OSI Model: A Practical Perspective - Networking Fundamentals - Lesson 2a

Summary

This video lesson delves into the OSI model, a foundational concept in networking. It illustrates how the seven layers of the OSI model facilitate data sharing between hosts, emphasizing the roles of the physical, data link, and network layers. The physical layer is responsible for transporting bits, while the data link layer ensures hop-to-hop delivery using MAC addresses. The network layer, utilizing IP addresses, achieves end-to-end delivery, with routers playing a key role. The lesson clarifies the necessity of both MAC and IP addresses in data transmission and hints at the Address Resolution Protocol (ARP) for linking these addresses. The instructor invites viewers to engage with the content and contribute to the course's development.

Takeaways

• 📚 Start with lesson one for a complete understanding of the OSI model.
• 🌐 Networking allows hosts to share data automatically across wires, replacing manual data transfer.
• 🖧 The OSI model divides networking rules into seven layers, each with a specific function.
• 🏗️ The physical layer (Layer 1) is responsible for transporting bits (ones and zeros) between hosts using cables or wireless technologies like Wi-Fi.
• 🔁 Devices like repeaters and hubs, which extend and amplify signals, are considered Layer 1 technologies.
• 🔌 Layer 2, the Data Link Layer, handles hop-to-hop delivery of data using network interface cards (NICs) and MAC addresses.
• 📟 Switches, which facilitate communication within a network, are Layer 2 devices.
• 📡 Layer 3, the Network Layer, is responsible for end-to-end delivery of data using IP addresses.
• 🖧 Routers are Layer 3 devices that help route data between networks.
• 🔗 The Address Resolution Protocol (ARP) links IP addresses to MAC addresses, aiding in data flow through the network.

Q & A

What is the primary goal of networking as an industry?

The primary goal of networking is to allow two hosts to share data with one another automatically across the wire, without the need for manual data transfer between hosts.

What is the OSI model and why is it important?

The OSI model is a framework that divides the rules for networking into seven different layers. It is important because it standardizes the way data is transmitted between devices, similar to how language rules standardize communication between people.

What is the purpose of the Physical Layer (Layer 1) in the OSI model?

The purpose of the Physical Layer is to transport bits (ones and zeros) from one computer to another. This includes various types of cables and wireless technologies like Wi-Fi, which are considered Layer 1 technologies.

What is a repeater and why is it considered a Layer 1 device?

A repeater is a device that amplifies signals from one end to the other, effectively extending a wire. It is considered a Layer 1 device because its primary function is to contribute to the transportation of bits, which aligns with the goal of the Physical Layer.

What is the role of Layer 2 in the OSI model?

Layer 2, also known as the Data Link Layer, is responsible for hop-to-hop delivery of data. It uses MAC addresses to facilitate the movement of data between network interface cards (NICs) or Wi-Fi access points.

What is a MAC address and why is it used in Layer 2?

A MAC address is a 48-bit address that uniquely identifies a network interface card. It is used in Layer 2 to enable the hop-to-hop delivery of data by identifying the source and destination NICs for each data packet.

What is the difference between a switch and a hub, and why are they both considered Layer 2 devices?

A switch is a more intelligent device that facilitates communication within a network and can connect many devices, while a hub is a simpler device that connects multiple devices without much intelligence. Both are considered Layer 2 devices because they aid in the delivery of data between NICs.

What is the purpose of Layer 3 in the OSI model?

Layer 3, known as the Network Layer, is responsible for end-to-end delivery of data. It uses IP addresses to identify hosts and routers, ensuring that data reaches its intended destination across multiple hops.

Why are both MAC and IP addresses necessary in networking?

Both MAC and IP addresses are necessary because they serve different purposes. MAC addresses are used for hop-to-hop delivery within a local network, while IP addresses are used for end-to-end delivery across multiple networks or hops.

What is the Address Resolution Protocol (ARP) and its role in networking?

The Address Resolution Protocol (ARP) is a protocol that links a Layer 3 address (IP address) to a Layer 2 address (MAC address). It is crucial for understanding how data flows through a network by facilitating the translation between these two types of addresses.

