Engineering

1. Types of Wireless Networks

2. Need:
• With the increasing use of small portable computers, wireless
networks, and satellites, a trend to support computing on the
move has emerged—this trend is known as mobile computing
or nomadic computing (also called anywhere/anytime
computing)

3. • Mobile computing has several interesting and important
applications like:
• Telecommunications
• National defense (tracking troop movements),
• Emergency and disaster management,
• Remote operation of appliances, and in
• Accessing the Internet.

4. Challenges:
• The channel capacity typically available in wireless systems
is much lower than what is available in wired networks
• Noise and interference have more impact on systems design
for wireless systems than on wired systems
• security is a greater concern in wireless systems than in wired
systems since information may be traveling in free space

5. Wireless & Mobile Networks
• Mobile networks provide support for routing (how to maintain
communication with mobility) and location management
(keeping track of the location) functions.
• Wireless networks provide wireless interfaces to users (both
mobile and stationary) by supporting bandwidth allocation and
error-control functions

7. Wireless LAN
• WLANs are typically restricted in their diameter to buildings,
a campus, single rooms etc
• Advantages of WLANs are:
• Flexibility: Within radio coverage, nodes can communicate
without further restriction. Radio waves can penetrate walls,
senders and receivers can be placed anywhere.
• Planning: Only wireless ad-hoc networks allow for
communication without previous planning, any wired network
needs wiring plans. As long as devices follow the same
standard, they can communicate. For wired networks,
additional cabling with the right plugs and probably
interworking units (such as switches) have to be provided.

8. • Design: Wireless networks allow for the design of small,
independent devices which can for example be put into a
pocket.
• Robustness: Wireless networks can survive disasters, e.g.,
earthquakes or users pulling a plug. If the wireless devices
survive, people can still communicate. Networks requiring a
wired infrastructure will usually break down completely
• Cost: After providing wireless access to the infrastructure via
an access point for the first user, adding additional users to a
wireless network will not increase the cost. This is, important
for e.g., lecture halls, hotel lobbies or gate areas in airports
where the numbers using the network may vary significantly.

9. • WLANs disadvantages:
• Quality of service: WLANs typically offer lower quality than
their wired counterparts. The main reasons for this are the
lower bandwidth due to limitations in radio transmission,
higher error rates due to interference.
• Safety and security: Using radio waves for data transmission
might interfere with other high-tech equipment in, e.g.,
hospitals. The open radio interface makes eavesdropping much
easier in WLANs than, e.g., in the case of fiber optics.

10. Transmission technologies in
WLAN
• One technology is based on the transmission of infra red light
(e.g., at 900 nm wavelength),
• The other one, which is much more popular, uses radio
transmission in the GHz range (e.g., 2.4 GHz in the license-
free ISM band).

11. • Infrared technology:
• It allows computing devices to communicate via short-range
wireless signals
• Infrared networks were designed to support direct two-
computer connections only, created temporarily as the need
arises. However, extensions to infrared technology also
support more than two computers and semi-permanent
networks.
• Infrared network signals cannot penetrate walls or other
obstructions and work only in the direct "line of sight”
– IrDA-SIR (slow speed) infrared supporting data rates up to 115 Kbps
– IrDA-MIR (medium speed) infrared supporting data rates up to 1.15 Mbps
– IrDA-FIR (fast speed) infrared supporting data rates up to 4 Mbps

12. • Radio transmission:
• It include the long-term experiences made with radio
transmission for wide area networks (e.g., microwave links)
and mobile cellular phones.
• Radio transmission can cover larger areas and can penetrate
(thinner) walls, furniture, plants etc.
• Additional coverage is gained by reflection. Radio typically
does not need a LOS if the frequencies
• Furthermore, current radio-based products offer much higher
transmission rates (e.g., 54 Mbit/s)
• Interference & limited range of license free bands

13. Infrastructure-based wireless
networks

14. • Communication takes place only between the wireless nodes
and the access point
• The access point does not just control medium access, but also
acts as a bridge to other wireless or wired networks.
• Infrastructure-based networks lose some of the flexibility
wireless networks can offer, e.g., they cannot be used for
disaster relief in cases where no infrastructure is left.

15. Ad-hoc wireless networks

16. • Nodes within an ad-hoc network can only communicate if they
can reach each other physically
• In ad-hoc networks, the complexity of each node is higher
because every node has to implement medium access
mechanisms, mechanisms to handle hidden or exposed
terminal problems

17. The transmission range of A reaches B, but
not C (the detection range does not
reach C either). The transmission range of
C reaches B, but not A. Finally, the
transmission range of B reaches A and C,
i.e., A cannot detect C and vice versa.

18. • A starts sending to B, C does not receive this transmission. C
also wants to send something to B and senses the medium. The
medium appears to be free, the carrier sense fails. C also starts
sending causing a collision at B. But A cannot detect this
collision at B and continues with its transmission. A is hidden
for C and vice versa.
• B sends something to A and C wants to transmit data to some
other mobile phone outside the interference ranges of A and B.
C senses the carrier and detects that the carrier is busy (B’s
signal). C postpones its transmission until it detects the
medium as being idle again.

