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Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards. The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools. Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards.

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Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards


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    1. Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools

    2. Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools

    3. IEEE 802 Active Working Groups and Study Groups • 802.1 HigherLayer LAN ProtocolsWorkingGroup • Link Security ExecutiveCommitteeStudyGroupisnowpart of 802.1 • 802.3 Ethernet WorkingGroup • 802.11 Wireless LAN WorkingGroup • 802.15 Wireless Personal Area Network (WPAN) WorkingGroup • 802.16 BroadbandWireless Access WorkingGroup • 802.17 ResilientPacket Ring WorkingGroup • 802.18 Radio Regulatory TAG • 802.19 Coexistence TAG • 802.20 Mobile BroadbandWireless Access (MBWA) WorkingGroup • 802.21 Media IndependentHandoffWorkingGroup • 802.22 Wireless Regional Area Networks

    4. Historical notes • The IEEE Working Group for WLAN Standards was created in 1997: • http://www.ieee802.org/11/index.shtml • Defines the MAC and 3 different physical layers that work at 1Mbps and 2Mbps: • Infrared (IR) in base band • Frequency hopping spread spectrum (FHSS), band de 2,4 GHz • Direct sequence spread spectrum (DSSS), band de 2,4 GHz • IEEE Std 802.11b (September 1999): • Extension of DSSS; Up to 11 Mbps • IEEE Std 802.11a (December 1999): • A different physical layer (OFDM): Orthogonal frequency domain multiplexing • Up to 54 Mbps • IEEE Std 802.11g (June 2003) • ...

    5. Evolution of the IEEE 802.11 standard • OFFICIAL IEEE 802.11 WORKING GROUP PROJECT TIMELINES • IN PROCESS  - Standards, Amendments, and RecommendedPractices • http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm • 802.11p: Inter car communications • Communication between cars/road side and cars/cars • Planned for relative speeds of min. 200km/h and ranges over 1000m • Usage of 5.850-5.925GHz band in North America • 802.11s: Mesh Networking • Design of a self-configuring Wireless Distribution System (WDS) based on 802.11 • Support of point-to-point and broadcast communication across several hops • 802.11r: Faster Handover between BSS • Secure, fast handover of a station from one AP to another within an ESS • Current mechanisms (even newer standards like 802.11i) plus incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANs • Handover should be feasible within 50ms in order to support multimedia applications efficiently

    6. Evolution of the IEEE 802.11 standard • Other interesting groups • 802.11t: Performance evaluation of 802.11 networks • Standardization of performance measurement schemes • 802.11v: Network management • Extensions of current management functions, channel measurements • Definition of a unified interface • 802.11w: Securing of network control • Classical standards like 802.11, but also 802.11i protect only data frames, not the control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged. • Note: Not all “standards” will end in products, many ideas get stuck at working group • Standards are available here: http://standards.ieee.org/getieee802/

    7. IEEE 802.11 and WiFi • Wi-Fi is a set of standards for wireless networks based on IEEE 802.11 specifications. • Wi-Fi is a trademark of the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies that equipments meet the IEEE 802.11x standards. • The main problem which is intended to solve through normalization is compatibility. This means that the user is assured that all devices having the seal Wi-Fi can work together regardless of the manufacturer of each. • A complete list of devices that have the certification Wi-Fi: • http://certifications.wi-fi.org/wbcs_certified_products.php?lang=en.

    8. Redes Inalámbricas – Tema 2.CWireless LANs: the IEEE 802.11 standards The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools

    9. Spread Spectrum Transmission

    10. Comparison of Wireless Modulation Schemes • FHSS transmissions less prone to interference from outside signals than DSSS • WLAN systems that use FHSS have potential for higher number of co-location units than DSSS • DSSS has potential for greater transmission speeds over FHSS • Throughput much greater for DSSS than FHSS • Amount of data a channel can send and receive

