3.802.11n wlan 優(yōu)化

1、802.11n WLAN 優(yōu)化,Xie QingNov, 2009,802.11n WLAN 優(yōu)化特性,,ClientLink,對 11a/g 客戶端的波束成形,什么是 ClientLink?,思科稱之為 “Legacy Beam Forming”。區(qū)別于 802.11n 標(biāo)準(zhǔn)的“Beam Forming”，只作用于 802.11n 客戶端。通過兩個天線指導(dǎo)信號的強(qiáng)度指向客戶端的方向只工作在 OFDM 數(shù)據(jù)率只有 802.11a

2、/g 客戶端獲益802.11b 客戶端不會從中獲得任何好處需要:WLC 6.0 or higher1250 or 1140 Access Points,,,思科 ClientLink 技術(shù) 保護(hù)現(xiàn)有11a/g 設(shè)備的投資,,,802.11n,,挑戰(zhàn) #2: 在混合類型客戶端設(shè)備的網(wǎng)絡(luò)中提供公平,挑戰(zhàn) #1:延長11a/g 設(shè)備的使用壽命,,,,,802.11n,,300 Mbps,54 Mbps,,,,11a/g de

3、vices reaching max. performance but too costly to upgrade,11a/g devices consume valuable “airtime”, reducing the performance of 11n devices,,ClientLink 技術(shù)提供下列益處：為11a/g 設(shè)備提供一致的高吞吐量為11a/g 和 11n 設(shè)備增加顯著的系統(tǒng)容量在復(fù)雜而有挑戰(zhàn)性的射頻環(huán)境中

4、減少覆蓋漏洞,,,,,,,,,,,,,,,,,,,,,802.11a/g,未優(yōu)化的802.11a/g客戶端連接, 產(chǎn)生覆蓋漏洞,802.11n,X,現(xiàn)有的 802.11n 解決方案 波束強(qiáng)度沒有朝向客戶端,,,,ClientLink 技術(shù)通過波束成形將無線信號導(dǎo)向客戶端， 改善 802.11a/g 設(shè)備的性能和覆蓋,,波束成形,,,,,,,,,,,,,,802.11a/g,802.11n,思科 M-Drive ClientLink

5、 技術(shù) 思科的創(chuàng)新： 智能的波束成形,,射頻技術(shù)領(lǐng)先：波束成形,什么是波束成形 ?來自多個發(fā)射天線的信號被聚焦到接受客戶端:增加了覆蓋面積，提高連接數(shù)據(jù)率減少了無線信號的覆蓋盲點(diǎn),,,用戶獲益 ?所有的 802.11a/g 客戶端下行速率更快無線信號在更長的距離內(nèi)更穩(wěn)定可靠極大改善整個無線系統(tǒng)的性能,,,NO BEAM FORMING,BEAM FORMING,,,,,獲益 #1: 改善吞吐量ClientLink 技術(shù)為

6、11a/g設(shè)備提供更高的吞吐量,No Connection without ClientLink,Throughput vs. Distance,Test: 802.11a/g device with 802.11n networkSource: Miercom,,高達(dá) 65% 的吞吐量增長,13.6%,87.7%,70.4%,89.5%,ClientLink 技術(shù)允許客戶端以一致的高數(shù)據(jù)率連接。更快的數(shù)據(jù)傳輸，更少的重試 = 整體上

7、更有效的利用射頻信道。11a/g設(shè)備更快的處理意味著11n設(shè)備可以利用更多的“空口” 時(shí)間，同樣改善了11n設(shè)備的性能。,Test: 802.11a/g device measured at 16 antenna orientations w/ 802.11n networkSource: Miercom,獲益 #2: 更大的系統(tǒng)容量 在覆蓋區(qū)域內(nèi)提供一致的高吞吐量,,高達(dá) 27% 的信道容量增長,在16個不同位置測量吞吐量,Ch

8、annel Util of 74.2%,Channel Util of 45.2%,ClientLink Disabled,ClientLink Enabled,Lower Data Rates,Higher Data Rates,Source: Miercom; AirMagnet 6.0 Iperf Survey,獲益 #3: 減少覆蓋漏洞ClientLink 技術(shù)提供更高的物理層數(shù)據(jù)率,ClientLink Disabled,C