19. System architecture

20. • The components of an infrastructure and a wireless part as specified for
IEEE 802.11. Several nodes, called stations (STAi), are connected to
access points (AP).
• Stations are terminals with access mechanisms to the wireless medium and
radio contact to the AP.
• The stations and the AP which are within the same radio coverage form a
basic service set (BSSi)
• A distribution system connects several BSSs via the AP to form a single
network and thereby extends the wireless coverage area. This network is
now called an extended service set (ESS)

21. • The APs support roaming (i.e., changing access points), the
distribution system handles data transfer between the different
APs.
• APs provide synchronization within a BSS, support power
management, and can control medium access to support time-
bounded service.
• Wireless access points (APs or WAPs) are specially
configured nodes on wireless local area networks (WLANs).
Access points act as a central transmitter and receiver of
WLAN radio signals.

23. Mobile ip
• Systems like GSM have been designed with mobility in mind,
the internet started at a time when no one had thought of
mobile computers
• IP is the common base for thousands of applications and runs
over dozens of different networks. This is the reason for
supporting mobility at the IP layer; mobile phone systems, for
example, cannot offer this type of mobility for heterogeneous
networks.
• To merge the world of mobile phones with the internet and to
support mobility in the small more efficiently, so-called micro
mobility protocols have been developed.

25. • Entities and terminology:
• Mobile node (MN): A mobile node is an end-system or router
that can change its point of attachment to the internet using
mobile IP. The MN keeps its IP address and can continuously
communicate with any other system in the internet as long as
link-layer connectivity is given.
• Mobile nodes are not necessarily small devices such as laptops
with antennas or mobile phones; a router onboard an aircraft
can be a powerful mobile node.

26. • Correspondent node (CN): At least one partner is needed for
communication. In the following the CN represents this
partner for the MN. The CN can be a fixed or mobile node.
• Home network: The home network is the subnet the MN
belongs to with respect to its IP address. No mobile IP support
is needed within the home network.
• Foreign network: The foreign network is the current subnet the
MN visits and which is not the home network.
• Care-of address (COA): The COA defines the current location
of the MN from an IP point of view.

27. Packet delivery to and from the mobile node

28. • Advantage:
• Mobile IP provides users the freedom to roam beyond their
home subnet while consistently maintaining their home IP
address.
• This enables transparent routing of IP datagrams to mobile
users during their movement, so that data sessions can be
initiated to them while they roam; it also enables sessions to be
maintained in spite of physical movement between points of
attachment to the Internet or other networks

29. Satellite systems
• Satellites offer global coverage without wiring costs for base
stations and are almost independent of varying population
densities.
• Satellite communication began after the Second World War
• 1957, SPUTNIK- first satellite by soviet union
• 1960-ECHO (it enables communication by reflecting signals)
• 1963-SYNCOM(geostationary satellite)
• 1965-INTELSAT1 (first commercial geostationary satellite)

30. • Applications :
• Weather forecasting: Without the help of satellites, the
forecasting of hurricanes would be impossible
• Radio and TV broadcast satellites:
• Military satellites: Many communication links are managed
via satellite because they are much safer from attack by
enemies.
• Satellites for navigation:

32. • Within the footprint, communication with the satellite is
possible for mobile users via a mobile user link (MUL)
• Base station controlling the satellite and acting as gateway to
other networks via the gateway link (GWL)
• Satellites may be able to communicate directly with each other
via intersatellite links (ISL)
• Footprint can be defined as the area on earth where the signals
of the satellite can be received.

33. • The loss L depending on the distance r between sender and
receiver can be calculated as:
f being the carrier frequency and c the speed of light

34. • Different types of orbits can be identified:
• Geostationary (or geosynchronous) earth orbit (GEO): GEO satellites have
a distance of almost 36,000 km to the earth. Examples are almost all TV
and radio broadcast satellites, many weather satellites and satellites
operating as backbones for the telephone network
• Medium earth orbit (MEO): MEOs operate at a distance of about 5,000–
12,000 km. eg, navigation
• Low earth orbit (LEO): While some time ago LEO satellites were mainly
used for espionage, several of the new satellite systems now rely on this
class using altitudes of 500–1,500 km

35. Wireless local loop

36. • Wireless Local Loop: adopting radio as the transmission
medium
• WLL is a technology that uses radio signals to substitute for
copper wires
• WLL services are referred as fixed cellular services
• FSU (Fixed Subscriber Unit) : interface between subscriber’s
wired devices and WLL network
• A BSC controls one or more BTS and provide an interface to
the local exchange (switch) in the central office.

