Transcript Wu0009_Where - Columbia University

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
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Most services can be in end system
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Where should service reside
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End system vs. Network server
Service architecture
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PSTN vs. Internet Telephony
Call waiting
Programming language model
DFC
Service examples for different models and
feature interaction between end system
and network server
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
PSTN vs. Internet Telephony
PSTN:
Internet
Telephone:
Signaling & Media
Signaling & Media
Signaling
Signaling
Media
Call waiting
Line 2 ringing
A
Talk on line 1
INVITE,
SDP’s c=0
Wait 2 minutes
Press line 2
180 Ringing INVITE
182 Wait 2 minutes
200 OK
B
C
Call waiting
A
Hold on line 1
200 OK
B
Talk on line 2
C
End system vs.
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 e d 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
A
Run c.cgi
New INVITE
INVITE
302 Ok
c.cgi handle busy
INVITE
302
486 busy
C
200 Ok
Talk on line 1
INVITE
B
D
Handle Call Waiting in DFC
A
LI
LI
Setup
Upack
Upack
CW
Upack
SwitchCW
LI
B
Setup
Setup
Setup
Setup
Router
Setup
C
Handle Call Waiting in DFC
A
LI
LI
CW
LI
B
Router
C
Call forwarding on busy in
end system
INVITE
A
C
302
200
INVITE
Talk on line 1
D
B
Feature interaction between
end system & network server
c.cgi
Run c.cgi
(Don’t disturb rule)
(I can accept
call on line 2)
302
INVITE
302 Ok
A
C
200 Ok
Talk on line 1
INVITE
B
D
Service location examples
Service
End system
Network (proxy)
Network with
Media (UA)
Distinctive ringing
Yes
Can assist
Can assist
Visual call id
Yes
Can assist
Can assist
Call waiting
Yes
No
Yes(*)
CF busy
Yes
Yes(*)
Yes(*)
CF no answer
Yes
Yes
Yes
CF no device
No
Yes
Yes
Location hiding
No
Yes
Yes
Transfer
Yes
No
No
Conference bridge
Yes
No
Yes
Gateway to PSTN
No
No
Yes
Firewall control
No
No
Yes
Voicemail
Yes
No
Yes
(*) = with information provided by end system
Conclusion
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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.