Allied Telesis AT-MC116XL - Manual (Page 16)

Overview
6
MDI/MDI-X Switch
An RJ-45 port on a 10 Mbps or 100 Mbps Ethernet network device can have
one of two possible wiring configurations: MDI or MDI-X. The RJ-45 port on a
PC, router or bridge is typically wired as MDI, while the twisted pair port on a
switch or hub is usually MDI-X.
To connect two 10 Mbps or 100 Mbps network devices together that have
dissimilar port wiring configurations, such as MDI to MDI-X, you use a
straight-through cable. To connect two network devices that have an RJ-45
port with the same wiring configuration, such as MDI to MDI, you use a
crossover cable.
The RJ-45 port on the media converters features an MDI/MDI-X switch. You
can use this switch to configure the twisted pair port on the media converter
as either MDI or MDI-X. This feature allows you to use a straight-through
cable regardless of the type of end-node connected to the port.
NML/LNK TST Switch
The NML/LNK TST (Normal MissingLink/Link Test) button allows you to
perform a link test on the ports on the media converter. This button also
allows you to activate the MissingLink feature on the unit. The MissingLink
and Link Test features are describe below.
MissingLink. The MissingLink feature allows the ports on the media converter
to pass the “Link” status of their connections to each other. When the media
converter detects a problem with one of the ports, such as the loss of
connection to a node, the media converter shuts down the connection to the
other port, thus notifying the node that the connection has been lost.
For example, if the twisted pair cable to the AT-MC115XL were to fail, the
media converter would respond by dropping the link on the fiber optic port. In
this way, the AT-MC115XL notifies the end-node connected to the fiber optic
port that the connection on the twisted pair port has been lost. If the failure
had started with the fiber optic cabling, the media converter would drop the
link to the twisted pair port.
The value to this type of network monitoring and fault notification is that
some hubs and switches can be configured to take a specific action in the event
of the loss of connection on a port. In some cases, the unit can be configured to
seek a redundant path to a disconnected end-node or send out a trap to a
network management station, and so alert the network administrator of the
problem.