CobraNet unicast vs multi-unicast... what if...

[Dan Lynch]

With the addition of Multi-Unicast bundles to London Architect, there have been a lot of people asking what in the heck is a Multi-Unicast bundle and what exactly happens if something gets setup wrong?

First of all, what do all of these terms mean? Unicast and Multicast are the two main types of CobraNet bundles. Multi-Unicast is a variation of Unicast. The rules are:

Multicast Bundle
* has a bundle number from 1 through 255
* is placed in an ethernet frame that does not have a destination MAC address so it goes everywhere on the network.

Unicast Bundle
* has a bundle number greater than 255 and less than 65,280
* is placed in an ethernet frame which DOES have a destination MAC address which means it goes to a specific destination.
* has a txMaxUnicast value of 1

Multi-Unicast Bundle
* has a bundle number greater than 255 and less than 65,280
* is placed in an ethernet frame which DOES have a destination MAC address which means it goes to a specific destination.
* has a txMaxUnicast value of 2 or 3 or 4

So, what in the heck is txMaxUnicast? If you click on a CobraNet output node in London Architect and take a look at the Properties window, you'll see a parameter called Maximum Receivers. This parameter sets txMaxUnicast and defaults to 1. This means that only one receiver is allowed to receive that bundle. If more than one device requests that bundle, only the first requesting device will be sent the bundle (this is all controlled by the conductor). If you change that value to 2, then the first two devices which request the bundle will receive it and any additional devices will get nothing. This can not be increased beyond 4.





Dan
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