1. expanded by Jozef Goetz, 2012 The McGraw-Hill Companies, Inc., 2007
Lesson 7 - 8
Wireless
LANs
April 22, 2017
expanded by Jozef Goetz, 2012
The McGraw-Hill Companies, Inc., 2007

2. Topics discussed in this section:
IEEE
IEEE has defined the specifications for a wireless LAN, called IEEE , which covers the physical and data link layers.
Topics discussed in this section:
Architecture MAC Sublayer
Physical Layer

3. LANs
Wireless LANs are found on college campuses, office buildings, and public areas.
At home, a wireless LAN can connect roaming devices to the Internet.
In this chapter, we concentrate on two promising wireless technologies for LANs:
IEEE wireless LANs, sometimes called wireless Ethernet, and
Bluetooth, a complex technology for small wireless LANs.

4. LANs IEEE 802.11, which covers the physical and data link layers.
The Industrial, Scientific and Medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for Industrial, Scientific and Medical purposes other than communications.

5. WIRELESS LANs
A set of wireless LAN standards has been developed by the IEEE committee.
Three transmission schemes are defined in the current standard:
[1] Infrared: at 1 Mbps & 2 Mbps.
[2] Direct-sequence spread spectrum: 2.4GHz ISM band
[3] Frequency-hopping spread spectrum: 2.4GHz ISM band
802.11b - 11 Mbps
802.11g - 54 Mbps

6. Basic Service Set BSS (Cell)
IEEE defines the Basic Service Set (BSS) or Cell as the building block of a wireless LAN.
The Basic Service Set (BSS) is made of stationary or mobile wireless stations and a possible central Base Station (BS), known as the Access Point (AP).
BSS without an AP is a stand-alone network and cannot send data to other BSSs.

7. a BSS without an AP is called an ad hoc network;
Note
a BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.

8. Extended Service Set (ESS)
An Extended Service Set (ESS) is made up of two or more BSSs with APs.
In this case, the BSSs are connected through a distribution system, which is usually a wired LAN.
The distribution system connects the APs in the BSSs.
IEEE does not restrict the distribution system;
it can be any IEEE LAN such as an Ethernet.
Note that the extended service set uses two types of stations: mobile and stationary.
The mobile stations are normal stations inside a BSS.
The stationary stations are AP stations that are part of a wired LAN.
When BSSs are connected, we have what is called an infrastructure network.

9. Extended Service Set (ESS)
In this infrastructure network, the stations within reach of one another can communicate without the use of an AP.
However, communication between two stations in two different BSSs usually occurs via two APs.
The idea is similar to communication in a cellular network
if we consider each BSS to be a cell and each AP to be a base station.
Note that a mobile station can belong to more than one BSS at the same time.

10. WIRELESS LANs
ESS
Wired Backbone LAN
functions as a bridge
BSS

11. Wireless LAN
A multicell network (WiFi).
The connection between the system and the outside world is called a portal
All the base stations are wired together using copper or fiber
Unlike cellular tel. systems, each cell has only one channel, covering the entire available bandwidth ( 11 – 54 Mbps) and covering all the stations in its cell

12. Station Types
IEEE defines 3 types of stations based on their mobility in a wireless LAN: no-transition, BSS-transition, and ESS-transition.
No-Transition Mobility
A station with no-transition mobility is either stationary (not moving) or moving only inside a BSS.
BSS-Transition Mobility
A station with BSS-transition mobility can move from one BSS to another, but the movement is confined inside one ESS.
ESS-Transition Mobility
A station with ESS-transition mobility can move from one ESS to another.
However, IEEE does not guarantee that communication is continuous during the move.

13. The Protocol Stack
ISM: Abbreviation for Industrial, Scientific, and Medical applications (of radio frequency energy).
range is 7 times greater

14. Figure MAC layers in IEEE 802.11 standard

15. Reminder: IEEE standard for wired LANs
Note: there is one LLC sublayer for all IEEE LANs
Reminder: IEEE standard for wired LANs

16. Modulation
In analog transmission, the sending device produces a high-frequency signal that acts as a base for the information signal.
This base signal is called the carrier signal or carrier frequency.
The receiving device is tuned to the frequency of the carrier signal that it expects from the sender.
This kind of modification is called modulation (shift keying).

17. Modulation
Modulation - is the process of encoding source data onto a carrier signal with frequency carrier fc
i.e. process of modulating the carrier signal by modifying one or more of parameters:
amplitude,
frequency, &
phase
of a sine wave.

