centaur: realizing the full potential of centralized wlans through a hybrid data path vivek...
TRANSCRIPT
![Page 1: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/1.jpg)
CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid
Data Path
Vivek Shrivastava* , Shravan Rayanchu, Suman BanerjeeUniversity of Wisconsin-Madison
Nabeel Ahmed, Srinivasan KeshavUniversity of Waterloo, Ontario
Konstantina PapagiannakiIntel Labs, Pittsburgh
Arunesh MishraGoogle Inc.
![Page 2: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/2.jpg)
2
Centralization of Enterprise WLANs
2Vivek Shrivastava
Wireless controller
Access Point
Clients
Internet
![Page 3: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/3.jpg)
3
Centralization of Enterprise WLANs
3Vivek Shrivastava
Power controlChannel assignment
Common control plane functions
![Page 4: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/4.jpg)
4
Centralization of Enterprise WLANs
4Vivek Shrivastava
What about data plane functions?
Power controlChannel assignmentData scheduling ?
![Page 5: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/5.jpg)
5 5Vivek Shrivastava
Can centralized scheduling help?
![Page 6: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/6.jpg)
6 6Vivek Shrivastava
Can centralized scheduling help?
Hidden terminals
![Page 7: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/7.jpg)
7 7Vivek Shrivastava
Hidden terminals
Can centralized scheduling help?
![Page 8: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/8.jpg)
8 8Vivek Shrivastava
Hidden terminals
Can centralized scheduling help?
![Page 9: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/9.jpg)
9 9Vivek Shrivastava
1. Carrier sense
Hidden terminals
Can centralized scheduling help?
![Page 10: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/10.jpg)
10 10Vivek Shrivastava
2. Channel free, transmit
Hidden terminals
Can centralized scheduling help?
![Page 11: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/11.jpg)
11 11Vivek Shrivastava
• Collision!• Backoffs• Low throughputs
3. Collision !
Can centralized scheduling help?
![Page 12: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/12.jpg)
12
How bad is it ?
12Vivek Shrivastava
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
![Page 13: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/13.jpg)
13 13Vivek Shrivastava
A lost opportunity ?
Suppose infrastructure can gather conflict data
![Page 14: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/14.jpg)
14 14Vivek Shrivastava
A lost opportunity ?
And when packets arrive …
![Page 15: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/15.jpg)
15 15Vivek Shrivastava
A lost opportunity ?
… realize interference will happen …
![Page 16: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/16.jpg)
16 16Vivek Shrivastava
A lost opportunity ?
1. Transmit first packet
![Page 17: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/17.jpg)
17 17Vivek Shrivastava
A lost opportunity ?
1. Transmit first packet2. Transmit second packet
with delay
![Page 18: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/18.jpg)
18 18Vivek Shrivastava
Use an in-band scheduler
Simple FIFO schedule with interference
avoidance
Scheduling functionality
![Page 19: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/19.jpg)
19
What about exposed terminals ?
