Page 74 - Handout Computer Network.

• On a 10 Mbps Ethernet, 1 bit at the MAC sublayer requires 100 nanoseconds
(ns) to transmit.

• At 100 Mbps, that same bit requires 10 ns to transmit.

• At 1000 Mbps, it takes only 1 ns.

Table 3-2 summarizes the bit-time of different types of Ethernets.

Table 3-2 shown the bit-time of different types of Ethernet

As a rough estimate, 8 inches (20.3 cm) per nanosecond often is used for calculating
propagation delay down a UTP cable. For 100m of UTP, this means that it takes just under 5
bittimes for a 10BASE-T signal to travel the length of a 100m cable (about 4.92 bit-times).
Simply moving the decimal point over results in 49.2 bit-times at 100 Mbps, and 492 bit-times
at 1000 Mbps.

For CSMA/CD Ethernet to operate, the sending station must become aware of a
collision before it has completed transmission of a minimum-size frame. At 100 Mbps, the
system timing is barely capable of accommodating 100m cables. At 1000 Mbps, special (very
inefficient) adjustments were required because nearly an entire minimum-size frame has been
transmitted before the first bit reaches the end of the first 100 meters of UTP cable. It is easy
to see why half duplex was not permitted in 10-Gb Ethernet.
https://www.youtube.com/watch?v=HLziLmaYsO0&t=43s

3.8 Collision Domains and Broadcast Domains

It is important to identify the medium as a shared environment because this shared
environment causes collisions. A similar situation can occur with an automobile on a highway.
If there is only one car, there is nothing to collide with. However, if more than one automobile
is trying to use the same section of road at the same time, as shown in Figure 3-20, a collision
occurs. The same is true for networks.

If more than one computer tries to transmit data on the same network segment at the
same time, a collision occurs.
A collision is a situation that can occur when 2 bits propagate at the same time on the
same network.

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