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So a quick recap of the OSI model.

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At layer 1 we have the physical layer, physicals specification like Rj-45

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are defined at this layer, option such as cables specifications, voltage

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and other physical parametera are defined at the physical layer.

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At layer 2 we have the data link layer and this is where Mac address is reside.

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I’m going to explain Mac addresses in more detail in a moment.

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At layer 3 we have IP addresses and this is where routing takes place

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routers reside at this layer and addresses such as IPv4 or IPv6 exist at layer 3.

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At layer 4 we have protocol such as TCP and UDP

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now some of this information was covered in the OSI model videos

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but here I'm gonna look at some of the layers in more detail.

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So Ethernet was born in the 1970's which for a lot of us

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seems like a really long time ago.

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Robert Metcalfe was one of the people involved in Ethernet development.

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he also started the company called 3Com in 1979 which is subsequently

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been purchase by Hewlett-Packard,  what's important to understand is that Ethernet

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and networking is very young when compared to telephony environments.

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Alexander Graham Bell invented the telephone system many, many years ago

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long before the advent of Ethernet.

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I’m gonna give you a brief history lesson but it's worthwhile knowing

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some of the history of the Ethernet because it explaines

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how we've got to where we are today, it also explains some of the concepts

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which are still relevant in today’s networks.

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Now in the original Ethernet implementation.

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The network architecture that was use was a bus topology.

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In a bus topology, each devices connected to a single cable

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and the clients therefore share a communication line or bus.

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This is similar in concept to what we use to have in telephony environment

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which was called a telephone party line, where a single cable

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was used to provide telephone services to remote areas.

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In that example you would have a single cable and multiple telephones

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would hang off the so called party line, now before you made a call

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in those days you have to listen to hear if anyone else was speaking.

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So before you made a call you would pick up your handset and listen

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and make sure that no one else was using the line.

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When someone made a call to that telephone line

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all telephones connected to the party line would ring.

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And the same thing happens in an Ethernet environment when using a bus topology.

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When traffic is sent on that cable it is received by all devices connected to the bus.

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This is the shared infrastructure and it means that when any device on that network

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sends traffic all other devices connected to the same cable will receive the traffic.

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When a device wants to speak or communicate it needs to ensure that no other device

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speaking, otherwise collision can occur.

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In some of the original implementations of Ethernet, we had what was called

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10 base5 also called thicknet and it had a maximum segment size of 500 meters.

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There was also another physical implementation known as 10base2

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also called thinnet this had a maximum distance of 185 meters.

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This early implementations of Ethernet use a bus topology which means

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that when a device on the cable sends a signal all devices

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connected to that cable will receive the signal.

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So now let’s discuss one of the implementations 10base2 which will hopefully help you

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understand the reasons why we do things in Ethernet today.

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Basically because of historical reasons, certain things are done in the certain way.

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So 10base2 use coaxial cable or coax cable it had a maximum speed of 10mbps

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the 10 in 10base2 indicates a speed of 10mbps, 2 indicates a maximum segment length

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of 185 meters, and the word base indicates baseband rather than broadband.

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Now what is the difference between baseband and broadband

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now baseband only allows for a single signal to traverse the wire at any given time.

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The signal uses all the frequencies.

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Broadband on the other hand which in some cases

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is used for cable television also uses coaxial cable.

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Broadband allows for multiple signals to be sent across the wire at any given time.

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If you had a cable television service which only allowed you to receive

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a single television station that wouldn’t be a very good service.

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Broadband on the other hands allows for multiple signals

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to be sent across a single coaxial cable at any given time.

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So once again broadband television uses coaxial cable which is similar to the

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coaxial cable that was use in the early Ethernet implementations.