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 • Packetize (place in packets) and send over IP packet-switched networks • Reverse at other end Packetize Digitize
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
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
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
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
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
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)
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
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
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
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
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
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
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
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?
