UNIT II WIRELESS NETWORKS Wireless LAN – IEEE 802.11 Standards – Architecture – Services – Mobile Ad hoc Networks- WiFi and WiMAX - Wireless Local Loop

1. IT 2402 Mobile Communication
By
Dr Gnanasekaran Thangavel

2. UNIT II WIRELESS NETWORKS
Wireless LAN(WLAN) –
IEEE 802.11 Standards –
Architecture Services –
Mobile Ad hoc Networks-
Wi Fi and WiMAX –
Wireless Local Loop(WLL)
2

3. IEEE 802.11
Wireless LAN Technology
• The Institute of Electrical and Electronics Engineers developed
the 802.11 standard to improve compatibility of products for
Wireless Local Area Networks (WLANs).
• The standard has similarities with the 802.3 standard for
ethernet wired LANs.
• The 802.11 series are the most well-known Wireless LAN
standards.
3

4. Name, Description
IEEE 802.1, Bridging (networking) and Network Management
IEEE 802.2, LLC
IEEE 802.3, Ethernet
IEEE 802.4, Token bus
IEEE 802.5, Defines the MAC layer for a Token Ring
IEEE 802.6, MANs (DQDB)
IEEE 802.7, Broadband LAN using Coaxial Cable
IEEE 802.8, Fiber Optic TAG
IEEE 802.9, Integrated Services LAN (ISLAN or iso Ethernet)
IEEE 802.10, Interoperable LAN Security
IEEE 802.11 a/b/g/n, Wireless LAN (WLAN) & Mesh (Wi-Fi)
IEEE 802.12, 100BaseVG
IEEE 802.13, Unused
IEEE 802.14, Cable modems
IEEE 802.15, Wireless PAN
IEEE 802.15.1, Bluetooth certification 4

5. IEEE 802.15.2, IEEE 802.15 and IEEE 802.11 coexistence
IEEE 802.15.3, High-Rate wireless PAN
IEEE 802.15.4, Low-Rate wireless PAN
IEEE 802.15.5, Mesh networking for WPAN
IEEE 802.15.6, Body area network
IEEE 802.16, Broadband Wireless Access (WiMAX certification)
IEEE 802.16.1, Local Multipoint Distribution Service
IEEE 802.17, Resilient packet ring
IEEE 802.18, Radio Regulatory TAG
IEEE 802.19, Coexistence TAG
IEEE 802.20, Mobile Broadband Wireless Access
IEEE 802.21, Media Independent Handoff
IEEE 802.22, Wireless Regional Area Network
IEEE 802.23, Emergency Services Working Group
IEEE 802.24, Smart Grid TAG
IEEE 802.25, Omni-Range Area Network
5

6. 6

7. 7

8. Wireless LAN Applications
 LAN Extension
 Cross-building interconnect
 Nomadic Access
 Ad hoc networking
8

9. LAN Extension
 Wireless LAN linked into a wired LAN on same premises
 Wired LAN
 Backbone
 Support servers and stationary workstations
 Wireless LAN
 Stations in large open areas
 Manufacturing plants, stock exchange trading floors, and
warehouses
9

10. Cross-Building Interconnect
 Connect LANs in nearby buildings
 Wired or wireless LANs
 Point-to-point wireless link is used
 Devices connected are typically bridges or routers
10

11. 11

12. Nomadic Access
 Wireless link between LAN hub and mobile data terminal
equipped with antenna
 Laptop computer or notepad computer
 Uses:
 Transfer data from portable computer to office server
 Extended environment such as campus
12

13. WDS-Wireless Distribution
System
13

14. Ad Hoc Networking
 Temporary peer-to-peer network set up to meet immediate
need
 Example:
 Group of employees with laptops convene for a meeting;
employees link computers in a temporary network for
duration of meeting
14

15. Infrastructure-based wireless network
15

16. Infrastructure-based wireless network
16

17. Ad hoc network
17

18. 18

19. Wireless LAN Requirements
 Throughput
 Number of nodes
 Connection to backbone LAN
 Service area
 Battery power consumption
 Transmission robustness and security
 Collocated network operation
 License-free operation
 Handoff/roaming
 Dynamic configuration
19

