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1 教育部資通訊科技人才培育先導型計畫 IEEE 技術簡介任課老師 : 陳懷恩助理教授兼任資訊工程研究所所長電算中心資訊網路組組長國立宜蘭大學 wechen@niu.edu.tw

2 Outline IEEE Family IEEE Standard s Evolution Management features of How does a station join an existing cell Competing technologies to IEEE

3 Advantages Adv. vs. Disadv. Without cabling for client devices Low cost Wi-Fi Certified Widely available Disadvantages Spectrum assignments not consistent worldwide Power consumption Limited range Wi-Fi pollution 3

4 a b d e f g h High-speed Physical Layer in the 5GHz Band Family Higher-speed Physical Layer Extension in the 2.4GHz Band Specification for operation in additional regulatory domains MAC Quality of Service (QoS) Enhancements Inter-Access Point Protocol (IAPP) Further Higher Data Rate Extension in the 2.4 GHz Band Spectrum and Transmit Power Management Extensions in the 5 GHz band in Europe Finished Finished Finished Finished Finished Finished i MAC Security Enhancements Finished i j k 4.9 GHz 5 GHz Operation in Japan Finished Specification for Radio Resource Measurement m Revision of n p r s t u v Enhancements for Higher Throughput Wireless Access for the Vehicular Environment Fast Roaming/Fast BSS Transition ESS Mesh Networking Recommended Practice for Evaluation of Wireless Performance Interworking with External Networks Wireless Network Management 4

5 Standards Evolution of Mesh Extensions s QoS Extensions e, r Security i Extensions Radio & Regulatory d, h, j, k Higher Data b, a, g, Rates n 5

6 Standard d Evolution Goal Quality of Service Security Interconnection Performance & Coverage Performance improvement Modulation Scheme Channel Bonding Frame Burst mode MISO, MIMO Coverage extension Smart Antenna MIMO 6

7 Family : the original standard with 1Mbit/s and 2Mbit/s in the 2.4GHz band a: High-speed physical layer (OFDM) operates in 5 GHz band with a maximum raw data rate of 54 Mbit/s b: Enhancements to to support 5.5 and 11 Mbit/s FHSS, DSSS Operates in 2.4 GHz band 7

8 802.11d: International (country-to-country) roaming extensions (2001) e: Medium Access Control (MAC) Quality of Service (QoS) enhancement f: It Inter-Access Point tp Protocol g: Applied OFDM to the 2.4 GHz band Data rate up to 54 Mbit/s backwards compatible with b 8

9 802.11h provides Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) to the a MAC solves problems like interference with satellites and radar using the same 5 GHz frequency band i Medium Access Control (MAC) security enhancements j designed specially for Japanese market allowsoperationin49to5ghzband operation in 4.9 to n Higher throughput improvements using MIMO (multiple input, multiple output antennas) 9

10 Primary IEEE Specifications b a g n Standard Approved Maximum Data Rate Different Data Rates Configurations Dec-99 Jan-00 Jun-03 Dec-07 (Expected) 11 Mbps 54Mbps 54 Mbps 600 Mbps Typical Range 70m 30 m 50m 60m Modulation techniques DSSS, CCK OFDM DSSS, CCK, OFDM DSSS, CCK, OFDM (HT) RF Band 24GHz 2.4GHz 5GHz 24GHz 2.4GHz 2.4/5GHz Number of Spatial Streams and Antenna Channel bandwidth 20MHz 20MHz 20MHz 20 or 40MHz Number of Non-Interleaving Channels

11 Standard Pros Pros & Cons Cons lowest cost; signal range is b good and not easily obstructed slowest maximum speed; home appliances may interfere on the unregulated frequency band fast maximum speed; regulated ltd highest h cost; shorter range signal a frequencies prevent signal that is more easily obstructed interference from other fast maximum speed; signal g range is good and not easily obstructed fastest maximum speed and n best signal range; more resistant to signal interference from outside sources costs more than b; appliances may interfere on the unregulated signal frequency standard is not yet finalized; costs more than g; the use of multiple signals may greatly interfere with nearby b/g based networks 11

12 Introduction of n SISO and diversity antennas Single Input and Single Output is common architecture. 12

13 Introduction of n Antenna Diversity To reduce the effects of multipath, dropouts on signal quality and throughput. Two independent antennas and radio systems are used for transmitting and receiving signals. Voting processor choose which radio has better signal path to client. 13

14 Introduction of n Diversity Reception Reflected Path Antenna A Antenna B LOS Path Receiver A Receiver B Voting Processor or 14

15 How does MIMO works? A data stream is divided into multiple unique streams. Data streams are transmitted at the same time. MIMO takes the advantage of multipath. MIMO receiver combines all streams. DSP Radio Radio Radio Radio DSP MIMO enabled client MIMO enabled AP 15

