1 / 37

Presented by Sundar P Subramani

Bandwidth Estimation: Metrics Mesurement Techniques and Tools By Ravi Prasad, Constantinos Dovrolis, Margaret Murray and Kc Claffy IEEE Network, Nov/Dec 2003. Presented by Sundar P Subramani. Outline. Introduction Metrics Capacity Available bandwidth

kiara
Télécharger la présentation

Presented by Sundar P Subramani

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. Bandwidth Estimation: Metrics Mesurement Techniques and ToolsBy Ravi Prasad, Constantinos Dovrolis, Margaret Murray and Kc ClaffyIEEE Network, Nov/Dec 2003 Presented by Sundar P Subramani

  2. Outline • Introduction • Metrics • Capacity • Available bandwidth • TCP throughput and Bulk transfer capacity • Bandwidth estimation techniques • Taxonomy of tools • Conclusion

  3. Introduction • Bandwidth • Physical layer – Spectral width of electromagnetic signals • Data networks – Data rate • In this paper they discuss about the data networks

  4. Why b/w estimation needed? • P2P applications form user-level networks based on b/w between them • Overlay n/w s configure routing tables based on b/w of the links • Service agreements between n/w provider and consumer done based on b/w availability at crucial points of the n/w

  5. Why can’t SNMP be used? • Network administrators can read router/switch information using SNMP protocol • End-to-end bandwidth estimation cannot be done in the above way

  6. Outline • Introduction • Metrics • Capacity • Available bandwidth • TCP throughput and Bulk transfer capacity • Bandwidth estimation techniques • Taxonomy of tools • Conclusion

  7. Hops and segments • Segment • Links at layer 2 • Physical point-to-point link • Virtual circuit • Shared access LAN (ETHERNET, FDDI) • Hop • Links at layer 3 • Sequence of segments connected by switches, bridges and other layer 2 devices • Path p from s to v • Sequence of hops from s to v

  8. Capacity • Transmission rate limited by • Capacity of the physical link • Speed of the transmitter/receiver hardware • Overhead in Layer 2 in terms of encapsulation and framing produces lower rate as far as layer 3 is concerned

  9. Capacity • Tx time of IP packet of size LL3 in a link of capacity CL2 is • Where, HL2 is the length of the layer 2 header

  10. Capacity of layer 3

  11. Effect of packet size on capacity usage

  12. Capacity • Capacity of a hop • Maximum possible IP layer transfer rate at that hop • Maximum layer 2 transfer can occur only with MTU sized packets • Bit rate mesured at IP layer transferring MTU sized packets

  13. Capacity of a path • Minimum link capacity determines capacity of the path • Where • H is the number of hops • Ci Is the capacity of the ith hop

  14. Problems • Traffic shapers • Rate limiters • Wireless networks like 802.11 • Operate at different rates • 11, 5.5, 2 or 1 Mbps • Definition holds during time at which the capacity remains constant

  15. Average utilization • At any time • Link used fully  utilization =1 • Not used  utilization =0 • Avg utilization from time t-α to t is given by

  16. Utilization of a link Link used 8 out of 20 time slots until T So the link utilization is 40%

  17. Available bandwidth • Let ui be the average utiliztion of the link i over a period of time • Let Ci be the capacity of the hop i • Then the available bandwidth during that period • Ai = (1 – ui) Ci • Available bandwidth along the path

  18. Pipe model

  19. Assumptions • Link utilization remains constant over the duration of mesurement • Reasonable for short intervals • Load variations impact the measurement over a long period • So available b/w mesurements should be done quickly • Since capacity remains constant those measurements need not be made quickly

  20. TCP throughput and Bulk transfer capacity • TCP throughput depends on various parameters • Congestion window • RTT • Slow start mechanism • Capacity and load along the path • BTC • Maximum capacity obtainable by a TCP connection

  21. Difference between BTC and available b/w • BTC is TCP specific • Available b/w is transport protocol independent • BTC depends on the how a TCP connection throughput is affected by other flows • Available b/w assumes average load remains constant and estimates additional bandwidth

  22. Outline • Introduction • Metrics • Capacity • Available bandwidth • TCP throughput and Bulk transfer capacity • Bandwidth estimation techniques • Taxonomy of tools • Conclusion

  23. Variable size packet probing • Measures capacity of each hop • Measure RTT • Limit packet propogation by TTL • Uses ICMP to measure RTT until that hop

  24. Variable size packet probing • RTT includes: • Serialization delay • Delay to send packet of length L across channel of capacity C = L/C • Propogation delay • Time taken to traverse the link • Queuing delay • Delay in routers/Switches

  25. Variable size packet probing • Send multiple packets and calculate minimum RTT • Assumption: for minimum RTT no queuing delay • RTT has two terms • Delay independent of packet size = α • Based on packet size where

  26. Variable size packet probing

  27. packet size vs RTT

  28. Packet pair dispersion probing • Measures end-to-end capacity

  29. Problems • Assumption that no other traffic exists is not real • Existing traffic can increase/decrease the estimate • Solution? • Send multiple pairs and get a statistical estimate • Does not always yield a correct estimate

  30. Self-loading periodic streams • Measures end-to-end available bandwidth • Sends k packets at different rates • Receiver notifies the “one way delay trends” • If stream rate greater than available b/w • One way delay will grow large • Else • Packets will not make the one way delay large

  31. One way delay

  32. Train dispersion probing • Similar to packet pair dispersion probing • Instead of sending just two packets send a train of packets • Calculate the average dispersion rate

  33. Taxonomy of estimation tools Per-hop capacity estimation tools • Pathchar • First tool to implement • Clink • On routing instability collects data along all paths • Until one path provides statistically significant estimate • Pchar • Uses linear regression algorithms

  34. Taxonomy of estimation tools end-to-end capacity estimation tools • BProbe • Uses packet pair dispersion • Uses variable sized packets to improve efficiency • Access needed only in sender side, uses ICMP messages • Nettimer • Uses sophisticated “kernel density algorithm” to provide better accuracy • Pathrate • Sprobe

  35. Available bandwidth estimation tools • CProbe • Measures dispersion of a train of eight maximum sized packets • It measures dispersion rate and not available bandwidth • Dispersion rate depends on all links of the path and the train’s initial rate • Available b/w depends only on tight link of the path • Pathload • Implements SLoPS • Used UDP and requires access at both ends • Reports range • Center represents the average • Range represents values during mesurement period

  36. TCP throughput and BTC measurement tools • Treno • emulates TCP sends UDP packets to receiver • Replies with ICMP port unreachable • Does not require access to remote end • ICMP rate limited • Accuracy of Treno affected • Cap • More accurate than Treno • Uses UDP for TCP data and ACK • Requires access at both ends

  37. Intrusiveness • If probe packets comparable to available b/w • VPS are non intrusive • One packet per RTT • PPTD tools create bursts which last only for a very short duration • Only a small fraction of available b/w used • BTC tools are intrusive • They capture all b/w for a specific duration

More Related