37. Connection Setup
PSTN
Switch
function
WLL
Controller
AM
HLR
Transceiver WASU
Trunk
Air
Interface
TWLL
Wireless Access Network Unit(WANU)
– Interface between underlying telephone
network and wireless link
– consists of
• Base Station Transceivers (BTS)
• Radio Controller(RPCU)
• Access Manager(AM)
• Home Location Register(HLR)
WANU
Wireless Access Subscriber
Unit(WASU)
– located at the subscriber
– translates wireless link into a
traditional telephone connection

38. Wireless in Local Loop (WLL) Mobile
Telephone Connections
• BSNL WLL-M is a communication system that connects
customers to the The BSNL Landlinenetwork using radio
frequency signals instead of conventional copper wires, for the
full or part connection between the subscriber and the
exchange
• This comes with superior voice quality and high speed data
capabilities.
• CDMA is popular with more than 100 million subscribers
worldwide, and the number keeps on increasing exponentially.

39. Sensor networks
• A sensor network is an infrastructure comprised of sensing
(measuring), computing, and communication elements that
gives an administrator the ability to instrument, observe, and
react to events and phenomena in a specified environment.
• Sensor devices, or wireless nodes (WNs), are also (sometimes)
called motes

40. • IEEE 802.15.4 operates in the 2.4-GHz industrial, scientific,
and medical (ISM) radio band and supports data transmission
at rates up to 250 kbps at ranges from 30 to 200 ft.
• ZigBee/IEEE 802.15.4 is designed to complement wireless
technologies such as Bluetooth, Wi-Fi, and ultra-wideband
(UWB), and is targeted at commercial point-to-point sensing
applications where cabled connections are not possible and
where ultralow power and low cost are requirements

41. Typical sensing node

42. Micaz mote
Macro mote

43. MicaZ mote Moteiv Corporation's Tmote Sky
Cricket Mote

44. Sink
Sensors Field
Medical
Monitoring
Indoor
Control
Wireless Sensor Network
• Elements
– Sink : sends queries and collects data from sensors
– Sensor : monitors phenomenon and reports to sink
Applications
Environment
Monitoring
Object
Tracking

46. Challenges for WSNs
• Quality of Service In some cases, only occasional delivery of
a packet can be more than enough; in other cases, very high
reliability requirements exist.
• In yet other cases, delay is important when actuators are to be
controlled in a real-time fashion by the sensor network.
• Fault tolerance Since nodes may run out of energy or might
be damaged, or since the wireless communication between two
nodes can be permanently interrupted, it is important that the
WSN as a whole is able to tolerate such faults.
• To tolerate node failure, redundant deployment is necessary,
using more nodes than would be strictly necessary if all nodes
functioned correctly.

47. • Lifetime In many scenarios, nodes will have to rely on a
limited supply of energy (using batteries). Replacing these
energy sources in the field is usually not practicable, and
simultaneously, a WSN must operate at least for a given
mission time or as long as possible.
• Hence, the lifetime of a WSN becomes a very important figure
of merit. Evidently, an energy-efficient way of operation of the
WSN is necessary.

48. • Maintainability As both the environment of a WSN and the
WSN itself change (depleted batteries, failing nodes, new
tasks), the system has to adapt.
• It has to monitor its own health and status to change
operational parameters or to choose different trade-offs (e.g. to
provide lower quality when energy resource become scarce).
• Scalability Since a WSN might include a large number of
nodes, the employed architectures and protocols must be able
scale to these numbers

49. • Generic protocol stack for sensor networks:

51. • Physical Layer : Can provide an interface to transmit a stream
of bits over physical medium. Responsible for frequency
selection, carrier frequency generation, signal detection,
Modulation and data encryption.
• MAC layer: Responsible for Channel access policies,
scheduling, buffer management and error control. In WSN we
need a MAC protocol to consider energy efficiency, reliability,
low access delay and high throughput as a major priorities
• Network layer: The major function of this layer is routing.
This layer has a lot of challenges depending on the application
but apparently, the major challenges are in the power saving,
limited memory and buffers, and have to be self organized.

52. • Transport layer: The function of this layer is to provide
reliability and congestion avoidance
• Application layer: Responsible for traffic management and
provide software for different applications that translate the
data in an understandable form or send queries to obtain
certain information.

53. Sensors Vs Conventional Networks
Property Conventional Sensor
Power Unlimited power
(power supply)
Battery-powered
processing fast processors
3.4GHz
Severely Constrained
16MHz
Memory Large Memory
2GB RAM
Severely constrained
4-10KB of RAM
Communication Wired/wireless Wireless
Topology Structured Ad-hoc
Scalability Highly-Scalable Scalable to certain extent
Security Developed & extensive Requires more developments
Life-time Unlimited Limited

54. Peer to Peer networks

55. • Client/Server Limitations:
• Scalability is hard to achieve
• Presents a single point of failure
• Requires administration

56. • P2P Computing:
• P2P computing is the sharing of computer resources and
services by direct exchange between systems.

