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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
Why VoIP?Why VoIP?
Personalized ServiceLocation-based ServiceEmergency Service
IP
Voice Service
Why 802.11?Why 802.11?Unlicensed channels
Easy to install
High speed
Widely deployed
Cheap
VoIP over 802.11 WLANsVoIP over 802.11 WLANs
PBX
InternetInternet
WIFI
AP (Access Point)
QoS of VoIP in Wireless LANs QoS of VoIP in Wireless LANs
Handoff Capacity
Call Admission Control
QoS
HandoffHandoff
Handoff Time500 ms ~ 1 s
4 ms ~ 100 ms
Selective Scanning& Caching
Layer 2 (MAC layer) Handoff
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!
HandoffHandoff
Handoff Time 1 min
20 ms ~ 300 ms
Fast L3 Handoff
Passive DAD
Layer 3 (IP layer) Handoff
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
CapacityCapacity
Theater Stadium
More simultaneous calls
Low VoIP capacity in WLANs
Low bandwidth
Low utilization of VoIP traffic
CapacityCapacity
802.11 MAC
PCF DCF
DPCF
APC
VoIP Capacity 25%~30%
Reduce polling overhead
Fair resource distribution
Call Admission Control (CAC)Call Admission Control (CAC)
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
QoS
Call Admission Control (CAC)Call Admission Control (CAC)
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
QoS
CAC
Call Admission Control (CAC)Call Admission Control (CAC)
CAC
QoS Utilization
90% 80%
CAC with QP-CAT
QoS Utilization
Call Admission Control (CAC)Call Admission Control (CAC)
CAC
QoS Utilization
90% 80%
100% 98%
QP-CAT ?QP-CAT ?
QoS
DelayPredicted delay with QP-CAT
Queue size Prediction (QP)
Computation of Additional Transmission (CAT)
MAC
Capacity for VoIP traffic in 802.11 Capacity for VoIP traffic in 802.11 WLANsWLANs
ExperimentsExperiments
DPCF
APCQP-CAT
Thank you !
