Link Beat - HP AdvanceStack 10Base-T Hub-12 Installation And Reference Manual

Hub Reference
Late collisions occur when a node starts transmitting after another node
has already transmitted at least 512 bits. They are usually caused when
network topology rules (such as cable length limitations or hub hop
counts) do not meet the IEEE 802.3 specifications. Late collisions may
also be caused by faulty wiring that prevents a hub from being able to
detect traffic on a network port.
N o t e
Because failures due to late collisions are the result of critical network
design errors or cabling errors, the hub will not automatically re-enable
the port. You must manually re-enable the port (after the problem is re-
solved) either through the HP Stack Manager's "Port" function or an
SNMP network management station.
Late Collision Monitoring is configurable for either single node
connections—to isolate problem nodes, or multiple node connections
(cascaded ports or backbone connections)—to isolate parts of the
network. The Late Collision Monitoring feature is enabled through the
"Robust" function in HP Stack Manager or the RObustness command in
the ASCII console. The default setting is OFF.

Link Beat

Type 10Base-T devices use a signal called link beat (also called link test
pulse). This signal informs the hub of the presence of a device
connected to it over twisted-pair cable and of the integrity of the
twisted-pair link between them. The hub will not transmit packets out of
twisted-pair ports that do not sense the link beat signal.
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