57. • All nodes are both clients and servers
• Provide and consume data
• Any node can initiate a connection
• No centralized data source
• P2P Network Characteristics:
• Clients are also servers and routers
• Nodes are autonomous (no administrative authority)
• Network is dynamic: nodes enter and leave the network
“frequently”

58. • P2P Benefits
• Efficient use of resources
• Scalability
• Reliability
– No single point of failure
• Ease of administration
– No need to deploy servers to satisfy demand

59. • Popular P2P Systems:
• Napster, Gnutella, Kazaa, Freenet
• Large scale sharing of files.
• User A makes files (music, video, etc.) on their computer
available to others
• User B connects to the network, searches for files and
downloads files directly from user A
• Drawback:
• Issues of copyright infringement

60. Napster (search – centralized & file
transfer– P2P)
A way to share music files with
others
• Users upload their list of files to
Napster server
•You send queries to Napster server for
files of interest -- Keyword search (artist,
song, album,etc.)
•Napster server replies with IP address of
users with matching files
•You connect directly to user A to download
file

61. Gnutella
Share any type of files
(not just music)
•You ask your neighbours
for files of interest
•Neighbours ask their neighbours,
and so on
• TTL field quenches messages
after a number of hops
•Users with matching files
reply to you

62. Mobile routing protocols
• Mobile networks can be classified into infrastructure networks
and mobile ad hoc networks (MANETs) according to their
dependence on fixed infrastructures.
• In an infrastructure mobile network, mobile nodes have wired
access points (or base stations) within their transmission range.
• The access points compose the backbone for an infrastructure
network.
• In contrast, mobile ad hoc networks are autonomously self-
organized networks without infrastructure support.
• In a mobile ad hoc network, nodes move arbitrarily; therefore
the network may experience rapid and unpredictable topology
changes.

63. • Types of routing protocols:
• In proactive routing protocols, the routes to all the destinations
(or parts of the network) are determined at the start-up and
maintained by using a periodic route update process.
• In reactive protocols, routes are determined when they are
required by the source using a route discovery process.
• Hybrid routing protocols combine the basic properties of two
classes of protocols into one. That is, they are both reactive
and proactive in nature.

64. Ad Hoc On-Demand Distance
Vector (AODV)

65. • AODV belongs to the class of Distance Vector Routing
Protocols (DV). In a DV every node knows its neighbours and
the costs to reach them. A node maintains its own routing
table, storing all nodes in the network, the distance and the
next hop to them.

66. • The Ad Hoc On-Demand Distance Vector (AODV) algorithm
enables dynamic, self-starting, multihop routing between
participating mobile nodes wishing to establish and maintain
an ad hoc network.
• AODV allows mobile nodes to obtain routes quickly for new
destinations, and does not require nodes to maintain routes to
destinations that are not in active communication.
• AODV allows mobile nodes to respond quickly to link
breakages and changes in network topology.

67. • AODV uses symmetric links between neighboring nodes. It
does not attempt to follow paths between nodes when one of
the nodes cannot hear the other one.
• Path Discovery:
• The path discovery process is initiated whenever a source node
needs to communicate with another node for which it has no
routing information in its table.
• Every node maintains two separate counters: a node sequence
number and a broadcast ID.

68. • The source node initiates path discovery by broadcasting a
Route REQuest (RREQ) packet to its neighbors.
• The RREQ contains the following fields:
• <source_addr source sequence# broadcast id dest_addr dest
sequence# hop cnt>

69. t sequence number rece

70. • J Join flag; reserved for multicast.
• R Repair flag; reserved for multicast.
• G Gratuitous RREP flag
• Reserved Sent as 0; ignored on reception.
• Hop Count The number of hops from the Source IP Address to
the node handling the request.
• Flooding ID A sequence number uniquely identifying the
particular RREQ when taken in conjunction with the source
node's IP address.
• Destination IP Address The IP address of destination for which
a route is desired.

71. • Destination Sequence Number The last sequence number
received in the past by the source for any route towards the
destination.
• Source IP Address The IP address of the node which
originated the Route Request.
• Source Sequence Number The current sequence number to
be used for route entries pointing to (and generated by) the
source of the route request.

72. • broadcast_id is incremented whenever the source issues a
new RREQ.
• Each neighbor either satisfies the RREQ by sending a Route
REPly (RREP) back to the source, or broadcasts the RREQ to
its own neighbors after increasing the hop_cnt.
• Notice that a node may receive multiple copies of the same
route broadcast packet from various neighbors.
• When an intermediate node receives an RREQ, if it has
already received an RREQ with the same broadcast_id and
source address, it drops the redundant RREQ and does not
rebroadcast it.
• If a node cannot satisfy the RREQ, it keeps track of the
following information to implement the reverse-path setup as
well as the forward-path setup that will accompany the
transmission of the eventual RREP.

73. • Destination IP address
• Source IP address
• Broadcast ID
• Expiration time for reverse-path route entry
• Source node’s sequence number

74. • Reverse-Path Setup:
• There are two sequence numbers (in addition to the
broadcast_id) included in an RREQ:
• the source sequence number and the last destination sequence
number known to the source
• As the RREQ travels from a source to various destinations, it
automatically sets up the reverse path from all nodes back to
the source.
• To set up a reverse path, a node records the address of the
neighbor from which it received the first copy of the RREQ.

