网络WiFi-香港大学802.11n无线部署介绍_英文
IEEE 802.11p的英文文档
Runtime Optimization of IEEE802.11Wireless LANs PerformanceLuciano Bononi,Marco Conti,and Enrico GregoriAbstract—IEEE802.11is the standard for Wireless Local Area Networks(WLANs)promoted by the Institute of Electrical and Electronics Engineers.Wireless technologies in the LAN environment are becoming increasingly important and the IEEE802.11is the most mature technology to date.Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism(i.e.,the backoff algorithm)can drive the IEEE802.11protocol close to its optimal behavior.To perform this tuning,a station must have exact knowledge of the network contention level;unfortunately,in a real case,a station cannot have exact knowledge of the network contention level(i.e.,number of active stations and length of the message transmitted on the channel),but it,at most,can estimate it.This paper presents and evaluates a distributed mechanism for contention control in IEEE802.11Wireless LANs.Our mechanism,named Asymptotically Optimal Backoff(AOB),dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE802.11WLAN asymptotically achieves its optimal channel utilization.The AOB mechanism measures the network contention level by using two simple estimates:the slot utilization and the average size of transmitted frames.These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol.AOB can be used to extend the standard802.11access mechanism without requiring any additional hardware.The performance of the IEEE802.11protocol,with and without the AOB mechanism,is investigated in the paper through simulation.Simulation results indicate that our mechanism is very effective,robust,and has traffic differentiation potentialities.Index Terms—Wireless LAN(WLAN),IEEE802.11,multiple access protocol(MAC),protocol capacity,performance analysis.æ1I NTRODUCTIONF OR decades,Ethernet has been the predominant networktechnology for supporting distributed computing.In recent years,the proliferation of portable and laptop computers has led to the development of the wireless LAN(WLAN)technology([28],[43]).The success of WLANs is connected to the development of networking products that can provide wireless network access at a competitive price.A major factor in achieving this goal is the availability of appropriate networking standards.IEEE Standard802.11defines a Medium Access Control(MAC) and Physical Layer(PHY)specification for a wireless local area network to provide wireless connectivity for fixed, portable,and moving stations within a local area[42].Two different approaches can be followed in the implementation of a WLAN:an infrastructure-based ap-proach or an ad hoc networking one([18],[25],[50]). Infrastructure-based802.11WLANs are currently widely used,while the use of IEEE802.11-based ad hoc networks is an open research issue([3],[21]).Since the wireless links will continue to have signifi-cantly lower capacity than wired links,the WLAN conges-tion is more problematic than in wired networks.In WLANs,the medium access control(MAC)protocol is the main element that manages congestion situations that may occur inside the network.For this reason,in this paper,we focus on the efficiency of the IEEE802.11MAC protocol and we propose a solution for increasing both protocol efficiency and protocol’s ability to react to congestion conditions.The IEEE802.11access scheme incorporates two access methods:Distributed Coordination Function(DCF)for asynchronous,contention-based,distributed access to the channel and Point Coordination Function(PCF)for centra-lized,contention-free access([42],[50]).PCF is intended to support real-time services(by using a centralized polling mechanism),but is not generally supported by current cards. Hereafter,we will concentrate our study on DCF only.The DCF is based on a Carrier Sensing Multiple Access protocol with Collision Avoidance,CSMA/CA,see,for example,([19],[38],[53]).The CSMA/CA protocol is typically adopted in a wireless environment due to its reliability, flexibility,and robustness.However,the performance of a WLAN based on the CSMA/CA protocol may be degraded by the presence of hidden terminals[54].A pair of stations is referred to as being hidden from each other if a station cannot hear the transmission from the other station.This event makes the carrier sensing unreliable as a station wrongly senses that the wireless medium has been idle while the other (hidden)station is transmitting.To avoid the hidden terminal problem,the CSMA/CA protocols are extended with a virtual carrier sensing mechanism,named Request To Send (RTS)/Clear To Send(CTS).This mechanism has been studied extensively;several variations and analyses of the RTS/CTS scheme can be found in the literature,see,for example,([4], [31],[29],[32]).IEEE802.11includes an optional RTS/CTS mechanism.In this work,we do not explicitly consider the RTS/CTS mechanism.The results presented hereafter always refer to the data transmission using the basic access only.A.L.Bononi is with the Department of Computer Science,University ofBologna,Mura Anteo Zamboni,7,40127Bologna,Italy.E-mail:bononi@cs.unibo.it..M.Conti and E.Gregori are with the National Research Council(CNR),IIT Institute,Via G.Moruzzi,1,56124Pisa,Italy.E-mail:{marco.conti,enrico.gregori}@r.it.Manuscript received14Mar.2001;revised5Aug.2002;accepted29May2003.For information on obtaining reprints of this article,please send e-mail to:tpds@,and reference IEEECS Log Number113793.1045-9219/04/$17.00ß2004IEEE Published by the IEEE Computer Societymethodology for analyzing the optimal tuning of the backoff algorithm when a portion of the traffic is transmitted using the RTS/CTS mechanism can be found,for example,in([6], [13]).In addition,recent simulation and experimental results indicate that phenomena occurring at the physical layer make the effectiveness of the RTS/CTS mechanism arguable since the hidden station phenomenon rarely occurs([56],[11],[23]).The relevance of the IEEE802.11standard has generated extensive literature on its MAC protocol.A complete survey of the IEEE802.11literature is out of the scope of this paper.Below,we will show the main research areas together with some related references.Simulation studies of the IEEE802.11protocol performance are presented in([62] [2]).IEEE802.11analytical models are proposed and evaluated in([5],[6],[16],[17],[20],[59],[60]).The use of the PCF access method for supporting real-time applica-tions is investigated in([26],[57]).The optimization of the DCF mechanism from the power-saving standpoint is investigated in([7],[44]).Recently,considerable research activity has concentrated on supporting service differentia-tion on the IEEE802.11DCF access method(e.g.,[49],[58], [1],[47]),and on the use of IEEE802.11for constructing multihop ad hoc networks([63],[64]).In this paper,we propose and evaluate a mechanism, Asymptotically Optimal Backoff(AOB),for improving the efficiency of the IEEE802.11standard protocol.In the literature,it is extensively recognized that the backoff algorithm plays a crucial role in achieving a high aggregated throughput and a fair allocation of the channel to the stations,see[4].To meet this target,the backoff value should reflect the actual level of contention for the media. The IEEE802.11adopts a binary exponential backoff protocol([42],[36],[38])which does not always adequately guarantee the best time-spreading of the users’access for the current congestion level.Each station,to transmit a frame,accesses the channel within a random self-defined amount of time whose average length depends on the number of collisions previously experienced by the station for that frame.When the network is congested,for each transmitted frame,a station must experience several collisions to increase the backoff window size,thus achieving a time spreading of the transmission attempts that is adequate for the current congestion level.No experience from the previous transmitted frame is exploited.On the other hand,our AOB mechanism extends the binary exponential backoff algorithm of IEEE802.11to guarantee that the backoff interval always reflects the current congestion level of the system(in the standard backoff,any new transmission assumes a low congestion level in the system).Our mechanism forces the network stations to adopt a backoff window size that maximizes the channel utilization1for the current network condition. There are two main factors that reduce the channel utilization:collisions and idle periods(introduced by the spreading of accesses).As these two factors are conflicting (i.e.,reducing one causes an increase of the other),the optimal tuning of the backoff algorithm is approximately achieved by equating these two costs([15],[16],[30]).Since these costs change dynamically(depending on the network load),the backoff should adapt to congestion variations in the system.Unfortunately,in a real case,a station does not have an exact knowledge of the network and load configurations,but,at most,can estimate them.The most promising direction for improving backoff protocols is to obtain information of the network status through channel observation([34],[37],[45]).A great amount of work has been done on studying the information that can be obtained by observing the system’s parameters([33],[48],[55]).Our work follows the same direction of feedback-based proto-cols,but provides original contributions as it is based on an analytical characterization of the optimal channel utilization and uses a very simple feedback signal:slot utilization.Several authors have investigated the enhancement of the IEEE802.11backoff protocol to increase its performance. In[61],given the Binary