introduction to ad hoc networks and routing protocols presented by : karthik samudram jayaraman
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Introduction To Ad Hoc Networks and
Routing Protocols
Presented By :Karthik Samudram Jayaraman
Introduction• What is Ad Hoc Network?
• In Latin, ad hoc means "for this," further meaning "for this purpose only.”
• 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 is a major issue!
• Security new vulnerabilities, nasty neighbors.• Power running with batteries, little computing
power.
The Desired Properties of Protocols (For Routing)
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.
Two Main 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
Destination Sequenced Distance Vector Algorithm (DSDV)
1. Based on Bellman-Ford Next Hop Routing.
2. Each Node Maintains Tables for :
A. Next Hop on Path
B. Distance (in hops) to destination.
C. Sequence Number ( keep current route)
DSDV contd…
3. Nodes Exchange Updates With Neighbours
• Full Routing Updates• Incremental Updates
ClusterHead Gateway Switch Routing
• Adds hierarchical structure having DSDV as underlying routing algorithm.• Routing is performed over clusterheads and not individual nodes.• Requires Table to maintain cluster Membership, in addition to other routing tables.• Cluster heads are selected by a Least Cluster Change Algorithm to minimize routing changes
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
Wireless Routing Protocol
• 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
Wireless Routing Protocol
• Link-cost Table:• The cost of relaying information through each
neighbor
• Message retransmission list: • One or more retransmission entries
Wireless Routing Protocol
• 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
Wireless Routing Protocol
• 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
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
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 reinitiates 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 initiates 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 floodthrough 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
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.
Conclusion
• 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
• 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.
• 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
Erase route; notify source
Link reversal; route repair
Localized broadcast query
Erase route; notify source
Routing metric
Freshest and shortest path
Shortest path Shortest path Associativity and shortest path and others
Associativity and stability
Overview
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