March 20 06 Chuny u Hu, UIUC Slide 1 doc.: IEEE 802.11-06/0364r0 Submission EDCA Parameters Selection to Optimally Provide QoS in IEEE 802.11s Mesh WLANs 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: 2006-03-06 N am e C om pany A ddress Phone em ail Chunyu H u U IU C, IL 3111 SiebelCenter 201 N . G oodw in U rbana, IL 61801 (217)244-8433 [email protected]SaiN andagopalan Qualcom m 5775 M orehouse D r San D iego, CA 92121 (858)651-4218 nsai@ qualcomm.com Authors:
Transcript
March 2006
Chunyu Hu, UIUC
Slide 1
doc.: IEEE 802.11-06/0364r0
Submission
EDCA Parameters Selection to Optimally Provide QoS in IEEE 802.11s Mesh WLANs
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: 2006-03-06
Name Company Address Phone email Chunyu Hu UIUC, IL 3111 Siebel Center
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup
• Observations
• How to Handle Each Observation?
• Experimental Setup
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 3
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 4
doc.: IEEE 802.11-06/0364r0
Submission
Challenges in IEEE 802.11s Mesh Networks
• Challenges– Lack of central coordinators – Each node is a coordinator– Multi-hop environments
• For Absolute QoS Guarantees– Need to determine the optimal route and perform a hop-by-hop reservation
• For Prioritized QoS – Need to maximize throughput and maintain pre-specified throughput ratios
between different flows or classes, need to compute optimal CW for each class– Optimal CWj depends (1 or multi)-hop neighboring information: such as number
of nodes in each class and their traffic characteristics
March 2006
Chunyu Hu, UIUC
Slide 5
doc.: IEEE 802.11-06/0364r0
Submission
MAC layer issues in 802.11s Mesh Networks
• EDCA will be the basis of IEEE 802.11s MAC1
– EDCA will be used to provide prioritized QoS– Nodes (say i,j) forwarding their traffic to a particular node, (say x) will
have to have receive the EDCA parameters from Node x– If the forwarding node (x) is allowed to set parameters to individual flows
then it can provide absolute QoS for a particular flow
• Enable congestion control1
– Simple hop by hop congestion control enabled at each Mesh Point (MP)– Need to curtail a flow if it has violated its QoS agreements– Because the forwarding node has reduced channel capacity, it may ask all
nodes that forward traffic to it to reduce their rates. (By form of signaling newer EDCA parameters)
1DCN: IEEE802.11-06/0329r0: Joint SEE-Mesh/Wi-Mesh Proposal to 802.11 TGs Overview
March 2006
Chunyu Hu, UIUC
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Submission
Example WLAN Mesh
• Assume a simple clustering structure– Mesh Portals (MPs) are at level-0
• A level-i MP node estimates the number of nodes in each class by communicating with its parent and sister nodes, and by monitoring its children nodes
• The level-i MP node computes the optimal CW/AIFS for each traffic class and broadcasts them to its children nodes
• Level-(i+1) MP nodes use the designated CW/AIFS to access the channel
MP1 MP2
MP21MP212
MP211
MP212
• Now let us understand the performance of IEEE 802.11e EDCA ……
March 2006
Chunyu Hu, UIUC
Slide 7
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 8
doc.: IEEE 802.11-06/0364r0
Submission
Overview of EDCA: Enhanced Distributed Control Access
• 802.11 DCF enhanced with QoS
Figure 1. Four access categories with different QoS parameters
Decide the probability of gaining the channel access
Decide the time of occupying the channel
March 2006
Chunyu Hu, UIUC
Slide 10
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 11
doc.: IEEE 802.11-06/0364r0
Submission
The system in view of the channel
• Contention zone j:– Consecutive slots in which only the first j classes are eligible to access the
channel– Numbering the slot from the first slot after a busy period + SIFS, the j-th
contention zone starts from the aj-th idle slot and ends at the (aj+1-1)-th idle slot.