20. Wireless LAN Categories
 Infrared (IR) LANs
 Spread spectrum LANs
 Narrowband microwave
20

21. Strengths of Infrared Over
Microwave Radio
 Spectrum for infrared virtually unlimited
 Possibility of high data rates
 Infrared spectrum unregulated
 Equipment inexpensive and simple
 Reflected by light-colored objects
 Ceiling reflection for entire room coverage
 Doesn’t penetrate walls
 More easily secured against eavesdropping
 Less interference between different rooms
21

22. Drawbacks of Infrared Medium
 Indoor environments experience infrared background
radiation
 Sunlight and indoor lighting
 Ambient radiation appears as noise in an infrared receiver
 Transmitters of higher power required
 Limited by concerns of eye safety and excessive power consumption
 Limits range
22

23. IR Data Transmission Techniques
 Directed Beam Infrared
 Ominidirectional
 Diffused
23

24. Directed Beam Infrared
 Used to create point-to-point links
 Range depends on emitted power and degree of focusing
 Focused IR data link can have range of kilometers
 Cross-building interconnect between bridges or routers
24

25. Omini directional
 Single base station within line of sight of all other stations
on LAN
 Station typically mounted on ceiling
 Base station acts as a multiport repeater
 Ceiling transmitter broadcasts signal received by IR
transceivers
 IR transceivers transmit with directional beam aimed at
ceiling base unit
25

26. 26

27. Diffused
 All IR transmitters focused and aimed at a point on
diffusely reflecting ceiling
 IR radiation strikes ceiling
 Reradiated omnidirectionally
 Picked up by all receivers
27

28. Spread Spectrum LAN Configuration
 Multiple-cell arrangement (Figure 13.2)
 Within a cell, either peer-to-peer or hub
 Peer-to-peer topology
 No hub
 Access controlled with MAC algorithm
 CSMA
 Appropriate for ad hoc LANs
28

29. Multiple-cell Wireless LAN
UM-User module
CM- Control Module
29

30. Spread Spectrum LAN Configuration
 Hub topology
 Mounted on the ceiling and connected to backbone
 May control access
 May act as multiport repeater
 Automatic handoff of mobile stations
 Stations in cell either:
 Transmit to / receive from hub only
 Broadcast using Omni directional antenna
30

31.  RF: Spread Spectrum, no licensing required. Resistance to
interference
 Band: 915-Mhz, 2.4 GHz (worldwide ISM), 5.2 GHz
 Direct sequence spread spectrum (DSSS)
 broaden the signaling band by artificially increasing the
modulation rate using a spreading code. 2M or 10M.
 Frequency hopping spread spectrum (FHSS)
 hop from narrow band to narrow band within a wide
band, using each narrow band for a specific time period.
31

32. Narrowband Microwave LANs
 Use of a microwave radio frequency band for signal
transmission
 Relatively narrow bandwidth
 Licensed
 Unlicensed
32

33. Licensed Narrowband RF
 Licensed within specific geographic areas to avoid
potential interference
 Motorola - 600 licenses in 18-GHz range
 Covers all metropolitan areas
 Can assure that independent LANs in nearby locations don’t
interfere
 Encrypted transmissions prevent eavesdropping
33

34. Unlicensed Narrowband RF
 RadioLAN introduced narrowband wireless LAN in 1995
 Uses unlicensed ISM spectrum
 Used at low power (0.5 watts or less)
 Operates at 10 Mbps in the 5.8-GHz band
 Range = 50 m to 100 m
34

35. MAC Layer: Hidden Terminal Problem
 Node B can communicate with A and C both
 A and C cannot hear each other
 When A transmits to B, C cannot detect the transmission
using the carrier sense mechanism
 If C transmits, collision will occur at node B
A B C
35

36. MCAC (Multiple Access with Collision
Avoidance)
 When node A wants to send a packet to node B, node A first
sends a Request-to-Send (RTS) to B
 On receiving RTS, node B responds by sending Clear-to-Send
(CTS), provided node B is able to receive the packet
 When a node (such as C) overhears a CTS, it keeps quiet for the
duration of the transfer
 Transfer duration is included in RTS and CTS both
A B C
36

