Allied Telesis AT-MR912TX - Manual (Page 45)

AT-MR912TX Installation Manual
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Note
Once you connect AT-MR912TX hubs in a stacked configuration, they
effectively become Class I repeaters. That is, while you can cascade
two stacked hub configurations, you must pay careful attention to
Ethernet repeater timing rules which limit the way repeaters may be
connected. Foremost among these rules is the collision domain timing
constraint which addresses the propagation delay of a network.
Specifically, the propagation delay through a network depends on its
physical extent. As a network grows, the worst-case packet
propagation time lengthens. If a network becomes too large, it may
violate the collision domain timing constraint which, in turn, may
cause late collisions, lost packets and generally poor performance.
In any individual collision domain, the round-trip propagation delay
must not exceed 512 bit times. The bit budget calculation method
should be used to determine if your stacked/cascaded installation will
satisfy Ethernet topology constraints.
The procedures are straightforward. First, you are referred to the information
previously presented on stacking. This process will allow you to create two
separate stacks of hubs which are independent of each other.
Second, you are referred to the information previously presented on cascading.
This process will, in turn, allow you to electronically combine the two separate
stacks of hubs into a single network or collision domain.
Combining this information will result in a stacked/cascaded installation.
Additionally, we recommend that cascading be performed using the bottom
most hubs to mitigate internal propagation delays.