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TR 23.820 (CT4)
Study of
IMS restoration procedures

ToC   3GPP‑Page   Help    
V9.0.0 (Wzip)  2009/09  43 p.
V8.0.1  2008/12  42 p.

Rapporteur:  Mr. Blanco, German
See also:  IMS-Restoration-related TS/TR

Although network nodes in the IMS Core Network should have a very high availability, some maintenance downtime and occasional failures are unavoidable. Communication links although designed with robust protocols between the network elements are also subject to failures. A set of standardized procedures for automatic restoration after loss or corruption of data could reduce the impact of these problems resulting in the improved service to the users. The intention is that similar cases as in TS 23.007 for the CS and PS Domains are covered also for the IMS domain.

This TR identifies the changes required in the 3GPP IMS specifications so that a consistent state is restored in the IMS Core Network, after, or during a planned, or unplanned stop of a network element. The study will go through the following steps:
  • Establish the requirements that should be covered with these procedures. That is which are the impacts to the end user service that are acceptable and which are not, after a network failure.
  • List the service interruption scenarios that need to be studied.
  • Provide solutions, so that in all the service interruption scenarios listed, the impacts to the end user service comply with the requirements. These solutions provide procedures for the automatic restoration to a consistent state in the network and indicate how to trigger these procedures.
  • Analyze the impacts of the solutions in the current specifications.
  • Conclusion and recommended way forward.
It is important to realise that these procedures are meant to be operational procedures for restoration and so care must be taken with what is existing and will exist with OA&M procedures to avoid overlap which could cause clashes.


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1 Scope2 References3 Definitions, symbols and abbreviations3.1 Definitions3.2 Abbreviations4 Requirements analysis and assumptions4.1 Introduction4.2 Persistency Requirements for Data4.3 Impacts on Established Sessions4.4 Impacts on Session Establishment Time4.5 Required Manual Intervention4.6 Loss of service4.7 Avoidance of massive signalling4.8 Load balancing5 Service Interruption scenarios5.1 Introduction5.2 S-CSCF Service Interruption5.3 P-CSCF Service Interruption5.4 IMS-UE Service Interruption5.5 SIP-AS Service Interruption5.6 IP-CAN Service Interruption5.7 HSS Service Interruption6 Alternative solutions6.1 Backup of S-CSCF Information in the HSS6.2 Triggering of initial registration from the S-CSCF or P-CSCF6.2A Precautionary de-registration of un-registered users6.2B S-CSCF re-assignment for unregistered user6.3 Second P-CSCF and deregistration from S-CSCF6.4 Monitoring P-CSCF Health6.5 Possible Solution for SIP-AS Service Restoration6.6 Update of S-CSCF Name in the HSS after Loss of Data6.7 Forking Service Restoration6.8 Possible Solutions for SIP-AS Service Restoration6.9 AS Behaviour After HSS Recovery6.10 HSS Failover with no loss of service7 Conclusions and recommendations7.1 S-CSCF Service Interruption7.2 S-CSCF Re-Selection during Re-Registration7.3 SIP-AS Service Interruption7.4 HSS Service Interruption7.5 P-CSCF Service InterruptionA Change history


1  ScopeWord-p. 6
2  References
3  Definitions, symbols and abbreviations
4  Requirements analysis and assumptions
5  Service Interruption scenarios
6  Alternative solutions
6.1  Backup of S-CSCF Information in the HSSUp
6.2  Triggering of initial registration from the S-CSCF or P-CSCFWord-p. 25
6.2A  Precautionary de-registration of un-registered usersWord-p. 28
6.2B  S-CSCF re-assignment for unregistered user
6.3  Second P-CSCF and deregistration from S-CSCF
6.4  Monitoring P-CSCF HealthWord-p. 31
6.5  Possible Solution for SIP-AS Service RestorationWord-p. 34
6.6  Update of S-CSCF Name in the HSS after Loss of DataWord-p. 35
6.7  Forking Service RestorationWord-p. 37
6.8  Possible Solutions for SIP-AS Service RestorationWord-p. 38
6.9  AS Behaviour After HSS RecoveryWord-p. 39
6.10  HSS Failover with no loss of serviceWord-p. 40Up
7  Conclusions and recommendations
A  Change historyWord-p. 43

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