37. Reliability
 Wireless links are prone to errors. High packet loss rate
detrimental to transport-layer performance.
 Mechanisms needed to reduce packet loss rate experienced by
upper layers
 When node B receives a data packet from node A, node B
sends an Acknowledgement (Ack).
 If node A fails to receive an Ack, it will retransmit the packet
A B C
37

38. Protocol Architecture
38

39. IEEE 802 Protocol Layers
39
Please Do Not forget To feed Steve's Pet Alligator

40. Protocol Architecture
 Functions of physical layer:
 Encoding/decoding of signals
 Preamble generation/removal (for synchronization)
 Bit transmission/reception
 Includes specification of the transmission medium
Two sub layers physical layer
 Physical layer convergence procedure(PLCP)
Mapping MAC layer protocol data units(MPDU)
 Physical medium dependent sub layer(PMD)
Defines methods of transmitting and receiving
40

41. Protocol Architecture
 Functions of medium access control (MAC) layer:
 On transmission, assemble data into a frame with address
and error detection fields
 On reception, disassemble frame and perform address
recognition and error detection
 Govern access to the LAN transmission medium
 Functions of logical link control (LLC) Layer:
 Provide an interface to higher layers and perform flow and
error control
41

42. Separation of LLC and MAC
 The logic required to manage access to a shared-access
medium not found in traditional layer 2 data link control
 For the same LLC, several MAC options may be provided
42

43. MAC Frame Format
 MAC control
 Contains Mac protocol information
 Destination MAC address
 Destination physical attachment point
 Source MAC address
 Source physical attachment point
 CRC
 Cyclic redundancy check
43

44. MAC Frame Format

45. MAC Frame Fields
 Frame Control – frame type, control information
 Duration/connection ID – channel allocation time
 Addresses – context dependant, types include source
and destination
 Sequence control – numbering and reassembly
 Frame body – MSDU or fragment of MSDU
 Frame check sequence – 32-bit CRC

46. Frame Control Fields
 Protocol version – 802.11 version
 Type – control, management, or data
 Subtype – identifies function of frame
 To DS – 1 if destined for DS
 From DS – 1 if leaving DS
 More fragments – 1 if fragments follow
 Retry – 1 if retransmission of previous frame

47. Frame Control Fields
 Power management – 1 if transmitting station is in
sleep mode
 More data – Indicates that station has more data to
send
 WEP – 1 if wired equivalent protocol is implemented
 Order – 1 if any data frame is sent using the Strictly
Ordered service

48. Control Frame Subtypes
 Power save – poll (PS-Poll)
 Request to send (RTS)
 Clear to send (CTS)
 Acknowledgment
 Contention-free (CF)-end
 CF-end + CF-ack

49. Data Frame Subtypes
 Data-carrying frames
 Data
 Data + CF-Ack
 Data + CF-Poll
 Data + CF-Ack + CF-Poll
 Other subtypes (don’t carry user data)
 Null Function
 CF-Ack
 CF-Poll
 CF-Ack + CF-Poll

50. Management Frame Subtypes
 Association request
 Association response
 Reassociation request
 Reassociation response
 Probe request
 Probe response
 Beacon

51. Logical Link Control
 Characteristics of LLC not shared by other control
protocols:
 Must support multiaccess, shared-medium nature of the link
 Relieved of some details of link access by MAC layer
51

52. LLC Services
 Unacknowledged connectionless service
 No flow- and error-control mechanisms
 Data delivery not guaranteed
 Connection-mode service
 Logical connection set up between two users
 Flow- and error-control provided
 Acknowledged connectionless service
 Cross between previous two
 Datagrams acknowledged
 No prior logical setup
52

53. Differences between LLC and HDLC
 LLC uses asynchronous balanced mode of operation of
HDLC (High-Level Data Link Control) (type 2
operation)
 LLC supports unacknowledged connectionless service
(type 1 operation)
 LLC supports acknowledged connectionless service (type
3 operation)
 LLC permits multiplexing by the use of LLC service
access points (LSAPs)
53

54. IEEE 802.11 Architecture
 Distribution system (DS)
 Access point (AP)
 Basic service set (BSS)
 Stations competing for access to shared wireless medium
 Isolated or connected to backbone DS through AP
 Extended service set (ESS)
 Two or more basic service sets interconnected by DS
54

