Mobile Ad hoc Networks

1
UNIT-7
Mobile Ad hoc Networks
2
Contents

• MANET overview
• Properties of MANET
• MANET applications
• Routing and various routing algorithms
• Unicast routing protocols for MANET
• Broadcasting protocols for MANET
• Multicasting Protocols for MANET
• QOS Routing
• Security in MANETS.

Syllabus from chapter 15, 17 in handbook of
wireless networks and mobile computing. By Ivan
Stojmenovic
3
Mobile Ad Hoc Networks

• Formed by wireless autonomous hosts
• Without (necessarily) using a pre-existing
  infrastructure
• Routes between hosts may potentially contain
  multiple hops
• Host mobility cause route changes
• Shared wireless channel

4
Why Ad Hoc Networks ?

• Ease of deployment
• Speed of deployment
• Decreased dependence on infrastructure
• User flexibility

5
Application areas

• Military environments
• Battle field sensors, soldiers, vehicles
• Emergency operations
• search-and-rescue
• policing and fire fighting
• Civilian environments
• conference halls
• sports stadiums, Library, etc.
• Personal area networking
• laptop, PDA, cell phone, ear phone, wrist watch

6
Challenges

• Lack of centralized entity
• Shared unreliable wireless medium
• Low bandwidth
• Hidden/exposure node effect
• Ease of snooping on wireless transmissions
• Mobility-induced route changes/packet losses
• Battery constraints
• Asymmetric Capabilities
• transmission ranges
• battery life
• processing capacity
• Speed/pattern of movement

7
Why is Routing in MANET Different?

• Host mobility
• link failure/repair due to mobility
• different characteristics than those due to other
  causes
• Rate of link failure/repair may be high when
  nodes move fast
• Distributed Environment
• New performance criteria may be used
• Route stability despite mobility
• Packet delivery ratio
• Routing Overhead

8
Unicast Routing Protocols in MANET
9
Routing

• Routing protocols in ad hoc networks need to deal
  with the mobility of nodes and constraints in
  power and bandwidth
• Current transport protocols (e.g. TCP) are not
  designed for wireless ad hoc networks

10

• The properties of the ad-hoc network routing
  protocol
• Simple
• Less storage space
• Loop free
• Short control message (Low overhead)
• Less power consumption
• Multiple disjoint routes
• Fast rerouting mechanism

11
Unicast Routing Protocols for Ad Hoc Networks

• Many protocols have been proposed
• Some specifically invented for MANET
• Others adapted from protocols for wired networks
• No single protocol works well in all environments
• some attempts made to develop adaptive/hybrid
  protocols
• Standardization efforts in IETF
• MANET, MobileIP working groups
• http//www.ietf.org

12
ZRP
13
Ad Hoc Unicast Routing Protocols

• Proactive protocols
• Traditional distributed shortest-path protocols
• Maintain routes between every host pair at all
  times
• Based on periodic updates High routing overhead
• Example DSDV (destination sequenced distance
  vector)
• Reactive protocols
• Determine route if and when needed
• Source initiates route discovery
• Example DSR (dynamic source routing)
• Hybrid protocols
• Adaptive Combination of proactive and reactive
• Example ZRP (zone routing protocol)

14
Proactive unicast routing protocols

• Continuously makes routing decisions so routes
  are available when packets need to be transmitted
• Traditional distributed shortest-path protocols
• Maintain routes between every host pair at all
  times
• They consume a great deal of radio resources to
  exchange routing information
• Based on periodic updates
• High routing overhead
• However, pre-determined routes may rapidly lose
  their validity in an ad hoc network
• because its topology changes rapidly
• These attempt to maintain the network topology
  always updated by periodically exchanging control
  packets
• Every node has a complete forwarding table
• i.e. for any destination it knows the right
  next-hop, and optimal routing (e.g. shortest
  path) is possible
• Their problem is that the amount of control
  traffic is huge and often disproportionate
• In highly dynamic networks, it is likely to
  happen that most of the bandwidth is wasted in
  vain because nodes reaction to topological
  changes is slower than the topological changes
  themselves
• Examples DSDV (destination sequenced distance
  vector).