75. • Forward-Path Setup:
• If an intermediate node has a route entry for the desired
destination, it determines whether the route is current by
comparing the destination sequence number in its own route
entry to the destination sequence number in the RREQ.
• If the RREQ’s sequence number for the destination is greater
than that recorded by the intermediate node, the intermediate
node must not use its recorded route to respond to the RREQ.
Instead, the intermediate node rebroadcasts the RREQ.
• The intermediate node can reply only when it has a route with
a sequence number that is equal or greater to that contained in
the RREQ.
• If it does have a current route to the destination and if the
RREQ has not been processed previously, the node then
unicasts a route reply packet (RREP) back to its neighbor from
which it received the RREQ.

76. • An RREP contains the following information:
• <source_addr, dest_addr, dest_sequence #, hop_cnt, lifetime>
• The forward path setup as the RREP travels from the
destination D to the source node S. Nodes that are not along
the path determined by the RREP will time out after
ACTIVE_ROUTE_TIMEOUT (3000 milliseconds) and will
delete the reverse pointers.

78. • Type 2
• R Repair flag; used for multicast.
• A Acknowledgment required
• Reserved Sent as 0; ignored on reception.
• Prefix Size If nonzero, the 5-bit Prefix Size specifies that the
indicated next hop may be used for any nodes with the same
routing prefix
(The Prefix Size Field indicates the nodes within a
destination's subnet that are reachable via the same route.)
• Lifetime The time for which nodes receiving the RREP
consider the route to be valid.

80. • Type 3
• N No delete flag; set when a node has performed a local
repair of a link, and upstream nodes should not delete the
route.
• Reserved Sent as 0; ignored on reception.
• DestCount The number of unreachable destinations included
in the message; MUST be at least 1.
• Unreachable Destination IP Address The IP address of the
destination which has become unreachable due to a link
break.
• Unreachable Destination Sequence Number The last known
sequence number, incremented by one,

81. • Local Connectivity Management:
• Hello message, a special RREP containing its identity and
sequence number. The node’s sequence number is not changed
for Hello message transmissions.
• Receiving a broadcast or a Hello message from a new
neighbor or failing to receive Hello messages from a node
previously in the neighborhood is an indication that the local
connectivity has changed.
• The local connectivity management with Hello messages can
also be used to ensure that only nodes with bidirectional
connectivity are considered to be neighbors.

83. Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L

84. Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents links on Reverse Path
Z
Y
M
N
L

85. Reverse Path Setup in AODV
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

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

87. Reverse Path Setup in AODV
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 RREQ
M
N
L

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

90. Dynamic Source Routing (DSR)
Protocol
• The DSR Protocol is composed of two mechanisms:
• Route discovery is the mechanism by which a node S wishing
to send a packet to a destination node D obtains a source route
to D. Route discovery is used only when S attempts to send a
packet to D and does not already know a route to D.
• Route maintenance is the mechanism by which node S is able
to detect, while using a source route to D, if the network
topology has changed such that it can no longer use its route to
D because a link along the route no longer works.

91. • This entirely on-demand behavior and lack of periodic activity
allow the number of overhead packets caused by DSR to scale
all the way down to zero.
• “In response to a single route discovery a node may learn and
cache multiple routes to any destination”.
• The operations of route discovery and route maintenance in
DSR are designed to allow unidirectional links and
asymmetric routes to be easily supported (in wireless networks, it
is possible that a link between two nodes may not work equally well in
both directions, due to differing antenna or propagation patterns or sources
of interference)

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

93. 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]
[X,Y] Represents list of identifiers appended to RREQ

94. Route Discovery in DSR
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]

95. Route Discovery in DSR
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]

96. Route Discovery in DSR
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]

97. Route Discovery in DSR
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]

98. RREQ

99. • Opt Data Len --- 8-bit unsigned integer.
• Identification A unique value generated by the initiator
(original sender) of the Route Request.
• Address[1..n] Address[i] is the IPv4 address of the i-th node
recorded in the Route Request option.

100. 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

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

102. RREP

103. • Last Hop External (L) it denotes that the last hop indicated by
the DSR Source Route option

104. 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

105. Route Error

106. • Option Type 3. Nodes not understanding this option will
ignore this option.
• Error Type
• 1 = NODE_UNREACHABLE
• 2=FLOW_STATE_NOT_SUPPORTED
• 3 = OPTION_NOT_SUPPORTED
• Packet Salvage if route is broken (from A to E) the neighbor
(C) salvage the packet (after sending Rerr) by checking it’s
own cache to see if it has route to target (E) and replacing the
packet’s route with the new

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

108. Route maintenance
• Passive Acknowledgments
– Half duplex operation: transmit packet, go into
receive mode, receive ack, receive next packet, go
into transmit mode, repeat
– Original sender hears forwarding transmission
from next hop node in the route:
D E F
D transmits to E E transmits to F
D hears E to F transmission
as implicit ACK

