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Subject

Author

Date

SIP querries

Lalatendu Das

03-16-2006

Prasanna

Sandeep_french

Prasanna

Sandeep_french

Posted by Lalatendu Das on March 16, 2006, 6:40 am

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hi ,
i am learning SIP stack developemnt in a company as induction training
can any one suggest me answers to below questions
1. how come u know that which transport protocol is used
(TCP/UDP/SCTP)from the SIP stack
2. where HASHING technique is used in a SIP Stack and how.
3. What is SAP (service Access POint ) from the point of veiw of SIP
Stack.

Posted by Prasanna on March 19, 2006, 6:14 am

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(a) Transport Protocol
Provided that the system supports more than one transport protocols, to
choose one, DNS is used (typically use NAPTR to get the SIP service
handle) then use SRS on each of the handle to obtain the host names for
difference transports.
However if the hosts obtained for all transports, then choosing one is
a local policy.

(b) Hashing in a SIP stack is used for locating transactions from
Branch-Ids, Dialogs from Call-IDs. For SIP itself it is used for
security purposes.

Posted by Sandeep_french on March 20, 2006, 3:36 am

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It is good to listen from u sir. i have never expected u like this .
sir there is aniother querry

1>why i need an early dialog . The presence of early media needs to
solve some scenarios like
colouring service and passing info regarding session .Simillarly is
there anty need of early dialog.

2 >why it is recomended that after 200-OK if one want tochange the
media one should use Re-invite rather than UPDATE . somebooks saying
this is because update needs instant answer unlike INVITE . But how
comethis be an answer.

3> Sir is there any way one can make a functuon re-entrant .

Posted by Prasanna on March 20, 2006, 3:56 am

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Early dialog is used to handle forking, so that multiple 180/200 can
establish different dialogs and give the user the control to choose one
callee to talk to.

As per RFC-3311, what you told is correct. As per basic SIP
understanding, except INVITE no othe transaction should wait for user
intervention, so answering of the UPDATE will be done by the stack it
cannot wait for the user.

The easiest way to make a function re-entrant is avoid global variables.

Posted by Sandeep_french on March 21, 2006, 1:45 am

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Sir ,
i am sorry for the previous querry as i have sent that from one of
my alias one mistakenly . however this one related to authentication .
the scenario is like below :
Let's say there is third party registration is happening inside a
network . So, Is the third party can ever be challenged ? if yes then
how the configruation will be done between users and the third party .

other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

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