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.
2.
3.
4.
5.
A routing protocol should be distributed.
Assume routes as unidirectional links.
Power efficient.
Consider its security.
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)
3. Nodes Exchange Updates With Neighbours
• Full Routing Updates
• Incremental Updates
DSDV
contd…
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 countto-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
2.
3.
4.
5.
Routing
Dynamic Source Routing Protocol
Temporally Ordered Routing Algorithm
Associativity Based Routing
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 source broadcasts a route packet
The neighbors in turn broadcast the
source
RREQ
packet till it reaches the destination
destination
RREP
Reply packet follows the reverse path of route
request packet recorded in broadcast packet
The node discards the packets having been seen
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.
source broadcasts a packet containing address of source and destination
source
(1,4)
1
4
The destination sends a reply packet to source.
8
(1,3)
destination
3
7
2
(1,2)
(1,4,7)
The node discards the packets having been seen
5
(1,3,5)
6
(1,3,5,6)
The route looks up its route caches to look for a route to destination
If not find, appends its address into the packet
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
The source broadcasts a QRY packet with height(D)=0, all others NULL
(0,0,0,3,a)
(-,-,-,-,a)
source
a
(-,-,-,-,d)
(0,0,0,2,d)
QRY
d
Only the non-NULL node (destination) responds with a UPD packet.
QRY
QRY
(-,-,-,-,c)
(0,0,0,4,c)
UPD
h
Dest.
(0,0,0,0,h)
c
g
(-,-,-,-,g)
(0,0,0,1,g)
b
(-,-,-,-,b)
(0,0,0,4,b)
e
(-,,-,-,-e)
(0,0,0,3,e)
f
(0,0,0,2,f)
(-,-,-,-,f)
A node receiving a UPD sets its height to one more than UPD
Source receives a UPD with less height
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.
Link failure with no reaction
(0,0,0,3,a)
(0,0,0,2,d)
a
d
h
c
Dest.
(0,0,0,0,h)
(0,0,0,4,c)
g
(0,0,0,1,g)
b
(0,0,0,4,b)
e
f
(0,0,0,2,f)
(0,0,0,3,e)
Re-establishing route after link failure
(1,d,0,-2,s)
(0,0,0,4,s)
s
A new reference level is defined
(1,d,0,-1,a)
(0,0,0,3,a)
(1,d,0,0,d)
UDP (0,0,0,2,d)
a
d
UDP
h
c
Dest.
(0,0,0,0,h)
(0,0,0,4,c)
g
(0,0,0,1,g)
b
(0,0,0,4,b)
e
f
(0,0,0,2,f)
(0,0,0,3,e)
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.
Advantage and Disadvantage
• 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
Overview
On-Demand
Overall
complexity
Overhead
Loop-free
Beaconing
requirements
Multiple
route support
Routes
maintained in
Route
reconfigurati
on
methodology
Routing
metric
AODV
Medium
DSR
Medium
TORA
High
ABR
High
SSR
High
Low
Yes
No
Medium
Yes
No
Medium
Yes
No
High
Yes
Yes
High
Yes
Yes
No
Yes
Yes
No
No
Route table
Route cache
Route table
Route table
Route table
Erase route;
notify source
Erase route;
notify source
Link reversal;
route repair
Localized
broadcast
query
Erase route;
notify source
Freshest and
shortest path
Shortest path
Shortest path
Associativity
and shortest
path and
others
Associativity
and stability
Reference
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Routing Protocols for Ad Hoc Mobile Wireless Networt by Padmini Misra,
ftp://ftp.netlab.ohio-state.edu/pub/jain/courses/cis78899/adhoc_routing/index.html#CBRP
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/
A New Routing Protocol for the Reconfigurable Wireless Networks, Zygmunt J Hass
Caching strategies in on-demand routing protocols for wireless ad hoc networks, by
Yih-chun hu and Divid B. Johnson, http://monarch.cs.cmu.edu
Highly Dynamic Destination-Sequenced Distance-Vector Routing for Mobile
Computers, Pravin Bhagwat, Charles E. Perkins
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.pdf
A Performace Comparison of Multi-Hop Wireless Ad Hoc Network Routing
Protocols, Josh Broch etc
An Efficient Routing Protocol for Wireless Netwrok, Shree Murthy etc
Temporally-Ordered Routing Algorithm (TORA) Version 1 Funtional
Specification, by V. Park, S. Corson, http://www1.ics.uci.edu/~atm/adhoc/papercollection/corson-draft-ietf-manet-tora-spec-00.txt
Ad Hoc On Demand Distance Vector (AODV) Routing, by Charles Perkins,
http://www1.ics.uci.edu/~atm/adhoc/paper-collection/perkins-draft-ietf-manet-aodv00.txt
Reference (cont.)
7.
8.
9.
10.
11.
12.
13.
14.
An Introduction to Mobile Ad Hoc Network, by Ming Yu Jiang,
http://kiki.ee.ntu.edu.tw/mmnet1/adhoc/
Scalable Routing Strategies for Ad hoc Wireless Network, by Atsushi Iwata , ChingChuan Chiang etc.
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/johnsonperformance-comparison-mobicom98.pdf
Fisheye State Routing: A Routing Schema for Ad Hoc Wireless Networks, by
guangyu Pei, Mario Gerla, Tsi-Wei Chen
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
CEDAR: a Core-Extraction distributed Ad Hoc Routing Algorithm, Prasun Sinha,
Vaduvur Nharghavan, etc
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
Performance Comparison of On-demand Routing Protocols in Ad Hoc Network by
Sohela Kaniz http://fiddle.visc.vt.edu/courses/ecpe6504wireless/projects_spring2000/pres_kaniz.pdf