CS2.ppsx

FDP on Computing & Communication Resources C. Rama Krishna, NITTTR, Chandigarh
CEC, Landran, Mohali
Dr. C. Rama Krishna
Dept. of CSE
NITTTR, Chandigarh
Email: rkc at nitttrchd.ac.in

Cellular Technologies
 2G Systems
 2.5G Systems
 3G Systems
 4G Systems
 NextG Systems
Short range Technologies
 Home RF
 Bluetooth
 ZigBee
Wireless LAN Technology
• 2.4/5 GHz Wireless LAN
• Ad-hoc / Infrastructure
Mode
Long Range Technologies
 Internet
Which Technology ?

Outline
• History and Introduction
• Brief Introduction to Physical Layer
• Medium Access Control (MAC) Layer
• Routing and Transport Layer Issues
• Quality-of-Service Issues
• Security Issues
• Additional Resources

History and Introduction

History
• Packet Radio NETwork (PRNET) by DARPA - late 1960s
• Military Communications
• Disaster Management
• Survivable Packet Radio Networks (SURAN) – 1980s
• MANET group formed under Internet Engineering Task Force
(IETF) – 1990s
• IEEE released 802.11 PHY and MAC standard – 1995 (later
updated versions evolved)

What is an Ad hoc Network ?
• Network of wireless nodes (may be static/mobile)
– No infrastructure (e.g. base stations, fixed links, routers,
centralized servers)
– Data can be relayed by intermediate nodes
– Routing infrastructure created dynamically
A
B
C
D
radio
range of node A
traffic from A D is
relayed by nodes B and
C

• Does not depend on pre-existing infrastructure
• Ease of deployment
• Speed of deployment
• Anytime-Anywhere-Any device network paradigm
Why an Ad hoc Network?

Mobile Ad hoc Network Example
• Communication between nodes may be in single/multi-hop
• Each of the nodes acts as a host as well as a router

Typical Applications
• Military environments
• soldiers, tanks, planes
• Emergency operations
• search-and-rescue
• Personal area networking
• cell phone, laptop, etc.
• Civilian environments
• meeting rooms, sports stadiums, hospitals
• Education
• virtual classrooms, conferences
• Sensor networks
• homes, environmental applications

Ad hoc Network Architecture
physical
Data link
network
transport
application
physical
Data link
network
transport
application
physical
Data link
network
transport
application
wireless link
Source Destination
Intermediate node
wireless link

Some Challenges
• Limited wireless transmission range
• Broadcast nature of wireless medium
• hidden terminal and exposed terminal problems – MAC
problem
• Mobility-induced route changes – routing problem
• Packet losses due to: transmission errors and node mobility –
transport problem
• Battery constraints – energy efficiency problem
• Ease of snooping - security problem

Physical Layer

IEEE 802.11 WLAN standards
Sl.No Standard Specification
1 802.11 Physical Layer & MAC Layer
2 802.11a Physical Layer
3 802.11b Physical Layer
4
5
6
QoS enhancement in MAC
7
8
802.11g Physical Layer
9
10
802.11i Security enhancement in MAC
802.11e
802.11n 600 Mbps with MIMO
Very High Throughput
802.11ac
802.11ad
802.11p WAVE
Very High Throughput

• Supports networking in two modes:
• Infrastructure based WLAN using access points (APs)
• Infrastructure-less ad hoc networks – widely used in
simulation studies and testbeds of MANET
IEEE 802.11 standard

Basic service area (BSA)
Access Point (AP)
Basic Service Set (BSS)
Wire line
PC
Laptop
IEEE 802.11 based infrastructure WLAN

Independent Basic Service Set (IBSS)
Laptop
IEEE 802.11 based infrastructure-less
Adhoc Network

IEEE 802.11 Physical Layer Specification
Standard
Parameter
802.11 802.11a 802.11b
Bandwidth 83.5MHz 300MHz 83.5MHz
Frequency band 2.4-2.4835
GHz
5.15-5.35 GHz and
5.725 – 5.825 GHz
2.4-2.4835 GHz
Channels 3 12 3
Data Rate
( in Mbps)
1, 2 6, 9, 12, 18, 24, 36, 48
and 54
1, 2, 5.5, and 11
Transmission
Scheme
FHSS, DSSS
with QPSK
OFDM (with PSK and
QAM )
DSSS(with
QPSK & CCK
modulation)

