Anyone supplying an answer would be guessing...you haven't really provided much detail.
- Are the clients that submitted the request waiting, on the same socket, for a reply? Or is it fire-and-forget?
- Is the FIFO requirement literal, as in, request #2 blocks until request #1 is fully completed...even if it could be run in parallel? Even if the two requests came from different connected clients?
- How large are the requests (bytes), and response (if there is one)?
- As mentioned in another reply, are the clients on a local LAN or remote? Is cleartext okay? Do the clients need to authenticate?
- Are the clients cell phones? web browsers? Something else?