1. 2/07/03 Telchemy 2003 1 QoS for VoIP: Measuring its Effectiveness Bob Massad Telchemy ®, Inc www.telchemy.com rmassad@telchemy.com

2. 2/07/03 Telchemy 2003 2 Agenda QoS Definitions The need for QoS Defining QoS Effectiveness as QoE Measuring QoS Effectiveness Concluding Remarks

3. 2/07/03 Telchemy 2003 3 What is QoS? “… providing consistent, predictable data delivery service.” (QoS Forum) “…the … assurance that requirements can be satisfied.” (QoS Forum) “…service requirements to be met … while transporting a flow.” (RFC 2386) In short: managing bandwidth, priority and queues – not QUALITY

4. 2/07/03 Telchemy 2003 4 QoS Mechanisms ToS – Type of Service 802.1p – Layer 2 IntServ – Integrated Services DiffServ – Differentiated Services RSVP – Resource Reservation CoS – Class of Service CAR – Committed Access Rate CIR – Committed Information Rate

5. 2/07/03 Telchemy 2003 5 2 Interesting QoS Services Integrated Services (RFC 1633, RSVP 2205) –Dynamic per hop RSVP request for a “quantity” –Per node parameters signaled per flow –Two currently defined services: Guaranteed service Controlled-load service Differentiated Services (RFCs 2475 & 3086) –Uses TOS byte (DSCP) to classify packets –DSCP used to “treat” (PHB) packets per hop e2e –3 PHBs: EF - low latency, jitter, loss - Virtual Leased Line AF - classifies precedence levels: G, B, S (Olympic) DE – Default/Best Effort

6. 2/07/03 Telchemy 2003 6 Why Internets need QoS? IP provides few packet services –Routing/Addressing –Fragmentation and Reassembly TCP provides reliability but… –No throughput management –No latency management UDP only provides port multiplexing Internets are shared media New Apps on the Horizon – VoIP…

7. 2/07/03 Telchemy 2003 7 From: Ryan Koga, rkoga@caida.org and Sean McCreary, mccreary@caida.orgrkoga@caida.orgmccreary@caida.org

8. 2/07/03 Telchemy 2003 8 Heterogeneous Apps

9. 2/07/03 Telchemy 2003 9 QoS Effectiveness for VoIP Different than typical Internet apps –Typical Apps Email File transfer HTTP/Web –Measured via Thru-put, Response Time, Retries… VoIP Uses UDP VoIP Real-time VoIP Sense/Experience oriented Measured via Quality of Experience (QoE)

10. 2/07/03 Telchemy 2003 10 What is QoE for VoIP? Listening Quality (LQ) - call clarity and presence/absence of disturbing effects Conversational Quality (CQ) – degree of support or interference with dialog, i.e. conversation.

11. 2/07/03 Telchemy 2003 11 Factors in VoIP Call Quality IP Network Packet Loss, Delay, Jitter CODEC type Local Loop

12. 2/07/03 Telchemy 2003 12 The short stories Jitter –Jitter Buffer moderates effects Turns Jitter into small Delay Turns problematic delay into packet loss Delay –Not indicative of LQ unless excessive –More indicative of CQ –Excessive delay becomes packet loss Leaving packet loss…

13. 2/07/03 Telchemy 2003 13 The Key VoIP Problem: Packet Loss/Discards Gateway Lost Packets CODEC Jitter Buffer Discards Jitter Buffer

14. 2/07/03 Telchemy 2003 14 Packet Loss is Bursty

15. 2/07/03 Telchemy 2003 15 Packet Loss Concealment For consecutive packets lost, same packet repeated multiple times ! Worse if long or multiple voice frames per packet! 2 frames lost Same frame repeated 3 times

16. 2/07/03 Telchemy 2003 16 Expect more packet loss in UDP apps! 1% of loss bursts can account for 50% of all losses! One study showed mean packets lost in burst = 6.9 ! …Another shows when 1 packet is lost the probability increases that next packet will be lost too!

17. 2/07/03 Telchemy 2003 17 End-user Perception Transitional Quality Recognition –From bad to good –From good to bad Recency –Short term auditory memory –Length of time since last impairment

18. 2/07/03 Telchemy 2003 18 “Recency” effect “Good” 4.3MOS “Bad” 1.8 MOS (3dB SNR) MOS 3.8 MOS 3.3 MOS 3.2 Source AT&T T1A1.7/98-031 60 seconds Start Of call End Of call

19. 2/07/03 Telchemy 2003 19 Enhanced E-Model Delay Network R Factor IeIe Packet Loss Jitter Codec type Loss Model Jitter Model Codec Model Burst model Recency model User R Factor Delay model Extensions incorporated in ETSI Standard TS 101329-5 Annex E

20. 2/07/03 Telchemy 2003 20 Comparison with E Model

21. 2/07/03 Telchemy 2003 21 Call Quality Monitoring IP Network QoS Domain QoS Domain Jitter buffer simulator IP Network CODEC VQmon VoIP End-Point SLA monitor

22. 2/07/03 Telchemy 2003 22 Conclusions Control of QoS for VoIP involves control of key parameters within IP Net. Real-time monitoring of Call Quality/QoE provides a comprehensive means of measuring the effectiveness of network QoS parameters and points to remedial actions. Non-intrusive objective Measurement based on Enhanced E-Model provides an accurate metric of instantaneous Call Quality/QoE. It’s a similar case for Video!

23. 2/07/03 Telchemy 2003 23 About Telchemy Founded - Late ‘99 Location - Atlanta, GA Focus - embedded tools to optimize V²oIP Approach - open software architecture First products - VQmon ® /EP and /SA - lightweight embedded call quality monitoring agents for integration in VoIP endpoints and management devices.