    11. Orthogonal Frequency Division Multiplexing (OFDM) • With multipath distortion, receiving device must wait until all reflections received before transmitting • Puts ceiling limit on overall speed of WLAN • OFDM: Send multiple signals at same time • High number of low BW ‘modems’ are used, each on a different sub channel • The ‘slow’ sub channels are multiplexed into a ‘fast’ combined channel • Error correction is done with FEC and bit stripping • Avoids problems caused by multipath distortion • Used in 802.11a networks

    12. Notion of a channel Wireless communication is carried over a set of frequencies called a channel Signal Power Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    13. Channels in Wireless Available spectrum is typically divided into disjoint channels Channel A Channel B Channel C Channel D Fixed Block of Radio Frequency Spectrum Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    14. Ideal Spectrum Usage • Use entire range of frequencies spanning a channel • Usage drops down to zero right outside a channel Channel A Channel B Power Frequency Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    15. Channel A Channel B Wastage of spectrum Real Usage Realistic Spectrum Usage • In reality, this is what communication circuits can achieve • Results in inefficient usage of spectrum Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    16. Channel A Channel B Wastage of spectrum Real Usage Realistic Spectrum Usage Is it possible to eliminate such inefficiencies ? Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    17. Channel A Channel B Channel A’ Define a new channel • Define a new channel as shown • Overlaps with neighboring two channels • Called a `partially overlapped’ channel Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    18. Channel A Channel B Channel A’ Define a new channel • Channel A’ would interfere with both A and B • Is it possible to get any gains from using A, A’ and B ? Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    19. In the UK and most of EU: 13 channels, 5MHz apart, 2.412 – 2.472 GHz Each channel is 22MHz Significant overlap Best channels are 1, 6 and 11 802.11b Channels

    20. Link A Ch 1 Link B Ch 3 Link C Ch 6 Amount of Interference An 802.11 Experiment • Can we use channels 1, 3 and 6 without interference ? Ch 1 Ch 3 Ch 6 Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    21. Link A Ch 1 Link B Ch X An 802.11 Experiment 35 meters 60 meters Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison

    22. IEEE 802.11b • Data rate • 1, 2, 5.5, 11 Mbit/s, depending on SNR • User data rate max. approx. 6 Mbit/s • Transmission range • 300m outdoor, 30m indoor • Max. data rate ~10m indoor • Frequency • Free 2.4 GHz ISM-band • Security • Limited, WEP insecure, SSID • Availability • Many products and vendors • Connection set-up time • Connectionless/always on • Quality of Service • Best effort, no guarantees (unless polling is used, limited support in products) • Manageability • Limited (no automated key distribution, sym. Encryption) • Pros • Many installed systems and vendors • Available worldwide • Free ISM-band • Cons • Heavy interference on ISM-band • No service guarantees • Relatively low data rate

    23. IEEE 802.11a • Data rate • 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR • User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54) • 6, 12, 24 Mbit/s mandatory • Transmission range • 100m outdoor, 10m indoor • E.g., 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m • Frequency • Free 5.15-5.25, 5.25-5.35, 5.725-5.825 GHz ISM-band • Security • Limited, WEP insecure, SSID • Availability • Some products, some vendors • Connection set-up time • Connectionless/always on • Quality of Service • Best effort, no guarantees (same as all 802.11 products) • Manageability • Limited (no automated key distribution, sym. Encryption) • Pros • Fits into 802.x standards • Free ISM-band • Available, simple system • Uses less crowded 5 GHz band • Higher data rates • Cons • Shorter range

    24. IEEE 802.11g • Ratified in June 2003 by the IEEE Standards Board • standard preliminary draft submitted in December 2001; • Uses the 2.4 GHz band • OFDM and codification PBCC • Backward compatibility IEEE 802.11b • They can co-exist in the same WLAN • New transmission speeds: 6, 9, 12, 18, 24, 36, 48 & 54 Mbps

    25. Examples of the physical parameters of a real deviceal • DATA SHEET of a Cisco Aironet 802.11a/b/g CardBusWireless LAN ClientAdapter

