Download Voice Over IP - Computer Science and Engineering

Voice Over IP
Presented By
Jas Ahluwalia
Tony Chen
May 29, 2003
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Introduction
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Voice has been transmitted over PSTN (POTS)
since 1878.
U.S. Long-Distance Market is $100 billion a year
$100 billion?!! Businesses and consumers wish to
reduce this cost.
Over the last decade the emergence of the
internet has caused a significant investment in IP
based networks
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Can we use these IP based networks for voice?
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VoIP – Big Picture
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User’s voice converted
from analog to digital
signal.
Digital signal is
compressed.
Compressed signal is
assembled into packets.
Packets transported over
IP networks.
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Technical Issues
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For good voice quality we need to ensure that latency
does not exceed 200ms.
IP Networks have several sources of delay which
increase latency
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Protocols
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Uses Resource Reservation Protocol (RSVP)
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Applications request resources from the network
Each hop conducts admission control decision for the
request and sets up per-flow state.
Two Components
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Resource Allocation (How much to reserve)
Packet Filters (what packets get to use these resources)
Uses the User Datagram Protocol (UDP) over IP
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Avoids Acknowledgments for lost packets
Acknowledgements trigger retransmissions which increase
network traffic and decrease Quality of Service (QoS)
Packets could come out of order though. What do we do?
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Protocols
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Realtime Transport Protocol (RTP)
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Used to support transport of real-time media
RTP packets contain:
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Media information
Header provides information to receiver that allows reordering of
out-of-sequence packets.
Several Companion protocols
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Real Time Control Protocol (RTCP)
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Provides QoS feedback to sending device.
Real Time Streaming Protocol (RTSP)
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Used to control stored media devices
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Architecture
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H.323 – provides foundation for audio, video, and data
communications across IP Networks
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Terminals
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Gateways
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Used for protocol conversion between IP and circuit-switched
networks
Gatekeepers
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Device the user is using (phone, pc, etc.)
Used for bandwidth management, address translation, and call
control
Multipoint Control Unit (MCU)
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Supports multicast conferences among three or more end points.
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Architecture
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H.323
Gatekeeper
Terminal
Multipoint
Control Unit
Packet Based
Circuit Switched
Networks
Networks
Gateway
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Big Picture Again
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Architecture: H.323 or MGCP
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MGCP: Media Gateway Control Protocol
QoS: RSVP
Protocols: RTP over UDP over IP
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RTP over UDP over IP
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PSTN Vs. VoIP
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Current VoIP Implementations
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Coexistence
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Telcordia’s Next Generation Network and Voice
over Packet architecture (NGN/VOP)
Core Packet Network
 Call Connection Agent
 Signaling Gateway
 Trunk gateway
 Access gateway
 Billing agent.
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Coexistence
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Veraz Networks
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Provide Carrier Grade Solution for companies like AT&T, MCI,
etc
MCI creates dedicated IP network for voice traffic termed
“Engineered IP Network”
Benefits of Engineered IP Network:
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A 20,000 Telephone Line Exchange costs $12-$14 Million
Exchanges are huge and require special housing (protection for fire,
flooding, etc.)
Next Generation Solution cost $2-$3 million and is small (desktop size).
Call between LA and NY goes over several nodes in telephone sytem.
Only one Next Generation Solution is needed for same call.
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Veraz Networks
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2 part solution
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Softswitch
Software brains of the system
 Make/break connections, etc.
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Media Gateway
Interface to existing telephone system
 Interface to IP Network.
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Veraz/Nexverse wish to bring about the same
evolution that the computing world saw.
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Smaller, more powerful, cheaper computers
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Conclusion
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VoIP provides a cost effective solution
Can envision a wide array of applications that
can complement VoIP
However, previous slide shows several issues
that need to be resolved before widespread
deployment.
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