15
DSDVDestination-Sequenced Distance-Vector
Routing Protocol
16
Introduction

• Routing Algorithm
• Link-State algorithm
• Each node maintains a view of the network
  topology
• Distance-Vector algorithm
• Every node maintains the distance of each
  destination

17
Link-State

• Like the shortest-path computation method
• Each node maintains a view of the network
  topology with a cost for each link
• Periodically broadcast link costs to its outgoing
  links to all other nodes such as flooding

18
Link-State
A
link costs
F
H
B
E
C
G
D
19
Distance-Vector

• known also as Distributed Bellman-Ford or RIP
  (Routing Information Protocol)
• Every node maintains a routing table
• all available destinations
• the next node to reach to destination
• the number of hops to reach the destination
• Periodically send table to all neighbors to
  maintain topology

20
Distance Vector (Tables)
1
2
C
B
A
Dest. Next Metric
A A 1
B B 0
C C 2
Dest. Next Metric
A A 0
B B 1
C B 3
Dest. Next Metric
A B 3
B B 2
C C 0
21
Distance Vector (Update)
B broadcasts the new routing information to his
neighbors
Routing table is updated
(A, 1) (B, 0) (C, 1)
(A, 1) (B, 0) (C, 1)
1
1
C
B
A
Dest. Next Metric
A A 0
B B 1
C B 3 2
Dest. Next Metric
A A 1
B B 0
C C 1
Dest. Next Metric
A B 3 2
B B 1
C C 0
22
Distance Vector (New Node)
broadcasts to update tables of C, B, A with new
entry for D
(A, 2) (B, 1) (C, 0) (D, 1)
(A, 1) (B, 0) (C, 1) (D, 2)
(D, 0)
1
1
1
C
B
A
D
Dest. Next Metric
A B 2
B B 1
C C 0
D D 1
Dest. Next Metric
A A 1
B B 0
C C 1
D C 2
Dest. Next Metric
A A 0
B B 1
C B 2
D B 3
23
Distance Vector (Broken Link)
1
1
1
D
C
B
A
Dest.c Next Metric

D C 2
Dest. Next Metric

D B 3
Dest. Next Metric

D B 1
Dest. Next Metric

D D ?
24
Distance Vector (Loops)
(D, 2)
(D, 2)
1
1
1
D
C
B
A
Dest. Next Metric

D B 3
Dest. Next Metric

D C 2
Dest. Next Metric

D B 3
25
Distance Vector (Count to Infinity)
(D,5)
(D,4)
(D,4)
(D,3)
(D,2)
(D,2)
1
1
1
D
C
B
A
Dest. Next Metric

D B 3, 5,
Dest. Next Metric

D B 3, 5,
Dest.c Next Metric

D C 2, 4, 6
26
Distance Vector

• DV not suited for ad-hoc networks!
• Loops
• Count to Infinity
• New Solution -gt DSDV Protocol

27
DSDV Protocol

• DSDV is Destination Based
• No global view of topology

28
DSDV Protocol

• DSDV is Proactive (Table Driven)
• Each node maintains routing information for all
  known destinations
• Routing information must be updated periodically
• Traffic overhead even if there is no change in
  network topology
• Maintains routes which are never used

29
DSDV Protocol

• Keep the simplicity of Distance Vector
• Guarantee Loop Freeness
• New Table Entry for Destination Sequence Number
• Allow fast reaction to topology changes
• Make immediate route advertisement on significant
  changes in routing table
• but wait with advertising of unstable
  routes(damping fluctuations)

30
DSDV (Table Entries)
Destination Next Metric Seq. Nr Install Time Stable Data
A A 0 A-550 001000 Ptr_A
B B 1 B-102 001200 Ptr_B
C B 3 C-588 001200 Ptr_C
D B 4 D-312 001200 Ptr_D

• Sequence number originated from destination.
  Ensuresloop freeness.
• Install Time when entry was made (used to delete
  stale entries from table)
• Stable Data Pointer to a table holding
  information on how stable a route is. Used to
  damp fluctuations in network.

31
DSDV (Route Advertisements)

• Advertise to each neighbor own routing
  information
• Destination Address
• Metric Number of Hops to Destination
• Destination Sequence Number
• Rules to set sequence number information
• On each advertisement increase own destination
  sequence number (use only even numbers)
• If a node is no more reachable (timeout) increase
  sequence number of this node by 1 (odd sequence
  number) and set metric ?

