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APRS and Igate
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Bill Horne wrote: Gary, AX.25 is the protocol that was used for packet transmission on ham radio when I was using packet: I assume it's still the standard, since Linux still has the option. Yes, it is. It's showing its age but is still in use. It might help you to think of it as TCP/IP with ham calls signs added. I think it's more proper to think of it as a lower-level protocol... more like Ethernet, with callsigns taking the place of Ethernet MAC addresses. AX.25 can transmit its own style of datagrams, or data streams (analogous to UDP and TCP respectively), and it can also carry IP packets (and thus TCP and UDP). If the Windows-based software is free, reliable, and meets your needs, and you already have a Windows-based PC you're willing to dedicate to an Igate, then you can certainly use that. However, I find Linux to be an excellent substitute for Windows, especially for "single function" machines such as a BBS or packet gateway. Linux is also able to run on much older hardware than Windows, and (most importantly) offers native support for the AX.25 protocol stack, allowing full use of higher-level applications without modification: to Linux, AX.25 and TCP/IP are just two different MAC layers. Yup. 'Tis a definite advantage. Once you've cut your teeth on handling a single AX.25 hookup on a Linux system, you can (if desired) expand to running a whole stack of AX.25 ports on the same system, with the same applications... doing AX.25 routing, running a BBS, and so forth. There are at least four ways to run ham packet on Linux: - A full-powered TNC (like a PackRatt or a TAPR or MFJ TNC-2 or clone), connected via a serial port - just like Windows. In this arrangement, the TNC itself handles the full AX.25 protocol, and you talk to it (via Linux) using a terminal emulator. - With a TNC (full-featured or limited function) in "KISS" mode. In this mode, the TNC handles the over-the-air transmission and reception of packets, the Linux kernel handles all of the higher- level AX.25 protocol support, and Linux applications provide the connection management, BBS capability, etc. - With a sound-card interface and a "soft modem" application. There's no separate TNC - Linux uses the CPU (as a DSP, in effect) and sound card to implement a modem, which then registers itself with the Linux kernel as a "KISS" TNC... everything above this point is just like the previous approach. - Linux kernel AX.25, encapsulated into Ethernet (and then into IP if you want). Good for connecting together multiple packet nodes into a network via the Internet. You can run two or more of these approaches on the same Linux system at the same time, if you wish. Not to mention that Linux is free-as-in-speech, and the license says so. And also very close to free-as-in-beer, if you're already paying for a broadband connection through which you can download it. With Linux you can also see the source code to the full software stack (which can be very good at times, and can also cause you the screaming horrors occasionally) and make changes if you wish. In fairness, Windows also supports at least three of these modes (full TNC, KISS TNC, and sound-card "softmodem TNC"). I don't know about Ethernet/IP encapsulation of AX.25. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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