Allied Telesis AT-MR908TX - Manual (Page 38)

Installation
18
8. Plug all 100BASE-TX cables in the 100BASE-TX network ports (RJ-45
connectors) on the back panel of each unit.
You are now ready to operate your 100BASE-TX network in a stacked hub
configuration.
Stacked/Cascaded Installation
First, recall that the basic 803.2u rule is that, for cascading Fast Ethernet
networks, the maximum number of Class II repeaters in the data path
between any two nodes cannot exceed two.
A stacked/cascaded installation is simply two AT-MR908TX stacked hub
configurations which are joined through the cascading ports of any two
individual hubs in those stacks. This configuration will support up to 94
network nodes in a single collision domain. Cable lengths to the nodes will
need to be reduced to minimize signal delays in a stacked/cascaded
installation.
Note
Once you connect AT-MR908TX 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.
This process will allow you to create two separate stacks of hubs which are
independent of each other. The procedures are straightforward. First, you are
referred to the information previously presented on stacking.