prentice hallhigh performance tcp/ip networking, hassan-jain chapter 6 tcp/ip performance over...
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Chapter 6
TCP/IP Performance over Wireless
Networks
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Contents
Wireless networks TCP performance issues over wireless
links Improve TCP performance over wireless
links Evolution of wireless systems
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Wireless
Networks
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Generic characteristics of Wireless Networks
Similar propagation delay as wireline networks
High error rateInterferenceAtmospheric conditionMultipath fading
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Cellular Communications (CC) Networks
First generation (e.g. AMPS)Analog
Second generationDigitalModest bit rateCircuit-switchedEmployed TDMA/CDMA for medium control
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
CC Networks (Cont.)
Higher transmission and propagation delays, compared with WLAN
FEC added to each frame Interleaving (of frames) implemented
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
CC Networks (Cont.)
Interconnected to other networks using Interworking Function (IWF)
Fig. 6.1
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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)
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Examples of CC Systems (Cont.)
IS-95 (CDMA)Data rate: 8.6 Kbps172 bits ARQNegative ACKTrade reliability for limited delay variance
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
TCP
Performance over
Wireless
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Improving TCP
Performance
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
TCP Enhancement Schemes
Splitting TCP ConnectionsSplit TCP connections at wireless gatewaysReduce TCP end-to-end pathSignificant processing overhead
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
TCP Enhancement Schemes (cont.)
Snooping TCP at BSBetter than split TCPConfine retransmission to wireless paths onlyFig. 6.4
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Comparison
Things need to consider when assess TCP enhancement schemesEnd-to-end semanticsIP payload accessWireless gateway overheadEase of deploymentTable 6.4
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Evolution of Wireless Systems
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Evolution of Wireless Systems
Trends in CC systemsSupport high bit rate data service
HSCSDGPRSEDGE
Third generation CC systemsUMTS3G
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Trends in WLAN
Provide high speeds Support mobility between adjacent
networks Develop more efficient MAC protocols Personal Area Network (PAN) Bluetooth LMDS
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Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
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)