1. 802.11 PCF Model Progress Update Nov 2000
Month 2000
doc.: IEEE /xxx
November 2000
PCF Model Progress Update Nov 2000
Author:
Matthew Sherman
AT&T Labs - Research
180 Park Avenue
Florham Park, NJ
Date: November 8, 2000
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

2. Introduction / Background
Month 2000
doc.: IEEE /xxx
November 2000
Introduction / Background
Prior descriptions in:
IEEE /264r1
IEEE /318r1
PCF model developed by AT&T Labs
Validation still required
Jumping off point for MAC enhancements
Currently available under NDA from AT&T
May become part of OPNET Standard Library
Eventual contributed model with enhancements
No NDA for contributed model
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

3. Mods Since Sept ‘00 Meeting
Month 2000
doc.: IEEE /xxx
November 2000
Mods Since Sept ‘00 Meeting
Implemented more_data bit in frame format
PCF use only
Streamlined frame formats
New packet formats called:
Wlan_mac_pcf
Wlan_control_pcf
Added all possible fields that might be needed for data / management frames
Reduced Control Frame fields since some irrelevant
Fix to beacon header size
Off by 6 bytes
Receiver busy / SIFS fix
Receiver busy now ignored during SIFS
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

4. Mods Since Sept ‘00 Meeting (Cont.)
Month 2000
doc.: IEEE /xxx
November 2000
Mods Since Sept ‘00 Meeting (Cont.)
Fixed frame timeout for PCF side traffic
AP was not waiting long enough for traffic
EIFS fix
Was still being set in NAV for some cases
PCF Duration field fixes
Was setting to 0 rather than 32768
AP NAV reset at start of CFP
May reconsider later
Option to reset NAV for CF_END for all BSSs or only own BSS
NS Compatible trace capability
Update to October models capability
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

5. Mods Since Sept ‘00 Meeting (Cont.)
Month 2000
doc.: IEEE /xxx
November 2000
Mods Since Sept ‘00 Meeting (Cont.)
Assorted Retry fixes
Wrong frame type, duration filed, trace info, etc.
Added support for multi-source model
“Ghost Packet” and other receiver fixes
TBTT overrun fix
Max packet size fix
Broadcast packet CW reset fix
Fragment train before Beacon Fix
Various other minor fixes
PCF poll flag fixes
sometimes PCF active flag was set by mistake
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

6. Current Scenario Simulated
Month 2000
doc.: IEEE /xxx
November 2000
Current Scenario Simulated
Based on most current “Model 3 Scenario”
Modified Video Conference packet generation
Packets were too large
Added bulk traffic stream 10 sec into simulation
Load system beyond channel capacity
Addresses assigned to favor higher priority traffic
Addresses used as AID by poll scheduler
Will update scenario to final “Model 3” once completed
MPEG sources
Finalize Video Conference and data streams
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

7. OPNET Scenario Month 2000 doc.: IEEE 802.11-00/xxx November 2000
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

8. MAC Parameters Month 2000 doc.: IEEE 802.11-00/xxx November 2000
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

9. Traffic Sources Month 2000 doc.: IEEE 802.11-00/xxx November 2000
Source Address
Start Time
(Sec)
ON State Time
OFF State Time
Interarrival Time
Packet Size (Bytes)
Stop Time (Sec)
Destination Address
Type of Service
Stream ID
0.02
3600. 0.
Uniform ( ,0.25)
815
Never 3 5
0.012
0.088
0.001
1464 4 6
10.02
Poisson (0.005)
2300 1 92 2 40 7
1504 8
Lognormal ( , ) 64 9
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

10. Global Stats PCF DCF Month 2000 doc.: IEEE 802.11-00/xxx November 2000
100 values / bin
Collection mode - Total / time.
PCF
DCF
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

11. Global Stats 100 values / bin in simulations
Month 2000
doc.: IEEE /xxx
November 2000
Global Stats
100 values / bin in simulations
Groups of values (100) are processed at a time to generate displayed statistics
Global Stats are aggregate values across all streams
Delay is time from when packet queued in MAC until final Ack indicating successful delivery
Load is traffic presented to MAC from upper layers
Media Access Delay is time from packet queued in MAC until first access of medium
Throughput is traffic forwarded to upper layers
Packets dropped self explanatory
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

12. Global Stats - Performance
Month 2000
doc.: IEEE /xxx
November 2000
Global Stats - Performance
PCF outperforming DCF from start
Some packet drops on DCF, none on PCF
PCF delays lower
See effects of Bulk data kick in at 10 sec
Large number of packet drops
Delays start getting really bad
Throughput on PCF increases slightly when Bulk data starts
Throughput on DCF seems to slightly decrease
More retrys / backoffs
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