What will be the focus of the next part of the discussion on the OSI model?

The next part of the discussion will focus on the Transport Layer, which is Layer 4 of the OSI model. This layer is responsible for end-to-end communication and ensures the reliable delivery of data.

Outlines

00:00

📚 Introduction to Networking Fundamentals and OSI Model

This paragraph introduces the lesson on networking fundamentals, focusing on the OSI model. It emphasizes the importance of networking to enable data sharing between hosts and the necessity of a set of rules, similar to language rules, for effective communication. The OSI model is presented as a structured framework with seven layers, each serving a specific function. The analogy of the human body's systems is used to illustrate the interdependence of these layers in achieving the overall goal of networking. The objective of this lesson is to understand the purpose of each OSI layer and their contribution to data sharing between hosts.

05:00

🔌 The Physical Layer and Layer 1 Technologies

The first layer of the OSI model, the physical layer, is discussed in this paragraph. It explains that the physical layer's purpose is to transport bits between hosts using cables or Wi-Fi, which are categorized as layer 1 technologies. The concept of a repeater, which extends the reach of a cable by amplifying signals, is introduced as a layer 1 device. The paragraph clarifies that the term 'physical' in the OSI model predates wireless communication but includes Wi-Fi due to its role in transmitting binary data. The physical layer is fundamental to the process of moving data across networks.

10:03

🔄 Layer 2: Data Link Layer and MAC Addresses

This paragraph delves into the second layer of the OSI model, known as the data link layer. It describes the role of this layer in facilitating hop-to-hop delivery of data using MAC addresses, which are unique identifiers for network interface cards (NICs). The paragraph explains that switches, which connect multiple devices and manage data flow within a network, are considered layer 2 technologies. It also discusses the importance of MAC addresses in enabling data to move from one NIC to another across multiple hops, and how layer 2 operates in conjunction with the physical layer to achieve networking goals.

🌐 Layer 3: Network Layer and IP Addresses

The paragraph introduces the network layer, or layer 3, which is responsible for end-to-end data delivery across networks. It explains the use of IP addresses, a 32-bit addressing scheme, to identify hosts and route data from the source to the destination. Routers, which are devices that forward data packets to their next destination, are identified as layer 3 technologies. The paragraph also addresses the relationship between IP and MAC addresses, highlighting the need for both addressing schemes to facilitate the flow of data across multiple network hops. The importance of the Address Resolution Protocol (ARP) in linking IP and MAC addresses is briefly mentioned, setting the stage for further discussion in subsequent lessons.

Keywords

💡OSI Model

The OSI Model, or Open Systems Interconnection Model, is a conceptual framework used to understand and implement networking protocols in seven distinct layers. Each layer has a specific function that contributes to the process of data exchange between computers. In the video, the OSI Model is explained as a fundamental aspect of networking, where each layer (from physical to application) plays a crucial role in allowing hosts to share data seamlessly.

💡Physical Layer

The Physical Layer is the first layer of the OSI Model and is responsible for the physical connection between devices. It involves the transmission and reception of raw binary data over a communication medium, such as cables or wireless signals. The video describes the Physical Layer as the medium that physically transports the 1s and 0s, highlighting the use of cables and wireless technologies like Wi-Fi as examples.

💡Layer 2

Layer 2 of the OSI Model is known as the Data Link Layer. It handles the node-to-node data transfer and error detection/correction that may occur in the Physical Layer. It uses MAC addresses to ensure data is sent to the correct device on a network. In the video, Layer 2 is discussed in terms of its role in 'hop-to-hop' delivery, with network interface cards (NICs) and switches being examples of technologies that operate at this layer.

💡Layer 3

Layer 3, also known as the Network Layer, is responsible for routing data from the source to the destination across multiple networks, typically through the use of IP addresses. The video describes Layer 3 as handling 'end-to-end' delivery of data packets and introduces the concept of IP addresses and routers as core components of this layer, facilitating data movement across diverse networks.