109. Mobility Models
• A mobility model should attempt to mimic the movements of
real mobile nodes. Changes in speed and direction must occur,
and they must occur in reasonable time slots.
• For example, we would not want mobile nodes to travel in
straight lines at constant speeds, because real mobile nodes
would not travel in such a restricted manner.
• Mobility models mainly are of two types:
1. Entity Mobility Model
2. Group Mobility Model

110. • Entity Mobility Model:
• Entity Mobility Models represent mobile nodes whose
movements are independent of each other. Examples of Entity
Mobility Models are as follows:
• Random Walk Mobility Model: A simple mobility model based
on random directions and speeds
• Random Waypoint Mobility Model: A model that includes
pause times between changes in destination and speed
• Random Direction Mobility Model: A model that forces Mobile
Nodes (MNs) to travel to the edge of the simulation area
before changing direction and speed
• City Section Mobility Model: A simulation area that represents
streets within a city

111. Classification of Mobility
Patterns
• Deterministic Mobility Model
• The Deterministic Mobility Model describes the most
predictable type of motion and is the most simplistic of all
mobility models.
• A sample scenario resembling a Deterministic Mobility Model
would be cars moving in an urban traffic area, where the speed
of the cars is restricted and the direction in which the cars can
move is also predefined, that is, either in a straight line or
turning only at cross lights.

112. • Semideterministic Mobility Pattern:
• Consider, for example, a battalion of battle tanks marching
ahead. Here, the path followed by each tank is not specified,
but they do move in a general direction (i.e., toward the war
front).
• Even though the individual tanks do not have a specified
direction, we can see a general pattern of a column evolving
out of it. Such a mobility pattern is termed a “Column Model.”

113. • Random Mobility Pattern:
• This motion is totally stateless, that is, the future movement
here is completely independent of the past movement and
hence there are no bounds imposed on the max deviation
which the nodes can take up for their next movement.
• And this randomness in choosing the next direction vector
renders this type of motion completely unpredictable.

114. Random Walk
• In this mobility model, an MN moves from its current location
to a new location by randomly choosing a direction and speed
in which to travel.
• The new speed and direction are both chosen from pre-defined
• ranges, [speedmin; speedmax] and [0;2π] respectively. Each
movement in the Random Walk Mobility Model occurs in
either a constant time interval t or a constant distance traveled
d, at the end of which a new direction and speed are
calculated.
• If an MN which moves according to this model reaches a
simulation boundary, it “bounces” off the simulation border
with an angle determined by the incoming direction. The MN
then continues along this new path.

115. • The Random Walk Mobility Model is a memoryless mobility
pattern because it retains no knowledge concerning its past
locations and speed values .
• The current speed and direction of an MN is independent of its
past speed and direction . This characteristic can generate
unrealistic movements such as sudden stops and sharp turns.

116. Random Waypoint Model
• The Random Waypoint Model was first proposed by Johnson
and Maltz. Soon, it became a “benchmark” mobility model to
evaluate the MANET routing protocols because of its
simplicity and wide availability.
• The Random Waypoint Mobility Model includes pause times
between changes in direction and/or speed.

117. • The implementation of this mobility model is as follows:
• As the simulation starts, each mobile node randomly selects
one location in the simulation field as the destination.
• It then travels toward this destination with constant velocity
chosen uniformly and randomly from [0,Vmax], where the
parameter Vmax is the maximum allowable velocity for every
mobile node.
• The velocity and direction of a node are chosen independently
of other nodes.

118. • Upon reaching the destination, the node stops for a duration
defined by the “pause time” parameter Tpause.
• If Tpause = 0, this leads to continuous mobility.
• After this duration, it again chooses another random
destination in the simulation field and moves toward it.
• The whole process is repeated again and again until the
simulation ends.

119. Node movement in the Random
Waypoint Model

120. • Limitations of the Random Waypoint Model:
• Temporal Dependency of Velocity
– the velocity at the current epoch is independent of the previous epoch.
Thus, some extreme mobility behavior, such as sudden stopping,
sudden accelerating, and sharp turning, may frequently occur in the
trace generated by the Random Waypoint Model.
• Spatial Dependency of Velocity
– in some scenarios, including battlefield communication and museum
touring, the movement pattern of a mobile node may be influenced by a
certain specific “leader” node in its neighborhood. Hence, the mobility
of various nodes is indeed correlated.
• Geographic Restrictions of Movement
– in many realistic cases, especially the applications used in urban areas,
the movement of a mobile node may be bounded by obstacles,
buildings, streets, or freeways.

121. Random Direction
• In this model, MNs choose a random direction in which to
travel similar to the Random Walk Mobility Model.
• An MN then travels to the border of the simulation area in that
direction. Once the simulation boundary is reached, the MN
pauses for a specified time, chooses another angular direction
(between 0 and 180 degrees) and continues the process.

