Ethernet
5-22
Segmentation
These self-repeating MIMs are called RMIMs, for Repeating Media Interface
Modules. As the Product Descriptions chapter of this Networking Guide shows,
RMIMs are available in most of the media connection types available for standard
Ethernet Channel A MIMs. These RMIMs, however, cannot access Ethernet
Channel A, much the same as the standard MIMs which cannot access Channels B
or C. The two different MIMs communicate through the internal bridging
capabilities of the EMME.
Using the Multichannel Ethernet configuration yields a path cost throughout the
hub equivalent to only one repeater hop. From one Channel B module to any
other Channel B modules within the chassis is only one repeater hop. Since the
repeater rule holds repeater hops to a maximum of four, being able to use
multiple RMIMs as a single logical repeater is a great advantage. Another benefit
to the onboard repeater functionality of RMIMs is a fault-tolerance not found in
the standard MIMs; if the management module is removed from a single-channel
Ethernet hub, the loss of repeating services shuts down all Ethernet MIMs. Since
the RMIMs incorporate their own repeating, the modules can function in what is
called standalone mode, operating without a dedicated repeating module present
in the chassis.
Looking at the RMIM information in Chapter 11, Product Descriptions, you may
notice that most of the RMIMs have covered openings labeled “EPIM” on them.
These are additional port spaces. EPIM stands for Ethernet Port Interface Module.
An EPIM is a user-configurable port that can be used for a connection to a
backbone, another department, a router, or any other standards-based Ethernet
network device, and it can be specified in any media the customer wishes. EPIMs
also save customers who are planning to alter their cabling in the future a lot of
money and hassle. If a customer was replacing a populated thick coaxial cable
backbone with a fiber optic link to a separate hub when the money became
available, an EPIM-A would provide a transceiver connection for right now, and
later an EPIM-F2 could be swapped in, for a couple hundred dollars, saving the
customer from ordering an entirely new RMIM board or buying a more expensive
external transceiver.
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