Introduction
Chapter 1
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Instructor
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Textbook
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Ming-Feng Chang, mfchang@csie.nctu.edu.tw
EC 425, 5731812
“Carrier Grade Voice over IP.” D. Collins, 2nd ed.,
McGraw-Hill, 2003.
Additional technique reports and papers
Requirements
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Homework and machine problems
One mid-term exam
One term project
25%
45%
30%
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Telephone
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1876 Alexander Graham Bell transfered voice over
wire for the first time.
Direct connection; telephones are sold in pair
F
A
E
B
D
C
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Switches
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As the number of users increases, switching centers
are more economical
F
A
E
B
D
C
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Digital Switches
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Took more than 100 years from
analog to digital voice transmission
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Better quality for long distance calls
Demands to telephone network
become constantly higher
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World-wide communication network
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Mobile Communications
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Bell Laboratories
introduced the idea of
cellular communications
in 1947
Motorola and Bell Labs
in the 60s and early 70s
were in a race to design
portable devices
Dr. Cooper, 2-pound
Motorola handset (1973)
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The Internet
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Data Networks since 1960’s
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ARPA*-Net 1969
Internet since early 1990’s
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What is VoIP?
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Use a LAN and/or WAN to carry voice in the
same way as the telephone system.
Why?
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Save costs
Improve facilities.
IP WAN/
INTERNET
VoIP
VoIP
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VoIP Gateway
The interface between VoIP and PSTN
PSTN to IP
Gateway
Internet
VoIP
POTS
•An essential feature for VoIP
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Cheap phone-cards/voice carriers
POTS
POTS
PSTN to IP
Gateway
IP Network
PSTN to IP
Gateway
(with QoS for voice)
e.g. UK
e.g.
Australia
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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
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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
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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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Everything can be done on the net? “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
10
Router
20
ATM
40
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
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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 the codec
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The Widespread Availability of IP
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IP
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VoFR or VoATM
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LANs and WANs
The ubiquitous presence
Only for the backbone of the carriers
Voice over WLAN
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Voice over WiFi for now
Voice over WiMax could be a real threat for PLMN
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The VoIP Market
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The revenue projection
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Value-added service
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Revenue breakdown
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VoIP
Fax over IP
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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
iLBC
13.33/15.2kbps high robustness to packet loss
iSAC
10-32kbps
wideband codec
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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
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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
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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
WiFi phone
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Skype
 A peer-to-peer VoIP client developed by
KaZaa in 2003
 Skype can
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work almost seamlessly across NATs and firewalls
has better voice quality than the MSN and Yahoo IM
applications
encrypts calls end-to-end, and stores user information in a
decentralized fashion
SkypeOut, SkypeIn
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New applications
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The networks are converging
Possible applications
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Video Phones
Conferencing
Collaboration Tools
Distance Learning / Training
Tele-medicine, tele-repair, tele-…
On-line gaming
Dating Applications
Skype is rolling out developer kits and programs to
encourage innovation, similar to the wireless industry
promoting application development on their platforms
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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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VoIP Spectrum
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Traditional Telecomm Segments in transition to VoIP
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International Low cost calling
Internal networks of large carriers
Numerous equipment makers, software providers
Residential VoIP phone service
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Office PBX systems
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Using VoIP inside a company location, and between corporate branches
Call Center
Instant Messaging
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This area is exploding: Vonage, Packet8, Broadvoice …
Not only the traditional big 3, but newcomers like Skype …
Consumer and Business Application Areas
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Voice applications
Wireless Internet applications
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Course Overview
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VoIP and RTP
Voice codecs
H.323
SIP – simple and flexible
MGC and softswitch
SS7, UMTS
QOS
Voice over WLAN
P2P IP communications
Charging and payments
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