Transcript Survey of Admission Control of Supporting VoIP Services in R93725003 卓德忠

Survey of Admission Control of
Supporting VoIP Services in
IEEE 802.11e QoS-enabled WLAN
R93725003 卓德忠
R93725010 鍾佳芳
2 Jan. 2006
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Outline




Introduction
Admission Control
Parameterized EDCA
Conclusions
2
Introduction
Motivation
Introduction
of 802.11e features
Introduce the reference design of HCCA in
802.11e
3
Motivation

802.11e is an enhanced QoS support in WLANs


The most promising framework among QoS
enhancements of WLANs
The contention-based MAC access scheme is
hard to provide quality of service (QoS)
assurance for VoIP services.
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Introduction of 802.11e


IEEE 802.11 WG, “Draft Supplement to Standard for
Telecommunications and Information Exchange
between Systems-LAN/MAN Specific
Requirements — Part 12: Wireless MAC and PHY
Specifications: MAC Enhancements for QoS,” IEEE
802.11e/draft 12.0, Nov. 2004.
Qiang Ni,”Performance Analysis and Enhancements
for IEEE 802.11e Wireless Networks,” in IEEE
Network, July/August 2005
5
Introduction of 802.11e

A new MAC layer function called the hybrid
coordination function (HCF) is proposed.

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
HCF uses a contention-based channel access method, also
called enhanced distributed channel access (EDCA)
Polling-based HCF-controlled channel access (HCCA)
method
Transmission opportunity (TXOP) refers to a time
duration during which a QSTA is allowed to transmit a
burst of data frames


EDCA-TXOP
HCCA-TXOP
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MAC Architecture for QoS
L.W Lim, R. Malik, P.Y. Tan, C. Apichaichalermwongse, K. Ando, Y. Harada, “A QoS scheduler
for IEEE 802.11e WLANs”, First IEEE Consumer Communications and Networking
7
Conference, 2004. Jan 2004, pp.199 – 204
HCCA Features
1.
2.
3.

Different traffic classes called traffic streams (TSs) are
introduced in HCCA.
QSTA is not allowed to transmit a packet if the frame
transmission cannot finish before the next beacon
TXOPLimit is used to bound the transmission time of a
polled QSTA.
In order to initiate a TS connection, a QSTA sends a
traffic specification (TSPEC) to the QAP. A TSPEC
describes the QoS requirements of a TS



Mean Data Rate,
Nominal MSDU Size
Maximum Service Interval or Delay Bound
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Reference scheduling algorithm in
802.11e

The schedule for an admitted stream is calculated in
three steps.
1.
2.
3.
1.
Calculation of the Scheduled Service Interval (SI).
Calculation of TXOP duration for a given SI
Admission control scheme
Service Interval (SI)
calculates the minimum of all Maximum Service Intervals
for all admitted streams. Let this minimum be "m".
 chooses a number lower than "m" that is a submultiple of
the beacon interval.
Ex. MSI1=15ms, MSI2=20ms, beacon interval = 100
=>SI = 10ms

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Reference scheduling algorithm in
802.11e
2.
Calculation of TXOP duration



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Mean Data Rate (ρ)
Nominal MSDU Size (Li) from the negotiated TSPEC
Scheduled Service Interval (SI) calculated in the first step,
Ni: the number of MSDUs that arrived at the
Mean Data Rate during the SI
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Reference scheduling algorithm in
802.11e
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Parameters
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

3.
Nominal MSDU Size (Li) from the negotiated TSPEC
Min Physical Transmission Rate (R),
Maximum allowable MSDU size (M)
Overheads in time units (O): IFSs, ACKs, and CF-Polls
Admission Control
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Admission Control
AC
for CBR traffic
AC for VBR traffic
12
Survey of Admission Control

Deyun Gao, Jianfei Cai and King Ngi Ngan,
“Admission Control in IEEE 802.11e Wireless
LANs,”in IEEE Network, July/August 2005
 Admission Control for CBR Traffic
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
physical-rate-based admission control PRBAC
Admission Control for VBR Traffic
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
Effective TXOP duration
Variable Service Interval
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Admission Control for CBR Traffic

Gao, D.; Cai, J.; Zhang, L., “Physical rate based
admission control for HCCA in IEEE 802.11e
WLANs”, Advanced Information Networking
and Applications, 2005. AINA 2005



physical-rate-based admission control (PRBAC)
long-term average physical rates for admission control
instantaneous physical rates to distribute TXOPs
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Admission Control for CBR Traffic
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The maximum numbers of VoIP
traffic stream


