1. Enhanced-DCF Wireless MAC Protocol: Some Simulation Results
doc.: IEEE /457
January 2001
Enhanced-DCF Wireless MAC Protocol: Some Simulation Results
Mathilde Benveniste
AT&T Labs, Research
Mathilde Benveniste, AT&T Labs - Research

2. Simulation Study Overview
January 2001
Simulation Study Overview
TCMA and V-DCF are compared for two network configurations and various traffic loads
Three priority classes are considered: High, Medium, and Low
Packets from legacy stations are treated the same as medium priority packets
The following statistics are plotted for stream aggregates referred to as “calls”:
Total throughput for all calls (bits per sec)
Goodput by call (bits per sec)
Goodput/Application load by call
Data sent by call (bits per sec)
Dropped traffic by call (bits per sec)
Media access delay (queueing plus contention time) by call (sec)
Retransmissions by call (packets per sec)
Mathilde Benveniste, AT&T Labs - Research

3. Compared Features January 2001 Features simulated for TCMA
doc.: IEEE /457
January 2001
Compared Features
Features simulated for TCMA
Differentiation by UAT (urgency arbitration time)
… by backoff parameters (offset and contention window) used on first transmission attempt
… by persistence coefficient used on retrial
Absent from simulation
‘Slow’ adaptation to traffic (initial and retrial backoff parameters)
‘Fast’ adaptation to traffic (during backoff)
Differentiation by contention time limit
Urgency class upgrade
Differentiation by limit on queueing time
Refs: IEEE /375; -00/456; -00/457; -01/002; -01/003
Features simulated for VDCF
Differentiation by backoff offset* used on first transmission attempt
… by backoff contention window
Absent from simulation
‘Slow’ adaptation to traffic (initial and retrial backoff parameters)
Refs: IEEE /398; -00/399; -00/412r1; -00/429; -01/011
*Offset can be used only for priorities below legacy-equivalent
Mathilde Benveniste, AT&T Labs - Research

4. Class Description January 2001 doc.: IEEE 802.11-00/457
*Factor multiplying contention window following collision
Mathilde Benveniste, AT&T Labs - Research

5. OPNET Simulations Network Configuration WLAN Parameters
doc.: IEEE /457
January 2001
OPNET Simulations
Network Configuration
Pairs of stations generate bi-directional traffic streams
One direction generates twice the volume of the other
Note: Under certain scheduling assumptions, a node with streams destined to different stations can be modeled approximately as a cluster of stations
WLAN Parameters
DS, 11 Mbps channel rate
Buffer size -- 2,024,000 bits
RTS/CTS suppressed
Maximum retry limit -- 7
[See Notes below for OPNET Model settings]
Traffic Statistics
Frames of fixed size bytes
Inter-arrival times exponentially distributed
Packet arrival rate determined from scenario traffic load
Adjustment for PHY overhead of 192 microsecs must be made
OPNET Simulation Assumptions
Specified on Transmitter:
Modulation bpsk
Transmission delay model dra_txdel
Receiver Group Model wlan_rxgroup
Closure Model dra_closure_all
Channel Match Model wlan_chanmatch
Transmission Gain Model dra_tagain
Propagation Delay Model wlan_propdel
Specified on Receiver
Modulation bpsk
Noise figure 1.0
ECC Threshold 0.
Receiver Gain Model dra_gain
Receiver Power Model wlan_power
Background Noise Model dra_bkgnoise
Interference Noise Model dra_noise
Signal to Noise Ratio Model dra_snr
Bit Error Rate Model dra_ber
Error Model dra_error
Error Correction Control Model wlan_ecc
__________________
dra_ are OPNET default radio models.
wlan_ are specific models.
Mathilde Benveniste, AT&T Labs - Research

6. Network Configuration A
doc.: IEEE /457
January 2001
Network Configuration A
Traffic
8 stations generate 4 bi-directional streams;
stream load split 1-to-2 between two directions
WLAN Parameters
DS, 11 Mbps channel
buffer size=2.024 Mbits; no fragmentation
RTS/CTS suppressed; max retry limit=7
Mathilde Benveniste, AT&T Labs - Research