💡MAC Address

A MAC Address, or Media Access Control Address, is a unique identifier assigned to network interfaces for communications at the Data Link Layer. It consists of 48 bits and is used to identify devices on a local network. In the video, MAC addresses are highlighted as essential for Layer 2 operations, enabling data to be transferred between specific NICs or devices within a network segment.

💡IP Address

An IP Address is a numerical label assigned to devices connected to a computer network that uses the Internet Protocol for communication. It serves two main functions: identifying the host or network interface and providing a location address. In the video, IP addresses are discussed in the context of Layer 3, where they play a vital role in the end-to-end delivery of data across networks.

💡Repeater

A repeater is a network device that amplifies and retransmits signals to extend the range of a network. It operates at the Physical Layer (Layer 1) of the OSI Model. In the video, repeaters are described as devices that help extend the physical transmission medium, ensuring that data signals can travel further without degradation.

💡Switch

A switch is a network device that operates at Layer 2 (Data Link Layer) of the OSI Model. It connects devices within a local network and uses MAC addresses to forward data to the correct destination within that network. The video explains how switches facilitate communication between multiple devices on a network, emphasizing their role in handling data transfer between NICs within the same network segment.

💡Router

A router is a networking device that forwards data packets between computer networks, operating primarily at Layer 3 (Network Layer) of the OSI Model. It uses IP addresses to determine the best path for data to travel across networks. The video describes routers as crucial for end-to-end data delivery, directing traffic from one network to another and handling multiple hops in the process.

💡Address Resolution Protocol (ARP)

The Address Resolution Protocol (ARP) is a network protocol used to find the MAC address associated with a given IP address. It bridges Layer 2 and Layer 3 of the OSI Model by linking the IP address to the hardware MAC address. In the video, ARP is mentioned as a vital protocol that enables the smooth operation of networking by ensuring that data packets are sent to the correct physical device on a network.

Highlights

Introduction to the OSI model and its importance in networking.

Analogy between the OSI model and the human body systems to explain the layered approach.

Explanation of the physical layer (Layer 1) and its role in transporting bits across the network.

Discussion on physical layer technologies such as cables and Wi-Fi.

Introduction to repeaters and hubs as Layer 1 technologies.

Explanation of the data link layer (Layer 2) and its function in hop-to-hop delivery.

Description of Network Interface Cards (NICs) and Wi-Fi access cards as Layer 2 technologies.

Introduction to MAC addresses and their format in different operating systems.

Role of switches in Layer 2 for facilitating communication within a network.

Introduction to Layer 3 (the network layer) and its goal of end-to-end delivery.

Explanation of IP addresses and their structure.

Discussion on the role of routers in Layer 3 for aiding end-to-end data delivery.

Comparison of MAC addresses and IP addresses and their different purposes.

Explanation of the Address Resolution Protocol (ARP) for linking Layer 3 and Layer 2 addresses.

Summary of how Layer 1, Layer 2, and Layer 3 work together to move data across a network.