Woo-Yong Choi, “A Centralized MAC-Level
Admission Control Algorithm for Traffic Stream
Services in IEEE 802.11eWireless LANs”,
International Journal of Electronics and
Communications, 2004
obtain the maximum numbers of VoIP traffic
streams that can be admitted to IEEE 802.11a/e,
IEEE 802.11b/e and IEEE 802.11g/e wireless LANs
for various delay requirements.
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Arrival Pattern
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Di: the constant inter-arrival of burst
Li: burst size, [0, maximum burst size]
Pi: the length of the burst period,
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Arrival Pattern (cond)
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Li: burst size, [0, maximum burst size]
PRi: the peak data rate
MRi: the mean data rate
Pi: the length of the burst period,
Di: the constant inter-arrival of burst
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Max Queue Size




^
B:
the maximum queue state
Si: constant service rate
Pi: the length of the burst period
PRi: the peak data rate
PRi-Si
Si
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Max delay
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
Ti : the maximum delay
provide the traffic stream with the constant
service rate, Si (bits/second).
==>

Admission Control
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ΣSi < available service rate (AR)
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Numerical examples
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Burst length Pi = 1.5 sec
Burst inter-arrival time Di = 1 sec
IMBE codec:4.8Kbps
User payload of VoIP MPDU is 88 bits
Number of MPDU = 4.8*1.5/88 = 82
Burst size Li
= 4.8*1.5 + 82*(UDP, IP and MAC)
= 7200 + 82*(16 + 224 + 240) = 46560 bits
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Numerical examples

Peak data rate PRi = Li/Pi = 31Kbps
Mead data rate = PRi*1.5/(1.5+1) = 18.6Kbps
Actual available service rate R

R=11.34Mbps(a, g), 2.2Mbps(b)

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Numerical examples
5 times
About 35 VoIP pairs
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Admission control for VBR traffic

W.F. Fan, D.Y. Gao, D. H.K. Tsang and B. Bensaou, "Admission
Control for Variable Bit Rate traffic in IEEE 802.11e WLANs,”
to be appewed in The Joint Conference of 10th Asia-Pacific
Conference on Communications and 5th International
Symposium on Multi-Dimensional Mobile Communications, Aug.
2004
introducing Effective TXOP duration (the necessary
TXOPs which can statistically guarantee that the
packet loss probability is less than a threshold )
 guarantee the packet loss rate

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Admission control for VBR traffic

W. F. Fan;Tsang, D.H.K.; Bensaou, B., “Admission
Control for Variable Bit Rate traffic using variable
Service Interval in IEEE 802.1 le WLANs”, ICCCN
2004. Proceedings
 using Variable Service Interval
 avoid over-guarantee on packet delay (which with
large delay bound)
 guarantee the packet loss rate
 The larger the service interval, the less TXOP
durations required
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Parameterized EDCA
Comparison
of HCCA and EDCA
Admission Control algorithm
Resource Allocation algorithm
Performance Evaluation
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Parameterized EDCA


Chun-Ting Chou, Sai Shankar N and Kang G.
Shin, “Achieving Per-Stream QoS with Distributed
Airtime Allocation and Admission Control in IEEE
802.11e Wireless LANs, “ INFOCOM 2005
Chun-Ting Chou, Kang G. Shin and Sai Shankar,
“Distributed Control of Airtime Usage in Multi-rate
Wireless LANs,” under review of the
IEEE/ACM Transactions on Networking
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Comparison of HCCA and
EDCA

Challenges of HCCA
The HC needs to re-compute the service schedule
whenever a new traffic stream is added to, or deleted
from a WLAN
 When two WLANs using HCCA operate on the
same channel, it requires additional coordination
between them


802.11k
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Comparison of HCCA and
EDCA (cont’d)

Challenges of EDCA
A quantitative control of stations’ medium
occupancy cannot be achieved via the current
EDCA
 The link adaptation allows stations to vary their
PHY transmission rate based on the link condition
makes the airtime usage control even harder

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Admission Control Algorithm
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Guaranteed Rate (g) -----------------Appendix A
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C is the channel capacity
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Dependent on PHY rates
We must consider multi-rate 802.11 environment

airtime ratio(ri,j)
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Admission Control Algorithm
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New condition
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Overall conditions
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EA: Efficient Airtime Ratio
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Allocation of Airtime
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EDCA
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Control the TXOP Limit of each stations
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Same EDCA parameters
Control the frequency of station’s access to the
wireless medium
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Same TXOP (access duration)
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Controlling the TXOP Limit

