* 1) what is Media Negosiation ?If SDP is not sent in Invite,when that will be sent?
A: Media Negotiation is nothing but exchange of Media parameters required to establish the session.There is a two- phase exchange done in Invite and 200 OK ,negotiation capabilities is based on basic Offer/Answer model of SDP exchnage.
Note: If SDP is not sent in Invite, then it can sent in ACK request.
* 2) What is dialog? How do we identify a dialog?
A: Dialog is a peer-Peer connection between the end points . An initial request from UAC contains a tag in 'From' header and Call ID. At this point we have half dialog completed. And tag in 'To' header is added by UAS in Provisional responses other than 100-Trying.This completes the "dialog"
Dialog = From tag + To tag + Call Id
* 3) What is Transaction? How to identify?
A: A Request followed by the Final Response is called a "Transaction".
*It is identified by "C-seq" and "Branch Parameter".
* 4) What is Session? When does Session is Established?
A: Session is exchange of media between two or more endpoints. After receving ACK request only Session is established.If we don't receive ACK ,session is not Established.
* 7) If Max-Forwards reaches to Zero, what response is sent?
A: 483-Too Manys Hops response is sent from proxy.
* 20) How can we recognize a retransmitted, duplicate or looped request?
A: a) The max forward count is decremented to zero.
b) The Expires time has elapsed.
c) The Server finds itself in the requests via list, including any branch parameter.
5) What is SDP? How can we know that is an Audio/Video Call?
A: SDP is also Called Message Body.It describes type media to be used for call.
Audio call: m=audio
Video call: m=audio
m=video
6) How can we know that call is on Hold?
A: 1) If SDP contains an attribute a=sendonly or Inactive, then call is on hold.
2) Zeroing the IP address or port number in the media descriptor of the stream.
8) Why ACK is considered as Seperate Transaction?
A: Since this ACK is only re-transmitted by the UAC, Its effectively considered its own transaction.
(Ex: Basic call flow)
--> If response was not 2XX, then ACK is Considered as Same transaction.
(Ex: Call Busy)
* 9) Types of Proxies? Difference between Statefull and Stateless Proxies?
A : Two Types of proxies, Statefull and Stateless poxies.
Statefull Proxy:
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.
Stateless Proxy:
a) It doesn't maintains state.
b) It just forwards the received requests to other end and send responses on behalf of other.
* 10) What are mandatory header fields?
A : To, From, Via, C-seq, Max Forwards, Call-ID.
A: Media Negotiation is nothing but exchange of Media parameters required to establish the session.There is a two- phase exchange done in Invite and 200 OK ,negotiation capabilities is based on basic Offer/Answer model of SDP exchnage.
Note: If SDP is not sent in Invite, then it can sent in ACK request.
* 2) What is dialog? How do we identify a dialog?
A: Dialog is a peer-Peer connection between the end points . An initial request from UAC contains a tag in 'From' header and Call ID. At this point we have half dialog completed. And tag in 'To' header is added by UAS in Provisional responses other than 100-Trying.This completes the "dialog"
Dialog = From tag + To tag + Call Id
* 3) What is Transaction? How to identify?
A: A Request followed by the Final Response is called a "Transaction".
*It is identified by "C-seq" and "Branch Parameter".
* 4) What is Session? When does Session is Established?
A: Session is exchange of media between two or more endpoints. After receving ACK request only Session is established.If we don't receive ACK ,session is not Established.
* 7) If Max-Forwards reaches to Zero, what response is sent?
A: 483-Too Manys Hops response is sent from proxy.
* 20) How can we recognize a retransmitted, duplicate or looped request?
A: a) The max forward count is decremented to zero.
b) The Expires time has elapsed.
c) The Server finds itself in the requests via list, including any branch parameter.
5) What is SDP? How can we know that is an Audio/Video Call?
A: SDP is also Called Message Body.It describes type media to be used for call.
Audio call: m=audio
Video call: m=audio
m=video
6) How can we know that call is on Hold?
A: 1) If SDP contains an attribute a=sendonly or Inactive, then call is on hold.
2) Zeroing the IP address or port number in the media descriptor of the stream.
8) Why ACK is considered as Seperate Transaction?
A: Since this ACK is only re-transmitted by the UAC, Its effectively considered its own transaction.
(Ex: Basic call flow)
--> If response was not 2XX, then ACK is Considered as Same transaction.
(Ex: Call Busy)
* 9) Types of Proxies? Difference between Statefull and Stateless Proxies?
A : Two Types of proxies, Statefull and Stateless poxies.
Statefull Proxy:
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.
Stateless Proxy:
a) It doesn't maintains state.
b) It just forwards the received requests to other end and send responses on behalf of other.
* 10) What are mandatory header fields?
A : To, From, Via, C-seq, Max Forwards, Call-ID.
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