Adhoc and Sensor Networks - Chapter 03

Copyright © 2006, Dr. Carlos Cordeiro and Prof. Dharma P. Agrawal, All rights reserved. 1
 Introduction
 The Broadcast Storm
 Broadcasting in a MANET
 Flooding-Generated Broadcast Storm
 Redundancy Analysis
 Rebroadcasting Schemes
 Multicasting
 Issues in Providing Multicast in a MANET
 Multicast Routing Protocols
 Comparison
 Geocasting
 Geocast Routing Protocols
 Comparison
 Conclusion and Future Directions
Table of
Contents

Routing Protocols
Topology-Based:
Depends on the information about existing links
 Position-Based Approaches
 Proactive (or table-driven)
 Proactive (Table-driven) 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 (On-Demand) 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)

Routing Approaches
 Broadcasting
 Is a common operation in many applications, e.g., graph-related
and distributed computing problems
 It is also widely used to resolve many network layer problems
 Multicasting
 Transmission of datagrams to a group of hosts identified by a
single destination address
 Hence is intended for group-oriented computing
 Can efficiently support a variety of applications that are
characterized by close collaborative efforts
 Geocasting
 Aims at delivering data packets to a group of nodes located in a
specified geographical area
 Can be seen as a variant of the conventional multicasting
problem, and distinguishes itself by specifying hosts as group
members within a specified geographical region
 Since all these three do communication to a group of recipients, it
is imperative to determine what is the best way to provide these
services in an ad hoc (MANET) environment
 Comparison of broadcast, multicast and geocast protocols for ad
hoc networks provided

The Broadcast Storm
 MANET consists of a set of MHs that may communicate
with one another from time to time
 No base stations are present
 Each host is equipped with a CSMA/CA
 Transmission of a message to all other MHs required
 The broadcast is spontaneous
 Due to MH mobility and lack of synchronization, any
kind of global topology knowledge is prohibitive
 Little or no local information may be collected in
advance
 The broadcast is frequently unreliable
 Acknowledgement mechanism is rarely used
 Distribute a broadcast message to as many MHs as
possible without putting too much effort
 A MH may miss a broadcast message because it is off-
line, it is temporarily isolated from the network, or it
experiences repetitive collisions

The Broadcast Storm
 Broadcast
 Acknowledgements may cause serious medium
contention
 In many applications 100% reliable broadcast is
unnecessary
 MH can detect duplicate broadcast messages
 If flooding is used blindly, many redundant messages
will be sent and serious contention/collision will be
incurred
 Redundant rebroadcasts
 When a MH decides to rebroadcast, all its neighbors
may already have the message
 Contention
 Transmissions from neighbors may severely contend
with each other
 Collision
 Due to absence of collision detection, collisions are
more likely to occur and cause more damage

Example (simple flooding)
Source node
Rebroadcast node
S
1
2
4
7
8
96
5
3
1st
step: S
2nd
step: 1, 5, 6, 9
3rd
step: 2, 3, 7, 8
4th
step: 4
Total: 9 Rebroadcast nodes
S
1
2
4
7
8
96
5
3
Better Solution: Only
4 Rebroadcast nodes

Example broadcast storm
problem in a 13 node MANET
S
D
A
D
C
B
M
H
G
F
E
LK
J
I
1
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
4
4
44
4
4
4
55
5
55
5 6
A and D collide
at C at step 2
H and K contend
at step 5
Message still
propagates …..
I and J
collide at M
at step 4
D and E
contend at
step 2
Average degree 2.6

Redundancy Analysis
D
11
2
S
D
1
1
1
22
2
S
Optimal Broadcast in MANETs

Redundancy Analysis
 Assume that the total area
covered by the radio signal
transmitted by a transceiver is a
circle of radius r
 Intersection area of two circles of
radio r whose centers are d apart
be INTC(d)
 Additional coverage provided by a
host to who rebroadcasts the
packet is equal to πr2
– INTC(d)
 When d = r, the additional
coverage is approximately 0.61πr2
(maximum)
 Average additional coverage by
rebroadcasting from randomly
located host is 0.41πr2
 Expected additional coverage
provided by a host’s rebroadcast
after the same broadcast packet
received by host k times is denoted
by EAC(k)
r
r
d
Randomly deployed MANET

