1. A-Level Computing#BristolMet Session Objectives#11 MUST identify the hardware required to connect to the Internet SHOULD describe how data is transmitted using serial, parallel, simplex and duplex modes. COULD explain 3 methods of error checking transmitted data Using FOR and WHILE loops to move images across the app screen

2. A-Level Computing#BristolMet Data Transmission Types Data Transmission is the process of transporting data from one place or device to another. There are different ways of doing this: Consider 1 byte of data (8 bits): Serial Data Transmission – sends data bit by bit (1 bit at a time) through a single wire. Parallel Data Transmission – sends all 8 bits at the same time using a number of wires (one for each bit). Can you think of any example where serial and parallel data transmission has been used? You would think parallel would be the preferred method as it seems quicker BUT because serial requires less signal processing, there are less chances for error than parallel transmission thus the transfer rate of each individual path may be faster.

3. A-Level Computing#BristolMet Data Transmission Modes Direction of data movement: Simplex = One way Duplex = Both Directions at the same time Half Duplex = Both Direction but one after the other.

4. A-Level Computing#BristolMet Data Transmission Speed Bit Rate (Baud Rate) Bit Rate – The number of bits that can be transferred in a given space of time i.e bits per second. This is measured in units called baud which is also known as the baud rate. The bit rate is really determined by file use rather than file type. For example, a film could take days to download at a slow rate and watched later but if it were to be streamed, then it would need a high bit rate to ensure the data is available at the right time and not cause lag to the audio visual output. Files that are time sensitive are files that lose their value unless they arrive in a particular time period.

5. A-Level Computing#BristolMet Recap Let’s Recap the key terms on data transmission so far: Name 2 types of transmission. Serial, Parallel Name 3 modes of transmission. Simplex, Duplex, half duplex What is transmission speed referred to and what is it measured in? Bit Rate and baud

6. A-Level Computing#BristolMet Error Checking We have already mentioned that some data may get lost or be transmitted in the wrong order. A bit which starts with 1 may end with 0, for example. This causes the data or file to become corrupt in its new location. To reduce this chance 3 methods are used to check that data integrity (staying in its original state) is kept when being transmitted. Echoing Back Check Sums Parity check TASK: In small groups research one of the methods and prepare to feedback your explanation in the form of a role play, song or rhyme

7. A-Level Computing#BristolMet Error Checking Echoing Back: When a set of data has been sent, a copy or echo is sent back to the sender to compare the accuracy against the original. If there are any errors then the data will be sent again.. Check Sums: The bytes of data being sent are added together and the answer is sent with the data ‘packet’. When the data bytes are received they are added together and their ‘check sum’ is calculated. If the sum totals are the same then it is assumed that the data has not been corrupted, if they are different the data will be sent. Parity Check: Data is sent in fixed byte sizes (usually 8 bits). The data being sent is in the first 7 bits and the 8 th bit is kept for use in parity. It works by organising the number of 1s in each byte to an odd or even number, for example four 1s, which is an even number and so the parity bit would be set to 0. If there were an odd number then this would be 1. i.e even parity = 01101101 and odd parity = 01101100