HP AdvanceStack J2610B, Installation And Reference Manual

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Hub Operation
The HP AdvanceStack Hub-8U is a multiport repeater that conforms to the
IEEE 802.3 repeater specification. Data signals coming into the hub from
any of its ports are automatically regenerated and transmitted to all the
other hub network ports. The hub regenerates the data without interpreting
the contents, so it can be used in either IEEE 802.3 or Ethernet networks
and with any upper-level protocol.
Collision Detection
The hub also performs collision detection. A collision occurs when two
nodes try to transmit at the same time. When the hub detects a collision, it
stops repeating the colliding transmissions and starts transmitting a jamming
signal. The jamming signal tells the transmitting nodes that a collision has
occurred. The colliding nodes then stop transmitting for a random amount of
time before attempting to retransmit the data. Once the collision condition is
removed, the hub stops transmitting the jamming signal and normal operation
is resumed.
Auto-Partitioning
The hub will automatically partition (temporarily disable) one of its ports if
a collision condition exists for an excessive duration (between 1024 and
2048 bit times) or occurs during each of 32 consecutive attempts to transmit.
The hub monitors the partitioned port and automatically re-enables the port
when a minimum length packet can be successfully transmitted or received
without a collision occurring.
Excessive collisions may be caused by faulty wiring. If a port’s transmit
(Tx +/-) wires have been shorted to the receive (Rx +/-) wires of any port,
a collision will be detected when that port attempts to transmit. If a port’s
receive (Rx +/-) wires are not connected properly, collisions may occur
because the hub cannot detect the presence of network traffic on that port
and may thus transmit at inappropriate times.
A port may occasionally also become partitioned when network traffic is
extremely heavy causing an abnormally high collision rate.
Hub Ref
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Hub Reference
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