Slide 1

Dr. C. Rama Krishna
Dept. of CSE
NITTTR, Chandigarh
Email: rkc at nitttrchd.ac.in

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Slide 2

Which Technology ?
Cellular Technologies

Wireless LAN Technology



2G Systems

•



2.5G Systems

•



3G Systems



4G Systems



NextG Systems

Short range Technologies


Home RF



Bluetooth



ZigBee

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2.4/5 GHz Wireless LAN
Ad-hoc / Infrastructure
Mode

Long Range Technologies
 Internet

C. Rama Krishna, NITTTR, Chandigarh


Slide 3

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

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Slide 4

History and Introduction

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Slide 5

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)
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Slide 6

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

traffic from A
D is
relayed by nodes B and
C

radio
range of node A
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Slide 7

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

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Slide 8

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
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Slide 9

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
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Slide 10

Ad hoc Network Architecture
application

application

application

transport

transport

transport

network

network

network

Data link

Data link

Data link

physical

physical

physical

wireless link
Source

wireless link
Intermediate node

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Destination

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Slide 11

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
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Slide 12

Physical Layer

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Slide 13

IEEE 802.11 WLAN standards
Sl.No

Standard

1
2
3
4
5
6
7
8
9
10

802.11
802.11a
802.11b
802.11e
802.11g
802.11i
802.11n
802.11ac
802.11ad
802.11p

Specification

Physical Layer & MAC Layer
Physical Layer
Physical Layer
QoS enhancement in MAC
Physical Layer
Security enhancement in MAC
600 Mbps with MIMO
Very High Throughput
Very High Throughput
WAVE

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Slide 14

IEEE 802.11 standard
• 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

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Slide 15

IEEE 802.11 based infrastructure WLAN
PC
Access Point (AP) Wire line

Laptop
Basic Service Set (BSS)

Basic service area (BSA)

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Slide 16

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

Laptop

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Slide 17

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)

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Slide 18

Physical Layer for high speed MANET
• 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]

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Slide 19

Medium Access Control (MAC)

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Slide 20

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

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Slide 21

Classification of Wireless MAC Protocols
Wireless MAC protocols
Distributed
Random
Access

Centralized
Random
Access

Guaranteed
Access

Hybrid
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
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Slide 22

Distributed Random Access Protocols

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Slide 23

Pure ALOHA MAC Protocol

• Frames are transmitted as they are generated (No discipline!).
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Slide 24

Modeling of Pure ALOHA MAC Protocol
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]
Prob.Therefore:
[ a transmission attempt is successful ] = Prob. [ 0 arrivals in the period (t-1,t+1] ]
= Prob. [ 0 arrivals in 2 time units ]
= e−2G

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Slide 25

Throughput of Pure ALOHA MAC Protocol

Throughput = Offered Load (G) × Prob. [ a transmission attempt is successful ]

= G × e−2G

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Slide 26

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

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Slide 27

Slotted ALOHA MAC Protocol

• Frames are transmitted only at slot boundaries (some discipline!).
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Slide 28

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

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Slide 29

Throughput for pure and slotted ALOHA

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Slide 30

Carrier Sense Multiple Access (CSMA) MAC
Protocol
• Max. throughput : pure ALOHA slotted ALOHA -

18.4% and
36. 8%

• Listen to the channel before transmitting a packet
(better disciplined!)
• CSMA improves throughput compared to ALOHA
protocols
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Slide 31

Variants of CSMA
Unslotted Nonpersistent CSMA

Nonpersistent CSMA
Slotted Nonpersistent CSMA

CSMA
Unslotted persistent CSMA

Persistent CSMA
Slotted persistent CSMA
1-persistent CSMA
p-persistent CSMA
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Slide 32

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"

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Slide 33

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

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Slide 34

Carrier Sense Multiple Access (CSMA)
• 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

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Slide 35

Hidden Terminal Problem

B

A

!

C

Note: colored circles
represent the Tx range
of each node

• 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
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Slide 36

Exposed Terminal Problem

B

A

C

?

