VoIP

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VoIP

• EE 548
• Ashish Kapoor

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Characteristics Centralized and Distributed
Control

• H.323 pushes call control functionality to the
  endpoint, while still providing the service
  provider or enterprise with the option to control
  every aspect of a call.
• Endpoints can communicate directly.
• Endpoints can communicate through a server.

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Characteristics - Focused

• H.323 was designed with one clear objective to
  provide users with voice, video, and data
  conferencing capabilities over a packet-switched
  network.
• H.323 does not try to do more than it should and
  does not try to pretend to be something that it
  is not.

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Characteristics - Extensibility

• Fully backward compatible with previous versions.
• Equipment manufactures can extend functionality
  by inserting their own additions to the protocol.

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Characteristics - Integration with Internet
Standards

• The first standards-based protocol to adopt
  RTP/RTCP for multimedia transmission.
• Makes use of existing Internet technologies like
  URLs and DNS.
• Ability to click on URL to place call.
• Capable of performing DNS queries to locate a
  user or service.

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H.323 System and Components
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Components - Terminals

• Client endpoints on the LAN
• Must support voice data and video are optional
• All terminals must support
• H.245 Protocol
• Q.931
• RAS
• RTP/RTCP

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Terminal Side Protocol Stack
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Components Gateways I
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Components Gateways II

• Connects 2 dissimilar networks.
• The Gateway is an optional element in an H.323
  conference
• Establishing links with analog PSTN terminals.
• Establishing links with remote H.320-compliant
  terminals over ISDN-based switched-circuit
  networks.
• Establishing links with remote H.324-compliant
  terminals over PSTN networks

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Gateway Protocol Stack
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Components Gatekeepers I
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Components Gatekeepers II

• Acts as the central point for all calls within
  its zone
• Provides call control services to registered
  endpoints
• Translation from LAN aliases for terminals and
  gateways to IP or IPX addresses
• Bandwidth Control
• Optional Functions
• Call Control Signaling
• Call Authorization
• Bandwidth Management
• Call Management

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Gatekeeper Components
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Components - Multipoint Control Units I
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Components - Multipoint Control Units II

• Consists of
• Multipoint Controller (MC) - required.
• The MC handles H.245 negotiations between all
  terminals to determine common capabilities for
  audio and video processing.
• The MC also controls conference resources by
  determining which, if any, of the audio and video
  streams will be multicast.
• Zero or more Multipoint Processors (MPs)
• Mixes, switches, and processes audio, video,
  and/or data bits

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Components - Multipoint Control Units III
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H.225 AAAAarrrrrrrgggghhhhhh

• The H.225 RAS is used between H.323 endpoints
  (terminals and gateways) and gatekeepers for the
  following
• Gatekeeper Discovery (GRQ) - Static and Dynamic
• Endpoint Registration - used by the endpoints to
  join a zone and inform the gatekeeper of the
  zone's transport and alias addresses
• Endpoint Location - transport address of an
  endpoint is determined and given its alias name
• Admission Control
• Access Tokens

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H.225 Call Establishment and Release

• Release

• Establish

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VoIP QoS
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The Problem

• As the voice packets are sent over an IP network,
  they are subject to variable delays and network
  drops.
• An important component at the receiving end, is
  the playback buffer whose purpose is to absorb
  variations in delay and provide a smooth play
  out.
• Decoders often implement Packet Loss Concealment
  (PLC) that produces a replacement for a lost
  packet

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Quality

• Quality is a Function of Latency, Jitter and Loss

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Latency

• Encoding and packing delay at the sender.
• Propagation, transmission and queuing delays in
  the network.
• Buffering and decoding delay at the receiver

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Latency
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Jitters
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Loss
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Mean Opinion Score
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References

• A Primer on the H.323 Series Standard
• http//www.packetizer.com/iptel/h323/papers/primer
  /
• Why H.323?
• http//www.packetizer.com/iptel/h323/why_h323.html
  
• IEC H.323
• http//www.iec.org/online/tutorials/h323/index.htm
  l