18. Modulation of Digital Data
Basic Digital-to-Analog conversion or modulation or encoding
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature Amplitude Modulation
(QAM)

19. The digital data must be modulated on an analog signal
Figure Digital-to-analog modulation
The digital data must be modulated on an analog signal
Modulation of binary data or (digital-to-analog modulation)
is the process of changing one of the characteristics
of an analog signal
a sine wave is defined by 3 characteristics:
amplitude,
frequency, and
phase
based on the information in a digital signal (0s and 1 s).

20. Figure Digital-to-analog conversion

21. Figure Types of digital-to-analog modulation
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature Amplitude Modulation (QAM)

22. Note:
Bit rate is the number of bits per second [bps]
Baud rate is the number of signal elements (or impulses or symbols or signal units) per second [baud]
Baud rate <= Bit rate.

23. Bit rate N is the # of bits (passengers by analogy) per second.
Note
Bit rate N is the # of bits (passengers by analogy) per second.
Baud rate S is the # of signal
elements (vehicles by analogy) per second.
In the analog and digital transmission of digital data,
S <= N

24. In data transmission:
a signal element as the smallest unit of a signal that is constant
The baud rate determines the bandwidth required to send the signal.

25. In analog transmission:
We can define the data rate (bit rate) and the S signal rate (baud rate)
S = N / r [baud]
where N is the data rate (bps) and
r is the # of data elements (bits) carried in one signal element.
The value of r in analog transmission is
r = log2 L
where L is the # of signal elements (symbols), not the level
e.g. for FSK is # of different frequencies
S = N / r => N = S r

26. Example
An analog signal carries 4 bits in each signal element (unit).
If 1000 signal elements (units or pulses) are sent per second, find the baud rate and the bit rate
Solution
In this case, r = 4, S = 1000, and N is unknown. We can find the value of N from
S = N / r => N = S r
S = Signal rate =Baud rate = 1000 pulse/sec
N = Data rate = Bit rate = S r = [pulse/sec] 4 [bit/pulse] =
4000 bps

27. Example
The bit rate of a signal is If each signal element carries 6 bits, what is the baud rate?
Solution
Baud rate = N / r = 3000 [bit/sec] / 6 [bit/pulse] =
500 [pulse/sec] = 500 baud

28. DIGITAL DATA, ANALOG SIGNALS AMPLITUDE-SHIFT KEYING (ASK)
In ASK, the two binary values are represented by two different amplitudes of the carrier frequency.

29. DIGITAL DATA, ANALOG SIGNALS FREQUENCY-SHIFT KEYING (FSK)
In FSK, the two binary values are represented by two different frequencies. The frequencies of the modulated signal is constant for the duration of one signal element.

30. DIGITAL DATA, ANALOG SIGNALS PHASE-SHIFT KEYING (PSK)
In PSK, the phase of the carrier signal is shifted to represent data.

31. Figure Analog-to-analog modulation
needed when the medium has a band-pass nature or if only band-pass bandwidth is available
and e.g. a radio produced by each station is a low-pass signal.
So a low-pass signal need to be shifted.

32. ANALOG DATA, ANALOG SIGNALS
There are two principal reasons for analog modulation of analog signals:
A higher frequency may be needed for effective transmission.
Modulation permits frequency-division multiplexing.
Three techniques:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

33. Figure Amplitude modulation

34. ANALOG DATA, ANALOG SIGNALS
AM - MODULATION
Amplitude modulation (AM) is the simplest form of modulation.
Mathematically, the process can be expressed as
Carrier
Input signal
Modulation index

35. Figure Amplitude modulation

36. ANALOG DATA, ANALOG SIGNALS
FM - MODULATION
In frequency modulation (FM) we modulate the instantaneous frequency fi(t), with the signal s(t).
Mathematically, the process can be expressed as
Carrier
Input signal

37. ANALOG DATA, ANALOG SIGNALS
PM - MODULATION
For phase modulation (PM), the phase is proportional to the modulating signal s(t).
Mathematically, the process can be expressed as
Carrier
Input signal

38. Industrial, Scientific, and Medical (ISM) band
3 unlicensed bands in the 3 ranges

39. Frequency-Hopping Spread Spectrum FHSS IEEE 802.11
The band (from 2.4 GHz to 2.48 GHz) is divided into 79 subbands of 1 MHz.
FHSS is a method in which the sender sends on one carrier frequency for a short amount of time, then hops to another carrier frequency for the same amount of time, hops again to still another for the same amount of time, and so on.
After N hop­pings, the cycle is repeated.
If the bandwidth of the original signal is B, the allocated spread spectrum bandwidth is N x B.
Spreading makes it difficult for unauthorized persons to make sense of transmitted data.

