Doc.: IEEE 802.15-02/297r1 Submission July 2002 Mangharam/Demirhan, Intel LabsSlide 1 Project: IEEE...

July 2002

Mangharam/Demirhan, Intel LabsSlide 1

doc.: IEEE 802.15-02/297r1

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [Performance and Simulation Analysis of 802.15.3 QoS]Date Submitted: [July 7, 2002]Source: [Rahul Mangharam, Mustafa Demirhan] Company: [Intel]Address: [2111 NE 25th Ave, Hillsboro, OR 97124]Voice: [503-712-7914], FAX: [503-264-6619], E-Mail: [[email protected]

[email protected]]

Re: [Doc. 297r0]

Abstract: [Simulation and analysis of 802.15.3 multimedia QoS support.]

Purpose: [Presents current protocol performance and suggests changes for better QoS support. Introduces a 802.15.3 simulation tool available for distribution.]

Notice: This document has been prepared to assist the IEEE P802.15. 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 acknowledges and accepts that these viewgraphs becomes the property of IEEE and may be made publicly available by P802.15.

July 2002


doc.: IEEE 802.15-02/297r1

Submission

What this talk is about

• Objective analysis of the 802.15.3 MAC in servicing multi-media (MPEG-4) traffic in the uplink (node to PNC) or peer-to-peer mode

• Analysis of the good points and limitations of a dynamic-TDMA MAC for real-time applications (video-conferencing, interactive gaming, etc.)

• Simulation results for CBR and MPEG-4 performance at different loads and error rates

• Proposal for a ~60% improvement in MAC performance – with an addition of only a single byte

• Present an 802.15.3 simulator. It is open source.

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doc.: IEEE 802.15-02/297r1

Submission

802.15.3 Performance Analysis

1. Analysis of 802.15.3 MAC in terms of:a)Job Failure Rate (JFR) for Constant Bit Rate (CBR) and MPEG-4

traffici. JFR is the rate at which packets are dropped due to missing their deadlines

b)Effect of channel utilization on JFRi. Channel utilization is defined as the ratio of the average frame size (with

protocol overhead) and the average frame inter-arrival time

c)Performance of multimedia traffic for different error ratesi. Packet error rate is the effective error rate seen by the MAC after error

correction but does not include the effect of retransmissions.

2. Improved 802.15.3 MAC – with queue state informationa)Performance comparison to 802.15.3 MAC

3. Evaluation of aggressive packet scheduling for all traffic types

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doc.: IEEE 802.15-02/297r1

Submission

Assumptions

• For MPEG-4 flows, the frame rate is fixed to 30ms. If a packet is not completely delivered to the receiver within 30ms, it is dropped

• We use an MPEG-4 traffic generator that generates traffic which has the same first and second order statistics as an original MPEG4 trace. The code can be found at http://www.tik.ee.ethz.ch/~fiedler/provisioning.html

• All CBR flows are well behaved with a fixed packet size and fixed inter-arrival times

• The physical layer data rate is 100Mbps and the preamble is assumed to be 15s.

• MAC overheads such as header size, guard times, aFirstGTSGap and SIFS are as per 802.15.3 Draft D10.

• We use a uniform bit error model

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doc.: IEEE 802.15-02/297r1

Submission

802.15.3 MAC Simulation Model• We modeled and simulated the 802.15.3 MAC in nsV2. This is an open source

network simulator available at http://www.isi.edu/nsnam/ns/

• The 802.15.3 simulation model includes:1. Beaconing2. GTS assignment3. Downlink, uplink and peer-to-peer packet exchange4. Packet retransmissions (with max. retry count set to 3)5. Packet fragmentation6. Flexible super-frame size

• Various traffic types (TCP/UDP/RTP) and applications (CBR/MPEG) can be simulated

• Various error modules can be used • The 802.15.3 MAC source code is available. Contact authors for more

information.

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doc.: IEEE 802.15-02/297r1

Submission

MPEG-4 Frame Size Distribution Examples “Jurassic Park” Frame statistics (1 Hour sample)

compression ratio YUV:MP4 9.92

# of Frames - 89998

mean frame size byte 3.8e+03

var frame size - 5.1e+06

min frame size byte 72

max frame size byte 16745

Mean bit rate bit/sec 7.7e+05

Peak bit rate bit/sec 3.3e+06

Peak/Mean of bit rate - 4.37

“The Firm” Frame statistics (1 Hour sample)

compression ratio YUV:MP4 25.93

# of Frames - 89998

mean frame size byte 1.5e+03

var frame size - 1.3e+06

min frame size byte 32

max frame size byte 10204

Mean bit rate bit/sec 2.9e+05

Peak bit rate bit/sec 2e+06

Peak/Mean of bit rate - 6.96

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doc.: IEEE 802.15-02/297r1

Submission

Multimedia (MPEG-4) Traffic

Source: Frank H.P. Fitzek, Martin Reisslein, "MPEG-4 and H.263 Video Traces for Network Performance Evaluation“, IEEE Network Vol. 15, No. 6, pages 40-54, Dec 2001. http://www-tkn.ee.tu-berlin.de/~fitzek/TRACE/trace.html

Overload

Average

UnderutilizedChannel

Frame size trace of Jurassic Park

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doc.: IEEE 802.15-02/297r1

Submission

802.15.3 MAC - Job Failure Rate Vs. Network Load for 4Mbps MPEG-4 flows (0% PER)

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Channel Utilization (Number of flows)

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802.15.3 Performance with MPEG-4 Traffic1. With 10x4Mbps flows, the

bandwidth required by the application layer is 40Mbps.

2. With 3 packets per GTS for each flow, the MAC and PHY overhead is approx. 26% (26Mbps).

3. The total network load is ~66% and we allocate the remaining 34% of channel capacity equally among all flows. Thus we allocate the entire 100Mbps for the given number of flows.

