HP Fiber-Optic Hub Plus User's Guide download pdf (Page 14)

How the Hub Works

The HP Fiber-Optic Hub Plus is a multiport repeater. Data signals coming into the hub from

any of its ports are automatically regenerated and transmitted to all the other hub 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 performs collision detection. A collision occurs when two nodes try to transmit at the

same time. When the hub detects this, 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 restored.

Auto-Segmentation

The hub will automatically disable (auto-segment) a port if it experiences excessive collisions

(greater than 30 consecutive collisions). The port will automatically return to operation if the

excessive collision condition is removed and normal traffic is restored. Auto-segmentation can

also be caused by improper termination of cabling attached to the AUI or ThinLAN ports, or by

having nothing connected to the ThinLAN port when it is enabled.

If a port is auto-segmented, its port LED and the Fault LEDs will flash. A segmented ThinLAN

port will not cause the Fault LED to flash unless Thinwatch has been explicitly enabled with the

Thinwatch console command. The Thinwatch command is described in chapter 3.

If a port is auto-segmented, only the LAN segment attached to that port is affected. The other

LAN segments will operate normally.

If a port is disabled explicitly, by using the console port or from an HP network management

station, it must be enabled explicitly. It will not be enabled automatically.

1-6 Introducing the HP Fiber-Optic Hub Plus

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HP Fiber-Optic Hub Plus User's Guide Page 14