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.
(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.
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 .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.
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 .
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