Presentation on theme: "Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE standards"— Presentation transcript:
1 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
2 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
3 IEEE 802 Active Working Groups and Study Groups 802.1 Higher Layer LAN Protocols Working GroupLink Security Executive Committee Study Group is now part of 802.1802.3 Ethernet Working GroupWireless LAN Working GroupWireless Personal Area Network (WPAN) Working GroupBroadband Wireless Access Working GroupResilient Packet Ring Working GroupRadio Regulatory TAGCoexistence TAGMobile Broadband Wireless Access (MBWA) Working GroupMedia Independent Handoff Working GroupWireless Regional Area Networks
4 Historical notesThe IEEE Working Group for WLAN Standards was created in 1997:Defines the MAC and 3 different physical layers that work at 1Mbps and 2Mbps:Infrared (IR) in base bandFrequency hopping spread spectrum (FHSS), band de 2,4 GHzDirect sequence spread spectrum (DSSS), band de 2,4 GHzIEEE Std b (September 1999):Extension of DSSS; Up to 11 MbpsIEEE Std a (December 1999):A different physical layer (OFDM): Orthogonal frequency domain multiplexingUp to 54 MbpsIEEE Std g (June 2003)...
5 Evolution of the IEEE 802.11 standard OFFICIAL IEEE WORKING GROUP PROJECT TIMELINESIN PROCESS - Standards, Amendments, and Recommended Practices802.11p: Inter car communicationsCommunication between cars/road side and cars/carsPlanned for relative speeds of min. 200km/h and ranges over 1000mUsage of GHz band in North America802.11s: Mesh NetworkingDesign of a self-configuring Wireless Distribution System (WDS) based onSupport of point-to-point and broadcast communication across several hops802.11r: Faster Handover between BSSSecure, fast handover of a station from one AP to another within an ESSCurrent mechanisms (even newer standards like i) plus incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANsHandover should be feasible within 50ms in order to support multimedia applications efficiently
6 Evolution of the IEEE 802.11 standard Other interesting groups802.11t: Performance evaluation of networksStandardization of performance measurement schemes802.11v: Network managementExtensions of current management functions, channel measurementsDefinition of a unified interface802.11w: Securing of network controlClassical standards like , but also i protect only data frames, not the control frames. Thus, this standard should extend i 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 groupStandards are available here:
7 IEEE and WiFiWi-Fi is a set of standards for wireless networks based on IEEE 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 x 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:
8 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
10 Comparison of Wireless Modulation Schemes FHSS transmissions less prone to interference from outside signals than DSSSWLAN systems that use FHSS have potential for higher number of co-location units than DSSSDSSS has potential for greater transmission speeds over FHSSThroughput much greater for DSSS than FHSSAmount 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 transmittingPuts ceiling limit on overall speed of WLANOFDM: Send multiple signals at same timeHigh number of low BW ‘modems’ are used, each on a different sub channelThe ‘slow’ sub channels are multiplexed into a ‘fast’ combined channelError correction is done with FEC and bit strippingAvoids problems caused by multipath distortionUsed in a networks
12 Notion of a channel Signal Power It is common knowledge that wireless communication happens over a fixed set of frequencies, called a channel. Such a system makes efficient use of such spectrum while allowing for multiple parties to communicate on orthogonal or independent channels.This figure shows the power spectral density of a transmission, or which frequency is being utilized with how much aggregate output power.Wireless communication is carried over a set of frequencies called a channelThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
13 Available spectrum is typically divided into disjoint channels Channels in WirelessChannel AChannel BChannel CChannel DFixed Block of Radio Frequency SpectrumGiven a fixed amount of RF spectrum, communication engineers divide it up into disjoint channels. Each channel carries some communication traffic independent of the rest. The capacity of the wirelessAvailable spectrum is typically divided into disjoint channelsThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
