2 Data Transmission Flashcards by DY Lee

Data sent over long distance is usually broken into ______ _______

data packets

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What are the 3 parts of a dat packet

headler

payload

trailer

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What is in the header? (4)

IP address of the sender

IP address of the receiver

Sequence number of the packets

Size of the packet (in bytes)

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What does the payload contain? (1)

The actual data in the packets (64KiB)

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What does the Trailer contain? (2)

Methods of identifying the end of a packet

Some forms of error checking to ensure packet arrives error free

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Define packet switching

method of transmission in which a message is broken up into a number of packets

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Describe how packet switching occurs (4)

Each packet sent independently from start point to end point

At the destination, packets reassembled into their correct order

At each stage of transmission, there are nodes that contain a router

Each router determines the route the packet needs to take

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Benefits of packet swtiching(3)

no need to tie up a single communication line

possible to overcome failed, busy, faulty lines by rerouting packets

high data transmission rate is possible

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Drawbacks of packet switching(3)

packets can be lost and need to be resent

method is prone to errors with real time streaming

delay at destination while the packets are restructured

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Why might pathways become clogged (2)

packets keep bouncing around from router to router

Lost packets mount up, clogging the system

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What is simplex transmission mode

data can be sent in only one direction only

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What is half-duplex transmission mode

When data is sent in both directions but not at the same time

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What is full-duplex transmission mode

Both directions at the same time

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What are the two types of data transmission (2)

Serial data transmission

Parallel data transmission

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What is serial data transmission (2)

ONE BIT AT A TIME over a SINGLE WIRE/CHANNEL

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What is parallel data transmission? (2)

SEVERAL BITS OF DATA over SEVERAL WIRES/CHANNELS

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Advantage of serial data transmission (4)

reliable over long distances

Data arrives in order as bits transmitted through single wire

less risk of external interference than parallel

less expensive than parallel data transmission (fewer wires)

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Disadvantage of serial data transmission (2)

relatively slower than parallel data transmission

not suitable for transmitting data over short distances

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Advantage of parallel data transmission (2)

faster than serial data transmission

works well over short distances

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Disadvantage of parallel data transmission (2)

expensive than serial (requires more hardware)

bits can arrive out of synchornisation (skewed)

What does USB stand for

Universal Serial Bus

What happens when a device is plugged into a USB? (3)

computer automatically detects that device is present (small change in voltage in the USB cable)

device is automatically recognised, appropriate device driver loaded so that computer and device can communicate

if a new device detected, computer looks for device driver that matches device

Benefits of USB systems (4)

industry standard Devices automatically detected and device drivers automatically loaded backwards compatible (older versions still supported) connections can only be one way, prevents incorrect connection being made

Drawbacks of USB systems (2)

Very old USB versions not supported maximum cable length is roughly 5 metres

What are the 4 ways of data can be checked for errors (4)

Parity checks checksum echo check Automatic repeat request (ARQ)

Why might errors occur during data transmission

Interference skewing of data probelsm during packet switching

Describe what a parity check is (2)

A method used to check if data has been transmitted properly makes use of even parity and odd parity

What is a parity bit

a bit added to a byte of data to ensure that the byte follows the correct even or odd parity protocol

What is a parity block

A horizontal and vertical parity check on a block of data being transmitted

What is the limitation of parity check? (1)

Cannot tell which bit has been corrupted or changed

Describe the checksum process (5)

when a block of data is about be transmitted, checksum value calculated checksum transmitted with block of data at the receiving end, checksum is recalculated using the blocks of data recalculated checksum is compared with the initial checksum value If they are the same, no errors have taken place during transmission

Describe the process of echo check (3)

a copy of data is sent back to the sender the returned data is compared with original data by the sender's computer if there are no diffrerences, then data sent without errors

Describe the process of Automatic repeat request (ARQ) (3)

uses positive and negative acknowledgements and timeout receiving device receives an error detection code as part of the data transmission (used to detect where data has any errors) If no error detected, positive acknowledgment sent to sender

What happens if an error is detected in a computer system that uses ARQ (1)

negative acknowledgement sent to sender and requests data to be resent

What happens if no acknowledgement of any sort has been received by the sending device after a certain amount of time (ARQ) (1)

resends data until positive acknowledgement is sent to sender

What is the original data being sent also known as in encryption?

plaintext

Define encryption

the process of making data meaningless using encryption keys; without the correct decruption key the data cannot be decoded [unscrambled]

What is symmetric encryption

both parties given identical secret key to encrypt or decrypt information

What is the main problem with symmetric encryption

if hacker gains access to the key, they can decrypt the information

What is asymmetric encryption

type of encryption that uses both public and private key to ensure data is secure

define public key

a key known to everyone

define private key

a key known to the receiver

Describe the process of asymmetric encryption (3)

Sender encrypts data using public key Encrypted data is sent to the receiver Receiver decrypts the encrypted data using a MATCHING private key

Advantage of asymmetric encryption

much more reliable compared to symmetric key

What is check digit

extra digit added to a number that is calculated from the existing digits in the number.

Examples of when check digit is used (2)

ISBN barcodes (used to check for errors during data entry)