    26. WiFi and health RFR'sbiologicaleffects are measured in terms of specificabsorptionrate (SAR) -- howmuchenergyis absorbed intohumantissue -- whichisexpressed in Watts per kilogram (W/kg). A dangerouslevel (by U.S. standards) isconsideredtobeanythingabove 0.08 W/kg.Thusfar, RFR measurementsforWi-Fi, both at home and abroad, are a minute fraction of emissionsthatcouldamounttothislevel. Wi-Fi, in fact, emitslessthanothercommonsources of RFR likemicrowaves and mobilephones. Sincemobilephoneswererecentlycleared as a potentialcarcinogenby a comprehensive, long-termstudyconductedbytheDanishInstitute of CancerEpidemiology in Copenhagen, itseemsveryunlikelythatdevicesemitting a lower (and lessfrequent) levelcouldbe more dangerous. • ByNaomiGraychase, January 12, 2007 • http://www.wi-fiplanet.com/news/article.php/3653711 • More information: • http://www.fcc.gov/oet/rfsafety/

    27. Redes Inalámbricas – Tema 2.CWireless LANs: the IEEE 802.11 standards The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools

    28. Available architectures • Independent Basic Service Set (IBSS) • is the simplest of all IEEE 802.11 networks in that no network infrastructure is required. As such, an IBSS is simply comprised of one or more Stations which communicate directly with each other. • Do not confuse it with ad hoc!! • infrastructure Basic Service Set (BSS) • Components: • Station (STA) • Access Point (AP)or Point Coordinator (PC) • Basic Service Set (BSS) • Extended Service Set (ESS)

    29. Services with contention Services without contention Point CoordinationFunction (PCF) MAC Distributed Coordination Function (DCF) DIFS DIFS Contention window PIFS busy medium SIFS defer access slot The MAC basics CSMA/CA with binary exponential backoff The protocol, at its minimum, consists of two frames: data and ack The 5 timing values: • Slot time • SIFS: short interframe space (< slot time) • PIFS: PCF interframe space (=SIFS+1slot) • DIFS: DCF interframe space (=SIFS+2slots) • EIFS: extended interframe space

    30. B1 = 25 B1 = 5 wait data data wait B2 = 10 B2 = 20 B2 = 15 DCF example • The backoff intervals are chosen within the contention window. That is in the interval [0, CW] • The CW can vary between 31 slots (CWmin) and 1023 slots (CWmax) • CW increases after a failed transmission and re-initialized after a successful transmission • B1 and B2 are the backoff intervals in STA 1 and 2 • CW = 31

    31. Hidden node Exposed node A couple of problematic configurations A A B C B C D

    32. Hiddennodessituations MU3 cannot hear MU1 or MU2 because of the distance The obstacle prevents MU1 and MU2 from hearing one another

    33. SIFS SIFS SIFS RTS/CTS mechanism • Based on the network allocation vector (NAV) DIFS+contention source data RTS destination ACK CTS DIFS Other STA Contention window NAV (RTS) NAV (CTS) defer access

    34. PIFS SIFS SIFS SIFS PIFS SIFS SIFS PC Data+Poll Data+Poll Data+Poll CF-End Beacon DATA+ACK ACK SIFS (no response) STA1 CP Contention Free Period CP NAV Reset STA2 Station 2 sets NAV(Network Allocation Vector) Station 3 is hidden to the PC, it does not set the NAV. It continues to operate in DCF. STA3 Time PCF: Point Coordination Function • The beacons are used to maintain synchronization of the timers in the stations and to send control information • The AP generates the beacons at regular intervals • The stations know when the next beacon will arrive • the target beacon transmission time (TBTT) are announced in the previous beacon

    35. Función To DS From DS Addr. 1 Addr. 2 Addr. 3 Addr. 4 IBSS 0 0 RA = DA SA BSSID - From the AP 0 1 RA = DA BSSID SA - To the AP 1 0 RA = BSSID SA DA - Wireless DS 1 1 RA TA DA SA Frames structure Types of addresses: • Source address (SA) • Destination Address (DA) • Transmitter Address (TA) • Receiver Address (RA) • BSS identifier (BSSID) • management (00) • control (01), • data (10), • reserved (11)

