With this knowledge and the information about the network technology being used, the maximum size of a collision domain can be calculated. If you assume you’re dealing with a classic half-duplex Ethernet network, this has a data transmission rate of 10 Mbps. The smallest data package, which accordingly takes the shortest time for complete transmission, and is the most extreme case, has a size of 512 bits (64 bytes). This results in a slot time of 51.2 μs (microseconds). The slot time describes the length of time a signal may take to the end of the collision domain and back again.
Data in networks, however, is not sent through empty space at the speed of light. You’re bound to the physical conditions of the transmission medium. The nominal velocity of propagation (NVP) is the percentage of the speed of light that’s reached in the medium. For example, the twisted-pair cables that are typical for local networks have an NVP value of 0.6 and the slightly older coaxial cables a value of 0.77. Data can therefore reach 180,000 km/s (112.000 m/s) (60%) or approx. 230.000 km/s (143.000 m/s) (77%) of the speed of light.
All data is used to the purpose of maximising the availability of a collection of data, to guarantee the accuracy of the CSMA/CD.
Data management x duration of transmission = twice the maximum length
230.000 km/s x 0.0000512 s = 11.776 km
(143.000 m/s x 0.0000512 s= 7.32 m)
A collision domain in a network based on coaxial cables may therefore have a maximum spread of 5.89 km (3.66 m). When calculating, the signals going in both directions need to be taken into account. The maximum size of a collision domain cannot be extended by interconnecting signal amplifiers (repeaters) either, as these have no influence on the CSMA/CD procedure.