1. Chapter: 05-Mobile Computing
Mobile Adhoc Networks
By: Mr. Abdul Haseeb Khan

2. Outline Routing Protocol MANETS Definition
Ad hoc vs. cellular networks
MANETS Applications
MANETS Challenges
Routing Protocol
Expected Properties of Ad-hoc Routing Protocols
A taxonomy for routing protocols in Mobile ad
common protocols(DSDV, AODV, DSR, ZRP, TORA)

3. Infrastructure-based wireless networks
Typical wireless network: Based on infrastructure
E.g., GSM, UMTS, …
Base stations connected to a wired backbone network
Mobile entities communicate wirelessly to these base stations
Traffic between different mobile entities is relayed by base stations and wired backbone
Mobility is supported by switching from one base station to another
Backbone infrastructure required for administrative tasks
IP backbone
Further networks
Gateways
Server
Router

4. Infrastructure-based wireless networks – Limits?
What if …
No infrastructure is available? – E.g., in disaster areas
It is too expensive/inconvenient to set up? – E.g., in remote, large construction sites
There is no time to set it up? – E.g., in military operations

5. Possible applications for infrastructure-free networks
Factory floor automation
Disaster recovery
Car-to-car communication
Military networking: Tanks, soldiers, …
Finding out empty parking lots in a city, without asking a server
Search-and-rescue in an avalanche
Personal area networking (watch, glasses, PDA, medical appliance, …) …

6. Factory floor automation

7. Disaster recovery

8. Car-to-car communication

9. Solution: (Wireless) ad hoc networks
Try to construct a network without infrastructure, using networking abilities of the participants
This is an ad hoc network – a network constructed “for a special purpose”
Simplest example: Laptops in a conference room – a single-hop ad hoc network

10. Problems/challenges for ad hoc networks
Without a central infrastructure, things become much more difficult
Problems are due to
Lack of central entity for organization available
Limited range of wireless communication
Mobility of participants
Battery-operated entities

11. No central entity ! self-organization
Without a central entity (like a base station), participants must organize themselves into a network (self-organization)
Pertains to (among others):
Medium access control – no base station can assign transmission resources, must be decided in a distributed fashion
Finding a route from one participant to another

12. Limited range ! multi-hopping?
For many scenarios, communication with peers outside immediate communication range is required
Direct communication limited because of distance, obstacles, …
Solution: multi-hop network

13. Mobility ! Suitable, adaptive protocols
In many (not all!) ad hoc network applications, participants move around
In cellular network: simply hand over to another base station
In mobile ad hoc networks (MANET):
Mobility changes neighborhood relationship
Must be compensated for
E.g., routes in the network have to be changed
Complicated by scale
Large number of such nodes difficult to support

14. Battery-operated devices ! energy-efficient operation
Often (not always!), participants in an ad hoc network draw energy from batteries
Desirable: long run time for
Individual devices
Network as a whole
! Energy-efficient networking protocols
E.g., use multi-hop routes with low energy consumption (energy/bit)
E.g., take available battery capacity of devices into account
How to resolve conflicts between different optimizations?

15. MANETs characteristics
Heterogeneous nodes
Do not need backbone infrastructure support
Self-creating
not rely on a pre-existing fixed infrastructure
Self-organizing
no predetermined topology
Self-administering
no central control
creating a network “on the fly”
Are easy to deploy
Useful when infrastructure is absent, destroyed or impractical
Infrastructure may not be present in a disaster area or war zone
because there is no dependence on infrastructure, the network is robust and low-cost.
Finally, MANETs form the basis of all pervasive and ubiquitous computing.

16. MANETs Applications Military environments Emergency operations
Soldiers, tanks, planes
Emergency operations
Search-and-rescue
Policing and fire fighting
Civilian environments
Taxi cab network
Meeting rooms
Sports stadiums

17. Ad hoc networks & Cellular networks
Infrastructure less
Multiple hop
Radio power limitation, channel utilization, and power-saving concerns
DCF(distributed coordination function)
Cellular networks
Infrastructure-based
one hop(uplink or downlink)
PCF(pointed coordination function)

18. MANETs Challenges Spectrum allocation Self-configuration
Medium access control (MAC)
Energy efficiency
TCP Performance
Mobility management
Security & privacy
Routing protocols
Multicasting
QoS
Service Location, Provision, Access

19. Routing in MANET
In general, MANET routing protocols are expected to satisfy the following essential principles:
Tolerance of unexpected network faults (e.g. device and link failures)
Flexibility to increasing traffic loads
Minimal energy consumption (especially for smaller clients)
Mobile IP needs infrastructure
Home Agent/Foreign Agent in the fixed network
DNS, routing etc. are not designed for mobility
MANET
No default router available
“every” node also needs to be a router