    36. Función To DS From DS Addr. 1 Addr. 2 Addr. 3 Addr. 4 IBSS 0 0 RA = DA SA BSSID - From the AP 0 1 RA = DA BSSID SA - To the AP 1 0 RA = BSSID SA DA - Wireless DS 1 1 RA TA DA SA Addressing and DS bits DS TA RA (BSSID) SA/TA AP AP SA RA Client AP DA Client DA Server Server

    37. Services • The IEEE 802.11 architecture defines 9services • Station services: • Authentication • Deauthentication • Privacy  WEP • Data delivery • Distribution services: • Association generate a connection between a STA and a PC • Disassociation • Reassociationlike association but informing the previous PC • Distribution • integration Similar to plugging in and out in a regular network

    38. State variables and services In a IBSS there is no auth. nor ass. Data service is allowed State 1: unauthenticated, unassociated Class 1 frames Successful authentication Deauthentication notification State 2: authenticated, unassociated Class 1 & 2 frames Deauthentication notification Successful authenticationor reassociation Disassociation notification State 3: authenticated, associated A STA can be authenticated by several AP but associated only with one AP Class 1, 2 & 3 frames

    39. BSSID y SSID • BSSID (Basic Service Set Identity) • BSS: MAC address of the AP • Ad-Hoc: 46 bits random number • SSID (Service Set ID) • Known as the Network Name because it is basically the name that identifies the WLAN • Lenght: 0~32 octets • 0: it is the broadcast SSID • Used to distinguish WLAN among them • The access points and stations who want to connect to a single WLAN must use the same SSID

    40. BSS AP WLAN LAN The Extended Service Set (ESS) Distribution System (DS) • Inter-accespoint protocol (IAPP)

    41. IAPP and the Task Group f • Scope of Project: to develop recommended practices for an Inter-Access Point Protocol (IAPP) which provides the necessary capabilities to achieve multi-vendor Access Point interoperability across a Distribution System supporting IEEE P802.11 Wireless LAN Links. • Purpose of  Project: ... including the concepts of Access Points and Distribution Systems. Implementation of these concepts where purposely not defined by P802.11 ... As 802.11 based systems have grown in popularity, this limitation has become an impediment to WLAN market growth. This project proposes to specify the necessary information that needs to be exchanged between Access Points to support the P802.11 DS functions. The information exchanges required will be specified for, one or more Distribution Systems; in a manner sufficient to enable the implementation of Distribution Systems containing Access Points from different vendors which adhere to the recommended practices • Status • The 802.11F Recommendation has been ratified and published in 2003. • IEEE 802.11F was a Trial Use Recommended Practice. The IEEE 802 Executive Committee approved its withdrawal on February 03, 2006

    42. Wireless Distribution System • IEEE 802.11, WDS means • Multiple wireless “ports” inside the access-point, to wirelessly interconnect cells (access-points connecting to other access-points) • pre-IEEE 802.11, did not support WDS: • Three ports exist in one access-point (one Ethernet, and two wireless cells) • One wireless backbone extension can be made (using two radio modules in the access-point) • WDS allows: • Extending the existing infrastructure with wireless backbone links • Totally wireless system without any wired backbones, needed in locations where large areas are to be covered and wiring is not possible

    43. Bridgingtwowirednetworks As a repeater to extend a network WDS examples

    44. Bridge learn table Bridge learn table Packet for STA-2 ACK ACK Packet for STA-2 ACK Packet for STA-2 Operational processesTraffic flow - WDS operation AP-1000 or AP-500 STA-2 AP-1000 or AP-500 2 Avaya Wireless PC-Card STA-1 2 STA-2 Association table 2 STA-2 Avaya Wireless PC-Card STA-1 2 Association table Wireless Backbone WDS Relay STA-1 WDS Relay BSS-B STA-2 STA-1 BSS-A

    45. Linksys Wireless-G Access Point

    46. Linksys Wireless-G Access Point

    47. Linksys Wireless-G Access Point

    48. Linksys Wireless-G Access Point

    49. Linksys Wireless-G Access Point

    50. Linksys Wireless-G Access Point