40. Frequency-Hopping Spread Spectrum FHSS IEEE 802.11
The band (from 2.4 GHz to 2.48 GHz) is divided into 79 subbands of 1 MHz.
In FHSS the sender and receiver agree on the sequence of the allocated bands.
In the figure, the first bit (or group of bits) is sent in subband 1, the second bit (or group of bits) is sent in subband 2, and so on.
An intruder who tunes his or her receiver to frequencies for one subband may receive the first group of bits, but receives nothing in this subband during the second interval.
The amount of time spent at each subband, called the dwell time, is 400 ms or more.
Note that this is not a case of multiple access;
all stations contend to use the same subbands to send their data.
Contention is a function of the MAC sublayer.

41. Frequency-Hopping Spread Spectrum FHSS
Band FHSS uses a 2.4-GHz industrial, scientific, and medical (ISM) band.
The band in North America is from 2.4 GHz to 2.48 GHz.
The band is divided into 79 subbands of 1 MHz.
A pseudorandom number generator selects the hopping sequence.
Modulation and Data Rate
The modulation technique in this specification is FSK (Freq. Shift Keying) at 1 Mbaud/s.
The system allows 1 or 2 bits baud (two-level FSK or four-level FSK), which results in a data rate of 1 or 2 Mbps.

42. Direct Sequence Spread Spectrum DSSS
IEEE
IEEE DSSS describes the direct sequence spread spectrum (DSSS) method for signal generation in a 2.4-GHz ISM band.
In DSSS, each bit sent by the sender is replaced by a sequence of bits called a chip code.
To avoid buffering, however, the time needed to send one chip code must be the same as the time needed to send one original bit.
If N is the number of bits in each chip code, then the data rate for sending chip codes is N x the data rate of the original bit stream.

43. Direct Sequence Spread Spectrum DSSS
DSSS is implemented at the physical layer. It is not a multiple-access method for the data link layer.
We need a contention method at the data link layer, and that will be discussed shortly.
Band DSSS uses a 2.4-GHz ISM band. The bit sequence uses the entire band.
Modulation and Data Rate The modulation technique in this specification is PSK (Phase Shift Keying) at 1 Mbaud/s.
The system allows 1 or 2 bits baud (BPSK or QPSK), which results in a data rate of 1 or 2 Mbps.

44. The Protocol Stack
ISM: Abbreviation for Industrial, Scientific, and Medical applications (of radio frequency energy).
range is 7 times greater

45. Orthogonal Frequency-Division Multiplexing (OFDM)
IEEE a
OFDM is the same as FDM, with one major difference:
All the subbands are used by one source at a given time.
Sources contend with one another at the data link layer for access.
The specification uses a 5-GHz ISM band.
The band is divided into 52 subbands, with 48 subbands for sending 48 groups of bits at a time and 4 subbands for control information.
Dividing the band into subbands diminishes the effects of interference.
If the subbands are used randomly, security can also be increased.
Modulation and Data Rate OFDM uses PSK and QAM for modulation. The common data rates are
18 Mbps (PSK) and
54 Mbps (QAM) – quadrature amplitude modulation.

46. High-Rate DSSS (HR-DSSS)
IEEE b
method for signal generation in a 2.4-GHz ISM band.
HR-DSSS is similar to DSSS except for the encoding method, which is called Complementary Code Keying (CCK).
CCK encodes 4 or 8 bits to one CCK symbol.
Modulation and Data Rate
To be backward-compatible with DSSS, HR-DSSS defines four data rates: 1, 2, 5.5, and 11 Mbps.
The first two 1, 2 Mbps use the same modulation techniques as DSSS.
The 5.5-Mbps version uses BPSK and transmits at Mbaud/s with 4-bit CCK encoding.
The 11-Mbps version uses QPSK and transmits at Mbps with 8-bit CCK encoding.
Note that the 11-Mbps version has a data rate close to 10-Mbps Ethernet.

47. Orthogonal Frequency-Division Multiplexing (OFDM)
IEEE g
This relatively new specification uses OFDM with a 2.4-GHz ISM band.
The complex modulation technique achieves a 54-Mbps data rate.

