Understanding the network.pdf - Back to Home

Figure 4.12. A basic 3-cable 10Base-T horizontal
cable path.
The 10Base-T hub behaves differently than a multiport MAU, which simply emulates
the behavior of the coaxial segment. The 10Base-T hub must perform specific
functions: it operates like a standard two-port repeater, and it receives signals from
end-devices connected to its ports, then retimes, regenerates, and retransmits
them to all its active ports. The hub also monitors the collision rates and packet
integrity of all its ports. On some hubs, in the event a station generates an excessive
amount of consecutive collisions, the hub will disable the port. This prevents the
network segment from being effectively halted by a broadcast or collision storm that
results from a defective NIC or circumstances when end-stations are connected to
hubs over cable segments that exceed the distance specification. The hub will not
regenerate packets that exceed the maximum permitted packet length of 1,518
bytes. These packets are commonly the result of collisions or the byproduct of the
PMA interface enforcing jabber control. 10Base-T hubs also use a special signal
generated by end-stations, known as a link pulse, to verify port operation. If the link
between the end-station and the hub is lost, the hub disables the port until a link
signal returns.