[ax25-layer2] Layer 2 Digipeating

[pete at ae5pl.net]

You are correct, routing and general networking is a layer 3 or higher
issue.  However, repeating is a layer 2 or layer 1 issue (in this case
layer 2) and is not a duplication of layer 3 networking.  In fact, you
make a very important point that I was trying to make and that is that
digipeating is _not_ layer 3 networking and that all attempts at making
it so have failed.

Keep in mind that AX.25 is not "pure" from the ISO standpoint (the
definition you are basing your layer 2 requirements on, by the way, post
dates AX.25).  To remove functionality in the AX.25 protocol for the
sake of keeping up with the current ISO definition is, IMO, a mistake.
It has been said that callsign-SSID is not a MAC address.  True, it is
not the same MAC address used in the Ethernet specification.  However,
the Ethernet MAC address can be changed (look at most NAT router
configurations today) which takes it out of the realm of being hardware
specific.  The same is true for callsign-SSID.  It was intended to
identify specific devices (up to 16 SSIDs) on a channel operated by the
same control operator (callsign).  This is, in fact, the equivalent to a
MAC address.  It is not generated by layer 3 but instead is resident in
the layer 2 device.

Amateur radio communications many times requires repeaters to obtain
reasonable coverage.  This is the purpose of the digipeater fields in
AX.25.  As you point out, however, networking those digipeaters is _not_
the purpose of the digipeater fields.

73,

Pete Loveall AE5PL

> -----Original Message-----
> From: Glenn Thomas
> Sent: Friday, September 16, 2005 11:06 AM
> To: Discussion of Link Layer use of AX.25
> Subject: Re: [ax25-layer2] Layer 2 Digipeating
> 
> Routing and general networking is a layer 3 (or higher) 
> issue. What is the point of complicating layer 2 with 
> something that is properly part of layer 3? Put the 
> networking stuff in layer 3 where it belongs. It's not clear 
> why duplicating it in layer 2 will provide any advantage.
> 
> The only other layer 2 issue is hardware addresses (a la 
> etherNet), which is a complication we don't need.
> 
> The only AX.25 layer 2 changes I can see would be to save 
> some small amount of bandwidth by removing the existing 
> digipeat capability completely and leave networking issues to 
> layer 3. That would degrade
> AX.25 capabilities that have proven to be useful in the name 
> of ISO-purity. This would not be worth the effort.
> 
> 73 de Glenn wb6w