[SIPForum-discussion] Query related to 3GPP IMS implementation

[dushyant]

Hi All,

 

We are developing IMS node specifically P-CSCF. I have a query related to
IMS implementation - 

 

3GPP TS 24.229 specifies different set of procedures for Target Refresh
Request and other Subsequent Request in a dialog. As of now (RFC 5057) the
target refresh requests are INVITE, UPDATE, SUBSCRIBE, NOTIFY and REFER.

 

My question is - Is UPDATE a target refresh request in all cases or it's a
target refresh request in the scenarios where remote target gets changed? 

 

Secondly, in a call between UE A and UE B, if UE A sends an UPDATE to UE B
for changes in SDP parameter can UE B modify its CONTACT in the response to
this UPDATE (Since UPDATE is a target refresh request) or UE B has to
exclusively issue a new UPDATE request to modify its CONTACT parameter and
this second UPDATE would be regarded as a Target Refresh Request and the
first UPDATE is not a target refresh request.

 

Third, in IMS scenario as per 3GPP TS 24.229 on receiving a target refresh
request originating P-CSCF, originating S-CSCF, terminating S-CSCF should
add its Record-Route but shouldn't save its list of Record-Route whereas
terminating P-CSCF has to save the list. In such a case if let's say one of
the S-CSCF changes the user part of its record route entry and terminating
P-CSCF  has to release the dialog by issuing BYE which Record-Route should
it use - the one received in INVITE or the one received in target refresh
request?

 

Another query related to related to Subscribe-Notify scenario in IMS
environment. 

Can Notify be responded with 4xx response?

The exact scenario is -

On successful registration UE sends subscription to SCSCF for Event -"reg".
In return SCSCF sends back Notify with XML body. My query is can UE send
back 4xx response if the XML body is corrupted or there is any other error
e.g SCSCF doesn't send back P-Charging Vector?

 

 

Dushyant P S Dhalia

 

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