14 Ideal Spectrum UsageChannel AChannel BPowerFrequencyUse entire range of frequencies spanning a channelUsage drops down to zero right outside a channelThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
15 Realistic Spectrum Usage Channel AChannel BReal UsageWastage of spectrumIn reality, this is what communication circuits can achieveResults in inefficient usage of spectrumThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
16 Realistic Spectrum Usage Channel AChannel BReal UsageWastage of spectrumIs it possible to eliminate such inefficiencies ?Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
17 Define a new channel Define a new channel as shown Channel BChannel A’Define a new channel as shownOverlaps with neighboring two channelsCalled a `partially overlapped’ channelThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
18 Define a new channel Channel A’ would interfere with both A and B Channel BChannel A’Channel A’ would interfere with both A and BIs it possible to get any gains from using A, A’ and B ?Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
19 802.11b ChannelsIn the UK and most of EU: 13 channels, 5MHz apart, – GHzEach channel is 22MHzSignificant overlapBest channels are 1, 6 and 11
20 An 802.11 Experiment Amount of Interference Can we use channels 1, 3 and 6 without interference ?Link A Ch 1Link C Ch 6Link B Ch 3Ch 1Ch 3Ch 6Amount of InterferenceThanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
21 An 802.11 Experiment 35 meters 60 meters Link A Ch 1 Link B Ch X Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison
22 IEEE 802.11b Data rate Transmission range Frequency Security 1, 2, 5.5, 11 Mbit/s, depending on SNRUser data rate max. approx. 6 Mbit/sTransmission range300m outdoor, 30m indoorMax. data rate ~10m indoorFrequencyFree 2.4 GHz ISM-bandSecurityLimited, WEP insecure, SSIDAvailabilityMany products and vendorsConnection set-up timeConnectionless/always onQuality of ServiceBest effort, no guarantees (unless polling is used, limited support in products)ManageabilityLimited (no automated key distribution, sym. Encryption)ProsMany installed systems and vendorsAvailable worldwideFree ISM-bandConsHeavy interference on ISM-bandNo service guaranteesRelatively low data rate
23 IEEE 802.11a Data rate Transmission range Frequency Security 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNRUser throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54)6, 12, 24 Mbit/s mandatoryTransmission range100m outdoor, 10m indoorE.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 mFrequencyFree , , GHz ISM-bandSecurityLimited, WEP insecure, SSIDAvailabilitySome products, some vendorsConnection set-up timeConnectionless/always onQuality of ServiceBest effort, no guarantees (same as all products)ManageabilityLimited (no automated key distribution, sym. Encryption)ProsFits into 802.x standardsFree ISM-bandAvailable, simple systemUses less crowded 5 GHz bandHigher data ratesConsShorter 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 bandOFDM and codification PBCCBackward compatibility IEEE bThey can co-exist in the same WLANNew 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 a/b/g CardBus Wireless LAN Client Adapter
26 WiFi and healthRFR's biological effects are measured in terms of specific absorption rate (SAR) -- how much energy is absorbed into human tissue -- which is expressed in Watts per kilogram (W/kg). A dangerous level (by U.S. standards) is considered to be anything above 0.08 W/kg. Thus far, RFR measurements for Wi-Fi, both at home and abroad, are a minute fraction of emissions that could amount to this level. Wi-Fi, in fact, emits less than other common sources of RFR like microwaves and mobile phones. Since mobile phones were recently cleared as a potential carcinogen by a comprehensive, long-term study conducted by the Danish Institute of Cancer Epidemiology in Copenhagen, it seems very unlikely that devices emitting a lower (and less frequent) level could be more dangerous.By Naomi Graychase, January 12, 2007More information:
27 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