• Present physical Layer
• IEEE 802.11, 11a, 802.11b and 802.11g
• Supports 1/ 2 /11/ 22/ 54 Mbps data rate in static indoor
environment
• DSSS is not suitable for data rate more than 10Mbps
• OFDM based Physical layer design for high data rate
transmission up to 54 Mbps [ 802.11a & g]
Physical Layer for high speed MANET

Medium Access Control (MAC)

Need for a MAC Protocol
• Wireless channel is a shared medium and bandwidth is a
scarce resource.
• Need access control mechanism to avoid collision(s)
• To maximize probability of successful transmissions by
resolving contention among users
• To avoid problems due to hidden and exposed nodes
• To maintain fairness amongst all users

Classification of Wireless MAC Protocols
Wireless MAC protocols
Distributed Centralized
Random
Access
Hybrid
Access
Guaranteed
Access
Random
Access
• Guaranteed Access and Hybrid Access protocols require infrastructure
such as Base Station or Access Point – Not suitable for MANETs
• Random Access protocols can be operated in either architecture
– suitable for MANETS

Distributed Random Access Protocols

Pure ALOHA MAC Protocol
• Frames are transmitted as they are generated (No discipline!).

The transmission x is successful:
if and only if:
There are no transmission attempts that begins (=arrives) during
the time interval (t-1, t+1]
Therefore:
Prob. [ a transmission attempt is successful ] = Prob. [ 0 arrivals in the period (t-1,t+1] ]
= Prob. [ 0 arrivals in 2 time units ]
= e−2G
Modeling of Pure ALOHA MAC Protocol

Throughput = Offered Load (G) × Prob. [ a transmission attempt is successful ]
= G × e−2G
Throughput of Pure ALOHA MAC Protocol

The throughput for pure ALOHA is
S = G × e −2G
The maximum throughput
Smax = 0.184 , when G = 0.5

Slotted ALOHA MAC Protocol
• Frames are transmitted only at slot boundaries (some discipline!).

The throughput for slotted ALOHA is
S = G × e−G
The maximum throughput
Smax = 0.368, when G = 1

Throughput for pure and slotted ALOHA

Carrier Sense Multiple Access (CSMA) MAC
Protocol
• Max. throughput : pure ALOHA - 18.4% and
slotted ALOHA - 36. 8%
• Listen to the channel before transmitting a packet
(better disciplined!)
• CSMA improves throughput compared to ALOHA
protocols

Variants of CSMA
CSMA
Nonpersistent CSMA
Persistent CSMA
Unslotted Nonpersistent CSMA
Unslotted persistent CSMA
Slotted Nonpersistent CSMA
Slotted persistent CSMA
1-persistent CSMA
p-persistent CSMA

CSMA/CD
• Adds collision detection capability to CSMA; greatly
reduces time wasted due to collisions
• Standardized as IEEE 802.3, most widespread LAN
• Developed by Robert Metcalfe during early 1970s.....
led to founding of “3COM” company. [later Metcalfe
sold his company for $400M)
• The name 3COM comes from the company's focus on "COMputers,
COMmunication and COMmpatibility"

Why can’t we use CSMA or CSMA/CD in
a Wireless LAN or Adhoc Network?

• If the channel is idle, transmit
• If the channel is busy, wait for a random time
• Waiting time is calculated using Binary Exponential Backoff
(BEB) algorithm
• Limitations of carrier Sensing
- hidden terminals
- exposed terminals
Carrier Sense Multiple Access (CSMA)

Hidden Terminal Problem
!
• Node A can hear both B and C; but B and C cannot hear each other
• When B transmits to A, C cannot detect this transmission using the carrier
sense mechanism
• If C also transmits to A, collision will occur at node A
• Increases data packet collisions and hence reduces throughput
• Possible solution: RTS (request-to-Send)/ CTS (Clear-to-Send) handshake
C
B
A Note: colored circles
represent the Tx range
of each node

