Voice over IP

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Voice over IP

• B90901033 ???

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Outline

• Introduction
• Some Protocols
• Example - Skype
• Conclusion

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Introduction

• What is VoIP?
• The transport of voice traffic using the Internet
  Protocol (IP)

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Introduction (cont.)

• Why VoIP?
• Lower cost
• The widespread availability of IP
• Reduced bandwidth
• Integration of voice and data applications
• New service features

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Introduction (cont.)

• VoIP Challenges
• Speech quality
• Managing access and prioritizing traffic
• Speech-coding techniques
• Network reliability and scalability

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Introduction (cont.)

• Speech Quality
• Delay
• Jitter
• Packet Loss
• Call Set-up Time

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Outline

• Introduction
• Some Protocols
• Example - Skype
• Conclusion

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Some Protocols

• RTP and RTCP
• For data transport
• SIP
• For signaling use
• MEGACO
• Between signal and data

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RTP and RTCP

• RTP (Real-Time Transport Protocol)
• A transport protocol for real-time applications
• RTCP (RTP Control Protocol)
• A companion protocol with RTP

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RTP and RTCP (cont.)

• Voice over UDP, not TCP
• Data traffic
• Asynchronous
• Extremely error sensitive
• Voice traffic
• Synchronous stringent delay requirements
• Tolerant of errors at most 5

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RTP and RTCP (cont.)

• RTP over UDP
• Sequence number
• Timestamp
• Payload type, marker, etc.
• Does not solve the QoS problems simply provides
  additional information

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RTP and RTCP (cont.)

• RTCP
• Exchange messages between session users
• Quality feedback
• Number of lost packets
• Delay
• Inter-arrival jitter
• Implicitly open when an RTP session is open

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SIP

• SIP (Session Initiation Protocol)
• A signaling protocol
• Setup, modification, tear-down of mutimedia
  sessions
• A powerful alternative to H.323
• More flexible, simpler

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SIP (cont.)

• SIP Network Entities
• User agents
• User agent client
• User agent server
• Servers
• Proxy server
• Location server (Registrar)
• Redirect server

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SIP (cont.)

• SIP Messaging
• Text-based
• SIP Message
• Start line
• Request or status
• Message headers
• Additional information of the request or response
• Message Body
• Describe the type of session

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MEGACO

• MEGACO (Media Gateway Control Protocol)
• Network Gateway
• Signaling conversion
• Media conversion

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MEGACO (cont.)

• MGC (Media Gateway Controller)
• Handling call control
• Call-control intelligence
• Call-related signaling
• MG (Media Gateway)
• Performing the media conversion
• A line or trunk on circuit-switched side
• An RTP port on the IP side

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MEGACO (cont.)
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Outline

• Introduction
• Some Protocols
• Example - Skype
• Conclusion

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Skype

• A peer-to-peer VoIP client developed by KaZaa in
  2003
• Allowing its users to place voice calls and send
  text messages to other users

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Skype (cont.)
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Skype (cont.)
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Skype (cont.)
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Skype (cont.)

• Advantages
• It can work seamlessly across NATs and firewalls
• Better voice quality than the MSN and Yahoo IM
  applications

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Skype (cont.)

• Disadvantages
• The protocol is proprietary
• It provides a single service, not an architecture
  of new services
• It still has centralized elements for login
  authentication

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Outline

• Introduction
• Some Protocols
• Example - Skype
• Conclusion

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Conclusion

• Some Topics
• QoS Management Improvement
• Mobility
• Teleconferencing System

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Reference

• Daniel Collins, Carrier Grade Voice over IP,
  McGraw-Hill, 2003
• Salman A. Baset and Henning Schulzrinne, An
  Analysis of the Skype Peer-to-Peer Internet
  Telephony Protocol, 2004
• http//www.skype.com/