Data Transmission

Data Transmission

Sending and Receiving Data

Data Transmission

Data is sent from one computer to another or to another device for communication or to be used on the target device like printer.

Three important factors to be considered when data is transmitted

• Direction of data transfer

• Method of Data Transmission

• Synchronising the transmission

Direction of Data Transfer

• Simplex Transmission

• Half Duplex Transmission

• Full Duplex Transmission

Simplex Data Transmission

Data transfer takes places in one direction only. A sending device can send the data to a receiving device and not the other way.

Example : Computer to Printer

Half Duplex Transmission

Data transmission is possible in both directions but only one direction at a time.

Full Duplex Transmission

Data transmission is possible in both the directions simultaneously

Serial Data Transmission

Data is sent one bit at a time over a single wire or channel

Features of Serial Data Transmission

• Simple technique of data transmission

• Slow speed of transmission

• Since only one wire is used so no need of Synchronization between sender and receiver

• Cheaper to implement

• Used for long distance data transmission

• Universal Serial Bus connection (USB)

Parallel Data Transmission

Data is transmitted over several channels several bits at a time

Poll

Is Parallel going to be faster or slower than Serial data transmission

• Faster

• Slower

Poll

Is Parallel transmission cheaper or expensive as compared to Serial transmission

• Cheaper

• Expensive

Features of Parallel Data Transmission

• Data flows through multiple lines

• Faster speed of data transmission

• Complex technology

• Used for short distance transmission

• Sending print data to printer or video data to a monitor using VGA cable

Data Packets

A packet is a small unit of data that can be transmitted from a sending device to a receiving device

Why Use Data Packets?

• Data broken into smaller pieces to ease communication

• Upon reaching the endpoint, these pieces get reassembled to become readable.

• Data packet use ensures the reliable and efficient transfer of information.

• Sending huge data as smaller packets improves transmission

Parts of Data Packet

• Header - Address of sending and receiving machines and packet sequence number

• Payload - Actual data

• Trailer - Indicates the end of packet

Synchronous Transmission

• Continuous stream of data is sent

• Both devices uses a ticking clock to synchronize

• Data is sent in the form of packets of bits

• Used to transfer large amounts of data quickly

Features of Synchronous transmission

• Bit oriented transmission

• Used for high speed continuous data transfer

• Uses a synchronization signal to start the data transfer

Asynchronous Data Transmission

• Data is sent in intervals

• Start and end of the data is signaled by a Start and Stop bit

• Slower transmission speed due to extra bits

• Cheap and easy to implement

• Data can be transmitted at any time, no synchronization is required

• Synchronization is needed only during data transfer

• Used for mouse, keyboard etc.

USB - Universal Serial Bus

Asynchronous Serial transmission

Universal Serial Bus

• Common method of transferring data between computer and a number of electronic devices.

• Transfer of Data and Power using the same cable

• Self configuring connection. Settings are selected automatically upon connecting the device.

• Limited cable length

Error Detection

Digital signals suffer from noise that can introduce errors in the bits.

That means a 0 bit may change to 1 or a 1 bit may change to 0.

Error Detecting Codes

• Error-detecting codes are additional data added to a given digital message to detect if an error occurred during transmission of the message.

• Example : Parity Check

Error Correcting Code

Some additional data can also be sent to figure out the original message from the corrupt message that we received.

Such codes also detect the exact location of the corrupt bit and then it can be corrected to get the original message.

Parity Bit

• To detect and correct the errors, additional bits are added to the data bits at the time of transmission.

• The additional bits are called parity bits.

• The data bits along with the parity bits form a word

Even Parity

• In case of Even parity the number of 1's in the given word including the parity bit should be even (2,4,6,8)

• ​Number of 1 bits in the data given below is 5 (odd number)

• ​To make the number of 1 bits even, Parity bit 1 must be added to data.

• ​Adding 1 as parity bit will make the number of 1 bits 6 (even number)

Odd Parity

• In case of Odd parity the number of 1's in the given word including the parity bit should be odd (1,3,5,7)

• ​Number of 1 bits in the data given below is 5 (odd number)

• ​To make the number of 1 bits odd, Parity bit 0 must be added to data.

• ​Adding 0 as parity bit will keep the number of 1 bits 5 (odd number)

​Limitation of Parity Bit

• No information about which bit in the data is corrupted​.

• ​Even number of error bits can be detected.

• ​Even number of bits changing is called Transposition error.

​Parity Blocks

• Parity blocks can detect and also correct the error bits without the need to retransmit the data.

• ​Data is transmitted in the form of blocks. Parity bit is used for each row and each column of the block.

​Automated Repeat Request

• It is an error-control method for data transmission that uses acknowledgements and timeouts to achieve reliable data transmission over an unreliable communication channel.

• ​Acknowledgements are the messages sent by the receiver to indicate a successful transmission

• ​Timeout is the specified amount of time for sending the acknowledgement messgae.

​CHECKSUM

• An additional value called as Checksum is sent along with the data.

• ​Method used to generate this value is called Checksum Algorithm

​ECO CHECK

• ​After receiving the data is sent back to the sender.

• ​Sender compares the original and sent data to check for errors.

• Not reliable as there is no way to tell when the error occured (during transmission or retransmission)​