Exposed Terminal Problem
D
B C
A ?
• When A transmits to B, C detects this transmission using carrier sense
mechanism
• C refrains from transmitting to D, hence C is exposed to A’s transmission
• Reduces bandwidth utilization and hence reduces throughput
• Possible solution: Directional Antennas, separate channels for control
and data

• Uses Request-To-Send (RTS) and Clear-To-Send (CTS)
handshake to reduce the effects of hidden terminals
• Data transfer duration is included in RTS and CTS, which helps
other nodes to be silent for this duration
• If a RTS/CTS packet collides, nodes wait for a random time
which is calculated using BEB algorithm
Multiple Access Collision Avoidance
(MACA)
Drawback:
• Cannot avoid RTS/CTS control packet collisions

A B
C
D
E
DATA
A B
C E
D
RTS
CTS
RTS-CTS Handshake in Action
• A is the source which is in the range of B, D and C
• B is the destination which is in the range of A, D and E
radio range of A
radio range of B

A B
C
D
E
DATA
RTS
CTS
• A is the source which is in the range of B, D and C
• B is the destination which is in the range of A, D and E
• B sends ACK after receiving one data packet
• Improves link reliability using ACK
MACA for Wireless LANs (MACAW)
ACK
A B
C E
D

• Has provision for two modes
- Point Coordination Function (PCF)
- Distributed Coordination Function (DCF)
• Point Coordination Function
- Provides contention-free access
- Requires Access Point (AP) for coordination
- Not suitable for a MANET
IEEE 802.11 MAC Protocol

Two schemes:
• Basic access scheme (CSMA/CA)
• CSMA/CA with RTS (Request-to-Send)/CTS (Clear-to-
Send) handshake (optional)
Distributed Coordination Function (DCF)

CSMA/CA with RTS/CTS
C F
A B E
D
RTS
RTS = Request-to-Send

CSMA/CA with RTS/CTS (contd.)
C F
A B E
D
RTS
RTS = Request-to-Send
NAV = 20
NAV (Net Allocation Vector) = indicates remaining duration
to keep silent

C F
A B E
D
CTS
CTS = Clear-to-Send

C F
A B E
D
CTS
CTS = Clear-to-Send
NAV = 15
NAV (Net Allocation Vector) = indicates remaining duration
to keep silent

C F
A B E
D
DATA
• DATA packet follows CTS. Successful data reception
acknowledged using ACK.

C F
A B E
D
ACK
ACK = Acknowledgement packet

C F
A B E
D
ACK
Reserved area for
transmission between
node C and D

Limitations of DCF MAC
• Performance of Basic Access Method (CSMA/CA) degrades due to
hidden and exposed node problems
• CSMA/CA with RTS/CTS – consumes additional bandwidth for
control packets transmission
• may introduce significant delay in data packet transmission if RTS/CTS
control packets experience frequent collisions and retransmissions (possible
in case of high node concentration)

Example: RTS/CTS packet collisions
A B
RTS
CTS
C
D
E
• Node C (which is hidden from node A) misses the CTS packet
from node B due to a collision with an RTS packet from D

Multi-Channel MAC Protocols
• Divides bandwidth into multiple channels
• Selects any one of the idle channels
Advantages:
• Improves throughput performance in the network by distributing
traffic over time as well as over bandwidth
Disadvantages:
• Increases hardware complexity

Example: Single-channel/Multiple-Channel
MAC Protocol
PEF
D
C
PAB
Bandwidth
(a) Single Channel
time
PAB PCD PEF
PAB
PCD
PEF
Channel 1
Channel 2
Channel 3
time
Bandwidth
(b) Multiple Channels (3 channels)
PCD
A
B
E
F
• Node A, C and E are in radio
range

Use of Directional Antennas
• Wireless nodes traditionally use omni-directional antennas
e.g., IEEE 802.11.MAC
• Disadvantage: Increases exposed node problem
RTS
CTS
A B C D
G
E
H
RTS
RTS
CTS
F
X
Reserved Area
Example: IEEE 802.11 MAC
Node B, E, G & H
(colored red) are
exposed nodes, hence
cannot communicate