Rebroadcasting Schemes
 Minimize number of retransmissions of a
broadcast message
 Attempt to deliver a broadcast packet to each and
every node in the network
Common Attributes of Broadcast Protocols
 Jitter and Random Delay Timer (RDT)
 Jitter allows one neighbor to acquire the channel first
while other neighbors detect that the channel is busy
 RDT allows a node to keep track of redundant packets
received over a short time interval
 Loop Prevention
 Node rebroadcasts a given packet no more than one
time by caching original source node ID of the packet
and the packet ID

Categories of Broadcasting
Protocols
 Simple flooding
 A source node broadcasting a packet to all neighbors
 The neighbors, upon receiving the broadcast packet,
rebroadcast the packet exactly once
 Probability-based methods
 Similar to ordinary flooding
 Nodes only rebroadcast with a predetermined probability
 In dense networks, multiple nodes share similar
transmission coverage
 Counter-Based Scheme: relationship between number of
times a packet is received and the probability of a node’s
transmission to cover additional area on a rebroadcast
 Area-based methods
 Neighbor knowledge methods

Protocols Area-based methods
 If a sender is located only one meter away, the additional area
covered by the retransmission by a receiving node
rebroadcasts is quite low
 Distance-based scheme compares the distance between itself
and each of its neighbor nodes that has previously rebroadcast
a given packet
 Location-based scheme uses a more precise estimation of
expected additional coverage area
 Neighbor knowledge methods
 Flooding with Self Pruning requires each node to have
knowledge of its one-hop neighbors
 Scalable Broadcast Algorithm (SBA) requires that all nodes
have knowledge of their neighbors within a two-hop radius
 Each node searches its neighbor tables for the maximum
neighbor degree of any neighbor node, say, dNmax
 Calculates a Random Time Delay (RDT)
based on the ratio of
where dme is the number of current
neighbors for the node








me
N
d
d max

Protocols
 Neighbor knowledge methods…..
 Dominant Pruning: Uses two-hop neighbor knowledge, but
proactively choosing some or all of its one-hop neighbors as
rebroadcasting nodes
 Multipoint Relaying: Similar to Dominant Pruning, but
rebroadcasting nodes, [Multipoint Relays (MPRs)] are explicitly
chosen by upstream senders
Algorithm for a node to choose its MPRs
1. Find all two-hop neighbors that can only be reached by one one-
hop neighbor and assign those one-hop neighbors as MPRs
2. Determine the resultant cover set (i.e., the set of two-hop
neighbors that will receive the packet from the current MPR set)
3. From the remaining one-hop neighbors not yet in the MPR set,
find the one that would cover the most two-hop neighbors not in
the cover set
4. Repeat from step 2 until all two-hop neighbors are covered

Protocols Ad Hoc Broadcast Protocol (AHBP)
 Approach similar to Multipoint Relaying by designating
nodes as a Broadcast Relay Gateway (BRG)
 AHBP differs from Multipoint Relaying in three ways:
 Connected Dominating Set-Based Broadcast Algorithm
 A dominating set for a graph is a set of vertices whose neighbors, along with
themselves, constitute all the vertices in the graph
 A connected dominating set of minimum size in a graph includes vertices in
the dominating set to be connected as well
 Considers the set of higher priority BRGs selected by the
previous sender
1. A node using AHBP informs one-hop neighbors of the BRG
designation by a field in the header of each broadcast packet
as opposed to done by hello packets in Multipoint Relaying
2. In AHBP, when a node receives a broadcast packet listed as a
BRG, it uses two-hop neighbor knowledge to find which
neighbors also received the broadcast packet in the same
transmission so as to remove from the neighbor graph
3. AHBP is extended to account for high mobility networks

