In a CSMA/CD environment how many repeaters may be used between end systems?

Question

networking

Answer 1

Hi Zabair,
The classic 5-4-3 rule of Ethernet often applies. You can have a maximum of 5 segments in a linear fashion joined by 4 repeaters and 3 of these segments can have end-devices connected to them. So if you're talking 10Base5 thicknet for example, that gives a maximum network length of 2500 meters, and for 10Base2 about 925 meters. This limit of 5 segments with 4 repeaters also usually applies to 10BaseT environments.

But for 100BaseT fast ethernet environments, the rules change because it's still a 512 bit slot time like in 10BaseT, but it's 10X the speed so the restrictions on repeaters are tighter. There, you are allowed only 1 class-1 repeater or 2 class-2 repeaters. You'll probably always have class-2 repeaters unless you're translating to/from 100BaseT4. Class-2 repeaters are for 100BaseTx and 100BaseFx connections and you can only have TWO of these when using the maximum cable lengths. The other restriction here is that if you do use 2 of them, they can be no more than 5 meters apart, giving a maximum 100BaseT length of about 205 meters.