RFC_ERROR_COMMUNICATION between Portal and R/3 backend

We are experiencing periodic JCOExceptions with RFC_ERROR_COMMUNICATION from our Portal to the backend R/3 system that state "A connection with the remote socket was reset by that socket". Can anyone provide some background on "RFC_ERROR_COMMUNICATION" issues. I realize that the exception is a blanket error for any network-related drop in communication that may happen during the conversation between the host and partner but how do I go about diagnosing and troubleshooting. When the issue occurs for the client they typically can close the browser and open a new session and the problem goes away. There have been times where we see the problem so frequently that the result is we have to restart our j2ee engine on the portal, but those are rare and the problem tends to only be an annoyance for the client. Has anyone experienced similar issues with communication from their Portal to the backend R/3 system and if so what changes, if any, were utilized to resolve what you saw. Any help would be appreciated. Thanks!