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Introduction Chapter 1 Instructor Ming-Feng Chang, EC 425, 5731812 Textbook “ Carrier Grade Voice over IP. ” D. Collins, 2nd ed., McGraw-Hill, 2003. Additional technique reports and papers Requirements Homework and machine problems 25% One mid-term exam 45%

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Chapter 1

    • Ming-Feng Chang,
    • EC 425, 5731812
  • Textbook
    • “Carrier Grade Voice over IP.” D. Collins, 2nd ed., McGraw-Hill, 2003.
    • Additional technique reports and papers
  • Requirements
    • Homework and machine problems 25%
    • One mid-term exam 45%
    • One term project 30%
  • 1876 Alexander Graham Bell transfered voice over wire for the first time.
  • Direct connection; telephones are sold in pair














  • As the number of users increases, switching centers are more economical
digital switches
Digital Switches
  • Took more than 100 years from analog to digital voice transmission
    • Better quality for long distance calls
  • Demands to telephone network become constantly higher
    • World-wide communication network
the telephone network

SS7 Signaling

ISUP Messages

INAP/TCAP Messages

The Telephone Network











Control Layer



Transport Layer

Class 4

Tandem Switch

Class 5

End Office Switch

Circuit Switched Network

mobile communications
Mobile Communications
  • 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)
the internet
The Internet
  • Data Networks since 1960’s
    • ARPA*-Net 1969
    • Internet since early 1990’s
what is voip
What is VoIP?
  • Use a LAN and/or WAN to carry voice in the same way as the telephone system.
  • Why?
    • Save costs
    • Improve facilities.
voip gateway
VoIP Gateway

The interface between VoIP and PSTN

  • An essential feature for VoIP
critical thinking
Critical Thinking

The critical habit of thought, if usual in society, will pervade all its mores, because it is a way of taking up the problems of life. Men educated in it cannot be stampeded by stump orators ... They are slow to believe. They can hold things as possible or probable in all degrees, without certainty and without pain. They can wait for evidence and weigh evidence, uninfluenced by the emphasis or confidence with which assertions are made on one side or the other. They can resist appeals to their dearest prejudices and all kinds of cajolery. Education in the critical faculty is the only education of which it can be truly said that it makes good citizens.