Exponential Backoff scheme adopted by the Standard,heuristic solutions have been proposed for a better time spread of the transmission attempts.In([5],[6],[15],[16],[17]),feedback-based mechanisms have been proposed for adapting the station backoff to the network congestion and maximizing channel utilization.Recently,these mechanisms have been general-ized to achieve both optimal channel utilization and weighted fairness in an IEEE802.11network with traffic streams belonging to different classes[47].All the feedback-based mechanisms cited above are based on analytic models of an IEEE802.11network.These models provide the optimal setting of the backoff parameters for achieving the maximum channel utilization.Unfortunately,these methods require an estimation of the number of users in the system that could prove expensive,difficult to obtain, and subject to significant error,especially in high contention situations[17].The AOB mechanism proposed in this paper goes a step further:1.By exploiting the analytical characterization of theoptimal IEEE802.11channel utilization presented in[16],we show that the optimal value is almostindependent of the network configuration(numberof active stations)and,hence,the maximum channelutilization can be obtained without any knowledgeof the number of active stations.2.The AOB mechanism tunes the backoff parameters tothe network contention level by using two simple andlow-cost load estimates(obtained by the informationprovided by the carrier sensing mechanism):slotutilization and average size of transmitted frames.3.AOB extends the standard802.11access mechanismwithout requiring any additional hardware. Specifically,AOB schedules the frames’transmission accord-ing to the IEEE802.11backoff algorithm,but adds an additional level of control before a transmission is enabled.A transmission already enabled by the standard backoff algorithm is postponed by AOB in a probabilistic way.The probability of postponing a transmission depends on the network congestion level and is equal to one if the channel utilization tends to exceed the optimal value.The postponed transmission is rescheduled as in the case of a collision,i.e., the transmission is delayed by a further backoff interval.In this paper,via simulation,we have extensively evaluated the performance of the IEEE802.11access scheme,with and without the AOB mechanism.The IEEE 802.11performance has been investigated both in steady-state and under transient conditions.Furthermore,we also1.In the literature,the maximum channel utilization is called protocol capacity;see[22].For this reason,hereafter,maximum channel utilization and protocol capacity are used interchangeably.investigate the mechanism robustness to errors and its potential for traffic differentiation.The work is organized as follows:In Section2,we present a brief explanation of the IEEE802.11standard,and we sketch the critical aspects connected to the contention level of the system.In Section3,we present a simple mechanism to extend the IEEE802.11standard and,in Section4,we discuss its tuning.In Sections5,6,and7,the AOB performance is deeply investigated through simula-tion.Section8discusses an AOB potential for traffic differentiation.Conclusions and future research are out-lined in Section9.2IEEE802.11In this section,we only sketch the portions of the IEEE802.11 standard that are relevant for this paper.A detailed description can be found in([42],[13],[27]).The IEEE802.11standard defines a MAC layer and a Physical Layer for WLANs.The basic access method in the IEEE802.11MAC protocol is the Distributed Coordination Function(DCF),which is a Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA)MAC protocol.Besides the DCF,the IEEE802.11also incorporates an alternative access method known as the Point Coordination Function(PCF)—an access method that is similar to a polling system and uses a point coordinator to determine which station has the right to transmit.The DCF requires that every station,before transmitting, perform a carrier sensing activity to determine the state of the channel(idle or busy).If the medium is found to be idle for an interval exceeding the Distributed InterFrame Space(DIFS),the station continues with its transmission.If the medium is busy, the transmission is deferred until the ongoing transmission concludes.When the channel becomes idle,a Collision Avoidance mechanism is adopted.The IEEE802.11Collision Avoidance mechanism is a Binary Exponential Backoff scheme ([42],[36],[38],[39]).According to this mechanism,a station selects a random interval,called a backoff interval,that is used to initialize a backoff counter.When the channel is idle,the length of the time is measured in constant units(Slot_Time) indicated as slots in the following.The backoff interval is an integer number of slots and its value is uniformly chosen in the interval(0,CW_Size-1),where CW_Size,in each station is a local parameter defining the current station Contention Window size.Specifically,the backoff value is defined by the following expression[42]:Backo ff Counter¼INT RndðÞÁCW SizeðÞ; where Rnd()is a function that returns pseudorandom numbers uniformly distributed in[0,1).The backoff counter is decreased as long as the channel is sensed to be idle,stopped when a transmission is detected on the channel,and reactivated when the channel is sensed to be idle again for more than a DIFS.A station transmits when its backoff counter reaches zero.The Binary Exponential Backoff is characterized by the expression giving the dependency of the CW_Size parameter by the number of unsuccessful transmission attempts(N_A)already performed for a given frame.In[42],it is defined that the first transmission attempt for a given frame is performed adopting CW_Size equal to the minimum value CW_Size_min(assuming low contention). After each unsuccessful(re)transmission of the same frame,the station doubles CW_Size until it reaches the maximum value fixed by the standard,i.e.,CW_Size_MAX,as follows: CW SizeðN AÞ¼min CS Size MAX;CW Size minÁ2ðN AÀ1Þ: Positive acknowledgments are employed to ascertain a successful transmission.This is accomplished by the receiver(immediately following the reception of the data frame),which initiates the transmission of an acknowl-edgment frame(ACK)after a time interval Short InterFrame Space(SIFS),which is less than DIFS.If the transmission generates a collision,2the CW_Size parameter is doubled for the new scheduling of the retransmission attempt,thus further reducing contention.The increase of the CW_Size parameter value after a collision is the reaction that the IEEE802.11standard DCF provides to make the access mechanism adaptive to channel conditions.In[8],by analyzing the behavior of the IEEE 802.11DCF mechanism,it was shown that the channel utilization is negatively affected by the increase of the contention level.This occurs because1)the increase in the CW_Size is obtained at the cost of a collision,and2)after a successful transmission,no memory of the actual contention level is maintained.3L OW-C OST D YNAMIC T UNING OF THEB ACKOFF W INDOW S IZEThe drawbacks of the IEEE802.11backoff algorithm, explained in the previous section,indicate a direction for improving the performance of a random access scheme by exploiting the information on the current network conges-tion level that is already available at the MAC level. Specifically,the utilization rate of the slots(Slot Utilization) observed on the channel by each station is used as a simple and effective estimate of the channel congestion level.The estimated Slot Utilization must be frequently updated.For this reason,in[9],it was proposed that an estimate be updated by each station in every Backoff interval,i.e.,the defer phase that precedes a transmission attempt.A simple and intuitive definition of the slot utilization ðS UÞis then given by:S U¼Num Busy SlotsNum Available Slots;where:.Num_Busy_Slots,hereafter referred to as busy slots,is the number of slots in the backoff interval in whichone or more stations start a transmission attempt.Atransmission attempt can be either a successfultransmission or a collision;and.Num_Available_Slots is the total number of slots available for transmission in the backoff interval,i.e.,the sum of idle and busy slots.In the IEEE802.11standard mechanism,every station performs a Carrier Sensing activity and,thus,the proposed S_U estimate is simple to obtain.The information required to estimate S_U is already available to an IEEE802.11 station and no additional hardware is required.The current S_U estimate can be used by each station (before trying a“blind”transmission)to evaluate the2.A collision is assumed whenever the ACK from the receiver is missing.opportunity to either perform or defer the scheduled transmission attempt.In other words,if a station knows that the probability of a successful transmission is low,it should defer its transmission attempt.This can be achieved in an IEEE 802.11network by exploiting the DCC mechan-ism proposed in [9].According to DCC,each IEEE 802.11station performs an additional control (beyond carrier sensing and backoff algorithm)before any transmission attempt.This control is based on a new parameter,named Probability of Transmission P_T(...),whose value depends on the current contention level of the channel,i.e.,S_U .The heuristic formula proposed in [9]for P_T (...)is:P T S U;N A ðÞ¼1ÀS U N A ;where,by definition,S U assumes values in the interval [0,1],and N_A is the number of attempts already performed by the station for the transmission of the current frame.3The N_A parameter is used to partition the set of active stations in such a way that each stations’subset