| |
VK2RQ > SYSOP 22.12.12 07:16l 91 Lines 3622 Bytes #999 (0) @ WW
BID : 941_VK2RQ
Read: GUEST
Subj: Re: UDP Forwarding I'm confused?
Path: IZ3LSV<IW0QNL<JH4XSY<F1OYP<PI8SNK<VK2DOT<VK6ZRT<VK2RQ
Sent: 121222/0604Z @:VK2RQ.#SYD.NSW.AUS.OC #:941 [Sydney] $:941_VK2RQ
From: VK2RQ@VK2RQ.#SYD.NSW.AUS.OC
To : SYSOP@WW
Hi Tubby,
You probably know that packet is based on a protocol called AX.25.
Normally this is carried over the air using an FSK modem. However,
it is possible to transport AX.25 frames using other forms of
transmission besides HDLC streams over radio.
One such method is to transport the AX.25 frames in UDP/IP
packets. UDP (User Datagram Protocol) is a transport protocol
that sits on top of IP (Internet Protocol), which is the basis
of the Internet. UDP is a connectionless, unreliable transport,
and is well suited to the transport of AX.25 frames which are
designed to be carried over unreliable radio links. If you
set up an AXUDP tunnel over the internet, then you can
transport AX.25 frames from one packet station to another,
just as if they had been transported over the air.
Why is this interesting? Well, it means that you can access
a remote packet station over the internet in the same way as
you would access it over the air. You can connect to Net/Rom
nodes, DX Clusters, BBS systems, etc.. This makes it very
close to what we do over the radio, and you can even make
a NET/ROM connection which consists of a mix of radio and
AXUDP links, transparently to the end user.
Because we can connect to a BBS over AXUDP in the same way
as we connect to it over the air, we can do FBB forwarding
over those AXUDP links, just the same as we do it over radio
links. Here is the protocol stack we use for AXUDP:
+----------+ +----------+
| BBS | | BBS |
+----------+ +----------+
| ^
V |
+----------+ +----------+
| FBB Fwd | | FBB Fwd |
| protocol | | protocol |
+----------+ +----------+
| AX.25 | | AX.25 |
+----------+ +----------+
| UDP | | UDP |
+----------+ +----------+
| IP | | IP |
+----------+ +----------+
| Ethernet |-------------->| Ethernet |
+----------+ +----------+
Compare that to using telnet forwarding:
+----------+ +----------+
| BBS | | BBS |
+----------+ +----------+
| ^
V |
+----------+ +----------+
| FBB Fwd | | FBB Fwd |
| protocol | | protocol |
+----------+ +----------+
| TCP | | TCP |
+----------+ +----------+
| IP | | IP |
+----------+ +----------+
| Ethernet |-------------->| Ethernet |
+----------+ +----------+
It is very similar, except that there is no AX.25 involved,
and so we can't do other activities that depend on AX.25.
To set up AXUDP, you need to open a UDP port on your firewall,
in the same way you had to open a TCP port on your firewall
to allow telnet. Normally for AXUDP we use port 10093, but
you can choose any available port you like.
I am running linux for my system, so the operating system
has native support for AX.25, which is very convenient.
If you run another operating system link Windows, then
you need to use some other software to provide an AX.25
stack, for example BPQ32, XRouter32, etc.. Others who are
running such configuations would be in a better position
than I to advise you on how to set that up.
This post has been a bit lengthy, but hopefully it helps
explain a bit what this AXUDP is all about.
73, Matt VK2RQ
Read previous mail | Read next mail
| |
