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Chapter 5

Chapter 5. TCP Modeling. Objectives. Appreciate mathematical modeling of TCP for performance optimization of TCP/IP networks Understand the fundamental relationship between packet loss probability and TCP performance Apply a range of mathematical models to predict TCP performance. Contents.

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Chapter 5

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  1. Chapter 5 TCP Modeling

  2. Objectives • Appreciate mathematical modeling of TCP for performance optimization of TCP/IP networks • Understand the fundamental relationship between packet loss probability and TCP performance • Apply a range of mathematical models to predict TCP performance

  3. Contents • Motivation • Essentials of TCP modeling • TCP models

  4. Motivation

  5. Motivation for TCP Modeling • TCP operating scale is very large • Models are required to gain deeper understanding of TCP dynamics • Uncertainties can be modeled as stochastic processes • Drive the design of TCP-friendly algorithms for multimedia applications • Optimize TCP performance

  6. Essentials of TCP Modeling

  7. TCP Modeling Essentials • Mainly Reno flavors are modeled • Two main features are modeled • Window dynamics • Packet loss process

  8. Window Dynamics • Linear increase and multiplicative decrease is modeled • The standard assumption • X(t) = W(t)/RTT

  9. Packet Loss Process • Packet loss triggers window decrease • Packet loss is uncertain • This uncertainty is typically modeled as a stochastic process • E.g. probability p of losing a packet

  10. TCP Models

  11. Gallery of TCP Models • Periodic model • Detailed packet loss model • Stochastic model • Control system model • Network system model

  12. Periodic Model • Simplest model for TCP • No specific flavor assumed • Assumes a periodic pattern of congestion window • See Fig 5.1 • X(p) = (1/RTT)*Root(3/2p) • P is the packet loss probability

  13. Example 1 - Question If a TCP connection has an average RTT of 200ms, and packet loss probability 0.05, what is the average throughput?

  14. Example 1 - Answer RTT=0.2, p=0.05. Using Eq. (5.4), throughput is obtained as: X=(1/0.2)*(root(3/2x0.05)) = 27.4 pkts/sec

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