is associated with a different level of privilege to access the channel.Stations that have performed several unsuccessful attempts have the highest transmission privilege [9].The P_T parameter allows filtering the transmission attempts.When,according to the standard protocol,a station is authorized to transmit (backoff counter is equal to zero and channel is idle)in the protocol extended with the Probability of Transmission,a station will perform a real transmission with probability P_T ;otherwise (i.e.,with probability 1-P_T )the transmission is rescheduled as a collision would have occurred,i.e.,a new backoff interval is sampled.To better understand the relationship between the P_T definition and the network congestion level,we can observe Fig.1.In Fig.1,we show the P_T curves (for users with different N_A )with respect to the estimated S_U values.Assuming S_U is close to zero,we can observe that each station,independently of its number of performed attempts,obtains a Probability of Transmission (P_T )close to 1.This means that the proposed mechanism has no effect on the system and each user performs its accesses as in the standard access scheme,without any additional contention control.This point is significant as it implies the absence ofoverhead introduced in low-load conditions.The differ-ences in the users’behavior as a function of their levels of privilege (related to the value of the N_A parameter)appear when the slot utilization grows.For example,assuming a slot utilization close to 1,say 0.8,we observe that the stations with the highest N_A value obtain a Probability of Transmission close to 1,while stations at the first transmis-sion attempt transmit with a probability equal to 0.2.It is worth noting a property of the DCC mechanism:The slot utilization of the channel never reaches the value 1.Assuming S_U is close to or equal to 1,the DCC mechanism reduces the Probabilities of Transmission for all stations close to zero,thus reducing the network contention level.This effect is due to the P_T definition and,in particular,to the explicit presence of the upper bound 1for the slot utilization estimate.The DCC choice to use 1as the asymptotic limit for the S_U is heuristic and does not guarantee the maximum channel utilization.To achieve the maximum channel utilization,we need to know the optimal congestion level,i.e.,the optimal upper bound for the S_U value (opt_S_U).It is worth noting that,if opt_S_U is known,the P_T mechanism can be easily tuned to guarantee that maximum channel utilization is achieved.Intuitively,if the slot-utilization boundary value (i.e.,the value one for DCC)is replaced by the opt_S_U value,we reduce all the probabilities of transmission to zero in correspondence with slot utilization values greater than or equal to the opt_S_U .This can be achieved by generalizing the definition for the Probability of Transmission:P T opt S U;S U;N A ðÞ¼1Àmin 1;S U opt S UNA:ð1ÞSpecifically,by applying this definition of the transmission probability,we obtain the P_T curves shown in Fig.2.These curves were obtained by applying the generalized P_T definition with opt_S_U =0.80.As expected,the curves indicate the effectiveness of the generalized P_T definition to limit S_U to the opt_S_U value.The generalized Probability of Transmission provides an effective tool for controlling the congestion inside an IEEE 802.11WLAN in an optimal way,provided that the opt_S_U value is known.In the following,we will present a simple mechanism to set the opt_S_U value.Our mechanism is named Asymptoti-cally Optimal Backoff as it guarantees that the optimal utilization is asymptotically achieved,i.e.,for large M values.3.Atthe first transmission attempt,N Ais equal to 1.Fig.1.DCC probability of transmission.Fig.2.Generalized probability of transmission.4A SYMPTOTICALLY O PTIMAL B ACKOFF(AOB) M ECHANISMThe aim of the AOB mechanism is to dynamically tune the backoff window size to achieve the theoretical capacity limit of the IEEE802.11protocol.The AOB mechanism is simpler, more robust,and has lower costs and overhead introduced than the contention mechanisms proposed in[16],[17]. Specifically,the AOB mechanism requires no estimate of the number M of active stations.An accurate M estimate may be very difficult to obtain because M may be highly variable in WLANs.In this section,we exploit the results obtained from the analysis of the theoretical capacity limits of the IEEE802.11 protocol to develop the AOB mechanism.For this reason, below,we briefly summarize the results derived in[16].In [16],to study the protocol capacity,a p-persistent IEEE 802.11protocol was defined.This protocol differs from the standard protocol only in the selection of the backoff interval.Instead of the binary exponential backoff used in the standard,the backoff interval of the p-persistent IEEE 802.11protocol is sampled from a geometric distribution with parameter p.Specifically,at the beginning of an empty slot,a station transmits(in that slot)with a probability p, while it defers the transmission with a probability1-p and then repeats the procedure at the next empty slot.4Hence, in this protocol,the average backoff time is completely identified by the p value.By setting p¼1=ðE½B þ1Þ(where E½B is the average backoff time of the standard protocol5), the p-persistent IEEE802.11model provides an accurate approximation(at least from a capacity analysis standpoint) of the IEEE802.11protocol behavior[16].The IEEE802.11p-persistent model is a useful and simple tool for analytically estimating the protocol capacity in a network with a finite number,M,of stations operating in asymptotic conditions.Furthermore,to simplify the discussion,hereafter we assume that stations transmit messages whose lengths are a geometrically distributed (with parameter q)number of slots.By denoting with t slot the length of a slot,the average message length, m,is: m¼t slot=ð1ÀqÞ.By exploiting the p-persistent model,in[16],a closed analytical formula for the channel utilization, ,is derived¼ m=fðM;p;qÞ:ð2ÞBy noting that fðÞis a function of the protocol and traffic parameters,it results that,for a fixed network and traffic configuration(i.e.,constant M and q),the maximum channel utilization corresponds to the p value,p min,that minimizes fðÞ.Due to the correspondence(from the capacity stand-point)between the standard protocol and the p-persistent one,the IEEE802.11maximum channel utilization is closely approximated by adopting,in the standard protocol,a contention window whose average size is identified by the optimal p value,i.e.,E½CW ¼2=p minÀ1.The previous analysis shows that the IEEE802.11 theoretical capacity is identified by p min.Hereafter,we will show the relationship between p min and the opt_S_U value of the AOB mechanism.To this end,we will further elaborate the capacity analysis presented in[16].4.1Theoretical Capacity Limits:An Invariant Figure Results presented in this section(see Table1)point out that the increase in the number of active stations has an almost negligible impact on the theoretical capacity bounds,while the average payload size(indicated as MFS in the following)greatly affects the optimal utilization level.Results presented in Table1are numerically derived by computing the optimal p value,i.e.,p min,according to formulas presented in[16].Specifically,in this table,we report,for various network and traffic configurations (defined by the(M,q)couples),the p min values derived analytically as explained before.In this table,we also report for each configuration the value MÁp min.It is worth noting that,while p min is highly affected by the M value,given a q-value,the product MÁp min is almost constant.Specifically,results indicate that,for a given message length,the product MÁp min has an asymptotic value with respect to M.Furthermore,when M!4,the MÁp min values are very close to the asymptotic value. This is the reason for calling MÁp min an invariant figure, i.e.,for a given MFS,it is almost constant.Hereafter,we will analytically investigate the rationale behind the MÁp min quasi-constant value(for a given MFS). To perform this analysis,instead of the exact p min derivation presented in[16](it is too complex for our purpose),we approximate p min with the p value that satisfies the following relationship:E½Coll ¼E½Idle p Át slot;ð3ÞOptimal pValues4.On the other hand,in the standard protocol,a station transmits in theempty slot selected uniformly inside the current contention window.5.Note that E½B ¼ðE½CW À1Þ=2,where E½CW is the average contention window.。
802.11n简述
802.11k
一个无线基站可以要求另一个基站测量和报告如下情况： • 在那个基站的覆盖范围内，一个信道上或者所有信道上的基站数量。 • 每一个基站的信标信号强度。 • 在一个具体时间间隔期间接收的帧的数量，负载情况。 • 每一个信道上的无线局域网活动水平。 • 便携式电话和微波炉等设备对每个信道产生的非无线局域网无线电 活动。
中国规定2.4GHz 频段范围是2.4~2.4835GHz, 1-13信道 (1信道为2.412GHz，每两个相邻信道间隔为5MHz); 5GHz频段范围是5.725~5.825GHz, 149/153/157/161/165信 道(149信道为5.745GHz)
Frame Aggregation
MIMO增强- diversity（分集）
•天线数量多于空间流数量，则把多个天线组合起来或选 择一个天线组合的最佳子集 • 更好利用多余天线
• 可获得更大的覆盖范围：使用两根天线的输出组合来接
收一个空间流，获得更远的传输距离 • 发送分集/接收分集
MIMO增强 –Beam-forming（聚束）
802.11n
600Mbps >100Mbps
20MHz /& 40MHz
DataRate和吞吐量
DateRate
DataRate指物理层传输速率，是传输信号的速度，不管这是 数据帧还是其他的控制帧。11N提供最高达600M的物理层传 输速率
吞吐量
吞吐量指的是真正的数据载荷部分传输的速率。一般测试结果 大致为总传输速率的一半左右它是不计算诸如：TCP负载，MAC 头负载，和PHY负载，以及控制帧管理帧，和空闲时间，冲突 造成的负载等
MAC层增进 QoS，增加了包突发机制 ------
802.11无线局域网缩写词及中文含义（一）解析