55. 55

56. 56

57. IEEE 802.11 Services
57

58. Distribution of Messages Within a DS
 Distribution service
 Used to exchange MAC frames from station in one BSS to
station in another BSS
 Integration service
 Transfer of data between station on IEEE 802.11 LAN and
station on integrated IEEE 802.x LAN
58

59. Transition Types Based On Mobility
 No transition
 Stationary or moves only within BSS
 BSS transition
 Station moving from one BSS to another BSS in same ESS
 ESS transition
 Station moving from BSS in one ESS to BSS within another
ESS
59

60. Association-Related Services
 Association
 Establishes initial association between station and AP
 Reassociation
 Enables transfer of association from one AP to another,
allowing station to move from one BSS to another
 Disassociation
 Association termination notice from station or AP
60

61. Access and Privacy Services
 Authentication
 Establishes identity of stations to each other
 Deauthentication
 Invoked when existing authentication is terminated
 Privacy
 Prevents message contents from being read by unintended
recipient
61

62. IEEE 802.11 Medium Access Control
 MAC layer covers three functional areas:
 Reliable data delivery
 Access control
 Security
62

63. Reliable Data Delivery
 More efficient to deal with errors at the MAC level
than higher layer (such as TCP)
 Frame exchange protocol
 Source station transmits data
 Destination responds with acknowledgment (ACK)
 If source doesn’t receive ACK, it retransmits frame
 Four frame exchange
 Source issues request to send (RTS)
 Destination responds with clear to send (CTS)
 Source transmits data
 Destination responds with ACK
63

64. Access Control
64

65. Medium Access Control Logic
65

66. Inter frame Space (IFS) Values
 Short IFS (SIFS)
 Shortest IFS
 Used for immediate response actions
 Point coordination function IFS (PIFS)
 Midlength IFS
 Used by centralized controller in PCF scheme when using
polls
 Distributed coordination function IFS (DIFS)
 Longest IFS
 Used as minimum delay of asynchronous frames contending
for access
66

67. IFS Usage
 SIFS
 Acknowledgment (ACK)
 Clear to send (CTS)
 Poll response
 PIFS
 Used by centralized controller in issuing polls
 Takes precedence over normal contention traffic
 DIFS
 Used for all ordinary asynchronous traffic
67

68. Management Frame Subtypes
 Announcement traffic indication message
 Dissociation
 Authentication
 Deauthentication
68

69. Wired Equivalent Privacy
69

70. Authentication
 Open system authentication
 Exchange of identities, no security benefits
 Shared Key authentication
 Shared Key assures authentication
70

71. Physical Media Defined by
Original 802.11 Standard
 Direct-sequence spread spectrum
 Operating in 2.4 GHz ISM band
 Data rates of 1 and 2 Mbps
 Frequency-hopping spread spectrum
 Operating in 2.4 GHz ISM band
 Data rates of 1 and 2 Mbps
 Infrared
 1 and 2 Mbps
 Wavelength between 850 and 950 nm
71

72. IEEE 802.11a and IEEE 802.11b
 IEEE 802.11a
 Makes use of 5-GHz band
 Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps
 Uses orthogonal frequency division multiplexing (OFDM)
 Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-
QAM
 IEEE 802.11b
 Provides data rates of 5.5 and 11 Mbps
 Complementary code keying (CCK) modulation scheme
72

73. Mobile Ad Hoc Networks

74. What is a MANET (Mobile Ad Hoc Networks)?
 Formed by wireless hosts which may be mobile
 No pre-existing infrastructure
 Routes between nodes may potentially contain multiple hops
 Nodes act as routers to forward packets for each other
 Node mobility may cause the routes change
A
B
C
D
A
B
C
D

75.  Advantages: low-cost, flexibility
 Ease & Speed of deployment
 Decreased dependence on infrastructure
 Applications
 Military environments
 soldiers, tanks, planes
 Civilian environments
 vehicle networks
 conferences / stadiums
 outside activities
 Emergency operations
 search-and-rescue / policing and fire fighting
Why MANET?

