HF Packet radio

Discussion in 'Working Different Modes' started by KO4GA, Jul 11, 2010.

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  1. K8LEN

    K8LEN Ham Member QRZ Page

    HF PACKET

    HF PACKET..widely used...net105..14.105 is active...download multipsk for hf packet works great..

    POB/K8LEN
     
  2. AG3Y

    AG3Y Guest

    My impressions about HF packet, which I formed many years ago, were
    1. the paclen was always too long. If the entire packet wasn't received correctly by the receiving station, the entire thing had to be transmitted again. Always led to many delays.

    2. the delay between packets was always either too long, or too short ! "How can that be?" you say. Well, stations either sent their packets too rapidly, and would force everyone else to stand by with no sharing of the frequency as a result, or have their delay set so long that other stations would jump in with their packets, and force the original station back into a standby mode. Packet was designed so that multiple stations should be able to be on one frequency at the same time. The packet delay parameters were never coordinated, usually ending up in a jumble of stations trying to transmit nearly simutaneously!

    3. Retrys were excessive. A station would continue trying to send packets long after the band had gone kaput, resulting in a lot of excessive worthless transmissions, doing nothing but cluttering up the air !

    There are other things that caused problems with HF packet, but those are some of the outstanding ones that I can remember. Packet can and does do a fine job on a frequency where it is the almost exclusive user of the frequency, but on a shared band, with lots of QRM/N occuring at the same time, it just doesn't fill the bill.

    JMHO 73, Jim
     
  3. KC2UGV

    KC2UGV Ham Member QRZ Page

    Um, Jim. Packet uses CSMA/CA (Carrier Sense Multiple Access With Collision Avoidance)... It's made for shared bands and channels.
     
  4. NN4RH

    NN4RH Premium Subscriber QRZ Page


    Someone forget to tell QST magazine. If HF Packet is dead, then someone goofed putting that article about HF packet in the September issue.
     
    Last edited: Aug 15, 2010
  5. AG3Y

    AG3Y Guest

    Ummm, Corey, that is exactly my point. There were always too many collisions, and retries, and no-one seemed to be able to work out a timing scheme so that usually one station would end up "hogging" the frequency, forcing all the other stations to stand by.

    See my 2nd point. Believe me, I worked with Packet for a couple of years, and I KNOW how the system is supposed to work. Unfortunately, it never seemed to !
     
  6. KC2UGV

    KC2UGV Ham Member QRZ Page

    There is no "timing scheme" with CSMA/CA. If a station attempts to transmit and has a collision, both stations back off a random period and try again.

    If the channel is full, then it's full. That's not a problem of the mode, but rather the channel bandwidth. It's like the good ole days before switches when everyone had hubs.

    The throughput would drop off exponentially with each new node added. Because all nodes were using the same media. Once switches came onto the playing field, that was fixed.

    So, now, all we have to do is work out separate "cables" (ie channels) for stations, and somehow allocate who uses which one.
     
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