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2. Data Transmission
Computer Science CIE IGCSE
| Term | Definition |
|---|---|
| Data packet | A small part of a message/data that is transmitted over a network; after transmission all the data packets are reassembled to form the original message/data. |
| Packet header | The part of the data packet that contains the IP addresses of the sender and receiver, and includes the packet number which allows reassembly of the data packets. |
| Packet trailer | The part of a data packet that indicates the end of the data packet and cyclic redundancy check error check. |
| Cyclic Redundancy Check (CRC) | An error checking method in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer; the same calculation is repeated at the receiving station |
| Payload | The actual data being carried in a data packet. |
| Node | Stages in a network that can receive and transmit data packets; routers are nodes in communication networks |
| Packet Switching | A method of transmission in which a message is broken into many data packets which can then be sent along pathways independently of each-other. |
| Router | A device that enables data packets to be moved between networks, for example to join a LAN to a WAN. |
| Real time streaming | The transmission of data over a network for live events where the data is sent as soon as it is received or generated. |
| hopping/hop number | A number in a data packet header used to stop data packets that never reach their destination from 'clogging up' the data paths/routes. |
| Simplex | Data that can be sent in one direction only. |
| Half-duplex | Data that can be sent in both directions but not at the same time. |
| Full-duplex | Data that can be sent in both directions at the same time (simultaneously). |
| Serial data transmission | Sending data down one channel/wire one bit at a time. |
| Parallel data transmission | Sending data down several channels/wires several bits at a time (usually 1 byte). |
| Skewed data | Data that arrives at the destination with the bits no longer synchronised. |
| Universal Serial Bus (USB) | A type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port. |
| Parity check | A method used to check if data has been transferred correctly; it makes use of even parity (an even number of 1-bits) or odd parity (and odd number of 1-bits). |
| Parity bit | A bit (either 0 or 1) added to a byte of data in the most significant bit position; this ensures that the byte follows the correct even parity or odd parity protocol. |
| Parity block | A horizontal and vertical parity check on a block of data being transmitted. |
| Parity byte | An extra byte of data sent at the end of a parity block; it is composed of the parity bits generated from a vertical parity check of the data block. |
| Checksum | Verification method used to check if data transferred has been altered or corrupted, calculated from the block of data to be sent; the checksum value is sent after each data block. |
| Automatic Repeat Request (ARQ) | A method of checking transmitted data for errors; it makes use of acknowledgement and timeout to automatically request re-sending of data if the time interval before positive acknowledgement is too long. |
| Acknowledgement | A message sent to the receiver indicating that the data has been received (in the ARQ error detection method) |
| Timeout | The time interval allowed to elapse before an acknowledgement is received (in the ARQ error detection method). |
| Echo check | A method used to check if data has been transferred correctly; data is sent to a receiver and then immediately sent back to the sender; the sender then checks if the received data matches the sent data. |
| Check digit | An additional digit appended to a number to check if the entered number is error-free; check digit is a data entry check and not a data transmission check. |
| Eavesdropper | Another name for a hacker who intercepts data being transmitted on a wired or wireless network. |
| Encryption | The process of making data meaningless using encryption keys; without the correct decryption key the data cannot be decoded (unscrambled) |
| plaintext | The original text/message before it is put through an encryption algorithm. |
| Cyphertext | Encrypted data that is the result of putting a plaintext message through an encryption algorithm. |
| Encryption algorithm | A complex piece of software that takes plaintext and generates an encrypted string known as ciphertext. |
| Symmetric encryption | A type of encryption in which the same encryption key is used both to encrypt and decrypt a message. |
| Asymmetric encryption | A type of encryption that uses public keys and private keys to ensure data is secure. |
| Public key | A type of encryption key that is known to all users. |
| Private key | A type of encryption key which is known only to the single computer/user. |
| Quantum computer | A computer that can perform very fast calculations; it can perform calculations that are based on probability rather than simple 0 or 1 values; this gives a quantum computer the potential to process considerably more data than existing computers. |
Created by:
Ginny Martin
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