20. Properties of good routing protocol in MANET
Must be distributed
Adaptive to frequent topology changes
Must be localized, since global state maintenance involves a huge state propagation control overhead
Loop free and free from stale routes
Convergence should be quick

21. Issues in Routing in MANET
Mobility
Topology highly dynamic due to movement of nodes
Ongoing sessions suffer frequent path breaks
Even though wired network protocol find alternate paths when a path breaks, the convergence is slow
Bandwidth constraint
Limited bandwidth imposes constraint on routing protocols to maintain topological information
Due to frequent changes in topology the control overhead of keeping the topology current could be very high

22. MANET routing protocols
Proactive or Table-driven protocols
Traditional distributed shortest-path protocols
Example: DSDV (destination sequenced distance vector)
Reactive or On-demand routing protocols
Determine route if and when needed
Example: DSR (dynamic source routing)
Hybrid protocols
Adaptive; Combination of proactive and reactive
Example : ZRP (zone routing protocol)
Hierarchical
Geographical

23. Expected Properties of Routing
Ideally an ad hoc network routing protocol should
be distributed in order to increase reliability
assume routes as unidirectional links
be power efficient.
consider its security
be hybrid protocols
be aware of Quality of Service

24. Proactive routing protocols-DSDV
Is based on the idea of Bellman-Ford routing algorithm
Every mobile station maintains a routing table that lists
all available destinations
the number of hops to reach the destination
the sequence number assigned by the destination node
A station transmits its routing table
periodically
if a significant change has occurred in its table from the last update sent
The routing table updates can be sent in two ways
full dump
incremental update

25. Example DSDV
MH3
MH5
MH4
MH8
MH2
MH6
MH7
MH1
MH1

26. Example DSDV Destination Next hop Metric Sequence number MH1 MH2 2
Routing table at MH4
Destination
Next hop
Metric
Sequence number
MH1
MH2 2
S406_MH1 1
S128_MH2
MH3
S564_MH3
MH4
S710_MH4
MH5
MH6
S392_MH5
S076_MH6
MH7
S128_MH7
MH8 3
S050_MH8

27. Example DSDV Destination Metric Sequence number MH1 2 S406_MH1 MH2 1
Advertisement from MH4
Destination
Metric
Sequence number
MH1 2
S406_MH1
MH2 1
S128_MH2
MH3
S564_MH3
MH4
S710_MH4
MH5
S392_MH5
MH6
S076_MH6
MH7
S128_MH7
MH8 3
S050_MH8

28. Routing table at MH4 (after MH1 moves)
Example DSDV
Routing table at MH4 (after MH1 moves)
Destination
Next hop
Metric
Sequence number
MH1
MH6 3
S516_MH1
MH2 1
S128_MH2
MH3 2
S564_MH3
MH4
S710_MH4
MH5
S392_MH5
S076_MH6
MH7
S128_MH7
MH8
S050_MH8

29. Advertisement from MH4 (after MH1 moves)
Example DSDV
Advertisement from MH4 (after MH1 moves)
Destination
Metric
Sequence number
MH4
S710_MH4
MH1 3
S516_MH1
MH2 1
S128_MH2
MH3 2
S564_MH3
MH5
S392_MH5
MH6
S076_MH6
MH7
S128_MH7
MH8
S050_MH8

30. DSDV: Advantages & Disadvantages
Routes available to all destinations
Less latency in route set up
Disadvantages
Updates are propagated throughout the network
Updates due to broken link (due to mobility) can lead to heavy control traffic
Even a small network with high mobility or large network with low mobility can choke the network
In order to get information about a particular destination node, a node has to wait for a table update message initiated by the same destination node
This delay would result in stale routing information

31. Reactive routing protocols- DSR
Reactive routing protocols are intended to maintain routing information about ‘active’ routes only. Routes are created when desired by the source node. Hence, the protocols are known as on-demand routing protocols.
However, no periodic routing advertisement messages are sent, thereby reducing network bandwidth overhead, particularly during periods when little or no significant host movement is taking place.

