Using the Wisconsin Network - Part 39

by Any Nemec, KB9ALN

In this part of our series, we will take a look at a different way to network in Packet Radio - Flexnet.

Flexnet is a digipeater-based method of networking nodes, somewhat similar to "Net/Rom", which is used extensively in Wisconsin. Although I am not aware of any Flexnet digipeaters operating in Wisconsin, it is interesting to look at other networking options. Flexnet comes to us from Germany, and was developed nearly 10 years ago. It enjoys wide popularity in Europe. but has not caught on much here in the U.S.

Some may be wondering why Amateur Packet radio should use digipeaters - after all, they are inefficient and one missed packet can translate into several retries on a marginal path. With normal AX.25 digipeaters, this is indeed a probability. Flexnet, however, operates differently than digipeaters that you may be accustomed to. Packets are acknowledged over every step of a multiple-hop link. This makes for a reliable connection over several digipeating "nodes". The mechanism used to acknowledge packets is different than Net/Rom, and far more reliable (according to it's proponents). The end-to-end acknowledgment of basic, unenhanced digipeating is gone, along with it's problems.

Flexnet is AX.25 based, and has the ability to digipeat TCP/IP frames that are encapsulated in AX.25. Net/Rom does not have the same ability to carry TCP/IP - when forced to, it will, but very poorly. A thought may have occurred when comparing Flexnet with Net/Rom. Does a packet operator have to know the call-signs of every digipeater in the connection path? No, Flexnet is autorouting. In other words, it knows if it can get to a distant digipeating node, and which route to take in order to get there. All you need to know is the call-sign of the station you wish to connect to, the call-sign of the local digipeater (node), and the call-sign of the distant digipeater. From there, routing is automatic - the network knows the way.

The down side is that operators will not have the easy node aliases to remember - Flexnet seems to operate with call-signs only. It may be possible to use an alias as a call-sign, but the authors do not mention this in their introductory documentation.


One very attractive feature of Flexnet is compression - all packets sent between Flexnet Digipeaters are compressed to save bandwidth. This helps with speed - Flexnet spends a lot of time acknowledging packets between it's digipeaters. That acknowledgment makes for it's good reliability, and the compression is needed to make this operation speedier than it would normally be.

As was mentioned before, it acknowledgment method is different than Net/Rom. This means that "hung" Net/Rom connections would be a thing of the past. Connections across state lines with multiple digipeating "nodes" is theoretically possible (if enough nodes exist to make a path). It's authors say it is possible to make a connection across Germany and into other countries solely with RF based nodes. It should be noted though, that Germany and most of Europe enjoy an abundance of network nodes, so this more than anything makes this possible. However, it does effectively show that we can overcome the Net/Rom restriction on the number of links. And it also shows us that Flexnet is a workable networking system in a crowded packet radio environment.

Flexnet is not limited in it's architecture in most ways. It is capable of operation at both 1200 bps and 9600 bps. It is capable of multi-port operation, so it is possible to incorporate it into a LAN/backbone "node stack" setup. It should be noted that there are some serious hardware considerations that we will explore later on.

And one appealing feature certainly is cost - there is none. It is available through the Internet on the author's home page.


There are a certain number of drawbacks to Flexnet, and they would certainly have a bearing on it's implementation. While the software is free, a node operator may well have to make it all up with hardware.

The most common implementation involves a number of PC Packet cards, installed in a personal computer devoted to the task. It is possible to use a KISS TNC with Flexnet, but all of the Flexnet capabilities are generated in software. As of this writing (and this may be subject to change soon), there is no plug-in TNC-2 firmware chip that has Flexnet capabilities. So, a computer has to be used to perform the actual Flexnet operations. And based on experience, an 8088 may not be fast enough to do the trick in a multi-port "node-stack" type of setup. Now that 486 computers are getting fairly inexpensive on the used market, this may be less of problem than in years past. However, most node sites are remote and "unattended". One may go through more than a few 486 computers in a good lighting season!

TCP/IP operators may have an interesting time with Flexnet. The main difference between it, and say, an X-1J node is that it reverts to a "Virtual Connection" mode rather than a "Datagram mode". This means you will have a particularly difficult time with timing parameters like IRTT, for one.

The most significant drawback to Flexnet may be the very thing that may make it desirable - it is different. This means that any part of the network using it would not easily interface to a different network. Even if a large commitment to "change over" network software was agreed upon, there would be gaps in coverage while the changeover was taking place. Some may consider it a nuisance, others (like Emergency Coordinators) may look at changeover coverage gaps as a real handicap, temporary or not. In short, a changeover of this nature (Flexnet or some other system) would not be entirely painless.

Is Flexnet a workable networking option in Wisconsin? Only real working experience will truly tell if it is. It may appear not, simply because our neighbors would certainly have a tough time interfacing with us. Add to that the fact that there is no support for it in MSYS (the BBS software of choice in Wisconsin) as well as other popular Host TNC programs, and the deck is somewhat stacked against it.

With the continuing incorporation of the Internet into packet radio, it would seem most likely to use TCP/IP as a networking protocol. However, there are some elements of Flexnet that certainly can be incorporated in some kind of radio adaptation of TCP/IP. So it is certainly worth testing, for those of you who are interested in digital networking. So if you are hardy digital experimenter, research it via the World-Wide-Web and check it out yourself. Find out what others have to say about it and try it.

On to Part 40 - What is TNOS/Linux and do I need it?

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