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Internet Telephony

Internet Telephony. IP Telephony. Internet telephony refers to communications services—voice, facsimile, and/or voice-messaging applications—that are transported via the Internet, in real time rather than the public switched telephone network (PSTN). . Voice Based Applications.

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Internet Telephony

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  1. Internet Telephony

  2. IP Telephony • Internet telephony refers to communications services—voice, facsimile, and/or voice-messaging applications—that are transported via the Internet, in real time rather than the public switched telephone network (PSTN).

  3. Voice Based Applications • Automated Attendants • Voice Prompting • Voice Messaging • Faxing, Fax Services, Fax Broadcast • UnPBX • Speech Recognition • Text to Speech

  4. Phone-To-Phone Connection

  5. PC-To-Phone Topology

  6. IP Telephony Components • Gateway • Bridge between Internet and PSTN • Gatekeeper • Billing • Directory services • Authentication • Bandwidth Control

  7. PC-To-Phone Connection

  8. Components • Endpoints (Terminals) • Miltipoint Control Units (MCUs)

  9. H.323 Protocol Stack

  10. H.323 Standard • H.323 Specification • Real-time Transport Control Protocol (RTCP) • Session Layer (Monitors quality) • Real-time Transport Protocol (RTP) • Transport Layer (error control) • Resource Reservation Protocol (RSVP) • Network Layer (Reserves network bandwidth and assigns priority to traffic)

  11. What is a Codec? • A driver that converts from one format to another by compressing or uncompressing data. • Audio • G.711, G.722, G.723 • Video • MPEG-4, Vivo H.263

  12. Protocols • H.225 - call control protocol • Defines packet standards • Q.931 - digital subscriber signaling • Call signals at Network layer

  13. Protocols • H.245 - media control protocol • Provides end-to-end signaling for multimedia operation and signaling. • Determines Master and Slave • T.120 - Real time data conferencing protocol

  14. Protocols • H.235 – security • Authentication • Privacy (data encryption) • Key Exchange (RSA)

  15. Advantages • Packet switched which allows all of the bandwidth to be used. Circuit switched results in gaps. • Usage cost by bypassing PTSN • Ability to merge real-time voice into other Internet applications

  16. Obstacles • Setup Cost • Greater Adherence to Standards • Ease of Administration • Greater Public Awareness

  17. Technical Barriers • Reliability • Sound Quality (Limited Bandwidth) • Packet-switched connectionless network

  18. Potential Problems • Gateway Connection Ability (TEST!!!) • Must retain human voice characteristics • Latency (> 250ms) • Jitter • dropped packets (> 3%) • Passing of DTMF tones

  19. Any Questions???

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