TXOP
Ni

Ni : The number of data
frames per one access

Transmission time :
Ni
Ni
riTM
Ni 
rM Ti
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Controlling the TXOP Limit (cont’d)
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Example
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Li = 600, 600, 1200, 1200 bytes
Ri = 48, 48, 48, 24Mbps
Ti =100, 100, 200, 400(TM) sec
ri = 0.1, 0.2, 0.2, 0.1(rM)
Ni = 4, 8, 4, 1
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Controlling the Access Frequency

TXOP limit
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Access frequency approximation[24]
AFi ri

AFj rj
[24] Chun-Ting Chou, Kang G. Shin and Sai Shankar, “Distributed Control of Airtime
Usage in Multi-rate Wireless LANs,” under review of the IEEE/ACM Transactions
35
on Networking
Controlling the Access Frequency (cont’d)
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Example
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Li = 600, 600, 1200, 1200 bytes
Ri = 48, 48, 48, 24Mbps
Ti =100, 100, 200, 400(TM) sec
Ni = 4, 4, 2, 1
ri = 0.1, 0.2, 0.2, 0.1
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System Efficiency
37 Mbps
t =35 s
N=16
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Time-varying Transmission Rates
54Mbps → 24Mbps
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Conclusion

HCCA
High system efficiency (higher EA)
 Contention free
 with admission control mechanisms, the delay and
packet loss rate of VoIP / other multimedia streams
are guaranteed.
 However, the influence of Jitter is not discussed
here.

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Conclusion (cont’d)

Parameterized EDCA
No control overhead in overlapping multiple LANs
 No adjustment for change



HCCA needs to re-compute schedule
Easy adaptation of extra airtime for the change of
station’s PHY rate
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Reference




IEEE 802.11 WG, “Draft Supplement to Standard for
Telecommunications and Information Exchange between
Systems-LAN/MAN Specific Requirements — Part 12: Wireless
MAC and PHY Specifications: MAC Enhancements for QoS,”
IEEE 802.11e/draft 12.0, Nov. 2004.
Qiang Ni,”Performance Analysis and Enhancements for IEEE
802.11e Wireless Networks,” in IEEE Network, July/August
2005
Deyun Gao, Jianfei Cai and King Ngi Ngan, “Admission Control
in IEEE 802.11e Wireless LANs,”in IEEE Network,
July/August 2005
Gao, D.; Cai, J.; Zhang, L., “Physical rate based admission control
for HCCA in IEEE 802.11e WLANs”, Advanced Information
Networking and Applications, 2005. AINA 2005
41
Reference

W.F. Fan, D.Y. Gao, D. H.K. Tsang and B. Bensaou, "Admission Control for Variable
Bit Rate traffic in IEEE 802.11e WLANs,” to be appewed in The Joint Conference of
10th Asia-Pacific Conference on Communications and 5th International Symposium
on Multi-Dimensional Mobile Communications, Aug. 2004

W. F. Fan;Tsang, D.H.K.; Bensaou, B., “Admission Control for Variable Bit
Rate traffic using variable Service Interval in IEEE 802.1 le WLANs”,
ICCCN 2004. Proceedings
Woo-Yong Choi, “A Centralized MAC-Level Admission Control Algorithm
for Traffic Stream Services in IEEE 802.11eWireless LANs”, International
Journal of Electronics and Communications, 2004
Chun-Ting Chou, Sai Shankar N and Kang G. Shin, “Achieving Per-Stream QoS
with Distributed Airtime Allocation and Admission Control in IEEE 802.11e Wireless
LANs, “ INFOCOM 2005
Chun-Ting Chou, Kang G. Shin and Sai Shankar, “Distributed Control of Airtime
Usage in Multi-rate Wireless LANs,” under review of the IEEE/ACM
Transactions on Networking



42
Appendix A. Guaranteed Rate

Dual-token bucket filter
Tokens arrive at Mean Data Rate
Tokens arrive at Peak Data Rate
Bucket size B = σ (1-ρ/P)
MAC frame buffer
Arriving traffic stream
Bits
Data frames drained
at Guaranteed Rate
peak rate : P Arrival curve : A(t)
Guaranteed rate : g
mean rate : ρ
σ
d
error
Time
43