[AD Hoc Networks]
by: Farhad Rad
1
Agenda :

Definition of an Ad Hoc Networks
 routing in Ad Hoc Networks
 IEEE 802.11
 security in Ad Hoc Networks
 Multicasting Protocols for Ad Hoc Networks
2
3
Introductin:





MANET (Mobile Adhoc NETworks)
An ad hoc network is a collection of wireless mobile
hosts forming a temporary network without the aid
of any established infrastructure or centralized
administration”
Military Applications
Rescue Operations
Virtual Classrooms
solution
Mobile Ad hoc Networks
4
Routing in Ad Hoc Networks:




Challenges to Routing in MANETs
Routing Protocols for MANETs
Ad-hoc On Demand Distance Vector (AODV)
Comparisons and Conclusions
5
Challenges to Routing in MANETs
 Lack of a fixed infrastructure
 Each node in the network must route messages
towards their destination
 Nodes operate on battery power (Routing of
messages may cause faster battery consumption,
leading to node going offline)

Nodes are constantly moving, leaving, or joining
6
Routing Protocols for Ad-hoc
Networks:



Destination-Sequenced Distance Vector Protocol
(DSDV)
Dynamic Source Routing (DSR)
Ad-hoc On Demand Distance Vector (AODV)

7
8
9
Ad-hoc On Demand Distance Vector :
(AODV)
 Routes are discovered on demand
 AODV is capable of both unicast and multicast
routing
 AODV uses sequence numbers to ensure the
freshness of routes
 It is loop-free
 scales to large numbers of mobile nodes
 AODV maintains routes for as long as the route
is active.
10
Route Discovery:
 Node can initiate route discovery by broadcasting a

Route Request (RREQ) message
RREQ contains:
Source and Destination addresses
Sequence number of source
Last known sequence number of destination
Broadcast ID (incremented with each RREQ)
Number of hops
11
‫الگوريتمهاي ‪ DV‬يا بردار فاصله‬
‫• يكي از روشاي پويا در مسيريابي‬
‫• مورد استفاده در شبكه ‪ARPA‬‬
‫• استفاده در مسيريابهاي كوچك‬
‫• نامهاي متفاوت روش ‪DV‬‬
‫• پروتكل ‪RIP‬‬
‫• الگوريتم مسيريابي ‪Bellman - Ford‬‬
‫• الگوريتم مسيريابي ‪Ford – Fulkerson‬‬
‫• الگوريتم ‪Distance Vector Routing‬‬
‫‪12‬‬
‫اصول كار روش ‪DV‬‬
‫• محاسبه خطوطي را كه به صورت فيزيكي با مسيريابهاي ديگر دارد و درج در جدول‬
‫مسيريابي‬
‫• بينهايت درنظرگرفتن هزينة خطوطي كه مسيرياب با آنها در ارتباط مستقيم نيست‬
‫• ارسال ستون هزينه از جدول مسيريابي براي مسيريابهاي مجاور در بازههاي زماني مشخص‪،‬‬
‫توسط هر مسيرياب (“يعني فقط براي مسيريابهائي كه با آن در ارتباط است نه تمام‬
‫مسيريابها ”)‪ .‬دريافت اطالعات جديد ا زمسيريابهاي مجاور در در فواصل ‪ T‬ثانيهاي‬
‫• به هنگام نمودن جدول مسيريابي پس از دريافت جداول مسيريابي از مسيريابهاي مجاور ‪،‬‬
‫طبق يك الگوريتم بسيار ساده‬
‫‪13‬‬
‫الگوريتمهاي ‪ DV‬يا بردار فاصله‬
‫زيرساخت ارتباطي يك شبكة فرض ي‬
‫با دوازده مسيرياب‬
‫جدول مسيريابي مربوط به مسيرياب ‪J‬‬
‫‪14‬‬
‫مشكل عمده پروتكلهاي ‪DV‬‬
‫عدم همگرايي سريع جداول مسيريابي هنگام خرابي يك مسيرياب يا يك كانال ارتباطي = مشكل شمارش تا بينهايت‬
‫راه حل ‪:‬‬
‫ً‬
‫وقتي يك مسيرياب ميخواهد اطالعاتي را به همسايههايش بدهد هزينه رسيدن به آنهايي را كه قطعا بايد از همان‬
‫مسيرياب بگذرند را اعالم نميكند‪( .‬يا ‪ ‬اعالم ميكنند)‬
‫‪15‬‬
‫مسئله شمارش تا بينهايت‬
‫به خبرهاي خوب واکنش سريع ولي به خبرهاي بد واکنش کندي نشان مي دهد‪.‬‬
‫‪16‬‬
‫مسئله شمارش تا بينهايت‬
‫هرگاه مسيريابي از زيرشبکه خارج شود هرکدام از ساير مسيريابهاي فعال احساس ميكنند از طريق‬
‫ديگري مسيري بهتر به آن وجود دارد‪.‬‬
‫‪17‬‬
AODV introduction:
 Generating



