ISSUES RELATING TO CONGESTION MANAGEMENT

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ISSUES RELATING TO CONGESTION MANAGEMENT IN PSTN
EQUIVALENT VOIP NETWORK R.R.N.
PRASAD MEMBER S.N. GUPTA ADVISOR TELECOM
REGULATORY AUTHORITY OF INDIA NEW DLEHI  
PRESENTATION AT APT WORKSHOP ON NETWORKING
STRATEGIES REPUBLIC OF PALAU 9TH May2002.
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CONTENT

• INTRODUCTION PSTN V/S VOIP
• 2. NETWORK TRAFFIC MANAGEMENT IN TELECOM AND
  DATACOM NETWORKS
• 3. MONITORING QOS OF VOIP NETWORKS
• 4. CONCLUSION
• 5. REFERENCES

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INTRODUCTION

• Internet Protocol Version 4 (IPv4)-
• Salient Features
• It is based on the simple concept of dumb
  network.
• It provides Best Effort service with no
  guarantee.
• It is designed to carry delay non-sensitive data
  traffic and not the real-time voice.
• It is packet switching based and is
  connectionless.
• It relies on higher layers (TCP) for reliable
  data delivery which is not suitable for
  interactive communication.

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VOIP- QUALITY OF SERVICE ISSUES
-gt Poor Voice quality - Higher delay, jitter
and packet loss. -gt Lower Bandwidth
- Compression and congestion on the link. -gt
Loss of Faxes - Compression. -gt Loss of
in-band Modems call - Packet loss and
compression. -gt No Empirical Formula for
capacity provision - Rule of thumb -gtSmooth
Voice traffic have to live with Bursty data
traffic - Dissimilar nature traffics
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PSTN- SALIENT FEATURES

• PSTN traffic is smooth and non-bursty.
• Network can be dimensioned based on
  well-established traffic
• engineering rules and statistical tools.
• Probability of blocking due to congestion can be
  estimated.
• Empirical Formulae- Erlangs BC are the basis
  for dimensioning of PSTN.
• Based on Circuit switching which is
  connection-oriented.
• Guaranteed quality of service (Toll quality)

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PSTN- QUALITY OF SERVICE ISSUES

• SPEECH QUALITY (Toll quality)
• GRADE OF SERVICE (Probability of blocking and
  delay)
• POST DIAL DELAY
• CALL COMPLETION RATIO

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DEPLOYMENT OF VOIP IN A LONG DISTANCE NETWORK
1
2
Signaling Gateway (SG)
Signaling Gateway (SG)
Media Gateway (MG)
Media Gateway (MG)
VOIP Gateway
VOIP Gateway
3
Local Network
Local Network
Customer Premises Equipment
Customer Premises Equipment
VOIP NETWORK
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 DELAY BUDGET OF A VOIP NETWORK
VoIP Gateway
VoIP Gateway
A
Fixed Delays
B
B
C
Variable Delays
F
E
E
D
Variable Delays D Network Routing E-Queuing in
jitter buffer F- Network transmission
Total Fixed Delay 100 to 150 ms Total Variable
Delay -50 to 500ms or more Total Delay -150 to
650ms or more
Fixed Delays A- Compression B- Processing for
echo cancellation. C- Decompression
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END TO END DELAY IN VOIP
OFC/ Satellite (Transmission Network)
VOIP Gateway Codec Buffer Router
VOIP Gateway Router Buffer Codec
Local PSTN Link
Local PSTN Link
Long distance Transmission Link
60 to 400ms
20 to 50ms
20 to 50ms
25 ms
25ms
150 to 650 ms
End-to-End Delay
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PSTN versus VOIP
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NETWORK TRAFFIC MANAGEMENT SYSTEM FOR PSTN-
OUTLINE

• Automatic traffic measurement programmes to
  measure occupancy of critical internal resources.
• Critical alarms collected every 30 seconds and
  occupancy data collected every 5 minutes and sent
  to centralized NTM system.
• Congested nodes and links in the network
  displayed.
• An automated or manual system identifies the
  congested segment of the network.
• Traffic management controls applied to reroute
  traffic, through less congested segments of the
  network.

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NETWORK TRAFFIC MANAGEMENT SYSTEM FOR PSTN-
FUNCTIONING (contd..)

• Examples of network traffic management systems -
• NEMOS USA
• Netminder India
• NEXIS- Australia/ India

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PROVIDING QOS GUARANTEE FOR REAL-TIME TRAFFIC
OVER IP

• Various protocols related to guaranteeing QOS for
  real-time transmission of Voice over IP are-
• Integrated services /RSVP
• Differentiated Services (Diff Serv)
• Multi Protocol Label Switching (MPLS)
• Real-time Transport Protocol (RTP)

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MULTI PROTOCOL LABEL SWITCHING (MPLS)
Edge Router
Edge Router

• It is a traffic engineering protocol.
• MPLS works by the edge routers applying a simple
  Label to each packet.
• This Label contains all the information needed
  to route the packet, thereby removing the need
  for every router in the network to look through
  each packets header.
• It generates priority assigned packets and
  establishes Permanent Virtual Circuits (PVC)
  during the session (as in ATM).

