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Transcript of 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
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
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
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Wireless
Networks
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Generic characteristics of Wireless Networks
Similar propagation delay as wireline networks
High error rateInterferenceAtmospheric conditionMultipath fading
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
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
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
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
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
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
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
CC Networks (Cont.)
Interconnected to other networks using Interworking Function (IWF)
Fig. 6.1
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)
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
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
TCP
Performance over
Wireless
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
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
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Improving TCP
Performance
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
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
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
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
Prentice HallHigh Performance TCP/IP Networking, Hassan-Jain
Evolution of Wireless Systems
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
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
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)