32
DSDV (Route Selection)

• Update information is compared to own routing
  table
• 1. Select route with higher destination sequence
  number (This ensure to use always newest
  information from destination)
• 2. Select the route with better metric when
  sequence numbers are equal.

33
DSDV (Tables)
1
2
C
B
A
Dest. Next Metric Seq
A A 1 A-550
B B 0 B-100
C C 2 C-588
Dest. Next Metric Seq
A A 0 A-550
B B 1 B-100
C B 3 C-586
Dest. Next Metric Seq.
A B 1 A-550
B B 2 B-100
C C 0 C-588
34
DSDV (Route Advertisement)
B increases Seq.Nr from 100 -gt 102 B broadcasts
routing information to Neighbors A, C including
destination sequence numbers
(A, 1, A-550) (B, 0, B-102) (C, 1, C-588)
(A, 1, A-550) (B, 0, B-102) (C, 1, C-588)
1
1
C
B
A
Dest. Next Metric Seq
A A 0 A-550
B B 1 B-102
C B 2 C-588
Dest. Next Metric Seq
A A 1 A-550
B B 0 B-102
C C 1 C-588
Dest. Next Metric Seq.
A B 2 A-550
B B 1 B-102
C C 0 C-588
35
DSDV (Respond to Topology Changes)

• Immediate advertisements
• Information on new Routes, broken Links, metric
  change is immediately propagated to neighbors.
• Full/Incremental Update
• Full Update Send all routing information from
  own table.
• Incremental Update Send only entries that has
  changed. (Make it fit into one single packet)

36
DSDV (New Node)
2. Insert entry for D with sequence number
D-000Then immediately broadcast own table
1. D broadcast for first timeSend Sequence
number D-000
(D, 0, D-000)
C
B
A
D
Dest. Next Metric Seq.
A A 0 A-550
B B 1 B-104
C B 2 C-590

Dest. Next Metric Seq.
A A 1 A-550
B B 0 B-104
C C 1 C-590

Dest. Next Metric Seq.
A B 2 A-550
B B 1 B-104
C C 0 C-590
D D 1 D-000
37
DSDV (New Node cont.)
3. C increases its sequence number to C-592 then
broadcasts its new table.
4. B gets this new information and updates its
table.
(A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1,
D-000)
(A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1,
D-000)

C
B
A
D
Dest. Next Metric Seq.
A A 1 A-550
B B 0 B-102
C C 1 C-592
D C 2 D-000
Dest. Next Metric Seq.
A A 0 A-550
B B 1 B-104
C B 2 C-590

Dest. Next Metric Seq.
A B 2 A-550
B B 1 B-102
C C 0 C-592
D D 1 D-000
38
DSDV (no loops, no count to infinity)
2. B does its broadcast-gt no affect on C (C
knows that B has stale information because C has
higher seq. number for destination D) -gt no loop
-gt no count to infinity
1. Node C detects broken Link-gt Increase Seq.
Nr. by 1(only case where not the destination
sets the sequence number -gt odd number)
(D, 2, D-100)
(D, 2, D-100)
D
C
B
A
Dest.c Next Metric Seq.

D C 2 D-100
Dest. Next Metric Seq.

D B 3 D-100
Dest. Next Metric Seq.

D D ? D-101
39
DSDV (Immediate Advertisement)
3. Immediate propagation B to A(update
information has higher Seq. Nr. -gt replace table
entry)
2. Immediate propagationC to B(update
information has higher Seq. Nr. -gt replace table
entry)
1. Node C detects broken Link-gt Increase Seq.
Nr. by 1(only case where not the destination
sets the sequence number -gt odd number)
(D, ?, D-101)
(D, ?, D-101)
D
C
B
A
Dest.c Next Metric Seq.

D C 3 D-100
Dest. Next Metric Seq.

D B 4 D-100
Dest. Next Metric Seq.

D B 1 D-100
Dest. Next Metric Seq.

D D 1 D-100
D D ? D-101
Dest.c Next Metric Seq.
...
D C 2 D-100
D C ? D-101
Dest. Next Metric Seq.
...
D B 3 D-100
D B ? D-101
40
DSDV (Problem of Fluctuations)

• What are Fluctuations
• Entry for D in A D, Q, 14, D-100
• D makes Broadcast with Seq. Nr. D-102
• A receives from P Update (D, 15, D-102)-gt Entry
  for D in A D, P, 15, D-102 A must propagate
  this route immediately.
• A receives from Q Update (D, 14, D-102)-gt Entry
  for D in A D, Q, 14, D-102A must propagate
  this route immediately.
• This can happen every time D or any other node
  does its broadcast and lead to unnecessary route
  advertisements in the network, so called
  fluctuations.

