Adhoc and Sensor Networks - Chapter 02

Copyright © 2006, Dr. Carlos Cordeiro and Prof. Dharma P. Agrawal, All rights reserved. 1
 Introduction
Topology-Based versus Position-Based Approaches
Topology-Based Routing Protocols
 Reactive Routing Approach
 Hybrid Routing Approach
 Comparison
Position-Based Routing
 Principles and Issues
 Location Services
 Forwarding Strategies
 Comparisons
Other Routing Protocols
 Signal Stability Routing
 Power Aware Routing
 Associativity-Based Routing
 QoS Routing
Conclusion and Future Directions
Table of Contents

Illustration of Multi-hop
MANET
Due to movement of MHs, S now
uses A and B to reach D
S
B
D
A
MH S uses B to
communicate with MH D
A
S
D
B
Each color represents range of
transmission of a device

Routing Protocols
Topology-Based
- Depends on the information about existing links
 Position-Based Approaches
 Proactive (or table-driven)
 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
Topology-Based
Depends on the information about existing links to forward
packets
 Position-Based Approaches Sender uses location service to
determine the position of Destination node
 [Physical location of each or some nodes determine their
own position through GPS or some other positioning
technique]
Topology-Based
 Proactive (or table-driven)
 Node experiences minimal delay whenever a route is needed
 May not always be appropriate for high mobility
 Distance-vector or link-state routing
 Reactive (or on-demand)
 Consume much less bandwidth
 Delay in determining a route can be substantially large
 Hybrid protocols
 MHs determine their own position through GPS
 Position-based routing algorithms overcome some of the
limitations

Proactive Routing Approaches
 Destination-Sequenced Distance-Vector (DSDV)
Protocol
 A proactive hop-by-hop distance vector routing
protocol
 Requires each MH to broadcast routing updates
periodically
 Every MH maintains a routing table for all possible
destinations and the number of hops to each destination
 Sequence numbers enable the MHs to distinguish stale
routes from new ones
 To alleviate large network update traffic, two possible
types of packets: full dumps or small increment packets
 The route labeled with the most recent sequence
number is always used
 In the event that two updates have the same sequence
number, the route with the smaller metric is used in
order to optimize (shorten) the path

Destination-Sequenced
Distance-Vector (DSDV)
Assume that MH X receives routing information from
Y about a route to MH Z
Let S(X) and S(Y) denote the destination sequence
number for MH Z as stored at MH X, and as sent
by MH Y with its routing table to node X,
respectively
X Y Z

Destination-
Sequenced Distance-
Vector (DSDV)MH X takes the following steps:
If S(Y) > S(X), then X ignores the routing information
received from Y
If S(Y) = S(X), and cost of going through Y is smaller
than the route known to X, then X sets Y as the next
hop to Z
If S(Y) < S(X), then X sets Y as the next hop to Z, and
S(X) is updated to equal S(Y)
X Y Z

Proactive Routing
Approaches The Wireless Routing Protocol
 A table-driven protocol with the goal of maintaining
routing information among all MHs
 Each MH maintains four tables: Distance, Routing,
Link-cost, and the Message Retransmission List (MRL)
tables
 Each entry in MRL contains the sequence number of
the update message
 MHs keep each other informed of all link changes
through the use of update messages
 MHs learn about their neighbors from
acknowledgments and other messages
 If a MH does not send any message for a specified time
period, it must send a hello message to ensure
connectivity

Proactive Routing
Approaches Topology Broadcast based on Reverse Path
Forwarding Protocol
 Considers broadcasting topology information
(including link costs and up/down status) to all
MHs
 Each link-state update is sent on every link of the
network though flooding
 Communication cost of broadcasting topology
can be reduced if updates are sent along spanning
trees
 Messages are broadcast in the reverse direction
along the directed spanning tree formed by the
shortest paths from all nodes to source
 Messages generated by a given source are
broadcast in the reverse direction along the
directed spanning tree formed by the shortest
paths from all MHs (nodes) to the source