Figure 3. Following every busy period, the slots can be divided into contention zones. aj = AIFSNj + 1.
a1 = 3, a2 = 4, a3 = 8
March 2006
Chunyu Hu, UIUC
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Submission
Describe the channel state transition
• Assume attempt probability of each class, j, are known at this step.• The stable probabilities can be readily derived.• Details (see the Infocom2006 paper at http://lion.cs.uiuc.edu/~chunyuhu.)
Success states Collision states
Idle states
Figure 4. The discrete Markov chain that describes the channel state transition
March 2006
Chunyu Hu, UIUC
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doc.: IEEE 802.11-06/0364r0
Submission
Other elements in the model• Assumptions:
– Saturation condition: every node is back-logged– Every node has the same view of the channel state
• An iterative algorithm to obtain average contention window size, and attempt probabilities j
– Given [CWMIN(j), CWMAX(j)] and Lj
• Derive the performance, e.g., the throughput– Expected slot length
– Throughput of each class
Packet payload
Success probability of class j
March 2006
Chunyu Hu, UIUC
Slide 14
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 15
doc.: IEEE 802.11-06/0364r0
Submission
Simulation Setup
• Tools: – Simulator: ns-2, extended with EDCA– Analytical results: use Matlab
• PHY/MAC parameters:– Data rate 200 Mbps (all throughput results are normalized to it)– Slot time: 8 sec– SIFS: 10 sec– Retry times limit: 7
• Traffic:– All classes have the same number of nodes– All nodes transmit packets to a sink node– CBR (Constant-Bit-Rate), rate large enough to backlog every node– Packet size is 1024 bytes
March 2006
Chunyu Hu, UIUC
Slide 16
doc.: IEEE 802.11-06/0364r0
Submission
Impact of contention window size, CW
Figure 5-1. Three classes with the same AIFS:CW1, 2, 3 = [8, 16], [16, 32], [32, 64]
The temporary increase (will eventually decrease) is caused by the non-uniform access to the post-busy slot.
March 2006
Chunyu Hu, UIUC
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doc.: IEEE 802.11-06/0364r0
Submission
Impact of AIFS
Figure 5-2. Two classes with the same CW: AIFS1, 2 = 2, 3
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 20
doc.: IEEE 802.11-06/0364r0
Submission
Observation 1Observation 1 Higher priority traffic with smaller AIFS value can easily grab most of the Higher priority traffic with smaller AIFS value can easily grab most of the
bandwidth and starve other traffic.bandwidth and starve other traffic.
Figure 6-1. Two classes with the same CW but different AIFS. Left: AIFS1 = 2, AIFS2 = 3. Right: AIFS1 = 2, AIFS2 = 5.
March 2006
Chunyu Hu, UIUC
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doc.: IEEE 802.11-06/0364r0
Submission
Figure 6-2. Three classes: CW1, 2, 3 = [8, 16], [16, 32], [32, 64].Left: throughputs. Right: throughput ratios of class 2/1, and class 3/1.
Observation 2Observation 2 Bandwidth allocation fails to stay stable – it varies as the system load (the Bandwidth allocation fails to stay stable – it varies as the system load (the
number of nodes) varies.number of nodes) varies.
ratio
March 2006
Chunyu Hu, UIUC
Slide 22
doc.: IEEE 802.11-06/0364r0
Submission
Observation 3Observation 3 Bandwidth is under-utilized – the system is not operating at optimal condition Bandwidth is under-utilized – the system is not operating at optimal condition
(a problem known in 802.11 DCF).(a problem known in 802.11 DCF).
Figure 6-3. Existence of optimal operating points that can maximize the throughput.
Optimal operating points
March 2006
Chunyu Hu, UIUC
Slide 23
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 24
doc.: IEEE 802.11-06/0364r0
Submission
• Suggestion:– Small AIFS has to be carefully used to avoid burst contention
– Use by real-time traffic only for admission and reservation
– Real-time traffic, once admitted and made a reservation, access the channel using reservation-based access (e.g. poll-based)
– Normal contention-based access use the same AIFS
Observation 1Observation 1 Higher priority traffic with smaller AIFS value can easily grab most of the Higher priority traffic with smaller AIFS value can easily grab most of the
bandwidth and starve other traffic.bandwidth and starve other traffic.
