Rule#2: All links are Dedicated Point to Point Links.
Note: See also FAQ-HTS
, FAQ-Networking On Purpose
Going to faster bit-rates doesn't get rid
of Hidden Transmitter Syndrome.
Faster rates just makes collisions less likely with any given user and traffic volume.
- There are several problems which have caused very bad packet performance in
the past. Almost all of those problems either go away entirely or are much more
trivial to address if there are only two stations on every link.
- These are issues which need focus:
- Collisions leading to retries;
- Stations transmitting too frequently;
- Stations transmitting when another station
outside their range is already transmitting, causing loss of data;
- Station is weak to some stations, or station is heard by one or more other stations they
cannot hear, causing asymmetric links to occur, leading to timeouts and link failures;
- Station is in a position where it hears multiple LANs and because the station detects
carrier often, due to overlapping activity in the multiple LANs, the station is unable
to transmit, causing other stations to time out. This is
called Exposed Receiver Syndrome.
- Bad timing adjustment which is only noticeable at some stations on the channel;
- Audio levels or deviation settings which cause loss of data at some stations on the channel but
- Division of network bandwidth in order to counter channel overload, causing
a link to be very slow relative to the bit rate;
- Desire to upgrade a link is thwarted by inability to upgrade all participants on
the channel at the same time.
Any system which has hidden transmitters will begin to fail as the traffic
load from hidden stations exceeds between 10% and 20% of the available bandwidth.
Once the traffic reaches that level of saturation, collisions will result in
retries, which increases the traffic. Once that chain of events begins, the
channel will saturate and links will begin to time-out, resulting in what
appears to be a catastrophic network failure to most of the involved users.
The correct way to adapt to hidden transmitter syndrome is to address
it head-on by making sure everybody sets PPersistance
correctly, taking account of the maximum number of stations on frequency.
Everybody has to set their parameters correctly. Doing this
correctly could stave off catastrophic increases in retries and eventual
disconnection. This also results in a channel which is operated at a
fraction of the apparent bit rate. Cooperating on parameter setting to
make an artificially slow network isn't human nature. We cheat. This
will cause bad blood, bad performance, bad ham radio.
Rule = Design all links to be collision free.
At this time that means point to point links. See FAQ-Networking On Purpose.
At some point we'll create polling or other access control environments which are collision free.