16 Advantage of n Overcoming the multipath effect of RF Higher performance More coverage 16

17 What is n New IEEE Standard d (not approved yet) Uses MIMO radio technology Provides wire-like performance Data rate is from 100Mbps to 600Mbps which depends on implementation Supports both 2.4 GHz and 5 GHz Includes advances in QoS & Power Saving High definition video mode at 5 GHz Uses multiple streams Less interference and more channels 17

18 Major components of n Features Better OFDM Space- Division Multiplexing Diversity MIMO Power Save Definition Supports wider bandwidth & higher h code rate (max. data rate -- 65Mbps) Multiple streams transmitted through multiple antennas Exploits the existence of multiple antenna to improve range and reliability Limit power consumption by utilizing multiple antennas only on as-needed basis Standard Status Mandatory Optional Up to 4 spatial streams Optional Up to 4 antennas Mandatory 18

19 Major components of n (cont) Features 40MHz Channels Aggregation Reduced Inter-frame Spacing (RIFS) Greenfield Mode Definition Doubles data rates by doubling bandwidth from 20MHz to 40MHz Allowing bursts of multiple data packets between overhead communications Provides a shorter delay between OFDM transmissions than in a or g Eliminates support for a/b/g devices in an all n network to improve efficiency Standard Status Optional Required Required Optional 19

20 Time to transfer 30 min HD video. 20

21 Legacy a/g AP <5Mbps 10-15Mbps 20-30Mbps >40Mbps 5-10Mbps 15-20Mbps 30-40Mbps 21

22 MIMO Technology <5Mbps 10-15Mbps 20-30Mbps >40Mbps 5-10Mbps 15-20Mbps 30-40Mbps 22

23 Management Issues Without tethering a wired network, the wireless medium is unreliable. Users can take advantage of the lack of physical boundaries. For a mobile devices, power consumption is always a critical problem. 23

24 Management Architecture MAC PHY MLME MAC MIB PLME PHY MIB SME Relationship between management entities and components of specification MLME: MAC layer management entity PLME: PHY layer management entity SME: Station management entity MIB: Management information base 24

25 Howtojoinanexistingcell Scanning Authentication Association 25

What is scanning? Scanning IEEE The 802.2 process of identifying existing networks in the area.

2 (independent, infrastructure, or MAC both) Media Access Control (MAC) BSSID (individual or broadcast) Frequency 802.

26 What is scanning? Scanning IEEE The process of identifying existing networks in the area. Logical What are Link the Control parameters (LLC) used in the scanning What are the parameters used in the scanning procedure? IEEE BSSType (independent, infrastructure, or MAC both) Media Access Control (MAC) BSSID (individual or broadcast) Frequency a SSID (network Direct name) Infrared Hopping Sequence (IR) b Spread ScanType (active or passive) g Spread Spectrum ChannelList Spectrum (FHSS) (DSSS) With DS products, it is a list of channels. With FH products, it is a hop pattern PHY OSI Layer 2 (Data Link) OSI Layer 1 (Physical) 26

27 ProbeDelay MinChannelTime The minimum time to spend on each channel when scanning. ProbeDelay MaxChannelTime The maximum time to spend on each channel when scanning. MinChannelTime 27

28 Passive Scanning Passive scanning saves battery power. In passive scanning, a station moves to each channel on the channel list and waits for Beacon frames. AP1 AP2 Found BSSs: BSS 1, AP1 BSS 2, AP2 BSS 2, AP2 AP3 28

29 Active Scanning For each channel to be scanned, Move to the channel and wait for either an indication of incoming frame or for the ProbeDelay timer to expire. If an incoming frame is detected, the channel is in use and can be probed. The timer prevents an empty channel from blocking the entire procedure. Send Prove Request frame. Wait for MinChannelTime and check if channel is busy If idle, there is no network. Move to next channel. If busy, wait until MaxChannelTime and process any Probe Response frames. 29

30 Probe response request AP1 Probe response AP2 30

31 DIFS Min Response Time SIFS DIFS SIFS STA Probe Request Ack Ack AP1 Probe Response AP2 Probe Response 31

32 Scan Report The report lists all the BSSs that t the scan discovered d and their parameters. BSSID BSStype SSID Beacon intervals (integer) DTIM period Timing i parameters: Timestamp, an offset PHY, CF, IBSS parameters BSSBasicRateSet: Stations must be able to receive data at all the rates listed in the set. 32

33 Joining After compiling the scan results, a station can elect one of the BSSs to join. Choosing which BSS to join is an implementation- specific decision and may even involve user intervention. Common criteria: Power level, signal strength. The joining process involves matching local parameters to the parameters required by the selected BSS. One of the most important tasks is to synchronize timing i information. 33