Dominated Set
If you allow all
members of
dominating set to
retransmit,
all MHs in the
network are
guaranteed to be
covered
The black vertices are the
member of Dominating Set

Connected Dominating Set
A dominating set of a graph
G= (V, E) is a vertex subset
S V⊆ , such that every
vertex v V is either in S or∈
adjacent to a vertex of S
A connected dominating set (CDS) of
a graph G is a dominating set whose
induced graph is connected (this
enables any member to be within
communication range of another
member to enable broadcast)

Broadcast Nodes in Large
Networks?  Some nodes are highly
connected than others
 Similarily, some nodes
are sparsely connected
than others
 Some nodes are in
between
 Dominating Set?
 Complexity?
 Global connectivity
knowledge?
 Local knowledge: 2-hop
neighbors?
 Some nodes highly
connected than other
neighbors?
 Some nodes sparsely
connected than other
neighbors?
 Quantify nodes based on
connectivity?

Protocols
 Connected Dominating Set-Based Broadcast Algorithm
- MHs into four groups based on local information as
follows:
 Group 1: Nodes with degrees larger than the degree
of all neighboring nodes, where connectivity
represents the number of neighbors within the
directed transmitting range of a reference node
 Group 2: Nodes have a majority of neighbors with
smaller degree than the reference nodes
 Group 3: Remaining nodes not belonging to groups
1, 2 and 4
 Group 4: Nodes with degrees smaller than all the
neighbors
 A message forwarder is assigned in a decreasing
probability order as p1, p2, p3 and p4

Connected Dominating Set-
Based Broadcast Algorithm
 If A be the area of the MANET
 N be the number of mobile nodes
 r be the communication range of each mobile node with a
being the fraction of the area covered and α being the fraction
of area covered, then
 The average number of neighboring nodes Nneighbors can be given
by
 The probability pithat a mobile node has i neighbors, can be
given by
 The probability p1, p2, p3, and p4 can be given by
A
r 2
π
α=
α)1( −= NNneighbors
( ) iiN
i
i
N
p αα −−
−




 −
=
1
1
1
iN
i
j
j
i
i
j
j
N
i
i pp
i
N
pP
−−
−
=
−
=
−
=








−












 −
= ∑∑∑
1
1
1
1
1
1
1
1 1
1
∑ ∑ ∑∑
−
= =
−
−
=
−
= 





































=
1
1
2/
1
1
1
1
2
N
i
i
k
ki
i
j
j
k
N
ij
ji pp
k
i
pP
∑ ∑ ∑∑
−
= =
−
−
=
−
= 





































=
1
1 2/
1
1
1
3
N
i
i
ik
ki
i
j
j
k
N
ij
ji pp
k
i
pP
iN
N
ij
j
i
N
ij
j
N
i
i pp
i
N
pP
−−
−
+=
−
+=
−
=








−












 −
= ∑∑∑
1
1
1
1
1
1
1
4 1
1

Group Forwarding Probabilities for
N=100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1 1.2
α : Fraction of area A covered by each node
ForwardingProbability
P1
P2
P3
P4

Connected Dominating Set-Based
Broadcast Algorithm
 Total number of forwarding steps, NF :
where τiis the forwarding probability for the mobile node in group
 Such a scheme does not provide 100% coverage of all MANET
nodes
 A good coverage and excellent saving are achieved under mobility
and about 20% higher goodput is obtained than the conventional
AODV
 Lightweight and Efficient Network-Wide Broadcast: Relies on two-
hop neighbor knowledge obtained from hello packets; however
instead of a node explicitly choosing other nodes to rebroadcast, the
decision is implicit
( )44332211 PPPPNNF ττττ +++=

Lightweight and Efficient
Network-Wide Broadcast
 Relies on two-hop neighbor knowledge obtained
from hello packets
 Each node decides to rebroadcast based on
knowledge of which of its other one and two-hop
neighbors are expected to rebroadcast
 Knowledge of which neighbors have received a
packet from the same source node, and which
neighbors have a higher priority for
rebroadcasting
 The priority is proportional to the number of
neighbors of a given node
 The higher a node’s degree is, the higher is its
priority

Multicasting v/s
Broadcastng?

