Voice over IP (VoIP)
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Voice over IP (VoIP)






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Voice over IP (VoIP) Presentation Transcript

  • 1. Voice Over IP (VoIP) Mayoor Savla Vitaliy Zavesov
  • 2. What is VoIP?
    • VoIP is a term used in IP telephony to describe a set of facilities for managing the delivery of voice information using the Internet Protocol.
      • This means sending voice information in digital form in discrete packets rather than in the circuit committed protocols of the Public Switched Telephone Network (PSTN).
  • 3. Components of a VoIP System (1)
    • Speech is an analog signal that is converted to a digital signal at the sender using encoding schemes such as PCM.
      • Signal alternates between talkspurts and silence periods
      • CELP based encoders provider rate reduction
    • Encoded Speech is packetized into packets of equal size
  • 4. Components of the VoIP System (2)
    • Packets are sent over an IP network using a UDP Protocol
      • TCP is usually too heavy for voice applications
    • A playout buffer is used to smooth playout at the receiver
    • Content of received voice packets is delivered to the decoder which reconstructs the speech signal
      • May implement various packet loss concealment techniques to replace lost packets
  • 5. Technical Advantages of VoIP
    • With circuit-switched technology, capacity is allocated for the length of the call, regardless if voice is being transported at any time. VoIP technology uses bandwidth more efficiently
    • VoIP is perceived to be open and flexible, allowing providers to take advantage of equipment and technology at a higher level of productivity and cost savings
    • Offer customers exciting new phone features
      • Unified Messaging
      • Personal Portals
      • Caller ID on TV set
      • Point, Click and call personal directories
      • Talking email
    • Need a single line to talk on the phone and surf the Internet at the same time
  • 6. Business Advantages of VoIP
    • Cost Reduction: There can be a real savings in long distance telephone costs which is extremely important to most companies – especially those with International markets
    • Regionalize functions and equipment associated with delivering phone service – and spread costs across multiple markets
    • Simplification: Integrated Voice/Data Network allows more standardization and reduces total equipment needs.
      • Telecom providers can look to leverage their experience and infrastructure (i.e., existing nationwide backbone network)
    • Consolidation: Consolidation of accounting systems and combining operations leads to efficiency
    • Expand phone services into new markets (developing nations – Asia, Latin America)
      • No existing telephone/cable network and Costs are too high
      • VoIP Over Satellite - Use of VSATs
  • 7. Quality of Voice Issues(1)
    • Transmission of voice packets over a network is subject to packet loss due to network elements - causing degradation in voice quality at the receiver
      • Additional loss is incurred in the playout buffer at the receiver caused by network delay jitter
    • Interactivity between the communicating parties is affected by the delays incurred in the network
      • Large delay may lead to collisions whereby participants can talk in turns
      • Should be maintained below a certain maximum – NTE 150ms – possibly shorter for conversations with stringent interactivity delays
      • No control over how the packets are routed to reach their destination
  • 8. Quality of Voice Issues (2)
    • Voice Encoding affects the Quality of Speech
    • Presence of echo - a major source of quality degradation in voice communication
      • Reflection of signals at the four to two wire hybrids (combination of VoIP segment and a circuit segment)
      • PC-based phones – microphone at remote end picks up the voice played on the loud-speakers and echoes it back to the speaker
  • 9. Packet Loss
    • Loss Concealment Techniques
      • Insert Silence, Noise or a previously received packet
      • Interpolate, regenerate based on structure of codec and exploit decoder state
    • <5 consecutive packets
      • Increase in background noise as long as percentage of speech loss remains relatively low
      • Use of loss concealment techniques to mitigate packet loss
    • > ~20 consecutive packets
      • Cannot be concealed due to loss of intelligibility
      • Improve Network Reliability and decrease network configuration time when failures occur
  • 10. Packet Delay
    • Delay variations (Jitter)
      • Use of a playout buffer at the receiver to achieve a smooth playback of speech
      • Fixed Scheduling of packet playback – constant end-to end delay on all packets.
        • packets exceeding target delay are dropped
      • Adaptive Scheduling of packet playback – delay constant within a talkspurt but varies from one talkspurt to another.
    • Schemes are ineffective as it is impossible to have an apriori determination of variation in delay
      • Pattern of packet loss
      • Magnitude of delay variations
      • Rate at which variations take place
  • 11. Present Day Commercial Deployment
    • Presently used in Intranets to support full-duplex, real-time voice communications since they have more predictable bandwidth available than public network
    • Corporations limit their Internet voice traffic to half-duplex asynchronous applications such as voice messaging
    • Enterprise positions a VoIP device at a gateway
  • 12. VoIP Gateways
    • A gateway converts telephone conversation into the correct format as data packets to enable it to travel across a data network.
    • Gateways can be used with standard phone and fax equipment, connected to it through a PBX (Private Branch Exchange - private telephone switchboard)
    • Gateways contain such devices as signal translators, protocol translators, fault isolators, and other devices needed to implement VoIP communication.
    • Current gateway implementations include cable, DSL, wireless, and satellite (VSAT) gateways.
  • 13. Drawbacks of Current Internet Telephony Solutions
    • Voice Transmission are treated the same as data transmissions and providers have little control over the quality of the transmissions once they hit the public Internet
    • Internet Telephony does not offer emergency 911, operator services or QoS guarantees
    • Lack of standardized protocols imply that Internet Telephony products do not interoperate with each other or with PSTN
  • 14. Potential Future Markets for VoIP
    • Equipment developers and manufacturers see a window of opportunity to innovate and compete. They are busy developing new VoIP-enabled equipment attempting to break into the market in time.
      • 3Com NBX Solutions
      • Cisco Unity Bridge
      • Avaya ECLIPSE product suite
      • SysMaster VoiceMaster products
      • Alloptic GEAR family of products
    • Internet service providers see the possibility of competing with PSTN for customers
    • Users are interested in the integration of voice and data applications in addition to cost savings
  • 15. Issues for VoIP to be commercialized
    • Technology is not fully developed to the point where it can replace the services and quality provided by PSTN
    • Must be clear that VoIP is indeed cost-effective.
      • Protect its investment in circuit switched telecom operations since VoIP would be complementary to its existing technology
      • Significant costs to setup networks and other pieces of transport architecture
      • There must be significantly lower total cost of operation compared to today’s PSTN
    • Service Providers are awaiting the development of the remaining pieces of technology that will ensue quality transport in the last mile
      • Connection from homes and businesses to the IP back-bone
  • 16. References
    • Assessing the Quality of Voice Communications over Internet Backbones by A. Markopoulou, F. Tobagi, M. Karam
    • Is the Internet ready for VoIP by F. Tobagi, A. Markopoulou, M. Karam
    • Assessment of VoIP Service Availability in the Current Internet by W. Jiang and H. Schulzrinne
    • Whitepaper: Preparing for the Promise of Voice-over Internet Protocol (VoIP) – Cox Communications
    • http://www.nwfusion.com/research/voip.html