8 Error handling procedures

29.2283GPPIP Multimedia (IM) Subsystem Cx and Dx InterfacesRelease 16Signalling flows and message contentsTS

8.1 Registration error cases

This clause describes the handling of error cases, which can occur during the registration process. If the new and previously assigned S-CSCF names sent in the Multimedia-Auth-Request command are different and the Multimedia-Auth-Request is not indicating synchronisation failure (i.e. the request does not contain auts parameter), then the HSS shall overwrite the S-CSCF name.

If the new and previously assigned S-CSCF names sent in a command other than the Multimedia-Auth-Request command are different and the S-CSCF reassignment pending flag is not set, then the HSS shall not overwrite the S-CSCF name; instead it shall send a response to the S-CSCF indicating an error.

8.1.1 Cancellation of the old S-CSCF

It is possible that in certain situations the HSS receives a Multimedia-Auth-Request (MAR) command including a S-CSCF name, which is not the same as the previously assigned S-CSCF for the user. This can happen e.g. in case the new S-CSCF is selected due to a failure in the re-registration if the previously assigned S-CSCF does not respond to REGISTER message sent from the I-CSCF after a timeout.

In this case, the new S-CSCF is assigned for the user and if registrations in the previously assigned S-CSCF exist for the user, these registrations in the old S-CSCF are handled locally in the old S-CSCF, e.g. re-registration timers in the old S-CSCF shall cancel the registrations.

Additionally, the HSS should de-register the registrations in the old S-CSCF by using the Registration-Termination-Request command. In this case, the HSS shall first check whether the deregistration is really required by comparing the Diameter client address of the newly assigned S-CSCF received in the MAR command to the Diameter client address stored in the HSS. If the Diameter client addresses match, the deregistration shall not be initiated. Otherwise the deregistration should be initiated for all the registered Public User Identities for the corresponding IMS Subscription. HSS shall check whether IMS Restoration Procedures are supported to perform deregistration:

– If supported, Registration-Termination-Request shall be sent for all Public User Identities (with their associated Private User Identities), with Deregistration-Reason AVP value set to NEW_SERVER_ASSIGNED.

– Otherwise, Registration-Termination-Request shall be sent with different Deregistration-Reason AVP values, in the following order:

1. Deregistration-Reason AVP value set to NEW_SERVER_ASSIGNED, for the Public User Identity (with its associated Private User Identity), which is registered in the new S-CSCF.

2. Deregistration-Reason AVP value set to SERVER_CHANGE, for the user Public User Identities (with their associated Private User Identities), which are not yet registered in the new S-CSCF.

8.1.2 Error in S-CSCF name

If the S-CSCF name sent in the Server-Assignment-Request command and the previously assigned S-CSCF name stored in the HSS are different and the S-CSCF reassignment pending flag is not set, then the HSS shall not overwrite the S-CSCF name. If the Server Assignment Type indicates NO_ASSIGNMENT, the HSS shall send a response to the S-CSCF with Result-Code value set to DIAMETER_UNABLE_TO_COMPLY. For all other Server Assignment Types, the HSS shall send a response to the S-CSCF with Experimental-Result-Code value set to DIAMETER_ERROR_IDENTITY_ALREADY_REGISTERED.

If the S-CSCF name sent in the Server-Assignment-Request command and the previously assigned S-CSCF name stored in the HSS are different and IMS Restoration Procedures are supported and the S-CSCF reassignment pending flag is set, then the HSS shall allow overwriting of the S-CSCF name and proceed with the processing of the SAR command as defined in clause 6.1.2.

8.1.3 Error in S-CSCF assignment type

If the Server-Assignment-Type in the Server-Assignment-Request command sent by the S-CSCF to the HSS is not allowed (i.e if the Server-Assignment-Type is not applicable based on the user state or it is not applicable based on the user identity type), the HSS shall send a response to the S-CSCF with the Experimental-Result-Code value set to DIAMETER_ERROR_IN_ASSIGNMENT_TYPE.