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Introduction

Introduction

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Introduction

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  1. Introduction Chapter 1

  2. Instructor • Ming-Feng Chang, mfchang@csie.nctu.edu.tw • 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%

  3. Telephone • 1876 Alexander Graham Bell transfered voice over wire for the first time. • Direct connection; telephones are sold in pair F A E D B C

  4. F A E D B C Switches • As the number of users increases, switching centers are more economical

  5. 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

  6. 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)

  7. The Internet • Data Networks since 1960’s • ARPA*-Net 1969 • Internet since early 1990’s

  8. 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.

  9. VoIP Gateway The interface between VoIP and PSTN • An essential feature for VoIP

  10. Cheap phone-cards/voice carriers

  11. 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

  12. VoIP • 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

  13. IP • 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

  14. 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

  15. 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

  16. 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

  17. Moore’s Law • Processing power doubles every 18 months • Frame 10 • Router 20 • ATM 40 • Circuit 80

  18. 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

  19. 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

  20. 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

  21. The VoIP Market • The revenue projection • Value-added service

  22. Revenue breakdown • VoIP • Fax over IP

  23. 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

  24. 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

  25. 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

  26. 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

  27. VoIP Implementations • IP-based PBX solutions • A single network • Enhanced services

  28. 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

  29. IP user devices • VoIP protocols, SIP • Integrated functions • Telephony, WWW, e-mail, voice mail, address-book • WiFi phone

  30. Skype • 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

  31. 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

  32. 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

  33. 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

  34. 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