IP Telephony

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IP Telephony

• Voice-Data Convergence

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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
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IP Telephony

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

Digitize
Packetize
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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

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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
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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

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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

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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

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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)

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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
Often High Latency
Usually Low Latency
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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
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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
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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
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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
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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

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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

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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?