Doc.: IEEE 802.11-01/133 Submission March 2001 G. Chesson, A. Singa - Atheros Slide 1 VDCF Simulations Greg Chesson, [email protected] Aman Singla, [email protected]

March 2001

G. Chesson, A. Singa - AtherosSlide 1

doc.: IEEE 802.11-01/133

Submission

VDCF Simulations

Greg Chesson, [email protected]

Aman Singla, [email protected]

March 2001


doc.: IEEE 802.11-01/133

Submission

Overview• Notation

• Load(a,b,c) means there are a highest-priority stations, b at the next priority, c at the next priority, etc. May be shown as L(a,b,c,d).

• CWmin(a,b,c) describes the assignment of CWmins to Traffic Categories where a is assigned to the highest priority, b at the next, etc. May be shown as W(a,b,c,d).

• QIFS(a,b,c), or Q(a,b,c), captures the setting of the QIFS[i] values by TC.

• Simulation Software– Public version of the Berkeley NS2 software suite– Contact authors for details

• Results– Usually 3 graphs per simulation

• BW - An instantaneous bandwidth slot for one or more flows• LAT – a per-frame latency plot over the lifetime of the run• Lat-dist – latency distribution (i.e P% of the packets had latency less than x)

• Scenarios– Usually fixed topology, varying load– Stations are added or removed usually on 3-sec intervals

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doc.: IEEE 802.11-01/133

Submission

Scenarios

1. Basic differentiation demonstration and comparison with legacy DCF

2. Load(4,2,10) – phones, 2 videos, 10 background stations

3. Load(4,4,8) – constant demand from stations, uses same W/Q settings as scenario (2), demonstrates robust behavior of mechanism

4. Extreme differentiation: 8 active TCs

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doc.: IEEE 802.11-01/133

Submission

Scenario 1

• A simple scenario meant only to compare with DCF and to observe the effects of CWmin and QIFS controls.

• Load(2,4): two high-priority stations and 4 low-priority stations, all stations with backlogged queues (always ready to transmit) using UDP datagrams.

• Topology: an AP is sinking all traffic from the 6 stations.

• Simulation Runs (3 plots for each run: bw, lat, lat-dist):a) DCF only - for comparison

b) W(15,31) Q(0,0) - uses CWmin but not QIFS

c) W(15,15) Q(0,1) - uses QIFS but not CWmin

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doc.: IEEE 802.11-01/133

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1 a bw

Per-flow Dropped packet counts for IFQ/MAC IFQ means dropped from software queue MAC means retry count exceeded

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1 a lat

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1 a lat-dist

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1 b bw

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1 b lat

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1 b lat-dist

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1 c bw

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1 c lat-dist

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Scenario 2

• Load(4,2,10)– 4 phone-like CBR flows (100 Kbit/s with 120B frames)

• Bidirectional flows: 2 Stations plus AP, 4 flows, each STA is source+sink

– 2 video-like CBR flows: 1 at 3 Mbit/s, 1 at 8 Mbit/s

– 10 background flows: 5 UDP and 5 TCP

– All other flows sink to AP unless specified otherwise

– New station added every 3 sec.

– Stations removed in same order after peak load is reached

• Runsa. W(15,15,31) Q(0,2,7)

b. W(15,15,31) Q(0,0,7)

c. W(15,15,31) Q(0,2,7) - video flows sourced at AP

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doc.: IEEE 802.11-01/133

Submission

2 a bw

phones

videos

background

Remove loads

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2 a lat

phone

video

statistics

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2 a lat-dist

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2 a vdcf-background vs dcf-background

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2 b bw

Background flows not shown

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2 b lat

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2 b lat-dist

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2 c bw video sourced at AP

Background flows not shown

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2 c lat video sourced at AP

Lower latency than 2 b lat.Fewer phone-video collisions than 2-b.

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2 c lat-dist video sourced at AP

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Submission

Scenario 3

• Load(4,4,8) – differentiation test using same W/Q as scenario 2– 4 high priority stations, 4 middle priority, 8 low priority

– All stations sending with backlogged queues to AP

– Stations are sequenced on at 3-sec intervals, high-priority stations first

– Stations are sequenced off after peak load is attained

• Demonstrates good differentiation without needing to adjust W/Qa. Uses W(15,15,31) Q(0,2,7) - same as scenario 2

b. Uses W(15,15,15) Q(0,1,2) - different recipe

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Submission

3 a bw

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3 b bw

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3 a lat

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3 b lat

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3 a lat-dist

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3 b lat-dist

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Scenario 4

• 8 streams, 8 TCs

• Backlogged queues

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4 bw

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4 lat

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4 lat-dist

Documents

Doc.: IEEE 802.11-01/133 Submission March 2001 G. Chesson, A. Singa - Atheros Slide 1 VDCF Simulations Greg Chesson, [email protected] Aman Singla, [email protected]