Doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 1...

May 2007

Alex Ashley (NDS Ltd), Robert Miller (AT&T)

Slide 1

doc.: IEEE 802.11-07/0086r3

Submission

Access Point Collaboration for enhancing QoS and Spectrum Efficiency

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair [email protected] as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <[email protected]>.

Date: 2007-04-14

Name Company Address Phone email

Alex Ashley NDS Ltd NDS Ltd, One London Road, Staines, Middlesex, TW18 4EX, UK

+44 1784 848770 [email protected]

Robert Miller AT&T AT&T Labs - Research 180 Park Avenue, Bldg. 103, Room B251 Florham Park, NJ 07932

+1 973 236 6920 [email protected]

Yongho Seok LG Electronics 16 Woomyeon-Dong, Seocho-Gu, Seoul 137-724, Korea

+8225264225 [email protected]

Authors:

May 2007


Slide 2

doc.: IEEE 802.11-07/0086r3

Submission

Abstract

This presentation describes a mechanism to allow multiple APs on the same channel to cooperatively share time on the wireless medium

This enables enhanced QoS by allowing collaborating APs to avoid allocating overlapping CFPs and reduced probability of EDCA collisions

Proposal fulfils item 2a “Access Point Coordination – Intra ESS” in the TGV accepted work list

May 2007


Slide 3

doc.: IEEE 802.11-07/0086r3

Submission

Introduction

• We want to use 802.11 for “carrier grade” wireless voice & video distribution system

• Current QoS solutions not well suited to multiple BSS on the same channel– In some bands there are insufficient channels for every home to

have its own channel– Enterprise environment may have even higher AP densities

• Fulfils item 2a on TGv work list– “Time coordination between APs for resource management.

Could be useful for 802.11e to perform time slicing. Site Survey mode to perform tuning of the APs. Could be an initial install or on-going process.”

May 2007


Slide 4

doc.: IEEE 802.11-07/0086r3

Submission

Scope

• Improved throughput & QoS for multiple BSS on same channel within RF range– In both domestic and enterprise environments

• Domestic– Over-the-air communication

– No central management entity

• Enterprise– Wireless or DS used for communication

– Possibly a central management entity

May 2007


Slide 5

doc.: IEEE 802.11-07/0086r3

Submission

Example Domestic Application

Multiple dwelling unit• Many homes within

radio range of each other

• Homes share channels either due to insufficient channels or imperfect channel selection

May 2007


Slide 6

doc.: IEEE 802.11-07/0086r3

Submission

A Typical Enterprise Application

AccessPoint

MobilityServer

RadioResourceManager

1

23

4

5

6

7

8

910

11

Co-Channel InterferersUsing Same Frequency(coupled via stairwell)

Router

May 2007


Slide 7

doc.: IEEE 802.11-07/0086r3

Submission

Requirements

• Provides benefits in all QoS modes and even non-QoS BSS– DCF, EDCA, PCF, HCCA

• Simple to implement– Simple to implement in AP

– No changes to non-AP STAs

May 2007


Slide 8

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Submission

Requirements

• Compatible with legacy equipment

• Does not reduce robustness to rogue STAs– Based on “politeness” rather than ordering neighbours

to be silent

• Allows for dynamic changes in each BSS– E.g.

• Number of active streams in a BSS changes• Channel conditions change

May 2007


Slide 9

doc.: IEEE 802.11-07/0086r3

Submission

Assumptions

• Only consider time-based collaboration– Assume existing amendments / management entity for optimal

channel selection

• Relatively few BSS on same channel within radio range– Typically 2 to 3 overlapping BSS

• Does not try to provide perfect solution in all cases– Worst case behaviour is no worse than existing standard

– Optimal solution in general case probably NP-complete

May 2007


Slide 10

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Submission

Time-sharing on a channel

• Allow two or more APs to share time on a channel– Without coordination, collisions & back-offs can cause total

throughput to fall below required level

• Can be used to improve PCF & HCCA selection of CFP– Contention free period assumes no uncoordinated traffic

• Also helps CSMA/CA traffic– Reduces chances of collision with traffic from other BSS– Improves EDCA by silencing AC from other QBSS

May 2007


Slide 11

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Submission

AP Collaboration Proposal

• AP advertises that it supports collaboration– A new capability bit (from Extended Capabilities IE) in beacons

and probe responses

Bit Information Notes

2 Time Collaboration A STA shall set the Time Collaboration capability bit to true if dot11WirelessManagementImplemented is true and the AP supports sharing of time on the wireless medium and implements the CFP Offer and CFP Offer Response action frames. Otherwise this capability bit shall be set to false.