Proactive Routing
Approaches The Optimized Link State Routing Protocol
 Based on the link state algorithm
 All links with neighboring MHs are declared
and are flooded in the entire network
 Minimizes flooding of this control traffic by
using only the selected MHs, called multipoint
relays
 Only normal periodic control messages sent
 Beneficial for the traffic patterns with a large
subset of MHs are communicating with each
other
 Good for large and dense networks
 An in-order delivery of its messages is not
needed as each control message contains a
sequence number

Proactive Routing Approaches
 Multipoint Relays
 Minimize the flooding of broadcast packets in
the network by reducing duplicate
retransmissions in the same region
 Each MH selects a set of neighboring MHs, to
retransmit its packets and is called the
multipoint relays (MPRs)
 This set can change over time and is indicated
by the selector nodes in their hello messages
 Each node selects MPR among its one hop bi-
directional link neighbors to all other nodes
that are two hops away

Illustration of Multipoint
Relays
Retransmitting
node or
multipoint
relays
N
One hop node
NOT selected
for relays
Two hop
nodes

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

Route Discovery in DSR
B
A
[S] E
F
H
J
[D]
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L
[S] Represents the source; [D] represents the
destination

B
A
[S] E
F
H
J
[D]
C
G
I
K
• Node H receives packet RREQ from two neighbors:
potential for collision
Z
Y
M
N
L
[S,E]
[S,C]
[X,Y] Represents list of identifiers appended to RREQ

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

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

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

 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 MH (node) D

1
4
5
Source
Destination
Hop1
<1>
<1>
<1>
Hop2
<1,2>
<1,3>
<1,4>
Hop4
<1,3,5,7>
<1,3,5>
Hop3
<1,4,6>
(a) Building Record Route During Route Discovery
1
4
6
8
72
3
<1,4,6>
<1,4,6>
<1,4,6>
(b) Propagation of Route Reply with the Route Record
(a) Building Record Route During Route Discovery
4
Source
Destination
1
2
3
5
6
7
8

 AODV supports the use of symmetric channels
 If a source MH moves, it reinitiates route discovery
protocol to find a new route
 If a MH along the route moves, its upstream neighbor
notices the move and propagates a link failure
notification message to each of its active upstream
neighbors
 These MHs propagate link failure notification to their
upstream neighbors, until the source MH is reached
 Hello messages can be used to maintain the local
connectivity in the form of beacon signals
 Designed for unicast routing only, and multi-path is
not supported

Temporarily Ordered Routing
Algorithm (TORA)
 TORA is a highly adaptive loop-free
distributed routing algorithm based on the
concept of link reversal
 TORA minimizes reaction due to topological
changes
 Algorithm tries to localize messages in the
neighborhood of changes
 TORA exhibits multipath routing capability
 Can be compared with water flowing downhill
towards a sink node
 The height metric is used to model the routing
state of the network
 Nodes maintain routing information to one-
hop neighbors

Illustration of TORA height metric
TORA (Cont’d)
Height = 3
Destination
Source
Height = 1
Height = 0
Height = 2

TORA (Cont’d)
 The protocol performs three basic functions:
 Route creation
 Route maintenance
 Route erasure
 A separate directed acyclic graph (DAG) is maintained by
each node (MH) to every destination
 Route query propagates through the network till it
reaches the destination or an intermediate node
containing route to destination
 This node responds with update and sets its height to a
value greater than its neighbors
 When a route to a destination is no longer valid, it adjusts
its height
 When a node senses a network partition, it sends CLEAR
packet to remove invalid routes
 Nodes periodically send BEACON signals to sense the
link status and maintain neighbor list

1
2
3
4
5
6
7
8
(-,-)
(-,-)
(-,-)
(-,-)
(-,-)
(-,-)
(-,-)
(0,0)
(0,2)
(0,2)
(0,3) (0,3)
(0,3)
Source Destination
(0,1)
(0,1)
2
5
7
(0,0)
1 3
4
6
8 DestinationSource
Propagation of the query message
Node’s height updated as a result of the update message
TORA (Cont’d)

TORA Characteristics
 The height metric in TORA depends on logical time
of a link failure
 The algorithm assumes all nodes to be synchronized
 TORA has 5-tuple metric:
 Logical time of link failure
 Unique ID of the node that defined the new
reference level
 A reflection indicator bit
 A propagation ordering parameter
 Unique ID of the node
 The first three elements together describe the
reference level
 Oscillation can occur using TORA, similar to count-
to-infinity problem
 TORA is partially reactive and partially proactive

