Hi,
I think User A's SIP Transaction layer receives User C's INVITE and then
it(Transaction layer) will pass it(C's INVITE) to TU, User A then can get the
information that User C is calling him or her.
see below...
>Hi,
>
>I would like to know how this scenario is practically possible. When
>User A has initialized a call by sending an Invite to User B, how can
>user C send an Invite to User A, since A would be off-hook. I think C
>would get a " User Busy" response when he tries to reach A. Even if you
~~~~~~~~~~~can this response be sent by User A's Transaction layer
and the TU (User A) does not know this information at all?
>assume User A has some feature like Call Waiting, how can he know the
>identity of User C, at this stage, to prefer C over A?
>
>Thanks in advance,
>
>Sridhar
>
>
>
>-----Original Message-----
>From: [EMAIL PROTECTED]
>[mailto:[EMAIL PROTECTED]] On Behalf Of Nicky Song
>Sent: Tuesday, August 13, 2002 2:06 PM
>To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
>Subject: Re: [Sip-implementors] Call Flow problem
>
>
>Scenario 2:
>
>A must send ACK to B since all transactions MUST be terminated. Then A
>can send BYE to B instead of CANCEL because the 200 has already be
>received.
>
>
>----- Original Message -----
>From: "James" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Sent: Tuesday, August 13, 2002 4:19 PM
>Subject: [Sip-implementors] Call Flow problem
>
>
>> Hello All,
>>
>> Think about the scenarios below :
>>
>> 1) User A calls User B , User B responses with 180, at the same time ,
>User C calls
>>
>> User A, and User A does want to talk with User C ,what should User
>A do ?
>>
>> I think : User A should CANCEL User B first( the dialog between A
>and B is not setup yet,the Three HandShake INVITE/200/ACK is
>incomplete), and response User C with 200 OK, right?
>>
>> +---------+ +-----------+ +--------+
>> | User A | | User B | | User C |
>> +---------+ +-----------+ +--------+
>> | | |
>> | 1. INVITE | |
>> |------------------------->| |
>> | 2. 180 | |
>> |<-------------------------| 3. INVITE |
>> |<-------------------------------------------------|
>> |User A want to talk with User C |
>> | 4. 180 | |
>> |------------------------------------------------->|
>> | 5. CANCEL | |
>> | ------------------------>| |
>> | 6. 200 | |
>> |<-------------------------| |
>> | 7. 487 | |
>> |<-------------------------| |
>> | 8. ACK | |
>> |------------------------->| |
>> | 9. 200 OK |
>> |------------------------------------------------->|
>>
>> 2) Comparing with 1) , User A calls User B , User B responses with 200
>OK, and User A has not sent ACK to User B, at the same time , User C
>calls User A, and User A does want to talk with User C ,what should User
>A do ?
>> +---------+ +-----------+ +--------+
>> | User A | | User B | | User C |
>> +---------+ +-----------+ +--------+
>> | | |
>> | 1. INVITE | |
>> |------------------------->| |
>> | 2. 200 OK | |
>> |<-------------------------| 3. INVITE |
>> |<-------------------------------------------------|
>> | User A want to talk to User C
>> | What should User A do ? send BYE to User B ?
>> if User A sends BYE to User B , but the Three Handshake
>INVITE/200/ACK is also
>> incomplete( no ACK).
>> I think , User A should send CANCEL to User B ,right?
>>
>>
>> Thank you to give me an answer!
>>
>>
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