----- Original Message -----
From: Riley Williams <[EMAIL PROTECTED]>
To: Richard Bown <[EMAIL PROTECTED]>
Cc: Linux Ham Radio <[EMAIL PROTECTED]>
Sent: 31 July 1999 13:02
Subject: Re: CEPT callsigns
[snip]
> To be honest, the AX.25 specification needs SERIOUS revision in this
> area, to allow for callsigns of any length or pattern to be used.
> However, it needs to be done in a manner compatible with the current
> standard.
>
> My suggestion would be to make it dynamic to suit the callsigns, but
> allow individual callsigns in the address field to be padded with
> spaces. Here's my thoughts on the matter:
>
> 1. The actual callsign bytes in the address have the character
> in the top seven bits of the byte. The following ASCII codes may
> be considered for valid characters in that field:
>
> ' ', '/', '0' to '9', 'A' to 'Z', 'a' to 'z'.
>
> These correspond to the following bit patterns:
>
> ' ' 0100-0000
> '/' 0101-1110
> '0'-'7' 0110-xxx0
> '8'-'9' 0111-00x0
>
> 'A'-'G' 1000-xxx0
> 'H'-'O' 1001-xxx0
> 'P'-'W' 1010-xxx0
> 'X'-'Z' 1011-0xx0
>
> 'a'-'g' 1100-xxx0
> 'h'-'o' 1101-xxx0
> 'p'-'w' 1110-xxx0
> 'x'-'z' 1111-0xx0
ie - bit 0 is clear to say that more info follows...
>
> 2. Each callsign field is followed by an SSID byte, formatted as
> rrrssssf where the subfields are defined as follows:
>
> rrr Reserved for future use.
> ssss SSID for this callsign.
> f Final byte of address flag.
>
> I have a sneaking suspicion that some of the bits in the rrr
> field have been given meaning, but have no details to hand.
ie. bit 0 is set to say this is the end of the address field - by this
means,
AX25 (and X25 on which it is based) already support variable length
address fields.
That most implementations don't support it is another matter entirely!!!
[snip]
>
> Best wishes from Riley.
>
--
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