Route Request
Processing and Forwarding Route Requests
Generating Route Replies
Receiving and Forward Router Replies
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Aodv Algorithm:
Source: A
A
B
C
D
E
F
G
H
I
Dest. : I
A broadcast Route Request
packet.
 If the receiving node has a route to the
destination:
 Set up reverse path entry as
before
 Sends back a Route Reply
message
(RREP) to the source
containing :
o Last known sequence number
of destination
o Number of hops to destination
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Comparisons :

Percentage of Packets Received Correctly
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Routing Overhead in Packets
21
Conclusions:
 Routing protocols for MANETs will become



important due to of wireless devices
Different routing protocols for different needs
DSDV does not perform well with highly mobile
nodes
DSR and AODV seem to give similar results
22
An overview of IEEE 802.11
 802.11 refers to a set of WLANs that was

approved by IEEE in 1997.
Specifies the lowest two layers of the OSI model
Standard
Data rate
Physical
Layer
Operating
Frequency
802.11
1-2 Mbps
FHSS/DSSS
2.4 GHz
802.11b
11 Mpbs
Max.
DSSS/HRDSSS
2.4 GHz
802.11a
54 Mbps
Max.
OFDM
5.5 GHz
802.11g
54 Mbps
Max.
OFDM
2.4 GHz
23
IEEE 802.11
 IEEE 802.11 was first designed for wireless fixed


networks
Many problems occur when building ad hoc
Networks with the IEEE 802.11 standard as the lowest
two layers
Until now, IEEE 802.11 doesn’t function well in
wireless ad hoc netwroks
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Modes of operation:
 Infrastructure-based:
 The
main most mature technology for WLANs
 Most commonly used to construct Wi-Fi
hotspots
 Costly for dynamic environments
25
Modes of operation:
 Infrastructureless-based:
 Also
called Ad Hoc mode
 Stations form an Independent Basic Service Set
(IBSS)
 Any stations within the same transmission
range can communicate
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IEEE 802.11 Architecture:

Physical Layer :

infrared, FHSS, or DSSS in 1997

OFDM and HR-DSSS were added in 1999

MAC Layer:

Distributed Coordination Function (DCF):

Provides the basic access method to the
802.11 MAC protocol
Uses random backoff time following a busy
signal
Based on CSMA/CA

Point Coordination Function (PCF):

Only used in infrastructure-based


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Common Problems in Wireless
Ad Hoc Networks:
A
B
C
A
B
C
D
 The hidden-station problem
* The exposed-station problem

* Degradation in throughput
Collision occurs
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Solution for the hidden and exposed
station problems:

Hidden Station Problem Solution:

Extension for the DCF protocol by a virtual carrier sensing
mechanism.
Adding two control frames: Ready-To-Send (RTS), Clear-To-Send
(CTS)
Sending station transmits RTS to receiver and waits for CTS
Receiver will not send CTS if receiving from another station
Avoiding collision
Exposed Station Problem Solution:
A node can identify itself as an exposed node if it hears an RTS
frame but not a CTS frame from the other transmitting node.
Therefore, it concludes that it can have a simultaneous
transmission
Avoiding the reduction in throughput







29
Exposed node problem:


Add info of your
choice here
Add text, graphic or
photo at left
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Mobility Problem:



In ad hoc networks nodes can change their positions anytime
TCP protocol cannot distinguish between congestion on one
hand and route failure or packet loss due to transmission on
the other hand
This results in reduction in the performance of the network
because of the slow start mechanism of the TCP protocol

Mobility Problem Solutions:

Route Failure and Rout Re-establishment notifications
Explicit Link Failure Notification (ELFN) signal
Ad hoc TCP (ATCP) : by adding a thin layer between TCP and IP
layers


31
MAC Protocol & TCP :
 IEEE 802.11 was designed for wireless infrastructure LANs not
for multi-hop ad hoc networks
 802.11 doesn’t function well ad hoc networks because of the TCP
protocol mechanisms and the difference among the transmission,
sensing and interference ranges

Three major problems will occur:



Instability problem
In-compatibility problem
One hop Un-fairness problem
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Instability Problem:
2
1
3
4
5

If station 1 is sending to station 5, the throughput can drop down
to zero in some scenarios because of the following
 The hidden and exposed station problems that may prevent
station 2 from receiving RTS or sending CTS to station 1
 The random backoff time
 High window size that the TCP uses

Solutions for the Instability Problem
 Decreasing the maximum window size of the TCP layer
 making the interfering range the same as the
communication range
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In-Compatibility Problem:

This problem is defined as two simultaneous TCP traffics cannot coexist
in the network. Once one session develops, the other one is shut down.
The overturn can happen at any time randomly.

the main causes of this problem are the hidden station problem,
the exposed node problem and the exponential back-off scheme
in the MAC layer.

