Книга: Linux Network Administrator Guide, Second Edition

Communications Software for Modem Links

Communications Software for Modem Links

There are a number of communications packages available for Linux. Many of these packages are terminal programs, which allow a user to dial in to another computer as if she were sitting in front of a simple terminal. The traditional terminal program for Unix-like environments is kermit. It is, however, fairly ancient now, and would probably be considered difficult to use. There are more comfortable programs available that support features, like telephone-dialing dictionaries, script languages to automate dialing and logging in to remote computer systems, and a variety of file exchange protocols. One of these programs is minicom, which was modeled after some of the most popular DOS terminal programs. X11 users are accommodated, too. seyon is a fully featured X11-based communications program.

Terminal programs aren't the only type of serial communication programs available. Other programs let you connect to a host and download news and email in a single bundle, to read and reply later at your leisure. This can save a lot of time, and is especially useful if you are unfortunate enough to live in an area where your local calls are time-charged. All of the reading and replying time can be spent offline, and when you are ready, you can redial and upload your responses in a single bundle. This all consumes a bit more hard disk because all of the messages have to be stored to your disk before you can read them, but this could be a reasonable trade-off at today's hard drive prices.

UUCP epitomizes this communication software style. It is a program suite that copies files from one host to another and executes programs on a remote host. It is frequently used to transport mail or news in private networks. Ian Taylor's UUCP package, which also runs under Linux, is described in detail in Chapter 16, Managing Taylor UUCP. Other noninteractive communications software is used throughout networks such as Fidonet. Fidonet application ports like ifmail are also available, although we expect that not many people still use them.

PPP and SLIP are in between, allowing both interactive and noninteractive use. Many people use PPP or SLIP to dial in to their campus network or other Internet Service Provider to run FTP and read web pages. PPP and SLIP are also, however, commonly used over permanent or semipermanent connections for LAN-to-LAN coupling, although this is really only interesting with ISDN or other high-speed network connections.

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