Transcript Quality Of Service

Dave Martin
Vice President, Product Management
[email protected] 408.351.7209
Agenda
 Challenges for converged networks



Quality of Service
Monitoring VoIP performance
Troubleshooting
 Solutions and best practices
 Deployment examples


Service Provider
Enterprise
 Wrap-up/summary
Quality Of Service Why Is It Necessary?
“Becauszzzz wit_o_t it _sers w__l be unha_py!”
 PSTN has set the bar - VoIP as a replacement
technology must offer the same quality experience

Users will tradeoff voice quality for mobility - not true for
fixed line services
 VoIP has very stringent jitter, latency and packet loss
requirements…best effort IP forwarding is insufficient
Ensuring A High Quality Voice
Experience: Design Considerations
 Prioritize voice over data traffic

Take advantage of DiffServ routing if available in the network…
but remember… TOS bit setting is NOT traffic management !!
 Implement traffic shaping
 Provide call admission control
 Route media shortest path
Pay Close Attention To Access Links
LAN and network core
tend to be over-provisioned
OC-x MultiGigabit
100Mbps
T-1/E-1
Router
Congestion
Point
Managing Access Links
Traffic shaping
Priority queuing
Diffserv packet marking
Call Admission Control
High Priority
Queue
Low Priority
Queue
WAN/LAN Link
•Video calls established
•Data “shaped”
•New calls are blocked
•Data not starved
completely
time
Low Priority Queue
Video
High Priority Queue
T1 WAN Link
1.544Mbits/Sec
Data allowed to consume
available bandwidth as calls are
completed
Route Media Shortest Path:
Hosted PBX Scenario
Atlanta
Service Provider
San
Francisco
Softswitch
Dallas
Legend
Signaling path
Media path
VoIP Monitoring Issues
 Distributed nature of IP networking means no natural
demarcation point for problem resolution
 I just had a poor quality call…...but why?
 Difficult to monitor long term call performance and
identify consistently poor performers
Create Demarcation Points
Signaling
Media
VoIP Manager
Softswitch
or
IP PBX
IP Phone
A
Location #3
Location #1
Location #2
IP
network
B
C
D
IP Phone

Mean Opinion Score (MOS) provides a
simple listening quality scale the represents
the user experience

Monitoring at points A, B, C and D provides
a demarcation point between LAN and WAN
Use Call Quality Statistics To
Isolate Network Problems
Common causes of jitter:
• Ethernet link set at half duplex
• Ethernet link set to autonegotiate
• Congestion in upstream router
Provide Proactive Support
 Trend analysis at the
network level can spot
persistent problems
 Set quality thresholds
for advanced notification
Deployment Examples
• QoS
• Monitoring
• QoS
• Monitoring
• VPN
Best Practices Summary
 Quality of Service


Implement prioritization, traffic shaping, call admission control
Route calls shortest path to minimize jitter, latency, and
packet loss
 Monitoring



Create demarcation points
Build quality monitoring into the network
Use tools that report on the user experience and send
proactive notification of VoIP quality problems
Thank You!
Contact :
Dave Martin
Vice President, Product Management
[email protected]
408.351.7209