Section 6 Chapter 31 - Communication Methods Flashcards
Where data communication is used
Between computers
Between computer components
Serial Transmission
Bits are sent one at time over a single wire (or other communication media)
Parallel Transmission
Several bits are sent simultaneously over a number of wires
Skew
When bits travel at different speeds along parallel wires
Crosstalk
Interference between parallel wires
Where serial is used vs parallel
Serial used for long distance, parallel for short (e.g. in computer components)
Advantages of serial over parallel (4)
- Cheaper due to lower size and complexity
- Crosstalk
- Reliable over longer distances
- Can use higher frequencies due to no inteference
Bit rate
The rate at which data is serially transmitted
Baud rate
The rate at which the signal changes
Baseband
When only one bit is encoded per signal
baud rate = bit rate
Bandwidth
The amount of data that can be transmitted in a fixed amount of time (essentially the maximum bit rate)
Latency
The time delay between when a packet of communication is sent and when it is recieved
Parity bit
A bit that is set to 1 or 0 to make the total number of 1s and 0s either even or odd. Used to check if data has been correctly transmitted
Synchronous transmission
Data is transferred at regular intervals
Where synchronous transmission is commonly used
With parallel communication, a cpu clock is an example of synchronising transmission
Asynchronous transmission
One byte is sent at a time, with each byte encased with a stop and start bit
Property of the stop and start bits of asynchronous transmission
They are always opposite, either start=1 and stop=0 or start=0 and stop=1
Protocol
A set of rules relating to communication between devices which specifies how they should communicate and allows them to exchange details such as data format, speed, mode of transmission
When does crosstalk get more pronounced
Higher frequencies
Maximum length of parallel transmission
Around 2m
Makeup of an asynchronously sent packet
stop-parity-data(7)-start
Where asynchronous transmission is commonly used
Low speed connections such as a keyboard and mouse
Things that a protocol needs to define (5)
- Standards for physical connections
- Rate of transmission
- Data format
- Synchronous or asynchronous
- Error checking procedures
Broadband
More than one bit encoded onto each signal
Purpose of the start and the stop bit
Start bit alerts the receiver and synchronises the clock inside the receiver so it is ready to receive the packet.
Stop bit tells the receiver that it has received the whole packet
How bit rate is related to baud rate
Bit rate = Baud rate * bits per signal