Route Maintenance in TORA

Hybrid Routing
ApproachesZone Routing Protocol (ZRP):
 Hybrid of reactive and proactive protocols
 Limits the scope of proactive search to the node’s local
neighborhood
 The node need to identify all its neighbors which are one hop
away
 Nodes local neighborhood is defined as a routing zone with a
given distance
 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 X’s routing zone
 Intra-zone routing: Proactively maintain routes to all nodes
within the source node’s own zone
 Inter-zone routing: Use an on-demand protocol (similar to
DSR or AODV) to determine routes to outside zone

Zone Routing Protocol
(ZRP)
Radius of routing zone = 2

Hybrid Routing Approaches
 Interzone routing protocol (IERP) is responsible
 Uses a query-response mechanism by exploiting the structure
of the routing zone, through a process known as bordercasting
 Bordercast is more expensive than the broadcast flooding used
in other reactive protocols as there are many more border
nodes than neighbors
 Cost of bordercast redundancy reduced by suppressing
mechanisms based on query detection, early termination and
loopback termination
 Source generates a route query packet with source node’s ID
and request number
 Sequence of recorded node Ids specifies an accumulated route
from the source to the current routing zone
 If the destination is in routing zone, a route reply is sent back
to source, along the path specified by reversing the
accumulated route
 If the destination does not appear in the node’s routing zone,
the node bordercasts the query to its peripheral nodes

Hybrid Routing Approaches
Fisheye State Routing (FSR):
 Uses a multi-level Fisheye scopes to reduce
routing update overhead in large networks
 It helps to make a routing protocol scalable by
gathering data on the topology, which may be
needed soon
 FSR tries to focus its view on nearby changes
by observing them with the highest resolution
in time and changes at distant nodes

Hybrid Protocols
Landmark Routing (LANMAR) with group
mobility:
 Combines the features of FSR and landmark routing
 Uses a landmark to keep track of each set of nodes
that move together
 Borrows the notion of landmarks to keep track of
logical subnets
 The MHs exchange the link-state and topological
information only with their immediate neighbors
 It also piggybacks a distance vector with size equal to
the number of logical subnets and thus landmark
nodes
 A modified version of FSR used for routing by
maintaining routing table within the scope and
landmark nodes

Hybrid protocols
Cluster-based Routing (CBRP):
 This is a partitioning protocol emphasizing support for
unidirectional links
 Each node (MH) maintains two-hop topology
information to define clusters
 Each cluster includes an elected cluster head, with which
each member node (MH) has a bi-directional link
 In addition to exchanging neighbor information for
cluster formation, nodes must find and inform their
cluster head(s) of status of “gateway” nodes
 Cluster infrastructure is used to reduce the cost of
disseminating the request
 When a cluster head receives a request, it appends its ID
and a list of adjacent clusters and rebroadcasts it
 Each neighboring node which is a gateway to one of these
adjacent clusters unicasts the request to appropriate
cluster head

An Overview of
Protocol
CharacteristicsRouting
Protocol
Route
Acquisition
Flood for
Route
Discovery
Delay for
Route
Discovery
Multipath
Capability Upon Route
Failure
DSDV
Computed a
priori No No No
Flood route updates
throughout the
network
WRP
Computed a
priori No No No
Ultimately, updates
the routing tables of
all nodes by
exchanging MRL
between neighbors
DSR
On-demand,
only when
needed
Yes,
aggressive use
of caching may
reduce flood
Yes
Not explicitly, as the
technique of
salvaging may
quickly restore a
route
Route error
propagated up to
the source to erase
invalid path
AODV
On-demand,
only when
needed
Yes,
conservative
use of cache to
reduce route
discovery delay
Yes
Not directly,
however, multipath
AODV (MAODV)
protocol includes this
support
Route error
broadcasted to
erase multipath
TORA
On-demand,
only when
needed
Usually only
one flood for
initial DAG
construction
Yes, once the
DAG is
constructed,
multiple paths
are found
Yes
Error is recovered
locally and only
when alternative
routes are not
available
ZRP Hybrid
Only outside a
source's zone
Only if the
destination is
outside the
source's zone
No
Hybrid of updating
nodes' tables within
a zone and
propagating route
error to the source

