Final answer:
A reliable message-passing facility guarantees delivery if possible, but cannot guarantee delivery in all situations due to various factors.
Step-by-step explanation:
A reliable message-passing facility is one that guarantees delivery if possible. This means that the facility does its best to ensure that messages are successfully delivered to the intended recipient.
In the context of computer networks and communication protocols, a reliable message-passing facility often uses techniques such as acknowledgments, retransmissions, and error detection to ensure that messages are delivered accurately and in order. For example, the Transmission Control Protocol (TCP) is a reliable message-passing protocol used in the Internet.
However, it's important to note that while a reliable message-passing facility strives to deliver messages, it cannot guarantee delivery in all situations. Factors such as network failures, congestion, or hardware issues may still prevent the successful delivery of messages.