Speech Coders

1
Speech Coders a VoIP perspective

• Roar HagenCTO
• SIP/email roar.hagen_at_globalipsound.com

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Agenda

• Speech Coders a VoIP perspective
• Demo
• QA

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QoS (endpoints) statusA lot of talk, ... but
not much work

• Year after year the same story
• More then 3000 papers since 1984
• Limited ToS support at the end points

4
QoS statusIndustrys perspective
quality concerns
unproven technology
PSTN works fine
too busy to switch
not compelling economics
5
Background - Diverse Environment
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Packet Loss San Francisco Hong Kong
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Jitter San Francisco Hong Kong
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Homg Kong to China VoIP Call
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Wireless VoIP The Big Unknown ?
Mobility
Vehicle
2G/2.5G
3G
WLAN
Walk
Fixed
LAN
Bluetooth
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0.1
1
Mbps
100
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Approach

• We need holistic view/approach for both
• Horizontal (end-to-end) perspective
• Vertical (top-down) perspective

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Vertical (Top Down) Perspective
Presentation Speech Codecs/
Session SIP/H.323
Transport RTP/UDP/RSVP
Network IP/WFQ/IP-prec
Link MLPPP/FR/ATM AAL1
Physical
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VoIP Aspirations

• IP innovation rather than PSTN replication
• New features and services through voice and data
  convergence
• End-to-end IP
• Better than PSTN sound quality

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Current speech processing technology not designed
for packet switched environments
FALL OFF A CLIFF shape of curve forces over
provisioning
MOS USER EXPERIENCE
OVERPROVISIONED NETWORK
CONGESTED NETWORK
MEAN OPINION SCORE
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congestion related VoIP QoS problems can be
solved without over provisioning
MOS USER EXPERIENCE
Operate AT and ABOVE congestion point without
customer knowing
OVERPROVISIONED NETWORK
CONGESTED NETWORK
MEAN OPINION SCORE
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narrow band sound quality equal to PSTN
wide band sound quality
Better Than PSTN Quality
Matching PSTN Quality
Telephony bandwidth speech test result
Wideband speech
5
5
4.5
4.5
4.0
4.0
3.5
3.5
MOS
MOS
3.0
3.0
2.5
2.5
GIPS iPCM-wb
2.0
2.0
GIPS NetEQ-wb
G.722 GIPS NetEQ-wb
1.5
1.5
G.722.1
Source

no PLC
1.0
1.0
0 5 10 15
20 25
NETWORK CONDITION ( PACKET LOSS)
NETWORK CONDITION ( PACKET LOSS)
SOURCE LOCKHEED MARTIN GLOBAL TELECOMMUNICATION
(COMSAT)
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Jitter Buffer/PLC Enhancements
Source Lockheed Martin Global Telecommunications
(COMSAT)
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Delay gain with NetEQapprox. 30-60ms compared
to traditional jitter buffers
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The NextGen Speech Codec Ideal

• Need one concept that will work for a long time
• footprint importance
• Need to handle large diversity of transport
  network
• low rate
• high quality, high rate
• packet loss
• jitter
• low delay
• Manageable IPR situation
• Signal Robustness
• speech
• music
• Suitable for variety of applications, e.g. IP
  video-conferencing

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iLBC (internet Low Bitrate Codec)

• Speech sampled at 8 kHZ,
• using a block-independent linear-predictive
  coding (LPC) algorithm.
• Bandwidth 13.867 kbps (52 bytes per 30 ms)
• Frame size 30 ms (support for 20 ms in the next
  revision)
• Complexity and memory requirements are similar to
  ITU G.729A
• Basic Quality is equal to or better than G.729.
  Packet loss robustness is significantly better
  than G.729.
• Packet loss concealment - Integrated example
  solution

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MOS Results
Source Dynastat Inc.
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iLBC - IETF work

• IETF deliverables, submitted during February 02
• iLBC codec specification draft - experimental
  standards track
• iLBC RTP Payload Profile - regular standards
  track (AVT)
• Statement about IPRs in iLBC and its freeware
  nature
• MOS results submission to the AVT mailing list
  during March 02

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Why iLBC !?

• Current low bit rate codecs ITU G.729, G.723.1,
  GSM-EFR, and 3GPP-AMR were developed for circuit
  switched wireless telephony and are all based
  on the CELP (Code Excited Linear Prediction)
  paradigm.
• CELP coders are stateful, they have memory, error
  propagation results from lost or delayed packets.
  
• iLBC treats every packet individually, making it
  suitable for packet communications.

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More information

• Coming Soon - web site www.ilbcfreeware.org with
• Info about initiative
• Info about codec
• Latest iLBC IETF drafts (spec and payload format)
• Latest iLBC float point Source code
• FAQ list
• IETF drafts
• draft-andersen-ilbc-00.txt - codec spec (exper.
  stds track)
• draft-duric-rtp-ilbc-00.txt - RTP payload profile
  (AVT group)
• Web site www.globalipsound.com
• Free demo SIP client available, please request
  at
• SIP/email alan.duric_at_globalipsound.com

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Summary

• Current speech coding technology not suited for
  VoIP
• VoIP opens possibilities
• Move quality exprience to the next level with
  wideband coders
• NGN will not be NGN unless we move step forward
  on all of its fields
• iLBC internet Low Bit Rate Codec
• Provide an open standard the Internet way for
  coder

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Demo