Multicasting
 Routing protocols offering efficient multicasting in wired
networks may fail to keep up with node movements and
frequent topological changes
 Broadcast protocols cannot be used either as multicasting
requires a selected set of nodes to receive the message
 All multicast algorithm depend on the topology of the
network
 Majority of applications requiring rapid deployment and
dynamic reconfiguration, need multicasting such as
military battlefields, emergency search and rescue sites,
classrooms, and conventions
 Crucial to reduce the transmission overhead and power
consumption
 Multicasting in a MANET faces challenges such as
dynamic group membership and update of delivery path
due to MH movement

Multicast Routing Protocols
 Broadcast protocols cannot be used as
multicasting requires a selected set of MHs
to receive the message
 Protocols are classified into four categories
based on how route to the members of the
group is created:
 Tree-Based Approaches
 Meshed-Based Approaches
 Stateless Multicast
 Hybrid Approaches

Source
0
1
2
1
1
1
2
2
2
3
3
3
Illustration of Tree-Based
Multicast Nodes not a part
of Multicast
group

Tree-Based Approaches
 Extend tree-based approach to provide multicast in a
MANET
 A packet traverses each hop and node in a tree at most
once
 Very simple routing decisions at each node
 Tree structure built representing shortest paths amongst
nodes, and a loop-free data distribution structure
 Even a link failure could mean reconfiguration of entire
tree structure, could be a major drawback
 Consider either a shared tree or establish a separate tree
per each source
 For separate source trees, each router in multiple router
groups must maintain a list of pertinent information for each
group and such management per router is inefficient and not
scalable
 For shared trees, there is a potential that packets may not
only not traverse shorter paths, but routed on paths with
much longer distances

 Ad hoc Multicast Routing Protocol Utilizing Increasing Id-Numbers
 Utilizing Increasing id-numberS (AMRIS) is an on-demand protocol,
which constructs a shared multicast delivery tree to support multiple
senders and receivers in a multicast session
 AMRIS dynamically assigns an id-number to each node in each multicast
session and a multicast delivery tree – rooted at a special node with Sid
(Smallest-ID and is usually a source that initiates a multicast session) – is
created and the id-number increases as the tree expands from the Sid
 In case of multiple senders, a Sid is selected among the given set of senders
 Once a Sid is identified, it sends a NEW-SESSION message to its
neighbors
 This message includes Sid’s msm-id (multicast session member id) and the
routing metrics
 Nodes receiving the NEW-SESSION message generate their own msm-ids,
which is larger than the msm-id of the sender
 In case a node receives multiple NEW-SESSION messages from different
nodes, it keeps the message with the best routing metrics and calculates its
msm-ids
 To join an ongoing session, a node checks the NEW-SESSION message,
determines a parent with smallest msm-ids, and unicast a JOIN-REQ to its
potential parent node
 If parent node is already in the multicast delivery tree, it replies with a
JOIN-ACK.
 If a node is unable to find any potential parent node, it executes a branch
reconstruction (BR) process to rejoin the tree

 Ad hoc Multicast Routing Protocol Utilizing Increasing Id-Numbers
(AMRIS)
 Packet forwarding example
• Nodes X and 34 are sources
• Nodes 11, 24, and 28 are recipients

Route Discovery and Join for
Multicast Multicast Ad hoc On-Demand Distance Vector Protocol
 Follows directly from the unicast AODV
 Discovers multicast routes on-demand using a broadcast
route discovery mechanism employing the same Route
Request (RREQ) and Route Reply (RREP) messages
 A MH originates a RREQ message when it wishes to join a
multicast group, or when it has data to send to a multicast
group but it does not have a route to that group
 Only a member of the desired multicast group may respond
to a join RREQ
 If the RREQ is not a join request, any node with a fresh
enough route to the multicast group may respond
 As the RREQ is broadcasted across the network, nodes set
up pointers to establish the reverse route in their route tables
 A node receiving a RREQ first, updates its route table to
record the sequence number
 For join RREQs, an additional entry is added to the
multicast route table and is not activated unless the route is
selected to be a part of the multicast tree