Position Based Routing
 Routing protocols that take advantage
of location information
 Can be classified according to how
many MHs have the service
 Forwarding decision by a MH is
essentially based on the position of a
packet’s destination and the position of
the MH’s immediate one-hop neighbor

Three main packet forwarding schemes:
 Greedy forwarding
 Restricted directional flooding
 Hierarchical approaches
 For the first two, a MH forwards a given packet
to one (greedy forwarding) or more (restricted
directional flooding) one-hop neighbors
 The selection of the neighbor depends on the
optimization criteria of the algorithm
 The third forwarding strategy forms a hierarchy
in order to scale to a large number of MHs

Location Service
 Some-for some
 Some-for-all
 All-for some
 All-for-all
Forwarding Strategy
 Greedy forwarding
 Restricted directional
flooding
 Next-hop selection
 Recovery strategy
Hierarchical
Classification criteria for existing approaches:
+

Location Services
 MHs register their current position with this service
 When a node does not know the position of a desired
communication partner, it contacts the location service
and requests that information
 In classical one-hop cellular network, there are dedicated
position servers, with each maintaining position
information about all MHs
 In MANETs, such centralized approach is viable only as an
eternal service
 First, it would be difficult to obtain the location of a position
server if the server is a part of the MANET
 Second, since a MANET is dynamic, it might be difficult to
have at least one position server within a given MANET

Distance Routing Effect
Algorithm for Mobility
 Within Distance Routing Effect Algorithm for Mobility
(DREAM) framework, each MH maintains a position
database that stores the location information about other
MHs
 An entry in the position database includes a MH identifier,
the direction of and distance to the MH, as well as a time
value when this information has been generated
 A MH can control the accuracy of its position information
available to other MHs in two ways:
 By changing the frequency at which it sends position
updates and is known as temporal resolution
 By indicating how far a position update may travel
before it is discarded which is known as spatial
resolution

Distance Effect in DREAM
 Temporal resolution of sending updates is coupled with the
mobility rate of a MH, i.e., the higher the speed is, more
frequent the updates will be
 Spatial resolution is used to provide accurate position
information in the direct neighborhood of a MH and less
accurate information at nodes farther away
 Costs associated with accurate position information at remote
MHs can be reduced since greater the distance separating two
MHs is, slower they appear to be moving with respect to each
other
 For example, from MH A’s perspective, the change in
direction will be greater for MH B than for MH C
C BA
C B

Quorum-Based Location
Service Information updates (write operations) are sent to a
subset (quorum) of available nodes, and information
requests (read operations) are referred to a
potentially different subset
 When these subsets are designed such that their
intersection is nonempty, it is ensured that an up-to-
date version of the sought-after information can
always be found
 A set of MHs is chosen to host position databases
 Next, a virtual backbone is constructed among the
MHs of the subset by utilizing a non-position-based
ad hoc routing algorithm
 A MH sends position update messages to the nearest
backbone MH, which then chooses a quorum of
backbone MHs to host the position information

Quorum-Based Location
Service
3
1
S
D
A
B
C
2
4
5
6
 MH D sends its updates to node 6, which might then select quorum A with
nodes 1, 2, and 6 to host the information
 For example, MH 4 might, choose quorum B, consisting of MHs 4, 5, and 6
for the query
 Larger the quorum set is, higher the cost for position updates and queries
are
 Can be configured to operate as all-for-all, all-for-some, or some-for-some
approach

Grid Location Service
31Location
update
78
10
56
73
15
31
25
34
48
14
80
64 57
29
Quer
y7878
1010
18 73
15
2525
3434
48
1414
8080
64
43
57
29
36
31
56
 Divides the area that contains the MANET into a hierarchy of squares, forming a so
called quad tree
 Each node maintains a table of all other MHs within the local first-order square
 Establishes near MH IDs, defined as the least ID greater than a MH’s own ID
 Position information of 10 is available at nodes 15, 18, 73
 Second order squares Nodes 14, 25, and 29 are selected to host the node 10’s
position

