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Voice Over IP (VoIP)

Assessing the quality of voice communications over internet backbones by a. ... for the promise of voice-over internet protocol (voip) cox communications ... – powerpoint ppt presentation.

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

Jan 04, 2020

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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) 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. • 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) • 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) • 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 • 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 • 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) • 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) • 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 • 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 • 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 • 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 • 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 • 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 • 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 • 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 • 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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