That originated back in the day of coaxial cable based ethernet. 10 Base 5 10 Mbps, 500 meters.
It used a Collision Detection Multiple Access protocol. An ethernet adapter would come on line, blindly transmit and if it did not get an ACK it would back off for a random amount of time and transmit again. In order to attempt to guarantee a bit of performance, they had to limit the amount of time you would allow for a packet to go to the other end of the cable and bounce back before trying again. With higher speeds and more noise they reduced it to 100 meters. I have always been told it is a timing issue. But nowadays you really don’t see hubs, so you don’t see collisions. I have heard of people taking CAT5 out to 250 meters. From: Jesse DuPont Sent: Monday, January 14, 2019 4:11 PM To: AnimalFarm Microwave Users Group ; ch...@wbmfg.com Subject: Re: [AFMUG] Ethernet 100M Copper Limit Well, I meant Ethernet generically. Regardless of 4-wire vs 8-wire, in general, the purported safe distance for an Ethernet over copper (as opposed to fiber) connection is 100 meters. What drives this safe distance limitation spec? Jesse DuPont Network Architect email: jesse.dup...@celeritycorp.net Celerity Networks LLC Celerity Broadband LLC Like us! facebook.com/celeritynetworksllc Like us! facebook.com/celeritybroadband On 1/14/19 4:03 PM, ch...@wbmfg.com wrote: I presume you are talking about 4 wire Ethernet because we do GigE all the time on copper. GigE uses all 8 wires and has data flowing both directions. 100 Mbps E uses 4 wires (2 pair) with TX on one pair and RX on the other pair. GigE uses advanced modulation methods as well. Does that help? From: Jesse DuPont Sent: Monday, January 14, 2019 3:58 PM To: AnimalFarm Microwave Users Group Subject: [AFMUG] Ethernet 100M Copper Limit I figured this was the best place to ask this question: What is the primary reason for the 100M limit on copper Ethernet links? Is it related to bit errors/SNR or is there a timing element involved? Something else? Thanks! -- Jesse DuPont Network Architect email: jesse.dup...@celeritycorp.net Celerity Networks LLC Celerity Broadband LLC Like us! facebook.com/celeritynetworksllc Like us! facebook.com/celeritybroadband ------------------------------------------------------------------------------ -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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