19Vivek Shrivastava
• 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
![Page 20: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/20.jpg)
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
20Vivek Shrivastava
![Page 21: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/21.jpg)
21
Contributions
1.Design CENTAUR, a hybrid (partly centralized, partly distributed) scheduling approach
• Resolves hidden and exposed terminals
• Requires no client modifications
• Requires no carrier sense disabling
2.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
21Vivek Shrivastava
![Page 22: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/22.jpg)
22
Outline
• A naïve attempt at centralized scheduling (DET)
•Our hybrid centralized scheduler (CENTAUR)
•Evaluation
•Related Work
•Summary
22Vivek Shrivastava
![Page 23: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/23.jpg)
23
Outline
• A naïve attempt at centralized scheduling (DET)
•Our hybrid centralized scheduler (CENTAUR)
•Evaluation
•Related Work
•Summary
23Vivek Shrivastava
![Page 24: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/24.jpg)
24 24Vivek Shrivastava
DET: A Simple Deterministic Scheduler
![Page 25: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/25.jpg)
25 25Vivek Shrivastava
DET: A Simple Deterministic Scheduler
Input: Conflict graph
![Page 26: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/26.jpg)
26 26Vivek Shrivastava
DET: A Simple Deterministic Scheduler
Goal: Schedule each incoming downlink packet
Input: Conflict graph
![Page 27: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/27.jpg)
27 27Vivek Shrivastava
DET: A Simple Deterministic Scheduler
1 2 3 4Transmission
slots
Goal: Schedule each incoming downlink packet
Input: Conflict graph
![Page 28: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/28.jpg)
28 28Vivek Shrivastava
DET: A Simple Deterministic Scheduler
1 2 3 4Transmission
slots
1. New packet arrives
![Page 29: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/29.jpg)
29 29Vivek Shrivastava
DET: A Simple Deterministic Scheduler
1 2 3 4Transmission
slots
1. New packet arrives2. Find the earliest conflict
free slot
![Page 30: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/30.jpg)
30 30Vivek Shrivastava
DET: A Simple Deterministic Scheduler
1 2 3 4Transmission
slots
1. New packet arrives2. Find the earliest conflict
free slot
![Page 31: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/31.jpg)
31 31Vivek Shrivastava
DET: A Simple Deterministic Scheduler
1 2 3 4Transmission
slots
1. New packet arrives2. Find the earliest conflict
free slot3. Schedule the packet in that
slot
5
![Page 32: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/32.jpg)
Performance of DET
4xNo gains for exposed terminals; Non-
conflicting links perform worse under load
32Vivek Shrivastava
![Page 33: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/33.jpg)
33
Outline
• A naïve attempt at centralized scheduling (DET)
•Our hybrid centralized scheduler (CENTAUR)
•Evaluation
•Related Work
•Summary
33Vivek Shrivastava
![Page 34: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/34.jpg)
34
Overview of CENTAUR
• Incorporate basic DET scheduler
• Tackle DET’s shortcomings:
• Amortize scheduling overhead
• Improve performance for exposed links
• Avoid degrading normal links
• Coexist with non-enterprise and uplink traffic
34Vivek Shrivastava
![Page 35: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/35.jpg)
35
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
35Vivek Shrivastava
![Page 36: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/36.jpg)
36
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
36Vivek Shrivastava
![Page 37: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/37.jpg)
37
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
37Vivek Shrivastava
Wired ack
![Page 38: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/38.jpg)
38
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
38Vivek Shrivastava
![Page 39: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/39.jpg)
39
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
39Vivek Shrivastava
![Page 40: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/40.jpg)
40
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
40Vivek Shrivastava
![Page 41: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/41.jpg)
41
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
41Vivek Shrivastava
![Page 42: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/42.jpg)
42
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
42Vivek Shrivastava
Wired ack
![Page 43: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/43.jpg)
43
(1) Avoid Scheduling Overheads
• Problem: Per-packet scheduling performs poorly under high network loads
• Solution:
• Schedule packets in batches (or epochs)
43Vivek Shrivastava
![Page 44: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/44.jpg)
44
(2) Improve Exposed Terminals
44Vivek Shrivastava
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 45: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/45.jpg)
45 45Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 46: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/46.jpg)
46 46Vivek Shrivastava
Variable wired delay
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 47: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/47.jpg)
47 47Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 48: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/48.jpg)
48 48Vivek Shrivastava
Carrier sense, deferral
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 49: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/49.jpg)
49 49Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 50: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/50.jpg)
50 50Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 51: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/51.jpg)
51 51Vivek Shrivastava
Schedule packets in batches
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 52: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/52.jpg)
52 52Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 53: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/53.jpg)
53 53Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 54: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/54.jpg)
54 54Vivek Shrivastava
First packets can be out of sync
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 55: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/55.jpg)
55 55Vivek Shrivastava
Waiting packets synchronized by carrier sense !
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 56: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/56.jpg)
56 56Vivek Shrivastava
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 57: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/57.jpg)
57 57Vivek Shrivastava
After first packet, both APs transmit
simultaneously.
