Netrom link quality

Hier onder een stukje wat ik tegen kwam in het bbs, het gaat over de quality van een netrom link. Geschreven door John G8BPQ.

Quality isn’t measured. It is assigned by the sysop to a Netrom link,
and calculated by the node for a Netrom route. In this context a link is
the path between two adjacent stations, and a route is a path between
two stations over one or more links.

Quality doesn’t necessarily define how “good” a link is. It is used by
the software to select the route to use when more than one route exists
between two nodes. Desirability would be a better term. While this may
be related to how good the link is it might include other factors (eg
give preference to RF links and only use Internet links as a backup if
the radio link fails). It is expressed as a number between 0 and 255.
When a route is over two links, the route quality is calculated by
multiplying the link qualities together and dividing by 256. So for two
links of quality 192 the route quality is 144.

The “standard” default quality is 192. You might change this if you
had two links between two stations (maybe a UHF trunk link and a VHF
user link). By assigning a higher quality to the UHF link traffic would
be routed over it and would only use the other if the first failed.

The Netrom routing mechanism was designed to be self learning, building
routing tables from broadcasts heard from other nodes. This can work
quite well, but only if you don’t have any one way paths. If you can
hear a node but not connect to it the system simply doesn’t work. It
sounds from what you have said that is is what you are seeing. Unless
you deliberately disable the mechanism, BPQ will try to keep a link open
to each node it hears a routing broadcast from, and remove it from the
tables if the link can’t be established (or fails) but in the meantime
the routing entries will be used and may be passed on to other stations.

With your current configuration you will add to your table any stations
you hear a routing broadcast from with a quality of 192. This is a
reasonable starting point if you can connect to all the stations you can
hear. If not, there are two approaches you can use. You can ignore
routing messages from specific nodes that you know you can’t connect to
by adding a locked route with a link quality of zero, or you can set the
PORT QUALITY parameter below MINQUAL, so that nothing is automatically
added, and lock routes to the stations you know you can connect to with
a link quality of 192. The second option requires more active
management, but is likely to give a more stable network.

I’m not sure if this has directly answered your question, but hopefully
will help you understand the issues more.

John G8BPQ

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