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[ax25-layer2] 7-byte address proposal

Pete Loveall AE5PL pete at ae5pl.net
Wed Aug 2 19:43:43 UTC 2006

> -----Original Message-----
> From: Samuel A. Falvo II
> Sent: Wednesday, August 02, 2006 11:31 AM
> To: Discussion of Link Layer use of AX.25
> Subject: Re: [ax25-layer2] 7-byte address proposal
> On 8/2/06, Pete Loveall AE5PL <pete at ae5pl.net> wrote:
> > Also, I have seen comments about things like 
> voice-over-packet.  This 
> > is trying to move AX.25 out of layer 2 and writing AX.25 specific 
> > protocols.
> This is not true, and I don't see how or why you would come 
> to this conclusion.  Voice over IP has done absolutely 
> nothing to change IP as a layer-3 protocol -- most VoIP 
> implementations utilize UDP/IP or the new TCSP/IP protocols.

I didn't say it would change AX.25, I indicated that it would be a
protocol written to AX.25 instead of generic.  VOIP uses protocols that
are written expecting the networking capabilities of IP which are not
present in AX.25 (or Ethernet, or any other layer 2 protocol).  I was
pointing out that the focus of this list is to explore ways to make
AX.25 a more generic layer 2 protocol without regard to the applications
written for the protocols above it.  It is not to explore AX.25-specific
applications except to acknowledge that certain requirements of higher
level protocols must be accommodated within AX.25 (such as XID which is
in the 2.2 specification but needs some refining).

> Nonetheless, the use of AX.25 to propegate digital voice 
> cannot be discounted on links with sufficient bandwidth.  QoS 

What transfers on the higher layers is not what this list is all about,
except to understand if there are interface requirements placed on AX.25
at layer 2 to support those higher layer protocols.

> I truely don't see what needs to be changed in v2.2 going 
> forward to v2.3.  The only thing that I would say needs to be 
> "changed" is verbiage telling application developers that 
> certain antiquated modes of use are deprecated and not 
> guaranteed to be functional in an AX.25 v3.0 environment.
> Looking forward to v3.0, the only thing I see that needs to 
> be changed so far is the support for different addressing 
> formats, and maybe support for supporting XID information as well.
> Remember that AX.25 is a layer-2 protocol like Ethernet is.  
> How often does Ethernet change?  :)

AX.25 hasn't changed in 20 years but also has not been utilized as a
layer 2 protocol except in limited experiments.  There has been a lot
learned about networks, layers, etc. in those 20 years and we have the
opportunity to explore those here.  But one thing we must keep in mind
is that our frequencies are shared.  As such, we need to ensure some
sort of backwards compatibility to make sure we don't break the
thousands of AX.25 devices currently in use.  For things like XID, it is
already in the 2.2 document but does require further refinement.  There
is also support for extended packet numbering (modulo 128), extended
packet lengths, etc. which have all been discussed on this list and need
some further refinement.

> Heh, QoS at layer 2 with any kind of frame relay service on a 
> shared bandwidth medium, of which AX.25 over RF falls into, 
> is going to be nearly impossible.  The only reason VoIP works 

I fully understand (but then we have QoS on Ethernet and 802.11 now too,
don't we?).  I mentioned QoS as something that might have to be
considered when looking at the layer 2 and layer 3 interface.  It has
been done before with mixed results in other protocols.  Because this is
a forum on AX.25 as a layer 2 protocol, we should at least ask the
question before trying to write the spec in stone.


Pete Loveall AE5PL

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