William Graham Sumner, Folkways, 1906

carrier grade voip
Carrier Grade VoIP
  • Carrier grade and VoIP
    • mutually exclusive
    • A serious alternative with enhanced features
  • Carrier grade
    • 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
  • Transport voice traffic using IP
  • Voice over the Internet?
    • Interconnected networks
    • Applications: e-mail, file transfer, e-com
  • The greatest challenges
    • Voice quality and bandwidth
    • Control and prioritize the access
  • Internet: best-effort transfer
    • The next generation
    • VoIP != Internet telephony
  • A packet-based protocol
    • Routing on a packet-by-packet base
  • Packet transfer with no guarantees
    • May not receive in order
    • May be lost ore severely delayed
  • TCP/IP
    • Retransmission
    • Assemble the packets in order
    • Congestion control
    • Useful for file-transfers and e-mail
data and voice
Data and Voice
  • Data traffic
    • Asynchronous – can be delayed
    • Extremely error sensitive
  • Voice traffic
    • Synchronous – the stringent delay requirements
    • More tolerant of errors
  • IP is not for voice
  • VoIP must
    • Match the PSTN
    • Offer new and attractive capabilities at a lower cost
why voip
Why VoIP?
  • Why carry voice?
    • Internet support instant access to anything
      • 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?
    • Why try to fix something that is not broken?
    • Circuit-switching is not for datacom
    • IP
      • Equipment cost, integrated access, less bandwidth, and widespread availability
lower equipment cost
Lower Equipment Cost
  • PSTN switch
    • Proprietary – hardware, OS, applications
    • High operation and management cost
    • Training, support and feature development cost
  • Mainframe computer
  • The IP world
    • Standard hardware and mass-produced
    • Application software is quite separate
    • A horizontal business model
  • IN
    • does not match the openness and flexibility of IP
    • A few highly successful services
Moore’s Law
    • Processing power doubles every 18 months
    • Frame 10
    • Router 20
    • ATM 40
    • Circuit 80
voice data integration
Voice/Data Integration
  • Click to talk application
    • Personal communication
    • E-commerce
    • CTI – Computer Telephony Integration
  • Web collaboration
    • Shop on-line with a fried at another location
  • Video conferencing
  • IP-based PBX
  • IP-based call centers
lower bandwidth requirements
Lower Bandwidth Requirements
  • PSTN
    • G.711 - 64 kbps
    • Human speech bandwidth < 4K Hz
    • The Nyquist Theorem: sample rate twice the bandwidth
    • 8K * 8 bits
  • Sophisticated coders
    • 32kbps, 16kbps, 8kbps, 6.3kbps, 5.3kbps
    • GSM – 13kbps
    • Save more by silence-detection
  • Traditional telephony networks can use coders too
    • But it is difficult
    • So many switches
  • VoIP – two ends of the call negotiate the codec
the widespread availability of ip
The Widespread Availability of IP
  • IP
    • LANs and WANs
    • The ubiquitous presence
  • VoFR or VoATM
    • Only for the backbone of the carriers
  • Voice over WLAN
    • Voice over WiFi for now
    • Voice over WiMax could be a real threat for PLMN
the voip market
The VoIP Market
  • The revenue projection
    • Value-added service
Revenue breakdown
    • VoIP
    • Fax over IP
voip challenges
VoIP Challenges
  • Speech quality
    • Must be as good as PSTN
    • Delay
      • The round-trip delay
      • International calls through satellite – 500-600 ms
      • G.114 – < 300 ms
    • Jitter
      • Delay variation
      • Different routes or queuing times
      • Adjusting to the jitter is difficult
      • Jitter buffers add delay
Packet loss
    • Traditional retransmission cannot meet the real-time requirements
    • Packets must be played in order
  • Speech-coding techniques
    • 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
network reliability and scalability
Network Reliability and Scalability
  • PSTN system fails
    • Five-nines reliability
  • The office computer network fails
  • Today’s VoIP solutions
    • Redundancy and load sharing
    • Scalable too – easy to start small and expand
    • Fiber-optic transport, gigabit router, high-speed ATM base
managing access and prioritizing traffic
Managing Access and Prioritizing Traffic
  • 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
voip implementations
VoIP Implementations
  • IP-based PBX solutions
    • A single network
    • Enhanced services
IP voice mail
    • One of the easiest applications
  • Hosted PBX solutions
    • For SOHO
    • Internet and telephony access
  • IP call centers
    • Use the caller ID
    • Automatic call distribution
    • Load the customer’s information on the agent’s desktop
    • Click to talk
IP user devices
    • VoIP protocols, SIP
    • Integrated functions
      • Telephony, WWW, e-mail, voice mail, address-book
    • WiFi phone
    • A peer-to-peer VoIP client developed by KaZaa in 2003
    • Skype can
      • 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
new applications
New applications
  • The networks are converging
  • Possible applications
    • 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
homework 1
Homework #1

Skype has released APIs for Skype developers. (

1. Give a brief description (less than one page) on the functions the APIs.

2. Look on the web and list a number of interesting applications based on Skype API.

3. What other useful applications can be developed?

why internet telephony
Why Internet Telephony?
  • The business case
    • Integration of voice and data
    • Bandwidth consolidation
    • Tariff arbitrage
  • Universal presence of IP
  • Maturation of technologies
  • The shift to data networks
voip spectrum
VoIP Spectrum
  • Traditional Telecomm Segments in transition to VoIP
    • International Low cost calling
    • Internal networks of large carriers
    • Numerous equipment makers, software providers
    • Residential VoIP phone service
      • This area is exploding: Vonage, Packet8, Broadvoice …
    • Office PBX systems
      • Using VoIP inside a company location, and between corporate branches
    • Call Center
  • Instant Messaging
    • Not only the traditional big 3, but newcomers like Skype …
  • Consumer and Business Application Areas
    • Voice applications
    • Wireless Internet applications
course overview
Course Overview
  • 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