← WA Computer Science ATAR Unit 1

Mapping the TCP/IP model to the OSI model

Each TCP/IP layer covers one or more OSI layers: Application = OSI application, presentation and session; Network Access = physical and data link; Transport and Internet match one each.

Part of: WA Computer Science ATAR Year 11 — Network Communications — Module 27

Understanding Mapping the TCP/IP model to the OSI model in WA Computer Science ATAR Unit 1

What it does: Transport is a one-to-one match between the models, and TCP and UDP operate at this layer in both. The names differ but the job is the same: logical addressing and routing with IP. This is a one-to-one mapping. The TCP/IP Application layer combines the top three OSI layers: application, presentation and session. Network Access = OSI physical + data link. It covers cables, Wi-Fi signals and MAC addressing. TCP/IP merges OSI layers 1 and 2 into one layer that handles cables, Wi-Fi, MAC addresses and frames.

Common mistakes: The TCP/IP Transport layer matches OSI layer 4 (Transport). OSI layer 3 is the Network layer, which maps to the TCP/IP Internet layer. It should be m['Transport'] = [4]. The TCP/IP Application layer covers only OSI application, presentation and session (layers 5-7). OSI layer 4 is Transport, which has its own TCP/IP layer. It should be OSI 5-7.

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Learning

Duo

Which OSI layers does the TCP/IP Application layer cover?

Application, presentation and sessionPhysical and data link

Matches

TCP/IP Application = OSI Application only

↓

The TCP/IP Application layer also covers the OSI Presentation and Session layers, not just OSI Application

Applying

Meanings

Term

TCP/IP to OSI mapping

Meaning

Each TCP/IP layer covers one or more OSI layers: Application = OSI application, presentation and session; Network Access = physical and data link; Transport and Internet match one each.

Practice

Application = Application + Presentation + Session

Testing

Gaps

Presentation and

Check Answer

Spots

2m['Application'] = [7, 6, 5]

3m['Transport'] = [3]

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Quick Questions

1. Which OSI layers does the TCP/IP Application layer cover?

A. Physical and data link

B. Application, presentation and session ✓

The TCP/IP Application layer combines the top three OSI layers: application, presentation and session.

2. Which OSI layers does the TCP/IP Network Access layer cover?

A. Physical and data link ✓

B. Session and presentation

Network Access = OSI physical + data link. It covers cables, Wi-Fi signals and MAC addressing.

3. Which TCP/IP layer matches the OSI Transport layer?

A. Internet

B. Transport ✓

The Transport layers match one to one. TCP and UDP work at this layer in both models.

4. Which OSI layer matches the TCP/IP Internet layer?

A. Network (layer 3) ✓

B. Data link (layer 2)

The TCP/IP Internet layer matches the OSI Network layer. This is where IP addressing and routing happen.

5. The OSI session layer is part of which TCP/IP layer?

A. Application ✓

B. Transport

TCP/IP has no separate session layer. Session is folded into the Application layer along with presentation.

Match the Pairs

TCP/IP Application layer → Covers three OSI layers: Application, Presentation and Session

TCP/IP Network Access layer → Covers two OSI layers: Physical and Data Link

The OSI Transport layer (layer 4) matches one TCP/IP layer of the same job, which handles end-to-end delivery → OSI Transport = TCP/IP Transport (TCP, UDP)

The OSI Network layer (layer 3) matches the TCP/IP layer that addresses and routes packets → OSI Network = TCP/IP Internet (IP)

TCP/IP Application = OSI Application only → The TCP/IP Application layer also covers the OSI Presentation and Session layers, not just OSI Application

TCP/IP Network Access = OSI Network → Network Access maps to the OSI Physical and Data Link layers, not the OSI Network layer, which matches TCP/IP Internet

Key Term

TCP/IP to OSI mapping

Each TCP/IP layer covers one or more OSI layers: Application = OSI application, presentation and session; Network Access = physical and data link; Transport and Internet match one each.

Fill in the Blanks

1. TCP/IP Application = OSI Application, Presentation and Session

Hint: Type the name of the third OSI layer that the TCP/IP Application layer covers, after Application and Presentation.

2. Network Access = Physical + Data Link

Hint: Type the name of the OSI layer that joins Physical to make up TCP/IP Network Access.

3. TCP/IP Transport = OSI layer 4

Hint: Type the OSI layer number that matches the TCP/IP Transport layer.

4. TCP/IP Internet = OSI Network layer

Hint: Type the name of the single OSI layer that matches the TCP/IP Internet layer.

5. TCP/IP has 4 layers, OSI has 7

Hint: Type the total number of layers in the OSI model.

Spot the Error

Question 1

A m = {}

B m['Application'] = [7, 6, 5]

C m['Transport'] = [3]

D m['Internet'] = [3]

E m['Access'] = [2, 1]

Line C — The TCP/IP Transport layer matches OSI layer 4 (Transport). OSI layer 3 is the Network layer, which maps to the TCP/IP Internet layer. It should be m['Transport'] = [4].

Question 2

A TCP/IP Application: OSI 4-7

B TCP/IP Transport: OSI 4

C TCP/IP Internet: OSI 3

D TCP/IP Network Access: OSI 1-2

Line A — The TCP/IP Application layer covers only OSI application, presentation and session (layers 5-7). OSI layer 4 is Transport, which has its own TCP/IP layer. It should be OSI 5-7.

Question 3

A tcp = 'Network Access'

B osi = 'Physical + Network'

C print(tcp, '=', osi)

Line B — TCP/IP Network Access covers the OSI physical and data link layers. The OSI Network layer maps to the TCP/IP Internet layer. It should be 'Physical + Data Link'.

Question 4

A m = {'Application': 3}

B m['Transport'] = 1

C m['Internet'] = 1

D m['Access'] = 3

E print(sum(m.values()))

Line D — Network Access covers exactly two OSI layers: physical and data link. With 3 the total would be 8, but the OSI model has 7 layers. It should be m['Access'] = 2.

Question 5

A def to_tcpip(osi_layer):

B if osi_layer in [5, 6, 7]:

C return 'Application'

D if osi_layer == 3:

E return 'Transport'

Line D — OSI layer 4 (Transport) maps to the TCP/IP Transport layer. Testing for layer 3 would wrongly return 'Transport' for the Network layer. It should be if osi_layer == 4:.

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