Voice Over IP - University of California, San Diego
Voice Over IP Presented By Jas Ahluwalia Tony Chen May 29, 2003 1 Introduction 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 Can we use these IP based networks for voice? 2 VoIP Big Picture
Users voice converted from analog to digital signal. Digital signal is compressed. Compressed signal is assembled into packets. Packets transported over IP networks. 3 Technical Issues
For good voice quality we need to ensure that latency does not exceed 200ms. IP Networks have several sources of delay which increase latency 4 Protocols Uses Resource Reservation Protocol (RSVP)
Applications request resources from the network Each hop conducts admission control decision for the request and sets up per-flow state. Two Components Resource Allocation (How much to reserve) Packet Filters (what packets get to use these resources) Uses the User Datagram Protocol (UDP) over IP
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? 5 Protocols Realtime Transport Protocol (RTP) Used to support transport of real-time media
RTP packets contain: Media information Header provides information to receiver that allows reordering of out-of-sequence packets. Several Companion protocols Real Time Control Protocol (RTCP)
Provides QoS feedback to sending device. Real Time Streaming Protocol (RTSP) Used to control stored media devices 6 Architecture H.323 provides foundation for audio, video, and data communications across IP Networks Terminals
Gateways Used for protocol conversion between IP and circuitswitched networks Gatekeepers Device the user is using (phone, pc, etc.) Used for bandwidth management, address translation, and
call control Multipoint Control Unit (MCU) Supports multicast conferences among three or more end points. 7 Architecture H.323 Gatekeeper Terminal
Multipoint Control Unit Packet Based Circuit Switched Networks Networks Gateway 8 Big Picture Again Architecture: H.323 or MGCP
MGCP: Media Gateway Control Protocol QoS: RSVP Protocols: RTP over UDP over IP 9 RTP over UDP over IP 10 PSTN Vs. VoIP
11 Current VoIP Implementations 12 Coexistence Telcordias Next Generation Network and Voice over Packet architecture (NGN/VOP) Core Packet Network Call Connection Agent Signaling Gateway Trunk gateway Access gateway
Billing agent. 13 Coexistence 14 Veraz Networks 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: 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. 15 Veraz Networks 2 part solution Softswitch Software brains of the system Make/break connections, etc.
Media Gateway Interface to existing telephone system Interface to IP Network. Veraz/Nexverse wish to bring about the same evolution that the computing world saw. Smaller, more powerful, cheaper computers 16 17 Conclusion
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. 18
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