Transcript Where should service reside in Internet Telephony System

Where should services reside
in Internet Telephony
Systems?
Xiaotao Wu, Henning Schulzrinne
{xiaotaow, hgs}@cs.columbia.edu
Department of Computer Science,
Columbia University, New York
Outline

Most services can be in end system



Where should service reside


End system vs. Network server
Service architecture



PSTN vs. Internet Telephony
Call waiting
Programming language model
DFC
Service examples for different models
PSTN v.s. Internet Telephony
PSTN:
Internet
Telephone:
Signaling & Media
Signaling & Media
Signaling
Signaling
Media
PSTN vs. Internet Telephony
PSTN
Internet Telephony
end system
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
Call waiting
Line 2 ringing
Wait 2 minutes
Press line 2
Talk on line 1
INVITE,
SDP’s c=0
180 Ringing INVITE
182 Wait 2 minutes
200 OK
Call waiting
Hold on line 1
200 OK
Talk on line 2
End system v.s.
Network server
Network server
End system
Permanent IP address
Always on
(User can have unique address
and can always be reached)
Temporary IP address
Powered off so often
(User’s address always changed
and can not be reached sometime)
Ample computational capacity
High bandwidth
(Conference)
Limited computational capacity
Low bandwidth
(One to one or small size conf.)
Indirect user interaction
Usually only deals with signaling
(Based on predefined mechanisms,
or indirect user interaction, like
through web page)
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
End system
Information hiding
Busy handling
Logical call distribution
Call transfer
Gateway
Distinctive ringing
Service architecture
Programming language model
Service Logic
Programming
Interface
Requests
Requests
SIP Server Function
Responses
Responses
Service architecture
DFC
LR
PR
LR
PR
LR
PR
LI(TI)1
FB1
MB1
FB: Feature Box
LI: Line Interface Box
TI: Trunk Interface Box
M B : Mb o x ( M ed i a
Processing)
LR: Logical Router
PR: Positional Router
DB: Database
FB2
DB
DB
DB
LI(TI)2
MB2
DFC protocol msg
Media control msg
Media transmission
Other msg
Call forwarding on busy
c.cgi
Run c.cgi
c.cgi handle busy
New INVITE
INVITE
200 Ok
200 Ok
INVITE
302
INVITE
486 busy
Talk on line 1
Call forwarding on busy in
end system
INVITE
302
200
INVITE
Talk on line 1
Handle Call Waiting in DFC
LI
LI
Setup
Upack
Upack
CW
Upack
SwitchCW
LI
Setup
Setup
Setup
Setup
Router
Setup
Handle Call Waiting in DFC
LI
LI
CW
LI
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.