Where should services reside in Internet Telephony Systems? Xiaotao Wu, Henning Schulzrinne {xiaotaow, Department of Computer Science, Columbia University, New York

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

PSTN v.s. Internet Telephony Signaling & Media Signaling Media PSTN: Internet Telephone:

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

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

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

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)

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

Service architecture Programming language model

Service architecture DFC

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

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

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

Handle Call Waiting in DFC LI CW Router

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.