1 / 37

TCP/IP performance over 3G wireless links with rate and delay variation

TCP/IP performance over 3G wireless links with rate and delay variation. Mun Choon Chan and Ramjee, Bell Labes Presented by: Jinqiang Yang. Outline. Introduction Channel state based scheduling and variable rate and delay Performance evaluation

joan-nelson
Download Presentation

TCP/IP performance over 3G wireless links with rate and delay variation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. TCP/IP performance over 3G wireless links with rate and delay variation Mun Choon Chan and Ramjee, Bell Labes Presented by: Jinqiang Yang

  2. Outline • Introduction • Channel state based scheduling and variable rate and delay • Performance evaluation • “Ack” regulator to improve TCP/IP performance • Simulation results

  3. Introduction • 3G technologies provide wide band wireless data channel. • 3G1X 144Kbps • 3G1X-EVDO / HDR 2Mbps • Wireless channels are unstable / of poor quality • Neighbor channel interference, • Rayleigh fading • Multi-path fading

  4. Wireless channel quality • Packet losses are frequent • The TCP perceives packets lost over wireless channel as congestion • Loss over wireless channel decreases TCP throughput • Link layer retransmission / channels state based scheduling are employed to address this problem

  5. Link layer retransmission • Link layer retransmission: • Snoop agent: retransmits lost packet on wireless channel, suppresses duplicate Acks • Split TCP connection: the wireless part will do fast recovery and retransmission • Link layer retransmission is now part of the standards of CDMA2000 and UMTS

  6. Channel state based scheduling: variable rate and delay

  7. Channel state based scheduling • Intelligent packet scheduling mechanism • At the base station, wireless channel states are taken into account when scheduling data packets for different users • Give priority to users with better channel quality • Strict priority can lead to starvation of users with poor channel quality • Long term fairness can be achieved by proportional fair algorithm

  8. Channel state based scheduling • The gain It improves overall throughput • The cost Increased delay and rate variability

  9. Channel state based scheduling • Rate and delay variability effects: • The “Ack” arrivals are bursty => ( Ack compression) • Bursty Acks leads to bursty packet release from the source => • Then the bust of packets may experience multiple packet losses => • TCP throughput is degraded

  10. TCP/IP over wireless channel Performance evaluation

  11. Network architecture

  12. Experiment • 1000 ping packets were sent over CDMA 1X link. 144Kbps down link, 8 Kbps up link • Delay and Ack arrival time are measured. • No buffer overflow loss, because in this experiment buffer size is larger than the TCP window size.

  13. Ping Latency CDF of latency Latency: span from 150ms to 1s

  14. Ack inter arrival time CDF of Ack inter arrival time

  15. Ack inter arrival time • Evenly spaced Ack should be 172ms apart • 10% of the Ack arrive in 50ms after the previous one • significant Ack compression observed.

  16. Effect on Window size

  17. Effect on Window size

  18. Packet loss and window size

  19. Ack regulator

  20. Ack regulator • Goal: to achieve saw-tooth congestion window behavior even in presence of varying delay and rate • Method: by controlling the buffer overflow process in bottle-neck link • Ack regulator regulates the Ack flow back to the TCP source

  21. Ack regulator • RNC needs to maintain per-TCP flow queues instead of per-user queues. • Ack regulator is designed to avoid any buffer overflow loss until the TCP congestion window size reaches a preset threshold • Over the threshold, allow only a single buffer overflow loss.

  22. Ack regulator implementation

  23. Ack regulator • Conservative Mode: • Each time an Ack is sent back to the source, there is buffer space for at least two data packets from the source • Ensures that there is no buffer overflow loss even the TCP source increases window size

  24. Ack regulator • Non- conservative mode • Number of Acks sent back to source is less than or equal to the maximum packets the free buffer space can hold • A single packet loss occurs if TCP increases its window size by 1

  25. Ack regulator process

  26. Simulation Results

  27. Simulation topology

  28. Simulation parameters Single TCP flow n=1 FR=200Kb/s, RR=64Kb/s, FD has exponential distribution with mean between 20ms to 100ms RD= 400ms – mean(FD) Buffer size = 10 packets

  29. Variable delay

  30. Buffer size

  31. Variable delay • When delay variance increases from 20 to 100: • Throughput of Reno decrease by 30% • Throughput of Sack decreases by 19% • Throughput of Reno and Sack with Ack regulator decreases by 8% • Ack regulator is able to maintain a throughput of over 80% of maximum throughput (200Kbps)

  32. Variable Bandwidth Simulation parameters: • FR uniformly distributed with mean 200Kbps and variance from 20 to 75 • FD=200ms RR=64Kbps, RD=200ms • Buffer size=10

  33. Variable bandwidth

  34. Buffer size

  35. Variable bandwidth • Compared to TCP Reno, Ack regulator improves throughput by up to 15% • TCP Sack performs very well and has almost the same throughput as Ack regulator • If the rate variance is not large, Sack can handle the variance. For large rate variations, Sack performs better with Ack regulator.

  36. Summary • Ack regulator is able to increase TCP Reno and TCP Sack performance • Ack regulator delivers the same high throughput irrespective whether the TCP source is Reno or Sack • Ack regulator showed robust high throughput across different buffer sizes

  37. Thanks

More Related