Barox RY-LGSP28-52 Series Operating Instructions Manual page 16

Data flow Path Cost
Data flow
20,000
In the above example, the network consists of two central switches (A+B) and 5 other switches
that form the ring. All in all, 21 cameras have been installed − each supplying 5 Mbit/s of video
data, i.e. a total of over 100 Mbit/s of data.
Scenario 1: Only RSTP is active on all the switches
The switch with the lowest MAC address functions as the master. This may be the smallest
switch in the ring with the lowest CPU performance. The direction of data flow is not known.
In the case of an interruption, the switch-over may take a little longer as this small switch
cannot process the data so quickly.
Scenario 2: RSTP is active on all the switches, switch A has Prio 0 and switch B Prio 4096
In this case, switch A has been defined to assume the role of maste r. If this switch fails,
switch B will take over the role of master. Switch A monitors the ring. Should network traffic
be interrupted, switch A's CPU has enough power to be able to react quickly. Port 21 of
switch A may be marked as being "Blocked". The data from all the video cameras will then
be provided via port 22. Small switch C then has to process the data from all the video cameras,
causing a bottleneck.
Scenario 3: RTSP active, the master and Path Cost have been defined
This configuration precisely defines how the data should flow. The load is distributed on two
sides. None of the switches is pushed to the limit. As the path cost of switch D, port 10 and
switch E, port 9, is higher than that of all the other ports in the ring, this route will only be
activated, if network traffic is interrupted.
Path Cost − default setting:
The cost depends on the distance from the root bridge (master) and the available uplink to the
target. Normally, the path cost of reaching the target via a 100 Mbit/s uplink is higher than that
of a 1 Gbit/s uplink. In this case, the 100 Mbit/s link would be blocked from being used as a
redundant path. Although path costs have been standardised according to the IEEE provisions,
different values can be manually specified, for example, to select a preferred uplink where the
speeds are identical so as to reflect the real cost of a leased line.
➔
Wherever possible, one should aim to realise a configuration that corresponds to
the one illustrated in the above image.
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