doc.: ieee 802.11-07/0086r3 submission may 2007 alex ashley (nds ltd), robert miller (at&t)slide...
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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.
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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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
Slide 6
doc.: IEEE 802.11-07/0086r3
Submission
A Typical Enterprise Application
AccessPoint
MobilityServer
RadioResourceManager
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23
4
5
6
7
8
910
11
Co-Channel InterferersUsing Same Frequency(coupled via stairwell)
Router
May 2007
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
Slide 8
doc.: IEEE 802.11-07/0086r3
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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doc.: IEEE 802.11-07/0086r3
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
Slide 11
doc.: IEEE 802.11-07/0086r3
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
Slide 15
doc.: IEEE 802.11-07/0086r3
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
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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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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doc.: IEEE 802.11-07/0086r3
Submission
References
May 2007
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
Slide 25
doc.: IEEE 802.11-07/0086r3
Submission
(Backup Material)
May 2007
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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
Alex Ashley (NDS Ltd), Robert Miller (AT&T)
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.