← WA Computer Science ATAR Unit 1

The OSI seven-layer model

A seven-layer network model: physical, data link, network, transport, session, presentation, application. Layer 1 is physical (bottom) and layer 7 is application (top).

Part of: WA Computer Science ATAR Year 11 — Network Communications — Module 25

Understanding The OSI seven-layer model in WA Computer Science ATAR Unit 1

What it does: Bottom-up order starts at the physical layer and ends at the application layer, which is layer 7. The OSI model has seven layers. The TCP/IP model is the one with four layers. The network layer handles IP addresses and routing. The data link layer handles MAC addresses within a local network. The application layer is at the top (layer 7) and is where programs like browsers and email clients access the network. The transport layer manages ports and reliable delivery. Layer 1 is the physical layer. It deals only with the signals that carry the bits, such as cables and radio waves.

Common mistakes: Layer 2 is the data link layer. The network layer is layer 3, so line 3 should be print("2 data link"). Layer 1 is the physical layer at the bottom of the OSI model. The application layer is layer 7 at the top. The line should be name = "physical".

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Learning

Duo

Which list shows the OSI layers in order from layer 1 up to layer 7?

Physical, data link, network, transport, session, presentation, applicationPhysical, network, data link, transport, presentation, session, application

Matches

Layer 7 is the Physical layer, at the bottom of the OSI model

↓

Layer 7 is the Application layer at the top. The Physical layer is layer 1 at the bottom.

Applying

Meanings

Term

OSI model

Meaning

A seven-layer network model: physical, data link, network, transport, session, presentation, application. Layer 1 is physical (bottom) and layer 7 is application (top).

Practice

7 Application

Testing

Gaps

Layer 1: (cables and signals)

Check Answer

Spots

2print("1 physical")

3print("2 network")

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Quick Questions

1. Which list shows the OSI layers in order from layer 1 up to layer 7?

A. Physical, network, data link, transport, presentation, session, application

B. Physical, data link, network, transport, session, presentation, application ✓

Bottom-up order is physical, data link, network, transport, session, presentation, application. Data link comes before network, and session comes before presentation.

2. How many layers does the OSI model have?

A. Four

B. Seven ✓

The OSI model has seven layers. The TCP/IP model is the one with four layers.

3. Which layer is layer 1 (the bottom layer) of the OSI model?

A. Physical ✓

B. Application

Layer 1 is the physical layer, which deals with the cables, signals and bits. The application layer is layer 7 at the top.

4. Which OSI layer is responsible for IP addressing and choosing a route for packets between networks?

A. Network layer (layer 3) ✓

B. Data link layer (layer 2)

The network layer handles IP addresses and routing. The data link layer handles MAC addresses within a local network.

5. Which OSI layer uses MAC addresses to deliver frames between devices on the same local network?

A. Data link layer ✓

B. Transport layer

The data link layer (layer 2) uses MAC addresses for local delivery. The transport layer (layer 4) handles ports and end-to-end delivery.

Match the Pairs

Layer 1: Physical → The bottom OSI layer, which sends raw bits as electrical, light or radio signals over the medium.

Layer 4: Transport → The OSI layer that splits data into segments and manages delivery between devices using ports (TCP or UDP).

The seven OSI layers listed from the bottom (layer 1) up to the top (layer 7) → Physical, Data Link, Network, Transport, Session, Presentation, Application

The seven OSI layers listed top-down, in the order data moves when it is sent from an application → 7 Application, 6 Presentation, 5 Session, 4 Transport, 3 Network, 2 Data Link, 1 Physical

Layer 7 is the Physical layer, at the bottom of the OSI model → Layer 7 is the Application layer at the top. The Physical layer is layer 1 at the bottom.

OSI order from layer 1: Physical, Network, Data Link, Transport → Network and Data Link are in the wrong order. Layer 2 is Data Link and layer 3 is Network.

Key Term

OSI model

A seven-layer network model: physical, data link, network, transport, session, presentation, application. Layer 1 is physical (bottom) and layer 7 is application (top).

Fill in the Blanks

1. Layer 1: Physical (cables and signals)

Hint: Type the name of the bottom layer, which sends raw bits as electrical, light or radio signals.

2. Layer 2: Data Link (MAC addresses, frames)

Hint: Type the name of the layer above the bottom one that moves frames between neighbouring devices using MAC addresses.

3. Layer 3: Network (IP addresses, routing)

Hint: Type the layer number for the Network layer, counting up from the physical layer at the bottom.

4. Layer 4: Transport (TCP and UDP)

Hint: Type the name of the layer where the TCP and UDP protocols work.

5. Layer 5: Session Layer 6: Presentation Layer 7: Application

Hint: Type the name of the layer between session and application that formats, compresses and encrypts data.

Spot the Error

Question 1

A print("OSI layers, bottom up")

B print("1 physical")

C print("2 network")

D print("3 network")

Line C — Layer 2 is the data link layer. The network layer is layer 3, so line 3 should be print("2 data link").

Question 2

A layer = 1

B name = "application"

C print(layer, name)

Line B — Layer 1 is the physical layer at the bottom of the OSI model. The application layer is layer 7 at the top. The line should be name = "physical".

Question 3

A layer = 3

B name = "network"

C print(layer, name)

D job = "bit signals on cable"

Line D — The network layer handles IP addressing and routing. Sending bit signals over a cable is the job of the physical layer.

Question 4

A order = "top-down"

B first = "application"

C second = "presentation"

D third = "transport"

E last = "physical"

Line D — Going top-down the order is application (7), presentation (6), session (5). Transport is layer 4, so it comes after session. The line should be third = "session".

Question 5

A order = "bottom-up"

B first = "physical"

C second = "network"

D third = "network"

Line C — Going bottom-up, layer 2 is data link, directly above physical. The network layer is third. The line should be second = "data link".

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