In last 40 years, significant research have happened on how to preserve and enhance fundamental quality of voice when it traverses in "packet" form over networks. The author presents here his earlier work carried out in the context of VoATM, VoFR, VoIP. With current interest in VoLTE (Voice over LTE) and Voice-based Intelligent Systems, work on essence of voice quality in packet communication has emerged very meaningful. The article covers how Quality-of-Service could be enhanced by combating latency, jitter, noise, echo, packet error, packet loss, activity discontinuity as well as codec tandemming.

1. Essence of Voice Quality in
Packet Communication
Aloknath De, Ph.D. (McGill),
Chief Technology Officer—Samsung India (SRI-B)
26th Nov. 2016

2. 26 Nov., 2016 Copyrighted Material Authored by:: Dr. Aloknath De
Importance of Quality Voice
 Circuit-Switched: P2P Real-time Comm.
 Packet-Switched: Voice over ATM, Frame Relay,
IP and recently over LTE
 Adaptive Scheme for Voice over Ad-hoc
Networks
 Voice based Intelligent Systems and Services
that may require Packet-based Storage,
Processing and Transmission
 Quality-of-Service Enhancement by combating
Delay, Noise, Echo, Packet Error, Packet Loss,
Activity Discontinuity and Tandemming.

3. Voice Quality
in Packet Communication
(IEEE—Workshop on Communication Technologies)
Dr. Aloknath De, Head---Telecom Unit,
STMicroelectronics India
02-March-2006
Copyrighted Material (use by reference)
Copyrighted Material Authored by:: Dr. De
Material Authored by:: Dr.

4. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
The Route ...
 Overview of Voice QoS
 VoP Components
 Reference Network Configurations
 Vocoder Descriptions
 Subjective and Objective Measurements
 Voice Quality Parameters
 Methods to Maintain Good Voice Quality

5. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Overview
 Circuit-Switched: P2P Real-time Comm.
 Packet-Switched: Connection-oriented
ATM, Frame Relay
 Connection-less Network: Data transport
using routers, bridges, switches
 IP: Classless best-effort
 QoS and Voice Quality Parameters

6. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
VoIP Components
Packet Based Network
Circuit Switched
Network
PictureTel PictureTel
PictureTel
MCU
H.323
Terminal
H.323
Gateway
H.323
Gatekeeper
 Terminals
 Gateways (GW)
 Gatekeepers (GK)
 Multipoint Control Units (MCU)
 Multipoint Controllers (MC)
 Multipoint Processors (MP)
 Broadly classified into:
 GK
 Endpoints (Terminal, GW, MCU)

7. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Reference Configuration - I
IP Network to CSN
Circuit Switched
Network
Phone
IP Network
Client
Inter-working
Function
Access
Connection
Gateway

8. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Reference Configuration - II
CSN to CSN over IP network
PhonePhone
IP Network
Circuit Switched
Network
Circuit Switched
Network
Inter-working
Function
Inter-working
Function
Gateway
Gateway

9. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Reference Configuration - III
IP Network
Client Client
IP Network
Access
Connection
Circuit Switched
Network
Access
Connection
Inter-working
Function
Inter-working
Function
IP to IP over CSN Network
GatewayGateway

10. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Integrated PBXes
Circuit Switched
Network
Phone
IP Network
Client
Integrated PBX
Phone
Phone
Enterprise
Network

11. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Integrated Router
Circuit Switched
Network
IP Network
Client
Integrated Router
Phone
Phone
Enterprise
Network
IP Phone
IP Phone

12. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
PBX + Gateway
Circuit Switched
Network
Phone
IP Network
Client
PBX
Phone
Phone
Enterprise
Network
Gateway
Gateway

13. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Router + Gateway
Circuit Switched
Network
IP Network
Client
Integrated Router
Phone
Phone
Enterprise
Network
IP Phone
IP Phone
Gateway

14. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Vocoders and Speech Quality
 Waveform, Parametric and Hybrid
Coders
 Compression using Perceptually
Important Information
 Speech Quality Measurement---
Subjective and Objective Measures
 Error-free and Error-induced Channels
 Clean Speech and with BG Noise

15. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Voice Quality Parameters
 Fundamental Speech Quality (Clean and/or
with Background Noise)
 Filtering/Gain/Non-linearity/Switchover
 Voice Activity Detection/Comfort Noise
 Tandemming
 Latency and Jitter
 Presence of Echo
 Packet Loss---Delay or Otherwise

16. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Speech Quality
 Mean Opinion Score
 Other Subjective Measures (ACR, Pairwise
Comparison etc.)
 Objective Measures---LAR, LLR, BSD
 Cognitive Measures---Neural Distance
 P.800 Standard---PSQM, PASM etc.

17. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Filtering/Gain/Nonlinearity/
Switchover
 IRS and other Filters---Pre-processors and
Post-processors/Post-filters
 Gain Pad in System---Level Adjustment
 Non-linearity---System, Codec Design
 Voice/Fax Switchover in Integrated
Network---Speech Correlation-based, Tone-
based as well as Fax Data Preamble-based
Detection

18. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Transmission Quality Category
 G.100 series---Transmission Planning
Guidance
 G.107---E-model for Planning End-to-End
Transmission Quality
 R Values: ISDN-ISDN: 94, PSTN-PSTN:
82, Mobile-PSTN: 74 (mobile side), Mobile-
PSTN: 60 (PSTN side), Mobile to ISDN
with High Delay: 52

19. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Voice Activity Detector (VAD)/
Comfort Noise Generator (CNG)
 Silence Suppression---Better Bandwidth
Utilization
 VAD with PCM and CELP-type Codecs
 Front-end Clipping
 Long and Short Holdover Time
 Match between “Generated Comfort Noise”
and “True Background Noise”
 CNG---Canned and Dynamic Noise

20. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Tandemming and TFO
 Multiple (similar or dissimilar) Codecs in
Tandem---Quality Degradation
 Typical Scores (LAR)--> G.729=3.5, G.729-
G.729=5.6, G.723.1=8.25, G.729-
G.723=8.5, G.723-G.729=8.15, G.723-
G.723=8.6
 Vocoder Performance Better in Bursty
Channel than Random-Error Channel

21. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Tandemming and TFO (contd.)
 Application: Mobile-toMobile and Mobile-
to-Landline (with Mailbox)
 Tandem-Free Operation (TFO)
 In-band or Out-band Signaling Protocol
 MOS Score Improvement: GSM-HR: 0.70-
1.07, GSM-FR: 0.49-0.77, GSM-EFR: 0.14-
0.67

22. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Components of Latency/Jitter
 Fixed and Network-dependent Delays
 Average Delay and Standard Deviation
 Codec Processing Delay
 Hardware, Modems, OS Delays
 Transmission Media Delay
 Congestion and Routing Delay
 Play-out Buffering Delay

23. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Practical Examples
 “Transaction-Oriented” Applications: low-
latency systems
 Prioritization of Voice Packets (gateway’s
UDP number or RSVP...)
 Teledesic Systems: Terrestrial (100-
150ms); LEOs (~200ms); GEOs (~600ms)
 Comparison: D=50ms; J=20ms vs. D=25ms;
J=60ms

24. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Effect on Voice Quality
 Delay: Effect on Conversational Dynamics
 Replication Technique for Too Many
Packets: Quality Degradation
 Non-Deterministic delay: Private vs.
Public Networks
 Forward Error Correction Adopted

25. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Design Reducing Latency/Jitter
 Non-Deterministic delay: Latency/Jitter
 Out-of-Sequence Packets or Packet Loss
 Careful Examination of Network Components
Causing Delay/Variation
 Continuous Playback Point Change based on
Network’s Delivery Capability

26. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Echo and Control/Cancellation
 Network Echo due to Hybrid in SLIC
 Network Echo Control per G.164
 Network Echo Canceller per G.165, G.168
 Acoustic Echo Heard at Landline for
Mobile or Hands-free Calls
 Acoustic Echo Canceller per G.167

27. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Txt, bmp
to
bitstream
Modem
Echo-
CancellersHybrid
Transcoder
Channel
Coding
Modem
Transcoder
T.38
Modem
T.30
Wireless
IP
T.38
USER
EQUIPMENT
SWITCH
GATEWAYS
2 wire
Connection
4 wire
Connection
DSP APPLICATION FOR TRANSMIT
PATH OF A TYPICAL
COMMUNICATION SYSTEM
FAX

28. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Sources of Packet Loss
 Packets with undefined format or incorrect
checksum dropped
 Input Drop related to Router processing;
Output Drop when outgoing link busy
 RED--Packet loss due to Back-off/Slow-
start
 Improper Playout point setting in Receive
buffer

29. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Effect on Voice Quality
 With silent gaps replacing missing speech
packets---1% packet loss rate tolerable
 half-duplex perception when delay high
 artifacts in synthesized speech signal;
noticeable quality degradation

30. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Packet Recovery Technique for
LD-CELP (G.728) Coders
 No change to G.728---decoder decodes
excitation with low energy or with previous
frame excitation char.
 Decoder change
 extrapolation of gain-scaled excitation and
LPC coeff.
 replacement of LPC by Kalman filter
 hybrid Kalman filter: retains performance
gain, reduces complexity

31. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Packet Recovery Technique for
LD-CELP (G.728) Coders
 Encoder and Decoder change
 spectral smoothing---frequency-domain
Gaussian window
 bandwidth expansion for LPC/gain predictors
by reducing expansion factor
 modification of backward adaptation
algorithms in encoder and decoder to
increase inherent convergence speed

32. 02 March, 2006 STMicroelectronics
Authored by:: Dr. Aloknath De
Summary
 Signal Processing and Transportation
 Speech Compression Technology
 Packet Network Configurations
 Control of Speech Quality (service, sound
and conversation) Degradation in Packet
Network
 Methods to Combat Delay, Echo, Noise,
Error, Discontinuity, Packet Loss

33. 26 Nov., 2016 Copyrighted Material Authored by:: Dr. Aloknath De
Published Work by Author
• A.De, “Voice Quality in Packet Communication”, IEEE Workshop on
Communication Technologies, IIT-Roorkee, Mar.2006.
• A.De, “Quality in Packetized Voice Communication”, Tutorial in National Conf on
Communications (NCC2002), IIT-Bombay, Jan.2002.
• A.De and A.Kumar, “End-to-End Voice Quality in Packet Networks”, Tutorial in
IEEE Annual Convention, New Delhi, Dec.2001.
• S.Gote, A.Nasipuri and A.De, “Source-Aided Error Concealment in Packetized
Voice Communication”, Proc. International Conference on Communications,
Computers and Devices (ICCCD2000), pp. T3.3.1—T3.3.4, IIT-Kharagpur,
Dec.2000.
• A.De, “Packet Loss and Recovery Mechanisms for an IP Network”, Invited
Presentation in ITU Seminar on IP, Bangalore, Mar.2000.
• A.De, “Latency and Jitter---Two Issues in Packetized Voice Communication,” 6th
National Conference on Communications (NCC2000), IIT-Delhi, Jan.2000.