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Jabber At times, Ethernet network interface card s and external transceivers also generate a problem called jabbering. This is when garbled bits of data are emitted within the frame sequence in a continuous transmission fashion. The packet length is usually more than 1,518 bytes. This can be identified by a protocol analyzer as a CRC error. As mentioned earlier, when nodes detect collisions they emit a normal JAM signal on the network segment to clear transmission. Sometimes certain nodes attempt to keep jamming the network due to excessive high collision rates; this also can be captured as high CRC or late collision error rate. The cause can be overloaded traffic levels. If the bandwidth- utilization levels are normal or low for the particular Ethernet segment, it is possible that the collision detection pair of a jamming node's NIC or transceiver cannot hear the network signal and may not know a collision has stopped. If this occurs, it continues to jam the network.
If a certain node on an Ethernet segment emits a lot of jabber, the node's NIC and transceiver should be troubleshot through consecutive replacement and re-analysis.
If an Ethernet network has intermittent high network bandwidth usage that causes performance problems, the cause can be re-created by loading the network with traffic-generation features in a protocol analyzer. But you must be careful when using this technique. First, be aware of the current network usage and any possible impacts to the network-user community. Second, you really have to understand all the Ethernet network bandwidth considerations discussed earlier, including the actual maximum bandwidth available, the overall network bandwidth baseline view and individual Ethernet node bandwidth consumption. Make sure that a proper baseline is performed on the lower and upper layers of the Ethernet.

November 15, 1996