Homezone
 Two almost identical location services have
been proposed independently
 Both use the concept of a virtual Homezone
where position information for a node is
stored
 By applying a well-known hash function to
the node identifier, it is possible to derive
the position C of the Homezone for a node
 All nodes within a disk of radius R centered
at C have to maintain position information
for the node

D
S B
C
A
r
Greedy Packet Forwarding
Sender includes an approximate position of the recipient in the packet
This information is gathered by an appropriate location service
Intermediate node forwards packet to a neighbor lying in the direction of
recipient
This process can be repeated until recipient has been reached
A good strategy when sender cannot adjust the transmission signal
strength
r indicates the maximum
transmission range of node S

S
D
Greedy Packet
Forwarding (Compass
Routing)
Forwarding packets in which the
neighbor closer to the straight line
between sender and destination is
selected
 It is possible to let the sender
randomly select one of the nodes
closer to the destination than
Greedy routing may fail to find a path
between a sender and a destination,
even though one does exist
To counter this problem, the packet
should be forwarded to the node
with the least backward (negative)
progress
However, this raises the problem of
looping

Greedy Perimeter Stateless Routing
Protocol
A
B
C
D
 Based on planar graph traversal
 Nodes do not have to store any
additional information
 A packet enters the recovery mode
when it arrives at a local maximum
 It returns to greedy mode when it
reaches a node closer to the
destination
 The graph formed by a MANET is
generally not planar as shown
An edge between two nodes A and B is included in the graph only if the
intersection of the two circles with radii equal to the distance between
node A and B around those two nodes does not contain any other nodes
The edge between nodes A and C would not be included in the planar
subgraph since nodes B and D are contained in the intersection of the
circles

D
S
Planar Graph Traversal
 A simple planar graph traversal is used
to find a path toward the destination
 Forward packet on faces of planar
subgraph progressively closer to the
destination
 On each face from node S toward node
D, the packet is forwarded along the
interior of the face: forward the packet
on the next edge counterclockwise from
the edge on which it arrived
 Algorithm guarantees that a path will be
found in case at least one exists
 The header of a packet contains
additional information such as the
position of the node, the position of the
last intersection that caused a face
change, and the first edge traversed on
the current face

Restricted Directional
Flooding  Sender node S of a
packet with destination
node D forwards the
packet to all one-hop
neighbors that lie “in
the direction of node D”
 Expected region is a
circle around position
of node D as it is known
by node S
 “Direction towards
node D” is defined by
the line between nodes
S and D and the angle φ

Expected Zone Routing
 Location-Aided Routing (LAR) uses position information to enhance the
route discovery phase of reactive ad hoc routing approaches
 LAR uses this position information to restrict the flooding to a certain
area called request zone at the time of route discovery
 If node S knows that node D travels with average speed v, then the
expected zone is the circular region of radius v(t1 - t0), centered at
location L
 Expected zone is only an estimate made by node S to determine a
region that potentially contains D at time t1
Lv (t1
– t0
)
L

Expected Zone Routing
A(XS, Yd+R) P(Xd, Yd+R)
Q(Xd+R, Yd)
B(Xd+R, Yd+R)
C(Xd+R, YS)
Request zone
J(Xj, Yj) Expected zone
R
S(XS, YS)
D(Xd, Yd)
I(Xi, Yi)
 Request zone can be defined based on the expected zone
 Node S defines a request zone for the route request
 A node forwards a route request only if it belongs to the request zone
 To increase the probability to reach node D, the request zone should
include the expected zone
 Additionally, the request zone may also include other regions around
the request zone

Relative Distance Micro-
Discovery Ad Hoc Routing
 Relative Distance Micro-discovery Ad Hoc Routing
(RDMAR) routing protocol, an adaptive and scaleable
routing protocol, is well suited in large mobile networks
whose rate of topological changes is moderate
 Design is a typical localized reaction to link failures in a
very small region of the network near the change
 Desirable behavior is achieved through the use of a
flooding mechanism for route discovery, called Relative
Distance Micro-discovery (RDM)
 An iterative algorithm calculates an estimate of their RD
given their previous RD, an average nodal mobility and
information about the elapsed time since they last
communicated
 Query flood is then localized to a limited region of the
network centered at the source node of the route discovery
and with maximum propagation radius that equals to the
estimated relative distance

