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Authors: Károly FarkasPolly Huang
Balachander KrishnamurthyYin Zhang
Jitu Padhye
EidgenössischeTechnische HochschuleZürich
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2Károly Farkas, [email protected] 28th May, 2002
Talk Outline
� Introduction� Design Space of
TCP/HTTP Parameters
� Simulation Experiments
� Live Experiments � Conclusions� Future Plans
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3Károly Farkas, [email protected] 28th May, 2002
Introduction
Carrier A
Carrier B
ISP A
ISP B ISP C
ISP D
Internet
HTTP/1.0, HTTP/1.1Application Layer - HTTPApplication Layer - HTTP
Transport Layer - TCPTransport Layer - TCP Tahoe, Reno, NewReno, SACK, …
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4Károly Farkas, [email protected] 28th May, 2002
Comprehensive studyComprehensive study
TCP/HTTP aspects ⇒ Web performanceTCP/HTTP aspects ⇒ Web performance
Motivations & Goals
� Provide a taxonomy� Metodology to study
the key facets� ns based simulations� Live measurement
NO!
How?TCP/HTTP aspects ⇒ Web performanceTCP/HTTP aspects ⇒ Web performance
Comprehensive studyComprehensive studyGeneric Performance Forecast
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5Károly Farkas, [email protected] 28th May, 2002
Design Space
Taxonomy of Parameters
TCP and HTTP interactionHTTPTCP
which may influence Web performance:» user perceived latency» server load» network load
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6Károly Farkas, [email protected] 28th May, 2002
TCP Parameters� TCP variants
» Tahoe» Reno» NewReno» SACK
� MSS (Max. Segment Size)
� Delayed ACK (Acknowledgement)
� Timer granularity� Initial RTO
(Retransmission Timeout)
� ICW (Initial Congestion Window)
� Timestamp
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7Károly Farkas, [email protected] 28th May, 2002
HTTP Parameters� Connection management
» Parallel connections – multiple connections between client ⇔ server at the
same time
» Persistent connections– the connection stays open ⇒ some TCP overhead can
be avoided
» Pipelining– multiple requests without waiting for individual
responses ⇒ latency could be reduced
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8Károly Farkas, [email protected] 28th May, 2002
TCP and HTTP Interaction� Network condition
» diff. degree/distribution of packet drops ⇒ diff. recovery of TCP variants
� Persistent connections» effect depending on initial RTO, timer granularity
� Parallel connections» effect depending on initial CW, drop handling
� TCP implementations» memory/computation resource consumption
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9Károly Farkas, [email protected] 28th May, 2002
Simulation Experiments� Simulation software
» ns-2 (Network Simulator) � Simulation scenario ⇒ 50 ms
1 Mbps10 ms
10 Mbps10 ms
10 Mbps
from SURGEmodel⇐
� Workload settings
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10Károly Farkas, [email protected] 28th May, 2002
Simulation Experiments (2)
� Parameter space ⇒
� Other settings» duration of the simulations: 30 min» 3 loss levels (0.1%, 1%, 3%)» number of repetitions: 10 with diff. seed values» one parameter was changed at a time in every simulation
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11Károly Farkas, [email protected] 28th May, 2002
Simulation Results� Page download time
» MSS ↑ ; delayed ACK: off ⇒» TCP variants ⇒» Persistency: off ⇒» Parallel connections ↑ (loss: 0.1%; 1%) ⇒
� First response time» MSS ↑ ⇒
» Persistency: off ⇒» Pipelining; Parallel connections ↑ ⇒
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12Károly Farkas, [email protected] 28th May, 2002
Simulation Results (2)� Object download time
» MSS ↑ ⇒
» Pipelining: on ⇒» Number of parallel connections ⇒
� Server load» TCP parameters ⇒» Persistency: off » Pipelining: on ⇒» Parallel Connections ↓
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13Károly Farkas, [email protected] 28th May, 2002
Live Experiments� Measurement software
» Networking stack– the Alpine user-level library
» HTTP Client software–httperf
» HTTP Server software–boa Web server
� Test environment» local environment with dummynet
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14Károly Farkas, [email protected] 28th May, 2002
Measurement Results� Content for study
» canonical page: 54 images with emp. distribution» downloaded images: first 6, 12, 18, 54
� Results» Tahoe: data limited, small CW ⇒» SACK: large amount of data ⇒» SACK: high loss, small CW ⇒» MSS ↑ , delayed ACK: off ⇒» A good value for initial CW: 4
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15Károly Farkas, [email protected] 28th May, 2002
Conclusions� Impact of TCP parameters
» MSS ↑ , delayed ACK: off ⇒ �
» other parameters ⇒ �
� Impact of HTTP parameters» pipelining + HTTP/1.1 � ⇔ serial + HTTP/1.0 ∅∅∅∅
� Combined Impact of TCP & HTTP parameters» high loss, short flows, serial HTTP/1.1 ⇒ SACK �» long flows, serial HTTP/1.1 ⇒ Tahoe �» low loss, short flows ⇒ every TCP variant �
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16Károly Farkas, [email protected] 28th May, 2002
�To investigate the combined effect when more than one parameter has been changed
�To extend the live experiments from local area to wide area
Future Plans
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17Károly Farkas, [email protected] 28th May, 2002