Voice Over Internet Protocol VoIP

1
Voice Over Internet ProtocolVoIP

• Yan Li
• Arsalan Khalid
• March 14th 2002
• This report was prepared for Professor L.
  Orozco-Barbosa in partial fulfillment of the
  requirements for the courseCEG 4183

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Contents

• Telephony standards
• How the PSTN works
• PSTN Components
• VoIP Network
• VoIP Components
• VoIP Protocols and Standards
• Emerging Technologies
• Business Model for VoIP
• Questions?
• References

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Telephony Standards

• The International Telecommunications Union (ITU)
  plays a major role in standardizing the
  technology of the PSTN.
• The ITU includes a specific division known as the
  Telecommunications Standardization Sector, or
  ITU-T.
• G Transmission systems and media, digital
  systems and networks
• H Audiovisual and multimedia systems
• P Telephone transmission quality, telephone
  installations, local line networks
• The Category letter is followed by a period and a
  number, such as G.711 or H.323. An ITU-T standard
  recommendation is said to be In Force when the
  standard has been approved by ITU-T membership.
• Standards are absolutely crucial to the success
  of technologies like VoIP. Without standards,
  your phone call would very likely be dropped when
  it passed from Vendor As network toVendor Bs
  network. Accordingly, many VoIP vendors have
  drawn on the expertise of the ITU-T and built
  VoIP products based on well-known standards.

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How the PSTN works
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Components of PSTN

• Voice encoding
• Switches
• Private Branch Exchange (PBX)
• Signaling
• Telephones

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VoIP Network

• The caller enters a telephone number, which will
  be mapped to the IP address of the callee.
• 2) Call setup protocols are invoked to locate
  the callee and send a signal to produce a ring.
• 3) The destination phone rings, indicating to
  the callee that a call has arrived.
• 4) The callee picks up the telephone handset and
  begins a two-way conversation. The audio
  transmission is encoded using a codec and travels
  over the IP network using a voice streaming
  protocol.
• 5) The conversation ends, call teardown occurs,
  and billing is performed.

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VoIP Components

• Codecs
• TCP/IP and VoIP Protocols
• IP telephony servers and PBXs
• VoIP gateways and Routers
• IP phones and softphones

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Codecs

• A codec (which stands for compressor/decompressor
  or coder/decoder) is the hardware or software
  that samples analog sound and converts it to
  digital bits, which it outputs at a predetermined
  data rate. The codec often performs compression
  as well, to save bandwidth.There are dozens of
  available codecs, each with its own
  characteristics.

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TCP/IP and VoIP Protocols

• Call Setup
• Voice Streaming

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IP Telephony Servers and PBXs

• An IP PBX typically serves as the core IP
  telephony server. On the PSTN, the PBX is often a
  closed-box systemit provides all the voice
  functions and features you need, but usually in a
  proprietary manner. Management of the closed-box
  platform is left up to the PBX vendor. With VoIP,
  an IP PBX can be built on a PC platform running
  on an operating system like Microsoft Windows,
  Linux, or Sun Solaris.

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VoIP Gateways and Routers
VoIP gateways and IP routers move RTP voice
datagrams through an IP network. VoIP gateways
provide a connection between the VoIP network and
the PSTN.
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IP Phones and Softphones

• Where are the codecs located?
• Older analog telephones, the codecs are located
  in the IP PBX. Incoming calls are digitized
  there, before being forwarded onto the IP
  network.
• Codecs can be located in the telephones
  themselves. These new digital telephones are
  called IP phones.
• Have an Ethernet LAN connection. An IP phone
  makes data connections to an IP telephony server,
  which does the call setup processing.
• Another ChoiceThe PC.

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VoIP Protocols and Standards

• More than One choice
• H.323 ITU standard, implementations
• SIP IETF developed protocol
• MGCP
• Client server, telephony device
• Used in Cable network
• Not really adequate for mobility support
• H.248

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H.323 Protocol Stack

• H.323 Architecture
• terminals,
• gateways,
• gatekeepers
• multipoint control units(MCU)

GATEKEEPERS

• Provide call control services to registered end
  points.
• One gatekeeper can serve multiple LANs
• Admission Control Authorization
• Bandwidth management (Limit number of calls on
  the LAN)
• Zone Management Serve all registered users
  within its zone of control
• May optionally handle Q.931 call control

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SIP Session Initiation Protocol

• Application Layer Protocol
• Overcome H.323s Shortcomings
• Enable VoIP clients, gateways and PBXs to
  communicate
• In Conjunction with RSVP, RTP, RTSP, SAP, SDP
• Low Overhead

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MGCP (Media Gateway Control Protocol)

• Conversion of signals from PSTN to data packets
• Enables media controllers and media gateways to
  communicate
• Master/Slave
• Losing ground to H.248

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H .248

• Successor to MGCP
• Peer to peer interoperability
• Control for IP phones in Master/Slave
• Breaks down H.323 and sets protocols for each
  component
• Leverages existing PSTN

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Emerging TechnologiesVoIP over Wireless (VoIPoW)

• IMT-2000(ITU)
• UMTS
• EDGE (ETSI/3GPP)
• Challenges for VoIPoW
• ________________________________________
• Quality
• Spectrum efficiency

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QoS Role to support VoIP

• Delay variation (jitter)
• Packet Loss
• Excessive Delay
• Different Codec, Different Bandwith Requirements
• Call Provisioning

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Business Model for VoIP

• Cost Savings
• Long Distance Savings
• Single Network Infrastructure Savings
• Productivity Savings
• Management and support savings.
• Maintenance, upgrades, and additions.
• Obstacles
• Capital Investent
• Business Risk
• New Features
• Unified messaging.
• Advanced call routing.
• Integration into business applications.
• Easier to add new features.

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Questions?

• What does VoIP stand for?
• Voice Over Internet Protocol
• VoIP is in which layer?
• Application layer
• How many protocols for VoIP?
• a. 1 b. 2 c. 3 d. 4
• d

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Questions?

• What are the differences between PSTN and VoIP?
• What are the components of VoIP?

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References

• Good TCP/IP primers
• 1. Comer, D. E. Internetworking with TCP/IP Vol.
  I Principles, Protocols, and Architecture.
  Prentice Hall, Englewood Cliffs, NJ, 2000. (ISBN
  0-13-018380-6).
• 2. Stevens, W. R. TCP/IP Illustrated, Volume 1.
  Addison-Wesley, Reading MA, 1994 (ISBN
  0-201-63346-9).
• 3. Walker II, J. Q. and J. T. Hicks. Protocol
  ensures safer multimedia delivery, Network
  World, volume 16, number 44, November 1, 1999,
  page 53.
• Good VoIP overviews
• 1. Davidson, J. and J. Peters. Voice over IP
  Fundamentals. Cisco Press, Indianapolis, IN,
  2000. (ISBN 1-57870-168-6).
• 2. Newton, Harry. Newtons Telecom Dictionary.
  CMP Books, New York, New York, 2001. (ISBN
  1-57820-069-5).
• 3. Checklist of VoIP Network Design Tips, John Q.
  Walker, NetIQ Corporation, April 2001,
  www.netiq.com/products/chr/whitepapers.asp.
• 4. What You Need to Know before You Deploy VoIP,
  Scott Hamilton and Charles Bruno, Tolly Research,
  April 2, 2001, www.netiq.com/products/chr/whitepap
  ers.asp.