Relative Distance Micro-
Discovery Ad Hoc Routing
 Packets are routed between the stations of the network by using routing
tables which are stored at each station
 Each routing table lists all reachable destinations, wherein for each
destination j, it includes: the “Default Router” field
 “Time_Last_Update” (TLU) field that indicates the time since the node last
received routing information for j
 “RT_Timeout” field which records the remaining amount of time before the
route is considered invalid
 “Route Flag” field which declares whether the route to j is active
Two main algorithms are:
 Route Discovery
 When an incoming call arrives at node i for destination node j and there
is no route available, i initiates a route discovery phase
 Either to flood the network or limit discovery in a smaller region of the
network
 Route Maintenance
 Upon receipt of a data packet, first processes the routing header,
forwards the packet to the next hop, and send an explicit message to
examine whether a bi-directional link can be established with the
previous node

Hierarchical Routing
Complexity of the routing algorithm can be reduced tremendously by establishing
some form of hierarchy
Terminodes Routing
 Combines hierarchical and position-based routing with two levels of hierarchy
 Packets are routed according to a proactive distance vector scheme if the destination is
close to the sending node
 Once a long distance packet reaches the area close to the recipient, it continues to be
forwarded by means of the local routing algorithm
 To prevent greedy forwarding, the sender includes a list of positions in the packet header
Grid Routing
 Position-based hierarchical routing
 A proactive distance vector routing protocol is used at the local level, while position-
based routing is employed for long-distance packet forwarding
 Packets that are addressed to a position-unaware node arrives at a position-aware proxy
 Then forwarded according to the information of the proactive distance vector protocol
 As a repair mechanism for greedy long-distance routing, a mechanism called
Intermediate Node Forwarding (INF) is proposed
 If a forwarding node has no neighbor with forward progress, it discards the packet and
sends a notification to the sender of the packet

Other Position-based
Routing
The GPS-based systems do not provide good accuracy inside
the building and the surrounding area can be classified in
the following five categories:
 Typical office environment with no line-of-sight (NLOS)
with 50ns delay spread
 Large open space with 100ns delay spread with NLOS
 Large indoor or outdoor space with 150ns delay spread
with NLOS
 Large indoor or outdoor space with line-of-sight and 140ns
delay spread
 Large indoor or outdoor space with NLOS and 250ns delay
spread

Comparison of Location
Services

Comparison of location
services DREAM is fundamentally different from other
position services, as it requires all MHs to
maintain position information about every other
MH
 The time required to perform a position update in
DREAM is a linear function of the diameter of the
network, leading to a complexity of O( )
 Quorum system requires the same operations for
position updates and position lookups
 Quorum system depends on a non-position-based
ad hoc routing protocol
 Each node in GLS and Homezone selects a subset
of all available nodes as position servers
n

Comparison of forwarding
schemes (n = number of
nodes)

Summary of Forwarding
Schemes Communication complexity indicates the average number of
one-hop transmissions required to send a packet from one
node to another node with known position
 Need to tolerate different degrees of inaccuracy with regard
to the position of the receiver
 Forwarding requires all-for-all location service criterion
 Robustness is high if the failure of a single MH does not
prevent the packet from reaching its destination
 Greedy forwarding is efficient, with a communication
complexity of O( ), and is well suited for use in MANETs
with a highly dynamic topology
 The face-2 algorithm and the perimeter routing of GPSR are
currently the most advanced recovery strategies
 Restricted directional flooding, as in DREAM and LAR, has
communication complexity of O(n) and therefore does not
scale well for large networks with a high volume of data
transmissions
n

