Glossary - Siemens Advance Network Gateway User Manual

Definitions,
Continued
Late Collision
FCS - Frame Check
Sequence Error
Ghosts
Jabber
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Glossary

A Late Collision is one that occurs after the first 64 bytes in a frame or
packet. Since the smallest Ethernet frame (packet) is 64 bytes in length,
late collisions will not be detected on small packets. Ethernet controllers
do not retransmit packets with late collisions resulting in lost packets.
Late Collisions usually appear as a bad FCS frame. The only time a late
collision can be detected on a 10BaseT network is when the detecting
device is transmitting at the same time.
The CRC (Cycle Redundancy Check) remainder transmitted at the end
of a frame. A FCS error is a legal sized Ethernet frame with a bad frame
check sequence.
Ghosts are energy on the cable that appears to be a frame, but does not
have a valid beginning of frame pattern (start delimiter 10101011).
Ground loops and other wiring problems cause some repeaters to be-
lieve that a frame is being received. Since the repeater is only reacting to
an AC voltage riding on the cable, there is not a valid frame to pass
along. The repeater, however, transmits this energy along the network.
This may be a jam pattern or a very long preamble. Ghosts events con-
sume bandwidth and can slow down a network. Ghosts are the result of
network elements reacting to noise. The effect of noise on network wiring
is indeterminate. Some network devices will react while others will not.
Ghosts cause random events and can be hard to correct.
The term Jabber refers to an Ethernet frame that is greater than the
maximum legal size (Greater than 1518 bytes). Many 10BaseT HUBS
will partition a port that is jabbering.
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