Voice Quality in IP Telephony Vesa Kosonen Networking

Voice Quality in IP Telephony Vesa Kosonen Networking Laboratory Helsinki University of Technology P. O. Box 3000, FIN-02015 HUT, FINLAND vesa. kosonen@hut. fi Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 1

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-38. 130 Licentiate course on Telecommunications, April 2001 2

Introduction • • • SCN voice quality has been developed since 1876 G. 711 with 8 k. Hz 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-38. 130 Licentiate course on Telecommunications, April 2001 3

End-to-End Call Scenarios by ETSI/TIPHON (1/3) • Scenario 0: IP network to IP network IP Network TIPHON Terminal IP Access Vesa Kosonen IP Access S-38. 130 Licentiate course on Telecommunications, April 2001 4

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 Call initiated from IP Network to SCN IWF 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-38. 130 Licentiate course on Telecommunications, April 2001 5

End-to-End Call Scenarios by ETSI/TIPHON (3/3) • Scenario 3: SCN to SCN over IP network IP Network IWF SCN network Vesa Kosonen SCN network S-38. 130 Licentiate course on Telecommunications, April 2001 6

Path of Voice (end-to-end call) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 7

Impairments on Voice Path (1/3) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 8

Impairments on Voice Path (2/3) Talker echo Listener echo Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 9

Impairments on Voice Path (3/3) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 10

Methods to Assess Voice Quality (1/5) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 11

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-38. 130 Licentiate course on Telecommunications, April 2001 12

Methods to Assess Voice Quality (3/5) Comparing R-value and MOS Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 13

Methods to Assess Voice Quality (4/5) • R = R 0 - Is - Id - Ie + A – R 0 => 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-38. 130 Licentiate course on Telecommunications, April 2001 14

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-38. 130 Licentiate course on Telecommunications, April 2001 15

Measurements (1/8) • Environment Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 16

Measurements (2/8) • Packet Spacing Different, Playout, Jitter Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 17

Measurements (3/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 18

Measurements (4/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 19

Measurements (5/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 20

Measurements (6/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 21

Measurements (7/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 22

Measurements (8/8) Vesa Kosonen S-38. 130 Licentiate course on Telecommunications, April 2001 23

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-38. 130 Licentiate course on Telecommunications, April 2001 24