122. City Section Mobility Model
• In the City Section Mobility Model, the simulation area is a
street network that represents a section of a city where the ad
hoc network exists
• The streets and speed limits on the streets are based on the
type of city being simulated.
• Each MN begins the simulation at a defined point on some
street. An MN then randomly chooses a destination, also
represented by a point on some street. The movement
algorithm from the current destination to the new destination
locates a path corresponding to the shortest travel time
between the two points; in addition, safe driving characteristics
such as a speed limit and a minimum distance allowed
between any two MNs exists.

123. • Upon reaching the destination, the MN pauses for a specified
time and then randomly chooses another destination (i.e., a
point on some street) and repeats the process.

125. Group Mobility Model
• Exponential Correlated Random Mobility Model: A group
mobility model that uses a motion function to create
movements
• Column Mobility Model: A group mobility model where the
set of MNs form a line and are uniformly moving forward in a
particular direction
• Nomadic Community Mobility Model: A group mobility
model where a set of MNs move together from one location to
another.
• Pursue Mobility Model: A group mobility model where a set of
MNs follow a given target.
• Reference Point Group Mobility Model: A group mobility
model where group movements are based upon the path
traveled by a logical center.

126. Exponential Correlated
Random Mobility Model
• The first group mobility models to be proposed is the
Exponential Correlated Random Mobility Model.
• In this model, a motion function is used to create MN
movements.
• Given a position (MN or group) at time t, b(t) is used to define
the next position (MN or group) at time t +1, b(t +1):

127. • where τ adjusts the rate of change from the MN’s previous
location to its new location
• r is a random Gaussian variable with variance σ

128. Column Mobility Model
• This model represents a set of MNs that move around a given
line (or column), which is moving in a forward direction (e.g.,
a row of soldiers marching together towards their enemy).
• For the implementation of this model, an initial reference grid
(forming a column of MNs) is defined
• Each MN is then placed in relation to its reference point in the
reference grid; the MN is then allowed to move randomly
around its reference point via an entity mobility model.

129. advance_vector is a predefined offset that
moves the reference grid.
The predefined offset that moves the
reference grid is calculated via a random
distance and a random angle (between 0
and π since movement is in a forward
direction only)

130. Nomadic Community Mobility
Model
• Just as ancient nomadic societiesmoved fromlocation to location, the
Nomadic CommunityMobilityModel represents groups of MNs that
collectively move from one point to another
• Within each community or group of MNs, individuals maintain their own
personal ”spaces” where they move in random ways.
• For example, consider a class of students touring an art museum. The class
would move from one location to another together; however, the students
within the class would roam around a particular location individually.
• in the Nomadic Community Mobility Model, the MNs may be allowed to
travel for 60 seconds before changing direction and speed.

132. Pursue Mobility Model
• The Pursue Mobility Model attempts to represent MNs
tracking a particular target.
• For example, this model could represent police officers
attempting to catch an escaped criminal. The Pursue Mobility
Model consists of a single update equation for the new
position of each MN:

133. Reference Point Group
Mobility Model
• Reference Point Group
Mobility Model
– Group movements are based
on the path traveled by a
logical center for the group
– GM: Group Motion Vector
– RM: Random Motion Vector
– Random motion of individual
node is implemented by
Random Waypoint without
Pause

134. • The new position for each MN is then calculated by summing
a random motion vector, RM, with the new reference point.
• The length of RM is uniformly distributed within a specified
radius centered at RP(t +1) and its direction is uniformly
distributed between 0 and 2π.

135. Location Aided Routing
• It makes use of location information to reduce routing
overhead. Location information used in the LAR protocol may
be provided by the Global Positioning System (GPS)
• Assumption:
– Each host knows its current location precisely (i.e., no error)

136. Problem
A
B
E
C
X
S D
D
C
X
S D
C
S
D
C
X
S
t0
t1

137. • As the route request is propagated to various nodes, the path
followed by the request is included in the route request packet.
Using the above flooding algorithm, provided that the intended
destination is reachable from the sender, the destination should
eventually receive a route request message.
• On receiving the route request, the destination responds by
sending a route reply message to the sender the route reply
message follows a path that is obtained by reversing the path
followed by the route request received by D (the route request
message includes the path traversed by the request).
• It is possible that the destination will not receive a route
request message (for instance, when it is unreachable from the
sender, or route requests are lost due to transmission errors). In
such cases, the sender needs to be able to reinitiate route
discovery.

138. Route Discovery Using Flooding
A
B
C
E
X
S D
route request
route reply

139. • Therefore, when a sender initiates route discovery, it sets a
timeout. If during the timeout interval, a route reply is not
received, then a new route discovery is initiated (the route
request messages for this route discovery will use a different
sequence number than the previous route discovery – recall
that sequence numbers are useful to detect multiple receptions
of the same route request).
• Timeout may occur if the destination does not receive a route
request, or if the route reply message from the destination is
lost

140. • Location-Aided Routing (LAR), as it makes use of location
information to reduce routing overhead. Location information
used in the LAR protocol may be provided by the Global
Positioning System (GPS).
• With the availability of GPS,it is possible for a mobile host to
know its physical location

141. • Expected zone and request zone
• Consider a node S that needs to find a route to node D. Assume
that node S knows that node D was at location L at time t0,
and that the current time is t1.
• Then, the “expected zone” of node D, from the view-point of
node S at time t1, is the region that node S expects to contain
node D at time t1.
• Node S can determine the expected zone based on the
knowledge that node D was at location L at time t0. For
instance, if node S knows that node D travels with average
speed v,then S may assume that the expected zone is the
circular region of radius v(t1 - t0), centered at location L

142. • If node S does not know a previous location of node D, then
node S cannot reasonably determine the expected zone – in
this case, the entire region that may potentially be occupied by
the ad hoc network is assumed to be the expected zone.
• In this case, the algorithm reduces to the basic flooding
algorithm.

