AUTOQUAL(9) XR32 REFERENCE MANUAL 7/2/2013
NAME
AUTOQUAL -- Automatic Route Quality.
DESCRIPTION
Automatic Route Quality Measurement" (Autoqual) is an optional
tool to help sysops set consistent and meaningful NetRom route
qualities.
Background
~~~~~~~~~~
NetRom makes routing decisions based on a fairly arbitrary
metric, i.e. the "route quality", which is assigned by sysops,
and disseminated in nodes broadcasts.
In the better-managed parts of the NetRom network, route
qualities tend to be assigned according to the baud rate of
the link, with adjustments for retry rates, duplex / simplex
and shared channels.
However, there is no standard methodology for assigning
quality, so not only will each sysop's notion of quality
differ from that of other sysops, but also he will probably
incorrectly assign the relative qualities of his own links.
This leads to inconsistency and distorted routing.
In other parts of the network, route qualities are simply
assigned to 192 regardless of how good or bad the link is.
This also leads to inconsistency and less-than-optimal
routing decisions.
The actual "goodness" of a link may continually change with
atmospheric conditions, data throughput, other channel
activity, QRM etc. At certain times of day for example, it
may be better to use an alternative link.
A more accurate notion of "goodness" is simply the "Round
Trip Time" (RTT) for the link, i.e. the time taken to send a
packet and get a reply. After all, this is what *really*
matters to users. A link which responds quickly (i.e. with a
low RTT) is perceived by users to be better than a link which
responds slowly. The RTT will track changes in retry rate,
channel loading etc.
The RTT can be easily and consistently measured by software
on a continuous basis, thus the "goodness" of the link is
accurately known at all times, and all routers of the same
type will give comparable values independently of the sysop's
notions of quality.
Implementation
~~~~~~~~~~~~~~
XR32 continually measures the RTT of neighbour links and uses
the smoothed value to calculate a notional "route quality"
every 5 minutes. The maximum, minimum and standard deviation
of this quality are calculated and recorded for later display,
and the value is further smoothed.
The smoothed calculated quality is displayed by the "R Q"
command, and can either be used as a guide to allow the sysop
to fix the RQ at a sensible value, or if the route has been
configured for it, XR32 can use it dynamically, by setting the
route's quality to the calculated value.
This RTT to quality conversion is tailored to the British
notion of quality, which gives somewhat lower but more
meaningful qualities than used elsewhere. For example, a
typical 1200 baud half-duplex link with low retry rate would
produce a calculated quality around 120. A good 9600 baud half
duplex link would equate to around 190, with 210 for a really
good full duplex 9k6 link.
RTT measurement primarily uses L3RTT frames, but in their
absence it also uses measurements of traffic throughput and
retry rate.
Enabling Automatic Route Quality
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Route quality calculation is automatic and continuous.
However the calculated value is not actually used without the
sysop's consent.
In order to allow the route quality to be automatically
adjusted, the sysop must specify a RQ between 256 and 511
when adding a route using the "ROUTE ADD" command.
Alternatively, setting the PORT quality between 256 and 511
will cause all *new* routes (not locked in ones) learned on
that port to use automatic quality.
A quality between 256 and 511 will instruct XR32 to use
"automatic" quality, with an initial value of (qual-256).
SEE ALSO
ROUTES(1)
QUALITY(1)
AUTOQUAL(9) END OF DOCUMENT
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