9、lientLink Enabled,High Retry Rates,Low Retry Rates,Source: Miercom; AirMagnet 6.0 Iperf Survey,獲益 #3: 減少覆蓋漏洞 (cont.)ClientLink 技術(shù)交付更低的數(shù)據(jù)重試率,ClientLink可以做什么和不能做什么！,可以做什么:,改善802.11a/g 客戶端的性能clients 在一定的距離通過增加下行數(shù)據(jù)率，減少 80

10、2.11a/g 客戶端的“空口占用時(shí)間”在混合部署環(huán)境間接增加 802.11n 的吞吐量,不能做什么:,近距離改善性能使 802.11b 客戶端受益直接增加 802.11n 吞吐量,Cisco Internal,ClientLink 可以做什么,波束成型只有在數(shù)據(jù)率開始 下降時(shí)才能改善性能意味著 --> 如果連接質(zhì)量已經(jīng)很好 (例如數(shù)據(jù)率達(dá)到 54Mbps) ，沒有什么可以改善可衡量的優(yōu)勢:在蜂窩邊緣增加 信噪比

11、在蜂窩邊緣增加下行 數(shù)據(jù)率在蜂窩邊緣增加下行 吞吐量,Provides,Provides,Cisco Internal,基本事實(shí)流量類型,需要雙向流量 通知無線接入點(diǎn)將波束導(dǎo)向哪里TCP 下行 (TCP ACKs 提供無線射頻模塊需要的反饋信息)TCP 雙向UDP 雙向,Downstream Data,TCP ACK,,提供客戶端的位置并更新波束成型表,Cisco Internal,,基本事實(shí)閥值和擴(kuò)展性,Client

12、Link 只在客戶端的接收信號強(qiáng)度指示低于某一閥值時(shí)才發(fā)生作用對于 802.11a, 閥值為 -60dBm 或更弱對于 802.11g, 閥值為 -50dBm 或更弱一般在客戶端距離無線接入點(diǎn) ~40ft 或更遠(yuǎn)時(shí)發(fā)生作用ClientLink 可以對每個射頻模塊中的 15 個客戶端 產(chǎn)生作用對于雙頻AP – 總計(jì) 30 個客戶端當(dāng)波束成型表滿員, 最老的客戶端被新的客戶端取代15 并 不 是每個射頻模塊支持的最大客戶端數(shù)

13、量，每個射頻模塊支持的最大客戶端數(shù)量并不會被波束成型特性改變,Cisco Internal,基本事實(shí)每個射頻模塊 15 個波束成型客戶端,15 并 不 是每個射頻模塊支持的最大客戶端數(shù)量例如右圖:15 個波束成型客戶端6 個非波束成型客戶端共 21 個客戶端,如何配置Enabled per Network (11a/n or 11b/g/n),默認(rèn)為關(guān)閉,ClientLink（Beamforming）全局配置,Data Ra

14、tes need to support client hardware as well as user application requirements.,,如何配置Enabled per Radio (11a/n or 11b/g/n),默認(rèn)在所有 11n 射頻模塊上打開The network-level setting overrides the per radio setting,在單個無線接入點(diǎn)上配置 ClientLink（

15、Beamforming）,如何配置通過CLI,For the 802.11a network:(Cisco Controller) >config 802.11a disable network(Cisco Controller) >config 802.11a beamforming global enable(Cisco Controller) >config 802.11a enable network

16、For the 802.11b/g network:(Cisco Controller) >config 802.11b disable network(Cisco Controller) >config 802.11b beamforming global enable(Cisco Controller) >config 802.11b enable networkShow configuration sta

17、tus:(Cisco Controller) >show 802.11a802.11a Network.................................. Enabled11nSupport....................................... EnabledLegacy Tx Beamforming setting.................... Enabled,Clie

18、ntLink 故障排查,SSH/Console into AP when running commandsTo show that ClientLink is enabled on a radio:AP#show controllers | inc BeamLegacy Beamforming: Configured Yes, Active Yes, RSSI Threshold -50 dBmLegacy Beamformin

19、g: Configured Yes, Active Yes, RSSI Threshold -60 dBmTo show that ClientLink is beam forming to a particular clientAP#show interface dot11radio 1 lbf rbfRBF Table:Index Client MAC Reserved Valid Tx BF

20、Aging 1 0040.96BA.45A0 Yes Yes Yes No,,Beam Forming is Active,Cisco Internal,ClientLink 故障排查,To show number of beam formed packets:AP#show controllers dot11Radio 1 | beg LBF LBF