143. • Request zone:
• Limited flooding
• A node forwards a route request only if it belongs to the
request zone
• The request zone should include
• expected zone
• other regions around the expected zone

145. LAR Scheme 1

146. • Assume that node S knows that node D was at location (Xd,
Yd) at time t0. At time t1, node S initiates a new route
discovery for destination D. We assume that node S also
knows the average speed v with which D can move. Using
this, node S defines the expected zone at time t1 to be the
circle of radius R = v(t1- t0) centered at location (Xd, Yd).
• In our first LAR algorithm, we define the request zone to be
the smallest rectangle that includes current location of S and
the expected zone (the circular region defined above), such
that the sides of the rectangle are parallel to the X and Y axes.
In figure (a), the request zone is the rectangle whose corners
are S, A, B and C, whereas in figure (b), the rectangle has
corners at point A, B, C and G – note that, in this figure,
current location of node S is denoted as (Xs, Ys).

147. • The source node S can, thus, determine the four corners of the
request zone. S includes their coordinates with the route
request message transmitted when initiating route discovery.
When a node receives a route request, it discards the request if
the node is not within the rectangle specified by the four
corners included in the route request.
• When node D receives the route request message, it replies by
sending a route reply message (as in the flooding algorithm).
However, in case of LAR, node D includes its current location
and current time in the route reply message.
• When node S receives this route reply message (ending its
route discovery), it records the location of node D. Node S can
use this information to determine the request zone for a future
route discovery.

148. LAR Scheme 2
S knows the location (Xd, Yd) of node
D at time t0
Node S calculates its distance from
location (Xd, Yd): DISTs
Node I receives the route request,
calculates its distance from location (Xd,
Yd): DISTi
For some parameter δ,
If DISTs + δ ≥ DISTi, node I replaces
DISKs by DISKi and forwards the
request to its neighbors; otherwise
discards the route request

149. • In LAR scheme 1, source S explicitly specifies the request
zone in its route request message. In scheme 2, node S
includes two pieces of information with its route request:
• Assume that node S knows the location (Xd, Yd) of node D at
some time to - the time at which route discovery is initiated by
node S is tl, where tl>= to. Node S calculates its distance from
location (Xd, Yd), denoted as DISTs, and includes this
distance with the route request message.
• The coordinates (Xd, Yd) are also included with the route
• request

150. • When a node I receives the route request from sender node S,
node I calculates its distance from location (Xd, Yd),denoted
as DISTi, and
• For some parameter δ , if DISTs, + δ > DISTi, then node I
forwards the request to its neighbors. When node I forwards
the route request it now includes DISTi and (Xd, Yd) in the
route request (ie., it replaces the DISTs, value received in the
route request by DISTi, before forwarding the route request).
• Else DISTs + δ < DISTi. In this case, node I discards the route
request

151. • When some node J receives the route request (originated by
• node S) from node I, it applies a criteria similar to above: If
node J has received this request previously, it discards the
request Otherwise, node J calculates its distance from (Xd,
Yd), denoted as DISTj. NOW,
• The route request received from I includes DISTi. If
• DISTi + δ > DISTj, then node J forwards the request to its
neighbors (unless node J is the destination for the route
request).
• Before forwarding the request J replaces the DISTi value in the
route request by DISTj.
• Else DISTi + δ < DISTj. In this case,node J discards the
request

152. Error in Location Estimate
• Let e denote the maximum error in the
coordinates estimated by a node.
• Modified LAR scheme 1
D (Xd, Yd)
e+v(t1-t0)
Expected Zone

153. • However, in reality there may be some error in the estimated
location.
• Let e denote the maximum error in the coordinates estimated
by a node. Thus, if a node N believes that it is at location (Xn,
Yn), then the actual location of node N may be anywhere in
the circle of radius e centered at (Xn, Yn).
• In the above LAR schemes, we assume that node S obtained
the location (Xd, Yd) of node D at time t0, from node D
(perhaps in the route reply message during the previous route
discovery). Thus, node S does not know the actual location of
node D at time t0 – the actual location is somewhere in the
circle of radius e centered at (Xd, Yd).

154. • To take the location error e into account, we modify LAR
scheme 1 so that the expected zone is now a circle of radius
e + v(t1- t0).
• The request zone may now be bigger, as it must include the
larger request zone