Multicast AODV
 Multicast Ad hoc On-Demand Distance Vector
Protocol
 Follows directly from the unicast AODV
Multicast
Member

Core Node Selection and
Multicast Routing Protocol
Core
Mesh
Tree

Core-Based Approaches
 Lightweight Adaptive Multicast (LAM)
 Draws on the Core-Based Tree (CBT) protocol and the
TORA unicast routing algorithm
 Each multicast group initialized and maintained by a
multicast server, or core
 Any node which wants to communicate with a specific
multicast group can query the directory server
 It is more efficient due to elimination of duplicated control
functionality between different protocol layers
 LAM builds a group-shared multicast routing tree for each
multicast group centered at the CORE
 A multicast tree is source-initiated and group-shared and
nodes in LAM maintain two variable, POTENTIAL-
PARENT and PARENT, and two lists POTENTIAL-
CHILD-LIST and CHILD-LIST
 These potential data objects are used when the node is in a
“join” or “rejoin” waiting state
 LAM is based on CBT approach to build the multicast
delivery tree
 With one CORE for a group, LAM is not very robust

Small Group Multicast
 Location Guided Tree Construction Algorithm for Small
Group Multicast
 This is a small group multicast schemes based on packet
encapsulation
 It builds an overlay multicast packet distribution tree on top of the
underlying unicast routing protocol
 Based on two types of tree: location-guided k-array (LGK) tree
and a location-guided Steiner (LGS) tree
 Geometric location information of the destination nodes is utilized
to construct the packet distribution tree without knowing the
global topology of the network
 Protocol also supports an optimization mechanism through route
caching
 In LGK tree approach, the sender first selects nearest k
destinations as children nodes
 The sender then groups the rest of the nodes to its k children as per
the closeness to geometric proximity
 Once the group nodes are mapped to its corresponding child
nodes, the sender forwards a copy of the encapsulated packet to
each of the k children, with its corresponding subtree as
destinations
 Process stops when an in-coming packet has an empty destination
list

Location Guided Tree Construction
 Location Guided Tree Construction Algorithm for Small
Group Multicast

Zone Routing based
Multicast Multicast Zone Routing
 Takes into consideration the hierarchical structure used by the ZRP
unicast routing protocol
 Network is partitioned into zones
 Each node computes its own zone, determined by nodes lieing within a
certain radius of the node
 ZRP is described as a hybrid approach between the proactive and reactive
routing protocols
 Routing is proactive inside the zones and reactive between the zones
 To create a zone, a MZR node A broadcasts an ADVERTISEMENT
message with a time-to-live (TTL) equal to a pre-configured ZONE-
RADIUS
 Node B within the zone radius decrements the TTL and forwards the
message if appropriate
 Node B makes an entry in its routing table for node A, with the last hop of
the ADVERTISEMENT message as the next hop towards destination
 Nodes ZONE-RADIUS hops away from node A become border nodes, and
serve as a gateway between node A’s zone and the rest of the network
 MZR begins its search within the zone before extending outward
 A source wants to start sending multicast traffic, it initiates the
construction of a multicast tree
 A TREE-CREATE-ACK packet is sent back to the source and
intermediate nodes mark in their routing tables the last hop of the TREE-
CREATE-ACK as a downstream node

Multicast Zone Routing
 Border node unicasts a TREE-
CREATE-ACK to the multicast
source to create a link between
the border node and the source
 This sequence continues until
receives a TREE-CREATE
message
 Routes in MZR are updated
through the use of TREE-
REFRESH packets
 If a node on the multicast tree
fails to receive a
TREEREFRESH message after
a certain time, it deletes its
multicast entry
 TREE-REFRESH packets
could be piggybacked on
multicast data whenever
possible
 MZR creates a source specific, on-demand multicast tree with a minimal
amount of routing overhead
 Hierarchical approach of MZR does not conserve bandwidth during the
initial TREE-CREATE flood

