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Active Queue Management for Web Traffic. Mark Claypool, Bob Kinicki and Matt Hartling Worcester Polytechnic Institute Computer Science Department Worcester, MA 01609 {claypool,rek}@cs.wpi.edu. Outline. Motivation RED SHRED Algorithm Performance Metrics Web Traffic Model

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active queue management for web traffic

Active Queue Management for Web Traffic

Mark Claypool, Bob Kinicki and Matt Hartling

Worcester Polytechnic Institute

Computer Science Department

Worcester, MA 01609

{claypool,rek}@cs.wpi.edu

IPCCC04 April 16, 2004

outline
Outline
  • Motivation
  • RED
  • SHRED Algorithm
  • Performance Metrics
  • Web Traffic Model
  • Topology and Experimental Procedures
  • RED, SHRED and Drop Tail Results
  • Conclusions

IPCCC04 April 16, 2004

motivation for active queue management
Motivation for Active Queue Management
  • Congestion is still an Internet problem.
  • Short TCP Web flows dominate the Internet.
  • Mice – Web objects yield short-lived flows {smaller than 2KB}.
  • TCP slow-start provides biased performance for short Web flows.

IPCCC04 April 16, 2004

motivation for shred
Motivation for SHRED
  • TCP uses cwnd to limit a flow’s sending rate.
  • Fast Retransmit is ineffective when cwnd is less than four and for last three packets of a flow.
  • Retransmission Time Out [RTO] penalty is high in the first few packets of a flow.

IPCCC04 April 16, 2004

red routers
RED Routers
  • Random Early Detection (RED) detects congestion “early” by maintaining an exponentially-weighted average queue size.
  • RED probabilistically drops packets before the queue overflows to signal congestion to TCP sources.
  • RED attempts to avoid global synchronization and bursty packet drops.

IPCCC04 April 16, 2004

slide6
RED

packet

maxth

minth

minth::average queue length threshold for triggering probabilistic drops/marks.

maxth ::average queue length threshold for triggering forced drops.

IPCCC04 April 16, 2004

red parameters
RED Parameters

qavg:: average queue size

qavg = (1-wq) * qavg + wq* instantaneous queue size

wq::weighting factor 0.001 <= wq<= 0.004

maxp:: maximum dropping/marking probability

pb = maxp * (qavg – minth) / (maxth – minth)

pa= pb / (1 – count * pb)

buffer_size ::the size of the router queue in packets.

IPCCC04 April 16, 2004

red router mechanism
RED Router Mechanism

1

Dropping/Marking Probability

maxp

0

Min-threshold

Queue Size

Max-threshold

AverageQueue Length (avgq)

IPCCC04 April 16, 2004

short lived flow friendly red shred
SHort-lived flow friendly REDSHRED

Basic SHRED Idea

To lower the drop probability for flows with small cwnds and to increase the drop probability for flows with relatively large cwnds.

IPCCC04 April 16, 2004

shred
SHRED

SHRED uses an ‘edge hint’ and inserts the current value of TCP cwnd into IP packet header.

Upon packet arrival at SHRED router:

cwndavg = (1 – wc) cwndavg + (wc) cwndsample

where

wc set to 0.002

IPCCC04 April 16, 2004

shred1
SHRED

SHRED modifiesminth and maxp

minth-mod =minth

+(maxth – minth) x (1 – cwndsample / cwndavg)

maxp-mod =maxp x (maxth – minth-mod) / (maxth – minth)

and re-computes pb

pb = maxp-modx (qavg – minth-mod) /(maxth – minth-mod)

IPCCC04 April 16, 2004

shred mechanism using gentle red
SHRED Mechanismusing gentle RED

IPCCC04 April 16, 2004

web traffic characterization
Web Traffic Characterization
  • General Web flow modeling through congestion yields increased response times that in turn decrease the load generated by a Web client.
  • The model constructed has multiple objects per Web page downloaded in parallel and followed by a waiting period determined by the page generation rate.

