The Service Specific Connection Oriented Protocol (SSCOP) is used in the Signaling ATM Adaptation Layer (SAAL), it can also be used in end-to-end user data transfer. However, the flow control algorithm of SSCOP has ot been defined in the specification. In this work, we propose a rate-based flow control approach for use in SSCOP, named RB-SSCOP, which provides an end-to-end reliable data transfer over ATM UBR service. The goal of the flow control approach is to achieve a stable, fairness and high-throughput by maintaining the bottleneck queue occupancy at a predefined level. We derived control rules through the analysis of SSCOP operations. Two basic mechanisms, Bottleneck Rate Probing (BRP) and Bottleneck Queue Occupancy Estimation (BQOE) used in the control rules are proposed. The former probes the service rate and the latter estimates the per-vc queue occupancy. The simulation results of BRP, BQOE and RB-SSCOP are presented and discussed.