Delta RMC101 - Manual (Page 365)

Ethernet 5.2
Communications 5-115
For the first two collisions domains types, we will assume all devices are connected to a switch. For
the third, we will assume all devices are connected to a hub.
• The collision domain from the switch to an RMC ENET.
When the switch does not support IGMP, this collision domain will receive all frames consumed
by the RMC, plus all frames produced by any RMC on the network.
When the switch does support IGMP, then this collision domain will receive all frames consumed
and produced by the RMC. Multicast packets sent by other RMCs are filtered out by the IGMP-
capable switch.
Example (IGMP not supported by switch):
In the example above, there are four RMC/switch collision domains: one each for RMC1 to
RMC4. All four of these segments will include the four frames produced by the four RMCs.
The bandwidth required for these is as follows:
Produced Frames/Second = 2 / 0.010s + 1 / 0.005s + 1 / 0.007s = 543
Next, we need to add the frames consumed by each RMC. This can be different for each
RMC/switch collision domain.
RMC1 Frames/Second = 543 + 2 / 0.010s0 = 743
RMC2 Frames/Second = 543 + 2 / 0.010s = 743
RMC3 Frames/Second = 543 + 1 / 0.005s = 743
RMC4 Frames/Second = 543 + 1 / 0.007s = 686
Example (IGMP supported by switch):
In the example above, there are four RMC/switch collision domains: one each for RMC1 to
RMC4. The bandwidth of each is computed based on the number of frames consumed by the
RMC (one or two in this example) and the number of frames produced by the RMC (always
one) each RPI:
RMC1 Frames/Second = (2 + 1) / 0.010s = 300
RMC2 Frames/Second = (2 + 1) / 0.010s = 300
RMC3 Frames/Second = (1 + 1) / 0.005s = 400
RMC4 Frames/Second = (1 + 1) / 0.007s = 286
• The collision domain from the switch to the 1756-ENET/ENBT. It should be noted first that if a
1756-ENBT is used and the switch supports full-duplex Ethernet, then there will be no collisions,
and therefore this collision domain need not be considered.
When the switch does not support IGMP, this collision domain sees all frames produced by the
ControlLogix for an RMC, plus all frames produced by any RMC on the network.
When the switch does support IGMP, this collision domain sees all frames produced by the
ControlLogix for any RMC, plus all frames produced by any RMC destined for this ControlLogix.