How to check if sockets are sending/receiving data on linux?

I often have to debug processes which involve a server client tcp connection. I'd like to check, during times where a client might seem stuck, whether the server is sending it data or not. I can use:

'netstat -tpe | grep PID_SERVER'

to find the socket for the server, or 'netstat -tlpe | grep PID_CLIENT' to find that of the client. Is there a way to further inspect that particular socket once I identify it? Other than just its State? I feel like Recv-Q or Send-Q might be useful though I'm not sure what it refers to - but in addition to that, what else can I use to diagnose what is going on between them? Was thinking, possibly something in /proc/PID/fd?

Any insight would be appreciated...