Data Transmission

• Data is broken down into packets to be transmitted from one device to another.
• Each packet contains three parts: the packet header, the payload, and the trailer.
• The packet header includes the destination address, the packet number, and the originator’s address.
• The payload is the data the sender wants to transmit.
• The trailer contains data such as the error detection method to be used.
• A process called packet switching can be used to send the data from one device to another across a network.
• Data is transmitted using serial or parallel transmission.
• Data is also tranmitted using simplex, half-duplex, or full-duplex transmission.
• An interface called USB (Universal Serial Bus) can be used to transmit data. This is often used to connect hardware such as a keyboard to a computer.
• Errors can occur when transmitting data due to interference.
• Methods are required to detect any errors in transmission.
• A parity check is an error detection method uses a parity bit to detect errors. An odd or even parity check method can be used.
• A checksum is an error detection method that uses a calculated value to detect errors.
• An echo check compares data that is sent and received to see if they match, to detect errors.
• Encryption is a method of securing data for storage or transmission that scrambles it and makes it meaningless.
• Data before encryption is called plain text. An encryption algorithm is called an encryption key, it is used to scramble the data and make it meaningless. This meaningless data is called cipher text.
• Symmetric encryption process is: Plain text is encrypted into cipher text using an encryption key. The cipher text and the encryption key are sent separately to the recieving device.
• Asymmetric encryption process: Plain text is encrypted into cipher text using a public key. This is also a type of encryption algorithm. The cipher text is transmitted to the receiving device. The cipher text cannot be decrypted using the public key, it is decrypted using a private key.
• Check digit process: A check digit value is previously calculated from the data that will be entered at some point. This number is stored with the data. When the data is entered, the check digit is recalculated from the data entered. If the previously calculated check digit and the stored check digit match, the data entered is correct.
• Echo check process: The sending device transmits the data back to the reveiving device. The receiving device then transmits it back. The sending device compares the data it received to see if it matches with the original data. If they match, then no error has occured.
• Check sum process: A value is calculated from the data that will be transmitted, before transmission takes place. A method such as modulus 11 could be used to calculate the value. Once the checksum value has been calculated it is added to the data to be transmitted with it. After transmission, the receiving device uses the same method to calculate a value from received data. If the values match, no error has occurred.
• Automatic repeat request (ARQ) is a type of error detection method that uses a positive or negative acknowledgement and timeout to see if the data has arrived correctly after transmission.
• Acknowledgement is a message that is sent from one device to another to indicate whether data is received correctly.
• Timeout is a period of time that is set and used to wait for an acknowledgement to be received.
• Symmetric encryption uses the same key to encrypt and decrypt the data.
• Asymmetric encryption uses different keys, a public and a private key, to encrypt and decrypt the data.
• Data can be encrypted to keep it secure during transmission.
• Parity check is a type of error detection method that adds an additional bit to each byte to create an odd or even sum.
• Advantages of USB: Simple interface, the USB cable to device can only fit into the USB one way - less errors can be made. The speed of USB connection is relatively high, so data can be transferred quickly. The USB interface is a universal standard, so a USB port is included in many devices. A USB connection can also be used to power a device.
• Disadvantages of USB: The length of a USB cable is limited, normally to 5 metres. The transmission speed is relatively high for a USB connection, but it isn’t as high as other types of connection, such as Ethernet.
• Ethernet is a type of connection that can be used to transmit data within a network.