# Q6(c) · TCP/IP layers

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2024-feb-reexam/q6c

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2024-feb-reexam--q6c/

Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.

### Q6(c). Explain briefly the functionalities of layers of TCP/IP protocol suite. [5 marks]

### Answer

The **TCP/IP model** describes the Internet protocol suite in four layers. Many teaching books split the link layer into data link and physical, making a five-layer teaching model; identify the convention before drawing.

Swipe across the diagram to read its labels ↔

![OSI layers mapped to the four-layer TCP/IP model](https://deep-learning-study-room.vercel.app/cn/fig/tee-models.5bff0518c8.svg)

Diagram: OSI layers mapped to the four-layer TCP/IP model. Labels: OSI layers mapped to the four-layer TCP/IP model | OSI layers mapped to the four-layer TCP/IP model | 7 Application | 6 Presentation | 5 Session | 4 Transport | 3 Network | 2 Data link | 1 Physical | Application | HTTP, DNS, FTP, SMTP | Transport | Internet | Link / network access | Includes physical access | Some textbooks split link into data link + physical: five layers.

Four TCP/IP layers; the link layer includes the physical medium.

| TCP/IP layer | Function | Examples |
| --- | --- | --- |
| Application | Defines application message formats and exchanges for Web access, naming, email and file transfer; includes presentation/session functions as needed | HTTP, DNS, SMTP, FTP |
| Transport | End-to-end process communication | TCP, UDP, SCTP |
| Internet | IP addressing, routing and best-effort datagrams | IPv4/IPv6 |
| Link/network access | Local delivery and physical access | Ethernet/Wi-Fi and their medium |

| Point | OSI | TCP/IP |
| --- | --- | --- |
| Layer count | Seven | Four here; five-layer teaching variant splits link |
| Upper functions | Application, presentation, session separated | Grouped under application |
| Lower functions | Data link and physical separated | Grouped under link/network access |
| Purpose | General reference architecture | Architecture of deployed Internet protocol family |
| Network service | Reference model can describe different services | Internet layer uses connectionless IP |
| Transport | Conceptual transport service | TCP reliable byte stream; UDP datagrams; SCTP messages |

#### Practical example

An application can use UDP without changing the IP or Ethernet layers. Layering lets one protocol vary without redesigning every network function.

**Yaad rakho:** OSI 7; TCP/IP four mein upper three merge, lower two merge.

### Internet and transport protocols

| Layer | Protocol | Role |
| --- | --- | --- |
| Internet | IPv4 / IPv6 | Address and deliver best-effort packets across networks |
| Internet | ICMP / ICMPv6 | Report selected IP errors and operational information; used by diagnostic exchanges |
| Transport | TCP | Reliable, ordered byte stream with connection establishment, flow and congestion control |
| Transport | UDP | Connectionless message delivery using ports, without built-in retransmission or ordering |
| Transport | SCTP | Reliable message-oriented association with multiple streams and multihoming support |