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Voice Quality

Voice Quality. John Horrocks (DTI). Email: RJHorrocks@cs.com Direct line: 01483 797807 Date: 20 November 2001 www.horrocks.co.uk. Overall Packet Loss. Network Packet Loss. Codec Performance. Perceived Speech Quality. Jitter Buffers. Network Jitter. Overall Delay. Network Delay.

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Voice Quality

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  1. Voice Quality John Horrocks (DTI) Email: RJHorrocks@cs.com Direct line: 01483 797807 Date: 20 November 2001 www.horrocks.co.uk

  2. Overall Packet Loss Network Packet Loss Codec Performance Perceived Speech Quality Jitter Buffers Network Jitter Overall Delay Network Delay • Application Factors QoS Service Level Inter-relationship of factors

  3. 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).

  4. Narrowband Unguaranteed(Best Effort) Class Wideband High Medium Acceptable Listener Speech Quality (One-way Non-conversational) Equivalent or better than G.726 at 32 kbit/s Equivalent or better than GSM-FR Better than G.711 Undefined Undefined End-to-end Delay (G.114) < 400ms < 100ms < 100ms < 150ms < 400ms* Overall Transmission Quality Rating (R) N.A. > 80 > 70 > 50 > 50* Specifying the TIPHON Speech QoS Classes (MOS>2.5) (MOS>3.6) (MOS>4.0) • * Target (MOS: 5=Excellent, 4=Good, 3= Fair, 2= Poor, 1=Bad)

  5. TIPHON QoS Classes High Medium Acceptable Best effort

  6. Packet Flow Transport Domain 1 Transport Domain 2 Transport Domain 3 Call Signalling Today’s Internet QoS Model Application Plane Transport Plane

  7. Packet Flow Transport Domain 1 Transport Domain 2 Transport Domain 3 Call Signalling Tomorrow’s Internet QoS Model Application Plane Transport Plane QoS Signalling if same technology eg RSVP

  8. BUT • Transport domains may support different QoS mechanisms and policies. • Who owns the end to end picture? • No mechanism to select transport domain on basis of QoS levels supported. c.f choice of alternative long distance carriers. • QoS messages are not signalled to the service provider - how can he control the QoS levels offered? • Need a business model for supplying and charging for QoS Problems with Today’s Approach

  9. Service Domain 1 Transport Domain 1 Transport Domain 2 Transport Domain 3 The TIPHON Application Controlled Approach to QoS Application Plane Transport Plane Packet Flow QoS Signalling Call Signalling

  10. 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

  11. 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

  12. Application Plane Transport Plane Transport Domain 4 (RSVP) Transport Domain 1 (RSVP) Transport Domain 2 (Diff Serv) Transport Domain 3 (MPLS/ATM) Service Domain 1 Service Domain 2 Mixed Transport QoS Mechanisms Media Flow QoS Signalling Call Signalling

  13. QoS Signalling & Addressing - from Application Plane TPE TRM Media stream Media stream ICF ICF RSVP Signalling Call Control Signalling Transport Domain QoS Signalling Media Path RSVP Example TRM=Transport Resource Manager TPE= Transport Policy

  14. QoS Signalling & Addressing - from Application Plane TPE TRM Add Diff Serv Marker Media stream Media stream ICF ICF Policy Enforcement Element Call Control Signalling Transport Domain QoS Signalling Media Path Diff Serv Example

  15. TIPHON uses a layered architecture which separates Application and Transport Planes. • Administrative Domains define roles of End User, Service Provider (SP) and Transport Operator. Basis for security protection and SLAs. • End-to-end QoS is responsibiliy of initiating SP. • The initiating SP negotiates transport QoS budgets, domain by domain, with transport network operators and other SPs • TRM and ICF model enables any transport QoS mechanisms to be deployed in transport plane • ICF models QoS boundaries, firewalls and NATs. Summary

  16. Documents

  17. 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

  18. 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

  19. 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 go…with some tough decisions to come…

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