32. DSR
A node maintains route caches containing the source routes that it is aware of
The node updates entries in the route cache as and when it learns about new routes
route discovery
route request packet contains
the address of the source
the destination
a unique identification number
route reply is generated by
an intermediate node with current information about the destination
route maintenance
Route error packets are generated at a node when the data link layer encounters a fatal transmission problem
Acknowledgements, including passive acknowledgments

33. Dynamic Source Routing (DSR)
Source S initiates a route discovery by flooding Route Request (RREQ)
Each node appends its own identifier when forwarding RREQ
Destination D on receiving the first RREQ, sends a Route Reply (RREP)
RREP sent on route obtained by reversing the route appended in RREQ
RREP includes the route from S to D, on which RREQ was received by D
S routes data using “source route” mechanism

34. Dynamic Source Routing (DSR)
Routing Discovery Example: A H I B C J
Destination G
Source D E F K
Source:
The following series of slides illustrates the behavior of the DSR’s Route Discovery algorithm
Advantages:
Adapts quickly to frequent node movement resulting in need to change packet routes
Does not require significant overhead in periods when node movement is low
Tests show algorithm performs well in conditions with large host density and high movement
Route lengths have been shown to be within factor of 1.01 of optimal path

35. Dynamic Source Routing (DSR)

36. Represents a node that has received RREQ for D from S
Route Discovery in DSR Y Z S E F B C M L J A G H D K I N
Represents a node that has received RREQ for D from S
Source: Vaidya

37. Route Discovery in DSR Y Broadcast transmission Z [S] S E F B C M L JG H D K I N
Represents transmission of RREQ
[X,Y] Represents list of identifiers appended to RREQ

38. Route Discovery in DSR Y Z S [S,E] E F B C M L J A G [S,C] H D K I N
Node H receives packet RREQ from two neighbors:
potential for collision

39. Route Discovery in DSR Y Z S E F B [S,E,F] C M L J A G H D K [S,C,G] I
Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once

40. Route Discovery in DSR Y Z S E F [S,E,F,J] B C M L J A G H D K I N
[S,C,G,K]
Nodes J and K both broadcast RREQ to node D
Since nodes J and K are hidden from each other, their
transmissions may collide

41. Route Discovery in DSR Y Z S E [S,E,F,J,M] F B C M L J A G H D K I N
Node D does not forward RREQ, because node D
is the intended target of the route discovery

42. Represents RREP control message
Route Reply in DSR Y Z S
RREP [S,E,F,J,D] E F B C M L J A G H D K I N
Represents RREP control message

43. Packet header size grows with route length
Data Delivery in DSR Y Z
DATA [S,E,F,J,D] S E F B C M L J A G H D K I N
Packet header size grows with route length

44. Route Error (RERR) Y Z RERR [J-D] S E F B C M L J A G H D K I N
J sends a route error to S along route J-F-E-S when its attempt to forward the data packet S (with route SEFJD) on J-D fails (an ACK mechanism has to be there in packet forwarding)

45. Route caching Uses: Problems:
Finding alternate routes in case original route breaks
Route reply from intermediate nodes
Problems:
Cached routes may become invalid over time and due to host mobility
Stale caches can adversely affect performance

46. DSR: Route caching Each node caches a new route it learns by any means
When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F
When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S

47. Route caching
When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D
When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D
A node may also overhear Data to learn routes

48. Use of route caching [S,E,F,J,D] [E,F,J,D] S E [F,J,D],[F,E,S] F B
[J,F,E,S] C M L
[G,C,S] J A G
[C,S] H D K
[K,G,C,S] I N
RREP
RREQ Z
When Z sends a route request for C, node K sends back a route reply [Z,K,G,C] to Z using a locally cached route
Source: Vaidya

49. DSR: Advantages
Routes maintained only between nodes who need to communicate
reduces overhead of route maintenance
Route caching can further reduce route discovery overhead
A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches

50. DSR: Disadvantages
Packet header size grows with route length due to source routing
Latency to discover a route before data can be sent
Flood of route requests may potentially reach all nodes in the network
An intermediate node may send Route Reply using a stale cached route, thus polluting other caches
Inconsistency during route reconstruction phase

51. MANET Routing Algorithms
FLOODING
TABLE-DRIVEN
ON-DEMAND
HYBRID
+ Simplicity
+ Multiple path to the destination
- High Overhead
- Lower reliability of data delivery : Because of broadcast behavior of flooding
? Network properties :
+ Rate of topology changes increase
- Number of communications increases
- Number of nodes in the network increases
+ Delay of route determination decreases
-Communication overhead increases
-Storage requirements increases
+ Number of communication increases
- Rate of topology changes increases
+ Communication overhead decreases but it is subject to number of communications in the network
- Not optimal bandwidth utilization
- Delay of route determination increases
+ Rate of topology changes increases
o Better trade-off between communication overhead and delay
? Network properties :o Rate of topology changes increases
o Number of communications increases
o Number of nodes in the network increases