The scope of the technical report is to capture the results of a study into the feasibility of enhancing IMS network architecture. This report intends to study the feasibility of enhancing IMS network architecture as follows,

• Investigating architectural improvements to reduce the complexity of signalling procedures by reducing the signalling hops, or the number of options and combinations (by looking at different groupings of combining existing entities);
• Investigating means to improve system-level load balancing and reliability;
• Investigating possibilities for reducing configuration workload to save OPEX.
• Investigating the introduction of IMS Overload Control mechanisms.

Backward compatibility with current IMS specifications shall be ensured. This report is intended to explore potential architecture improvements and also provide conclusions on the above aspects with respect to potential future normative specification work. There are a number of functions involved in call session setup in IMS network. Interfaces and interactions between network elements may be a little complicated and not that efficient. It is deemed beneficial to review the current IMS architecture including aspects such as the possible optimization of interfaces/reference points (by looking at different groupings of combining existing entities), reducing options of solutions for the same issues, relevancy of certain functions etc. IMS network service availability largely relies on the reliability of network entities. If some network elements implementing critical functions (e.g. S-CSCF, HSS) fail, service availability may be impacted. Moreover network elements may not be fully utilized because network load may not be well distributed, e.g. some nodes may be overloaded due to sudden traffic increase, while others may be under loaded to some extent. Though there are some element level approaches to solve these problems, some system level solutions should be studied, for example, the method to distribute load between network elements in different geographical locations especially when a disaster happens, such as earthquake. Network expansion may require significant manual configurations, and the network maintenance and upgrade may be time-consuming and also may be costly for operators. Introducing self-organization features may improve the network intelligence and reduce the efforts of manual configuration. The objectives of the study for investigating the introduction of IMS Overload Control mechanisms are to:

• Determine the parts of IMS architecture for which overload control mechanisms are needed;
• Evaluate the applicability of candidate solutions for Overload Control to the SIP entities of the IP multimedia core network architecture, including:
  • mechanisms having already been specified or studied within 3GPP and their possible enhancements,
  • mechanisms specified or studied by other bodies (e.g. ETSI TISPAN, IETF) and their possible enhancements,
  • other mechanisms, if proposed within this work item;
• Provide recommendations based on analysis.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.