Switches and Switching• The switch is the backbone of nearly every

network in use.• It generally comprises of 4 to 64 ports.• Each port on a switch operates in it’s own

collision domain. This is different to a hub as a hub is a single collision domain.

• Switches operate on MAC Addresses and not IP Addresses.

• The switch learns MAC addresses as each frame is sent from the connecting computer. It then broadcasts this frame to all ports to find the destination. This is why you can often see the lights flashing in unison on the switch every few seconds.

OSI Model• In most cases the switch will sit

on the 2nd Layer of the OSI Model – The Data Link Layer. This layer deals with the physical addressing (MAC Addresses and LLC).

• Smart Switches such as Cisco switches which can be programmed also utilise the 3rd Layer of the OSI Model – The Network Layer. These switches are more common in larger businesses or corporations. 3rd layer switches are often routers.

• A switch that operates on more than one of the layers is known as a multilayer switch.

Network Segmentation is when every device in a network communicates using the same physical layer. Segments can be extended by using repeaters or hubs.

A network segment may also be referred to as a collision domain.

• Repeaters extend the network segment. They replicate the signal they receive and at the same time boost it to avoid signal decay. They are more prevalent in wireless devices in recent years as switches can perform port mirroring and act just like a repeater.

• The more network segmentation, the greater the chance that there will be collisions. Collisions negatively impact speed.

• More network segmentation also impacts bandwidth.

Network Segmentation

• A half-duplex system allows for two way communication, that is, transmitting and receiving, but only one way at a time. Half-duplex is not simultaneous. It functions in a similar way to how walkie-talkies function. Only one person can speak at any one time. Half-duplex is hardware controlled, one end will be given a certain amount of time and then the other end will be given the same. Collisions are more likely to occur in half-duplex systems.

• Full-duplex allows two way communication simultaneously. A telephone call is a full-duplex system, in that both parties can talk at the same time. A full-duplex Ethernet makes use of two pairs of twisted cable, one pair for receiving packets and the other pair for sending. 100Mbit Ethernet requires two pairs, 1000Mbit or 1Gbit requires four pairs. Full-duplex can avoid collisions and also is able to skip the frame delay associated with half-duplex. Nodes or devices no longer have to wait for others to complete their transmission as there is only a single transmitter for each pair.

Duplexing

Half-duplex vs Full-duplex

RJ45 Pairs

Cable Layout

Ethernet Transmission Frames

Fast Ethernet Standard is a term that carries many network standards under it that all have a 100Mbit/s rate. The original Ethernet speed was 10Mbit/s, hence, Fast Ethernet. The most commonly used Fast Ethernet Standard is 100BASE-TX. The majority of all network hardware is based on Fast Ethernet Standard currently. Fast Ethernet was introduced in 1995 and remained the fastest form of Ethernet for three years until Gigabit Ethernet was introduced.

Fast Ethernet Standard