(2) Improve Exposed Terminals
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets, fix backoff periods
![Page 58: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/58.jpg)
58
(3) Avoid Degrading Normal Links
58Vivek Shrivastava
A B
C D
Hidden terminals
Non-hidden/Non-exposed
![Page 59: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/59.jpg)
59
(3) Avoid Degrading Normal Links
59Vivek Shrivastava
A B
C D
Scheduler
![Page 60: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/60.jpg)
60
(3) Avoid Degrading Normal Links
60Vivek Shrivastava
A B
C D
Scheduler
![Page 61: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/61.jpg)
61
(3) Avoid Degrading Normal Links
61Vivek Shrivastava
A B
C D
Scheduler
![Page 62: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/62.jpg)
62
(3) Avoid Degrading Normal Links
62Vivek Shrivastava
A B
C D
Scheduler
Hybrid scheduling
![Page 63: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/63.jpg)
63
Outline
• A naïve attempt at centralized scheduling (DET)
•Our hybrid centralized scheduler (CENTAUR)
•Evaluation
•Related Work
•Summary
63Vivek Shrivastava
![Page 64: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/64.jpg)
64
Large-Scale Experiments
•Platform:
• Two WLAN testbeds in separate buildings
•Topology
• Representative: 7 APs, 12 clients
•Traffic and metrics
• UDP, TCP, VoIP, HTTP (real traces)
• Throughput, delay, MOS, web transaction delay
64Vivek Shrivastava
![Page 65: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/65.jpg)
65
Result 1: UDP/TCP Performance
65Vivek Shrivastava
![Page 66: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/66.jpg)
66
Result 1: UDP/TCP Performance
66Vivek Shrivastava
DCF
![Page 67: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/67.jpg)
67
Result 1: UDP/TCP Performance
67Vivek Shrivastava
DCF
![Page 68: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/68.jpg)
68
Result 1: UDP/TCP Performance
68Vivek Shrivastava
DCF Per Packet
![Page 69: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/69.jpg)
69
Result 1: UDP/TCP Performance
69Vivek Shrivastava
DCF Per Packet
![Page 70: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/70.jpg)
70
Result 1: UDP/TCP Performance
70Vivek Shrivastava
Epoch BasedDCF Per Packet
![Page 71: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/71.jpg)
71
Result 1: UDP/TCP Performance
71Vivek Shrivastava
Epoch BasedDCF Per Packet
Hidden terminal starves some clients
![Page 72: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/72.jpg)
72
Result 1: UDP/TCP Performance
72Vivek Shrivastava
Epoch BasedDCF Per Packet
Better fairness
than DCF
![Page 73: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/73.jpg)
73
Result 1: UDP/TCP Performance
73Vivek Shrivastava
Epoch BasedDCF Per Packet
Exploits exposed
terminals, higher system
throughput
![Page 74: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/74.jpg)
74
Result 1: UDP/TCP Performance
74Vivek Shrivastava
Epoch BasedDCF Per Packet
Avg. delay is smallest for epoch
based scheduling
![Page 75: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/75.jpg)
75
Result 1: UDP/TCP Performance
75Vivek Shrivastava
Epoch BasedDCF Per Packet
90th percentile delays are higher for
epoch based scheduling
![Page 76: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/76.jpg)
76
Result 1: UDP/TCP Performance
76Vivek Shrivastava
Epoch BasedDCF Per Packet
CENTAUR yields up to 60% higher total throughput and 50% lower per-packet delay
compared to DCF
![Page 77: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/77.jpg)
77
More Results in Paper
•Centaur micro-benchmarks: performance for exposed and hidden terminals under centaur
•Uplink traffic: coexistence and persistent gains with different fractions of uplink traffic
•Data rate: robust to changes in data rate and ARF
•Realistic HTTP traces: significant reduction in web transaction delay
•VoIP traffic: better performance (MOS) for voice traffic with small epoch duration
77Vivek Shrivastava
![Page 78: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/78.jpg)
78
Related Work
•Commercial WLAN offerings (Aruba, Meru)
•Theoretical formulations (Vaidya ‘00, Kanodia ‘01)
•Epoch based scheduling (Kompella ‘05, 802.11n/e)
• Interference mitigation (CMAP, SIC, Shuffle)
78Vivek Shrivastava
![Page 79: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/79.jpg)
79
Summary
• Interference a growing problem in enterprises
•Careful design of a centralized data plane provides substantial performance gains
•CENTAUR implements a hybrid data path to improve aggregate performance without client modifications
•CENTAUR does not disable carrier sense and co-exists with non-enterprise and uplink traffic
79Vivek Shrivastava
![Page 80: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/80.jpg)
Vivek Shrivastava 80
Future work
•Even more efficient conflict graph generation
•What if we were allowed client modifications ?