76.  Collaboration
 Collaborations are necessary to maintain a MANET and
its functionality.
 How to collaborate effectively and efficiently?
 How to motivate/enforce nodes to collaborate?
 Dynamic topology
 Nodes mobility
 Interference in wireless communications
Challenges

77.  Proactive protocols
 Determine routes independent of traffic pattern
 Traditional link-state and distance-vector routing protocols are
proactive
 Examples:
 DSDV (Dynamic sequenced distance-vector)
 OLSR (Optimized Link State Routing)
 Reactive protocols
 Maintain routes only if needed
 Examples:
 DSR (Dynamic source routing)
 AODV (on-demand distance vector)
 Hybrid protocols
 Example: Zone Routing Protocol (intra-zone: proactive; inter-zone:
on-demand)
Routing Protocols: Overview

78.  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 may be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
 Reactive protocols may have lower overhead since routes are
determined only if needed
 Proactive protocols can (but not necessarily) result in higher
overhead due to continuous route updating
 Which approach achieves a better trade-off depends on the
traffic and mobility patterns
Routing Protocols: Tradeoff

79. • J. Broch, D. Johnson, and D. Maltz, “The dynamic source
routing protocol for mobile ad hoc networks,” Internet-
Draft Version 03, IETF, October 1999.
• When node S wants to send a packet to node D, but does
not know a route to D, node S initiates a routing process
• Runs in three phases
 Route Discovery  Route Reply  Path Establishment
• Route Discovery
 Source node S floods Route Request (RREQ)
 Each node appends own identifier when forwarding RREQ
Dynamic Source Routing

80. 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

81. 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
Route Discovery in DSR

82. B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
[S,E]
[S,C]
Route Discovery in DSR

83. B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
[S,C,G,K]
[S,E,F,J]
Route Discovery in DSR

84. Route Reply 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

85. 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
Route Reply in DSR

86. • 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
Route Reply in DSR

87. 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
Data Delivery in DSR

88. Some Other Routing Protocols
• Location information aided protocols
• Power-aware protocols
• Others …
• e.g., considering the stability of topology

89. Location-Aided Routing (LAR)
• Y. Ko and N. Vaidya, “Location-aided routing (LAR) in mobile
ad hoc networks,” MobiCom'98.
• Exploits location information to limit scope of route request
flood
 Location information may be obtained using GPS
• Expected Zone is determined as a region that is expected to
hold the current location of the destination
 Expected region determined based on potentially old location
information, and knowledge of the destination’s speed
• Route requests limited to a Request Zone that contains the
Expected Zone and location of the sender node
• B. Karp, and H. Kung, “Greedy Perimeter Stateless Routing
for Wireless Networks,” MobiCom 2000.

90. Power-Aware Routing
• Modification to DSR to make it power aware (for
simplicity, assume no route caching):
 Route Requests aggregate the weights of all traversed
links
 Destination responds with a Route Reply to a Route
Request if
 it is the first RREQ with a given (“current”) sequence number,
or
 its weight is smaller than all other RREQs received with the
current sequence number

91. Geography Adaptive Fidelity
• Each node associates itself with a square in a virtual grid
• Node in each grid square coordinate to determine who
will sleep and how long
[Y. Xu, et al. “Geography Adaptive Fidelity in Routing,”
Mobicom’2001]
Grid head

92. Research in Other Layers
• Transport layer
• A survey: A. Hanbali, E. Altman, P. Nain, “A Survey of TCP
over Mobile Ad Hoc Networks (2004)”.
• Application layer
 Data management
 e.g., B. Xu, A. Ouksel, and O. Wolfson, "Opportunistic Resource
Exchange in Inter-vehicle Ad Hoc Networks," MDM, 2004.
 Distributed algorithms
 clock synchronization
 mutual exclusion
 leader election
 Byzantine agreement

93. Security in Mobile Ad Hoc
Networks

94. Problems
• Hosts may misbehave or try to compromise security at all
layers of the protocol stack
• Transport layer: securing end-to-end communication
 Need to know keys to be used for secure communication
 May want to anonymize the communication
• Network layer: misbehaving hosts may create many hazards
 May disrupt route discovery and maintenance:
Force use of poor routes (e.g., long routes)
 Delay, drop, corrupt, misroute packets
 May degrade performance by making good routes
look bad
• MAC layer: misbehaving nodes may not cooperate
 Disobey protocol specifications for selfish gains
 Denial-of-service attacks

