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Conformity assessment of IMS-based equipment used on fixed networks

VoIP_59607379.jpgThe direct “IP-IP” interconnection of fixed network operators using the IP Multimedia Subsystem (IMS) through Inter-IMS Network to Network Interface (NNI) is a complex issue due to differences in IMS implementations (see further background below).

Addressing this challenge, fixed network operators have initiated a Session Initiation Protocol – IMS (SIP-IMS) standardization plan in ITU-T Study Group 11 (Signalling requirements, protocols, test specifications and combating counterfeit products). The plan will guide ITU-T SG11’s development of a set of international standards (ITU-T Recommendations) and related test specifications to provide a unified international reference for the implementation of SIP-IMS on fixed networks. These standards may be used for the conformity assessment of SIP-IMS-based equipment on fixed networks.

The plan provides for ITU-T SG11 to perform a gap analysis of all existing standards related to SIP-IMS profiles maintained by other standards-developing organizations (SDOs). Given the expectation that ITU-T will endorse certain ETSI standards during this standardization effort, ITU-T SG11 and ETSI TC INT will hold joint meetings to ensure the involvement of all relevant parties.

ITU-T SG11 is inviting fixed network operators to establish an alliance to promote these basic requirements for IMS-based equipment. A plan to develop a list of terminal equipment compliant with the ITU-T Recommendations is also under discussion.
The detailed SIP-IMS standardization work plan is available here TIES or Guest account required


IMS was invented as a platform to provide value-added services over mobile networks and enable mobile network operators to achieve ‘all-IP’ communications. IMS has also come to be widely used in fixed networks as a unified architecture that eases heterogeneous terminals’ access to IP voice and multimedia applications.

Despite the benefits of IMS, its implementation in fixed networks is a complex undertaking, for reasons including:
    • Different regulations: Fixed network operators are required to comply with certain national/regional regulations that include stipulations based on legacy technologies, e.g. the obligation to provide a minimum set of services in line with the concept of “universal service”. When implementing such services using the IMS platform, these services place additional requirements on existing IMS standards.
    • Different IMS implementations: For interconnection between two operators, service limitations may arise when establishing a phone call from one operator to another. For example, some IMS implementations do not support the P-Early Media Header and the PSTN XML schema. In this regard, ISDN services cannot be provided between interconnected operators due to limitations of the transmission of ISDN Specific parameters. As a result, there are some restrictions of rendering voice announcements and double ringing tones.
Fixed network operators must therefore tune their IMS platform to such requirements and upload necessary updates (patches) into the embedded IMS software. This is a very costly, time-consuming process, which must be performed by every operator implementing the IMS platform.