Ethernet, Aloha and CSMACD 2395

the big transition for ethernet was adding listen before transmit (and adapting t-r cat5 hub-spoke)

my vague recollection was early ethernet was 3mbit-sec, didn't do listen before transmit and had this big thick cables ... looked a lot like the pcnet cables (which i believe did 1mbit-sec but used a tv head-end type implementation).

when we had come up with 3-tier architecture and were out pitching in in executive presentations

we were getting a lot of push-back from the saa and token-ring folks. some characterized the saa effort as trying to put the client-server genie back into the bottle ... aka maintain the terminal emulation operation

and since we were pitching enet ... the token-ring people were also getting really upset. some t-r person from the dallas engineering & science center had done a report that showed enet typically only got 1mbyte-sec thruput (we conjectured that they based the numbers on old 3mbit-sec implementation before listen before transmit).

research had done a new bldg. up on the hill ... and it was completely wired with cat5 supposedly for t-r ... but they found that they were getting higher thruput and lower latency using it for star-wired 10mbit ethernet (even compared to 16mbit t-r). adapting the t-r hub&spoke cat5 configurations to ethernet tended to reduce the worst case latency on listen before transmit. this improved further by making the hub active ... so worst case was longest leg to the hub rather than latency across the hub between two longest legs.

then a paper came out in 88 acm sigcomm showing that a typical 10mbit ethernet star-wired hub configuration with all stations doing worst case, low-level device driver loop transmitting minimum sized packets was getting aggregate effective thruput of 85 percent of media capacity.

misc. past refs:

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