1. Performance of Voice over 802.11 Networks
Date: January 18, 2005
Performance of Voice over Networks
Author: Fanny Mlinarsky, Azimuth Systems
Fanny Mlinarsky, Azimuth Systems

2. Discussion Outline VoIP Cell WiFi VoIP and VoWiFi history
Cell-WiFi convergence
Voice network requirements
Emerging voice standards
Quality of Service
Security
Roaming
VoWiFi performance and certification testing
Future trends and opportunities
Cell
WiFi
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3. VoIP-Data Convergence
Traditional Enterprise connectivity
VoIP converges telephony and data networks
First VoIP products emerged in 1996
PSTN = Public Switched Telephone Network
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4. VoWiFi - Legacy PBX Systems
VoWiFi manufacturers
Cisco, Symbol, Spectralink
Spectralink WiFi phones available since 1999
802.11b only for now
Most IP PBXs use proprietary protocols
Cisco SCCP (skinny call control protocol)
Alcatel UA
NEC Protims
Avaya CCMS
Nortel UniStim
Siemens CorNet IP
Mitel MiNet
Standard IP telephony protocols
H.323
Media Gateway Control Protocol (MGCP)
Session Initiation Protocol (SIP)
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5. Voice over WiFi Use Cases
SOHO
WiFi or WiFi-Cell handset, soft phone
Service providers: Vonage, ATT CallVantage, Net2Phone
No handoff, low capacity, basic security
Range
Enterprise
Handoff speed
Call capacity
Security
Public access (WiFi hotspots)
WiFi-Cell handset, soft phone
Call Capacity
Roaming issues
Net2Phone WiFi handset
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6. Cell-WiFi Convergence Standards
UNC Server
SCCAN - seamless converged communication across networks
First converged system
Proxim, Motorola, Avaya
UMA - unlicensed mobile access
An extension of GSM/GPRS to WiFi
Alcatel, AT&T Wireless, British Telecom, Cingular, Ericsson, Kineto Wireless, Motorola, Nokia, Nortel Networks, O2, Rogers Wireless, Siemens, Sony Ericsson, T-Mobile US
Internet
UMA-enabled components:
- UNC (UMA Network Controller) server
- Handset
DSL/Cable Modem
Router AP
Wi-Fi
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7. Voice Network Requirements
Client
Range
Power-save
Fast roaming
Infrastructure
Call capacity
Delay, jitter, packet loss
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8. IEEE 802.11 Standards for VoWiFi
Minimize bursty packet loss by controlling roaming time
802.11r Fast Roaming
802.11k Radio Resource Measurement (RRM)
802.11i Pre-authentication
Manage power consumption
802.11e Power-save
Maintain isochronous nature of voice packet streams by controlling delay, jitter and packet loss
802.11e Quality of Service (QoS) prioritization
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9. QoS Protocols WMM (Wireless MultiMedia) AC (Admission Control)
Subset of e
Specifies 4 priorities: voice (highest), video, background, best effort (lowest)
Wi-Fi certification has started in September 04
AC (Admission Control)
Enables APs to reject calls when call capacity is reached
WMM SA (WMM Scheduled Access)
Specifies polling mechanism to optimize bandwidth utilization
Wi-Fi certification expected in July 05
APSD (Automatic Power Save Delivery)
Unscheduled APSD works with WMM
Scheduled APSD works with WMM-SA
SVP (Spectralink Voice Priority)
Proprietary prioritization scheme that combines priority mechanism with tight synchronization to optimize bandwidth utilization
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10. Security Protocols WPA WPA2 Subset of 802.11i TKIP, WEP
EAP-TLS, PSK (pre-shared key)
WPA Enterprise (TLS, PSK)
WPA Personal (PSK)
WPA2
Entire i
Superset of WPA
AES support
Pre-Authentication to help with r fast roaming
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11. Radio Resource Management
802.11k
Mechanism for stations and APs to discover neighboring APs and to learn about their traffic load and signal conditions
Helps r fast roaming
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12. IEEE 802.11 Standards Study groups Current work Published MAC PHY
(’99)
MAC +
2Mbps PHY
802.11s
Mesh
802.11p
WAVE
802.11r
Fast Roam
802.11u
WIEN SG
802.11h
DFS & TPC
802.11e
QoS
802.11v
WNM
802.11i
Security
ADS SG
802.11k
RRM
802.11n
High
Throughput
(>100 Mbps)
802.11f
Inter AP
APF SG
MAC
802.11m
Maint
802.11T
Test Methods
PHY
802.11a (’99)
54 Mbps
5GHz PHY
Study groups
802.11b (’99)
11 Mbps
2.4GHz PHY
802.11g
54 Mbps
2.4GHz PHY
Current
work
Published
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13. WiFi Alliance Roadmap
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14. Voice Quality
ITU-T Voice Quality Standards
MOS (mean opinion score) uses a wide range of human subjects to provide a subjective quality score (ITU-T P.800)
PESQ (perceptual speech quality measure) sends a voice pattern across a network and then compares received pattern to the original pattern and computes the quality rating (ITU-T P.862)
E-Model computes Rating Factor or R-Factor as a function of delay and packet loss; R-Factor directly translates into MOS (ITU-T G.107)
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15. ITU-T PESQ Model
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16. ITU-T E-Model E-Model based on ITU-T G.107 Packet-loss Latency
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17. E-Model Parameters Latency 500 ms max Packet loss 20% max
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18. Phone Range vs. MOS Vary attenuation between the phone and the AP
Measure packet loss, delay and jitter of a phone-AP link as a function of path loss
Use ITU-T E-Model to compute R-Factor and MOS vs. range
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19. MOS vs. Path Loss
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20. Measuring Call Capacity
Emulate voice traffic from multiple phones
Emulate background data traffic
Measure delay, jitter and packet loss* vs. number of calls and background traffic
* Per IETF RFCs 2544, 2889
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21. AP Call Capacity Test Results
% Frame Loss
# calls
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22. AP Call Capacity Test Results
Delay (usec)
# calls
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23. AP Call Capacity Test Results
Jitter (usec)
# calls
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24. AP Call Capacity Test Results
MOS
# calls
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25. Measuring Roaming Time
Emulate motion of the phone using programmable attenuators
Monitor source and destination WiFi channels and Ethernet
Derive roaming time from data captures
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26. Roaming Process AP1 AP2 AP1 max Path to AP1 Atten Path to AP2 min
Test cycle
Data rate transition
t ASSOCIATE
t DATA
t TRANSITION
t SCAN
t ROAM
Last data packet
before roam
First data packet
after roam
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27. Sample Roaming Test Results
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28. Sample Roaming Test Results
Multi Mode Clients (ABG)
Single Mode Clients (B only)
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29. Future Technology Environments Applications SOHO Enterprise
Public access
Outdoor campus
MAN/WAN
Transportation
Military
Applications
Data
Voice
Video
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