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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/Z7TC447CNDLWDYB6KCUY4MOJPFGRJJ4D/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "Z7TC447CNDLWDYB6KCUY4MOJPFGRJJ4D",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/Z7TC447CNDLWDYB6KCUY4MOJPFGRJJ4D/",
    "sender": {
        "address": "ross (a) topwire.co.nz",
        "mailman_id": "d9ef72508cbd4a2b812c57a87b7ef26a",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/d9ef72508cbd4a2b812c57a87b7ef26a/emails/"
    },
    "sender_name": "Ross Whenmouth",
    "subject": "Re: [amsat-bb] ISS ping box (now PBBS)",
    "date": "2016-09-24T01:48:34Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 23/09/16 23:50, [email protected] wrote:\n> Packet BBS operation via space was proved to be entirely inoperable,\n> impossible total congestion,, inefficient, impractical, wasteful and\n> discunctional use of packet via satllites 20 years ago.\n\nYes, connected AX.25 is the wrong protocol for a PBBS on the ISS, and \nCSMA simply WILL NOT WORK when most user nodes can't hear each other \n(aka Hidden Transmitter Syndrome).\n\nMy understanding of PBBS operation is that the vast majority of users \n\"download\" far more data than they \"upload\", and that most of what is \ndownloaded is bulletins (think - large numbers of hams downloading the \nsame content as each other).\n\nUnlike 20 years ago, broadband receivers (and sufficient computing power \nfor demodulation in software) are now affordable - a cheap RTL-2832 \nDVB-T USB dongle (plus preamp, filter, and antenna), can receive a 2.4 \nMHz wide chunk of spectrum on 6m, 2m, 70cm, or 23cm and your PC is \nprobably already fast enough to keep up.\n\n\nSo, I think that a usable ISS-PBBS would be cross-band full-duplex (up \non 2m, down on 70cm or 23cm etc), with asymmetrical bit rates - slow \nuplink(s) which are compatible with ham's existing transmitters (1200 \nAFSK, 9600 K9NG/G3RUH, or maybe even n-QAM or OFDM via SSB?) and a fast \n(broadband) downlink that can be received with cheap equipment (RTL-SDR, \nAirspy, etc). Of course, data compression (LZW, LZMA, Brotli, etc) and \nForward Error Correction would be used.\n\nYes, a high speed broadband TX will require more power than a NBFM TX, \nbut presumably an ISS-PBBS would have a far more generous power budget \nthan a cube-sat.\n\n\"Spare\" bandwidth on the broadband downlink would be used to constantly \nstream PBBS bulletins (and maybe even personal messages when the \nISS-PBBS knows that the recipient is within radio range - see below re \ngrid squares), so that to get the latest messages, all you have to do is \nlisten (no ground station transmission required).\nThus, most users would only need to transmit when they have a bulletin \nor personal message to upload.\n\nI would have the ISS-PBBS co-ordinate channel access - ie ground \nstations only transmit when the ISS-PBBS tells them that they can \n(TDMA). The ISS-PBBS would have to reserve some of the uplink time for \nconnection requests, and there would of course be contention and \ncollisions between ground stations (which can not hear each other) \nattempting to connect. To alleviate this, when the ISS-PBBS hears a \ncollision in the \"connect request\" time slot, it could perform a binary \nsearch of the callsign space (as is done with some RFID systems - this \nhow they cope with multiple RFID tags within range of the reader at the \nsame time).\n\nI think that it would make sense for a ground station's connect request \npacket to include their grid square (Maidenhead locator), so that the \nISS-PBBS (which knows where it is on orbit) knows when that ground \nstation is out of radio range so that it can abandon attempting to \ncommunicate with it. A simple enforcement mechanism (ground station \nsends incorrect grid square) is that the ISS-PBBS would refuse to \ncommunicate with ground stations declaring a grid square which is not \nwithin what the ISS-PBBS considers to be radio range.\n\n\nIn areas of high amateur density, it will probably be more efficient \n(and cheaper) to equip the local terrestrial PBBS with equipment to talk \nto the ISS-PBBS, and then have the hams within the coverage area of the \nterrestrial PBBS use that instead of the ISS-PBBS (this would reduce \ncontention for on the \"connect request\" timeslot of the ISS-PBBS, and it \nwill be more efficient for one PBBS to upload say ten messages to the \nISS-PBBS in one go than it would be for ten different hams to each \nupload one messsage each to the ISS-PBBS).\n\n\nThis would give us global message forwarding that is not reliant on the \ninternet.\n\n\n73 ZL2WRW\nRoss Whenmouth\n",
    "attachments": []
}