Example: Directional Antennas
• Node B only is exposed for communication between C & D
• Communication between E & X is possible
• Use of directional antennas reduces exposed terminals
C
D
E
X
B
A
G
H
F

Directional Antennas: Advantages
& Disadvantages
• Reduces interference to neighboring nodes
- helps in frequency reuse
- increases packet success probability (or reduces number of collisions)
• Higher gain due to their directivity
- allows transmitters to operate at a smaller transmission power and still
maintain adequate signal-to-interference-plus-noise ratio (SINR)
- reduces average power consumption in the nodes
• Requires a mechanism to determine direction for transmission and
reception
• Cost of beam forming antennas is a concern

Energy Conservation
• Many wireless nodes are powered by batteries, hence needs MAC
protocols which conserve energy.
• Two approaches to reduce energy consumption
- power save: Turn off wireless interface when not required
- power control: Reduce transmit power
• Need for power-aware MAC protocols

Power Control
A B C D
Fig.1
• When node C transmits to D at a
higher power level, B cannot receive
A’s transmission due to interference
from C (Fig. 1)
A B C D
Fig. 2
• If node C reduces Tx power, it still
communicates with D (Fig. 2)
- Reduces energy consumption at node C
- Allows B to receive A’s transmission
(spatial reuse)
• Reduces interference and increases spatial reuse
• Energy Saving

Routing Protocols

Importance of Routing in MANET
• Host mobility
• link failure due to mobility of nodes
• Rate of link failure may be high when nodes move
fast
• Some desirable features of routing protocols
• Minimum route discovery and maintenance time
• Minimum routing overhead
• Shortest route despite mobility

Classification of Unicast Routing Protocols
STAR: Source Tree Adoptive Routing DSDV: Destination Sequence Distance Vector
WRP: Wireless Routing Protocol OLSR: Optimized Link State Routing,
CSGR: Cluster Switch Gateway Routing (CSGR) FSR : Fisheye State Routing
DSR: Dynamic Source Routing, ABR: Associativity Based Routing
TORA: Temporally Ordered Routing, SSR : Signal Stability-based Routing
AODV: Ad hoc On-Demand Distance Vector Routing LAR: Location Aided Routing,
LANMAR: Landmark Ad hoc Routing Protocol ZRP: Zone Routing Protocol,
PR: Preemptive Routing
STAR
Proactive Reactive Hybrid
DSDV WRP CSGR DSR AODV ZRP
ABR LANMAR
TORA LAR
SSR
OLSR FSR PR
Unicast Routing Protocols

Proactive Routing Protocols

Characteristics of Proactive Routing Protocols
• Distributed, shortest-path protocols
• Maintain routes between every host pair at all times
• Based on Periodic updates of routing table
• High routing overhead and consumes more bandwidth
• Example: Destination Sequence Distance Vector (DSDV)

Reactive Routing Protocols

Characteristics of Reactive Routing Protocols
• Reactive protocols
• Determine route if and when needed
• Less control packet overhead
• Source initiates route discovery process
• More route discovery delay
• Example: Ad hoc On-Demand Distance Vector Routing
(AODV)

Proactive and Reactive Protocol Trade-Off
• Latency of route discovery
• Proactive protocols may have lower latency since routes are
maintained at all times
• Reactive protocols may have higher latency because a route
from X to Y will be found only when X attempts to send a
packet to Y
• Overhead of route discovery and maintenance
• Reactive protocols may have lower overhead since routes are
determined only if needed
• Proactive protocols may result in higher overhead due to
continuous route updating
• Which approach achieves a better trade-off depends on
the type of traffic and mobility patterns

Transmission Control Protocol
(TCP)

Transmission Control Protocol (TCP)
• Reliable ordered delivery
• Implements congestion control
• Reliability achieved by means of retransmissions
• End-to-end semantics
• Acknowledgements (ACKs) sent to TCP sender confirm
delivery of data received by TCP receiver