49. 802.11n Uses 5 GHz and 2.4 GHz frequency ranges
Theoretical throughput is 300 to 600 mbps; realistically between 100 and 200 mbps
Maximum indoor distance is ~229 feet or 70 meters
Maximum outdoor distance is 820 feet or 250 meters
Uses channel bonding, where two or more adjacent channels are linked together

50. MAC layers in IEEE 802.11 standard
2 MAC sublayers: the Distributed Coordination Function (DCF) and Point Coordination Function (PCF).
PCF is an optional and complex access method that can be implemented in an infrastructure network (not in an ad hoc network).
We do not discuss this here; for more information refer to Forouzan, Local Area Networks, McGraw-Hill.
DCF is similar to CSMA/CA, Carrier sense multiple access (CSMA) Collision Avoidance (CA)

51. no central control and stations compete for air time as they do with Ethernet
base station polls asking them if they have any frames to send. Since transmission is controlled by the base station, no collision ever occurs

52. WIRELESS LANs - MAC Distributed Coordination Function (DCF)
If the medium is idle, the station may transmit; otherwise the station must wait until the current transmission is complete before transmitting.
Point Coordination Function (PCF)
The operation consists of polling with the centralized polling mater (point coordinator).
The point coordinator could issue polls in a round-robin fashion to all stations configured.

53. Wireless LAN Protocols
• Wireless LANs are inherently different than conventional LANs and require special MAC layer protocols.
With a wire, all signals propagate to all stations so only 1 transmission take place at once anywhere in the system
in a system on short-range radio waves, multiple transmission can occur simultaneously
• CSMA (Carrier Sense Multiple Access Protocols) doesn’t work
because there is no way to tell if interference (collision) is happening at the receiver – the sender may not hear it – see a hidden station problem.
most radios are half duplex - cannot transmit and listen for noise burst the same time
• CDMA (Code Division Multiple Access) doesn’t work
because when a receiver is within range of two transmitters the transmission is usually garbled
interference is happening at the receiver

54. • (a) The hidden station problem results when one station is transmitting data but a second station cannot “hear” the transmission and starts transmitting.
• (b) The exposed station (inverse) problem results when one station refrains from transmitting data due to another transmission that would not have affected the data transfer.
Also most radios are half duplex – cannot transmit and listen for noise burst the same time

55. Wireless LAN
<=
A and B are within each other’s range and can potentially interfere with one another
(a) A transmitting to B (while B and C are talking).
(b) B transmitting (D refrains from transmitting to C)
Can we use CSMA/CD for wireless LANs? NO
Even with CD (Collision Detection), “no sensed collision” does not mean “no collision”, because a collision could still occur at the receiver (hidden station problem) and the sender may not hear it.
Again, due to hidden station, A can create collision by sending a frame to B,
because, before transmission, A was not hearing C sending a frame to B.

56. CSMA/CA (Collision Avoidance) flowchart Frame Exchange Time Line
1. Before sending a frame, the source station senses the medium by checking the energy level at the carrier frequency.
a. The channel uses a persistence strategy with backoff until the channel is idle.
b. After the station is found idle, the station waits for a period of time, called the distributed interframe space (DIFS);
then the station sends a control frame called the Request To Send (RTS).
2. After receiving the RTS and waiting a short period of time, called the short interframe space (SIFS), the destination station sends a control frame, called the Clear To Send (CTS), to the source station.
This control frame indicates that the destination station is ready to receive data.
3. The source station sends data after waiting an amount of time equal to SIFS.
4. The destination station, after waiting for an amount of time equal to SIFS, sends an acknowledgment to show that the frame has been received.
Acknowledgment is needed in this protocol b/c the station does not have any means to check for the successful arrival of its data at the destination.

57. CSMA/CA (Collision Avoidance) flowchart Frame Exchange Time Line
Collision During Handshaking
What happens if there is collision during the time when RTS or CTS are in transition, often called the handshaking period?
Two or more stations may try to send RTS frames at the same time.
These control frames may collide.
However, because there is no mechanism for collision detection, the sender assumes there has been a collision if it has not received a CTS frame from the receiver.
The backoff strategy is employed, and the sender tries again.

