Discussion on:

Port to port network traffic

Hi All, I never had to worry about nitty gritties of Data Networks as I always had experts to do it for me. I am just trying to understand how network traffic travels to destination on a specific port. The reason I ask is:
We have recently put a SSH server in place for file transfer replacing our FTP server for obvious security reasons, this server is allowed to accept traffic on port 22. But one of our prominent clients is not willing to accept this change as they are not allowed to open port 22 on their firewall and requesting us to keep port 21 open, which is against our security policy. Please help me understand
1. Is there a need for the client to open port 22 at all?
2. Does the outbound traffic bound to a specific port has to pass through the same port on the source firewall?
3. What alternatives can be followed?

Thanks in advance