Questions ?
![Page 81: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/81.jpg)
Characterizing System Latencies
System delays are high and variable, leading to inaccuracies for per-packet
scheduling
81
![Page 82: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/82.jpg)
82
Evaluation of Micro-Probing
82Vivek Shrivastava
Topologies 20 node 30 nodeBandwidth
Tests16.2 mins 1hr 11 mins
Micro-Probing
~4 secs ~11 secs
Can be computed in stages with each instance taking ~
2.5ms
![Page 83: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/83.jpg)
83
Result 2: Impact of Uplink Traffic
83Vivek Shrivastava
•Vary proportion of downlink/uplink traffic
•6 different configurations
•80/20 ➔ 40/60 (downlink/uplink)
•Results:
•Downlink: 1.6x ➔ 6.8x gain in throughput
•Uplink: 1x ➔ 1.18x gain in throughput
CENTAUR provides persistent gains for different proportions of uplink and downlink
traffic load
![Page 84: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/84.jpg)
84
• Three topologies
• Hidden Heavy topology ➔ 10 links
• Exposed Heavy topology ➔ 6 links
• Mixed Topology ➔ 12 links
• Results: Up to 50% gain in overall system throughput
• Up to 6x gain for HT; Up to 1.7x gain for ET
Result 3: Impact of Topology
84Vivek Shrivastava
Improvements from using CENTAUR can be seen across many different network
topologies
![Page 85: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/85.jpg)
85
Result 2: Impact of Uplink Traffic
85Vivek Shrivastava
CENTAUR provides persistent gains for different proportions of uplink and downlink
traffic load
![Page 86: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/86.jpg)
86
Result 3: Impact of Topology
86Vivek Shrivastava
Improvements from using CENTAUR can be seen across many different network
topologies
![Page 87: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/87.jpg)
87
CENTAUR Micro-Benchmarks (1)
87Vivek Shrivastava
Exposed Terminals
![Page 88: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/88.jpg)
88
CENTAUR Micro-Benchmarks (II)
88Vivek Shrivastava
Hidden Terminals
![Page 89: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/89.jpg)
89
Result 1: UDP/TCP Performance
89Vivek Shrivastava
Client Index (1-12)
Client Index (1-12)
CENTAUR yields up to 60% higher total throughput and 50% lower per-packet delay
compared to DCF
![Page 90: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/90.jpg)
Other approaches to Hidden/Exposed Terminals
Mechanism
Target Proble
m
Approach
Client Changes Evaluation
CMAP [NSDI ‘07]
ZigZag [Sigcomm ’08] SIC [Mobicom ’08]
Centaur
Exposed
Hidden
ExposedHidde
n
Disable CS
Signal manipulatio
n
Centralized Scheduling
Yes
Yes
No
802.11
GNU Radio
802.11
Adaptive RTS/CTS [VTC ’03]
HiddenExtra
SignalingYes 802.1
1
![Page 91: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/91.jpg)
March,30 2009Prelim 2009
Other approaches to Hidden/Exposed Terminals
Mechanism
Target Proble
m
Approach
Client Changes Evaluation
CMAP [NSDI ‘07]
ZigZag [Sigcomm ’08] SIC [Mobicom ’08]
Centaur
Exposed
Hidden
ExposedHidde
n
Disable CS
Signal manipulatio
n
Centralized Scheduling
Yes
Yes
No
802.11
GNU Radio
802.11
Adaptive RTS/CTS [VTC ’03]
HiddenExtra
SignalingYes 802.1
1
Solve both hidden/expos
ed
![Page 92: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/92.jpg)
March,30 2009Prelim 2009
Other approaches to Hidden/Exposed Terminals
Mechanism
Target Proble
m
Approach
Client Changes Evaluation
CMAP [NSDI ‘07]
ZigZag [Sigcomm ’08] SIC [Mobicom ’08]
Centaur
Exposed
Hidden
ExposedHidde
n
Disable CS
Signal manipulatio
n
Centralized Scheduling
Yes
Yes
No
802.11
GNU Radio
802.11
Adaptive RTS/CTS [VTC ’03]
HiddenExtra
SignalingYes 802.1
1
No client side changes for
Centaur
![Page 93: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/93.jpg)
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 KeshavUniversity of Waterloo, Ontario
Konstantina PapagiannakiIntel Labs, Pittsburgh
Arunesh MishraGoogle Inc.