802.11无线局域网缩写词及中文含义（一）解析802.11无线局域网缩写词及中文含义（一）ACK (acknowledgment)应答AID (association identifier)关联识别码AP (accss point)访问点ATIM (announceent traffic indication message)广播传输指示消息BSA (basic service area)基本服务区BSS (basic service set)基本服务集BSSID (basic service set identification)基本服务集识别码CCA (clera channel assessment)干净信道评价CCK (complemenetary code keying)补码键控CF (contention free)无竞争CFP (contention-free period)无竞争期CID (connection identifier)连接标识符CP (contention period)竞争期CRC (cyclic redundancy code)循环冗余码CS (carrier serse)载波侦听CTS (clear to send)允许发送CW (contention window)竞争窗口DA (destination address)目的地址DBPSK (differential binary phase shift keying)差分二进制相移键控DCE (data communication equipment)数据通信设备DCF (distributed coordination function)分布式协调功能DCLA (direct current level adjustment)直接电平调整DIFS (distributed (coordination function)interframe space)分布式（协调功能）帧间间隔DLL (data link layer)数据链路层DP (desensitization)减敏现象DQPSK (differential quadrature phase shift keying)差分正交相移键控DS (ditribution system)分发系统DSAP (destination service access point)目的服务访问点DSM (distribution system medium)分发系统媒介DSS (distribution system service)分发系统服务DSSS (direct sequence spread spectrum)直接序列扩频DTIM (delivery traffic indication message)交付传输指示信息ED (energy detection) 能量检测EIFS (extended interframe space)扩展帧间间隔EIRP (equivalent isotropically radiated power)等效全向辐射功率ERS (extended rate set)扩展速率集ESA (extended service area) 扩展服务域ESS (extended service set) 扩展服务集FC (frame control) 帧控制FCS (frame check sequence) 帧校验序列FER (frame error ratio) 帧差错率FH (frequency hopping) 跳帧FHSS (frequency-hopping spread spectrum) 跳帧扩频FIFO (first in first out)先进先出GFSK (Gaussian frequency shift keying)高斯频移键控HEC (Header Error Check)头部差错校验HR/DSSS (High Rate direct sequence spreadd spectrum using the Long Preamble and header)使用长前导和长头部的高速直接序列扩频HR/DSSS/short (High Rate direct sequence spreadd spectrum using the optional Short Preamble and header mode)使用可选的短前导和短头部的高速直接序列扩频HR/DSSS/PBCC (High Rate direct sequence spreaddspectrum using the optional packet binary convolutional coding mode and the Long Preamble and header) 使用可选分组二进制卷积编码方式和长前导和长头部的高速直接序列扩频HR/DSSS/PBCC/short (High Rate direct sequence spreadd spectrum using the optional packet binary convolutional coding mode and the optional Short Preamble and header)使用可选分组二进制卷积编码方式和可选短前导和短头部的高速直接序列扩频IBSS (independent basic service set)独立基本服务集ICV (integrity check calue)完整性检验值IDU(inteface data unit) 接口数据单元IFS (interframe space)帧间间隔IMP (intermodulation)互调保护IR (infrared)红外线（的）ISM (industrial,scientific.and medical)工业科学医疗IV (initialization vector)初始化矢量LAN (local area network)局域网LLC (logical link control)逻辑链路控制LME (layer management entity)层管理实体LRC (long retry count)长重发计数器LSB (least significant bit)最低位比特MAC (medium access control)媒介访问控制MDF (management-defined field)管理定义域MIB (management information base)管理信息库协议层管理实体MMPDU (MAC management protocol data unit)媒介访问控制管理协议数据单元MPDU (MAC protocol data unit)媒介访问控制协议数据单元MSB(most significant bit)最高位比特MSDU(MAC service data unit)媒介访问控制服务数据单元N/A(not applicable)不可用NAV(network allocation vector)网络分配矢量PC(point coordinator)集中协调器PCF(point coordination function)集中协调功能PDU(protocol data unit)协调数据单元PHY(physical [layer])物理层PHY-SAP(physical layer service access point)物理层服务访问点PIFS(point [coordination function] interframe space)集中协调功能帧间间隔PLCP(physical layer convergence protocol)物理层收敛协议PLME(physical layer management entity)物理层管理实体PMD(physical edium dependent)物理媒介依赖PMD-SAP(physical medium dependent service access point)物理媒介依赖服务访问点PN(pseudo-noise [code sequence])随机噪声（码序列）PPDU(PLCP protocol data unit)物理层收敛协议协议数据单元ppm(paresper million)百万分率，百万分之。
英文版04 IEEE 802.11无线网
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infrastructure vs. ad-hoc networks
infrastructure network
AP
AP wired network AP: Access Point
AP
ad-hoc network
4
802.11 - Architecture of an infrastructure network
clear channel assessment signal (carrier sense) modulation, coding channel selection, MIB
MAC Management
PMD Physical Medium Dependent
PHY Management
Direct communication within a limited range
802.11 LAN
STA1
IBSS1
STA3
Station (STA): terminal with access mechanisms to the wireless medium Independent Basic Service Set (IBSS): group of stations using the same radio frequency
STA2
IBSS2 STA5
STA4
802.11 LAN
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IEEE standard 802.11
fixed terminal mobile terminal
infrastructure network access point
application
网络WiFi-20100811-HKU Introduction
Introducing University of Hong Kong
Peter Li Associate IT Director
August 2010
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The University of Hong Kong Information Technology Services
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The University of Hong Kong Information Technology Services
Experience in HPC and research computing :
Advancing HPC services
Deploy high performance and large scale computing facilities, and the latest software technology
Select & implement a single centrally supported LMS
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The University of Hong Kong Information Technology Services
ITIL Roadmap
Assessment and project starts Post
Architecture, Arts, Business and Economics, Dentistry, Education, Engineering, Law, Science, Social Sciences, Medicine Graduate School School of Professional and Continuing Education (HKU SPACE) 21600 students 6,500 staffs
802.11N协议基础及网络部署
802.11g
54Mbps (实际25Mbps）
带宽的大幅度提升使得每个接入点可以接入更多的客户端。
全面向下兼容a/b/g
2.4 GHz 5.8 GHz
Not support
b only
g only, b/g mix, b only
n only, b/g/n mix, g/n mix,b/g mix, g only, b only n only, a/n mix, a only
技术要求
在传输速率方面，802.11n可以将WLAN的传输速 率由目前802.11a及802.11g提供的54Mbps，提供 到300Mbps甚至高达600Mbps；覆盖范围可以扩 大到好几平方公里，使WLAN移动性极大提高； 兼容其他标准(包括3G) 。
802.11N技术简介
产生原因
Wi－Fi联盟在802.11a/b/g后面的一个无线传输标 准协议， 为了实现高带宽、高质量的WLAN服务， 使无线局域网达到以太网的性能水平，802.11任 务组N（TGn）应运而生。
目录
802.11n 概述 802.11n 关键技术 影响802.11n速率的关键因素 802.11n设备部署
802.11n部署——部署策略
2010年Q4-2011年Q4：
新建网络：以11n设备为主。 原有网络扩容：新增11n设备，与原有11g设备 混合部署。 利用2-3年时间逐步替换原有11g设备，实现11g 向11n的平滑升级。
IP报文长度（byte）
1*1实际速率 （无加密） Mb/s
1500
512
88
20MHz 60 40MHz 120
802.11n无线局域网部署指南
射频链路
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空间复用
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保护间隔
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20 MHz 与 40 MHz OFDM 信道
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天线分集
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传输波束成形
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数据链路层增强
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帧聚合ቤተ መጻሕፍቲ ባይዱ
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块确认
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速度与吞吐量
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调制编码方式
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合规、设计与集成
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Wi-Fi CERTIFIED™ n 认证项目
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PoE
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现有的基础架构
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2.4 GHz 与 5 GHz 频段
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20 MHz 与 40 MHz 模式
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向后兼容
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客户设备
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VoWiFi
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安全
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站点勘测
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迁移与部署策略
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结语
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802.11n 无线局域网部署指南
概述
1997 年，电子与电气工程师协会（IEEE）在 802.11 原始标准中对无线局域网（WLAN） 技术首次做出了定义。最初的 WLAN 设备采用称为直接序列扩频（DSSS）或跳频扩频（FHSS） 的射频技术，支持 1 Mbps 与 2 Mbps 的数据速率。从 1997 年开始，随着 IEEE 对 802.11 标 准进行修订以支持新的技术，WLAN 的数据速率逐渐增加。1999 年批准通过的 802.11a 修正 案采用正交频分复用（OFDM）技术，在 5 GHz 频段上支持 6～54 Mbps 的数据速率。同年， 802.11b 修正案定义的高速直接序列扩频（HR-DSSS）机制可在广泛使用的 2.4 GHz 频段上 支持 5.5 Mbps 与 11 Mbps 的数据速率。2003 年，IEEE 批准通过了 802.11g 修正案，后者同 样采用 OFDM 技术，在 2.4 GHz 频段上支持 6～54 Mbps 的数据速率。用户与企业一直期待 802.11-2009 修正案，它定义的高吞吐量（HT）技术可支持高达 600 Mbps 的数据速率。802.11n 技术增强并优化了物理层与 MAC 子层，从而支持如此高的数据速率。
WLAN--802.11N协议基础及网络部署
TD-SCDMA 2.8M TD-LTE 173M
802.11g
54Mbps (实际25Mbps）
带宽的大幅度提升使得每个接入点可以接入更多的客户端。
全面向下兼容a/b/g
2.4 GHz 5.8 GHz
Not support
b only
g only, b/g mix, b only
n only, b/g/n mix, g/n mix,b/g mix, g only, b only n only, a/n mix, a only
802.11n 关键技术 802.11n 的技术优势 影响802.11n速率的关键因素 802.11n设备部署
影响802.11n速率的关键因素——CSMA/CA机制
WLAN 采用CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) 机制来解决冲突问题。 终端在发送数据前首先监听信道，如果信道空闲，则随机退避一 个时间，如果这个时间内没有其他终端抢占信道，终端等待完后 可以立即占用信道并传输数据。 CSMA/CA决定了：终端越多，则冲突规避开销越大，信道可用 带宽越低。
MIMO：具有多个独立的接收和传输路径的无 线电射频系统，是11n的核心技术。 MIMO-OFDM：将高速码流拆分成多个低速码 流，每个低速码流在相同的频点上分别由不同 的天线同时发送。码流在接收端进行整合。
802.11n关键技术——信道捆绑技术
1Mbps 20MHz Channel 1Mbps 20MHz Channel 40MHz Channel 2Mbps
直接信号
反射信号
反射信号
802.11n关键技术-帧聚合技术
帧聚合技术原理：
802.11N关键技术介绍
802.11n关键技术标准发展历程IEEE 802.11工作组意识到支持高吞吐将是WLAN技术发展历程的关键点，基于IEEE HTSG （High Throughput Study Group）前期的技术工作，于2003年成立了Task Group n (TGn)。
n表示Next Generation，核心内容就是通过物理层和MAC层的优化来充分提高WLAN 技术的吞吐。
由于802.11n涉及了大量的复杂技术，标准过程中又涉及了大量的设备厂家，所以整个标准制定过程历时漫长，预计2010年末才可能会成为标准。
相关设备厂家早已无法耐心等待这么漫长的标准化周期，纷纷提前发布了各自的11n产品(pre-11n)。
为了确保这些产品的互通性，WiFi联盟基于IEEE 2007年发布的802.11n草案的2.0版本制定了11n 产品认证规范，以帮助11n技术能够快速产业化。
根据WIFI联盟2009年初公布的数据，802.11n产品的认证增长率从2007年成倍增长，截至目前全球已经有超过500款的11n设备完成认证，2009年的认证数量必将超出802.11a/b/g。
技术概述802.11n主要是结合物理层和MAC层的优化来充分提高WLAN技术的吞吐。
主要的物理层技术涉及了MIMO、MIMO-OFDM、40MHz、Short GI等技术,从而将物理层吞吐提高到600Mbps。
如果仅仅提高物理层的速率，而没有对空口访问等MAC协议层的优化，802.11n的物理层优化将无从发挥。
就好比即使建了很宽的马路，但是车流的调度管理如果跟不上，仍然会出现拥堵和低效。
所以802.11n对MAC采用了Block确认、帧聚合等技术，大大提高MAC层的效率。
802.11n对用户应用的另一个重要收益是无线覆盖的改善。
由于采用了多天线技术，无线信号（对应同一条空间流）将通过多条路径从发射端到接收端，从而提供了分集效应。
在接收端采用一定方法对多个天线收到信号进行处理，就可以明显改善接收端的SNR，即使在接受端较远时，也能获得较好的信号质量，从而间接提高了信号的覆盖范围。
无线通信 Lecture 11 802.11
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Named “Wi-Fi” by the Wireless Ethernet Compatibility Alliance ()
Goal is to promote interoperability between vendors’ products.
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802.11g – 54 Mbps in the 2.4 GHz band
The goal is to give insight into areas of potential research and economic development.
