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Data Transmission

2.1 Types and methods of data transmission

Candidates should be able to:

1. Understand that data is broken down into packets to be transmitted

  • Describe the structure of a packet

  • Describe the process of packet switching

Note and guidance

  • A packet of data in a unit of data contains a

    • packet header

    • payload

    • trailer

  • The packet header includes the:

    • destination address

    • packet number

    • originator’s address

  • Data is broken down into packets

  • Each packet could take a different route

  • A router controls the route a packet takes

  • Packets may arrive out of order

  • Once the last packet has arrived, packets are reordered

2. Describe how data is transmitted from one device to another using different methods of data transmission

  • Explain the suitability of each method of data transmission, for a given scenario

Note and guidance

  • Including:

    • serial

    • parallel

    • simplex

    • half-duplex

    • full-duplex

  • Including the advantages and disadvantages of each method

3. Understand the universal serial bus (USB) interface and explain how it is used to transmit data

Note and guidance

  • Including the benefits and drawbacks of the interface

2.2 Methods of error detection

Candidates should be able to:

1. Understand the need to check for errors after data transmission and how these errors can occur

Note and guidance

  • Errors can occur during data transmission due to interference, e.g. data loss, data gain and data change

2. Describe the processes involved in each of the following error detection methods for detecting errors in data after transmission: parity check (odd and even), checksum and echo check

Note and guidance

  • Including parity byte and parity block check

3. Describe how a check digit is used to detect errors in data entry and identify examples of when a check digit is used, including international standard book numbers (ISBN) and bar codes

4. Describe how an automatic repeat query (ARQ) can be used to establish that data is received without error

Note and guidance

Including the use of:- positive/negative acknowledgements

  • timeout

2.3 Encryption

Candidates should be able to:

1. Understand the need for and purpose of encryption when transmitting data

2. Understand how data is encrypted using symmetric and asymmetric encryption

Note and guidance

  • Asymmetric encryption includes the use of public and private keys

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