TCP in MANET
Several factors affect TCP performance in a MANET:
• Wireless transmission errors
– may cause fast retransmit, which results in
• retransmission of a lost packet
• reduction in Congestion Window (cwnd)
– reducing congestion window in response to transmission
errors is unnecessary
• Route failures due to mobility leads to packet losses

Impact of Transmission Errors on TCP
• TCP cannot distinguish between packet losses due to
congestion and mobility induced transmission errors
• Unnecessarily reduces congestion window size
• Throughput suffers

QoS Issues

• Guarantee by the network to satisfy a set of pre-determined service
performance constraints for the user:
- end-to-end delay
- available bandwidth
- probability of packet loss
- delay and jitter (variation in delay)
• Enough network resources must be available during service
invocation to honor the guarantee
• Power consumption and service coverage area- other QoS attributes
specific to MANET
• QoS support in MANETs encompasses issues at physical layer,
MAC layer, network, transport and application layers
Quality-of-Service (QOS)

QoS support in MANETs:
Issues and Difficulties
• Unpredictable link properties
• Node mobility
• Limited battery life
• Hidden and exposed node problem
• Route maintenance
• Security

Security Issues

Security Issues in
Mobile Ad Hoc Networks
• Wireless medium is easy to snoop
• Due to ad hoc connectivity and mobility, it is hard to
guarantee access to any particular node
• Easier for trouble-makers to insert themselves into a mobile
ad hoc network (as compared to a wired network)

Open Issues
in
Mobile Ad Hoc Networking

Open Problems
• Physical layer modeling to support broadband
services
• Efficient MAC protocols to support mobility, QoS
and security
• Efficient routing protocols with scalability, QoS and
security
• QoS issues at other layers
• Security issues at other layers
• Interoperation with Internet

References
[1] C.E. Perkins, Ad Hoc Networking, Addison-Wesley, 2002
[2] J. Broch et al., “A Performance Comparison of Multi-hop Wireless Ad
hoc Network Routing Protocols,” Proceedings of the 4th International
Conference on Mobile Computing and Networking (ACM
MOBICOM’98), pp. 85-97, October 1998.
[3] E. Royer and C.K. Toh, “A Review of Current Routing Protocols for Ad
hoc Mobile Wireless Networks,” IEEE Personal Communications
Magazine, Vol. 6, Issue 2, pp. 46-55, 1999.
[4] C.E. Perkins, E.M. Royer, and Samir Das, “Ad hoc On-Demand
Distance Vector Routing,” http://www.ietf.org/internet-drafts/draft-ietf-
manet-aodv-13.txt, (work in progress), February 2003.
[5] L. Bajaj et al., “GloMoSim: A Scalable Network Simulation
Environment,” CSD Technical Report, #990027, UCLA, 1997.

References (contd.)
[6] IEEE Standards Department, Wireless LAN Medium Access Control (MAC)
and PHYsical layer (PHY) specifications, IEEE standard 802.11-1997, 1997.
[7] B.P. Crow et al., “IEEE 802.11 Wireless Local Area Networks,” IEEE
Communications Magazine, Vol. 35, Issue 9, pp. 116-126, September 1997.
[8] C-K. Toh, Ad Hoc Mobile Wireless Networks: Protocols and Systems,
Prentice-Hall, 2002.
[9] Yiyan Wu and WilliumY. Zou, “Orthogonal Frequency Division Multiplexing,”
IEEE Trans.Consumer electronics, vol.41, no.3, pp. 392-399, Aug. 1995.
[10] Ramjee Prasad and Shinsuke Hara, “DS-CDMA,MC-CDMA and MT-CDMA
for Mobile Multimedia Communications” in Proc. IEEE VTC’96, pp. 1106-
1110, April 1996.

References (contd.)
[11] Hyumb Yang, Kiseon Kim, ”Multimedia Ad hoc wireless LANs with
Distributed Channel Allocation based on OFDM-CDMA,” in Proc.
ICT’03,p.p. 1428-1434,Feb. 2003.
[12] M.Conti et.al, “ Cross layering in mobile ad hoc network design,”
Computer, IEEE computer society, pp. 48-51, February 2004.
[13] F.H.P.Fitzek,Diego Angelini, G Mazzini, M.Z.U. Di Ferrara, “Design
and Performance of an Enhanced IEEE 802.11MAC Protocol for Multi-
hop Coverage Extension,” IEEE Wireless communication, PP. 30-39,
Dec.2004.
[14] Zhou Wenam, Li zheen, Song Junde, and Wang Daoyi, “Applying
OFDM in the Next Generation Mobile Communications,” in Proc. IEEE
Canadian Conf. Electrical & Computer Engineering 2002, pp.1589-
1593.