A
P
Q
10 Hops
11 Hops
(D,0,D-102)
D
41
DSDV (Damping Fluctuations)

• How to damp fluctuations
• Record last and avg. Settling Time of every Route
  in a separate table. (Stable Data)Settling Time
  Time between arrival of first route and the
  best route with a given seq. nr.
• A still must update his routing table on the
  first arrival of a route with a newer seq. nr.,
  but he can wait to advertising it. Time to wait
  is proposed to be 2(avg. Settling Time).
• Like this fluctuations in larger networks can be
  damped to avoid unececarry adverdisment, thus
  saving bandwith.

A
P
Q
10 Hops
10 Hops
11 Hops
D
42
Summery of DSDV

• Advantages
• Simple (almost like Distance Vector)
• Loop free through destination seq. numbers
• No latency caused by route discovery
• Disadvantages
• No sleeping nodes
• Overhead most routing information never used

43
Reactive unicast routing protocols

• Determine routes on an as-needed basis
• when a node has a packet to transmit, it queries
  the network for a route
• Source initiates route discovery
• They performed better than proactive protocols
• Reactive protocols are on-demand protocols
  routes are discovered only if needed
• i.e. when the source does not know a route to the
  destination.
• Nodes do not make any effort to keep routing
  table updated
• Most of the routing protocols are reactive
• Examples
• AODV
• DSR (dynamic source routing)
• TORA etc

44
Dynamic Source Routing (DSR)
Johnson-96
45

• When node S wants to send a packet to node D, but
  does not know a route to D, node S initiates a
  route discovery
• Source node S floods Route Request (RREQ)
• Each node appends own identifier when forwarding
  RREQ

46
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
47
Route Discovery in DSR
Y
Broadcast transmission
Z
S
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Represents transmission of RREQ
X,Y Represents list of identifiers appended
to RREQ
48
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

49
Route Discovery in DSR
Y
Z
S
E
F
S,E,F
B
C
M
L
J
A
G
H
D
K
S,C,G
I
N

• Node C receives RREQ from G and H, but does not
  forward
• it again, because node C has already forwarded
  RREQ once

50
Route Discovery in DSR
Y
Z
S
E
F
S,E,F,J
B
M
C
L
J
A
G
D
H
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

51
Route Discovery in DSR
Y
Z
S
E
S,E,F,J,M
F
B
L
C
M
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

52
Route Discovery in DSR

• Destination D on receiving the first RREQ, sends
  a Route Reply (RREP)
• RREP is sent on a route obtained by reversing the
  route appended to received RREQ
• RREP includes the route from S to D on which RREQ
  was received by node D

53
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
54
Dynamic Source Routing (DSR)

• Node S on receiving RREP, caches the route
  included in the RREP
• When node S sends a data packet to D, the entire
  route is included in the packet header
• hence the name source routing
• Intermediate nodes use the source route included
  in a packet to determine to whom a packet should
  be forwarded

55
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
56
DSR Optimization 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
• 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 learn a route when it overhears
  Data
• Problem Stale caches may increase overheads

57
Dynamic Source Routing 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

58
Dynamic Source Routing Disadvantages

• Packet header size grows with route length due to
  source routing
• Flood of route requests may potentially reach all
  nodes in the network
• Potential collisions between route requests
  propagated by neighboring nodes
• insertion of random delays before forwarding RREQ
• Increased contention if too many route replies
  come back due to nodes replying using their local
  cache
• Route Reply Storm problem
• Stale caches will lead to increased overhead

59
Location-Aided Routing (LAR)
Ko98Mobicom
60
Location-Aided Routing (LAR)

• Exploits location information to limit scope of
  route request flood
• Location information may be obtained using GPS
• Expected Zone is determined as a region that is
  expected to hold the current location of the
  destination
• Expected region determined based on potentially
  old location information, and knowledge of the
  destinations speed
• Route requests limited to a Request Zone that
  contains the Expected Zone and location of the
  sender node

61
Request Zone

• Define a Request Zone
• LAR is same as flooding, except that only nodes
  in request zone forward route request
• Smallest rectangle including S and expected zone
  for D

