voip over wireless lans sangho shin ph.d. candidate department of computer science columbia...
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VoIP over Wireless VoIP over Wireless LANsLANs
Sangho ShinSangho Shin
Ph.D. CandidatePh.D. CandidateDepartment of Computer ScienceDepartment of Computer Science
Columbia UniversityColumbia University
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Why VoIP?Why VoIP?
Personalized ServiceLocation-based ServiceEmergency Service
IP
Voice Service
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Why 802.11?Why 802.11?Unlicensed channels
Easy to install
High speed
Widely deployed
Cheap
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VoIP over 802.11 WLANsVoIP over 802.11 WLANs
PBX
InternetInternet
WIFI
AP (Access Point)
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QoS of VoIP in Wireless LANs QoS of VoIP in Wireless LANs
Handoff Capacity
Call Admission Control
QoS
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HandoffHandoff
Handoff Time500 ms ~ 1 s
4 ms ~ 100 ms
Selective Scanning& Caching
Layer 2 (MAC layer) Handoff
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1 2 3 4 5 6 7 8 9 10 11
2.402 GHz 2.468 GHz22 MHz
► Selective ScanningSelective Scanning
► CachingCaching LocalityLocality Store the scanned AP information to a cacheStore the scanned AP information to a cache
Layer 2 HandoffLayer 2 Handoff
802.11b channels
Only clients (driver) need to be modified!
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HandoffHandoff
Handoff Time 1 min
20 ms ~ 300 ms
Fast L3 Handoff
Passive DAD
Layer 3 (IP layer) Handoff
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Layer 3 HandoffLayer 3 Handoff
► Fast L3 Handoff (Client side)Fast L3 Handoff (Client side) Fast subnet discovery using a DHCP Fast subnet discovery using a DHCP
queryquery Scan unused IPs in a new subnetScan unused IPs in a new subnet
► Passive DAD (Server side)Passive DAD (Server side)
160.123.234.31160.123.231.32160.123.235.35160.123.232.36160.123.238.38
160.123.234.32 160.123.234.32 160.123.234.35 160.123.234.36 160.123.234.31 160.123.234.38
VVVV
Request
Response
Monitor Collect IPs Update IP list Fast Response
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CapacityCapacity
Theater Stadium
More simultaneous calls
Low VoIP capacity in WLANs
Low bandwidth
Low utilization of VoIP traffic
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CapacityCapacity
802.11 MAC
PCF DCF
DPCF
APC
VoIP Capacity 25%~30%
Reduce polling overhead
Fair resource distribution
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Call Admission Control (CAC)Call Admission Control (CAC)
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
QoS
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Call Admission Control (CAC)Call Admission Control (CAC)
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
QoS
CAC
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Call Admission Control (CAC)Call Admission Control (CAC)
CAC
QoS Utilization
90% 80%
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CAC with QP-CAT
QoS Utilization
Call Admission Control (CAC)Call Admission Control (CAC)
CAC
QoS Utilization
90% 80%
100% 98%
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QP-CAT ?QP-CAT ?
QoS
DelayPredicted delay with QP-CAT
Queue size Prediction (QP)
Computation of Additional Transmission (CAT)
MAC
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Capacity for VoIP traffic in 802.11 Capacity for VoIP traffic in 802.11 WLANsWLANs
ExperimentsExperiments
DPCF
APCQP-CAT
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Thank you !