Source Specific Multicast
Tree Multicast Optimized Link State Routing (MOLSR)
 MOLSR creates a source specific multicast tree
 MOLSR is dependent on OLSR as unicast routing algorithm
 Routers periodically advertise their ability to route and build
multicast routes
 MOLSR nodes can calculate shortest path routes to every
potential multicast source
 This is done in the same manner seen in OLSR, except that
now the routes consist entirely of multicast-capable OLSR
routers
 Multicast routes are built in a backward manner similar to
the method used in MZR
 A source that wants to send multicast traffic advertises its
intentions by broadcasting a SOURCE_CLAIM message to
 A multicast source periodically sends a SOURCE_CLAIM
message to every node in the network for two reasons
 First, it informs multicast receivers that the source is still
sending data
 Second, it allows unattached hosts to join the multicast group

Other Protocols
 The Associativity-Based Ad Hoc Multicast (ABAM)
 This is an on-demand source-initiated multicast routing protocol
 A multicast tree is built for each multicast group based on association stability
 The link status of each node is monitored by its neighbors
 ABAM deals with the network mobility on different levels according to varying
mobility effects: branch repair when the receiver moves, sub-tree repair when a
branching node moves, and full tree level repair when the source node moves
 On-demand Location-Aware Multicast (OLAM) protocol
 OLAM assumes each node to be equipped with GPS device
 Each node can process and take a snapshot of the network topology and make up a
multicast tree (minimum spanning tree)
 This protocol does not use any distributed data structures or ad hoc routing protocol
as foundation and full tree level repair when the source node moves
 Adaptive Demand-Driven Multicast Routing (ADMR)
 A protocol that attempts to reduce non-on-demand components
 ADMR uses tree flood to enable packets to be forwarded following variant branches in
the multicast tree
 A multicast packet in ADMR floods within the multicast distribution tree only towards
the group’s receivers
 The Spiral-fat-tree-based On-demand Multicast (SOM) protocol
 A spiral fat tree is built as the multicast tree to increase the stability of the tree
structure
 By using link redundancy of the fat tree, failed links will be easily replaced.

Spiral-fat-tree-based On-
demand Multicast (SOM)
protocol
A spiral fat tree is built to increase the
stability of the tree structure
Tree Fat-Tree Fat-Tree

Mesh based Approach
 Mesh-based multicast protocols may have
multiple paths between any source and
receiver pairs
 Mesh-based protocols seem to outperform tree-
based proposals due to availability of
alternative paths
 A mesh has increased data-forwarding
overhead
 The redundant forwarding consumes more
bandwidth
 The probability of collisions is higher when a
larger number of packets are generated

Mesh based Approach
 On-Demand Multicast Routing Protocol
 Core-Assisted Mesh Protocol
 Forwarding Group Multicast Protocol
 Other Protocols

On-Demand Multicast Routing
Protocol Mesh-based protocol employing a forwarding group
concept
 Only a subset of nodes forwards the multicast packets
 A soft state approach is taken in ODMRP to maintain
multicast group members
 No explicit control message is required to leave the
group
 The group membership and multicast routes are
established and updated by the source on demand
 If no route to the multicast group, a multicast source
broadcasts a Join-Query control packet to the entire
network
 This Join-Query packet is periodically broadcasted to
refresh the membership information and updates
routes

On-Demand Multicast Routing
Protocol
After establishing a
forwarding group and route
construction process, a
source can multicast packets
to receivers via selected
routes and forwarding
groups
To leave the group, source
simply stops sending Join-
Query packets
If a receiver no longer wants
to receive from a particular
multicast group, it does not
send the Join-Reply for that
group

