The authors investigate the impact of different implementations of an end-to-end transport service on the performance of high-volume data transfers in a local-area network. Of particular interest is the impact of using a connection-oriented logical-link control (LLC) protocol below a connection-oriented transport protocol. The performance measure is the throughput which can be achieved between two stations either from memory to memory or from disk to disk. The throughput was determined by simulation for various combinations of different LLC protocols, disk models, and processor speeds. The parameters for the simulation model were determined partially by measurements of an implemented file server. The results show that the performance penalty of a connection-oriented LLC protocol can be substantial, but can be significantly lowered when an acknowledgment accumulation strategy is applied.