-1-
IEEE
摘 要：吞吐量是衡量一个网络性能优劣的重要指标，在混合的
理开销和媒体竞争等因素的影响，网络的吞吐量会有所下降。本文在实际环境中对不同情况
下的
了混合网络吞吐量的改进方向。
关键词：无线局域网；混合网络；吞吐量；测量
1．引言
IEEE 标准使WLAN的吞吐量有了显著的提高，同时由于其对的后向兼
容，使得基于
网络，为保持与 的兼容性，同时支持CCK和OFDM编码方式。由于
与的物理层调制方式不同，在实际混合网络中，当设备使用OFDM调制模式
发送信号时，设备监听到信道有信号，但它无法确认是发送的信号正在占用
信道，它会将OFDM信号当作信道噪声，认为信道空闲，而向信道发送数据，从而引起冲突。
为了让二者协同工作，IEEE MAC层中使用保护机制：CTS-to-self机制或RTS/CTS
机制[1]。如果一台设备不知道整个无线局域网中有哪些设备存在，当它探测到信道空闲时，
它并不是立即向AP发送数据，而是先发送RTS信号。当AP收到RTS信号后，即向全网发送
CTS信号，网络中的其它设备都能收到此信号，并根据CTS信号等待一段时间，这样可以有
效减少冲突。但是由于这种保护机制的存在，保护帧以的速率传输，即使设
备并没有真正传输数据，而只是发出探测信息，也会降低整个网络的传输速率。
目前对于WLAN吞吐量多为理论研究[2,3,4]，而实际环境中网络性能[5]往往有所不同，本
文将通过测量实际的WLAN网络，对IEEE
2．网络吞吐量测量
测量环境
本文中，测试无线局域网的性能使用业界普遍认可的 Chariot应用性能测试软件，实验
中的测试数据均为网络的 TCP吞吐量。
图 1 测试网络示意图
Fig1 Test network structure
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测试中用到的 AP为 DWL-2100AP，无线网卡 TL-WN250/251若干个，
无线网卡 DWL-G122 和 DWL-G650+A 各若干个，测试中的台式机均为 Intel Pentium IV
处理器、512MB内存，笔记本电脑为 IBM T60。所有的设备均在 AP附近两米的范
围内，所有 设备工作在 11Mbps。图 1为测试网络环境的示意图，console为控制台，
终端 和 设备的数量可变，由此可以测试单一网络或混合网络等不同网络环
境下的网络性能。AP与控制台之间为 100Mbps的有线连接，远高于可用的无线带宽，以此
保证不会成为测试网络性能的瓶颈。表 1给出了我们进行测试的具体环境及其描述。
表 1测试环境及描述
Test network environment details
测试编号 网络组成 环境描述 测试项
I 2个 客户端 单纯 环境 网络吞吐量
II 2个 客户端 单纯 环境 不同包长、机制下 网络吞吐量
III 1个 与 1个
客户端
不同包长、机制下的网络吞吐量
IV 2个 与 1个
客户端
不同包长下的网络吞吐量
V 2个 与 2个
客户端
不同包长下的网络吞吐量
测量结果
对于每一种测试环境，我们进行了多次测试，每一次测试时间设为 2分钟。图 2到图 5
为其中一次吞吐量测试的实时曲线图。测试 I表明，单纯的 网络环境虽然理论上有
11Mbps数据通信带宽，但如图 2所示，实际的最大 TCP吞吐量约为 。测试 II表明，
虽然单纯 网络环境理论上可得到高达 54Mbps的数据通信带宽，但如图 3所示，实
际的最大 TCP吞吐量可高达约为 23Mbps。图 4为有效数据载荷长度一定、传输速率一定的
情况下，不同网络组成的网络吞吐量的比较。曲线自上而下，测试 II 环境的网络吞吐量约
，测试V环境中网络吞吐量约 ，测试 IV中网络吞吐量约 。
图 5为测试 II中改变有效数据载荷的结果，由上至下，有效数据载荷长度依次为 500Bytes 、
1000Bytes、1500Bytes，网络的平均吞吐量依次为 、、。
图 2 实际吞吐量 图 3 实际吞吐量
Fig2 Real throughputs of pure network Fig3 Real throughputs of pure network
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图 4 不同测试网络环境的实际网络吞吐量 图 5 不同有效载荷的实际网络吞吐量
Fig4 Real throughputs of different test network environments Fig5 Real throughputs of different payloads
3．吞吐量特性分析
图 6的（a）和（b）分别为采用 RTS/CTS机制与不采用 RTS/CTS机制时，单纯的
和 网络的吞吐量比较，等间隔 128bytes进行测试，实验数据为多次测量的平均值，
对比一次测试中的实时曲线图 2、图 3，我们的统计曲线要平滑的多。同时可以看出，对于
设备数量较少的单一网络，RTS/CTS 机制的采用导致了较低的吞吐量，虽然随着有效载荷
的增加，吞吐量有了一定的改善。另外可以看出，对于不同的机制，在取得最大吞吐量时，
对应的有效载荷长度不同，因此，如何能够正确的选择与动态调整有效载荷长度，是提高网
络吞吐量的一个措施。
200 400 600 800 1000 1200 1400
3
4
5
6
(a)有效载荷长度(bytes)
吞
吐
量
(M
bp
s)
200 400 600 800 1000 1200 1400
5
10
15
20
(b)有效载荷长度(bytes)
吞
吐
量
(M
bp
s)
11b without rts/cts
11b with rts/cts
11g without rts/cts
11g with rts/cts
图 6 不同有效载荷、不同机制下的单一网络吞吐量
Real throughputs of pure network with different payloads and access mechanisms
图 7为 1g1b网络组成情况下，设备采用 CTS-to-self机制、RTS/CTS机制以及
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设定 RTS门限的三种情况下的统计曲线，此时的 设备均采用基本接入机制。随着有