21、 Indx BfPkts NbfPkts BfTmr PktCnt0016.6fbe.16c6 RIA 1 48384 19059 4 5781,Beam Formed Packets,Client MAC Address,參考資料（中英文版）,Cisco M-Drive Technology: Simplify 802.11n Adoptionhttp://www.ci

22、sco.com/en/US/solutions/collateral/ns340/ns394/ns348/ns767/solution_overview_c11-516378.htmlCisco M-Drive 技術(shù)：簡化 802.11n 的采用http://www.cisco.com/web/CN/products/products_netsol/wireless/pdf/wireless_wb_1.pdfCisco Clie

23、ntLink: Optimized Device Performance with 802.11nhttp://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10092/white_paper_c11-516389.htmlCisco ClientLink：通過 802.11n 優(yōu)化設(shè)備性能http://www.cisco.com/web/CN/products/pro

24、ducts_netsol/wireless/pdf/wireless_wb_8.pdfMiercom Lab Testing Summary Report for Cisco ClientLinkhttp://www.cisco.com/en/US/solutions/collateral/ns340/ns394/ns348/ns767/Miercom_Test_Report_Cisco_ClientLink.pdfMierco

25、m 關(guān)于 Cisco ClientLink 的實(shí)驗(yàn)室測試總結(jié)報(bào)告http://www.cisco.com/web/CN/products/products_netsol/wireless/pdf/wireless_wb_2.pdf,參考資料,思科 11n 部署指南http://www.cisco.com/web/CN/products/products_netsol/wireless/pdf/wireless_cg_9.pdfCi

26、sco Networker 2009 BRKAGG-3012 設(shè)計(jì)和部署 802.11n 無線網(wǎng)絡(luò)\\bej-filer01b\wg-e\enterprisemobility\Published\04.Solution\SolutionSlide\802.11n_Solution\Desing&Deploy\BRKAGG-3012 設(shè)計(jì)和部署 802.11n 無線網(wǎng)絡(luò)(XieQing)20090619 v2.pptWNBU

27、TME ClientLink SiteIncludes a ClientLink test plan, results spreadsheet and scripted Iperf packagehttp://wnbu-tme.cisco.com/dokuwiki/doku.php/tme/clientlink,Aruba’s ARM 2.0 – 11n Preferred Access,聲稱: 11n 客戶端不會被速度較慢的11a

28、/g 客戶端 ‘處罰’ 漏洞:以犧牲現(xiàn)有的11a/g客戶端性能為代價(jià)增加11n 客戶端的性能。其結(jié)果是不公平的空口占用時(shí)間。,DownstreamThroughputComparison,Aruba’s ARM 2.0 – 11n Preferred AccessResult: Airtime Unfairness,11a Client – 5.4MbpsTotal – 77.3Mbps,11a Client – 12.5M

29、bpsTotal – 67.2Mbps,Aruba 提供 15% 的匯聚改善，但是 11a的性能下降 130%,Aruba’s ARM 2.0 vs. Cisco’s ClientLink,11a/g 客戶端的性能 下降11n 客戶端獲得大量帶寬這只適合所有的客戶端是 802.11n 客戶端的部署理想場景, 但是理想和現(xiàn)實(shí)的巨大差距是11a/g客戶端到處都是。Preferred access 是 ‘a(chǎn)irtime unfai

30、rness’,11a/g 客戶端的性能 增加11a/g 客戶端運(yùn)行在最大的數(shù)據(jù)率增強(qiáng)現(xiàn)有客戶端的性能并 減少他們空口占用時(shí)間，以便將介質(zhì)交與11n客戶端傳輸。,目標(biāo)的差異造成結(jié)果的不同,Cisco: 最大化 802.11a/g 客戶端性能結(jié)果:改善整個系統(tǒng)的性能包括 802.11a/g 和 802.11n 客戶端11a/g客戶端獲得更高的數(shù)據(jù)速率消耗較少的空口時(shí)間，從而減少與11n客戶端的介質(zhì)競爭，11n客戶端同時(shí)獲得高性能，

31、系統(tǒng)總體也大幅增加。Aruba:當(dāng) 802.11a/g 客戶端關(guān)聯(lián)時(shí)最大化 802.11n 客戶端性能結(jié)果: 只改善11n 客戶端性能但是沒有改善整個系統(tǒng)的性能雖然現(xiàn)有的11a/g客戶將逐漸被取代，但是他們還將在很長的時(shí)間內(nèi)和11n客戶端共存，他們的帶寬需求仍然必須兌現(xiàn)。,ClientLink Caveats,Clients may roam further with it enabledBased on the implem

