Page 75 - Handout Computer Network.

A small, slow network could work out a system that allows only two computers to send
messages, with both agreeing to take turns.

The problem is that many computers are connected to large networks, with each one
wanting to communicate millions of bits every section.

Figure 3-20 shown a Collision Phenomena

Collision domains are the connected physical network segments where collisions can
occur. Collisions cause the network to be inefficient. Every time there is a collision on a
network, all transmission stops for a period of time. This time is variable, as determined by a
back-off algorithm for each network device, which is necessary to allow broadcast
transmission to resume. Except for a single isolated Ethernet LAN environment, the types of
devices that interconnect the media segments define collision domains.
These devices have been classified as OSI Layers 1, 2, or 3 devices. Layer 1 devices do
not break up collision domains; Layers 2 and 3 devices do break up collision domains, as
described in Figure 3-21. Breaking up or increasing the number of collision domains with Layer
2 and 3 devices is known as segmentation.

Figure 3-21 shown a Collision Domain Segmentation

Layer 1 devices, such as repeaters and hubs, serve the primary function of extending
the Ethernet cable segments. By extending the network, more hosts can be added. However,
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