In this paper, we present a novel protocol called MUST (multicast synchronous transfer) which offers multicast file transfer service to the application layer. Synchronism is one of its attributes since MUST guarantees that all clients are receiving the information at the same time. For an efficient bandwidth utilization, MUST transmits IP packets by using multicast addressing. Also, it achieves a notable acknowledgement packets reduction by an appropriate mechanism. Thus, MUST can be employed in both LAN and intra-campus scenarios. Flow control and error recovery algorithms are also developed to satisfy features such as reliability, high throughput and low delay. To evaluate the protocol, we first implement an application based on it, that we test in a lab with up to ten computers. Secondly, we develop analytically its most important parameters and we compared them with real measures.