28 Available architectures Independent Basic Service Set (IBSS)is the simplest of all IEEE 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 The MAC basics CSMA/CA with binary exponential backoff The protocol, at its minimum, consists of two frames: data and ackPoint Coordination Function (PCF)Distributed Coordination Function (DCF)MACServices withoutcontentionServices withThe 5 timing values:Slot timeSIFS: short interframe space (< slot time)PIFS: PCF interframe space (=SIFS+1slot)DIFS: DCF interframe space (=SIFS+2slots)EIFS: extended interframe spaceDIFSPIFSSIFSContention windowdefer accessbusy mediumslot
30 DCF exampleThe 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 transmissionB1 = 25B2 = 20B1 = 5B2 = 15datawaitdatawaitB2 = 10B1 and B2 are the backoff intervals in STA 1 and 2CW = 31
31 A couple of problematic configurations Exposed nodeHidden nodeAABCBCD
32 Hidden nodes situations MU3 cannot hear MU1 or MU2 because of the distanceThe obstacle prevents MU1 and MU2 from hearing one another
33 RTS/CTS mechanism Based on the network allocation vector (NAV) source DIFS+contentionsourceRTSdataSIFSSIFSSIFSdestinationCTSACKDIFSOther STANAV (RTS)Contention windowNAV (CTS)defer access
34 PCF: Point Coordination Function Data+PollDATA+ACKBeaconACKStation 2 sets NAV(Network Allocation Vector)CF-EndPIFSSIFS(no response)CPPCSTA1Contention Free PeriodSTA2NAVResetTimeSTA3Station 3 is hidden to the PC, it does not set the NAV.It continues to operate in DCF.The beacons are used to maintain synchronization of the timers in the stations and to send control informationThe AP generates the beacons at regular intervalsThe stations know when the next beacon will arrivethe target beacon transmission time (TBTT) are announced in the previous beacon
35 Frames structure management (00) control (01), data (10), 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)SADATARA1Wireless DS-RA = BSSIDTo the APBSSIDRA = DAFrom the APIBSSAddr. 4Addr. 3Addr. 2Addr. 1From DSTo DSFunción
36 Addressing and DS bits AP Client Client Server Server DS RA (BSSID) TA SA/TAAPAPSARAClientAPDAClientDAServerServerSADATARA1Wireless DS-RA = BSSIDTo the APBSSIDRA = DAFrom the APIBSSAddr. 4Addr. 3Addr. 2Addr. 1From DSTo DSFunción
37 Services The IEEE 802.11 architecture defines 9 services Station services:AuthenticationDeauthenticationPrivacy WEPData deliveryDistribution services:Association generate a connection between a STA and a PCDisassociationReassociation like association but informing the previous PCDistributionintegrationSimilar 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 allowedState 1:unauthenticated,unassociatedClass 1framesSuccessful authenticationDeauthentication notificationState 2:authenticated,unassociatedClass 1 & 2 framesDeauthentication notificationSuccessful authentication or reassociationDisassociation notificationState 3:authenticated,associatedA STA can be authenticated by several AP but associated only with one APClass 1, 2 & 3 frames
39 BSSID y SSID BSSID (Basic Service Set Identity) SSID (Service Set ID) BSS: MAC address of the APAd-Hoc: 46 bits random numberSSID (Service Set ID)Known as the Network Name because it is basically the name that identifies the WLANLenght: 0~32 octets0: it is the broadcast SSIDUsed to distinguish WLAN among themThe access points and stations who want to connect to a single WLAN must use the same SSID
40 The Extended Service Set (ESS) BSSAPWLANLANDistribution System (DS)Inter-acces point 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 P Wireless LAN Links.Purpose of Project: ... including the concepts of Access Points and Distribution Systems. Implementation of these concepts where purposely not defined by P As 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 P 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 practicesStatusThe F Recommendation has been ratified and published in 2003.IEEE F was a Trial Use Recommended Practice. The IEEE 802 Executive Committee approved its withdrawal on February 03, 2006
42 Wireless Distribution System IEEE , WDS meansMultiple wireless “ports” inside the access-point, to wirelessly interconnect cells (access-points connecting to other access-points)pre-IEEE , 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 linksTotally wireless system without any wired backbones, needed in locations where large areas are to be covered and wiring is not possible
43 WDS examples Bridging two wired networks As a repeater to extend a network