95. Security in MANET: Agenda
• Key management
• Securing communications
• Dealing with MAC and Network layer misbehaviors

96. Key Management
• Challenges
 In “pure” ad hoc networks, access to infrastructure cannot
be assumed
 Network may also become partitioned
• Solutions
 Distributed public key infrastructure
Self-organized key management
Distributed key certification
 TESLA
 Others

97. Self-Organized Public Key Management
[Capkun03]
• Nodes form a “Certificate Graph”
 each vertex represents a public key
 an edge from Ku to Kw exists if there is a certificate signed
by the private key of node u that binds Kw to the identity
of some node w.
Ku Kw
(w,Kw)Pr Ku

98. • Four steps of the management scheme
• Step 1: Each node creates its own private/public keys.
Each node acts independently
Self-Organized Public Key Management
[Capkun03]

99. • Step 2: When a node u believes that key Kw belongs to
node w, node u issues a public-key certificate in which Kw
is bound to w by the signature of u
 u may believe this because u and w may have talked on a
dedicated channel previously
 Each node also issues a self-signed certificate for its own
key
• Step 3: Nodes periodically exchange certificates with
other nodes they encounter
 Mobility allows faster dissemination of certificates through
the network
Self-Organized Public Key Management
[Capkun03]

100. • Step 4: Each node forms a certificate graph using the
certificates known to that node
Authentication: When a node u wants to verify the
authenticity of the public key Kv of node v, u tries to
find a directed graph from Ku to Kv in the certificate
graph. If such a path is found, the key is authentic.
Self-Organized Public Key Management
[Capkun03]

101. • Misbehaving hosts may issue incorrect certificates
• If there are mismatching certificates, indicates
presence of a misbehaving host (unless one of the
mismatching certificate has expired)
 Mismatching certificates may bind same public key
for two different nodes, or same node to two
different keys
• To resolve the mismatch, a “confidence” level may
be calculated for each certificate chain that verifies
each of the mismatching certificates
 Choose the certificate that can be verified with high
confidence – else ignore both certificates
Self-Organized Public Key Management
[Capkun03]

102. • With the previously discussed mechanisms for key
distribution, it is possible to authenticate the
assignment of a public key to a node
• This key can then be used for secure communication
 The public key can be used to set up a symmetric key
between a given node pair as well
 TESLA provides a mechanism for broadcast
authentication when a single source must broadcast
packets to multiple receivers
Secure Communication

103. • Sometimes security requirement may include
anonymity
• Availability of an authentic key is not enough to
prevent traffic analysis
• We may want to hide the source or the destination of a
packet, or simply the amount of traffic between a given
pair of nodes
Secure Communication

104. Wireless
channel
Access Point
A B
• Nodes are required to follow
Medium Access Control
(MAC) rules
• Misbehaving nodes may
violate MAC rules
Wireless
channel
Access Point
C D
MAC Layer Misbehavior

105. • Causing collisions with other hosts’ RTS or CTS
• “Impatient transmitter”
 Smaller backoff intervals
 Shorter Inter-frame Spacings
Some Possible Misbehavior

106. • Diagnose node misbehavior
 Catch misbehaving nodes
• Discourage misbehavior
 Punish misbehaving nodes
• Details will be discussed later in this course
Solutions

107. • A node “agrees” to join a route
(for instance, by forwarding route request in DSR) but
fails to forward packets correctly
• A node may do so to conserve energy, or to launch a
denial-of-service attack, due to failure of some sort, or
because of overload
• Solutions
• Opt I: Detect the attacks  tolerate them
• Opt II: Avoid some attacks
Network Layer Misbehavior:
Drop/Corrupt/Misroute

108. Wireless Local Loop
 Wired technologies responding to need for reliable,
high-speed access by residential, business, and
government subscribers
 ISDN, xDSL, cable modems
 Increasing interest shown in competing wireless
technologies for subscriber access
 Wireless local loop (WLL)
 Narrowband – offers a replacement for existing telephony
services
 Broadband – provides high-speed two-way voice and data
service
108

109. WLL Configuration
109

110. Advantages of WLL over Wired
Approach
 Cost – wireless systems are less expensive due to cost
of cable installation that’s avoided
 Installation time – WLL systems can be installed in a
small fraction of the time required for a new wired
system
 Selective installation – radio units installed for
subscribers who want service at a given time
 With a wired system, cable is laid out in anticipation of
serving every subscriber in a given area
110

