On 2010/09/22 13:18, abhishek chattopadhyay wrote: > Hi Implementors, > > In 3261 the re-transmission of INVITE is stopped by 1xx responses. So to > stop the re-trnasmission of 200 OK, ACK is sent. > (Albait it would be worth considering that ACK is used for a lot of other > purposes.) > > Further form 3261 only, it is clear that for other methods the request would > be re-transmitted till a 200 is received. The entity sending a 200 OK would > understand that the 200 has been successfully received if the Method is not > re-transmitted again. > > > My question is, > Why at all a 3 way handshake is implimented for INVITE. > And > 100 trying is not restricted for any Method inside a dialog, so if a 100 > Trying is issued for say UPDATE then why it is not the same case as of the > Re-INVITE's arriving inside the same dialog.
The 3-way handshake, like that of TCP, lets * the caller know that the callee received the INVITE (it received a 200 OK), and * the callee knows that the caller received the reply (it received an ACK). In short, both parties now know that the other party is alive, and part of the connection. frank _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