3-n Reserved

May 2007


Slide 12

doc.: IEEE 802.11-07/0086r3

Submission

AP Collaboration Proposal (2)

• An AP can choose to offer silent time to another AP– If accepted, the AP silences its associated STAs for the specified time

• However, an AP can choose to “defect”– An AP does not have to repay the sacrifice of another AP

– An AP offering silence can choose not to honour its offer

• This is an example of the “Prisoner's Dilemma”– The incredibly simple “tit-for-tat” approach has been shown to be an

optimal solution

– “tit-for-tat with forgiveness” better suited to a wireless network as messages can be lost

May 2007


Slide 13

doc.: IEEE 802.11-07/0086r3

Submission

Tit-for-tat Collaboration

Round n Round n+1

AP1 AP2 AP1 AP2

Collaborate Collaborate Collaborate Collaborate

Collaborate Defect Defect Collaborate

Defect Collaborate Collaborate Defect

Defect Defect Defect Defect

AP1 AP2 Outcome

Collaborate Collaborate Both APs get some time on the network while the other one is silent

Collaborate Defect AP2 gains extra network time at the expense of AP1

Defect Collaborate AP1 gains extra network time at the expense of AP2

Defect Defect Both APs exhibit standard 802.11 behaviour

May 2007


Slide 14

doc.: IEEE 802.11-07/0086r3

Submission

Over-the-air Collaboration

• Uses 2 new action frames– CFP Offer, CFP Offer Response

• Contents of these action frames use existing IEs– No new IEs required

Order Information

1 Category

2 Action

3 Dialog Token

4 Quiet Element

Order Information

1 Category

2 Action

3 Dialog Token

4 Status Code

5 Quiet Element (optional)

Table v53—CFP Offer frame body Table v54—CFP Offer Response frame body

May 2007


Slide 15

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Submission

Via-DS Collaboration• Aimed at larger-scale enterprise applications• Favors more centralized coordination architectures• Key to organized radio resource reuse layouts• Uses Ethernet and possibly dedicated server to coordinate APs.• Contribution covers capability enablement rather than method• Assumes synchronization of APs (e.g., clocking, network time)• Sharing Period = Only 1 for efficiency/simplicity• Requires MIB variables and related Beacon/Silent Period

adjustment capability.– Capability bit (ability to comply with feature)– Beacon Offset (from absolute time reference) – Silent Period Offset (from beacon time reference)– Silent Period Duration– Grant Period Offset (from beacon time reference)– Grant Period Duration

May 2007


Slide 16

doc.: IEEE 802.11-07/0086r3

Submission

Via-DS Sharing DiagramBeaconAP #1

BeaconAP #2

Beacon Offset

Silent Period Offset

Exclusive Use - AP #2

CFPAP #2

Silent Period Duration

Grant PeriodOffset Grant Period Duration

May 2007


Slide 17

doc.: IEEE 802.11-07/0086r3

Submission

Collaboration State Machine

Send Offer Frame to all APs on this

channel

Wait for offer response

Offer Accepted?

Wait until agreed silence period

Silence BSS

Yes

Timeout

No

Wait until OfferSendTime

OW = OW_Min

Start

Double OW

OffsetSendTime = TSF + RAND[1 ..

OW]*beacon_interval

Is OW < OW_Max

No

Yes

Does offer period clash

with this AP’s silence period?

Send response frame with

response=”decline”

No

No

Send response frame with

response=”accept”

Wait until silence period

Use Silence(e.g. start CFP

period)

OfferSendTime = accepted silence period + offsetOW = OWmin

Offer frame received

Finish

Is collaboration supported and

enabled?