Transcripts

hello welcome to another lesson from the

first module of my new course on

networking fundamentals

in this lesson we'll be taking a

practical look at the osi model

if you haven't seen the videos for

lesson one i'd highly recommend you

start there

this lesson is simply a direct

continuation of what occurred in lesson

one

that said let's get into discussing the

osi model

the overall purpose of networking as an

industry

is to allow two hosts to share data with

one another

before networking if i want to get data

from this host to this host i'd have to

plug something into this host

walk it over to the other host plug it

into the other host

networking allows us to automate all

that by allowing the host to share data

automatically across the wire

for these hosts to do this they must

follow a set of rules

this is no different than any language

english has a set of rules that two

english speakers must follow

spanish has its own set of rules french

has its own set of rules

while networking also has its own set of

rules

the rules for networking are divided

into seven different layers and those

layers are known as the osi model

now to give you an analogy the human

body is made up of various systems

the skeletal system the respiratory

system the nervous system

the cardiovascular system the muscular

system

and if each of those systems are

operating as intended

then the goal of the human body is

attained meaning the human lives

well networking works the same way each

of the layers of the osi model

serve a specific function and if all

seven

functions are accomplished then the goal

of networking is attained

which is to say host can share data

and the goal of this lesson is not

simply to memorize the osi model

the goal this lesson is to take a look

at the purpose of

each layer in the osi model and see how

it contributes to the overall goal of

networking which is allowing two hosts

to share data with one another

that said let's just jump right into it

starting with the first layer of the osi

model known as the physical layer

data on computers exist in the form of

bits

that is ones and zeros well the first

thing that needs to exist for these

hosts to share a data with another

is something has to transport those ones

and zeros from this computer

to the next that something is the

physical layer

the goal of the physical error is

transporting bits

and anything that contributes to moving

ones and zeros from this computer to

this computer is considered a layer one

technology

for example cables all fall under the

concept of layer 1 technologies

all of these cables serve the purpose of

taking bits from one end

and taking them out to the other end but

don't get too caught up on the word

physical

the osi model was written well before

the idea of

wireless internet communication was ever

thought of

wi-fi is considered to be a layer one

technology because wi-fi

solely exists to carry ones and zeroes

from one computer to the next

now not only do these cables or wi-fi

exist at layer one

there are some devices that also exist

at layer one one of those devices is

known as a repeater

in the last lesson we identified the

repeaters simply amplify signals

from one end out the other end in a way

a repeater is really nothing more than

something that allows you to extend

a wire meaning it contributes to this

goal

therefore a repeater is considered to be

a layer 1 technology

which means that multi-port repeaters

like hubs would also be considered

layer 1 technologies all of these items

serve the function of transporting bits

from one computer to the next

that is the goal of layer 1 which brings

us

to layer 2. layer two is going to

interact with the physical layer it's

going to actually put

bits on the wire and retrieve bits from

the wire

which means whatever this wire actually

connects to on this pc

is considered a layer 2 item meaning the

nic

or the network interface card that this

wire is actually connected to on this

computer

is considered layer 2. the wi-fi access

card is also considered layer 2 because

it's interacting with those wi-fi radio

waves

now nicks and wi-fi access cards don't

really look like this anymore but there

was a time when you had to buy

separate cards and actually install them

into computers and able to access the

network or wi-fi

nowadays wi-fi access cards can fit in

your smartphone or your watch

the overall goal of layer 2 is what i'm

going to call

hop to hop delivery meaning layer 2

exists to take ones and 0s from this nic

and move it to the other nic this

is what i'm calling a hop now to

accomplish this goal

layer 2 is going to use a specific

addressing scheme

that addressing scheme is known as a mac

address

mac addresses are 48 bits which are

represented as 12

hex digits here are three examples of a

mac address

now in all cases these are the exact

same mac address

the only thing that's different is how

they're displayed

windows machines typically use the

dashes in between the hex digits

linux machines typically use those

colons and cisco

routers and switches typically use the

four hex digits with a dot in between

either way it's still just 12 hex digits

which are converted into 48 bits

the way it works is every single nick

has a unique

mac address meaning this computer's nick

over here has the mac address a1

a1 and this computer's nick has the mac

address e8e8

now i'm only showing you the first four

digits of the mac address simply to

conserve

screen real estate but in reality this

is what a mac address looks like

either way this mac address is what's

going to allow data to go

from one nic to the next ie from one hop

to the next

so we've identified that nics exist at

layer two

but there is another type of device that

also exists at layer 2 and that is

switches recall from the last lesson

that we discussed that switches are

devices which facilitate communication

within a network

meaning if these two hosts are connected

via this switch

the switch is what's going to help

traffic move along to accomplish

this hop moreover switches allow you to

connect

many devices to them if these two hosts

want to speak to each other

the switch is going to internally

connect these wires such that data

can traverse this hop from this nick to

this nic

so switches are considered layer 2

technologies because they aid in the

accomplishment of this goal

now generally with the internet you're

commuting with things that are far

away not necessarily things that are in

the same network

so it's very common for communication

between hosts to require multiple hops

meaning we need to jump across multiple

routers to get to the target host

well each of those routers are connected

to a wire using a nic

and therefore each of those nicks have

their own mac addresses

and layer two will handle taking data

from the first mac address

and delivering it to the next mac

address and then from this nic

to the next nic and then from this nick

to the next nick

and then finally from this neck to the

next nick as you'll notice

in all cases layer two is handling the

hop-to-hop

delivery of data which begs the question

if layer 2 is taking care of every hop

what's taking care of ensuring data goes

from this end point

to the next well that's where layer 3

comes into play

layer 3's goal is what's called end to

end delivery

to accomplish its goal player 3 is going

to use its own addressing scheme

known as ip addresses now we unpacked ip

addresses in the prior lesson

ip addresses are 32 bits represented as

4 octets

each that can be the number zero through

255.

