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Black Box Modular Switches Installation and User Guide (8/99)
33
One frequently-used application for the 4-Port-
Switch copper ports is to connect one
of them using a fiber media converter to another Switch in the network backbone, or to some
other remote 100Mb device. In this case, it is desirable to operate the fiber link at 100Mb speed,
and at either half- or full duplex mode depending on the capabilities of the remote device.
Standard commercially-available Fast Ethernet media converters mostly do not support auto-
negotiation properly, and require that the switched port to which they are connected be at
100Mb fixed speed. Attachment to 10/100 auto-negotiation ports typically will not work
properly. The 4-Port-Switch’s RJ-
45 ports handle this situation by changing the internal jumper
settings. (see Section 3.4)
When 4Port-Switch’s RJ-45 copper ports are set for auto-
negotiation and connected to
an another auto-negotiating device, there
are 4 different speed and F/H modes selection depending
on what the other device supports. These are: (1) 100Mb full-duplex, (2) 100Mb half-
duplex, (3)
10 Mb full-duplex and (4) 10 Mb half-duplex.
The auto-negotiation logic will attempt to operate in desce
nding order and will normally arrive at
the highest order mode that both devices can support at that time. (Since auto-negotiation is
potentially an externally-
controlled process, the original “highest order mode” result can change
at any time depending on
network changes that may occur). If the device at the other end is not
an auto-negotiating device, the 4Port-Switch’s RJ-45 ports will try to detect its idle signal to
determine 10 or 100 speed, and will default to half-duplex at that speed per the IEEE
standard.
General information -
Auto-negotiation per-port for 802.3u-compliant switches occurs when:
the devices at both ends of the cable are capable of operation at either 10 Mb or
100Mb speed and/or in full- or half-duplex mode, and can send/receive auto-
negotiation pulses, and . . .
-- when the second of the two connected devices is powered up*, i.e., when
LINK is established for a port, or
-- when LINK is re-established on a port after being lost temporarily.