58. Note
The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.

59. Collisions in Wireless LAN
The MACA protocol.
(a) A sending an RTS to B. C hears it but D doesn’t
(b) B responding with a CTS to A. D hears it but C doesn’t
E hears both RTS and CTS, so must be silent until during the CTS and data frame transmission
Idea: sender stimulate the receiver by sending RTS and receiving CTS, so stations nearby will avoid transmission for the duration of the upcoming data frame sent from the sender
Collisions are still possible!
Consider B and C sending an RTS to A:
both RTS are lost and retransmitted after a random interval

60. Collision Avoidance
How is the collision avoidance aspect of this protocol accomplished?
When a station sends an RTS frame, it includes the duration of the time that it needs to occupy the channel.
The stations that are affected by this transmission create a timer called a network allocation vector (NAV) that shows how much time must pass before these stations are allowed to check the channel for idleness.
Each time a station accesses the system and sends an RTS frame, other stations start their NAV.

61. CSMA/CA and NAV
each station, before sensing the physical medium to see if it is idle,
first checks its NAV to see if it has expired.

62. Hidden stations can reduce the capacity of the network
because of the possibility of collision.
Use of handshaking to prevent hidden station problem
When a station sends an CTS frame, it includes the duration of the time that it needs to occupy the channel and C will refrain from transmitting until that duration is over.

63. Use of handshaking in exposed station problem
In other words:
C is two conservative problem and wastes the capacity of the channel.
C cannot hear the CTS from D b/c of the collision.

64. It is more efficient to replace a small frame than a large one.
MAC Frame format
The wireless environment is very noisy; a corrupt frame has to be retransmitted.
The protocol, therefore, recommends fragmentation the division of a large frame into smaller ones.
It is more efficient to replace a small frame than a large one.
Frame control (FC) is 2 bytes long and defines the type of the frame and
some control information

65. Table 14.7 Subfields in FC field
Explanation
Version
The current version is 0.
Type
Type of information: management (00), control (01), or data (10).
Subtype
Defines the subtype of each type (RTS, CTS and ACK).
To DS
Defined later.
From DS
More flag
When set to 1, means more fragments.
Retry
When set to 1, means retransmitted frame.
Pwr mgt
When set to 1, means station is in power management mode.
More data
When set to 1, means station has more data to send.
WEP
Wired equivalent privacy. When set to 1, means encryption implemented.
Rsvd
Reserved.

66. In one control frame, this field defines the ID of the frame.
Frame format
Frame control (FC) is 2 bytes long and defines the type of the frame and some control information
D. In all frame types except one, this field defines the duration of the transmission that is used to set the value of NAV.
In one control frame, this field defines the ID of the frame.
Addresses. There are four address fields, each 6 bytes long.
The meaning of each address field depends on the value of the To DS and the From DS subfields and will be discussed later.
Sequence Control SC defines the sequence number of the frame to be used in flow control.
Frame body is between 0 and 2312 bytes, contains information based on the type and the subtype defined in the FC field.
FCS is 4 bytes long and contains a CRC-32 error detection sequence

67. Frame types
A wireless LAN defined by IEEE has 3 categories of frames:
1. Management frames,
2. Control frames, and
3. Data frames.
1. Management Frames are used for the initial communication between stations and access points.

68. In FC the Type = 01 (control frames)
Values of Subtype in FC
Subtype
Meaning
1011
Request to send (RTS)
1100
Clear to send (CTS)
1101
Acknowledgment (ACK)

69. Addressing Mechanism
There are 4 cases, defined by the value of the two flags in the FC field, To DS and From DS.
Each flag can be either 0 or 1, thus defining four different situations.
The interpretation of the four addresses (address 1 to address 4) in the MAC frame depends on the value of these flags

70. Table 14.3 Subfields in FC field
Distribution System - DS
To DS
From DS
Address 1
Address 2
Address 3
Address 4
Destination station
Source station
BSS ID
N/A 1
Sending AP
Receiving AP
Note that address 1 is always the address of the next device.
Address 2 is always the address of the previous device.
Address 3 is the address of the final destination station if it is not defined by address 1.
Address 4 is the address of the original source station if it is not the same as address 2.
In general: the order is destination the first, source the second one

71. Addressing mechanism: case 1
In this case, To DS = 0 and From DS = 0.
This means that the frame is not going to a Distribution System (To DS = 0) and is not coming from a distribution system (From DS = 0).
The frame is going from one station in a BSS to another without passing through the distribution system.
The ACK frame should be sent to the original sender.

72. Addressing mechanism: case 2
In this case, To DS = 0 and From DS = 1. This means that the frame is coming from a distribution system (From DS = 1).
The frame is coming from an AP and going to a station.
The ACK should be sent to the AP.
Note that address 3 contains the original sender of the frame (in another BSS).

