Voice Over Internet Protocol (VoIP)

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Voice Over Internet Protocol(VoIP)
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Basic Components of a Telephony Network
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Central Office Switches

• Classes of CO Switches
• Class 5 (C5)
• -End office Switches
• Class 4 (C4)
• -Tandem Switches
• C5s are considered the higher layer switches at
  the core of the switching network.
• C4s are more local switches and closer to the CO.

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Analog-to-Digital Voice Encoding
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Compression Bandwidth Requirements
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Supervisory Signaling
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Basic Call Setup
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What Is a PBX?
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Packetized Telephony Networks
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Packet-Switched Telephony vs. Circuit-Switched
Telephony

• More efficient use of bandwidth and equipment
• Lower transmission costs
• Consolidate network expenses
• Increased revenue from new services
• Service innovation

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Distributed Call Control
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Centralized Call Control
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Packet Telephony Components
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Real-Time vs. Best-Effort Traffic

• Real-time traffic needs guaranteed delay and
  timing.
• IP networks are best-effort with no guarantees of
  delivery, delay, or timing.
• The Solution is end-to-end quality of service
  (QOS).

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T1 Interface

• A US T1 with 1.54MB of bandwidth and 24-channels,
  can handle 23 voice calls at 64kbps each. One of
  the channels is dedicated for Data or T1 control.
• In comparison, a US T3 with 45MB of bandwidth can
  handle 672 voice calls at 64kbps each.

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Todays PSTN
So why cant our current PSTN handle the
emergence of VoiP, video, and data services all
on the same circuits of the original PSTN
network? Because, you cant run a converged
network on what is primarily a network that was
designed for just VOICE. Many US carriers and
private companies have large data buildings just
to ride VOICE traffic over a data network.
Equation? VOICE VIDEO DATA OVER A
DATA NETWORK CONVERGENCE
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Requirements of Voice in an IP Internetwork
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IP Internetwork

• IP is a connectionless protocol
• IP provides multiple paths from source to
  destination

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Packet Loss, Delay, and Jitter

• Packet loss
• Loss of packets severely degrades the voice
  application.
• Delay
• VoIP typically tolerates delays up to 150 ms
  before the quality of the call degrades.
• Jitter
• Instantaneous buffer use causes delay variation
  in the same voice stream.

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Reordering of Packets
c
A
B

• IP assumes packet-ordering problems will occur
• RTP reorders packets into their original form

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Reliability and Availability

• Traditional telephony networks claim 99.999
  uptime.
• Data networks must consider reliability and
  availability requirements when incorporating
  voice.
• Methods to improve reliability and availability
  include
• - Redundant hardware
• - Redundant links
• - UPS Power Systems
• - Proactive network management/monitoring

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Major VoIP Protocols
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VoIP Protocols and the OSI Model