Original subtitles

Even if it was running at only 10 Mbps

provides a full 10 Mbps to the PC connected to the port.

In other words PC A gets a full 10 Mbps

rather than sharing that bandwidth with other devices.

That�s very different to the 0.75 Mbps we had when we were using a hub.

10 Mbps is dedicated on individual ports rather than being shared between devices.

So if you add more devices on the switch

it doesn�t degrade the throughput that each device gets.

In addition you can increase the speed by changing the duplex. 10

So by setting this to full duplex you actually get 20 Mbps 11

hubs operated by using CSMA/CD which is very similar to 10base2. 12

with shared bandwidth they are collisions whereas 13

with a switch when full duplex is enabled it means that you can send 14

and receive traffic at the same time. 15

Half duplex communication is like a walky talky 16

where only one side can send at any given time. 17

So one party would say "Hello! How are you?" over 18

and over is used to indicate to the other party that they can speak. 19

The other party would then say something and end with the word over. 20

So that the first party could say something. 21

The moral of the story is that only one party can transmit at any given time 22

if both parties try to transmit at the same time, 23

there�ll be a collision that�s half duplex. 24

Full duplex communication on the other hand is like a landline telephone 25

where you can speak and listen at the same time. 26

Landline telephones use full duplex so both parties can speak 27

and listen simultaneously whereas walkie talkies are half duplex devices 28

where one party can transmit and the other party needs to receive. 29

Walkie talkies only one person can speak at a time 30

landline telephones both parties can speak at the same time. 31

Walkie talkies as an analogy are half duplex, landline telephones are full duplex. 32

Hubs once again use Carrier Sense Multiple Accesses Collision Detection 33

in other words half duplex where only one party can transmit at any given time. 34

An individual port on a switch however, you can set those ports to use full duplex 35

which means that both the switch and the PC 36

can transmit and receive at the same time. 37

Just be aware however that when you enable full duplex, 38

collision detection is turned off because the devices operate on that premise 39

that they can send and receive at the same time. 40

So there�s no need to have collision detection because no collections will take place. 41

That will cause issues however where 1 side is set to full duplex 42

and the other side is set to half duplex. 43

It is important that full duplex be enabled on both sides 44

if you wanna use full duplex. 45

But once again in this example if full duplex is enabled 46

rather than only having 10 Mbps in theory you can increase that to 20 Mbps 47

because both parties can transmit and receive at the same time. 48

So by just replacing a hub with a switch 49

we can increase the throughput of of this network from 0.75 Mbps to 20 Mbps 50

all we did was replace the hub with the switch and enabled full duplex. 51

Now full duplex is often negotiated automatically between devices. 52

So the switch and the PC will negotiate to use full duplex 53

if they both support it and will hopefully choose correctly. 54

In networks it does happen that 1 side chooses full duplex 55

and the other side chooses half duplex. 56

And that�s gonna cause a lot of problems on that link. 57

So if users complaining about slow throughput 58

check the duplex on both sides and check that it�s been negotiated correctly 59

because it may have negotiated incorrectly. 60

Speed by the same token can also negotiated between a switch in a PC 61

and that could also be incorrectly negotiated. 62

These days PCs tends to have gig ports 63

and thus the bandwidth can increase 64

from 0.75 Mbps when using a hub to 2 gigabits per second 65

The throughput of switches is much, much greater than hubs 66

and therefore switches are preferred today 67

over other devices like hubs or bridges. 68

Be aware however that in wireless networks 69

access points tend to operate like hubs 70

which have a shared infrastructure which therefore means 71

shared bandwidth where as with switches devices have dedicated bandwidth. 72

So in summary a switches a layer 2 device in the OSI model 73

it operates at the data link layer. 74

Switches have major advantages when compared with hubs 75

and bridges and that�s to do with the throughput 76

and scalability of networks using switches. 77

Switches process frames in hardware rather than in software 78

and can therefore process frames at wire speed 79

as well as supporting many more ports than bridges and hubs. 80

These days switches can also operated layer 3, hence the term layer 3 switches. 81

But for the moment we're just talking about pure layer 2 switches. 82

We'll know discuss routers and then we can talk about layer 3 switches.