From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ralf Baechle DL5RB Subject: Re: callsign limit Date: Thu, 1 Jun 2006 16:08:54 +0100 Message-ID: <20060601150854.GA19527@linux-mips.org> References: <200605310927.56706.vk3heg@iinet.net.au> <20060531093716.GA21395@cloud.net.au> <620c90570605310403o1e4b94bcgf4ab922ef26983e4@mail.gmail.com> <20060531111919.GA22980@cloud.net.au> <20060601014047.GB27504@linux-mips.org> <447ED7B2.3070701@sktc.net> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-hams-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Curt, WE7U" Cc: "David D. Hagood" , linux-hams@vger.kernel.org On Thu, Jun 01, 2006 at 07:31:54AM -0700, Curt, WE7U wrote: > Are we still talking about AX.25 here? This is from the AX.25 > version 2.0 spec, published in 1984: May it rest in peace. V2.2 dated 1997 is the latest. > "The characters of the call sign should be standard seven-bit ASCII > (upper case only) placed in the leftmost seven bits of the octet to > make room for the address extension bit. If the call sign contains > fewer than six characters, it should be padded with ASCII spaces > between the last call sign character and the SSID octet." > > So... We only have 7 bits to play with, not 8. I suspect that we > could still play some games though and compress the callsign into > the 42 bits available, plus up to 4 more bits for the SSID if we > wanted to mess with that. Many people like to have more than one > station on the same frequency though (as I do with APRS), so messing > with the SSID too much would be problematic. Perhaps one bit could > be borrowed from there leaving 8 possible SSID's per station instead > of 16? > > There are also two reserved bits in the SSID byte. I didn't check > the later version 2.2 spec (which isn't implemented anywhere as far > as I know) to see if they decided to use those two bits. There may > be some other reserved bits further down the header to use as well. DAMA packs some information into the the unused bits of the SSID field. 73 de DL5RB op Ralf -- Loc. JN47BS / CQ 14 / ITU 28 / DOK A21