ip telephony
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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
DigitizeDigitize PacketizePacketize
Why IP Telephony?
• 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
DigitizeDigitize 64 kbps
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
DigitizeDigitize12 kbps-16 kbps
Why IP Telephony?
• 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
PacketizePacketize
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
SiteSite ISPISP InternetBackbone
InternetBackbone ISPISP SiteSite
OftenHigh Latency
UsuallyLow 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
SiteSite Single ISPSingle ISP SiteSite
SLA forLow Latency
Reducing Latency
• Solution– Connect all corporate sites to a single packet-
switched PSDN– Packet-switched PSDNs also have low latency,
SLAs
SiteSite PSDNPSDN SiteSite
SLA forLow 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
SiteSite SiteSite
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
SiteSite SiteSite
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?