Client-server application for Windows with Delphi and Indy

I am developing a client-server application (TCP/IP) for Windows using Delphi XE3 and Indy 10, but have some problems that I can not solve by myself. So I need some expert, with advanced knowledge on this subjects (Delphi and Indy), to help me. Here is a overview on how it works: - Server side application will show all connected clients, and I can select some clients on the list and send them commands or streams/files. - Client side application runs hidden to process server commands, and sometimes must send string or stream to server, without request. - On both server and client applications there is a command queue and a process thread (read/write). Once I add a command to queue, the thread sends it to other side. On other side, the thread reads the command and execute it. Problem happens when client and server send commands to each other at the same time. I need to differentiate between overlapping commands and responses, maybe by using framing/multiplexing (this was a tip from a Stackoverflow expert). Thanks!