Exam 1: Introduction to Data Communications

Correct Answer:

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The five layers of the internet model are:

1. Physical layer: This layer deals with the physical connection between devices. It includes the cables, connectors, and other hardware used to transmit data.

2. Data link layer: This layer is responsible for the reliable transmission of data across the physical layer. It includes protocols for error detection and correction, as well as addressing and framing of data packets.

3. Network layer: This layer is responsible for routing data packets from the source to the destination. It includes protocols for addressing, routing, and forwarding of data packets.

4. Transport layer: This layer is responsible for the end-to-end communication between the source and destination. It includes protocols for reliable and efficient data transfer, as well as error detection and recovery.

5. Application layer: This layer is responsible for providing services to the end users. It includes protocols for various applications such as email, web browsing, and file transfer.

Using a diagram, the five layers in the network model can be represented as follows:

```
---------------------------------------------------------
| Application Layer | Transport Layer | Network Layer |
---------------------------------------------------------
| Data Link Layer | Physical Layer |
---------------------------------------------------------
```

Examples of standards for each layer in the diagram are:

1. Physical layer: Ethernet, Wi-Fi, USB
2. Data link layer: Ethernet, PPP, HDLC
3. Network layer: IP, ICMP, ARP
4. Transport layer: TCP, UDP, SCTP
5. Application layer: HTTP, FTP, SMTP

To explain how a message is transmitted from one computer to another using this model, let's consider the example of sending an email.

1. The email application at the source computer (Application layer) creates the email message and passes it to the Transport layer.
2. The Transport layer adds the necessary information for reliable transmission and passes the data to the Network layer.
3. The Network layer adds the source and destination addresses and routes the data packet to the destination computer.
4. The Data Link layer adds the necessary framing and error detection information and passes the data to the Physical layer.
5. The Physical layer transmits the data over the physical medium to the destination computer.
6. At the destination computer, the process is reversed, with each layer handling the data as it moves up the stack until it reaches the email application.