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Thursday, 22 August 2013

SIP Interview Questions 2

11)  What is Forking Feature and forking types?

 A:    It sends an Invite requests to all the available users.
         Two Types of Forking.
               Serial Forking:   In this  it sends request to one address, if  that fails then it try second  address.
              Parallel Forking : In this it sends request at a time to all addresses,If any of the user  accept the request others get disconnected.
             
12)  What is Call-ID ?

 A:  It contains a globally unique identifier for all requests and responses sent by either UA in a  dialog, and it is generated by the combination of 'random string' and 'IPaddress'.



* 13)  If user a doesn't have supported media what response is sent?

 A: UnSupported Media -415 is sent from proxy if Codecs doesn't match .


14)  what are SIP Entities/Components?


 A:  There are four Types :
                 a) Registrar Sever
                 b) Proxy Server
                 c) Redirect Server
                 d) UserAgent Server

15)  What are 1xx-responess do you know?


 A:    100- Trying
         180- Ringing
        


* 16)  What is magic cookie?


 A:    The branch ID inserted by an element always begin with the characters "z9hG4bK".                     These 7 characters are used as a "Magic cookie"

* 17)  what is B2BUA server?

 A:      It is a logical SIP Entity server and lies in between both the endpoints.  
  a) It maintains dialog state and must be a part of all the requests sent on the dialogs that it has  established.
 b) It Interprets and rewrites a request message before forwarding it. 


18) Does SIP carry DTMF?


 A:  There are atleast two options for carrying DTMF and smilar signals in a Voip N/W using  SIP.First DTMF can be transported as an RTP payload. This has the advantage that it  provides accurate timing  and alingment with RTP packet currently there is no standardized  solution with in SIP, but it has been proposed to carry DTMF information in SIP Info messages.

19) Do caller need to know the location of the location server?


 A:  The caller doesn't interact directly with the location server. A redirect or proxy server asks  the location  serve for advice.


21) Does SIP do admission control and administer Band width?


 A:  1) Since these offers no real security admission control is not supported by SIP
       2) No, that is the role of a resource reservation protocol.

22) Do i always need a proxy server or redirect server?


 A:  Proxy and Re-direct server are logical Entities.So,sip servers can contact each other  directly.

23) How does caller find its local registrar?


 A:  The local registrar is manually configured.

24) Are Ack requests retransmitted?


 A:  No, An Ack is sent when a response retransmission is received. Ack is only used for Invite.

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