There are several reasons you may wish to configure UUCP over TCP/IP. Some sites do not provide ftpd or rshd servers and/or their respective clients, ftp and rcp. Thus transferring files across a TCP/IP network is not an option with these systems. Additionally, some versions of TCP/IP do not provide the Simple Mail Transfer Protocol, SMTP, for mail transfer. In these cases, setting up UUCP to use TCP/IP may be an option to allow both file transfer and exchange of mail between such systems.
In the following paragraphs, the word ``client'' refers to a system that executes the uucp or uux command, while the term ``server'' or ``listener'' refers to a system that responds to a request from a client system.
There are two approaches to configuring UUCP over TCP/IP: the TCP socket interface and TLI/XTI (Transport Layer Interface and X/Open Transport Interface).
The server system uses the inetd superserver to listen
for incoming uucp requests on TCP port 540. When
receiving a request from a client uucico process, the
server system forks the uucpd daemon, which logs
in the client with the shell uucico. The two uucico
processes can then transfer information similar to the
way they would in a standard serial line configuration.
The server system uses a process called listen to wait for requests from a predefined TCP port and then when receiving a request, forks a uucico process directly, bypassing the standard UUCP login sequence.