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Transmitting Data
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- 1Transmitting DataFactors:
-Direction of data transmission
-Method of transmission
-Method of synchronization between the two devices - 2Simplex, Half-duplex & Full-duplexSimplex - Move in one direction only - Printer
Half-duplex - Both directions but not at the same time - Texting, Walkie-talkie
Full duplex - Both directions simultaneously - Phone call - 3Serial Transmission - one bit at a timeExamples:
Mouse, moderns, keyboard.
Features:
Cheaper, used over long distances. - 4Parallel transmission - 8 bits at a timeExamples:
Plug in thingies (so stuff like printers, scanners, microphones e.c.t)
Features:
Speed (faster), cable length (the longer the cable the more chance of corruption), less complexity. - 5Party CheckingUsed to check whether data has been changed or corrupted following transmission from one device or medium to another device or medium.
A byte of data - Parity Bit.
Even number of 1 bits - Even Parity.
Odd number of 1 bits - Odd Parity. - 6Automatic Repeat RequestAnother method used to check whether data has been correctly transmitted.
It uses an acknowledgement message sent by the receiver indicating that data has been received correctly and timeout (this is the time allowed to elapse before an acknowledgement is received).
If an acknowledgement isn’t sent back to the sender before timeout occurs, then the message is automatically resent. - 7Checksum- Another way to check if data has been changed or corrupted following data transmission.
Data is sent in blocks and an additional value(the check sum) is also sent at the end of the block of data.
Example:
Assume the check sum of a block of data is 1 byte in length. This gives a maximum value of 28 − 1 (i.e. 255). The value 0000 0000 is ignored in this calculation. - 8Echo CheckWhen data is sent to another device, this data is sent back again to the sender.
The sender compares the two sets of data to check if any errors occurred during the transmission process.
As you will have no doubt worked out, this isn’t very reliable.
If the two sets of data are different, it isn’t known whether the error occurred when sending the data in the first place, or if the error occurred when sending the data back for checking!
However, if no errors occurred then it is another way to check that the data was transmitted correctly.
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- Descripción
- Fichas sobre Transmitting Data, creado por 11.harvey el 16/10/2015.
- Creado por
- 11.harvey
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