Solutions for the In-Compatibility Problem:

Changing the back-off policy by penalizing stations that transmit
too much data, so the other stations can still use the media.

Adjusting the interfering and the sensing range
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One-hop unfairness problem:


If there are two simultaneous
TCP connections one is a
single-hop connection and
the other is a multi-hop
connection, the single-hop
connection will be activated
even if the multi-hop
connection started first.
1
2
First
Connection
3
4
5
6
Second
Connection
Causes are hidden station
problem, the exposed node
problem and the exponential
back-off scheme
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Unicast and Multicast:
128.146.199.0/24


Unicast :
With n receivers,
sender must
replicate the
stream n times
Sender
128.146.116.0/24
Receiver
128.146.222.0/24
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Multicast:

128.146.199.0/24
Source transmits one
stream of data for n
receivers
Sender

Replication happens
inside routers and
switches
128.146.116.0/24
Receiver
128.146.222.0/24
Receiver
Receivers
37
Multicast Routing Protocols for Ad
hoc Networks:

Tree Based Protocols
 Ad
hoc Multicast Routing (AMRoute)
 Ad hoc Multicast Routing Protocol utilizing
Increasing id numberS (AMRIS)
– Mesh Based Protocols
 On-Demand
Multicast Routing Protocol
(ODMRP)
 Core-Assisted Mesh Protocol (CAMP)
38
Multicast Routing Protocols:
protocol
AMRoute
ODMRP
AMRIS
CAMP
Configuratio
n
Tree
Mesh
Tree
Mesh
Loop - Free
No
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Dependency
on unicast
Protocol
Periodic
Messaging
Control
Packet
Flood
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On-Demand Multicast Routing Protocol (ODMRP):
Source broadcasts
periodically Join
Request.
Nodes receiving the
request, save upstream
node id and
rebroadcast the
message.
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ODMRP:
When a receiver gets the request,
it updates its member table and
return message Join Table to
its neighbors.
 Nodes that are on the path
from receiver to source,
become part of the Forwarding
Group
41
ODMRP:

If source wants to leave the group, simply
stop sending JOIN REQUEST packets

If a node wants to leave the group it stops
sending JOIN TABLE packets for that group
42
Simulation:
Metrics

Packet Delivery Ratio: The ratio of the number of data packets
actually delivered to the destinations versus the number of data
packets supposed to be received.
 Number of control packets transmitted per data packet delivered:
The ratio of control packets transmitted to data packets delivered
gives a measure of efficient utilization of control packets in
delivering data.


Number of data packets transmitted per data packet delivered
Number of control and data packets transmitted per data packet
delivered
43
Simulation Model:

network of 50 mobile hosts
 Radio propagation range for each
node was 250 meters and channel
capacity was 2 Mbits/sec.
 ….
ODMRP transmits more data packets
than AMRIS because it exploits
multiple redundant routes for data
delivery
2.5
D a t a P a c k e t s T X e d /D a t a P a c k e t D e liv e re d
 There are 21 nodes in the
multicast group and 5 nodes are
chosen as sources
Da ta P a cke ts T X e d /Da ta p a cke t De live re d a s a fu n ctio n o f M o b ility
2
1.5
ODMRP
A MRIS
1
0.5
0
0
1
2
5
10
20
M o b ility (m /s e c)
44
Simulation Model:
A ll Pack e ts T Xe d /Data Pack e t De live r e d as a fu n ctio n o f M o b ility
AMRIS has the smallest
number of packet
transmissions because it
uses a tree
A ll P a c k e t s T X e d /D a t a P a c k e t D e liv e re d
2.5
2
1.5
ODMRP
A MRIS
1
ODMRP transmits more
data packets on redundant
paths
0.5
0
0
1
2
5
10
20
M o b ility (m /s e c)
45
Network Traffic Load:

AMRIS is very sensitive to traffic
load
ODMRP is also affected at higher
loads, but the packet loss rate is
much lesser than AMRIS
PDR as a function of Network Traffic Load
1.2
1
Packet Delivery Ratio

0.8
AM RIS
0.6
ODM RP
0.4
0.2
0
1
5
10
25
Netw ork Traffic Load(pkts/sec)
46
Challenges:





Security in Ad Hoc Networks
Qos
Routing Protocol
Multicasting
………..
47