Core-Assisted Mesh Protocol
 Supports multicasting by creating a shared mesh for
each multicast group
 Meshes thus created, helps in maintaining the
connectivity to the multicast users, even in case of
node mobility
 It borrows concepts from CBT, but the core nodes are
used for control traffic needed to join multicast
groups
 Assumes a mapping service by building and
maintaining the multicast mesh
 Nodes are classified as: simplex, duplex and non-
member
 CAMP uses a receiver-initiated method for routers to
join a multicast group
 CAMP ensures the mesh to contain all reverse
shortest paths between a source and the recipients

Mesh based Approach
 Forwarding Group Multicast Protocol
 Can be viewed as flooding with “limited scope”
 Flooding is contained within a selected
forwarding group (FG) nodes
 Makes innovative use of flags and an associated
timer to forward multicast packets
 Uses two approaches to elect and maintain FG
of forwarding nodes: FGMP-RA (Receiver
Advertising) and FGMP-SA (Sender
Advertising)

Mesh based Approach
 Other Protocols
 A local routing scheme is proposed in the Neighbor
Supporting ad hoc Multicast routing Protocol (NSMP)
 Two types of route discovery: flooding route discovery
and local route discovery
 Intelligent On-Demand Multicast Routing Protocol
(IOD-MRP) is a modified version of CAMP by
employing an on-demand receiver initiated procedure
to dynamically build routes and maintain multicast
group membership instead of using cores
 Source Routing-based Multicast Protocol (SRMP)
applies the source routing mechanism defined by the
DSR unicast protocol in a modified manner, decreasing
the size of the packet header
 Protocol operates in a loop-free manner, minimizing
channel overhead and making efficient use of network
resources

Stateless Approaches
 Differential Destination Multicast
 Meant for small-multicast groups operating in dynamic
networks of any size
 DDM lets source to control multicast group membership
 Each node along the forwarding path remembers the
destinations to which the packet has been forwarded last time
and its next hop information
 At each node, there is one Forwarding Set (FS) for each
multicast session
 The nodes also maintain a Direction Set (DS) to record the
particular next hop to which multicast destination data are
forwarded
 Source node, FS contains the same set of nodes as the multicast
Member List (ML)
 In the intermediate nodes, the FS is the union of several subsets
based on the data stream received from upstream neighbors
 Associated with each set FS_k, there is a sequence number
SEQ(FS_k) which is used to record the last DDM Block
Sequence Number seen in a received DDM data packet from an
upstream neighbor k

Stateless Approaches
 DSR Simple Multicast and Broadcast
Protocol
 Designed to provide multicast and broadcast
functionality
 It utilizes the Route Discovery mechanism
defined by the DSR unicast protocol to flood the
data packets in the network
 It can be implemented as a stand-alone protocol
 In fact, it does not rely on unicast routing to
operate
 If DSR has already been implemented on the
network, minor modifications are required to
enable this protocol

Hybrid Approaches
 Ad hoc Multicast Routing Protocol
 Creates a bi-directional, shared tree by using only
group senders and receivers as tree nodes for data
distribution
 The protocol has two main components: mesh creation
and tree setup
 The mesh creation identifies and designates certain
nodes as logical cores and these are responsible for
initiating the signaling operation and maintaining the
multicast tree to the rest of the group members
 A non-core node only responds to messages from the
core nodes and serves as a passive agent
 The selection of logical core in AMRoute is dynamic
and can migrate to any other member node, depending
on the network dynamics and the group membership
 AMRoute does not address network dynamics and
assumes the underlying unicast protocol to take care

Hybrid Approaches
 Ad hoc Multicast Routing Protocol

Hybrid Approaches
 Multicast Core-Extraction Distributed Ad Hoc
Routing
 The main idea is to provide the efficiency of the tree-
based forwarding protocols and robustness of mesh-
based protocols by combining these two approaches
 The infrastructure is robust and data forwarding
occurs at minimum height trees
 Mobility-based Hybrid Multicast Routing
 Designed to provide multicast and broadcast
functionality
 Built on top of the mobility-based clustering
infrastructure
 The structure is hierarchical in nature
 The mobility and positioning information is provided via
a GPS for each node
 Cores are employed in both AMRoute and MCEDAR, as
well as in many tree and mesh multicast algorithms