2
I. The IEEE 802 Family of Standards
The Institute of Electrical and Electronics Engineers
3
Created by the IEEE LAN /MAN Standards Committee (LMSC)
Started in 1980
Working Groups
802.1 High Level Interface (HILI) Working Group (active) 802.2 Logical Link Control (LLC) Working Group (hibernating) 802.3 CSMA/CD Working Group (active) – Ethernet, standard for wired LAN’s 802.4 Token Bus Working Group (hibernating)
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802.11a – 54 Mbps in the 5.8 GHz band
Uses OFDM (Orthogonal Frequency Division Multiplexing)
WLAN 802.11n关键技术介绍及组网规划建议
WLAN 802.11n关键技术介绍及组网规划建议随着WLAN 802.11n标准的发布和产业链的不断成熟，支持802.11n的网络设备和终端产品普及率逐步提高。
802.11n不仅能够提供更高的接入速率，同时还具备很好的向下兼容型，可兼容802.11a/b/g标准，因此，在目前WLAN网络建设中802.11n将会成为主流。
但是，802.11n标准中引入了许多新的技术，使得802.11n具备了比以往802.11系列标准更多的可选特性，网络配置要比802.11g设备复杂，提升了网络规划的难度。
我们需要了解802.11n 各特性对网络性能的影响，合理的规划设计网络，充分发挥802.11n的网络性能。
一、802.11n的关键技术IEEE 802.11n技术通过物理层和MAC层的优化来充分提高WLAN网络的吞吐量，使带宽从802.11a/g的54Mbps提升到600Mbps。
1.1 物理层关键技术物理层引入的关键技术主要包括MIMO（多入多出）、更多子载波、信道绑定、Short GI （Guard Interval）等。
1.1.1MIMOMIMO是802.11n物理层的核心，802.11n通过使用MIMO（多入多出）技术，无线传输同时发送多个无线信号，并且利用多径效应，形成多个空间流，可以成倍提高数据传输速度。
在802.11n标准中定义了1～4空间流的MIMO技术，如采用2空间流可以将802.11的速率提升2倍，采用4空间流可以将802.11的速率提升四倍，达到600Mbps。
目前的802.11n 产品普遍支持到2空间流，理论峰值速率可达300Mbps。
1.1.2更多的子载波OFDM在802.11a/g时代已经成熟使用，与802.11a/g 相比，802.11n将20MHz带宽支持的子载波从52个提高到56个，除去4个pilot子载波，数据子载波达到52个。
此外，由于采用了更高效率的编码方案，使得单个空间流的数据速率可以达到最大65Mbps。
网络WiFi-香港大学802.11n无线部署介绍_中文 v.3
The University of Hong Kong Information Technology Services
近期主要更新
802.11n AP
Access switch
1Gbps 1Gbps
1Gbps
Distribution switch
HKU Campus Network
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The University of Hong Kong Information Technology Services
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The University of Hong Kong Information Technology Services
无线接入服务的扩展规划
Eduroam
Universities WiFi
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The University of Hong Kong Information Technology Services
香港大学无线网络建设历史
Year 2000-2003 2004-2005 2006-2007 2008 2009-2010
Standard 802.11b 802.11b/g
AP type Fat AP Fat AP
802.11b/g
802.11b/g/n (draft 2.0) 802.11b/g/n
演讲厅
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The University of Hong Kong Information Technology Services
无线覆盖典场景
教学实验室
10
The University of Hong Kong Information Technology Services
香港大学无线网络逻辑示意图
无线WiFi-12——802.11n高性能无线校园网方案
802.11n高性能无线校园网方案2009年9月11号，IETF正式通过了802.11n标准，无线局域网技术正式迈入300Mbps 时代。
标准发布后，802.11n技术凭借其高性能、高覆盖范围迅速在各行各业普及。
在教育行业，2010年新建的无线校园网超过50%采用了802.11n技术，但无线校园网是一个系统工程，不是仅使用支持802.11n协议的AP就能够获得高性能。
H3C凭借在802.11n技术方面的积累和多年对教育信息化的理解，提出了高性能无线校园网解决方案。
H3C高性能802.11n无线解决方案在网络核心，采用万兆高性能无线控制器和专业硬件IPS用以保证无线校园网的高性能。
在接入层，采用能够实现一体化管理的千兆PoE交换机来为AP供电和提供高性能上行链路。
在AP层面，H3C采用灵活的方案和全系列的802.11nAP为校园各种场景提供无缝高速无线信号覆盖。
在用户管理方面，H3C可以提供CAMS综合接入管理方案，也可以和学校现有的认证计费系统对接。
H3C高性能802.11n无线解决方案综合考虑了建设高性能无线校园网的各个环节的需求，从设备、管理、部署、安全等各个方面提升无线校园网的性能，高性能802.11n无线解决方案特点如下：端到端802.11n无线802.11n的物理接入速率最高能够达到300Mbps，实际使用带宽可以达到近200Mbps，跟传统的802.11a/b/g技术相比，有了6倍以上的性能提升，但只有无线控制器、无线接入点、无线网卡都提供相匹配的性能，用户才能这正享受到802.11n的高带宽。
在无线控制器方面，H3C能够提供目前业界性能最高的万兆无线控制器，最高处理性能可达20G，包括WX6103高端无线控制器，S7500E高端无线控制器插卡，S9500E 高端无线控制器插卡，确保在802.11n接入的情况下，无线控制器不成为性能的瓶颈；在无线无线接入点方面，H3C提供类型丰富的室内外802.11n产品：WA2620E 增强型双频802.11n接入点,WA2610E增强型单频802.11n接入点,WA2620室内双频802.11n接入点,WA2612室内单频802.11n接入点,WA2610-GNP大功率1×1 802.11n接入点,WA2610X-GNP室外型802.11n接入点,WA2360X-ANP专业802.11n 网桥,可以满足无线校园网各种场景下的无线覆盖需求。
802.11无线网络标准详解
802.11无线网络标准详解1990年，早期的无线网络产品Wireless LAN在美国出现，1997年IEEE802.11无线网络标准颁布，对无线网络技术的发展和无线网络的应用起到了重要的推动作用，促进了不同厂家的无线网络产品的互通互联。
1999年无线网络国际标准的更新及完善，进一步规范了不同频点的产品及更高网络速度产品的开发和应用。
一、1997年版无线网络标准1997年版IEEE802.11无线网络标准规定了三种物理层介质性能。
其中两种物理层介质工作在2400——2483.5 GHz无线射频频段（根据各国当地法规规定），另一种光波段作为其物理层，也就是利用红外线光波传输数据流。
而直序列扩频技术（DSSS）则可提供1Mb/S及2Mb/S工作速率，而跳频扩频（FHSS）技术及红外线技术的无线网络则可提供1Mb/S传输速率（2Mb/S作为可选速率，未作必须要求），受包括这一因素在内的多种因素影响，多数FHSS技术厂家仅能提供1Mb/S的产品，而符合IEEE802.11无线网络标准并使用DSSS直序列扩频技术厂家的产品则全部可以提供2Mb/S的速率，因此DSSS技术在无线网络产品中得到了广泛应用。
1.介质接入控制层功能无线网络（WLAN）可以无缝连接标准的以太网络。
标准的无线网络使用的是（CSMA/CA）介质控制信息而有线网络则使用载体监听访问/冲突检测（CSMA/CA），使用两种不同的方法均是为了避免通信信号冲突。
2.漫游功能IEEE802.11无线网络标准允许无线网络用户可以在不同的无线网桥网段中使用相同的信道，或在不同的信道之间互相漫游，如Lucent的WavePOINT II 无线网桥每隔100 ms发射一个烽火信号，烽火信号包括同步时钟、网络传输拓扑结构图、传输速度指示及其他参数值，漫游用户利用该烽火信号来衡量网络信道信号质量，如果质量不好，该用户会自动试图连接到其他新的网络接入点。
3.自动速率选择功能IEEE802.11无线网络标准能使移动用户（Mobile Client）设置在自动速率选择（ARS）模式下，ARS功能会根据信号的质量及与网桥接入点的距离自动为每个传输路径选择最佳的传输速率，该功能还可以根据用户的不同应用环境设置成不同的固定应用速率。
计算机毕业论文外文文献翻译中英文：IEEE802.11媒体接入控制
计算机毕业论⽂外⽂⽂献翻译中英⽂：IEEE802.11媒体接⼊控制英⽂资料与中⽂翻译IEEE 802.11 MEDIUM ACCESS CONTROLThe IEEE 802.11 MAC layer covers three functional areas：reliable data delivery, medium access control, and security. This section covers the first two topics.Reliable Data DeliveryAs with any wireless network, a wireless LAN using the IEEE 802.11 physical and MAC layers is subject to considerable unreliability. Noise, interference, and other propagation effects result in the loss of a significant number of frames. Even with error-correction codes, a number of MAC frames may not successfully be received. This situation can be dealt with by reliability mechanisms at a higher layer. such as TCP. However, timers used for retransmission at higher layers are typically on the order of seconds. It is therefore more efficient to deal with errors at the MAC level. For this purpose, IEEE 802.11 includes a frame exchange protocol. When a station receives a data frame from another station. It returns an acknowledgment (ACK) frame to the source station. This exchange is treated as an atomic unit, not to be interrupted by a transmission from any other station. If the source does not receive an ACK within a short period of time, either because its data frame was damaged or because the returning ACK was damaged, the source retransmits the frame.Thus, the basic data transfer mechanism in IEEE802.11 involves an exchange of two frames. To further enhance reliability, a four-frame exchange may be used. In this scheme, a source first issues a request to send (RTS) frame to the destination. The destination then responds with a clear to send (CTS). After receiving the CTS, the source transmits the data frame, and the destination responds with an ACK. The RTS alerts all stations that are within reception range of the source that an exchange is under way; these stations refrain from transmission in order to avoid a collision between two frames transmitted at the same time. Similarly, the CTS alerts all stations that are within reception range of the destination that an exchange is under way. The RTS/CTS portion of the exchange is a required function of the MAC but may be disabled.Medium Access ControlThe 802.11 working group considered two types of proposals for a MAC algorithm: distributed access protocols, which, like Ethernet, distribute the decision to transmit over all the nodes using a carrier-sense mechanism; and centralized access protocols, which involve regulation of transmission by a centralized decision maker. A distributed access protocol makes sense for an ad hoc network of peer workstations (typically an IBSS) and may also be attractive in other wireless LAN configurations that consist primarily of burst traffic. A centralized access protocol is natural for configurations in which a umber of wireless stations are interconnected with each other and some sort of base station that attaches to a backbone wired LAN: it is especially useful if some of the data is time sensitive or high priority.The end result for 802.11 is a MAC algorithm called DFWMAC (distributed foundation wireless MAC) that provides a distributed access control mechanism with an optional centralized control built on top of that. Figure 14.5 illustrates the architecture. The lower sub-layer of the MAC layer is the distributed coordination function (DCF). DCF uses a contention algorithm to provide access to all traffic. Ordinary asynchronous traffic directly uses DCE. The point coordination function (PCF) is a centralized MAC algorithm used to provide contention-free service. PCF is built on top of DCF and exploits features of DCF to assure access for its users. Let us consider these two sub-layers in turn.MAClayerFigure 14.5 IEEE 802.11 Protocol ArchitectureDistributed Coordination FunctionThe DCF sub-layer 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. The DCF does not include a collision detection function (i.e. CSMA/CD) because collision detection is not practical on a wireless network. The dynamic range ofthe signals on the medium is very large, so that a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission.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 inter-frame space (IFS). In fact, there are three different IFS values, but the algorithm is best explained by initially ignoring this detail. Using an IFS, the rules for CSMA access are as follows (Figure 14.6):Figure 14.6 IEEE 802.11 Medium Access Control Logic1. 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.2. 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.3. 