Packet Voice Protocols and VoIP

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Packet Voice Protocols and VoIP

• Fall 2002 Computer Networking
• Seyed Ali Ahmadi

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VoIP Technology

• Identify the different generations of VoIP
• Explain the basic operations of a VoIP Gateway
• Describe an ITSP business case
• How gateway architecture affects service providers

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VoIP technology

• Recent Evolution of packet voice and VoIP
• VoIP technology
• VoIP evolution scenarios

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1- Recent Evolutions in VoIP

• Describe existing voice over data architectures
  and name their predecessors
• How an ITSP work ?
• Characteristics of an Internet call
• Advantages and Disadvantages of ITSP

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VoFR and VoATM Are Similar to VoIP

• Voice is sent as packets intermingled with other
  traffic types
• Voice may be compressed for efficiency
• Delay and Delay variation are issues
• Priority for voice traffic is required for best
  performance

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VoIP Generations

• PC-to-PC
• PC-to-Phone
• Phone-to-Phone
• Traditional PBX migration to VoIP
• IP PBX

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ISTP Technology

• Different Types of IP calls
• How ITSP deploy gateways

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Generic Gateway
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Dedicated Infrastructure for ITSP

• Eliminate dependence on performance of the
  Internet
• Carries strictly voice traffic or Prioritize
  voice over data
• Offers cheap long distance as initial service
• Positioned as enhanced service provider from
  regulatory point of view

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• Place gateways in countries with high
  international tariffs or high calling volumes.
• These Gateways support standard end user business
  interfaces to PSTN
• T1
• E1
• Analog
• ISDN

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Regulatory Status

• Most of the world has taken a hands-off position
  in regulating the enhanced service providers
• In genera ITSPs have mostly positioned them as
  ISPs
• As a result, ITSPs typically do not pay carrier
  fees such as connection, access or settlement
  fees
• IP telephony is regulated in some countries and
  illegal in some others.

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2- VoIP Protocols and Technology
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• A little on history
• Communication pattern shift from PSTN to VoIP
• Why VoIP?
• Cost saving
• Open standards and Multivendor interoperability
• Integrated voice and Data network

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VoIP Protocols

• H.323
• Media Gateway Control Protocol (MGCP)
• Session Initiation Protocol (SIP)
• H.248Media Gateway Control (MEGACO)

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Great Voice Myth

• In order to have a reliable and robust Voice
  network, there should be one and only one
  protocol for each function in packet switch
  network.
• This is not how we are actually doing it now!!
• The VoIP networks of today and tomorrow will be
  constructed using the protocols and applications
  that best fit the associated technology and
  business requirements.

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Protocol Terminology

• ITU International Telecommunication Union
• IETF Internet Engineering Task Force

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Protocol Terminology

• H.248 Gateway Control Protocol
• Collaboration between ITU IETF
• Also referred to as IETF RFC 2885 (MEGACO)

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Protocol Terminology

• H.323
• ITU recommends for Packet based Multimedia
  communication systems.
• Most common VoIP protocol
• Distributed Architecture

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Protocol Terminology

• SIP Session Initiation Protocol
• IETF RFC 2543
• Distributed Architecture
• Real-time Transport Protocol RTP
• A transport protocol for real-time application
• IETF RFC 1889
• Provides transport for audio/media of VoIP
  communication
• Used by All of VoIP signaling protocols

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Protocol Terminology

• MGCP Media Gateway Control Protocol
• IETF RFC 2075
• Centralized Architecture for Multimedia
  applications such as VoIP

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Distributed vs. Centralized
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Centralized Architecture

• Mostly used in older networks
• Worked well for basic telephony services
• Trade off between easy management and endpoint
  innovation
• Associated with MGCP and H.248
• Intelligence focused in centralized Gateway unit
  (media agent)
• Endpoints are relatively or completely dumb.

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Centralized ArchitecturePros Cons

• Centralizes management, provisioning and call
  control
• Simplifies call flow for legacy voice features
• Stifles innovation of endpoint features
• Limitations in building VoIP networks beyond
  legacy voice features

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Distributed Architecture

• Associated with H.323 and SIP protocol
• Allows Network Intelligence to be distributed
  between endpoints and control devices.
• Intelligence
• Call state
• Calling features
• Calling routines
• any aspect of call handling

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Distributed Architecture Pros Cons

• More flexible
• VoIP is treated like any other distributed IP
  application
• Well understood by engineers who design and run
  IP data networks
• More complex than the Centralized Architecture

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H.323

• Originally designed as a transport protocol for
  MM Apps. in LAN
• Still used for Video Conferencing
• Most widely used VoIP signaling and call control
• Umbrella Protocol
• All aspects of call transmission
• From call establishment to capabilities exchange
  to network resources

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H.323

• Defines
• RAS
• Registration
• Admission
• Status
• H.225 for call set-up
• H.245 for capabilities exchange