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Voice Over IP (VoIP). Mayoor Savla Vitaliy Zavesov. 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.

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voice over ip voip

Voice Over IP (VoIP)

Mayoor Savla

Vitaliy Zavesov

what is voip
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).
components of a voip system 1
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
components of the voip system 2
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
technical advantages of voip
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
business advantages of voip
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
quality of voice issues 1
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
quality of voice issues 2
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
packet loss
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
packet delay
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
present day commercial deployment
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
voip gateways
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.
drawbacks of current internet telephony solutions
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
potential future markets for voip
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
issues for voip to be commercialized
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
references
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
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