7. Legacy Only Traffic Loading January 2001 30 90 5.0 Mbps 2.5 Mbps 150
doc.: IEEE /457
January 2001
Legacy Only
Time (sec) 30 90
5.0 Mbps
2.5 Mbps
150
Traffic
Loading
BL2
Mathilde Benveniste, AT&T Labs - Research

8. Legacy Only Traffic Loading January 2001 30 90 5.0 Mbps 2.5 Mbps 150
doc.: IEEE /457
January 2001
Legacy Only
Time (sec) 30 90
5.0 Mbps
2.5 Mbps
150
Traffic
Loading
BL2
Mathilde Benveniste, AT&T Labs - Research

9. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 5.0 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
5.0 Mbps
2.5 Mbps
150
Priority
QoS-Enhanced MAC
TCMA
TCMA A7
VDCF B7
V-DCF
Mathilde Benveniste, AT&T Labs - Research

10. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 5.0 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
5.0 Mbps
2.5 Mbps
150
Priority
QoS-Enhanced MAC
TCMA
TCMA A7
VDCF B7
V-DCF
Mathilde Benveniste, AT&T Labs - Research

11. Network Configuration B
January 2001
Network Configuration B
Traffic
60 stations generate 30 bi-directional streams;
stream load split 1-to-2 between two directions
WLAN Parameters
DS, 11 Mbps channel
buffer size=2.024 Mbits; no fragmentation
RTS/CTS suppressed; max retry limit=7
Mathilde Benveniste, AT&T Labs - Research

12. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.2 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.2 Mbps
1.6 Mbps
150
Priority
QoS-Enhanced MAC
TCMA
TCMA D4a
VDCF E4
V-DCF
Mathilde Benveniste, AT&T Labs - Research

13. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.2 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.2 Mbps
1.6 Mbps
150
Priority
QoS-Enhanced MAC
TCMA
TCMA D4a
VDCF E4
V-DCF
Mathilde Benveniste, AT&T Labs - Research

14. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.2 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.2 Mbps
1.6 Mbps
150
Priority
QoS-Enhanced MAC
Goodput / Application Load
0.2
0.4
0.6
0.8 1
1.2
1.4 20 40 60 80
100
Time (s)
Call 1
Call 2
Call 3
Call 4
Percent Retransmissions 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 20 40 60 80
Time
Call 1
Call 2
Call 3
Call 4
TCMA
TCMA D4a
VDCF E4
Goodput / Application Load
0.2
0.4
0.6
0.8 1
1.2
1.4 20 40 60 80
100
Time (s)
Call 1
Call 2
Call 3
Call 4
Percent Retransmissions 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100% 20 40 60 80
Time
Call 1
Call 2
Call 3
Call 4
V-DCF
Mathilde Benveniste, AT&T Labs - Research

15. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.0 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.0 Mbps
1.5 Mbps
150
Priority
QoS-Enhanced MAC
TCMA
TCMA D3
VDCF E3
V-DCF
Mathilde Benveniste, AT&T Labs - Research

16. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.0 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.0 Mbps
1.5 Mbps
150
1.0 Mbps
Priority
QoS-Enhanced MAC
TCMA
TCMA D3
VDCF E3
V-DCF
Mathilde Benveniste, AT&T Labs - Research

17. QoS-Enhanced MAC Priority TCMA V-DCF January 2001 30 90 3.0 Mbps
doc.: IEEE /457
January 2001
Time (sec) 30 90
3.0 Mbps
1.5 Mbps
150
1.0 Mbps
Priority
QoS-Enhanced MAC
TCMA
TCMA D4a
VDCF E4
V-DCF
Mathilde Benveniste, AT&T Labs - Research

18. Comparison of TCMA and VDCF
doc.: IEEE /457
January 2001
Comparison of TCMA and VDCF
Similarities
Both protocols differentiate between different priorities
Both protocols transmit comparable amounts of low priority traffic
Differences
TCMA transmits more of the high priority traffic
TCMA causes lower delay to the high priority traffic
TCMA results in fewer collisions
Mathilde Benveniste, AT&T Labs - Research