4. The average flow Job Failure Rate is 10% with no wireless channel error.

5. This graph shows the best possible average Job Failure Rate for 4Mbps MPEG-4 flows.

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doc.: IEEE 802.15-02/297r1

Submission

802.15.3 Performance with MPEG-4 Traffic (2)

802.15.3 MAC - Job Failure Rate Vs. Network Load for 16Mbps flows (0% PER)

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1. No more than two 16Mbps flows can be permitted with a JFR below 10%

2. The channel bit error rate is 0.

3. Each of the N flows is given 100Mbps/N channel utilization which is greater than the average data rate required.

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doc.: IEEE 802.15-02/297r1

Submission

So how can we improve the 802.15.3 MAC?

Frame size trace of “Jurassic Park”

Frame size trace of “The Firm”

1. MPEG-4 instantaneous data rate requirements oscillate widely about the mean data rate. The peak to mean data rate ratio varies from 3 to more than 10 (depending on the scenario and quality)

2. Since it would be wasteful to statically reserve the peak data rate, we must dynamically allocate resources to those flows experiencing overload. This must be done while maintaining fairness

3. We therefore need:a) A mechanism to communicate the

transient overload to the PNC in the case of uplink or peer-to-peer traffic

b) Need an scheduling algorithm that aggressively satisfies the overload, yet is fair in the long run

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doc.: IEEE 802.15-02/297r1

Submission

The 1 Byte Solution• Mechanism:

– By adding a single byte to the MAC header, a node can inform the PNC of its current queue size.

– Queue size information can possibly be encoded in bytes, Max. size packets (2KB), or according to a well defined table of queue size ranges.

– Thus, with every packet exchange, the PNC is aware of the instantaneous channel requirement (which may be temporarily more than the reserved bandwidth) of each flow.

• Packet Scheduling:– With the transient load information, the PNC can schedule the overloaded

flows in the next superframe by assigning them the idle bandwidth.

– Furthermore, the PNC can dynamically allocate the idle bandwidth of no load or lowly loaded nodes to the overloaded flows.

• 1 byte @ 100Mbps is <10ns overhead which is considerably smaller than the PHY preamble.

July 2002


doc.: IEEE 802.15-02/297r1

Submission

Improved MAC Performance – 4Mbps flows with no channel errors

Job Failure Rate Vs. Channel Utilization for 4Mbps MPEG-4 Flows (0% PER)

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Improved MAC 802.15.3 MAC

~95% Channel utilization

70% Average performance improvement over 802.15.3 MAC

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doc.: IEEE 802.15-02/297r1

Submission

MPEG-4 Frame Delivery

(Mean)Frame Size

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Unused (idle) capacity by lowly loaded frames

Successfully transmitted frames

Reserved bandwidth Overloaded frames that can be serviced by smart packet scheduling

Peak size frames that cannot be serviced due to maximum channel capacity limit

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doc.: IEEE 802.15-02/297r1

Submission

Comparison of Frames Delivered 802.15.3 MAC: Successfully Delivered MPEG-4 Frames

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Improved MAC: Successfully Delivered MPEG-4 Frames

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1. Successfully transmitted frame size profile of one of four 8Mbps flows

2. The improved MAC is able to service larger size frames by allocating ALL idle capacity to the overloaded flows

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doc.: IEEE 802.15-02/297r1

Submission


Job Failure Rate Vs. Channel Utilization for 8Mbps MPEG-4 flows (0% PER)

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doc.: IEEE 802.15-02/297r1

Submission


Job Failure Rate Vs. Channel Utilization for 16Mbps MPEG-4 flows (0% PER)

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doc.: IEEE 802.15-02/297r1

Submission

Improved MAC Performance – 8Mbps flows with channel errors

Packet Error Rate Vs. Job Failure Rate (for 4x8Mbps MPEG-4 Flows)

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Packet Error Rate (%)

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46% Average performance improvement over 802.15.3 MAC

July 2002


doc.: IEEE 802.15-02/297r1

Submission

Shortest Remaining Processing Time Packet Scheduling

1. The idea is simple. By servicing the shortest jobs first the mean service response time is minimized[1].

2. Once the queue size of a flow is known, the PNC can make more informed bandwidth allocation decisions in the next super frame.

3. The total instantaneous idle capacity is the sum of the unreserved bandwidth and the instantaneous unused reserved bandwidth by lowly loaded flows.

4. The overloaded flows are allocated excess capacity in the ascending order of their overload queue size (number of packets in excess of the reserved utilization).

5. All overloaded flows are always allocated at least their reserved utilization. Therefore, there is no unfairness.

6. All no-load or lowly loaded flows are given enough time to only communicate their queue size in the next superframe.

1. Linus E. Schrage and Louis W. Miller. The queue M/G/1 with the shortest remaining processing time discipline. Operations Research, 14:670--684, 1966.

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doc.: IEEE 802.15-02/297r1

Submission

Flow Isolation (Fairness)Flow Isolation with a mix of MPEG-4 and CBR flows

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16Mbps MPEG-4 8Mbps MPEG-4 4Mbps MPEG-4 4Mbps CBR 8Mbps CBR

July 2002


doc.: IEEE 802.15-02/297r1

Submission

Conclusion

1. With just 1 more byte in the MAC header, we can improve the 802.15.3 MAC performance by ~60% in terms of Job Failure Rate for multimedia traffic.

2. The Shortest Remaining Processing Time scheduling algorithm is the best, most aggressive and simplest packet scheduling algorithm for all traffic types.

Doc.: IEEE 802.15-02/297r1 Submission July 2002 Mangharam/Demirhan, Intel LabsSlide 1 Project: IEEE...

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