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 Heading Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

Path of Voice (end-to-end call) Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

Impairments on Voice Path (1/3) Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

Impairments on Voice Path (2/3) Talker echo Listener echo Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

Impairments on Voice Path (3/3) Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

Methods to Assess Voice Quality (1/5) Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

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

Methods to Assess Voice Quality (3/5) Comparing R-value and MOS Vesa Kosonen S-38.130 Licentiate course on Telecommunications, April 2001

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-38.130 Licentiate course on Telecommunications, April 2001

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

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

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

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

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

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

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

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

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

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-38.130 Licentiate course on Telecommunications, April 2001