March 2006
Chunyu Hu, UIUC
Slide 25
doc.: IEEE 802.11-06/0364r0
Submission
• Leverage our theoretical model to achieve– Deterministic weighted bandwidth allocation, and
– Maximize the bandwidth utilization
Observation 2Observation 2 Bandwidth allocation fails to stay stable – it varies as the system load (the Bandwidth allocation fails to stay stable – it varies as the system load (the
number of nodes) varies.number of nodes) varies.
Observation 3Observation 3 Bandwidth is under-utilized – the system is not operating at optimal condition Bandwidth is under-utilized – the system is not operating at optimal condition
(a problem known in 802.11 DCF).(a problem known in 802.11 DCF).
March 2006
Chunyu Hu, UIUC
Slide 26
doc.: IEEE 802.11-06/0364r0
Submission
Theoretically suggested CWs
• Theorem 1: For M classes traffic with the same AIFS value, to achieve proportional bandwidth allocation: rj, which is defined as the ratio of the throughput of class j and that of class 1, and maximum bandwidth utilization, the CW of each class shall be set as follows:
12 '
* j
Dj r
TCW
where
M
jjj
M
jjj rNrN
1
2
2
1
and TD’ is the duration
of a successful transmission in the unit of slots. r1 1.
March 2006
Chunyu Hu, UIUC
Slide 27
doc.: IEEE 802.11-06/0364r0
Submission
Numerical and simulation results
Figure 8. The throughput ratio among different traffic classesbefore (left) and after (right) optimization based on the theoretical model
March 2006
Chunyu Hu, UIUC
Slide 28
doc.: IEEE 802.11-06/0364r0
Submission
Simulation results
Figure 10. The total throughput and the throughput attained by each class in the presence of two real-time streams and two classes of best-effort traffic.
Left: pre-set bandwidth allocation ratio r3/2 = 0.5Right: pre-set bandwidth allocation ratio r3/2 = 0.25
March 2006
Chunyu Hu, UIUC
Slide 29
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 30
doc.: IEEE 802.11-06/0364r0
Submission
Experiment setup
• Device and driver– WLAN devices with the Atheros chipset (e.g. Netgear WG511T)
• Basic chipset – most of the MAC functionality is handled in the driver
– Linux-based MADWifi (Multiband Atheros driver for WiFi) driver
– Implement the enhanced EDCA in the Hardware Access Layer (HAL) module• HAL is similar to firmware and provides an interface to set some
parameters, such as CW
• Experiment scenarios– AP estimates number of stations in each class,
computes the optimal CW for each class, and broadcast these information in beacon messages.
– One AP and two classes, one station in each class– Pre-specify bandwidth allocation ratio
AP
March 2006
Chunyu Hu, UIUC
Slide 31
doc.: IEEE 802.11-06/0364r0
Submission
Experimental results
Figure 11. Throughputs attained by two traffic classes with on-off traffic.The pre-set ratio is r1/2 = 4.
Left: Throughputs (Mbps) Right: Throughput ratio.
March 2006
Chunyu Hu, UIUC
Slide 32
doc.: IEEE 802.11-06/0364r0
Submission
Outline
• Challenges and Overview of IEEE 802.11s Mesh WLAN
• Overview of EDCA
• Analytical Model of EDCA
• Simulation Setup and Results
• Observations
• How to Handle Each Observation?
• Experimental Setup and Results
• Conclusion
March 2006
Chunyu Hu, UIUC
Slide 33
doc.: IEEE 802.11-06/0364r0
Submission
Conclusions
• Have analytically studied the impact of CW and AIFS in EDCA and how to apply it to IEEE 802.11s WLAN
• Insights obtained– Tuning AIFS (small value) has to be cautiously used, so as not to starve
best-effort traffic– CW has to be tuned dynamically in response to varying load
• Can now apply these insights to provide per flow QoS or Prioritized QoS and effect congestion control in IEEE 802.11s MESH WLAN.
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