IPCCC04 April 16, 2004

web traffic characterization1
Web Traffic Characterization
  • For ns-2 simulations:

Pareto II used to generate Web objects {min =12 bytes, max = 2MB, average object size = 10KB, 1.2 shape parameter}.

  • Canonical experiment :: 1 object per page (unless otherwise specified).

IPCCC04 April 16, 2004

performance metrics
Performance Metrics
  • Object transmission time - the time to transfer a single Web object from a server to the client.
  • Web response time – the time to download all objects in a Web page.
  • goodput (Mbps) - the rate at which packets arrive at the receiver. Goodput differs from throughput in that retransmissions are excluded from goodput.

IPCCC04 April 16, 2004

performance metrics1
Performance Metrics
  • Jain’s fairness
    • For any given set of user throughputs (x1, x2, …, xn), the fairness index to the set is defined:

f (x1, x2, …, xn) =

  • Percentage of packets dropped per flow.

IPCCC04 April 16, 2004

simulation topology
Simulation Topology

Web

Source

Web

Sink

100 Mbps

1 ms.

100 Mbps

1 ms.

10 Mbps

60 ms.

Congested

Router

Router

FTP

Source

FTP

Sink

RED Parameters

Minth = 30 pkts

maxth = 90 pkts

maxp = 0.1

wq = 0.0008

avg pkt = 974 bytes

maxq = 225 pkts

FTP

Source

FTP

Sink

IPCCC04 April 16, 2004

experimental procedures
Experimental Procedures
  • Simulated RED, SHRED and Drop Tail.
  • A few early longer duration experiments were conducted to determine point when simulations were stable.
  • All experiments were 160 simulated seconds.
  • Measurements were taken after 20 seconds of warm-up period.
  • Simulated both FTP traffic and Web traffic using TCP Reno.

IPCCC04 April 16, 2004

traffic mixes
Traffic Mixes
  • Web-only experiments
    • similar to RED-Tuning paper procedures.
  • Web-mixed experiments
    • FTP flows fixed at 10.
    • Web flows varied from 40 to 80% of bottlenecked bandwidth (10Mbps).

IPCCC04 April 16, 2004

traffic mixes cont
Traffic Mixes (cont.)
  • FTP-mixed experiments
    • Web traffic load fixed at 50%.
    • FTP flows varied from 0 to 40.
  • FTP-only experiments
    • No Web flows.
    • FTP flows varied from 10 to 100.

IPCCC04 April 16, 2004

shred performance
SHRED Performance
  • Web-only: SHRED has best performance.
  • Web-mixed: SHRED closer to uncongested performance. SHRED is better than RED and Drop Tail in “heavy-tail” of CDF due to RTO issues.
  • With normalized transmission time, SHRED ~4% better than RED which is 8% better than Drop Tail.
  • As number of flows increase, the SHRED benefit in packet drops widens.

IPCCC04 April 16, 2004

web response time
Web Response Time
  • More simulations run where there are multiple objects per page.
  • Uniform random distribution of Web objects/page for (1 to 8), (1 to 16) and (1 to 32) for Web-only and Web-mixed experiments.
  • Response time – the time to download the whole page of objects.

IPCCC04 April 16, 2004

table 1 ftp only goodput mbps
Table 1FTP-only Goodput (Mbps)

IPCCC04 April 16, 2004

table 2 ftp only jain s fairness
Table 2FTP-only Jain’s Fairness

IPCCC04 April 16, 2004

conclusions
Conclusions
  • SHRED produces lower object transmission times than either RED or Drop Tail in We-only and mixed traffic simulations.
  • SHRED yields significant response time improvement when there are multiple objects per page.
  • SHRED improvements do not negatively impact FTP traffic.
  • Basic ‘SH’ scheme can be applied to other AQMs (e.g., research on PISA).

IPCCC04 April 16, 2004