses/CS595_Fall01/royer99review.pdf

12. CEDAR: a Core-Extraction distributed Ad Hoc Routing Algorithm, Prasun Sinha, Vaduvur Nharghavan, etc

13. Mobile computing today & in the future, by M.J. Fahham and M.K. Hauge. http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol4/mjf/report.html

14. Performance Comparison of On-demand Routing Protocols in Ad Hoc Network by Sohela Kaniz http://fiddle.visc.vt.edu/courses/ecpe6504-wireless/projects_spring2000/pres_kaniz.pdf

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Routing Protocols of Ad Hoc Network