Signal Stability Routing
Protocol On-demand Signal Stability-Based Adaptive Routing protocol (SSR)
selects routes based on the signal strength (weak or strong) between
nodes and a node’s location stability
 The net effect is to choose routes that have “stronger” connectivity
 Two cooperative protocols used: Dynamic Routing Protocol (DRP)
and Static Routing Protocol (SRP)
 DRP is responsible for the maintenance of Signal Stability Table
(SST) and the Routing Table (RT)
 DRP passes the packet to the SRP which passes the packet up the
stack if it is the intended receiver, or looks up in the routing table
for the destination
 If no entry is found in the routing table, a route search process is
initiated
 If there is no route reply received at the source within a specified
timeout period, the source changes the PREF field in the packet
header to indicate that weak channels have been accepted

Other Routing Protocols
Power Aware Routing
 Power-aware metrics are used for determining routes in
MANETs
 A shortest-cost routing algorithm reduces the cost/packet
of routing packets by 5 - 30 percent over shortest-hop
routing
 Mean time to node failure is increased significantly, while
packet delays do not increase
Associativity-Based Routing
 Objective: to derive long-lived routes for ad hoc networks
 A route is selected based on a metric that is known as the
degree of association stability
 Periodically generated beacon signifies existence
 The three phases are: Route discovery; Route
reconstruction (RRC); and Route deletion
 RRC may consist of partial route discovery, invalid route
erasure, valid route updates, and new route discovery

QoS Routing
 All routing protocols proposed either for routing along shortest
available path or within some system-level requirement
 Such paths may not be adequate for QoS required applications
 Shortest path route A-B-H-G will have a lower bandwidth
 The path A-B-C-D-E-F-G will have a minimum bandwidth of 4
A QoS routing
example in a MANET
Shortest path
QoS satisfying path
G
A
B
D
E
F
HIJ
4
5 5
4
4
43
1
3
5
6
Numbers
represent
available
bandwidth

Core Extraction
Distributed Ad Hoc
Routing Core Extraction: A set of nodes is elected to form the core that maintains
the local topology of the nodes in its domain and performs route
computation
 Link State Propagation: Propagates bandwidth availability information
of stable links to all core nodes
 Route Computation: Establishes a core path from the domain of the
source to the domain of the destination
Incorporating QoS in Flooding-based Route Discovery
 To limit the amount of flooding, a logical ticket-based probing algorithm
with imprecise state model for discovering a QoS-aware routing path
 A probing message is split into multiple probes and forwarded to
different next-hops, with each child probe containing a subset of the
tickets from their parents
 When one or more probe(s) arrive(s) at the destination, the hop-by-hop
path known and delay/bandwidth information can be used to reserve
QoS-satisfying path

QoS support using Bandwidth
Calculations
C
A B
Slots (1, 2, 3)
Slots (2, 3, 4)
 Involves end-to-end bandwidth calculation and allocation
 Source node can determine the resource availability for supporting the
required QoS
 Need to know how to assign the free slots at each hop
 Time slots 1, 2, and 3 are free between nodes A and B, and slots 2, 3, and 4
are free between nodes B and C
 There will be collisions at node B if node A tries to use all three slots 1, 2,
and 3 to send data to node B while node B is using one or both slots 2 and
3 to send data to node C
 Need to divide common free slots 2 and 3 between the two links

Multi-path QoS Routing
 Suitable for ad hoc networks with very limited bandwidth
for each path
 Algorithm searches for multiple paths for the QoS route
 Adopts the idea of ticket-based probing scheme
 Enhances routing resiliency by finding node/edge disjoint
paths when link and/or node fail
 Another approach is to use extension of AODV to
determine a backup source-destination routing path if the
path gets disconnected frequently due to mobility or
changing link signal quality
 A backup path can be easily piggybacked in data packets

Conclusions and Future
Directions
 Routing is undoubtedly the most studied aspect of ad hoc
networks
 Yet, many issues remain open such as more robust security
solutions, routing protocol scalability, QoS support, and so
on ….
 Integration of MANETs and infrastructure-based
networks such as the Internet will be an important topic in
wireless systems beyond 3G
 Availability of Dynamic Host Configuration Protocol
(DHCP) servers many not be practical to get IP addresses
 Nodes (MHs) have to resort to some heuristic to obtain
their IP addresses
 Routing algorithms for MANETs are equally applicable to
sensor networks except for low mobility, much larger
number of sensor nodes and use of small battery

Adhoc and Sensor Networks - Chapter 02

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