Comparison of Multicast
Approaches

Geocasting
 Geocasting is a variant of the conventional multicasting
problem
 Group members are within a specified geographical
region
 Whenever a node in the geocast region receives a geocast
packet, it floods the geocast packet to all its neighbors
 A geocast protocol works if at least one node in the
geocast region receives the geocast packet
 Protocols use a jitter technique in order to avoid two
packets colliding with each other by a broadcast
 Existing geocast protocols divided into two categories:
data-transmission oriented protocols and routing creation
oriented protocols
 The difference is how they transmit information from a
source to one or more nodes in the geocast region

Data-Transmission Oriented
Geocast Routing Protocols
 Location-Based Multicast
 Extends the LAR unicast routing algorithm for
geocasting
 Utilize location information to improve the
performance of a unicast routing protocol
 The goal is to decrease delivery overhead of
geocast packets by reducing the forwarding
space for geocast packets, while maintaining
accuracy of data delivery
 The algorithm is based upon a flooding
approach while a node determines whether to
forward a geocast packet further via one of two
schemes

LBM Scheme 1
 A node receives a
geocast packet, it
forwards the packet to
its neighbors if it is
within a forwarding
zone
 The size of the
forwarding zone
depends on (i) the size
of the geocast region
and (ii) the location of
the sender
 A parameter d
provides additional
control on the size of
the forwarding zone Box forwarding zone: Rectangle covering
source and the forwarding zone

LBM Scheme 2
 Does not have a
forwarding zone explicitly
 Forwarding is based on
the position of the sender
node and the position of
the geocast region
 Node B forwards a geocast
packet from node A if
node B is “at least d
closer” to the center of the
geocast region
 Node K will, however,
discard a geocast packet
transmitted by node B

Voronoi Diagram
The Voronoi
diagram partitions
the area in to a set
of convex polygons
such that all
polygon edges are
equidistance
S
Geo
area

Voronoi Diagram Based
Geocasting
 The goal is to enhance
the success rate and
decrease the hop count
and flooding rate
 The forwarding zone
defined in LMB may
be a partitioned
network between the
source node and the
geocast region

Voronoi Diagram and Request
Zone Neighbors that are
closest in the direction of
the destination forms the
forwarding zone
 Can be implemented
with a Voronoi diagram
for a set of nodes in a
given node’s
neighborhood
 VDG reduces the
flooding rates of LBM
Scheme 1, as fewer
packets should be
transmitted
 VDG may offer little
improvement over LBM
Scheme

GeoGRID
 GeoGRID protocol uses location information in
defining forwarding zone and elects a special host
in each grid area responsible for forwarding
geocast packets
 The forwarding zone in LBM incurs unnecessary
packet transmissions
 A tree-based solution is prohibitive in terms of
control overhead
 GeoGRID partitions the geographic area into two-
dimensional logical grids of size d X d
 Two schemes on how to send geocast packets in
GeoGRID: Flooding-Based GeoGRID and Ticket-
Based GeoGRID.

Flooding-Based GeoGRID
 Only gateways in every
grid within the
forwarding zone
rebroadcast the received
geocast packets
 A total of m + n tickets
are created by the source
if the geocast region is a
rectangle of m X n grid

Flooding-Based GeoGRID
Route Creation Oriented
 GeoTORA: reduce the
overhead of transmitting
geocast packets via
flooding techniques, while
maintaining high accuracy
 Mesh-based Geocast
Routing Protocol: uses a
mesh for geocasting to
provide redundant paths
between source and group
members

Conclusions and Future
Directions
 Scalability
 Applications for broadcast, multicast,
and geocast over MANETs
 QoS
 Address configuration
 Security
 Power control

Adhoc and Sensor Networks - Chapter 03

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