34 34

35 35

36 Authentication Wireless networks are attractive in large part because physical access is not required to use network resources. The authentication ti ti process only proves the identity of one station (not mutual authentication). Network administrators may wish to authenticate mobile stations, but mobile stations can not authenticate the AP. One-way street: stations authenticate to network. A man-in-the-middle attack: a rogue AP could send Beacon frame to steal Authentication information. Two approaches: open-system and shared-key authentication. 36

37 Open-system authentication. 1: From-source Authentication algorithm - 0 (open system) Sequence number - 1 2: Authentication algorithm - 0 (open system) Sequence number 2 Status code Open-system authentication exchange AP The identity of any station is its MAC address. 37

38 38

39 Shared-key Authentication Shared-key authentication makes use of WEP (Wired Equivalent Privacy). It requires that a shared key be distributed to stations before attempting authentication. The challenge text is composed of 128 bytes generated using the WEP keystream generator with a random key and IV. 39

40 1: From-source Authentication algorithm - 1 (shared key) Sequence number - 1 2: Authentication algorithm - 2 (shared key) Sequence number 2 Status code 0 (successful) Challenge text (clear) 3: Authentication algorithm - 2 (shared key) Sequence number 3 Challenge text AP 4: Authentication algorithm - 2 (shared key) Sequence number 4 Status code 0 (successful) Shared-key authentication exchange The challenge text is composed of 128 bytes generated using the WEP keysteam generator with a random key and IV. 40

41 Preauthentication AP1 AP2 Data Authentication Reassociation BSS1 BSS2 AP2 s Station signal begins moves is associated is using right stronger, into the with network the so AP1 station overlap Between decides to BSS1 move and association BSS2 to AP2 41

42 AP1 AP2 Data Preauthentication Reassociation BSS1 BSS2 AP2 s Station signal begins moves is associated is using right stronger, into the with network the so AP1 station overlap Between decides to BSS1 move and association BSS2 and to detects AP2 the presence of AP2 42

43 Association Association i is recordkeeping procedure that allows the distribution system to track the location of each mobile station. After association completes, an AP must register the mobile STA on the network so frames for the mobile STA are delivered to the AP. One method of registering is to send a gratuitous ARP explicitly forbids associating with more than one AP. 43

44 Associated procedure 1: Association request 2: Association response AID 3: Traffic AP Association request & reply are unicast frames. (ACK is required) 44

45 Reassociated procedure Old AP 1: Reassociation request My old AP was 3: IAPP Please send any buffered frames for 4: IAPP send buffered frames for 2: Reassociation response I am your new AP, and here is your new AID New AP 5: Here are some frames buffered dfrom your old ldap AP. 45

46 Reassociation with the same AP BSS 2: Reassociation exchange AP 46

47 Other Authentication Methods RADIUS (Remote Authentication Dial In User Service) Account/Password Registration ti of fmac address of mobile station ti 802.1x (WIRE1x) 47

48 48

49 States of Authentication and DeAuthentication Notification DeAuthentication Notification DeAssociation Notification Association State 1 Unauthenticated ti t and unassociated The node is disconnected from the network and not Successful associated to an access point. Authentication Authenticated and unassociated The node has been authenticated on the network but has not yet associated with the access point. Authenticated and associated Successful The node is connected to the Association or network and able to transmit Reassociation and receive data through the access point. Unauthenticated, Unassociated State 2 Authenticated, Unassociated State 1 Authenticated, Associated 49

50 Power Conservation Powering down the transceiver can lead to great power savings in wireless networks. sleeping, dozing, PS mode vs. awake, active, on Power conservation Minimizing the time spent in the awake stage. Maximizing the time in the PS mode. 50

51 Power Management in Infrastructure Networks In infrastructure networks: APs remain active at all time. APs are aware of the location of mobile STAs. STA can communicate its power management state to its AP. All traffic must go through APs. APs are an ideal location to buffer traffic. APs play a key role on power management in infrastructure networks. 51

52 Power Management in Infrastructure Networks (cont) AP have two power management-related task: Buffering frames AP can determine whether a frame should be delivered to the wireless network. Frames should be buffered if the station is asleep. Periodic announce buffer status AP should periodically announce which stations have frames waiting form them. A station only needs to power up the transmitter to transmit polling frames when there are buffered frames for it. 52

53 Power Management in Infrastructure Networks (cont) Listen Interval is the number of beacon periods for which the mobile station may choose to sleep. Longer listen intervals require more buffer space on the access point. AP must agree to wait for at least the listen interval before discarding frames. If a mobile station fails to check for waiting frames after each listen interval, they may be discarded without notification. i 53

