GarrettCom 4K16 - Manual (Page 26)

Magnum 4K16 Switches Installation and User Guide (12/05)
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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 descending 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 4K16-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.
•
NOTE – some NIC cards only auto-negotiate when the computer system
that they are in is powered up. These are exceptions to the “negotiate at
LINK – enabled” rule above, but may be occasionally encountered.
When operating in 100Mb half-duplex mode, cable distances and hop-counts
may be limited within that collision domain. The Path Delay Value (PDV) bit-times must
account for all devices and cable lengths within that domain. For Magnum 4K-Series
Fast Ethernet switched ports operating at 100Mb half-duplex, the bit time delay is 50BT.
4.5 Auto-negotiation full-duplex mode
Full-duplex Ethernet provides separate Transmit and Receive data paths,
enabling simultaneous bi-directional collision-free data movements on a port. The
network topology must be a “star” type, not a “bus” type. With full-duplex mode, the
cable distance is only limited by the physical layer line driver and cable attenuation.