Distributed Call Admission Control for VoIP over 80211 WLANs based on Chan

nel Load Estimation

Paolo Dini Nicola Baldo Jaume Nin-Guerrero Josep Mangues-Bafalluy IP Technologies Area

Sateesh Addepalli Lillian L Dai Cisco Research Centre

IEEE ICC 2010 proceedings

報告者李宗穎

2

Outline

Introduction CAC algorithm definition Channel Load Estimation Method Test Environment Setup and Performance Conclusion

3

Introduction

a distributed CAC solution in which the decision is performed by the mobile station the STA is in charge of deciding whether a parti

cular AP can offer a suitable service quality a user-centric approach is advantageous for the

end-user since the choice of the AP can be made also considering user preferences

4

Related Work

Time Between Idle Times (TBIT) the method for measuring the TBIT metric does

not consider the time consumed by erroneous transmissions (eg collisions)

the measured number and duration of the idle time periods are not correct

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

5

CAC algorithm definition

The observed channel can be in two different states busy when one or more transmissions are being performed or idle when there are no ongoing transmissions

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

2

Outline

Introduction CAC algorithm definition Channel Load Estimation Method Test Environment Setup and Performance Conclusion

3

Introduction

a distributed CAC solution in which the decision is performed by the mobile station the STA is in charge of deciding whether a parti

cular AP can offer a suitable service quality a user-centric approach is advantageous for the

end-user since the choice of the AP can be made also considering user preferences

4

Related Work

Time Between Idle Times (TBIT) the method for measuring the TBIT metric does

not consider the time consumed by erroneous transmissions (eg collisions)

the measured number and duration of the idle time periods are not correct

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

5

CAC algorithm definition

The observed channel can be in two different states busy when one or more transmissions are being performed or idle when there are no ongoing transmissions

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

3

Introduction

a distributed CAC solution in which the decision is performed by the mobile station the STA is in charge of deciding whether a parti

cular AP can offer a suitable service quality a user-centric approach is advantageous for the

end-user since the choice of the AP can be made also considering user preferences

4

Related Work

Time Between Idle Times (TBIT) the method for measuring the TBIT metric does

not consider the time consumed by erroneous transmissions (eg collisions)

the measured number and duration of the idle time periods are not correct

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

5

CAC algorithm definition

The observed channel can be in two different states busy when one or more transmissions are being performed or idle when there are no ongoing transmissions

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

4

Related Work

Time Between Idle Times (TBIT) the method for measuring the TBIT metric does

not consider the time consumed by erroneous transmissions (eg collisions)

the measured number and duration of the idle time periods are not correct

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

5

CAC algorithm definition

The observed channel can be in two different states busy when one or more transmissions are being performed or idle when there are no ongoing transmissions

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

5

CAC algorithm definition

The observed channel can be in two different states busy when one or more transmissions are being performed or idle when there are no ongoing transmissions

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

6

Two different channel

Busy channel successful or unsuccessful frame transmissions

(packet collisions among active stations andor channel errors)

based on stop-and-wait ARQ model Idle channel

no frame transmissions

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

7

CAC equation (12)

ρv + ρf + ρbg + ρbo 1≦ ρv the channel is occupied by successful voice

traffic transmissions ρf the channel is occupied by failed transmissi

ons ρbg the fraction of time dedicated to successful

background traffic transmissions ρbo the channel is occupied by the back-off pro

cedure

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

8

CAC equation (22)

the AP is said to be eligible for the new VoIP session

the forecast channel load ρv +ρf expected after the introduction of the new VoIP session is determined as a function of the actual values of ρv and ρf 10506011050601

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

9

Channel Load Estimation Method

Tw a STA can monitor the radio link over a time window of duration

Ti the index i denote the generic observed frame exchange sequence DIFS(or AIFS) + DATA + SIFS + ACK

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

10

ρv and ρv (voice traffic)

λnew is the cumulative number of packets per second of the two new VoIP flows

Tnew is the duration of the frame exchange sequences for these flows

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

11

ρf andρf (collisions or channel errors)

these events cannot be observed directly by a monitoring STA counting the number of PHY errors

more than one PHY error can be reported for the same frame and furthermore PHY errors often happen for other causes

some analytical models provide methods hypothesis that every station always has a new pack

et to transmit which clearly does not hold for the case of VoIP traffic

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

12

ρf andρf (collisions or channel errors)

the estimation of ρf based only on the observation of successful frame exchange sequences

nMSDU the total number of MAC Service Data Units (MSDUs) which have been successfully delivered ns first transmission attempt was successful nr retry transmission was successful

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

13

Failure Probability Pf

assume that transmissions fail mostly due to collisions and that consequently all frame transmission attempts in the observation period have the same failure probability Pf

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

14

Some expected value for ρf

paper can use Pf to calculate the expected value E[k] of the number k of failed transmission attempts per MSDU (by stop-and-wait ARQ)

rmax retransmission limit

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

15

Estimation ρf (12)

E[c] the average number of stations having a contemporary collision (approximate E[c] with a value of 2)E[k] the number k of failed transmission attempts per MSDU

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

16

Estimation ρf (22)

Where λnew has been defined in the previous sub-section and E[k] is calculated as per equation by substituting 10506011050601

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

17

ρbo (backoff procedure)

Paper focus on the AP since it is well known that the downlink is the bottleneck in a VoIP over WLAN scenario

σ duration of timeslot

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

18

Test Environment Setup and Performance

The scenario is composed of one AP and several mobile nodes sendingreceiving traffic tofrom an external fixed node (using ns3 simulator)

paper conclude with the evaluation of the performance of the proposed CAC algorithm and its comparison with the TBIT algorithm [7]

[7] K Yasukawa A G Forte H Schulzrinne ldquoDistributed Delay Estimation and Call Admission Control in IEEE 80211 WLANsrdquo in Proc of IEEE ICC June 2009

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

19

Determination of Pf and ρbg

Homogeneous traffic scenario Heterogeneous codec scenario Multi-rate scenario TCP background traffic scenario

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

20

Expected failure probability (Pf)

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

21

Background traffic channel time ratio (ρbg)

voice traffic is normally assigned the highest priority in medium contention

paper define ρbg as the minimum fraction of time which is expected that background traffic will occupy as a consequence of its lower medium access priority

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

22

CAC Algorithm Evaluation

the maximum number nreal of user which can be accepted with a good quality (ie Rgt70) in a given scenario and the maximum number nalg of users accepted by the algorithm being considered

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

23

Measurement campaign results for every tested scenario

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

24

Fraction of blocked users for G711 codec scenario at 12 Mbps

TBIT does not consider the channel time spent due to collisions

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

25

Fraction of blocked users for G711 codec + 1 TCP connection scenario at 2 Mbps

First TBIT recognizes it as congestion and therefore does not admit new voice calls

When most of the traffic in the network is voice then TBIT underestimates the network congestion

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature

26

Conclusion

The channel load estimation method accounts for both the fraction of time spent in successful and erroneous frame transmissions

the proposed scheme is more robust and accurate in making CAC decisions than the TBIT scheme which to our knowledge is the best among the CAC solutions for VoIP over WLAN previously appeared in the literature