Count collision domains in a mixed switch and hub topology, with CSMA/CD slot time and cable diameter limits.
CSMA/CD requires a sender to still be transmitting when a collision returns, which is why the minimum frame is 64 bytes and the slot time 512 bit times. That fixes a round-trip propagation budget and therefore a maximum network diameter, before repeater and transceiver latency is subtracted. Half-duplex Ethernet is rare but not gone — a duplex mismatch turns a switch port back into a collision domain, and the resulting late collisions and FCS errors look like a failing cable rather than a configuration fault.
Collision Domain
Each full-duplex switch port is its own collision domain; each hub or half-duplex segment is one shared domain whose bandwidth divides among its stations.
CSMA/CD timing
slot time = 512 ÷ line rate; cable budget = (slot time ÷ 2) × 0.65c.
Each full-duplex switch port is its own collision domain; each hub or half-duplex segment is one shared domain whose bandwidth divides among its stations. CSMA/CD requires a sender to still be transmitting when a collision returns, which is why the minimum frame is 64 bytes and the slot time 512 bit times. That fixes a round-trip propagation budget and therefore a maximum network diameter, before repeater and transceiver latency is subtracted.
Half-duplex Ethernet is rare but not gone — a duplex mismatch turns a switch port back into a collision domain, and the resulting late collisions and FCS errors look like a failing cable rather than a configuration fault.
This calculator takes 4 inputs: Switch ports, Hubs or half-duplex segments, Stations per shared segment, Shared segment speed. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
A non-zero late-collision counter on a gigabit port almost always means a duplex mismatch: one side auto-negotiated full duplex, the other is hard-coded to half. Fix the pair, do not replace the cable.