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CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path

Explore the advantages of centralized WLANs through a hybrid approach optimizing data path functions. Learn how CENTAUR enhances performance and resolves common interference issues.

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CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path

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  1. CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path • Vivek Shrivastava* ,Shravan Rayanchu, Suman Banerjee • University of Wisconsin-Madison Nabeel Ahmed, Srinivasan Keshav University of Waterloo, Ontario Konstantina Papagiannaki Intel Labs, Pittsburgh Arunesh Mishra Google Inc. * viveks@cs.wisc.edu 1

  2. Centralization of Enterprise WLANs Clients Internet Access Point Wireless controller Vivek Shrivastava 2

  3. Centralization of Enterprise WLANs Common control plane functions Power control Channel assignment Vivek Shrivastava 3

  4. Centralization of Enterprise WLANs What about data plane functions? Power control Channel assignment Data scheduling ? Vivek Shrivastava 4

  5. Can centralized scheduling help? Vivek Shrivastava 5

  6. Can centralized scheduling help? Hidden terminals Vivek Shrivastava 6

  7. Can centralized scheduling help? Hidden terminals Vivek Shrivastava 7

  8. Can centralized scheduling help? Hidden terminals Vivek Shrivastava 8

  9. Can centralized scheduling help? Hidden terminals Carrier sense Vivek Shrivastava 9

  10. Can centralized scheduling help? Hidden terminals 2. Channel free, transmit Vivek Shrivastava 10

  11. Can centralized scheduling help? • Collision! • Backoffs • Low throughputs 3. Collision ! Vivek Shrivastava 11

  12. How bad is it ? • Experiments on production building-wide WLANs • W1: 5 floors • 9 APs, 45 clients • W2: 1 floor • 21 APs, 51 clients 10% links suffer more than 70% throughput reduction Vivek Shrivastava 12

  13. A lost opportunity ? Suppose infrastructure can gather conflict data Vivek Shrivastava 13

  14. A lost opportunity ? And when packets arrive … Vivek Shrivastava 14

  15. A lost opportunity ? … realize interference will happen … Vivek Shrivastava 15

  16. A lost opportunity ? Transmit first packet Vivek Shrivastava 16

  17. A lost opportunity ? Transmit first packet Transmit second packet with delay Vivek Shrivastava 17

  18. Use an in-band scheduler Simple FIFO schedule with interference avoidance Scheduling functionality Vivek Shrivastava 18

  19. What about exposed terminals ? • In our experiments, about 41%of link pairs suffer from exposed terminal interference • Disabling carrier sense to solve the problem can be dangerous for uplink, non-enterprise traffic • We will show how centralization can help even here Vivek Shrivastava 19

  20. Challenge • Centralization has obvious overheads • How to make this feasible and useful under • Real applications • Common large-scale wireless environments • Presence of uplink and non-enterprise traffic • Requirements of no client modifications Vivek Shrivastava 20

  21. Contributions • Design CENTAUR, a hybrid (partly centralized, partly distributed) scheduling approach • Resolves hidden and exposed terminals • Requires no client modifications • Requires no carrier sense disabling • Evaluate CENTAUR on two WLAN testbeds with real-world traffic traces • 1.48x greater throughput for bulk data traffic • 1.38x reduction in web-transaction times Vivek Shrivastava 21

  22. Outline • A naïve attempt at centralized scheduling (DET) • Our hybrid centralized scheduler (CENTAUR) • Evaluation • Related Work • Summary Vivek Shrivastava 22

  23. Outline • A naïve attempt at centralized scheduling (DET) • Our hybrid centralized scheduler (CENTAUR) • Evaluation • Related Work • Summary Vivek Shrivastava 23

  24. DET: A Simple Deterministic Scheduler Vivek Shrivastava 24

  25. DET: A Simple Deterministic Scheduler Input: Conflict graph Vivek Shrivastava 25

  26. DET: A Simple Deterministic Scheduler Goal: Schedule each incoming downlink packet Input: Conflict graph Vivek Shrivastava 26

  27. DET: A Simple Deterministic Scheduler Goal: Schedule each incoming downlink packet Input: Conflict graph Transmission slots 1 2 3 4 Vivek Shrivastava 27

  28. DET: A Simple Deterministic Scheduler • New packet arrives Transmission slots 1 2 3 4 Vivek Shrivastava 28

  29. DET: A Simple Deterministic Scheduler • New packet arrives • Find the earliest conflict free slot Transmission slots 1 2 3 4 Vivek Shrivastava 29

  30. DET: A Simple Deterministic Scheduler • New packet arrives • Find the earliest conflict free slot Transmission slots 1 2 3 4 Vivek Shrivastava 30

  31. DET: A Simple Deterministic Scheduler • New packet arrives • Find the earliest conflict free slot • Schedule the packet in that slot Transmission slots 1 2 3 4 5 Vivek Shrivastava 31

  32. Performance of DET No gains for exposed terminals; Non-conflicting links perform worse under load 4x Vivek Shrivastava

  33. Outline • A naïve attempt at centralized scheduling (DET) • Our hybrid centralized scheduler (CENTAUR) • Evaluation • Related Work • Summary Vivek Shrivastava 33

  34. Overview of CENTAUR • Incorporate basic DET scheduler • Tackle DET’s shortcomings: • Amortize scheduling overhead • Improve performance for exposedlinks • Avoid degrading normal links • Coexist with non-enterprise and uplink traffic Vivek Shrivastava 34

  35. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 35

  36. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 36

  37. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Wired ack Vivek Shrivastava 37

  38. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 38

  39. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 39

  40. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 40

  41. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 41

  42. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Wired ack Vivek Shrivastava 42

  43. (1) Avoid Scheduling Overheads • Problem: Per-packet scheduling performs poorly under high network loads • Solution: • Schedule packets in batches (or epochs) Vivek Shrivastava 43

  44. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Vivek Shrivastava 44

  45. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Vivek Shrivastava 45

  46. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Variable wired delay Vivek Shrivastava 46

  47. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Vivek Shrivastava 47

  48. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Carrier sense, deferral Vivek Shrivastava 48

  49. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Vivek Shrivastava 49

  50. Problem: Exposed links can operate in parallel but don’t due to carrier-sensing • Solution: • Schedule batch of packets, fix backoff periods (2) Improve Exposed Terminals Vivek Shrivastava 50

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