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Back to SBC as P-CSCF

 

SBC as a P-CSCF supports S-CSCF restoration procedures as defined in 3GPP TS 23.380.  If the SBC as a P-CSCF does not receive any response to a SIP request, sent to the IMS core or if the next hop is blacklisted by SBC’s Address Reachability Service (ARS), it rejects the request with a 504 (Server Time-out) response. The SBC uses its path header as P-Asserted-Id header in the response message. The error response also carries MIME body type "application/3gpp-ims+xml" with the following content:

<ims-3gpp> root element with version set to 1
 
    <alternate-service> child element with parameters set as below:
        <type> child element set to "restoration"
        <reason> child element set to "IMS CN not reachable"
        <action>  child element set to "Initial Registration"
The SBC supports IMS restoration procedures using the IP Signaling Profile flag supportSCSCFRestorationProcedures on ePSX or external PSX. The flag is disabled by default. When enabled, SBC acting as P-CSCF rejects a request with 504 (Server Time-out) response carrying MIME body of type application/3gpp-ims+xml if SBC does not receive a response to the request from S-CSCF network, or if the next hop address is blacklisted as part of ARS (Address Reachability Service) service.

For SBC configuration details, see:

For PSX-related information, refer to the PSX documentation.

 

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