Request Zone
D
Expected Zone
x
Y
S
62
Location Aided Routing (LAR)

• Advantages
• reduces the scope of route request flood
• reduces overhead of route discovery
• Disadvantages
• Nodes need to know their physical locations
• Does not take into account possible existence of
  obstructions for radio transmissions

63
Ad Hoc On-Demand
Distance Vector Routing (AODV)
Perkins-99
64

• DSR includes source routes in packet headers
• Resulting large headers can sometimes degrade
  performance
• particularly when data contents of a packet are
  small
• AODV attempts to improve on DSR by maintaining
  routing tables at the nodes, so that data packets
  do not have to contain routes
• AODV retains the desirable feature of DSR that
  routes are maintained only between nodes which
  need to communicate

65
AODV

• Route Requests (RREQ) are forwarded in a manner
  similar to DSR
• When a node re-broadcasts a Route Request, it
  sets up a reverse path pointing towards the
  source
• AODV assumes symmetric (bi-directional) links
• When the intended destination receives a Route
  Request, it replies by sending a Route Reply
  (RREP)
• Route Reply travels along the reverse path set-up
  when Route Request is forwarded

66
Route Requests in AODV
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
67
Route Requests in AODV
Y
Broadcast transmission
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Represents transmission of RREQ
68
Route Requests in AODV
Y
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N
Represents links on Reverse Path
69
Reverse Path Setup in AODV
Y
Z
S
E
F
B
C
M
L
J
A
G
H
D
K
I
N

• Node C receives RREQ from G and H, but does not
  forward
• it again, because node C has already forwarded
  RREQ once

70
Reverse Path Setup in AODV
Y
Z
S
E
F
B
M
C
L
J
A
G
D
H
K
I
N
71
Reverse Path Setup in AODV
Y
Z
S
E
F
B
L
C
M
J
A
G
H
D
K
I
N

• Node D does not forward RREQ, because node D
• is the intended target of the RREQ

72
Forward Path Setup in AODV
Y
Z
S
E
F
B
L
C
M
J
A
G
H
D
K
I
N
Forward links are setup when RREP travels
along the reverse path Represents a link on the
forward path
73
Route Request and Route Reply

• Route Request (RREQ) includes the last known
  sequence number for the destination
• An intermediate node may also send a Route Reply
  (RREP) provided that it knows a more recent path
  than the one previously known to sender
• Intermediate nodes that forward the RREP, also
  record the next hop to destination
• A routing table entry maintaining a reverse path
  is purged after a timeout interval
• A routing table entry maintaining a forward path
  is purged if not used for a active_route_timeout
  interval

74
Link Failure

• A neighbor of node X is considered active for a
  routing table entry if the neighbor sent a packet
  within active_route_timeout interval which was
  forwarded using that entry
• Neighboring nodes periodically exchange hello
  message
• When the next hop link in a routing table entry
  breaks, all active neighbors are informed
• Link failures are propagated by means of Route
  Error (RERR) messages, which also update
  destination sequence numbers

75
Route Error

• When node X is unable to forward packet P (from
  node S to node D) on link (X,Y), it generates a
  RERR message
• Node X increments the destination sequence number
  for D cached at node X
• The incremented sequence number N is included in
  the RERR
• When node S receives the RERR, it initiates a new
  route discovery for D using destination sequence
  number at least as large as
• When node D receives the route request with
  destination sequence number N, node D will set
  its sequence number to N, unless it is already
  larger than N

76
AODV Summary

• Routes are not needed to be included in packet
  headers
• Nodes maintain routing tables containing entries
  only for routes that are in active use
• At most one next-hop per destination maintained
  at each node
• DSR may maintain several routes for a single
  destination
• Sequence numbers are used to avoid old/broken
  routes
• Sequence numbers prevent formation of routing
  loops
• Unused routes expire even if topology does not
  change

77
Temporally-Ordered Routing
Algorithm (TORA)
78

• Route optimality is considered of secondary
  importance longer routes may be used
• At each node, a logically separate copy of TORA
  is run for each destination, that computes the
  height of the node with respect to the
  destination
• Height captures number of hops and next hop
• Route discovery is by using query and update
  packets
• TORA modifies the partial link reversal method to
  be able to detect partitions
• When a partition is detected, all nodes in the
  partition are informed, and link reversals in
  that partition cease