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 back-off time, if the medium becomes busy, the back-off timer is halted and resumes when the medium becomes idle.4. If the transmission is unsuccessful, which is determined by the absence of an acknowledgement, then it is assumed that a collision has occurred.To ensure that back-off maintains stability, a technique known as binary exponential back-off is used. A station will attempt to transmit repeatedly in the face of repeated collisions, but after each collision, the mean value of the random delay is doubled up to some maximum value. The binary exponential back-off provides a means of handling a heavy load. Repeated failed attempts to transmit result in longer and longer back-off times, which helps to smooth out the load. Without such a back-off, the following situation could occur. Two or more stations attempt to transmit at the same time, causing a collision. These stations then immediately attempt to retransmit, causing a new collision.The preceding scheme is refined for DCF to provide priority-based access by the simple expedient of using three values for IFS:●SIFS (short IFS):The shortest IFS, used for all immediate responseactions，as explained in the following discussion●PIFS (point coordination function IFS):A mid-length IFS, used by thecentralized controller in the PCF scheme when issuing polls●DIFS (distributed coordination function IFS): The longest IFS, used as aminimum delay for asynchronous frames contending for access Figure 14.7a illustrates the use of these time values. Consider first the SIFS.Any station using SIFS to determine transmission opportunity has, in effect, the highest priority, because it will always gain access in preference to a stationwaiting an amount of time equal to PIFS or DIFS. The SIFS is used in the following circumstances：●Acknowledgment (ACK): When a station receives a frame addressed onlyto itself (not multicast or broadcast) it responds with an ACK frame after, waiting on1y for an SIFS gap. This has two desirable effects. First, because collision detection IS not used, the likelihood of collisions is greater than with CSMA/CD, and the MAC-level ACK provides for efficient collision recovery. Second, the SIFS can be used to provide efficient delivery of an LLC protocol data unit (PDU) that requires multiple MAC frames. In this case, the following scenario occurs. A station with a multi-frame LLC PDU to transmit sends out the MAC frames one at a time. Each frame is acknowledged after SIFS by the recipient. When the source receives an ACK, it immediately (after SIFS) sends the next frame in the sequence. The result is that once a station has contended for the channel, it will maintain control of the channel until it has sent all of the fragments of an LLC PDU.●Clear to Send (CTS):A station can ensure that its data frame will getthrough by first issuing a small. Request to Send (RTS) frame. The station to which this frame is addressed should immediately respond with a CTS frame if it is ready to receive. All other stations receive the RTS and defer using the medium.●Poll response: This is explained in the following discussion of PCF.longer than DIFS(a) Basic access methoddefers(b) PCF super-frame constructionFigure 14.7 IEEE 802.11 MAC TimingThe next longest IFS interval is the: PIFS. This is used by the centralized controller in issuing polls and takes precedence over normal contention traffic. However, those frames transmitted using SIFS have precedence over a PCF poll.Finally, the DIFS interval is used for all ordinary asynchronous traffic.Point C00rdination Function PCF is an alternative access method implemented on top of the DCE. The operation consists of polling by the centralized polling master (point coordinator). The point coordinator makes use of PIFS when issuing polls. Because PI FS is smaller than DIFS, the point coordinator call seize the medium and lock out all asynchronous traffic while it issues polls and receives responses.As an extreme, consider the following possible scenario. A wireless network is configured so that a number of stations with time, sensitive traffic are controlled by the point coordinator while remaining traffic contends for access using CSMA. The point coordinator could issue polls in a round—robin fashion to all stations configured for polling. When a poll is issued, the polled station may respond using SIFS. If the point coordinator receives a response, it issues another poll using PIFS. If no response is received during the expected turnaround time, the coordinator issues a poll．If the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this, an interval known as the super-frame is defined. During the first part of this interval, the point coordinator issues polls in a round, robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the super-frame, allowing a contention period for asynchronous access.Figure l4.7 b illustrates the use of the super-frame. At the beginning of a super-frame, the point coordinator may optionally seize control and issues polls for a give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the super-frame is available for contention based access. At the end of the super-frame interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle. the point coordinator gains immediate access and a full super-frame period follows. However, the medium may be busy at the end of a super-frame. In this case, the point coordinator must wait until the medium is idle to gain access: this result in a foreshortened super-frame period for the next cycle.OctetsFC=frame control SC=sequence controlD/I=duration/connection ID FCS=frame check sequence（a ） MAC frameBitsDS=distribution systemMD=more data MF=more fragmentsW=wired equivalent privacy RT=retryO=orderPM=power management (b) Frame control filedFigure 14.8 IEEE 802.11 MAC Frame FormatMAC FrameFigure 14.8a shows the 802.11 frame format when no security features are used. This general format is used for all data and control frames, but not all fields are used in all contexts. The fields are as follows:● Frame Control: Indicates the type of frame and provides contr01information, as explained presently.● Duration/Connection ID: If used as a duration field, indicates the time(in-microseconds) the channel will be allocated for successful transmission of a MAC frame. In some control frames, this field contains an association, or connection, identifier.●Addresses: The number and meaning of the 48-bit address fields dependon context. The transmitter address and receiver address are the MAC addresses of stations joined to the BSS that are transmitting and receiving frames over the wireless LAN. The service set ID (SSID) identifies the wireless LAN over which a frame is transmitted. For an IBSS, the SSID isa random number generated at the time the network is formed. For awireless LAN that is part of a larger configuration the SSID identifies the BSS over which the frame is transmitted: specifically, the SSID is the MAC-level address of the AP for this BSS (Figure 14.4). Finally the source address and destination address are the MAC addresses of stations, wireless or otherwise, that are the ultimate source and destination of this frame. The source address may be identical to the transmitter address and the destination address may be identical to the receiver address.●Sequence Control: Contains a 4-bit fragment number subfield used forfragmentation and reassembly, and a l2-bit sequence number used to number frames sent between a given transmitter and receiver.●Frame Body: Contains an MSDU or a fragment of an MSDU. The MSDUis a LLC protocol data unit or MAC control information.●Frame Check Sequence: A 32-bit cyclic redundancy check. The framecontrol filed, shown in Figure 14.8b, consists of the following fields.●Protocol Version: 802.11 version, current version 0.●Type: Identifies the frame as control, management, or data.●Subtype: Further identifies the function of frame. Table 14.4 defines thevalid combinations of type and subtype.●To DS: The MAC coordination sets this bit to 1 in a frame destined to thedistribution system.●From DS: The MAC coordination sets this bit to 1 in a frame leaving thedistribution system.●More Fragments: Set to 1 if more fragments follow this one.●Retry: Set to 1 if this is a retransmission of a previous frame.●Power Management: Set to]if the transmitting station is in a sleep mode.●More Data: Indicates that a station has additional data to send. Each blockof data may be sent as one frame or a group of fragments in multiple frames.●WEP：Set to 1 if the optional wired equivalent protocol is implemented.WEP is used in the exchange of encryption keys for secure data exchange.This bit also is set if the newer WPA security mechanism is employed, as described in Section 14.6.●Order：Set to 1 in any data frame sent using the Strictly Ordered service,which tells the receiving station that frames must be processed in order. We now look at the various MAC frame types. Control Frames Control frames assist in the reliable delivery of data frames. There are six control frame subtypes:●Power Save-Poll (PS-Poll): This frame is sent by any station to the stationthat 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 power saving mode.●Request to Send (RTS):This is the first frame in the four-way frameexchange 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.●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 tothe source that the immediately preceding data, management, or PS-Poll frame was received correctly.●Contention-Free (CF)-End: Announces the end of a contention-freeperiod that is part of the point coordination function.●CF-End+CF-Ack:Acknowledges the CF-End. This frame ends thecontention-free period and releases stations from the restrictions associated with that period.Data Frames There are eight data frame subtypes, organized into two groups. The first four subtypes define frames that carry upper-level data from the source station to the destination station. The four data-carrying frames are as follows: ●Data: This is the simplest data frame. It may be used in both a contentionperiod and a contention-free period.●Data+CF-Ack: May only be sent during a contention-free period. Inaddition to carrying data, this frame acknowledges previously received data.●Data+CF-Poll: Used by a point coordinator to deliver data to a mobilestation 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 andData+CF-Poll into a single frame.The remaining four subtypes of data frames do not in fact carry any user data. 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 withotit the data. Management FramesManagement frames are used to manage communications between stations and APs. The following subtypes are included:●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 indicatewhether it is accepting this association request.●Reassociation Request: Sent by a station when it moves from one BSS toanother and needs to make an association with tire 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 indicatewhether it is accepting this reassociation request.●Probe Request: Used by a station to obtain information from anotherstation 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 andidentify a BSS.●Announcement Traffic Indication Message: Sent by a mobile station toalert 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.●Authentication：Multiple authentication frames are used in an exchange toauthenticate one station to another.●Deauthentication:Sent by a station to another station or AP to indicatethat it is terminating secure communications.IEEE802.11 媒体接⼊控制IEEE 802．11 MAC层覆盖了三个功能区：可靠的数据传送、接⼊控制以及安全。