54 Unicast frame buffering and delivery When frames are buffered, the destination node s AID provides the logic link between the frame and its destination. (Multicast or Broadcast: AID = 0) APs assemble a TIM and transmit it in Beacon frames. TIM is a virtual bitmap composed of 2008 bits (251 B). Offsets are used so only a small portion of the virtual bitmap needs to be transmitted. Each bit corresponds to a particular AID. 54

55 Unicast frame buffering and delivery (cont) To retrieve buffered frames, mobile STA use PS-Poll Poll Control frame. When multiple stations have buffered frames, all STAs with buffered data must use random backoff algorithm to transmit the PS-poll. Each PS-Poll Poll is used to retrieve one buffered frames. ACK is required. 55

56 Buffered frame retrieval process Listen Intervals: 2 for STA1, 3 for STA2 BI AP TIM: Frame for 1 TIM: Frames TIM: Frame for 2 TIM: Frames TIM: No Frame for 1 & 2 for 1 & 2 Busy PS-PollPoll PS-PollPoll TIM: No Frame STA1 STA2 Busy CW Defer 56

57 PS-Poll Poll frame retrieval AP Time Frame 1, more data PS-Poll ACK Frame 1, more data PS-Poll Frame 2 ACK PS-Poll Poll ACK 57

58 STAs may switch from a PS mode to active mode at any time. If a STA switches to active mode, frames can be transmitted without waiting for a PS-Poll. Poll. APs use an aging function to determine when buffered frames are old enough to be discarded. Aging function should not discard frames before he listen interval has elapsed. 58

59 Delivering multicast and broadcast frame: DTIM Buffered broadcast and multicast frames are saved using AID 0. DTIM period Buffered broadcast and multicast traffic is transmitted after DTIM beacon. The AP may choose to defer the processing of incoming PS-Poll Poll frames. 59

60 Delivering multicast and broadcast frame: DTIM Listen Interval: 3 for STA1 BI DTIM interval TIM DTIM TIM TIM DTIM TIM AP BC MC BC MC PS-Poll STA1 BC MC BC MC Multicast and broadcast buffer transmission after DTIMs. 60

61 Timer synchronization Wireless network technologies depend a great deal on the distribution of timing information. Timing information is especially important in frequency-hopping networks. 61

62 Timer synchronization Timing information is especially important in frequency-hopping networks Timing synchronization function (TSF) is based on a 1-MHZ clock. (one tick = 1 micro sec) 62

63 Infrastructure timing synchronization APs are responsible for maintaining the TSF time, and any STAs associated with an AP must simply accept the AP s TSF as valid. Associated STAs maintain local TSF so that they can still remain roughly synchronized with the global TSF when missing a Beacon frame. Network timer Local timer Beacon/ Probe Response Save TSF value Local offset Timestamp + Local offset Begin join process Matching the local timer to a network timer 63

64 Competing technologies Bluetooth Version Version 1 1 Mbps Data Rate Version Mb Mbps EDR WiMedia Alliance 53 ~ 480 Mbps (3.0?) ZigBee IEEE operation in the unlicensed 2.4 GHz, 915 MHz and 868 MHz ISM bands 250kbps 64

65 UWB Competing technologies FCC authorizes the unlicensed use of UWB in GHz. 100 Mbps ~ 400 Mbps HomeRF 2.4 GHz, WBFH (Wide band frequency hopping) 10 Mbps, 150 ft. 3GPP The 3rd Generation Partnership Project 3.9G (HSDPA 3.5G) 100Mbps WiMAX 65

66 Road Map of Wireless Communication Distance 10km MWBA FWBA a/b/d 2008/9 2.5G 3G 3.5G 4G/LTE WAN 5km 2km MWiMAX e 2006/7 MAN 100m WLAN WLAN WLAN b g n a HyperLAN2 LAN 10m Zigbee a Bluetooth /1a Bluetooth Mbps 50Mbps 100Mbps 2006 UWB a PAN Bandwidth 66

67 References IEEE standard Wireless Networks The Definitive Guide, Oreilly Demystifying MIMO and n, Peter Reinders, Bluesocket, Inc n: Next-Generation Wireless LAN Technology, Broadcom Technologies: Past, Present and Future, TROPOS networks 67

WLAN 2

WLAN 2 1 WLAN 2 IEEE 802.11 HomeRF GSM/ GPRS CDMA 3 ( ) (Infrared) (Laser) (Microwave) (DSSS) (FHSS) (HomeRF) (Bluetooth) 4 ( ) IrDA (Direct-Beam IR, DB/ IR) (Diffuse IR, DF/ IR) (Ominidirectional IR, Omini/