44 Operational processes Traffic flow - WDS operation AP-1000 or AP-500Bridge learntableSTA-2AP-1000 or AP-5002Bridge learntableAvaya Wireless PC-CardSTA-12STA-2Association table2Avaya Wireless PC-CardSTA-2STA-12Association tableWireless BackboneSTA-1WDSRelayPacket for STA-2ACKWDSRelayPacket for STA-2ACKPacket for STA-2ACKBSS-BSTA-2STA-1BSS-A
56 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
57 Limitations of the MAC standard for QoS DCF (Distributed Coordination Function)Only support best-effort servicesNo guarantee in bandwidth, packet delay and jitterThroughput degradation in the heavy loadPCF (Point Coordination Function)Inefficient and complex central polling schemeUnpredictable beacon frame delay due to incompatible cooperation between CP and CFP modesTransmission time of the polled stations is unknown
58 Overview of eTask group e formed in Sep and Approved in July 2005Current version: IEEE P802.11e/D13.0Backwardly compatible with the DCF and PCFNew QoS mechanism: HCF (Hybrid Coordination Function)Contention-based channel accessEDCA (Enhanced Distributed Channel Access)was Enhanced Distributed Coordination Function (EDCF)Controlled channel access (includes polling)HCCA (HCF controlled channel access)The station that operates as the central coordinator for all other stations within the same QoS supporting BSS (QBSS) is called the hybrid coordinator (HC).The HC reside inside an APA BSS that includes an e-compliant HC is referred to as a QBSS.
59 EDCA parameters for AC 4 access categories (AC), AIFS[AC] = SIFS + AIFSN[AC] * aSlotTime, AIFSN[AC] 2.
61 HCF: Hybrid Coordination Function During CFPPoll STAs and give a station the permission to access channelStarting time and maximum duration of each TXOP are specified by the HCDuring CPCan use the EDCA rulesHC can issue polled TXOPs in the CP by sending CF-Poll after a PIFS idle periodControlled ContentionAllows STAs to request the allocation of polled TXOPsSTAs send resource request frames with the requested TC and TXOP durationHC sends an ACK for resource request to the STA
66 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement toolsThanks to: Paul Young / Bernie Rasenberger
67 What is “Wireless N”?802.11n is the long anticipated update to Wi-Fi standards.Ratified by IEEE in September 2009.“Pre-N” wireless devices were available prior to ratification (Draft N) with speeds of up to 300Mb/s and range of up to 300 metres (300x300).Increases channel utilisation through MAC aggregation (40MHz) and increased range & throughput through the use of MIMO (Multiple Input/Multiple Output) technology of 2+ antennas.Will co-exist with b/g networks, but can degrade them because of channel overlap caused by MAC aggregation.Same performance hit if you mix n clients with b clients, as you get with mixing g & b clients (OFDM).
68 What is “Wireless N”? 802.11n Release Date November 2009 Speed 300 MbpsThroughput74 MbpsFrequency2.4GHz &/or 5.0GHzRange (outdoor)250 meters802.11n’s improved technology802.11n’s version of OFDM: a/g already uses OFDM (Orthogonal Frequency-Division Multiplexing) to achieve data rates of 54 Mbps n OFDM technology builds on a/g OFDM modulation by creating support for multiple channels (MIMO), allowing more bandwidth per channel, and higher code rates. This brings the maximum data rate of a single n OFDM channel to 65 Mbps.MIMO antenna systems: The n standard allows up to 4 MIMO transmit/receive antenna pairings n OFDM has a maximum data rate of 65 Mbps, multiplying that by the 4 MIMO antenna channels raises the data rate to 260 Mbps, which is a significant improvement when compared to 54 Mbps.40 MHz channels: To further improve data rates, n allows the use of 40 MHz channels-twice the existing 20MHz channels used by a/b/g-which effectively doubles the data rate to over 500 Mbps. 40 MHz channel size is also the most controversial tenet of the new standard, having the potential to disrupt existing a/b/g networks due to co-channel interference.Aggregation: Aggregation is an important feature developed to overcome shortcomings of having to be backward compatible with a/b/g networks. It improves mixed-mode performance and efficiency by bundling several frames together that are destined for n devices, while still being able to transmit single data frames to legacy devices.RIFS (Reduced Inter-Frame Spacing): RIFS is a required n feature that also improves performance by reducing the amount of dead time required between OFDM transmissions. It should be noted that this feature is restricted to greenfield deployments.
