Fluke Series II user manual Interpreting Error Results, Late Collisions, Short Frames, Jabbers

Network Health

Introduction 3

Interpreting Error Results	propagation time is greater than the minimum legal frame
	size of ~57.6 microseconds for 10BASE-T).

Collisions

A collision is the result of two or more nodes transmitting at the same time on the segment. Collisions are not necessarily bad. They are a normal part of Ethernet’s operation. In general you need not worry about collisions unless the AVERAGE collision rate is greater than 20%.

Excessive collisions are more often associated with too much network traffic and less often a physical problem with the network. Usually the best way to fix a “collision problem” is to understand why there is excessive traffic.

You may find that the Network Assistant collision count does not agree with that of some protocol analyzers that under report collisions. Just like a Hub, the Network Assistant identifies collisions that occur in the frame’s preamble. These are the most common types of collisions in a 10BASE-T network.

Late Collisions

A late collision is one that occurs after the first 64 bytes in a frame. Consider late collisions a serious network error to be resolved quickly. Late collisions may manifest themselves as frames with a bad Frame Check Sequence (FCS). Late collisions are caused by either a faulty NIC or a network that is too long (i.e., end-to-end signal

Short Frames

A short frame is a frame that is less than the minimum legal size (less than 64 bytes) with a good frame check sequence. In general, you should not see short frames. The most likely cause of a short frame is a faulty card or an improperly configured or corrupt NIC driver file.

Jabbers

A jabber is a frame greater than the maximum legal size (greater than 1518 bytes) with a good or bad frame sequence.

Consider jabbers a serious network error to be resolved quickly. The most likely causes of Jabbers are a faulty NIC or driver or perhaps a cabling problem.

Bad Frame Check Sequence (FCS)

A legal sized frame with a bad frame check sequence (FCS) has been corrupted in some way. Bad FCSs can be caused by late collisions, a faulty NIC/driver, cabling, hub or induced noise.

3-7