Outgoing links from automatic and manual dialup endpoints use the UUCP facilities to select how the link is made. Usually the link is established via the telephone network using modems attached to both the remote host and the local host.
A dialup endpoint usually specifies the parameter uucp=name in its configuration file, /etc/ppphosts, to identify the remote system to which it will connect. There must also be an entry in the UUCP file, /usr/lib/uucp/Systems, whose ``sitename'' field is name. These two entries for name form the connection between PPP and UUCP. If uucp=name is not specified, then the remote hostname or IP address in /etc/ppphosts is used by default.
If you use the PPP Manager to define the remote system's name, it will edit the /etc/ppphosts and /usr/lib/uucp/Systems files for you.
An important aspect of PPP's use of UUCP is that it implies that the local and remote host may be connected without using PPP. When a link from an outgoing dialup endpoint is brought up, PPP requests a UUCP link to the remote host. UUCP must be able to establish a UUCP link using only UUCP information, such as that found in the files /usr/lib/uucp/Systems, /usr/lib/uucp/Devices, and /usr/lib/uucp/Dialers. During UUCP link establishment, characteristics such as serial line speed and flow control are determined by the UUCP information and not by the PPP link configuration. Once UUCP has established a UUCP link, it informs PPP of the tty being used for the link. At this point PPP takes over the link, and the local host, using the PPP endpoint configuration, may renegotiate link characteristics. Therefore, it is possible to test a UUCP link between the local and remote hosts before trying to run PPP over the link.
PPP can use telephone lines efficiently by dynamically disconnecting if a link is idle for more than a certain time. If additional data must be transferred over the link, PPP can reestablish the telephone connection automatically.
For complete information on configuring a UUCP link, see ``Connecting to other computers with UUCP''.