32、entation of client roaming algorithmsSince RSSI is increased, a client roaming based on this metric will roam at a different point,ClientLink Roaming Impact,,Iteration 1 – ClientLink On,Iteration 2 – ClientLink Off,11ft

33、,,BandSelect,將雙頻客戶端導(dǎo)向 5GHz 頻段,,5,2.4,,,Optimized RF Utilization by Moving 5 GHz Capable Client Out of the Congested 2.4 GHz Channels,802.11n,BandSelectAccess Point Assisted 5 GHz Band Selection,Dual-Band Client Radio2.

34、4/5GHz,Discovery ProbesLooking for AP,,Solution,BandSelect directs clients to 5 GHz optimizing RF usageBetter usage of the higher capacity 5GHz bandFrees up 2.4 GHz for single band clients,,Challenge,Dual-Band clients

35、 persistently connect to 2.4 GHz2.4GHz may have 802.11b/g clients causing contention2.4GHz is prone to interference,BandSelect in ActionPacket Capture,Client Probes on 2.4GHzInfrastructure doesn’t respond,Client Pro

36、bes on 5GHzInfrastructure responds,BandSelectAlgorithm,Probe suppression Identify dual band clients (2.4GHz and 5GHz capable) Suppress immediate probe response on 2.4 GHz channels Wait for dual band clients to scan

37、 into 5 GHz channels Do not respond to dual-band capable client on 2.4 GHzAccommodate 2.4GHz clients and dual band clients that fall back to 2.4GHz Time-out dual-band client 2.4GHz probe response suppression Mark 2.4

38、 GHz only clients and respond with probes,BandSelect Implementation,Distributed algorithmAlgorithm runs on AP firmwareConfiguration on controllerOff by defaultGlobal configuration for the algorithm parametersGlobal

39、 On/Off configurationPer WLAN ‘override’ controlSupport on 1140 and 1250 Access Points onlyImplemented in 6.0 releaseSupported in 6.0 MR1 release,(Cisco Controller) >config band-select probe-response enable WARNI

40、NG: Allowing global band-select may impact time sensitive application like VOICE. Continue? (y/N) y(Cisco Controller) >show band-select Band Select Probe Response.................... Enabled Cycle Count..........

41、......................... 3 cycles Cycle Threshold............................... 200 milliseconds Age Out Suppression........................... 20 seconds Age Out Dual Band............................. 60 seconds,Ba

42、ndSelectConfiguration,WLC,,BandSelectConfiguration,WLC,(Cisco Controller) >config band-select probe-response enable WARNING: Allowing global band-select may impact time sensitive application like VOICE. Continue?

43、(y/N) y(Cisco Controller) >show band-select Band Select Probe Response.................... Enabled Cycle Count................................... 3 cycles Cycle Threshold............................... 200 millis

44、econds Age Out Suppression........................... 20 seconds Age Out Dual Band............................. 60 seconds Client RSSI................................... -80 dBm,BandSelectConfiguration – Parameters,C

45、ycle Count (Default: 2)Number of client probe cycles to wait before marking client as 2.4GHz-onlyCycle Threshold (Default: 200msec)How long a client probe scanning cycle isAge Out Suppression (Default: 20 seconds)If

46、 any probe from a client is not seen within this time, the client is removed from the BandSelect tableAge Out Dual Band (Default: 60 seconds)If a 5GHz probe from the client is not seen within this timeout, the client i

47、s no longer considered dual-bandClient RSSI (Default: -80dBm)Minimum client RSSI for probe responses to be sent to client,BandSelectConfiguration – Per-SSID Override,WLC,(Cisco Controller) >config wlan disable 2 (

48、Cisco Controller) >config wlan band-select allow disable 2 (Cisco Controller) >config wlan enable 2(Cisco Controller) >show wlan 2 WLAN Identifier.................................. 2 Network Name (SSID)......