69 Why is it so fast? Spatial multiplexing With spatial multiplexing, the stream of data is split between 2 antennae and reassembled at the receiver. More data goes through in the same amount of time than when using a single antenna.
70 Why is it so fast? Support for 40Mhz Channels So far each b/g channel only used 20MHz of the spectrum. With more spectrum available, more data can go through.
71 Wireless N is also more reliable Through the use of Multipath we can achieve a more robust signalAntennas cleverly combine the same signal which has travelled through different paths. Even if the environment changes and some of the signal is obstructed, enough can still go through.This is how Wireless N achieves A ROBUST SIGNAL, less prone to interference and environmental changes.Resulting signalTransmitterReceiverMultiple copies of signal receivedAdjusted and combined signals
72 Deployment Considerations 802.11n can operate on 2.4 GHz or/and 5 GHz and is backward compatible with a/b/g. Access Points can be set to support 11n only.AP’s can be:single radio (2.4GHz only or 5GHz only)switchable dual radio (switchable between 2.4GHz and 5GHz)concurrent dual radio (operates 2.4GHz and 5GHz at the same time)
73 Deployment Considerations When introducing n into existing a/b/g WLANs both bands (2.4GHZ and 5GHz) can have n enabled.In case of dense AP architecture channel bonding for 2.4GHz should be disabled (set to 20MHz).Or if there are other 2.4GHz networks in the area – disable channel bonding for 2.4GHz.802.11n can be offered to throughput-critical clients only which support 11n: 5GHz band can be set as “11n only”. Leaving 2.4GHz for the rest of the clients which will not interfere with the critical data (802.11b/g/n).dual-radio n AP2.4GHz802.11b/g/n5GHz802.11n onlyHigh Speed Wi-FiLegacy mixed Wi-Fi802.11n client
74 The ‘Sting’Increased channel spectrum from 22Mhz to 40Mhz, using MAC aggregation techniques;Consumes 2 of 3 non overlapping 2.4Ghz channels;Not an issue in “pure N” networks, but will cause issues in hybrid networks;Uses OFDM, so if b clients on network performance degrades for all users.
75 Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards The 802 wireless familyIEEEThe physical layerThe MAC layerQuality of service: eMIMO: nManagement tools
76 Wireshark / EtherealWireshark is the world's foremost network protocol analyzer, and is the de facto (and often de jure) standard across many industries and educational institutions.Wireshark development thrives thanks to the contributions of networking experts across the globe. It is the continuation of a project that started in 1998.
77 Wireshark FeaturesDeep inspection of hundreds of protocols, with more being added all the timeLive capture and offline analysisStandard three-pane packet browserMulti-platform: Runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and many othersCaptured network data can be browsed via a GUI, or via the TTY-mode TShark utilityRich VoIP analysisRead/write many different capture file formats:Capture files compressed with gzip can be decompressed on the flyLive data can be read from Ethernet, IEEE , PPP/HDLC, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and othersDecryption support for many protocols, including IPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2Output can be exported to XML, PostScript®, CSV, or plain text
79 KismetKismet is an layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and can sniff b, a, and g traffic.Kismet identifies networks by passively collecting packets and detecting standard named networks, detecting (and given time, decloaking) hidden networks, and infering the presence of nonbeaconing networks via data traffic.Some of the featuresEthereal/Tcpdump compatible data loggingBuilt-in channel hopping and multicard split channel hoppingHidden network SSID decloakingGraphical mapping of networksManufacturer and model identification of access points and clientsDetection of known default access point configurationsRuntime decoding of WEP packets for known networksOver 20 supported card types
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