prentice hallhigh performance tcp/ip networking, hassan-jain chapter 6 tcp/ip performance over...

Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain

Chapter 6

TCP/IP Performance over Wireless

Networks


Objectives

Gain a high-level overview of the most widely used wireless networks

Understand how characteristics of wireless links adversely impact TCP performance

Learn techniques to enhance TCP/IP performance over wireless networks


Contents

Wireless networks TCP performance issues over wireless

links Improve TCP performance over wireless

links Evolution of wireless systems


Wireless

Networks


Generic characteristics of Wireless Networks

Similar propagation delay as wireline networks

High error rateInterferenceAtmospheric conditionMultipath fading


Wireless LAN (WLAN)

Wireless link layer Operate at 900 MHz/2.4 GHz/5 GHz band Ethernet connectivity to higher layers

Same headerSame checksumSame frame size


WLAN (Cont.)

MAC employs CSMANo Collision Detection (CD)Loss/error recovery left to higher layers

Interconnection with wired networksThrough a router equipped with both wired and

wireless interfacesThrough a transparent bridge


Examples of WLAN

Lucent’s WaveLan900 MHz or 2.4 GHz2 MbpsCSMA/CA

IEEE 802.11An enhancement over WaveLan

Optional ACKWLAN coordination (master host)

1 or 2 Mbps


Examples of WLAN (Cont.)

IEEE 802.11aOperate a 5 GHz bandBit rate: between 6 and 54 Mbps

IEEE 802.11bOperate a 2.4 GHz bandBit rate: 5.5/11 Mbps


Cellular Communications (CC) Networks

First generation (e.g. AMPS)Analog

Second generationDigitalModest bit rateCircuit-switchedEmployed TDMA/CDMA for medium control


CC Networks (Cont.)

Higher transmission and propagation delays, compared with WLAN

FEC added to each frame Interleaving (of frames) implemented


CC Networks (Cont.)

Interconnected to other networks using Interworking Function (IWF)

Fig. 6.1


Examples of CC Systems

GSMData rate: 9.6 Kbps240 bits ARQ (selective repeat)Variable throughput and delay

IS-136Data rate: 9.6 KbpsAdvanced ARQ (256 bits)


Examples of CC Systems (Cont.)

IS-95 (CDMA)Data rate: 8.6 Kbps172 bits ARQNegative ACKTrade reliability for limited delay variance


TCP

Performance over

Wireless


TCP Performance Issues

Inappropriate reduction of congestion windowTCP backs off upon detection of packet lossWireless transmission errors not related to

network congestion

Severe degradation in TCP throughput


TCP Performance Issues (Cont.)

Throughput loss WLAN

Frame Error Rate (FER)22% reduction in WaveLan

CC systemsIncreased processing delay due to interleavingWidely varying RTTDisruptions caused by link resets


Improving TCP

Performance


TCP Enhancement Schemes

Splitting TCP ConnectionsSplit TCP connections at wireless gatewaysReduce TCP end-to-end pathSignificant processing overhead


TCP Enhancement Schemes (cont.)

Snooping TCP at BSBetter than split TCPConfine retransmission to wireless paths onlyFig. 6.4


TCP Enhancement Schemes (Cont.)

Notifying the causes of packet lossExplicit Loss Notification (ELN)Work well together with Snoop TCP

Adding selective ACK to TCPSACKCombat multiple losses in one RTT


Comparison

Things need to consider when assess TCP enhancement schemesEnd-to-end semanticsIP payload accessWireless gateway overheadEase of deploymentTable 6.4


Evolution of Wireless Systems


Evolution of Wireless Systems

Trends in CC systemsSupport high bit rate data service

HSCSDGPRSEDGE

Third generation CC systemsUMTS3G


Trends in WLAN

Provide high speeds Support mobility between adjacent

networks Develop more efficient MAC protocols Personal Area Network (PAN) Bluetooth LMDS


TCP/IP over Heterogeneous Wireless Systems

ChallengesMultiple systems co-existDirect interoperability between different wireless

systemsHierarchical cellular systems

Research projectsMulti-Service Link Layer (MSLL)Wireless Internet Network (WINE)Wireless Adaptation Layer (WAL)

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