Re: BUGs into libax25

[Bernard Pidoux <pidoux@ccr.jussieu.fr>]

Hi,

Sorry, I wrongly wrote 6 letters callsigns where I wanted to say 6 
characters. Not the same of course.
My typo leaded to an interesting discussion.
Somedays I dreamt that we could increase the SSID number up to 31.
But the necessary bytes are already taken by DAMA protocol and EAX25 flags.

Back to the bug.
With previous loop limit (<6) into the code, a callsign like KD4YAL-8 
would not be correctly translated into shifted ASCII AX25 code.
Actually, with this 6 characters callsign, SSID was truncated and an 
error message sent complaining about SSID not being correctly entered.
I had seen it very often in FPAC. I am glad I found the error while 
investigating on other bugs.

73 de Bernard, f6bvp

Matti Aarnio a écrit :
> On Mon, Jun 02, 2008 at 11:36:25AM +0200, DL5DI wrote:
>   
>> This special event station callsign that we sometimes find like
>> DQ2008ANYEVENT will never work in packet radio.
>> The protocol header of ax25 frames only allows 6 bytes of callsign and 1
>> halfbyte of SSID.
>> Not only for the destiantion, also for all digipeaters inbetween.
>> We would need to change the whole protocol and all digipeaters and stations
>> using it worldwide to get that covered.
>> I expect that packet radio will be dead before that happens. :-)
>>     
>
> Arbitrary long callsigns...   Only OSI stack can handle that, and even it
> has some upper limits on address lengths.
>
> On IPv6 the addresses are 16 bytes long, and low 8 bytes (64 bits) of them
> are reserved for "link local" use.    Considering that..  one can encode
> any callsign with 38 characters, add couple codes for things like
> "no character here", and "next is ssid", that would be 40 codes.
> Using 6 bits per character one could encode 10 characters + 4 bits on IPv6-
> address "local half".  With arithmetic encoding (see APRS mic-e) maybe
> 17 code bytes.
>
> Would that be AX.25 ?  Definitely not.  That would be IPv6.
>
> On IPv6 the basic assumption is that link local area is /64 size slice,
> and thus "AX.25 space" would be something smaller..  like  /32.
>
> How could we implement smooth transition from AX.25 to IPv6 on data links ?
> Very good question...  old legacy junk will want to live a long time.
> (we are way too willing to recycle obsolete hardware...)
>
>   
>> 73 de Hans, DL5DI
>>     
>
> 73 de Matti, OH2MQK
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