Jul 10, 2009

Late Collision

在ICND1的Troubleshooting章節中,針對一些特定網路狀況的內容其實寫得不是很周全詳密,所以各位有可能會在其他書籍或文件中看到ICND1沒有提到的狀況,比方說 Late Collision 在ICND1指出這個狀況是因為Cable長度過長所導致,其實這只是原因之一而已。


Late Collision is a type of collision found in the CSMA/CD protocol standard. If a collision error occurs after the first 512 bit times of data are transmitted by the transmitting station, a late collision is said to have occurred. Importantly, late collisions are not re-sent by the NIC unlike collisions occurring before the first 64 octets; it is left for the upper layers of the protocol stack to determine that there was loss of data.

As a correctly set up CSMA/CD network link should not have late collisions, the usual possible causes are full-duplex/half-duplex mismatch, exceeded Ethernet cable length limits, or defective hardware such as incorrect cabling, non-compliant number of hubs in the network, or a bad NIC.
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