111. Propagation Considerations for
WLL
 Most high-speed WLL schemes use millimeter wave
frequencies (10 GHz to about 300 GHz)
 There are wide unused frequency bands available above 25
GHz
 At these high frequencies, wide channel bandwidths can be
used, providing high data rates
 Small size transceivers and adaptive antenna arrays can be
used
111

112. Propagation Considerations for
WLL
 Millimeter wave systems have some undesirable
propagation characteristics
 Free space loss increases with the square of the frequency;
losses are much higher in millimeter wave range
 Above 10 GHz, attenuation effects due to rainfall and
atmospheric or gaseous absorption are large
 Multipath losses can be quite high
112

113. Fresnel Zone
 How much space around direct path between
transmitter and receiver should be clear of obstacles?
 Objects within a series of concentric circles around the line
of sight between transceivers have constructive/destructive
effects on communication
 For point along the direct path, radius of first Fresnel
zone:
 S = distance from transmitter
 D = distance from receiver
DS
SD
R



113

114. Atmospheric Absorption
 Radio waves at frequencies above 10 GHz are subject to
molecular absorption
 Peak of water vapor absorption at 22 GHz
 Peak of oxygen absorption near 60 GHz
 Favorable windows for communication:
 From 28 GHz to 42 GHz
 From 75 GHz to 95 GHz
114

115. Effect of Rain
 Attenuation due to rain
 Presence of raindrops can severely degrade the reliability
and performance of communication links
 The effect of rain depends on drop shape, drop size, rain
rate, and frequency
 Estimated attenuation due to rain:
 A = attenuation (dB/km)
 R = rain rate (mm/hr)
 a and b depend on drop sizes and frequency
b
aRA 
115

116. Effects of Vegetation
 Trees near subscriber sites can lead to multipath
fading
 Multipath effects from the tree canopy are diffraction
and scattering
 Measurements in orchards found considerable
attenuation values when the foliage is within 60% of
the first Fresnel zone
 Multipath effects highly variable due to wind
116

117. Multipoint Distribution Service (MDS)
 Multichannel multipoint distribution service (MMDS)
 Also referred to as wireless cable
 Used mainly by residential subscribers and small businesses
 Local multipoint distribution service (LMDS)
 Appeals to larger companies with greater bandwidth
demands
117

118. Advantages of MMDS
 MMDS signals have larger wavelengths and can travel
farther without losing significant power
 Equipment at lower frequencies is less expensive
 MMDS signals don't get blocked as easily by objects and
are less susceptible to rain absorption
118

119. Advantages of LMDS
 Relatively high data rates
 Capable of providing video, telephony, and data
 Relatively low cost in comparison with cable alternatives
119

120. WiMax
Worldwide Interoperability for Microwave Access
120

121. WiMAX Introduction
 Worldwide Interoperability for Microwave Access
 The Institute of Electrical and Electronics Engineers
(IEEE) 802 committee (802.16 ).
 Orthogonal Frequency Division Multiplexing
(OFDM) (carriers of width of 5MHz or greater can be
used )
 connectivity at speeds up to 70 Mbps
 provide high speed access to about 60 businesses at
T1 speeds.
 can serve up to a thousand homes in term of DSL
speed.
121

122. How it works??
 WiMAX system consists of two parts:
 WiMAX Base Station: Typically, a base station can cover up to
10 km radius.
 WiMAX receiver: could be a stand-alone box or a PC card.
Several base stations can be connected with one another by
backhaul microwave links. wireline backhauling
microwave Point-to-Point connection
 what would happen if you got WiMAX ??
 Internet service provider
 WiMAX base station 10 miles from your home
 WiMAX-enabled computer
 receive a special encryption code
 base station beam data from the Internet to your computer
122

123. WiMax vs. WLAN
 WiMAX provides a media access control (MAC) layer.
 the support of real-time and voice applications is simple
 WiMAX proposes the full range of security
 Terminal authentication by exchanging certificates to
prevent rogue devices
 User authentication using the Extensible Authentication
Protocol (EAP)
 Data encryption using the Data Encryption Standard
(DES) or Advanced Encryption Standard (AES) , both
much more secure than the Wireless Equivalent Privacy
(WEP) used by WLAN
123

