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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
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