Internet Telephony

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Internet Telephony
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IP Telephony

• Internet telephony refers to communications
  servicesvoice, facsimile, and/or voice-messaging
  applicationsthat are transported via the
  Internet, in real time rather than the public
  switched telephone network (PSTN).

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Voice Based Applications

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

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Phone-To-Phone Connection
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PC-To-Phone Topology
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IP Telephony Components

• Gateway
• Bridge between Internet and PSTN
• Gatekeeper
• Billing
• Directory services
• Authentication
• Bandwidth Control

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PC-To-Phone Connection
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Components

• Endpoints (Terminals)
• Miltipoint Control Units (MCUs)

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H.323 Protocol Stack
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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)

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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

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Protocols

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

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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

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Protocols

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

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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

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Obstacles

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

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Technical Barriers

• Reliability
• Sound Quality (Limited Bandwidth)
• Packet-switched connectionless network

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Potential Problems

• Gateway Connection Ability (TEST!!!)
• Must retain human voice characteristics
• Latency (gt 250ms)
• Jitter
• dropped packets (gt 3)
• Passing of DTMF tones

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Any Questions???