![Page 94: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/94.jpg)
94
WLANs HP LabsSeoul
National University
Our Testbed
Exposed Terminals
39% 9% 50%
Hidden Terminals
43% 70% 39%
Growth of Interference in Enterprise Wireless LANs
94
Interference an increasing problem according to leading enterprise WLAN
vendor
Vivek ShrivastavaVivek Shrivastava
![Page 95: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/95.jpg)
95
Centralization of Enterprise WLANs
95
Centralized control for better network security and manageability
Vivek Shrivastava
![Page 96: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/96.jpg)
96
Can Centralized Data Plane Scheduling Help?
96Vivek Shrivastava
![Page 97: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/97.jpg)
97
(2) Improve Exposed Terminals
97Vivek Shrivastava
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets to each exposed AP
• Fix back-off periods and use carrier-sensing to align transmissions -- double throughput!
![Page 98: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/98.jpg)
98
Related Work
•Commercial WLAN offerings (Aruba, Meru)
•Research proposals (MiFi, DenseAP, Smarta)
•TXOP in 802.11e/802.11n packet aggregation
• Interference Mitigation (CMAPs, ZigZag, SIC)
98Vivek Shrivastava
![Page 99: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/99.jpg)
99
Types of Interference
Hidden Terminals
Collis
ions
CarrierSense
Exposed Terminals
Focus on downlink conflicts
Vivek Shrivastava 11
![Page 100: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/100.jpg)
100
Can Centralized Data Plane Scheduling Help?
100Vivek Shrivastava
X Y
![Page 101: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/101.jpg)
101
Can Centralized Data Plane Scheduling Help?
101Vivek Shrivastava
X Y
![Page 102: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/102.jpg)
102
Can Centralized Data Plane Scheduling Help?
102Vivek Shrivastava
X Y
![Page 103: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/103.jpg)
103 103Vivek Shrivastava
Can Centralized Data Plane Scheduling Help?Hidden
terminals
![Page 104: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/104.jpg)
104
Quantifying Downlink Hidden Terminals
104Vivek Shrivastava
10% links suffer severe hidden terminal interference
![Page 105: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/105.jpg)
105
Quantifying Downlink Exposed Terminals
105
41% links can obtain double the throughput with CS disabled, indicating
exposed terminal interference
Vivek Shrivastava
![Page 106: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/106.jpg)
106
Result 1: UDP/TCP Performance
106Vivek Shrivastava
![Page 107: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/107.jpg)
107
Result 1: UDP/TCP Performance
107Vivek Shrivastava
![Page 108: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/108.jpg)
108
Result 1: UDP/TCP Performance
108Vivek Shrivastava
![Page 109: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/109.jpg)
109
Centralization of Enterprise WLANs
109Vivek Shrivastava
![Page 110: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/110.jpg)
110
(2) Improve Exposed Terminals
110Vivek Shrivastava
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets to each exposed AP
• Fix back-off periods and use carrier sensing to align transmissions -- double throughput!
![Page 111: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/111.jpg)
111
(2) Improve Exposed Terminals
111Vivek Shrivastava
• Problem: Exposed links can operate in parallel but don’t due to carrier-sensing
• Solution:
• Schedule batch of packets to each exposed AP
• Fix back-off periods and use carrier sensing to align transmissions -- double throughput!
![Page 112: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/112.jpg)
112
(3) Avoid Degrading Normal Links
112Vivek Shrivastava
![Page 113: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/113.jpg)
113
1. Can it solve any interference problems prevalent in enterprise WLANs
• Hidden and exposed terminals
• 88% of links suffer some losses due to co-channel interference (Jigsaw, Sigcomm 2007)
2. If so, how can we implement it efficiently for practical WLAN deployments
• No client modifications, support legacy clients
• Coexistence with non-enterprise, uplink traffic
113Vivek Shrivastava
Can Centralized Data Plane Help?