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MULTI PROTOCOL LABEL SWITCHING (CONTD)
(Label Edge Router)
(Label Switched Router)
LSR

• Integrates layer 2 (Data Link) and layer 3 (IP)
  protocols by creating a Tunnel.
• Performs flow aggregation for unified flow to
  same destination.
• MPLS label is attached by Forward Equivalence
  Class (FEC) according to the priorities and class
  of service.
• The MPLS enabled traffic is forwarded over a
  Label switched path.
• MPLS enables IP-VPN and Managed services over
  multi-services network

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QOS MEASUREMENT - PRINCIPLES

• If you cannot measure- you cannot control.
• If you cannot control- you cannot improve.
• Measure the measurable.
• Measure quantitatively.
• Measure non-intrusively.
• Correlate objective measurements with the users
  
• perception (subjective).

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ITU StandardsITU issued following
recommendations for voice quality measurement.
1. Subjective Method Mean Opinion Score (MOS)
- P.800 2.Objective Method Perceptual Speech
Quality Measurement (PSQM) - P.8613. E-model
(R-Value)- G.107 (non-intrusive)British
Telecom DesignBritish Telecom has designed an
intrusive listening speech quality assessment
tool known as Perceptual Analysis Measurement
System(PAMS)
MONITORING OF QOS
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MEAN OPINION SCORE (MOS)

• MOS is derived from an evaluation of various
  pre-
• selected voice samples over different
  transmission
• media, replayed to a mixed group of men and
  women
• (on a scale of 1 to 5 where 1 is worst and 5
  is excellent).
• The MOS ranges for various speech quality are
  indicated
• below -
• 4-5             Toll Quality3-4            
  Communication Qualitylt3 Synthetic Quality

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PERCEPTUAL SPEECH QUALITY MEASUREMENT (PSQM)

• It is an automated scoring process.
• It generates computer-derived scores to correlate
  
• to MOS scores.
• It was originally designed for circuit switched
• networks.
• It does not take into account important
• parameters like jitter and packet loss which
  are
• very relevant to VOIP.

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PERCEPTUAL ANALYSIS/ MEASUREMENT SYSTEM(PAMS)

• It is an intrusive speech quality assessment tool
  where speech quality is
• computed by injecting a speech like signal at
  one end and analyzing the
• degraded signal at the other end of the
  network.
• Score and Grading in PAMS

• Score

• Grading

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E-MODEL (R-VALUE)
R Users satisfaction MOS 100 4.4 94
Very Satisfied 90 4.3 80
Satisfied 4.0 70 Some Users
Dissatisfied 3.6 60 Many Users
Dissatisfied 3.1 50 Nearly All Users
Dissatisfied 2.6 0 Not Recommended 1.0
G.107
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CONGESTION MANAGEMENT FOR QOS IN VOIP

• It means -
• Controlling Congestion by determining the order
  in which packets are transmitted out to an
  interface based on assigned priorities.
• It entails -
• Creation of queues.
• Assignments of packets to the queues based on
  classification.
• Scheduling of packets in a queue for
  transmission.
• Therefore, in context of VOIP -
• Congestion management is Queue management.
• Congestion management Queuing types -
• First In First Out Queuing (FIFO).
• Weighted Fair Queuing (WFQ).
• Custom Queuing (CQ).
• Priority Queuing (PQ).

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CONCEPTUAL MODEL FOR CONGESTION MANAGEMENT IN A
HYBRID PSTN/ VOIP NETWORK
Delay/ Jitter/ Packet loss
SS7
SS7
IP
IP
VOIP Gateway
VOIP Gateway
Packet sniffing Probe
Packet sniffing Probe
Packet sniffing Probe
Packet monitor
R-Value Analyzer/ PSQM / PAMS
Q 3
Q 3
Congestion management system
Network Traffic Management System
Network Traffic Management System
X
X
QA
Telecom Management Network (TMN)
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CONCLUSION

• It is not possible to deliver PSTN equivalent
  QOS from present generation VOIP networks without
  Congestion Management.
• VOIP networks should employ Label switching
  techniques at the second layer (data link layer)
  of OSI model.
• It is possible to specify QOS requirement for a
  VOIP network and to monitor it.
• Non-Intrusive tools for QOS measurements should
  be an integral part of network management system
  for VOIP.

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REFERENCES

• Expert System Applications to Telecommunications
  by Jay Liebowitz
• BROADBAND Business Services, Technologies and
  Strategic Impact
• by David Wright.
• Hand Book of Local Area Networks 1999 by John
  P.Slone
• Computer Networks Architecture, Protocols and
  Software by John Y. Hsu
• ATM Networks. Concepts and Protocols by Sumit
  Kasera and Pankaj Sethi.
• Unified IP Internet Working by Dhiman d.
  Chowdhury.
•        Paper presented by Mr. Jeffrey Johnson,
  Senior Consultatnt, BTexact Technologies at the
  European VoIP Congress held in Madrid
• October 2001.
• Consultation Paper released by TRAI in
  connection with opening of the Internet
  Telephony Market in India Dec2001.

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Thank You
S.N.GUPTA E-Mail trai09_at_bol.net.in