TOPIC 2.1.1 | METHODS OF DATA TRANSMISSION

Topics from the Cambridge IGCSE (9-1) Computer Science 0984 syllabus 2023 - 2025.

OBJECTIVES
(a)Understand that data is broken down into packets to be transmitted
​(b) Describe the structure of a packet
​(c) Describe the process of packet switching

ALSO IN THIS TOPIC
2.1.1 METHODS OF DATA TRANSMISSION
2.1.2 METHODS OF DATA TRANSMISSION
2.1.3 METHODS OF DATA TRANSMISSION
2.2 METHODS OF ERROR DETECTION
2.3 ENCRYPTION
TOPIC 2 KEY TERMINOLOGY
TOPIC 2 ANSWERS
TOPIC 2 TEACHER RESOURCES (CIE)

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DATA PACKETS

Before looking at how data is carried it is important to understand the principles of how the internet works so you understand the need for data transmission.  The internet is a series of networks, servers and clients connected together using protocols and infrastructure to allow smooth data sharing on a global scale. Most data is currently transmitted from one device to another through the use of cables, even with your mobile phone, although the data is transmitted a short distance wirelessly the majority of the journey will be through cables.

Data transmission is the process of sending information from one device to another over a network. To ensure efficient and reliable data transmission, the data is broken down into smaller units called "packets". Each packet contains a portion of the data, along with a header that contains information about the packet, such as its source and destination addresses, and the sequence number of the packet.

When the packets are transmitted, they are sent individually and can take different routes to reach their destination. At the receiving end, the packets are reassembled into the original data. The header information is used to ensure that the packets are received in the correct order and to check for any errors or lost packets during transmission. If a packet is lost or corrupted, it can be retransmitted, ensuring the integrity of the data. This process of breaking down data into packets and transmitting it over a network is called packet switching.

THE STRUCTURE OF A PACKET
A data packet is a small unit of data that is transmitted over a network. It consists of three main parts: header, payload, and trailer.

Header: The header is a collection of information about the packet, such as the source and destination addresses, sequence number, and packet type. It also includes information about routing and error detection, such as checksum values.

Payload: The payload is the actual data that is being transmitted. It can be a small amount of text, an image, a video, or any other type of digital information.

Trailer: The trailer contains error correction information, such as cyclic redundancy check (CRC) values. The trailer helps the receiving device to verify the integrity of the data in the packet and to detect any errors that may have occurred during transmission.

Together, the header, payload, and trailer form a complete packet, which is sent over a network from one device to another. At the receiving end, the information in the header is used to reassemble the packets into the original data, while the trailer information is used to verify the accuracy of the data.

THE PROCESS OF PACKET SWITCHING

Packet switching is the process of transmitting data over a network by breaking it down into small units called "packets". The process involves the following steps:

Data is broken down into packets: The data to be transmitted is divided into smaller units, each containing a portion of the data and a header with information about the packet, such as its source and destination addresses.

Each packet could take a different route: When the packets are transmitted, they may take different routes to reach their destination. This is because the network routes each packet independently based on the current network conditions, such as traffic levels, to optimize for efficiency and reliability.

A router controls the route a packet takes: A router is a device that connects different networks and routes packets to their destination. It decides which route to send each packet based on information in the header and current network conditions.

Packets may arrive out of order: Because packets may take different routes, they may arrive at their destination in a different order than they were sent. This is because different packets may take longer or shorter routes based on network conditions.

Once the last packet has arrived, packets are reordered: After all the packets have arrived at the destination, they are reassembled into the original data. The header information is used to determine the correct order of the packets and to ensure that all packets have been received. If any packets are missing or corrupted, they can be retransmitted, ensuring the integrity of the data.

In conclusion, packet switching is a technique for transmitting data over a network by breaking it down into smaller units, routing each packet independently, and reassembling the packets at the destination to form the original data.

1. What is the process of breaking down data into smaller units called?
2. What is the purpose of the header in a data packet?
3. What is the difference between a header and a payload in a data packet?
4. What is the function of the trailer in a data packet?
5. Can packets take different routes to reach their destination?
6. Who controls the route a packet takes in a network?
7. What happens if packets arrive at their destination out of order?
8. How are the packets reassembled into the original data at the destination?
9. Explain why packets take different routes to get to their destination?
10. What is the significance of packet switching in data transmission?

ALSO IN THIS TOPIC

2.1.1 METHODS OF DATA TRANSMISSION | Data Packets
2.1.2 METHODS OF DATA TRANSMISSION | Serial, Parallel, Simplex, Duplex
2.1.3 METHODS OF DATA TRANSMISSION | The Universal Serial Bus
2.2 METHODS OF ERROR DETECTION | Parity Checks, Check Sum, Check Digit, ARQ
2.3 ENCRYPTION | Symmetric and Asymmetric Encryption
TOPIC 2 KEY TERMINOLOGY
TOPIC 2 ANSWERS
TOPIC 2 TEACHER RESOURCES (CIE)