This Recommendation specifies the signalling protocol for ATM Traffic Descriptor modification with negotiation for the Broadband Integrated Services Digital Network (B-ISDN) at the TB reference point or coincident S, and T, reference point (as defined in Recommendation I.413 [i]) by means of the Digital Subscriber Signalling System No. 2 (DSS 2). This Recommendation extends the ATM Traffic Descriptor modification capability specified in Q.2963.2 to support the traffic parameter negotiation which is equivalent to that specified in Q.2962. In addition, this Recommendation specifies the protocol requirements at the T, reference point where the service is provided to the user via a private B-ISDN. The capability described in this Recommendation enables the connection owner to modifi the ATM Traffic Descriptor with negotiation for caWconnections that have already been established. This Recommendation specifies the procedure of the modification with negotiation of PCR, SCR and MBS using either an Alternative ATM traffic descriptor information element or a Minimum acceptable ATM traffic descriptor information element. ATM Traffic Descriptor modification with negotiation is applicable to all connection oriented telecommunication services that are based on single point-to-point calls/connections. The ATM Traffic Descriptor modification with negotiation for point-to-multipoint calls/connections is outside the scope of this Recommendation. This Recommendation is applicable to equipment, supporting ATM Traffic Descriptor modification with negotiation, to be attached at either side of a TB reference point or coincident SB, and TB reference point when used as an access to the public B-ISDN.