1. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Wireless LAN Standard Chapter 14

2. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Protocol Architecture Functions of physical layer: Encoding/decoding of signals Preamble generation/removal (for synchronization) Bit transmission/reception Includes specification of the transmission medium

3. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

4. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

5. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4

6. 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

7. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

8. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

9. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Services Unacknowledged connectionless service requires minimum logic and is useful in two contexts. First, it will often be the case that higher layers of software will provide the necessary reliability and flow-control mechanism, and it is efficient to avoid duplicating them. Second, there are instances in which the overhead of connection establishment and maintenance is unjustified e.g. data collection activities, monitoring applications.

10. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Services Connection-mode service very simple devices, such as remote sensors, that have little software operating above this level. In these cases, it would provide the flow control and reliability mechanisms normally implemented at higher layers of the communications software.

11. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Services Acknowledged connectionless service With the connection-mode service, the logical link control software must maintain some sort of table for each active connection, to keep track of the status of that connection. If the user needs guaranteed delivery but there is a large number of destinations for data, then the connection-mode service may be impractical because of the large number of tables required.

12. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Services An example is a process control or automated factory environment where a central site may need to communicate with a large number of processors and programmable controllers. Another use of this is the handling of important and time critical alarm or emergency control signals in a factory.

13. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Differences between LLC and HDLC LLC uses asynchronous balanced mode of operation of HDLC (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)

14. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Protocol type 1 operation, which supports the unacknowledged connectionless service, The unnumbered information (UI) PDU is used to transfer user data. There is no acknowledgment, flow control, or error control. There is error detection and discard at the MAC level.

15. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Protocol type 2 operation, a data link connection is established between two LLC SAPs prior to data exchange. Connection establishment is attempted by the type 2 protocol in response to a request from a user. Once the connection is established, data are exchanged using information PDUs, as in HDLC. Information PDUs include send and receive sequence numbers, for sequencing and flow control. Either LLC entity can terminate a logical LLC connection by issuing a disconnect (DISC) PDU.

16. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 LLC Protocol type 3 operation, each transmitted PDU is acknowledged. A new (not found in HDLC) unnumbered PDU, the acknowledged connectionless (AC) information PDU, is defined. User data are sent in AC command PDUs and must be acknowledged using an AC response PDU. To guard against lost PDUs, a 1-bit sequence number is used. The sender alternates the use of 0 and 1 in its AC command PDU, and the receiver responds with an AC PDU with the opposite number of the corresponding command. Only one PDU in each direction may be outstanding at any time.

17. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

18. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Architecture

19. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Terminology

20. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Services IEEE 802.11 defines nine services that need to be provided by the wireless LAN to provide functionality equivalent to that which is inherent to wired LANs. Two ways of categorizing them. The service provider can be either the station or the distribution system (DS). Station services are implemented in every 802.11 station, including access point (AP) stations. Distribution services are provided between basic service sets (BSSs); these services may be implemented in an AP or in another special purpose device attached to the distribution system.

21. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Services Three of the services are used to control IEEE 802.11 LAN access and confidentiality. Six of the services are used to support delivery ofMAC service data units (MSDUs) between stations. The MSDU is the block of data passed down from the MAC user to the MAC layer; typically this is a LLC PDU If the MSDU is too large to be transmitted in a single MAC frame, it may be fragmented and transmitted in a series ofMAC frames.

22. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Services

23. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

24. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Association-Related Services Before the distribution service can deliver data to or accept data from a station, that station must be associated. Before looking at the concept of association, we need to describe the concept of mobility.

25. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

26. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

27. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Access and Privacy Services There are two characteristics of a wired LAN that are not inherent in a wireless LAN. In order to transmit over a wired LAN, a station must be physically connected to the LAN. On the other hand, with a wireless LAN, any station within radio range of the other devices on the LAN can transmit. In order to receive a· transmission from a station that is part of a wired LAN, the receiving station must also be attached to the wired LAN. On the other hand, with a wireless LAN, any station within radio range can receive.

28. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Access and Privacy Services Authentication Establishes identity of stations to each other Deathentication Invoked when existing authentication is terminated Privacy Prevents message contents from being read by unintended recipient

29. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11 Medium Access Control MAC layer covers three functional areas: Reliable data delivery Access control Security

30. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

31. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 The 802.11 MAC Sublayer Protocol (a) The hidden station problem. (b) The exposed station problem.

32. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Medium Access Control Point Coordinated Function Distributed Coordinated Funnction

33. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Access Control

34. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Distributed Coordination Function The DCF sublayer makes use of a simple CSMA (carrier sense multiple access) algorithm, which functions as follows. If a station has a MAC frame to transmit, it listens to the medium. If the medium is idle, the station may transmit; Otherwise the station must wait until the current transmission is complete before transmitting.

35. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Distributed Coordination Function To ensure the smooth and fair functioning of this algorithm, DCF includes a set of delays that amounts to a priority scheme. Let us start by considering a single delay known as an interframe space (IFS).

36. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Medium Access Control Logic

37. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Distributed Coordination Function A station with a frame to transmit senses the medium. If the medium is idle, it waits to see if the medium remains idle for a time equal to IFS. If so, the station may transmit immediately. If the medium is busy (either because the station initially finds the medium busy or because the medium becomes busy during the IFS idle time), the station defers transmission and continues to monitor the medium until the current transmission is over.

38. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Distributed Coordination Function Once the current transmission is over, the station delays another IFS. If the· medium remains idle for this period, then the station backs off a random amount of time and again senses the medium. If the medium is still idle, the station may transmit. During the backoff time, if the medium becomes busy, the backoff timer is halted and resumes when the medium becomes idle. If the transmission is unsuccessful, which is determined by the absence of an acknowledgement, then it is assumed that a collision has occurred.

39. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 BINARY EXPONENTIAL BACKOFF ALGORITHM Randomization when a collision occurs After collision, time is divided up into discrete slots whose length is the worst case round-trip propagation time (2 tau) Assuming 2.5km and 4 repeaters the slot time is 51.2 microsec After i collisions (between one or more stations) each station picks a random number between [0 2^(i-1)] and that number of slots is skipped (work out for 1, 2, 3 collisions)

40. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 BINARY EXPONENTIAL BACKOFF ALGORITHM –After 10 collisions the max randomization interval is 1023 slots –After 16 collisions controller gives up and reports a failure. –Note CSMA/CD provides no acknowledgements. There are modifications to deal with this but you are not responsible in this course.

41. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Interframe 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

42. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

43. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Point Coordination Function an alternative access method implemented on top of the Dep. The operation consists of polling by the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PIFS is smaller than DIFS, the point coordinator can seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.

44. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 MAC Frame Format

45. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 MAC Frame Fields Frame Control – frame type, control information Duration/connection ID – channel allocation time for successful transmission of a MAC frame. In some control frames, this field contains an association, or connection, identifier.

46. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 MAC Frame Fields Addresses – context dependant, types include source and destination transmitting station and receiving station Sequence control – Contains a 4-bit fragment number subfield used for fragmentation and reassembly, and a 12-bit sequence number used to number frames sent between a given transmitter and receiver. Frame body – MSDU or fragment of MSDU Frame check sequence – 32-bit CRC

47. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

48. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

49. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

50. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Control Frame Subtypes Power save – poll (PS-Poll) : This frame is sent by any station to the station that includes the AP (access point). Its purpose is to request that the AP transmit a frame that has been buffered for this station while the station was in powersaving mode.

51. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Control Frame Subtypes Request to send (RTS) : This is the first frame in the four-way frame exchange discussed under the subsection on reliable data delivery at the beginning of Section 14.3. The station sending this message is alerting a potential destination, and all other stations within reception range, that it intends to send a data frame to that destination.

52. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Control Frame Subtypes Clear to send (CTS): This is the second frame in the four-way exchange. It is sent by the destination station to the source station to grant permission to send a data frame. Acknowledgment: Provides an acknowledgment from the destination to the source that the immediately preceding data, management, or PS- Poll frame was received correctly.

53. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Control Frame Subtypes Contention-free (CF)-end: Announces the end of a contention-free period that is part of the point coordination function. CF-end + CF-ack: Acknowledges the CF-end.This frame ends the contention free period and releases stations from the restrictions associated with that period.

54. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

55. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Data Frame Subtypes Data: This is the simplest data frame. It may be used in both a contention period and a contention-free period. Data + CF-Ack: May only be sent during a contention-free period. In addition to carrying data, this frame acknowledges previously received data.

56. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Data Frame Subtypes Data + CF-Poll: Used by a point coordinator to deliver data to a mobile station and also to request that the mobile station send a data frame that it may have buffered. Data + CF-Ack + CF-Poll: Combines the functions of the Data + CF-Ack and Data + CF-Poll into a single frame.

57. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Data Frame Subtypes The Null Function data frame carries no data, polls, or acknowledgments. It is used only to carry the power management bit in the frame control field to the AP, to indicate that the station is changing to a low-power operating state. The remaining three frames (CF-Ack, CF-Poll, CF-Ack + CF-Poll) have the same functionality as the corresponding data frame subtypes in the preceding list (Data + CF-Ack, Data + CF-Poll, Data + CF-Ack + CF-Poll) but without the data.

58. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Association request Association response Reassociation request Reassociation response Probe request Probe response Beacon

59. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Announcement traffic indication message Dissociation Authentication Deauthentication

60. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Association Request: Sent by a station to an AP to request an association with this BSS. This frame includes capability information, such as whether encryption is to be used and whether this station is pollable. Association Response: Returned by the AP to the station to indicate whether it is accepting this association request.

61. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Reassociation Request: Sent by a station when it moves from one BSS to another and needs to make an association with the AP in the new BSS. The station uses reassociation rather than simply association so that the new AP knows to negotiate with the old AP for the forwarding of data frames. Reassociation Response: Returned by the AP to the station to indicate whether it is accepting this reassociation request.

62. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Probe Request: Used by a station to obtain information from another station or AP. This frame is used to locate an IEEE 802.11 BSS. Probe Response: Response to a probe request. Beacon: Transmitted periodically to allow mobile stations to locate and identify a BSS.

63. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Announcement Traffic Indication Message: Sent by a mobile station to alert other mobile stations that may have been in low power mode that this station has frames buffered and waiting to be delivered to the station addressed in this frame. Dissociation: Used by a station to terminate an association.

64. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Management Frame Subtypes Authentication: Multiple authentication frames are used in an exchange to authenticate one station to another. Deauthentication: Sent by a station to another station or AP to indicate that it is terminating secure communications.

65. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Wired Equivalent Privacy

66. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 WEP WEP is used to provide privacy as well as data integrity. The integrity algorithm is simply the 32-bit CRC that is appended to the end of the MAC Frame. A 40-bit secret key is shared by the two participants in the exchange. An initialization vector (IV) is concatenated to the secret key.

67. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 WEP The resulting block forms the seed that is input to the pseudorandom number generator (PRNG). The PRNG generates a bit sequence of the same length as the MAC frame plus its CRC. A bit-by-bit exclusive OR between the MAC frame and the PRNG sequence produces the ciphertext. The IV is attached to the ciphertext and the resulting block is transmitted.

68. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 WEP The IV is changed periodically (as often as every transmission). Every time the IV is changed, the PRNG sequence is changed which complicates the task of an eavesdropper.

69. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 WEP At the receiving end, the receiver retrieves the IV from the data block. Concatenates IV with the shared secret key to generate the same key sequence used by the sender. The key sequence is then XORed with the incoming block to recover the plain text.

70. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Authentication Open system authentication Exchange of identities, no security benefits Shared Key authentication Shared Key assures authentication

71. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Authentication Open system authentication simply provides a way for twp parties to agree to exchange data and provides no security benefits. One party sends a MAC control frame known as authentication frame to the other party. The frame indicates that this is an open system authentication type. The other party responds with its own authentication frame and the process is complete. Thus open system authentication consists simply of the exchange of the identities between the two parties.

72. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Authentication Shared Key authentication requires the two parties share a secret key not shared by any other party. This key is used to assure that both sides are authenticated to each other. The procedure for authentication between two parties A and B is as follows

73. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Authentication A sends a MAC authentication frame with an authentication algorithm identification of shared key with a station identifier that identifies the sending station. B responds with an authentication frame that includes a challenge text. The challenge text is generated using WEP PRNG.

74. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 Authentication A transmits an authentication frame that includes the challenge text just received from B. The entire frame is encrypted using WEP. B receives the encrypted frame and decrypts it using WEP and the secret key shared with A. If decryption is successful ( Matching CRC’s) then B compares the incoming challenge text with the challenge text it sent. B then sends an authentication message to A with a status code indication success or failure.

75. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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

76. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 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 Extension of IEEE 802.11 DS-SS

77. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11g This works in the 2.4 GHz band (like 802.11b) uses the same OFDM based transmission scheme as 802.11aOFDM It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput 802.11g hardware is fully backward compatible with 802.11b hardware

78. Stallings, Wireless Communications & Networks, Second Edition, © 2005 Pearson Education, Inc. All rights reserved. 0-13-191835-4 IEEE 802.11n 802.11n is an amendment which improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO).multiple-input multiple-output 802.11n operates on both the 2.4 GHz and the lesser used 5 GHz bands. It operates at a maximum net data rate from 54 Mbit/s to 600 Mbit/s.