INVITE
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... SigComp can bring to SIP is
the ability to compress the initial INVITE of a dialog, when the user
is waiting for the session to be established. Therefore, clients ...
... The following example illustrates the use of the parameters defined
above. The call flow of Figure 1 shows an INVITE-200 OK-ACK
handshake ...
... |------------>| (2) INVITE | |
| |------------>| (3) INVITE |
| | |------------>|
| | | (4) 200 OK |
...
... UAC is configured to send compressed traffic to P1, and therefore, it
compresses the INVITE (1). In addition, the UAC wants to receive
future requests and responses for this dialog compressed. Therefore,
...
... sigcomp
P1 forwards the INVITE (2) to P2. P1 does not use compression by
default, so it sends the INVITE ...
... INVITE (2) to P2. P1 does not use compression by
default, so it sends the INVITE uncompressed to P2.
(3) INVITE ...
... UAS. P2 supports compression, but
it does not use it by default. Therefore, it sends the INVITE
uncompressed. P2 wishes to remain in the signalling path and
therefore it Record-Routes.
...
... UAS towards the
UAC (the opposite direction than the first INVITE), the next hop will
be the Contact header field ...
... next hop will
be the Contact header field of the INVITE, because P1 did not
Record-Route. That Contact identified the UAC ...
... Since the UAC wants to receive compressed requests (Contact of the
INVITE), P2 assumes that the UAC would also like to send compressed
requests (Record-Route ...
... entry in the Record-Route header field of the 200 OK (5). In the
INVITE (3), P2 did not used the comp=sigcomp parameter. Now it adds
it in the 200 OK (5). This will allow the UAC ...