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This International Standard specifies the signalling protocol for the support of the Transit Counter additional network feature (ANF-TC) at the Q reference point between Private Integrated Services Network Exchanges (PINXs) connected together within a Private Integrated Services Network (PISN).

ANF-TC is a feature that limits the number of Transit PINXs that a call setup request may be routed through e.g., to protect the network against indefinite looping.

The Q reference point is defined in ISO/IEC 11579-1.

Service specifications are produced in three stages and according to the method specified in CCITT Recommendation I. 130. This International Standard contains the stage 3 specification for the Q reference point and satisfies the requirements identified by the stage 1 and stage 2 specifications in ISO/IEC 15055.

The signalling protocol for ANF-TC operates in association with the signalling protocols for basic circuit switched call control (as specified in ISO/IEC 11572) and call independent (connection oriented) signalling connections (as specified in ISO/IEC 11582).

This International Standard also specifies additional signalling protocol requirements for the support of interactions at the Q reference point between ANF-TC and other supplementary services and ANFs.

This International Standard is applicable to PINXs that can interconnect to form a PISN.