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Where should service reside in Internet Telephony System

Explore the debate between having services reside in end systems or network servers in internet telephony systems. Discuss the architecture, programming models, and examples of service distribution.

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Where should service reside in Internet Telephony System

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  1. Where should service reside in Internet Telephony System Xiaotao Wu, Henning Schulzrinne {xiaotaow, hgs}@cs.columbia.edu Department of Computer Science, Columbia University, New York

  2. Outline • Most services can be in end system • PSTN v.s. Internet Telephony • Call waiting • Where should service reside • End system v.s. Network server • Service architecture • Programming language model • DFC • Service examples for different model

  3. PSTN v.s. Internet Telephony PSTN: Signal & Media Signal & Media Internet Telephone: Signal Signal Media

  4. PSTN v.s. Internet Telephony Internet Telephony end system PSTN Number of lines or pending calls is virtually unlimited More intelligence, PCs can be considered to be end-user devices Single line, 12 buttons and hook flash to signal

  5. Wait 2 minutes Line 2 ringing Press line 2 180 Ringing INVITE, SDP’s c=0 INVITE Talk on line 1 182 Wait 2 minutes 200 OK Call waiting

  6. 200 OK Talk on line 2 Call waiting Hold on line 1

  7. End system v.s. Network server Network server Permanent IP address Always on (User can have unique address and can always be reached) Ample computational capacity High bandwidth (Conference) Indirect user interaction Usually only deals with signaling (Based on predefined mechanisms, or indirect user interaction, like through web page) End system Temporary IP address Powered off so often (User’s address always changed and can not be reached sometime) Limited computational capacity Low bandwidth (One to one or small size conf.) Direct user interaction Signal and media converge (easier to deal with human interaction, easier to deal with interaction with media)

  8. End system v.s. Network server Network server Information hiding Logical call distribution Gateway End system Busy handling Call transfer Distinctive ringing

  9. Service architectureProgramming language model

  10. Service architectureDFC

  11. c.cgi handle busy Run c.cgi INVITE 302 New INVITE INVITE 486 busy 200 Ok 200 Ok Talk on line 1 INVITE Call forwarding on busy c.cgi

  12. INVITE 302 200 INVITE Call forwarding on busy in end system Talk on line 1

  13. Setup Router Upack Upack Setup Setup Setup Setup CW Upack Switch Setup Handle Call Waiting in DFC LI LI CW LI

  14. Router Handle Call Waiting in DFC LI LI CW LI

  15. Conclusion • Powerful end systems offer benefits such as flexibility and personalized services • End system implementation are good for user interaction • DFC and SIP proxy implementations make it possible to distribute services • The interaction between end system services and network services is still an open issue.

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