• packet radio info

    From Skuz@9:91/1 to All on Mon Mar 7 00:21:00 2016
    From: Tony Langdon
    To: Richard Menedetter
    Subj: Re: TNCs
    Date: 03/07/16 14:54
    Base: Fsxnet General chat

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    Richard Menedetter wrote to Paul Hayton <=-

    There's not too much to tell. I have used a TNC some time ago when my local amateur radio branch ran a packet BBS. I never liked the BBS software that HAMs used but enjoyed the concept of BBS over radio :)

    I have never used one, hence my asking.
    How is the adressing done on packet radio?
    IP addresses probably not.

    Packet radio has its own link layer called AX.25. As the name suggests, it is loosely based on X.25 (more specific the HDLC link layer). Addressing at this level is done using callsigns with the addition of a SSID as MAC addresses. AX.25 supports both connected mode and unconnected (UI) mode. It also
    supports
    digipeaters, which are a fixed list of hops that a packet can take. However, the link is end to end, so the packet has to traverse the entire chain, and
    any
    ACKs have to make their way back, which cam make it slow. Using a network layer on top can be more efficient at handling dropped packets.

    You can use your application directly on top of AX.25, which APRS does, and local BBS connections often do. This requires no more than a TNC (soft or hardware) and a suitable radio.

    However, there are at least 3 network protocols that can run on top of AX.25. The first of these is ROSE. I don't know much about ROSE, except that it's common in VK2 (New South Wales), but not used in VK3 (Victoria - where I am), to my knowledge. I do recall having to know the nearest node to the destination station to make a connection - having to use NET/ROM to get to the state border, then hop on to the ROSE network from there.

    The next network protocol is NET/ROM, which is a firmware addition that can be added to some TNCs, and is available for PCs, initially as a TSR called the G8BPQ Packet Switch, and later in NOS and later again, Linux. Routing in NET/ROM uses RIP like broadcasts of lists of heard nodes with a "quality" factor, which each node uses to build its routing table. Addressing is again done by callsigns. It's also possible to "downlink" from a NET/ROM node to an AX.25 only destination. The routing in NET/ROM was heavily influenced by the quality settings on each node, which could make or break a network. Changing atmospheric conditions could cause non viable paths to linger long after the conditions faded.

    Finally, we come to a protocol we know and love - TCP/IP (these days, known as IPv4). Yes, you could run IP over packet radio, and it worked quite well. Usually, unconnected mose was used on the AX.25 side (analagous to Ethernet frames on a WAN or 802.11 b/g/n on wifi - neither of which are connected
    modes)
    are used at the link layer, and IP sits on top of AX.25. In the DOS days, NOS was the software of choice - practically an OS in its own right that sat on
    DOS
    and offered a number of network services, including telnet, FTP, SMTP, POP and a chat service called ttylink, made available on port 87 of NOS boxes. Later on, Linux itself could be used for IP, though JNOS has been ported to Linux as well, so there's a choice of implementations on Linux. Amateur radio has its own IP net - net 44.x.x.x, which is not routed to the general Internet by default, though some amateurs have advertised parts of this block using BGP to offer public IPs for amateur radio applications.

    The hardest part about running packet radio on Linux is finding up to date documentation, much of the documentation around dates to 2000 or earlier, and the networking stack has changed a bit since then. I wouldn't mind running some IP over ham radio again.

    I am not part of the prepper community, and I do not want to be.
    But I am highly interested in exploring the technical details of packet radio. For other applications than you, but the technical basics should
    be the same.
    It may be also possible to use a HT to transmit/receive.

    I'll have to dust off both my TNC and my memories. :) Or perhaps I can use a spare Pi as a soft TNC. :)

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