every host is going to be identified by

its ip address

and these ip addresses are what's going

to allow data to go from here

all the way to here now as you can see

from this illustration

aiding in the goal of delivering data

from end to end

is routers so routers are considered to

exist at layer 3 of the osi model

hosts are also considered to exist at

layer 3 of the osi model

but really anything with an ip address

can be considered to exist at layer 3

of the osi model now at this point

a question typically comes up and that

question is

if we have ip addresses at layer 3 why

do we need mac addresses

or alternatively if we have mac address

to layer 2 why do we need ip addresses

answering that question will help reveal

how packets flow through the internet

the reason we have two different

addressing schemes is that each of those

addressing schemes

serve different purposes so let me show

you

let's say this host has some data that

needs to send

to this host now of course that data is

just a bunch of ones and zeroes

layer two and layer three don't know

what that data contains it's just an

arbitrary set of ones and zeros that

need to get to this host over here

since this computer knows the data needs

to get to this endpoint over here

it's going to add some layer 3

information to that data that layer 3

information is going to include the

source

ip address and the destination ip

address in order to get

this data from one end to the other but

now this computer knows that the first

step will be getting that data to the

first router which will prompt the

computer to add

layer 2 information to that data and

that layer 2 information is going to

have a source mac address of the

computer's nic

and a destination mac address of the

first router's nic

that's what's going to get this

information to the first router

once it gets there we can remove that

layer 2 information

remember the whole purpose of that layer

2 header was simply to get

this construct from here to here through

the first hop

from this point this router now knows

that this

needs to get moved to the next router

and it's going to do this by adding

another layer 2 header

but notice this time the source and

destination mac address

identify these two mac addresses that's

what's going to take

this packet to the next router

and here once again we can get rid of

that layer 2 information

again the whole purpose of that layer 2

header was simply to get the packet from

here

to here since it did that successfully

we no longer need it

this process will continue with this

middle router over here

adding layer 2 information that will

take care of this hop

and finally the last router in the

sequence will add the final layer 2

header

which will take the packet from this

nick to

the end host's nick once it gets to the

final host

again the layer 2 header can be removed

the purpose of that header was again

just to bring the packet from here

to here moreover the layer 3 header can

be removed

because the purpose of that header was

to bring the data from

here to here from end to end

finally this gets the data to the

computer and the data can be processed

by the receiving host

that is why we need both ip addresses

and mac addresses

because they serve different functions

and we've been talking about ip

addresses and mac addresses as

independent functions

and indeed they are but i should mention

at this point that there is a protocol

that's going to tie these together

that protocol is known as the address

resolution protocol

it's going to link a layer 3 address

like an ip address

to a layer 2 address like a mac address

arp is crucial to understanding how data

flows through a network

we're going to be talking about arp

later on in this module

but if you can't wait i did write an

article series that discusses all the

different forms of arp

you can access that series at

pracnet.net arp

as for us that wraps up the first part

of our practical discussion of the osi

model

in this video we discussed layer 1 layer

2 and layer 3

and how each of those layers have a

specific goal which contributes to how

data flows through a network

in particular we illustrated how layer

two and layer three

work together to move data across the

many different hops

required to get data from one end to

another

so that wraps up part one of our

discussion in part two we'll pick up

right where we left off discussing the

transport layer

but the main takeaways for this lesson

are on your screen right now

i hope you enjoyed this video i want to

thank you for watching and we'll see you

in the next video as we continue our

discussion of the osi model

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fundamentals

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covered

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