I believe you were referring to a discussion similar to this one: How to Decide Number of Agents. There might be a blurred line between a port and a functional interface. An interface serves as a communication channel. Depending on the protocol it supports, a channel can support either one-to-one or many-to-many connections. An agent typically represents one end of a connection. However, in some cases, a single agent may control multiple connections if they are tightly coupled. For instance, when dealing with dual-port RAM, you may to have an agent for each port.