Yes Send response frame with response=”decline” and a

suggested silence period that does not clash with this AP’s

silence period and of the same duration as the received offer

frame

May 2007


Slide 18

doc.: IEEE 802.11-07/0086r3

Submission

Simulation Results• Based on “medium” house model

– House size based on typical UK housing

– Based on typical UK construction materials

• Two video streams– At rates between 1Mbit/sec and 10Mbit

• 2.4GHz band– 11g, no throughput extensions

– No DLS, 2 hops per packet

– EDCA and HCCA modes

• Each combination repeated 20 times with different random number seed– 800 simulation runs, ≈6 simulated hours

May 2007


Slide 19

doc.: IEEE 802.11-07/0086r3

Submission

Simulation Results

For EDCA, average gain was 9% (peak gain 34%)For HCCA, average gain was 6% (peak gain 22%)

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

1 2 3 4 5 6 7 8 9 10

Input Rate (MBit/sec)

Re

ce

ive

Ra

te (

Pa

ck

ets

/se

c)

EDCA

HCCA

EDCA-C

HCCA-C

May 2007


Slide 20

doc.: IEEE 802.11-07/0086r3

Submission

0

2

4

6

8

10

12

14

Distance

% I

mp

rove

men

t

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

Bitrate (MBits/sec)

Imp

rove

men

t (%

)

When is collaboration beneficial?

1. On a lightly loaded network, no need for collaboration

2. As network load increases, chances of inter-BSS collisions increase. Collaboration reduces these collisions to allow greater throughout

3. As network load exceeds achievable throughput, benefits from collaboration reduce

4. At close distances, maximum probability of collisions.

5. Eventually a sufficient distance is reached so that BSS no longer overlap

1

2

4

3

5

May 2007


Slide 21

doc.: IEEE 802.11-07/0086r3

Submission

Summary

The proposal described in this presentation:

• Improves efficiency and QoS– Reduces chances of collisions for CSMA/CA traffic

– Reduces chances of CFP collisions when using PCF or HCCA

• Simple to implement– Largely based on existing 802.11 features

– A simple Tit-for-tat algorithm provides fairness

– Method to silence the BSS does not need to be specified

• Robust to rogue STAs– Does not provide a new vector for rogue STAs to perform denial-of-

service attacks

• Alternative Via-DS approach for Enterprise-like use– MIB-based

– Assumes synchronization means

May 2007


Slide 22

doc.: IEEE 802.11-07/0086r3

Submission

Motion

• Motion: “Instruct the editor to include the changes in document 11-07-0084-02-000v-access-point-collaboration-enhancing-qos-and-spectrum-efficiency.doc into the TGv draft”

• Mover/Seconder:

• Result– Yes

– No

– Abstain

May 2007


Slide 23

doc.: IEEE 802.11-07/0086r3

Submission

Straw Poll

• Would the group be supportive of the state diagrams from the “reference implementation” as an informative addition?

• Result– Yes

– No

May 2007


Slide 24

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Submission

References

May 2007


Slide 25

doc.: IEEE 802.11-07/0086r3

Submission

(Backup Material)

May 2007


Slide 26

doc.: IEEE 802.11-07/0086r3

Submission

Simulation Parameters• House

– Size 27’ x 27’ (729 sq feet) – Brick outer wall construction with plaster on inside face– 2 layers drywall inner wall construction– Plaster & wood floor construction– 2 floors– 8 rooms

• Network– 2.4GHz (11bg) in European regulatory domain (ETSI EN 300 328)– 100ms beacon interval– 1 AP per home– 6 STAs per home– 2 RTP UDP video streams, each from non-AP STA to non-AP STA– 7 MPEG-2 TS packets (of 188 bytes) per RTP packet

• Collaboration– owMin=1– owMax=16– offerDuration = 20ms

May 2007


Slide 27

doc.: IEEE 802.11-07/0086r3

Submission

Prisoner's Dilemma

Prisoner B Stays Silent Prisoner B Betrays

Prisoner A Stays Silent Both serve six months Prisoner A serves ten yearsPrisoner B goes free

Prisoner A Betrays Prisoner A goes freePrisoner B serves ten years

Both serve two years

Two suspects, A and B, are arrested by the police. The police have insufficient evidence for a conviction, and, having separated both prisoners, visit each of them to offer the same deal: if one testifies for the prosecution against the other and the other remains silent, the betrayer goes free.

Both prisoners only care about minimizing their own jail terms.

In the iterated prisoner’s dilemma, repeated rounds are made where each prisoner has memory of their previous encounters.

Doc.: IEEE 802.11-07/0086r3 Submission May 2007 Alex Ashley (NDS Ltd), Robert Miller (AT&T)Slide 1...

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