Voice Quality

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Voice Quality
John Horrocks (DTI)
Email RJHorrocks_at_cs.com Direct line 01483
797807 Date 20 November 2001 www.horrocks.co.uk
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Inter-relationship of factors
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Approach to Characterizing Speech QoS

• QoS is defined subjectively as perceived by the
  user,
• It is end to end (e.g. mouth to ear for speech),
• A number of QoS Service Classes are defined,
• Classes include guaranteed quality
  (statistically) and unguaranteed (best effort).

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Specifying the TIPHON Speech QoS Classes
(MOSgt2.5)
(MOSgt3.6)
(MOSgt4.0)

• Target

(MOS 5Excellent, 4Good, 3 Fair, 2 Poor,
1Bad)
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TIPHON QoS Classes
High
Medium
Acceptable
Best effort
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Todays Internet QoS Model
Application Plane
Transport Plane
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Tomorrows Internet QoS Model
Application Plane
Transport Plane
QoS Signalling if same technology eg RSVP
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Problems with Todays Approach
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The TIPHON Application Controlled Approach to QoS
Application Plane
Transport Plane
Packet Flow
QoS Signalling
Call Signalling
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Advantages of the TIPHON Approach to End-to-end
QoS

• CLEAR BUSINESS MODEL
• The Application Service Provider is in the
  driving seat. End-to-end (inter-domain) QoS
  control takes place within the Application Plane.
  (Between Service Providers)
• Required end-to-end QoS levels are established
  within the Application Plane (Between the End
  User and Service Provider)
• Transport Domains (Operators) provide a QoS
  service to the associated Service Domains
  (Service Providers). QoS controlwithin a
  Transport Domain is the responsibility of the
  Operator of that domain

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Advantages of the TIPHON Appoach to End-to-end
QoS (Cont)

• OTHER ADVANTAGES
• A common interface can be defined between a
  Transport Domain and its associated Service
  Domain even though different QoS mechanisms may
  be present within the Transport Plane
• No QoS information need be exchanged between the
  End User and Network Operator or between Network
  Operators
• Application Controlled Firewalls and NATS can be
  accommodated

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Mixed Transport QoS Mechanisms
Media Flow
QoS Signalling
Call Signalling
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RSVP Example
TRMTransport Resource Manager TPE Transport
Policy
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Diff Serv Example
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Summary
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Documents
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NICC VoIP Quality Group

• Working about a year to revise UK transmission
  plan for public networks
• Inputs from TIPHON
• Aims to complete by Easter 2002
• Assume normal NTP at customer premises

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Progress so far

• Delay is the most critical impairment
• Everyone should use G.711 standard PSTN coding
  to use less delay
• Minimise speech frame size and frames/packet
• Use RTP header compression and data packet
  fragmentation
• Keep packet loss below 1 overall
• Need to minimise the number of IP-Circuit
  switched transitions, but IP based
  interconnection will develop only slowly so this
  will be difficult
• Avoid transcoding

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Comments

• Some routings involving number portability and
  non-geographic services are very tortuous
• Use on onward routing solution
• Lack of direct interconnection routes
• Will need a statistical approach
• Not tackled the design / apportionment issue yet
• Still quite a long way to gowith some tough
  decisions to come