Transcript Course Outline

Introduction
Chapter 1
“Carrier Grade Voice over IP.”
D. Collins, 2nd ed., McGraw-Hill, 2003.
Carrier Grade VoIP
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Carrier grade and VoIP
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mutually exclusive
A serious alternative with enhanced features
Carrier grade
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The last time when it fails
99.999%, five-nines reliability
Verizon network supports 70M voice access lines
AT&T serves 300M voice calls a day
Short call setup time, high speech quality
no perceptible echos, noticeable delay or annoying
noises
Self-healing, highly scalable and manageable
Internet Telephony
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VoIP
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Transport voice traffic using IP
Voice over the Internet?
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The greatest challenges
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Interconnected networks
Applications: e-mail, file transfer, e-com
Voice quality and bandwidth
Control and prioritize the access
Internet: best-effort transfer
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The next generation
VoIP != Internet telephony
Internet Telephony
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IP
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A packet-based protocol
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Packet transfer with no guarantees
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Routing on a packet-by-packet base
May not receive in order
May be lost ore severely delayed
TCP/IP
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Retransmission
Assemble the packets in order
Congestion control
Useful for file-transfers and e-mail
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Data and Voice
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Data traffic
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Voice traffic
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Asynchronous – can be delayed
Extremely error sensitive
Synchronous – the stringent delay requirements
More tolerant of errors
IP is not for voice
VoIP must
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Match the PSTN
Offer new and attractive capabilities at a lower
cost
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Why VoIP?
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Why carry voice?
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Internet support instant access to anything
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“Dot-com guy”
Many new services and applications
However, voice services provide more revenues
Why use IP for voice?
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Why try to fix something that is not broken?
Circuit-switching is not for datacom
IP
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Equipment cost, integrated access, less bandwidth, and
widespread availability
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Lower Equipment Cost
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PSTN switch
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Mainframe computer
The IP world
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Proprietary – hardware, OS, applications
High operation and management cost
Training, support and feature development cost
Standard hardware and mass-produced
Application software is quite separate
A horizontal business model
IN
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does not match the openness and flexibility of IP
A few highly successful services
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Moore’s Law
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Processing power doubles every 18 months
Frame
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Router
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ATM
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Circuit
80
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Voice/Data Integration
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Click to talk application
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Web collaboration
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Personal communication
E-commerce
CTI – Computer Telephony Integration
Shop on-line with a fried at another location
Video conferencing
IP-based PBX
IP-based call centers
Internet Telephony
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Lower Bandwidth Requirements
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PSTN
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Sophisticated coders
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32kbps, 16kbps, 8kbps, 6.3kbps, 5.3kbps
GSM – 13kbps
Save more by silence-detection
Traditional telephony networks can use coders too
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G.711 - 64 kbps
Human speech bandwidth < 4K Hz
The Nyquist Theorem: sample rate twice the bandwidth
8K * 8 bits
But it is difficult
So many switches
VoIP – two ends of the call negotiate
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The Widespread Availability of IP
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IP
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LANs and WANs
The ubiquitous presence
VoFR or VoATM
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Only for the backbone of the carriers
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The VoIP Market
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The revenue projection
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Value-added service
Internet Telephony
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Revenue breakdown
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VoIP
Fax over IP
Internet Telephony
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VoIP Challenges
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Speech quality
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Must be as good as PSTN
Delay
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The round-trip delay
International calls through satellite – 500-600 ms
G.114 – < 300 ms
Jitter
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Delay variation
Different routes or queuing times
Adjusting to the jitter is difficult
Jitter buffers add delay
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Packet loss
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Traditional retransmission cannot meet the real-time
requirements
Packets must be played in order
Speech-coding techniques
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MOS, Mean Opinion Score >= 4
P.800, but subjective in nature
G.711
64kbps
4.3
G.726
32kbps
4.0
G.723 (celp) 6.3kbps
3.8
G.728
16kbps
3.9
G.729
8kbps
4.0
GSM
13kbps
3.7
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Network Reliability and Scalability
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PSTN system fails
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Five-nines reliability
The office computer network fails
Today’s VoIP solutions
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Redundancy and load sharing
Scalable too – easy to start small and expand
Fiber-optic transport, gigabit router, high-speed ATM
base
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Managing Access and Prioritizing Traffic
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A single network for a wide range of applications
Call admitted if sufficient resources available
Different types of traffic are handled in different
ways
QoS has required huge efforts
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VoIP Implementations
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IP-based PBX solutions
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A single network
Enhanced services
Internet Telephony
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IP voice mail
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Hosted PBX solutions
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One of the easiest applications
For SOHO
Internet and telephony access
IP call centers
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Use the caller ID
Automatic call distribution
Load the customer’s information on the agent’s
desktop
Click to talk
Internet Telephony
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Internet Telephony
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IP user devices
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VoIP protocols, SIP
Integrated functions
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Telephony, WWW, e-mail, voice mail, address-book
GUI
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Why Internet Telephony?
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The business case
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Integration of voice and data
Bandwidth consolidation
Tariff arbitrage
Universal presence of IP
Maturation of technologies
The shift to data networks
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Configuration Options
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Book Overview
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VoIP and RTP
Voice codecs
H.323
SIP – simple and flexible
MGC and softswitch
SS7
QOS
Design a VoIP network
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