49、........................ NoBandSelectBand Select...................................... Disabled,Band Select can introduce latency in connecting and roaming situationsThis latency is harmless for data applications but c

50、an negatively impact real-time applications.Recommendation: Disable band-select for WLANs that handle real-time applications such as voice and videoExample Below – disable band select for a specific WLAN,BandSelectCon

51、figuration – Per-SSID Override Cont’d,BandSelectViewing Statistics,Navigate to the ‘Monitor’ tab on the WLC GUI and click ‘Access Points -> Radios -> 802.11b/g/n’ then ‘Detail’.,,BandSelectViewing Statistics,WLC,

52、(Cisco Controller) >show ap stats 802.11b …………………………Band Select Stats Num of dual band client ....................... 26 Num of dual band client added.................. 64 Num of dual band client expired .....

53、.......... 38 Num of dual band client replaced............... 0 Num of dual band client detected .............. 0 Num of suppressed client ...................... 57 Num of suppressed client expired...............

54、 4602 Num of suppressed client replaced.............. 0,,,,,BandSelect Caveat — Roaming Delay,,2.4G band,5G band,,,No Delay,Some Delay (1.5s),Possible Delay,,Data Rate Tuning,優(yōu)化傳輸效果,Data Rate Tuning — Why?,Frame Size

55、vs. Channel TimeMeasured in Microseconds,Average Beacon Size,Using 12Mbps is ~10X more efficient than 1Mbps!,Real World ImprovementChannel Utilization from 40% to 5%,Optimizing Data RatesConfiguration,For 802.11b/g d

56、eploymentsDisable: 1, 2, 5.5, 6 and 9MbpsFor 802.11g-only deploymentsDisable: 1, 2, 5.5, 6, 9 and 11MbpsFor 802.11a deploymentsDisable: 6 and 9 MbpsEnsure one rate is always kept ‘mandatory’Higher rates can also b

57、e disabled (ex. 12, 18Mbps) – dependant on deployment,Tuned 802.11b/g Data Rates:,Optimizing Data RatesCaveats,Data rate changes are global across the controller and unique per frequency bandIndividual APs cannot be ‘t

58、uned’ differentlyDisabling too many data rates can decrease the maximum range of Access PointsDo not disable all 802.11b rates unless you have no 802.11b clients,,Load Balancing,將客戶端分布到多個無線接入點(diǎn),New Client Joining Netwo

59、rk,,,Load BalancingConcept,,,,Load,Min,Max,,,,Load,Min,Max,Assoc Req.,Denied,Assoc Req.,Success,Load Balancing in ActionPacket Capture,,,AP is loaded.AssociationDenied,Association Allowed,Load BalancingImplementatio

60、n,The threshold to start load balancing is configured as a number of clientsAssociation denied (Code 17) frames will be sent to clients who attempt to associate to loaded APsIf the client does not join a different AP,

61、the “l(fā)oaded” AP will allow the client to associate after a number of retries (default is 3)Configured on a per-controller basis at a global levelCan be overridden for specific WLANs,Load Balancing Configuration,(Cisco

62、 Controller) >config load-balancing aggressive enableWARNING: Allowing load balance may impact time sensitive application like VOICEContinue? (y/N)y(Cisco Controller) >show load-balancingAggressive Load Bala

63、ncing........................ EnabledAggressive Load Balancing Window................. 5 clientsAggressive Load Balancing Denial Count........... 3StatisticsTotal Denied Count............................... 0 client

64、sTotal Denial Sent................................ 0 messagesExceeded Denial Max Limit Count.................. 0 timesNone 5G Candidate Count.......................... 0 timesNone 2.4G Candidate Count................

65、........ 0 times,WLC,,Load BalancingConfiguration — Per-SSID Override,WLC,(Cisco Controller) >config wlan disable 2 (Cisco Controller) >config wlan load-balance allow disable 2 (Cisco Controller) >config wlan

66、 enable 2(Cisco Controller) >show wlan 2 WLAN Identifier.................................. 2 Network Name (SSID).............................. NoLoadBalanceLoad Balancing................................... Disabled

67、,Load Balancing can introduce latency in the association and roaming processThis latency is harmless for data applications but can negatively impact real-time applications.Recommendation: Disable load balancing for WLA

68、Ns that handle real-time applications such as voice and videoExample Below – disable load balancing for a specific WLAN,Load BalancingCaveats,Load balancing only occurs amongst APs on the same controllerLoad balancing

69、 requires that the client respect the “Code 17” association response and act accordinglyLoad Balancing only occurs at initial association, not on re-association.Some older clients simply ignore the “Code 17” response a