ASRock WiFi-802.11n Module Operation 说明书
ASRock WiFi-802.11n ModuleOperation Guide1. IntroductionASRock WiFi-802.11n module is an easy-to-use wireless local area network (WLAN) adapter to support WiFi+AP function. With ASRock WiFi-802.11n module, you can easily create a wireless environment and enjoy the convenience of wireless network connectivity. Therefore, from anywhere within the signal range, you will be able to play LAN games, connect to the internet, access and share printers, and make Internet phone calls easily. Please read this operation guide carefully before you start to set up ASRock WiFi-802.11n module.1.1 SpecificationsStandard - IEEE 802.11nData Rate - 15, 30, 45, 60, 90, 120, 135, 150Mbps Security - AES, TKIP, WEPNetwork Architecture Types - Access Point mode (AP mode)- Station mode: Infrastructure mode andAd-Hoc modeFrequency Band - 2.4GHz ISM radio bandOperating Range - Indoor: 330ft (100m)- Outdoor: 980ft (300m)* The range varies in differentenvironments- up to 16 stationsNumber of Connected Devices(AP Mode)Antenna - ASRock WiFi-802.11nomni-directional antennaLED - Green data transmission (AIR) LED Support OS - Windows® XP / XP 64-bit / Vista TM /Vista TM 64-bitCompatibility - Full compatible with IEEE 802.11nstandard productsSoftware Support - ASRock WiFi-802.11n Wizard1.2 LED Indicators and Antenna PortsASRock WiFi-802.11n module has a green LED for transmission status mountedonboard, and two antenna ports for connection to the external antennas.LED Status IndicationOn Power on, transmit/receive/site survey OffPower off, no wireless connection1.3 Signal RangeThe signal range of ASRock WiFi-802.11n module varies from the operatingenvironment. Obstacles such as walls and metal barriers could reflex and absorb ratio signals. Devices like microwave ovens may also interfere with the wireless network greatly.Signal range:Indoor 330ft (100m), outdoor 980ft (300m)By default, ASRock WiFi-802.11n module should automatically adjust the data rate. The closer the wireless stations are the better the signal and transmission speed they will receive.Note:* To reach higher data rate, we advise users to adjust the channel bandwidth of Wireless AP to 40MHz instead of 20MHz. However, under the circumstances of a noisy environment, users may adjust the setting back to 20MHz, which may get less interference.Antenna PortsLED2. Hardware & Software Installation2.1 System RequirementsBefore installing ASRock WiFi-802.11n module to your motherboard, please make sure your system satisfies the following requirements.1.ASRock motherboard with a USB/WiFi (yellow), WiFi (black) or WiFi/E (black)header. (Please refer to ASRock motherboard manual for the location ofUSB/WiFi, WiFi or WiFi/E header.)USB/WiFi Header (2 x 6 Pin) WiFi Header (2 x 6 Pin) WiFi/E Header (2 x 8 Pin)2. A minimum of 256MB system memory3. Operating system: Windows® XP / XP 64-bit / Vista TM / Vista TM 64-bit4. An optical drive / CD-ROM for driver and utility installation2.2 Installing ASRock WiFi-802.11n Module and AntennasAfter you make sure your system satisfies the requirements above, please follow below steps for installing your ASRock WiFi-802.11n module. If the motherboard you purchase is equipped with ASRock WiFi-802.11n module, which is screwed next to the audio jack of the I/O panel, please skip step 2 to 6.1. Shut off the PC before installing ASRock WiFi-802.11n module.2. Move out your motherboard from the chassis.3. Fasten the bracket to the proper position of the chassis with screws.4. Plug ASRock WiFi-802.11n module with its connector-side to the USB/WiFi (yellow), WiFi (black) or WiFi/E (black) header on the motherboard. (The location of the USB/WiFi, WiFi or WiFi/E header may vary on motherboard models. Pleaserefer to your motherboard manual for the motherboard layout.)5. Fasten ASRock WiFi-802.11n module to the motherboard with screws.Connector-sideUSB/WiFi, WIFI or WIFI/E Header6. Place your motherboard to the chassis.7. Connect the cable-end from the antennas to the antenna ports on ASRockWiFi-802.11n module.8. Place the antennas at an elevated location. A wide and open position will enhance the operating range.Note:* You may connect two antennas to ASRock WiFi-802.11n module. However, please place the two antennas apart for a distance of at least 50cm and put them on different elevation of height to avoid interference of each others.2.3. Driver and Utility InstallationAfter you finish the hardware installation, you need to install WiFi driver and utility to your system. Please boot your system and follow below steps to install the WiFi driver and utility.1. Insert ASRock motherboard support CD to the optical drive.2. The system will automatically display the driver menu. Click “ASRockWiFi-802.11n Driver and Utility” and follow screen instructions to finish the driver installation.After above steps, the WiFi driver and utility are installed to your system simultaneously.Note:* Microsoft® had released a hotfix to improve the connectivity and performance of wireless network in Windows® Vista-based system. To download the hotfix, please go to:/kb/928152/en-us* Microsoft® had also released three hotfix to improve the connectivity for transferring large file in Windows® Vista-based system. Please go to:z /kb/932045/en-us to download the necessary hotfix when thissituation happened: "The connection has been lost" – this error message may occur when you try to copy a large file from one Windows ® Vista-based computer to another Windows Vista-based computer. z/kb/932170/en-us to download the necessary hotfix when this situation happened: When you copy large files to or from earlier operating systems, the copy operation may be slower than expected on some Windows ® Vista-based computers. z/kb/931770/en-us to download the necessary hotfix when this situation happened: The copy process may stop responding when you try to copy files from a server on a network to a Windows ® Vista-based computer.2.4 Utility SetupAfter you have installed the driver and utility to your system, now you are ready to set up the utility in your network. ASRock WiFi-802.11n module supports two kinds of wireless network mode: Access Point Mode (AP Mode) and Station Mode. Please refer to below introduction and select the most appropriate mode when setting it up.A. Access Point Mode (AP Mode)If you want to share the Internet access with the wireless stations in yourenvironment, such as PC, notebook and other devices, you can configure ASRock WiFi-802.11n module in an access point mode (AP mode). In this mode, ASRock WiFi-802.11n module becomes the wireless access point that provides local area network and Internet access for your wireless stations. The AP Mode feature is ideal for home/SOHO networks with several computers, a shared printer, and a shared Internet connection.InternetADSL or Cable Modem (if any)Printer 1Station 1Station 2Station 3Station 4ASRock MB With WiFi-802.11n ModuleB.Station ModeIf you do not plan to use AP function with ASRock WiFi-802.11n module, but just want to use the wireless function to connect the access point (AP), or connectwith other stations in the wireless range instead, please set up ASRock WiFi-802.11n module in station mode. There are two choices provided in station mode: Infrastructure mode and Ad-hoc mode. Please read below introduction for the differences of these two modes.B-1. Infrastructure ModeIf you have a present access point (AP) in your wireless network environment for this station to join, you can set up ASRock WiFi-802.11n module in Infrastructure mode. In this mode, ASRock WiFi-802.11n module acts as a wireless adapter. In other words, it is centered on an AP that provides Internet access and LAN communication for the wireless stations, such as PC, notebook and other devices.Internet ADSL or Cable Modem(if any)Station2Station1Access PointASRock MB With WiFi-802.11nModuleB-2. Ad-hoc ModeIf you don’t have a present access point in your wireless network environment, you can set up ASRock WiFi-802.11n module in Ad-hoc mode. The wireless network brings together workstations, PC, notebook and other devices for wireless communication.Station 2Station 1ASRock MB WithWiFi-802.11nModule3. General Setup with ASRock WiFi-802.11n WizardIf you want to easily set up ASRock WiFi-802.11n for general use, please use ASRock WiFi-802.11n Wizard and follow below procedures according to the mode you choose.Here we take Windows® Vista TM for example in the following pictures. Sincethe setup procedures are quite similar in different operating systems, please refer to below procedures when setting up ASRock WiFi-802.11n wizard under other operating systems.3.1 Setting up the AP Mode1. Move your mouse cursor to the icon on the Windows® taskbar andright-click the icon.2. Select Wizard to launch the WiFi setup wizard.3. Select Create a wireless access point and click Next.4. The system will automatically generate a SSID for the AP mode. You can rename the SSID if you want.5. Select a Network Security level for your AP mode. The configurable options are None, WEP, WPA-Personal and WPA2-Personal. Select an appropriate level and click Next.7. Select your Internet connection and click Next.3.2 Setting up the Station ModeNote:* Please be noted that the wizard for WiFi-802.11n Module does not provides Ad-Hoc mode. If you want to set up Ad-Hoc mode, please refer to page 26 - page 36 for advanced setup.3.2.1 Setting up the Infrastructure Mode1. Move your mouse cursor to the icon on the Windows® taskbar and right-click the icon.2. Select Wizard to launch the WiFi setup wizard.3. Select Join an existing wireless network and click Next.4. Click Finish to exit the wizard.5. Move your mouse cursor to the Wireless Network Connection icon on the Windows® taskbar and right-click the icon. Click Connect to a network to select available internet network.6. Choose an available internet network and click Connect.