ASCOM i62 Troubleshooting Manual page 44

Troubleshooting Guide
Ascom i62 VoWiFi Handset
• RTP sessions are established between the users but are then put on hold pending the
transfer
• The signaling of the actual transfer takes place; existing RTP sessions are terminated
between the transferee (user1) and transferor (user2) and transferor and transfer
target (user3). A new RTP session is established between user1 and user3.
• One of the parties terminates the call, and a final exchange of SIP messages takes place
to signal the completion of the call.
Parties on Hold with Transferor
The flow of SIP messages in the setup between user1 and user 2 analogous to any
conventional SIP call between two parties such as that depicted in
INVITE message creates a header that would contain the following kind of sample data:
INVITE user1 -> user2
From:
To:
Call ID:
However, after the establishment of an RTP session between the parties, user2 initiates a
transfer of the call from the handset to user 3. This requires user2 to start the transfer by
putting user 1 on hold in the following way:
1 user2 sends user1 an INVITE to hold the current RTP exchange. The message header
contain the following sample data:
INVITE (hold) user2 -> user1
From:
To:
Call ID:
2 user1 responds with a 200 OK
3 user2 acknowledges with ACK
4 user1 indicates that it now neither wishes to send nor receive media from user2 by
marking the RTP stream as inactive through the SDP session attribute "a=inactive".
5 The RTP exchange stops and user1 is now on hold
user2 announces the transfer to user3 with a dialog of messages that is again identical to a
conventional SIP call, up to the establishment of an RTP exchange. The initial INVITE
message creates a header with the following sample data:
INVITE user2 -> user3
From:
To:
Call ID:
Of significance is the new user 2 tag, u2-2, associated with the invite. A new user2 tag is
required to differentiate between the tag used with user1 and the tag used with user3.
The dialog with user3 must also indicate that there is a pending transfer and this is also
achieved through an INVITE to hold message from user2 to user3. user2 puts user3 on hold
with the following dialog:
1 user2 sends user3 an INVITE to hold the current RTP exchange between user2 and
user3:
INVITE (hold) user2 -> user3
From:
28 June 2012 / Ver. A
6. Troubleshooting
user1 <sip: user1@servera.com>;tag=u1
user2 <sip: user2@serverb.com>
u1-to-u2-cid
user2 <sip: user2@servera.com>;tag=u2
user1 <sip: user1@servera.com>;tag=u1
u1-to-u2-cid
user2 <sip: user2@servera.com>;tag=u2-2
user3 <sip: user3@somewhereelse.com>
u2-to-u3
user2 <sip: user2@servera.com>;tag=u2-2
TD 92685EN
Appendix 10. The initial
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