13. Dropped Packets PCF DCF Month 2000 doc.: IEEE 802.11-00/xxx
November 2000
Dropped Packets
Voice
Voice
Voice
Audio Ack
Bulk Data
Audio
Video Conf.
100 values / bin
Collection mode - Total / time.
Video Conf.
MPEG
Data Ack
PCF
DCF
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

14. Month 2000
doc.: IEEE /xxx
November 2000
Dropped Packets
Clearly see that DCF is dropping MPEG traffic almost from the start
Probably running out of buffer room
When Bulk data starts, DCF drops even more MPEG and bulk video
No other data affected (in first 20 sec)
Video conferencing is affected in longer simulations (>30 sec)
Seems to be function of overall rate (buffer room)
PCF drops bulk data but nothing else
Only drops lowest priority stream
Maintains all QoS streams
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

15. Retransmission Attempts
Month 2000
doc.: IEEE /xxx
November 2000
Retransmission Attempts
100 values / bin
Collection mode - Total / time.
PCF
DCF
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

16. Retransmission Attempts
Month 2000
doc.: IEEE /xxx
November 2000
Retransmission Attempts
Substantial retransmission activity for DCF
Bulk Data has no obvious effects on retry
Medium already saturated
Retransmissions consume capacity
No Retransmissions required in PCF
Obvious and Expected
Efficiency advantage over DCF
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

17. Packet Delays PCF DCF Month 2000 doc.: IEEE 802.11-00/xxx
November 2000
Packet Delays
Voice
Voice
Voice
Audio Ack
Bulk Data
Audio
Video Conf.
Source MAC entry till Successful delivery (but includes Ack)
Collection Mode - Sample mean - Average does not show peak delay.
Need to investigate Gaps in results.
Video Conf.
MPEG
Data Ack
PCF
DCF
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

18. Month 2000
doc.: IEEE /xxx
November 2000
Packet Delays
PCF packet delays very stable and well bounded on all streams but bulk data
Can maintain QoS
Especially true for voice
Some dependence on polling order
DCF shows substantially greater delay variation in all streams
MPEG already degraded
Video Conferencing and Audio hit hard by bulk data
QoS is not maintained
Streams sharing AP with Bulk data hit hardest
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

19. DCF Trace - Synchronized Data
Month 2000
doc.: IEEE /xxx
November 2000
DCF Trace - Synchronized Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
d -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
r -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
Show Beacon collision
Effects of data synchronization / post backoff when Medium Idle
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

20. Key Trace features NS compatible First letter is event type
Month 2000
doc.: IEEE /xxx
November 2000
Key Trace features
NS compatible
First letter is event type
T: packet Tx start
X: packet Tx end
R: packet received
D: packet drop
-t indicates simulation time (rounded to microsec)
-Hs is observing (reporting) station address
-Na is Duration field
-Md is packet destination
-Ms is packet source
Frame type at end of line
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

21. DCF Trace - Synchronized Data
Month 2000
doc.: IEEE /xxx
November 2000
DCF Trace - Synchronized Data
Multi-packet collision is common in simulations
Prior to beacon all STA have completed post-backoff
Data frame generated in sources at same time
3 voice calls have identical parameters
Also synchronized with Beacon
Collisions could be avoided by phasing sources to discourage simultaneous triggering
What about network synchronization
Can devices in real network become synchronized so that this becomes a common problem?
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

22. DCF Trace - Delayed Beacon
Month 2000
doc.: IEEE /xxx
November 2000
DCF Trace - Delayed Beacon
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Data
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Ack
s -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
x -t Hs Hd -2 -Ni Nx Ny Nz Ne Nl MAC -Nw --- -Na Md Ms Mt WlanC_Beac
Show Beacon collision
Effects of data synchronization / post backoff when Medium Idle
Matthew Sherman, AT&T Labs - Research
John Doe, His Company

23. DCF Trace - Delayed Beacon
Month 2000
doc.: IEEE /xxx
November 2000
DCF Trace - Delayed Beacon
For DCF, Beacon is required to follow DCF rules
Must back off and defer like any other frame
In simulations backoff and deference can cause Beacon to be delayed beyond TBTT by several frames
In this case delayed 9 frames
Delayed roughly 3.6 milliseconds
Nothing wrong, but interesting to observe
Demonstrates utility of trace
100 values / bin
Collection mode - Total / time.
Matthew Sherman, AT&T Labs - Research
John Doe, His Company