* If you choose a security-enabled wireless network, you have to input the network key.7. Your system is now connecting to a network.8. You have connected to internet wireless network successfully. If you want to start the connection automatically next time, you may save the network by checking Save this network box, and click Close.4. Advanced Setup in ASRock WiFi-802.11n UtilityIf you want to set up ASRock WiFi-802.11n module for advanced use, please follow below procedures according to the mode you choose. For general users, it is unnecessary to read below advanced setup of ASRock WiFi-802.11n module.Here we take Windows® Vista TM for example in the following pictures. Sincethe setup procedures are quite similar in different operating systems, please refer to below procedures when setting up ASRock WiFi-802.11n wizard under other operating systems.4.1 Setting up the AP ModeIf you want to set up ASRock WiFi-802.11n module for advanced use in AP mode, please use ASRock WiFi-802.11n utility and follow below steps according to the operating system you install.1.Double-click the utility shortcut on the desktop or double-click theicon on your Windows® taskbar to open the setup utility.2. Refer to the mode indicator on the top-right corner of the main window to know which mode ASRock WiFi-802.11n is in. If it is in station mode, click the mode switch button to switch it to AP mode.3. The system will automatically generate a SSID for the AP mode. You can rename the SSID if you want.4. Select a Network Authentication for your AP mode. The configurable options are Open System, Shared Key, WPA-PSK and WPA2-PSK. Select an appropriate one.Note:* If your operating system is Windows® XP with Service Pack 2, it is required to install the Microsoft hotfix in order to support WPA2-Personal function. Please go to this link to download the necessary hotfix:/downloads/details.aspx?familyid=662BB74D-E7C1-48D6-95EE-145923 4F4483&displaylang=en5. If you select Open System, the configurable options of Data Encryption are Noneand WEP for you to choose. This option allows you to select Key Length.6. If you select Shared Key, the configurable options of Data Encryption is WEPonly. This option allows you to select Key Length.7. If you select WPA-PSK, the configurable option of Data Encryption is TKIP only. You can’t select Key Length in this option.8. If you select WPA2-PSK, the configurable option of Data Encryption is AES only. You can’t select Key Length in this option either.9. In this case, we select Open System for the rest of the setups. If you select WEP, please select the Key Length. The configurable options are 64 Bits and 128 Bits. (However, if you select None in the Data Encryption, you will not be able to choose the Key Length.)10. Key in the Network password and click Apply to confirm.11. Click ICS (Internet Connection Sharing) button on the left-bottom corner of the main window.12. Select the correct internet connection and click Apply.Note:* You need to have another LAN connector connected to your ADSL / cable modem, and already set it up for Internet access. Please refer to the manual from your ISP for detailed setup steps.13. The AP mode configuration is completed.4.2 Setting up the Station ModeThere are two choices provides in station mode: Infrastructure mode and Ad-hoc mode. For the differences of Infrastructure mode and Ad-hoc mode, please refer to page 5 and 6 for details.If you want to set up ASRock WiFi-802.11n module for advanced use in station mode, please use Windows® configuration and follow below steps according to the mode you choose and the operating system you install.4.2.1 Setting up the Infrastructure ModeFor Windows® XP / XP 64-bit:1.Move your mouse cursor to Wireless Network Connection icon on theWindows® taskbar and right-click the icon.2.Select View Available Wireless Networks.3.Choose an available wireless network. Click Connect.4.If you choose a security-enabled wireless network, input the network key andclick Connect.5.You are now connected to a internet wireless network successfully.For Windows® Vista TM / Vista TM 64-bit:1.Click Start. Click Settings. And select Control Panel.2.Click Network and Internet.3.Click Network and Sharing Center.4.Click Connect to a network.5.Choose an available network and click Connect.6.If you choose a security-enabled wireless network, input the network key andclick Connect.7.You have connected to internet wireless network successfully. If you want to startthe connection automatically next time, you may save the network by checking Save this network box, and click Close.4.2.2 Setting up the Ad-hoc ModeFor Windows® XP / XP 64-bit:1.Move your mouse cursor to Wireless Network Connection icon on theWindows® taskbar and right-click the icon.2.Select View Available Wireless Networks.3. Click Change advanced settings.4.Switch to Wireless Networks tab and click Advanced.5. Select Computer-to-computer (ad hoc) networks only and clear the Automatically connect to non-preferred networks box if it is selected. ClickClose.6. On the Wireless Networks tab, click Add. In the Wireless Network Propertiesdialog box, specify a Network name (SSID). Click OK to close all dialog boxes.7. Select the Network Authentication for advanced setups. The configurable options are Open, Shared and WPA2-None. Select an appropriate one.8. If you select Open, the configurable option of Data Encryption is WEP only. Youmay select Disabled or WEP. This option allows you to select Key Index.9. If you select Shared, the configurable option of Data Encryption is WEP only. Youmay select Disabled or WEP. This option allows you to select Key Index.10. If you select WPA-None, the configurable options of Data Encryption are TKIP and AES. You may select either TKIP or AES. You can’t select Key index in this option.11. Launch View Available Wireless Networks again. You are now in Ad-hoc network, you may wait for other users to connect you or you may select the desired ad-hoc network and click Connect.For Windows® Vista TM / Vista TM 64-bit:1.Click Start. Click Settings. And select Control Panel.2.Click Network and Internet.3.Click Network and Sharing Center.4.Click Manage wireless networks.5.In the Manage wireless networks that use (Wireless Network Connection)window, click Add.6.Click Create an ad hoc network.7.In the Set up a wireless ad hoc network window, click Next.8.Specify a network name, select the security type. The configurable options are NoAuthentications (Open), WEP and WPA2-Personal.9. Select an appropriate one, and key in the security password. Then click Next.10.You have completed setting up an Ad-hoc network. Click Close to exit.11. You are now in Ad-hoc network, you may wait for other users to connect you or you may select the desired ad-hoc network.。
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The University of Hong Kong Information Technology Services
Coverage of WiFi Network
Total no. of APs > 1500 Locations:
Classrooms & Lecture Theatres Libraries Residential Halls Departmental Offices and Premises Amenities Centres, PC laboratories and Open Areas (podia)
802.11b&g -> 802.11n
2008: 200 units of “IEEE 802.11n draft 2.0” Aruba access points as pilot test. Scope:
replaced 100 units of 802.11b access points installed over 5 years. added 100 new 802.11n access points to augment WiFi coverage.
27
The University of Hong Kong Information Technology Services
Recent Major Upgrades
Robert Black College
28
The University of Hong Kong Information Technology Services
WiFi Network Accessibility
PC Laboratories
10
The University of Hong Kong Information Technology Services
Schematic Diagram of HKU WiFi Network
Staff Network
530 new APs for student residential halls 810 mainly for replacing existing 802.11b&g Aps
22
The University of Hong Kong Information Technology Services
0
501
2004/05
537
2005/06
570
587
2006/07
2007/08
1,527 840
2008/09
2009/10
17
The University of Hong Kong Information Technology Services
WiFi Users
<presenter> Computer Centre
Recent Major Upgrades
WiFi for Student Residential Halls
Internet
Router
Access control
WiFi Network
11
The University of Hong Kong Information Technology Services
Simplified Thin-AP System Configuration
WiFi controller
Brief History
Year 2000-2003 2004-2005 2006-2007 2008 2009-2010
Standard 802.11b 802.11b/g
802.11b/g 802.11b/g/n (draft 2.0) 802.11b/g/n
AP type Fat AP Fat AP Thin AP Thin AP Thin AP
6
The University of Hong Kong Information Technology Services
WiFi Network Accessibility
Lecture Theatres
Departmental Conference Rooms
7
The University of Hong Kong Information Technology Services
2
The University of Hong Kong Information Technology Services
Brief history of WiFi development in HKU
3
The University of Hong Kong Information Technology Services
Components of WiFi network
DHCP Server
Radius Server
Core switch
WiFi Controllers
Tunnel
Tunnel
ITS Building
Router
Access switch
AP Distribution switch AP AP Access switch
23
The University of Hong Kong Information Technology Services
Recent Major Upgrades
WiFi for Student Residential Halls
1998: wired network connection for all student residential halls 2010: 570 APs for 17 halls, 1 guest house; 4700 places
WiFi controller
Primary link
Resilient links
Primary link
Campus network
Thin access points
12
The University of Hong Kong Information Technology Services
Schematic Diagram of HKU WiFi Network
Brand Orinoco/Proxim Orinoco/Proxim 3Com Aruba H3C
4
The University of Hong Kong Information Technology Services
Coverage, topology and usage statistics
Notebook
Notebook Mobile Device
13
The University of Hong Kong Information Technology Services
Schematic Diagram of WiFi Network – inside building
AP Access switch
2006/07
2007/08
2008/09
2009/10
16
The University of Hong Kong Information Technology Services
Number of WiFi Access Points
1,600 1,400 1,200 1,000
800 600 400 200
<date>
18
The University of Hong Kong Information Technology Services
WiFi Usage
19
The University of Hong Kong Information Technology Services
Recent Major Upgrades:
24
The University of Hong Kong Information Technology Services
Recent Major Upgrades
St. John’s College University Hall
25
The University of Hong Kong Information Technology Services
21
The University of Hong Kong Information Technology Services
Recent Major Upgrades
802.11b&g -> 802.11n
2009: wide deployment of 802.11n-ready access points in HKU 1340 H3C access points (H3C WA2620EAGN)
Recent Major Upgrades
802.11b&g -> 802.11n
6 H3C WX6103 controllers (3+3 redundancy) All 802.11n APs in HKU after this upgrade Upgrade expected to be completed before end of 2010.
Recent Major Upgrades
Ricci Hall
Simon K. Y. Lee Hall
26
The University of Hong Kong Information Technology Services
Recent Major Upgrades
Graduate House
Swire Hall