73. Addressing mechanism: case 3
In this case, To DS = 1 and From DS = 0.
This means that the frame is going to a distribution system (To DS = 1).
The frame is going from a station to an AP.
The ACK is sent to the original station.
Note that address 3 contains the final destination of the frame (in another BSS).

74. Addressing mechanism: case 4
To DS = 1 and From DS = 1.
This is the case in which the distribution system is also wireless.
The frame is going from one AP to another AP in a wireless distribution system.
We do not need to define addresses if the distribution system is a wired LAN because the frame in these cases has the format of a wired LAN frame (Ethernet, for example).
Here, we need four addresses to define the original sender, the final destination, and two intermediate APs.

75. Table 14.3 Subfields in FC field
Distribution System - DS
To DS
From DS
Address 1
Address 2
Address 3
Address 4
Destination station
Source station
BSS ID
N/A 1
Sending AP
Receiving AP
Note that address 1 is always the address of the next device.
Address 2 is always the address of the previous device.
Address 3 is the address of the final destination station if it is not defined by address 1.
Address 4 is the address of the original source station if it is not the same as address 2.
In general: the order is destination the first, source the second one

76. WIRELESS LANs - Summary
Table Physical layers

77. WIRELESS LANs

78. WLAN Standards (802.11) Wireless Local Area Networks Standard Spectrum
Maximum physical rate
Transmission
Disadvantages
Advantages
802.11
2.4 Ghz
2 Mbps
FHSS/DSSS
Limited bit rate
Higher range
802.11a
5.0 Ghz
54 Mbps
OFDM
Smallest range of all standards, not back compatible
Higher bit rate in less-crowded spectrum
802.11b
11 Mbps
DSSS
Bit rate too low for many emerging applications,
overcrowded
Widely deployed; higher range
802.11g
Limited number of collocated WLANs higher range that a
Higher bit rate in 2.4 GHz spectrum
Wireless Local Area Networks

79. WLAN Standards (802.11) Wireless Local Area Networks
802.11b 
• Runs on 3 channels in 2.4GHz, unregulated spectrum • Shares spectrum with cordless phones, microwave ovens and many Bluetooth products • Transfers data at speeds of 11 megabits per second per channel, at distances of up to 300 feet • Interference issues: In crowded 2.4GHz frequency, people may not be able to Web surf over a wireless network if they're using the microwave oven or using a cordless phone at the same time.
802.11a 
• Runs on 12 channels in 5GHz spectrum, reducing interference issues • Transfers data up to five times faster than b, improving quality of streaming media, extra bandwidth for big files • not backward-compatible with b, businesses or homes must tear down the old networks to use a equipment
802.11e
Viewed as essential for voice-over WLAN in the enterprise, e is a proposed quality-of service standard that gives priority to streaming media. A subset, WME (Wireless Multimedia Enhancements), is likely to emerge first.
802.11f
Also known as IAPP (Inter Access Point Protocol). Draft protocol specifies how APs (Access Points) should communicate on the layer 2 level in order to accommodate roaming users. Ratification is expected by the end of 2003.
802.11g
• Runs on 3 channels in 2.4GHz spectrum, the same as b • Has the speed of a, up to 5 times faster than b • Is more secure than b • Is backward-compatible with b
802.11h
A standard to enable WLANs that operate in the 5GHz range to comply with European RF regulations. Ratification by the European Union should be finalized by the end of the year (2003). It specifies spectrum and power control management.
802.11i
The overarching specification for enterprise-class Wi-Fi security, built on the 802.1x authentication scheme. It replaces WEP (Wired Equivalent Privacy) with AES (Advanced Encryption Standard), a much stronger encryption method. Ratification is expected by the end of 2003.
802.11k
A proposed standard to increase the manageability of WLANs by defining and exposing radio and network information, which can be used by network management applications.
802.11n
The next step up from the fastest current WLAN standards, a and g, both of which top out at 54Mbps. The proposed n spec, which will use the same 5GHz frequency range as a, will raise maximum throughput to 100Mbps or higher. The IEEE established an n working group in September; ratification is expected in 2005 or 2006.
802.1x
Provides for port-based authentication and authorization of wireless clients. Already implemented in marry devices as part of WPA, 802.1x incorporates EAP (Extensible Authentication Protocol), a framework that supports a variety of authentication servers, including RADIUS and Kerberos.
Wireless Local Area Networks

80. Idea Summary
• Ethernet idea, a station just waits until the ether goes silent and start transmitting.
if does not receive a noise burst back within 64 bytes, the frame has almost assuredly been delivered correctly
with wireless this situation does not hold