Appendix 3: Ring Protection
Ethernet wiring schemes are based on a ‘star’-wiring topology. Ring (or loop) data wiring –
where the last device in a chain is wired back to the first device – is forbidden. Only one data
path between any two devices is allowed.
But star-wiring layouts are prone to single point failures. Unlike DMX512 transmission,
passive data ‘thru’ connections are not possible with Ethernet, which means there is no
redundancy under normal operation. A severed cable or power loss to a switch can mean
the loss of some or even all show control.
Ring Protection allows the deliberate – and designed – use of a ring wiring system for
Ethernet communications. When in this mode, VIA switches ignore data traffic on one
segment of the ring, while monitoring the integrity of the remaining connections. If an
interruption is detected, the unused ring segment is activated and full communication is
restored. Fail-over time is between 50 and 75 milliseconds, or two to four DMX packets.
Requirements and Limitations
VLANs must be enabled to use Ring Protection. The mode uses a dedicated VLAN to monitor
the integrity of the ring, called a Control VLAN. All switches must use the same Control
VLAN. By default, VLAN 4095 is used. This does not mean your VLAN range needs to extend
to 4095. Typically an entertainment network may use 1-3 or 1-10 VLANs.
Only ports 15 thru 18 may be used with this feature.
Ring Protection works with Pathway VIA switches only. Switches from other manufacturers
can co-exist on the network, but should not be placed in-line with the ring.
Definitions
Master switch monitors the integrity of communications. Only one switch on the network
may be configured as the master. If choice is available, the least busy switch, with the most
reliable power source, preferably on an uninterruptible power supply, should be chosen as
the master.
Transit switches receive and forward the ring monitoring packets. All switches other than the
Master must be set as transit switches.
Note: Ring Protection wiring topology is not structured. No care need be taken when
connecting primary and secondary ports together – any arrangement is acceptable.