124. WiMax VS. WiFi
 WiFi connection can transmit up to 54Mbps (under
optimal conditions)
 WiMAX should be able to handle up to 70Mbps
 The biggest difference isn't speed!! 
 WiFi's range is about 100 feet (30 m)
 WiMAX will blanket a radius of 30 miles (50 km) with
wireless access
 due to the frequencies used and the power of the
transmitter.
 WiMAX(10-66 GHz frequency)
 WiFi(5GHz frequency maximum)
124

125. Where can be applied??
 large area public (airports, university
campuses,…)
 Large numbers of small and medium sized
businesses (for lower costs)
 High speed internet for areas where wired
connectivity is not viable.
125

126. 802.16 Standards Development
 Use wireless links with microwave or millimeter wave
radios
 Use licensed spectrum
 Are metropolitan in scale
 Provide public network service to fee-paying
customers
 Use point-to-multipoint architecture with stationary
rooftop or tower-mounted antennas
126

127. 802.16 Standards Development
 Provide efficient transport of heterogeneous
traffic supporting quality of service (QoS)
 Use wireless links with microwave or
millimeter wave radios
 Are capable of broadband transmissions (>2
Mbps)
127

128. IEEE 802.16 Protocol Architecture
128

129. Protocol Architecture
 Physical and transmission layer functions:
 Encoding/decoding of signals
 Preamble generation/removal
 Bit transmission/reception
 Medium access control layer functions:
 On transmission, assemble data into a frame with address and error
detection fields
 On reception, disassemble frame, and perform address recognition
and error detection
 Govern access to the wireless transmission medium
 Convergence layer functions:
 Encapsulate PDU framing of upper layers into native 802.16
MAC/PHY frames
 Map upper layer’s addresses into 802.16 addresses
 Translate upper layer QoS parameters into native 802.16 MAC format
 Adapt time dependencies of upper layer traffic into equivalent MAC
service
129

130. IEEE 802.16.1 Services
 Digital audio/video multicast
 Digital telephony
 ATM
 Internet protocol
 Bridged LAN
 Back-haul
 Frame relay
130

131. IEEE 802.16.3 Services
 Voice transport
 Data transport
 Bridged LAN
131

132. IEEE 802.16.1 Frame Format
132

133. IEEE 802.16.1 Frame Format
 Header - protocol control information
 Downlink header – used by the base station
 Uplink header – used by the subscriber to convey bandwidth
management needs to base station
 Bandwidth request header – used by subscriber to request
additional bandwidth
 Payload – either higher-level data or a MAC control
message
 CRC – error-detecting code
133

134. MAC Management Messages
 Uplink and downlink channel descriptor
 Uplink and downlink access definition
 Ranging request and response
 Registration request, response and acknowledge
 Privacy key management request and response
 Dynamic service addition request, response and
acknowledge
134

135. MAC Management Messages
 Dynamic service change request, response, and
acknowledge
 Dynamic service deletion request and response
 Multicast polling assignment request and response
 Downlink data grant type request
 ARQ acknowledgment
135

136. Physical Layer – Upstream
Transmission
 Uses a DAMA-TDMA technique
 Error correction uses Reed-Solomon code
 Modulation scheme based on QPSK
136

137. Physical Layer – Downstream
Transmission
 Continuous downstream mode
 For continuous transmission stream (audio, video)
 Simple TDM scheme is used for channel access
 Duplexing technique is frequency division duplex (FDD)
 Burst downstream mode
 Targets burst transmission stream (IP-based traffic)
 DAMA-TDMA scheme is used for channel access
 Duplexing techniques are FDD with adaptive modulation,
frequency shift division duplexing (FSDD), time division
duplexing (TDD)
137

138. References
 Book: Wireless Communications and Networks by
William Stallings
 PPT: WilliamStalling.com/StudentsSupport.html.
 http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol
2/mjf/article2.html
 http://www.wildpackets.com/resources/compendium/
wireless_lan/overview
 http://www.wirelesscommunication.nl/reference/cha
ptr01/dtmmsyst/80211early.htm
138

139. THANK YOU
139