![Page 114: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/114.jpg)
114
Quantifying Downlink Interference
•Prior Work: Jigsaw [Sigcomm2006] analysis reveals 56% of all interference traffic is downlink in nature.
•Our Work: Two production WLANs
• W1: 5 floors, 9 APs, 45 clients
• W2: 1 floor, 21 APs, 51 clients
•Download ‘bulk’ traffic from the Internet
114Vivek Shrivastava
![Page 115: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/115.jpg)
115
WLANsUW-
MadisonUW-
Ontario
Exposed Terminals
39% 9%
Hidden Terminals
43% 70%
Growth of Interference in Enterprise Wireless LANs
115
Interference an increasing problem according to leading enterprise WLAN
vendor
Vivek ShrivastavaVivek Shrivastava
![Page 116: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/116.jpg)
116
Centralization of Enterprise WLANs
116Vivek Shrivastava
Can centralized data plane be useful for improving performance in
WLANs ?• About 70-80% of enterprise traffic
is downlink in nature
![Page 117: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/117.jpg)
117
(3) Avoid Degrading Normal Links
117Vivek Shrivastava
A B
C D
Scheduler
![Page 118: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/118.jpg)
118
(3) Avoid Degrading Normal Links
118Vivek Shrivastava
A B
C D
Scheduler
![Page 119: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/119.jpg)
119
(3) Avoid Degrading Normal Links
119Vivek Shrivastava
A B
C D
Scheduler
![Page 120: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/120.jpg)
120
(3) Avoid Degrading Normal Links
120Vivek Shrivastava
A B
C D
Scheduler
Hybrid scheduling
![Page 121: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/121.jpg)
121
Outline
•DET - A deterministic scheduler
•CENTAUR - A hybrid centralized scheduler
•Evaluation
•Related Work
•Summary
121Vivek Shrivastava
![Page 122: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/122.jpg)
122
Outline
•DET - A deterministic scheduler
•CENTAUR - A hybrid centralized scheduler
•Evaluation
•Related Work
•Summary
122Vivek Shrivastava
![Page 123: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/123.jpg)
Performance of DET
4xNo gains for exposed terminals; Non-
conflicting links perform worse under load
123Vivek Shrivastava
![Page 124: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/124.jpg)
124
Outline
•DET - A deterministic scheduler
•CENTAUR - A hybrid centralized scheduler
•Evaluation
•Related Work
•Summary
124Vivek Shrivastava
![Page 125: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/125.jpg)
125
DET: A Simple Deterministic Scheduler
• Key Idea: Perform per-packet scheduling
• Given
• Conflict graph G = (L,E)
• Scheduled packets {P1, P2, ..., Pr}; Unscheduled Pr+1
• Objective
• Minimize t(Pr+1)
• Constraint: No two packets on interfering links are scheduled together
• Schedule downlink packets only
125Vivek Shrivastava
![Page 126: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/126.jpg)
126
1. What are the problems it can solve ?
• Hidden and exposed terminals
2. Can we implement it efficiently ?
• No client modifications
• Coexistence with non-enterprise & uplink traffic
• Don’t disable carrier sensing
126Vivek Shrivastava
Can centralized scheduling help?
![Page 127: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/127.jpg)
127 127Vivek Shrivastava
Can centralized scheduling help?
![Page 128: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/128.jpg)
128 128Vivek Shrivastava
DET: A Simple Deterministic Scheduler
Packets arriving
• Schedule one packet at a time• Consider packets in order of arrival
1 2 3 4Transmission
slots
![Page 129: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/129.jpg)
129
What about exposed terminals ?
129
41% links can obtain double the throughput with CS disabled, indicating exposed terminal
interference
Vivek Shrivastava
![Page 130: CENTAUR: Realizing the Full Potential of Centralized WLANs Through a Hybrid Data Path Vivek Shrivastava*, Shravan Rayanchu, Suman Banerjee University of](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e725503460f94b71c48/html5/thumbnails/130.jpg)
130 130Vivek Shrivastava
Use an in-band scheduler
Simple FIFO schedule with interference
avoidance
scheduler