79
Other Protocols

• Many variations of using control packet flooding
  for route discovery
• Power-Aware Routing Singh98Mobicom
• Assign a weight to each link function of energy
  consumed when transmitting a packet on that link,
  as well as the residual energy level
• Modify DSR to incorporate weights and prefer a
  route with the smallest aggregate weight
• Associativity-Based Routing (ABR) Toh97
• Only links that have been stable for some minimum
  duration are utilized
• Nodes increment the associativity ticks of
  neighbors by using periodic beacons
• Signal Stability Based Adaptive Routing (SSA)
  Dube97
• A node X re-broadcasts a Route Request received
  from Y only if the (X,Y) link has a strong signal
  stability
• Signal stability is evaluated as a moving average
  of the signal strength of packets received on the
  link in recent past

80
Hybrid Routing Protocols
81
Zone Routing Protocol (ZRP)
Haas98
82

• ZRP combines proactive and reactive approaches
• All nodes within hop distance at most d from a
  node X are said to be in the routing zone of node
  X
• All nodes at hop distance exactly d are said to
  be peripheral nodes of node Xs routing zone
• Intra-zone routing Proactively maintain routes
  to all nodes within the source nodes own zone.
• Inter-zone routing Use an on-demand protocol
  (similar to DSR or AODV) to determine routes to
  outside zone.

83
Zone Routing Protocol (ZRP)
Radius of routing zone 2
84
Ad Hoc Unicast Routing Summary

• Protocols
• Typically divided into proactive, reactive and
  hybrid
• Plenty of routing protocols. Discussion here is
  far from exhaustive
• Performance Studies
• Typically studied by simulations using NS,
  discrete event simulator
• Nodes (10-30) remains stationary for pause time
  seconds (0-900s) and then move to a random
  destination (1500m X300m space) at a uniform
  speed (0-20m/s). CBR traffic sources (4-30
  packets/sec, 64-1024 bytes/packet)
• Attempt to estimate latency of route discovery,
  routing overhead
• Actual trade-off depends a lot on traffic and
  mobility patterns
• Higher traffic diversity (more source-destination
  pairs) increases overhead in on-demand protocols
• Higher mobility will always increase overhead in
  all protocols

85
Multicasting
Protocols for
MANETS
86
Recap

• Multicasting
• Group communication
• One-to-many
• In Battle field
• Many-to-many
• Rescue team communication
• Why not using existing multicast protocol
• Resource constraints
• Frequent tree reorganization
• signaling overhead
• loss of datagram
• Protocol design
• robustness vs. efficiency

87
Multicasting in MANET

• Structure
• Tree-based
• Shared multicast tree
• Vulnerable to high mobility, load and large group
• Mesh-based
• Quick reconfigurable
• Excessive message overhead

88
MAODV (Royer and Perkins, 1999)

• Each multicast group has a group leader
• 1st node joining a group becomes Group Leader
• Responsible for maintaining group SN (sequence
  number)
• SN ensures freshness of routing information
• A node on becoming a group leader
• Broadcasts a Group Hello message

89
MAODV
Group Join Process
Broadcast - RREQ
Multicast Activation
Broadcast Group Hello
Only GM Responds
L
90
MAODV
Leaving a Multicast Group
Non leaf Node Must remain as a Tree member
L
Leaf Node Send a Prune
Again Leaf Node Remove himself from MT
91
MAODV

• Observation
• Similar to unicast AODV
• Leader helps in tree maintenance
• No alternate path as it forms a tree
• Excessive use of RREQ
• lead to multicast tree instability

92
ODMRP (Bae, Lee, Su, Gerla, 2000)
Join Reply
Join Request
Forwarding Group
Broadcast
Multicast RT
b
Y, Z
s
b, c
s
c
s
X
s
a, W
s
d, e
s
Sender
e
a
d
93
ODMRP
Robustness
94
ODMRP

• Observation
• Sender Forms and Maintains the multicast group
• Dont need to be built on top of a unicast
  routing protocol
• Richer connectivity
• May have multiple routes for one particular
  destination
• Helps in case of topology changes and node
  failures
• soft state
• Member nodes are refreshed as needed by source
• Do not send explicit leave message
• Periodic Broadcast of Join Request
• Control overhead of route refreshes gt
  Scalability issue.