L19 - W e have seen the basic principles of CSMA/CD and its...

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We have seen the basic principles of CSMA/CD and its application to ETHERNET. ETHERNET is a standard network, denoted IEEE 802.3. It is time to look at details of the standard, the frame format, and physical factors.
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Frame format Show Figure 4-14 (4-17 in old book) 48-bit addresses - 2 bits to distinguish local from global. Global addresses are unique. Type is the network protocol in use with this frame, which might be different for different frames in the same source-to-destination communication. 32 bit check sequence. Data field maximum is 1500 bytes. Minimum allowed frame size is 64 bytes, including data portion of at least 46 bytes. Raw bit rate is 10 megabits/second.
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Why is minimum frame 64 bytes? This is to make sure the frame duration is less than the maximum round trip time on the network, which is 50 microseconds (500 bit lengths) for the greatest allowed Ethernet station separation. What happens if frame is too short? Short frame from A would be received correctly at X, but would suffer collision at Y. A doesn’t know if its packet was received correctly. Maybe this isn’t so bad if you use a reliable data link protocol. If X is the destination, the frame mightn’t have to be repeated.
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Minimum 64 bytes ensures frame duration < maximum round trip time.
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L19 - W e have seen the basic principles of CSMA/CD and its...

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