1. Voice Quality in IP Telephony
Vesa Kosonen
Networking Laboratory
Helsinki University of Technology
P.O.Box 3000, FIN HUT, FINLAND
Heading
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

2. S-38.130 Licentiate course on Telecommunications, April 2001
Contents
Introduction
End-to-End Call Scenarios
Path of Voice (end-to-end call)
Impairments on Voice Path
Methods to Assess Voice Quality
Measurements
Conclusions
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

3. S-38.130 Licentiate course on Telecommunications, April 2001
Introduction
SCN voice quality has been developed since 1876
G.711 with 8 kHz gives MOS value 4.2
Why should we be satisfied with less?
But if SCN will be soon dead that is not a valid question
Then the future looks like this:
we have to be satisfied with lower quality
we have experience for that in GSM
we need to try to develop the quality
that is what we have been doing since 1876
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

4. End-to-End Call Scenarios by ETSI/TIPHON (1/3)
Scenario 0: IP network to IP network
IP Network
IP Network
TIPHON Terminal
TIPHON Terminal
ETSI/TIPHON has introduced four different scenirios to make an IP call:
1. IP to IP
2. IP to SCN
3. SCN to IP
4. SCN to SCN (cheap overseas calls are based on this)
IP Access
IP Access
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

5. End-to-End Call Scenarios by ETSI/TIPHON (2/3)
Scenario 1: IP network to SCN
Scenario 2: SCN to IP network
TIPHON Terminal
IP Network
IP Access
IWF
Call initiated from IP Network to SCN
SCN
network
Call initiated from SCN to
IP Network
Scenario 1: Call from IP Network to SCN
Scenario 2: Call from SCN to IP Network
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

6. End-to-End Call Scenarios by ETSI/TIPHON (3/3)
Scenario 3: SCN to SCN over IP network
IP Network
IWF
IWF
SCN
network
SCN
network
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

7. Path of Voice (end-to-end call)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

8. Impairments on Voice Path (1/3)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

9. Impairments on Voice Path (2/3)
Talker echo
Listener echo
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

10. Impairments on Voice Path (3/3)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

11. Methods to Assess Voice Quality (1/5)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

12. Methods to Assess Voice Quality (2/5)
E-model
A computational tool for network planners (customer satisfaction, avoid over-engineering)
Provides a prediction of the expected quality as perceived by the user at the receiving end
Accounts for low bit-rate coding devices as well as for impairments introduced by standard PCM coders
Accounts for impairments not directly related to digital processing
Combines different impairment factors
Rating Factor R => delay budget
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

13. Methods to Assess Voice Quality (3/5)
Comparing R-value and MOS
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

14. Methods to Assess Voice Quality (4/5)
R = R0 - Is - Id - Ie + A
R0 => S/N (circuit noise, room noise)
Is => simultaneously with voice signal
e.g. quantization distortion
Id => delay (echo, loss of interactivity)
Ie => special eq. (low bit rate codecs)
A => advantage factor (gsm = 10)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

15. Methods to Assess Voice Quality (5/5)
PSTN quality: R: 70 => 100
Default values: R = 93.2
With default values: a call retains its quality up to 150 ms
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

16. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (1/8)
Environment
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

17. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (2/8)
Packet Spacing Different, Playout, Jitter
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

18. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (3/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

19. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (4/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

20. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (5/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

21. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (6/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

22. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (7/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

23. S-38.130 Licentiate course on Telecommunications, April 2001
Measurements (8/8)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001

24. S-38.130 Licentiate course on Telecommunications, April 2001
Conclusions
It seems that we never can enjoy perfect voice quality
Voice quality of IPT is however improving
Methods to assess voice quality are needed ( to function as our ears)
Vesa Kosonen
S Licentiate course on Telecommunications, April 2001