D

• 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

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Slide 37

Multiple Access Collision Avoidance
(MACA)
• 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

Drawback:
• Cannot avoid RTS/CTS control packet collisions
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Slide 38

RTS-CTS Handshake in Action
radio range of B
radio range of A

C

A

B

D

E

RTS

D

CTS
C

A

B

E
DATA

• 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
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Slide 39

MACA for Wireless LANs (MACAW)
C

A

D

D

B E
RTS
CTS

C

A

B

E
DATA

ACK

• 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

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Slide 40

IEEE 802.11 MAC Protocol
• 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

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Slide 41

Distributed Coordination Function (DCF)

Two schemes:
• Basic access scheme (CSMA/CA)

• CSMA/CA with RTS (Request-to-Send)/CTS (Clear-toSend) handshake (optional)

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Slide 42

CSMA/CA with RTS/CTS

RTS
A

B

C

D

E

F

RTS = Request-to-Send

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Slide 43

CSMA/CA with RTS/CTS (contd.)

RTS

A

B

C

D

E

F

NAV = 20

RTS = Request-to-Send

NAV (Net Allocation Vector) = indicates remaining duration
to keep silent
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Slide 44

CSMA/CA with RTS/CTS (contd.)

CTS
A

B

C

D

E

F

CTS = Clear-to-Send

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Slide 45

CSMA/CA with RTS/CTS (contd.)

CTS
A

B

C

D

E

F

NAV = 15

CTS = Clear-to-Send

NAV (Net Allocation Vector) = indicates remaining duration
to keep silent
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Slide 46

CSMA/CA with RTS/CTS (contd.)
• DATA packet follows CTS. Successful data reception
acknowledged using ACK.

DATA
A

B

C

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E

F

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Slide 47

CSMA/CA with RTS/CTS (contd.)

ACK
A

B

C

D

E

F

ACK = Acknowledgement packet

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Slide 48

CSMA/CA with RTS/CTS (contd.)
Reserved area for
transmission between
node C and D

ACK
A

B

C

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F

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Slide 49

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)

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Slide 50

Example: RTS/CTS packet collisions

E
RTS

A

B
CTS

D

C

• 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
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Slide 51

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

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Slide 52

B

PAB

D
PCD

A

Bandwidth

Example: Single-channel/Multiple-Channel
MAC Protocol

C

E

F
• Node A, C and E are in radio
range

PCD

PEF

(a) Single Channel

Bandwidth

PEF

PAB

time
Channel 1

PAB

Channel 2

PCD
PEF

Channel 3

time
(b) Multiple Channels (3 channels)

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Slide 53

Use of Directional Antennas
• Wireless nodes traditionally use omni-directional antennas
e.g., IEEE 802.11.MAC
• Disadvantage: Increases exposed node problem
Example: IEEE 802.11 MAC
G
A

B

RTS
RTS

F

RTS
C

CTS
D

E

CTS

Node B, E, G & H
(colored red) are
exposed nodes, hence
cannot communicate
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X
H

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Slide 54

Example: Directional Antennas
F
E

G
D
A

B

C
H

X

• Node B only is exposed for communication between C & D
• Communication between E & X is possible
• Use of directional antennas reduces exposed terminals
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Slide 55

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
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Slide 56

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

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Slide 57

Power Control
• Reduces interference and increases spatial reuse
• Energy Saving
• When node C transmits to D at a

A

B

C

D

Fig.1

higher power level, B cannot receive
A’s transmission due to interference
from C (Fig. 1)

• If node C reduces Tx power, it still
communicates with D (Fig. 2)

A

B

C

D

- Reduces energy consumption at node C

- Allows B to receive A’s transmission
(spatial reuse)

Fig. 2
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Slide 58

Routing Protocols

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Slide 59

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

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Slide 60

Classification of Unicast Routing Protocols
Unicast Routing Protocols
Proactive

STAR DSDV WRP OLSR

Reactive

CSGR FSR

DSR

ABR TORA

Hybrid

SSR

LAR

AODV

ZRP

LANMAR

PR

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
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Slide 61

Proactive Routing Protocols

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Slide 62

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)

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Slide 63

Reactive Routing Protocols

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Slide 64

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)
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Slide 65

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
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Slide 66

Transmission Control Protocol
(TCP)

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Slide 67

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

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Slide 68

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

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Slide 69

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

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Slide 70

QoS Issues

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Slide 71

Quality-of-Service (QOS)
• 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
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Slide 72

QoS support in MANETs:
Issues and Difficulties
• Unpredictable link properties
• Node mobility
• Limited battery life

• Hidden and exposed node problem
• Route maintenance

• Security

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Slide 73

Security Issues

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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)

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Slide 75

Open Issues
in
Mobile Ad Hoc Networking

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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
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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-ietfmanet-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.
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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. 11061110, April 1996.
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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 Multihop 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.15891593.
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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.
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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
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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
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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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