If you are confused with the relation among Call, Dialog, Transaction
& Message, you are not alone. I think quite a good number of people
get confused regarding the relation in the beginning.
Messages are the individual textual bodies exchanged between a server and a client. There can be two types of messages. Bingo! You already know them ... Requests and Responses.
Transaction occurs between a client and a server and comprises all messages from the first request sent from the client to the server up to a final (non-1xx) response sent from the server to the client. If the request is INVITE and the final response is a non-2xx, the transaction also includes an ACK to the response. The ACK for a 2xx response to an INVITE request is a separate transaction.
Dialog is a peer-to-peer SIP relationship between two UAs that persists for some time. A dialog is identified by a Call-ID, a local tag and a remote tag. A dialog used to be referred as a 'call leg'.
Call of a callee comprises of all the dialogs it is involved in. I think a Call is same as a Session.
The following figure will make the relation clearer.
(RINGING is a 1xx response and OK is a 2xx response.)
A caller may have connections to a number of callees at a time forming a number of dialogs. All these dialogs make a single call.
Well, time to reveal a old secret! If you want to know how server1 knew the location of user2 during the call setup, the page about SIP registration will help you.
Messages are the individual textual bodies exchanged between a server and a client. There can be two types of messages. Bingo! You already know them ... Requests and Responses.
Transaction occurs between a client and a server and comprises all messages from the first request sent from the client to the server up to a final (non-1xx) response sent from the server to the client. If the request is INVITE and the final response is a non-2xx, the transaction also includes an ACK to the response. The ACK for a 2xx response to an INVITE request is a separate transaction.
Dialog is a peer-to-peer SIP relationship between two UAs that persists for some time. A dialog is identified by a Call-ID, a local tag and a remote tag. A dialog used to be referred as a 'call leg'.
Call of a callee comprises of all the dialogs it is involved in. I think a Call is same as a Session.
The following figure will make the relation clearer.
(RINGING is a 1xx response and OK is a 2xx response.)
A caller may have connections to a number of callees at a time forming a number of dialogs. All these dialogs make a single call.
Well, time to reveal a old secret! If you want to know how server1 knew the location of user2 during the call setup, the page about SIP registration will help you.
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