This is done by using the BYE
method to the other participants in the session. Each participant will then respond
with a 200 OK. There are some instances when the network itself wishes to terminate
a session.
For example, loss of signal to a device would leave a session in suspension. The physical
connection is lost, but any sessions would remain until they either timed out or the
network terminated them.
There are other cases where the network must terminate a session in progress. The
S-CSCF acts as a stateful proxy in the IMS and is therefore capable of terminating
session. If the S-CSCF must terminate a session, it will send a BYE message in two
directions: one to the originator and one to the called party. The BYE sent to the called
party would be populated with:
?– REQUEST-URI populated with the address of the called party
?– TO header populated with the address of the called party derived from the 200 OK
?– FROM header populated with the address of the calling party derived from the
INVITE
?– CALL-ID populated with the value from the INVITE
?– CSeq header incremented by one
?– ROUTE header populated with the address of the called party
?– Any additional headers deemed necessary by the network or operator
The same would be sent to the calling party, with the following headers and
parameters:
?– REQUEST-URI populated with the address of the calling party
?– TO header populated with the address of the calling party derived from the 200 OK
?– FROM header populated with the address of the called party derived from the
INVITE
?– CALL-ID populated with the value from the INVITE
?– CSeq header incremented by one
?– ROUTE header populated with the address of the calling party
?– Any additional headers deemed necessary by the network or operator
The S-CSCF will expect to receive a 2 xx response from both parties.
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