效载荷的不同，采用 CTS-to-self机制的曲线起伏较大，最大值与最小值的差约 10Mbps；采
用 RTS/CTS 机制的曲线波动较小、比较稳定，但同时吞吐量较小；我们设 RTS 门限为
1472bytes，当超过该值时启用 RTS/CTS机制，如图可以看出，此时我们得到的曲线波动较
小且吞吐量较大。因此，如何能够正确的选择 RTS门限值、确定何时启用 RTS/CTS机制，
也是提高网络吞吐量的一个措施。
0 500 1000 1500
6
8
10
12
14
16
18
20
有效载荷长度(bytes)
吞
吐
量
(M
bp
s)
11g with rts threshold 1472 11b with basic
11g with rts/cts 11b with basic
11g with cts-to-self 11b with basic
图 7 不同有效载荷、不同机制下的混合网络吞吐量
Fig7 Real throughputs of hybrid network with different payloads and access mechanisms
4．总结
在混合的
不同网络环境的
准网络的吞吐量较单一标准网络的吞吐量有所下降，同时，混合网络中 与
设备的数量以及发送的有效数据载荷长度都对吞吐量有影响，另外，采用何种接入机制及如
何选择接入机制的门限也会影响混合网络的吞吐量。结论的得出对于提高
的络吞吐量及优化宽带无线局域网络有一定的参考作用。
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参考文献
[1] IEEE Standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications,
Amendment 4: Further Higher Data Rate Extension in the GHz Band[S], June. 2003.
[2] BIANCHI G., Performance analysis of the IEEE distributed coordination function[J], IEEE Journal on
Selected Areas in Communications, 2000,18(3): 1265-1275.
[3] Shao-Cheng WAN, Yi-Ming CHEN, Tsem-Huei LEE, et al. Performance Evaluations for Hybrid IEEE
and [C], IPCCC 2005, 7-9 April 2005 Page(s):111–118.
[4] Ming-Ju HO, Jing WANG, Kevin SHELBY, et al. IEEE OFDM WLAN Throughput Performance[C],
Vehicular Technology Conference, 6-9 Oct. 2003, 4:2252 - 2256.
[5] Wei-Min GE, Yan-Tai SHU, Liang ZHANG, et al. Measurement and Analysis of TCP Performance in IEEE
Wireless NetWork[C], Electrical and Computer Engineering, Canadian Conference, May 2006
Page(s):1846 - 1849.
Throughput Research for Hybrid IEEE Network
Bai Guangyu
Institute of Continuing Education, Beijing University of Posts and Telecommunications, Beijing,
PRC (100876)
Abstract
Throughput is one of the key characters to describe the performance of a network. In a hybrid
b/g network, the throughput of devices is compromised because of not only the overhead to
interoperate with devices, but also the unbalanced medium contentions between devices with
different versions of the standard. This paper measures the throughput reduction effect in
mixed scenarios with different station number, access mechanisms and data pocket sizes, proves the
characters of hybrid network and put forwards how to improve the network throughput.
Keywords: Wireless LAN; hybrid network; throughput; measurement
作者简介：白光禹，男，1981年生，硕士研究生，主要研究方向为接入网与通信测试技术。
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/ITA <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>
/NOR <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>
/SVE <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>
>>
>> setdistillerparams
<<
/HWResolution [2400 2400]
/PageSize [ ]
>> setpagedevice
