Voice Over IP (VoIP)

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Voice Over IP (VoIP)

• Mayoor Savla
• Vitaliy Zavesov

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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).

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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

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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

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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

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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

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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

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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

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Packet Loss

• Loss Concealment Techniques
• Insert Silence, Noise or a previously received
  packet
• Interpolate, regenerate based on structure of
  codec and exploit decoder state
• lt5 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
• gt 20 consecutive packets
• Cannot be concealed due to loss of
  intelligibility
• Improve Network Reliability and decrease network
  configuration time when failures occur

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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

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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

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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.

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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

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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

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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 todays 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

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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