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IP Telephony

IP Telephony. Voice-Data Convergence. What is IP Telephony?. Transmit telephone conversations in IP packets sent over the Internet or another network, such as Ethernet, Frame Relay, or ATM carrying IP packets. IP Packet. IP Telephony. Digitize the outgoing voice signal

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IP Telephony

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  1. IP Telephony Voice-Data Convergence

  2. What is IP Telephony? • Transmit telephone conversations in IP packets sent over the Internet or another network, such as Ethernet, Frame Relay, or ATM carrying IP packets IP Packet

  3. IP Telephony • Digitize the outgoing voice signal • Packetize (place in packets) and send over IP packet-switched networks • Reverse at other end Packetize Digitize

  4. Why IP Telephony? Digitize 64 kbps • Save Money • Digitizing Voice More Efficiently • Current telephone system also digitizes voice for internal digital communication within the telephone network • Current telephone system generates a stream of 64 kbps, then steals 8 kbps for signaling, leaving 56 kbps • This is a lot of bits to move per second on expensive long-distance and international lines

  5. Why IP Telephony? • Save Money • Digitizing Voice More Efficiently • With newer technology, IP telephony digitizes voice to between 12 kbps and 16 kbps with good quality • Fewer bits to send means lower transmission cost 12 kbps- 16 kbps Digitize

  6. Why IP Telephony? Packetize • Save Money • Packet-Switched Network Delivery • Traditional telephony is circuit-switched • Charged for 56 kbps channels whether use them or not • Packet switching multiplexes transmissions • Only pay for capacity actually used

  7. Why IP Telephony? • Save Money • Voice-Data Convergence • Corporations now have separate networks for voice and data • This is expensive in terms of staffing labor and technical charges • Voice-data convergence: use one network (IP) for both • Reduces staff and technical costs

  8. Why IP Telephony? • Save Money: Recap • Efficient digitization to send less than 8 kbps • Multiplexing on packet-switched networks Internet connection is already in place • Voice-data convergence reduces staff, other costs

  9. Problem of Latency • Packet-Switched Networks Often Have Latency (Delay) • Latency is Bad for Voice Conversations • At latency of 200 milliseconds (ms), conversation is difficult because of turn-taking awkwardness • At latency of 500 ms, conversation is impossible • Variable latency from one packet to the next makes voice sound jittery (jitter)

  10. Reducing Latency • Problem is the Internet Backbone • Often has high latency • ISPs Have Lower Latency Internally • May offer service level agreements (SLAs) for latency Internet Backbone Site ISP ISP Site Usually Low Latency Often High Latency

  11. Reducing Latency • Solution • Connect all corporate sites to a single ISP • Possible because some ISPs have access points in many places around the country or even around the world Single ISP Site Site SLA for Low Latency

  12. Reducing Latency • Solution • Connect all corporate sites to a single packet-switched PSDN • Packet-switched PSDNs also have low latency, SLAs PSDN Site Site SLA for Low Latency

  13. Evolution of IP Telephony • Initially, Only Use Between Sites • Sites already have PBXs (Private Branch Exchanges) to handle internal site telephony • Add IP telephony modules to PBXs • Communicate over the Internet in IP • Use traditional telephony within sites • Saves on long-distance, which is expensive Site Site

  14. Evolution of IP Telephony • Initially, Only Use Between Sites • No need to change system within sites • Such changes would be expensive and would not reduce long-distance and international calling charges • Little agreement about what technology to use in internal telephone systems Site Site

  15. Evolution of IP Telephony • Eventually, Service to the Desktop • Combine with data service to the desktop • Computer-Telephony Integration (CTI) applications • When caller calls in, automatically linked with relevant data • To improve applications, not necessarily to save money • Problem: technology is not readily available or standardized

  16. IP Telephony Standards • Based on H.323 Videoconferencing Standard from ITU-T • For videoconferencing over the Internet or other IP networks • IETF, ITU-T have agreed to work together on IP telephony standards

  17. Questions about IP Telephony • Will it Really Save Money? • Was very promising when long-distance and international costs were very high • But these costs are falling rapidly and will continue to do so • Will it save enough money to be worthwhile? • Will it be Sufficiently Reliable? • Ordinary telephony is super reliable • Can IP telephony offer sufficient reliability?

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