References (contd.)
[15] R.V.Nee and Ramjee Prasad, OFDM for Wireless Multimedia
Communications, Artech House, Boston,London,2000.
[16] Y. B. Ko, V. Shankarkumar, and N. H. Vaidya, “Medium Access
Control Protocols using Directional Antennas in Ad hoc Networks,” In
Proceedings of IEEE INFOCOM’2000, Mar. 2000.
[17] G.Gaertner, V.Cahill, “Understanding Link Quality in 802.11 Mobile
Ad hoc Networks,” IEEE Internet computing, pp. 55-60, Jan.-Feb.
2004.
[18] X.Shugong,T.Saadawi,“Does the IEEE MAC protocol work well in
multi-hop wireless ad hoc networks?” IEEE Comm. magazine, pp.
130-137,June 2001.

References (contd.)
[19] T. Goff, N. B. Abu-Ghazaleh, D. S. Phatak, and R. Kahvecioglu, “ Preemptive
routing in ad hoc networks,” Proc. of ACM MOBICOM’2001, 2001.
[20] M.Tubaishat, S.Madria, ”Sensor networks: an overview,” IEEE potentials,
pp.20-23,April-May-2003.
[21] Prasant Mohapatra, J.Li, Chao Gui,” QoS in Mobile Ad hoc Networks,” IEEE
Wireless Communication, pp.44-52,June-2003.
[22] N,Choi,Y.Seok,Y.Choi, “Multi-channel MAC for Mobile Ad hoc Networks,”
Proc.VTC’03, pp.1379-1383, Oct. 2003.
[23] I.Bradaric and A.P.Petropulu, “Analysis of physical layer performance of IEEE
802.11a in an Ad hoc Network Environment,” in Proc. MILICOM’03, vol.2, pp.
1231-1236, Oct. 2003

References (contd.)
[24] C. Rama Krishna, S. Chakrabarti, and D. Datta, “A Modified Backoff
Algorithm for IEEE 802.11 DCF-based MAC Protocol in a Mobile Ad hoc
Network,” Proc. of the International Conference IEEE TENCON 2004,
Chiang Mai, Thailand, 21-24 November 2004.
[25] Nah-Oak, et. al, “Enhancement of IEEE 802.11 Distributed Coordination
Function with Exponential Increase and Exponential Decrease Backoff
Algorithm,” Proc. of the 57th IEEE Semiannual Vehicular Technology
Conference 2003-Spring, vol. 4, pp. 2775-2778, April 2003.
[26] V. Bhargavan et al., “MACAW: A New Media Access Protocol for Wireless
LANs,” Proc. of ACM SIGCOMM, pp. 212-225, 1994.
[27] P. Karn, “MACA – A New Channel Access Method for Packet Radio,” in
ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp.
134-140, 1990

References (contd.)
[28] A.Chandra, V.Gummalla, J.O.Limb, “Wireless Medium Access Control
Protocols,” IEEE Communications Survey, pp.2-15, Second Quarter 2000.
[29] T. Camp, Jeff Boleng, and V. Davis, “A Survey of Mobility Models for Ad
Hoc Network Research,” Wireless Communication & Mobile Computing
(WCMC): Special issue on Mobile Ad Hoc Networking: Research, Trends
and Applications, vol. 2, no. 5, pp. 483-502, 2002.
[30] L.Bajaj, M.Takai, R.Ahuja, K.Tang, R.Bagrodia, and M.Gerla, “GlomoSim:
A Scalable Network Simulation Environment,” CSD Technical report,
#990027,UCLA,1997.
[31] P. Karn, “MACA – A New Channel Access Method for Packet Radio,” in
ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp.
134-140, 1990

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