11. Communications Flashcards
Serial Data Transmission
Bits are sent via an interface one bit at a time through a single wire from source to the destination.
This allows for very high data transfer rates ranging from 50Mbps to 1Gbps.
Parallel Data Transmission
Several bits are sent simultaneously over a number of parallel wires.
This method is used inside computers and for very short distances.
Problems with Parallel Data Transmission
More expensive as there are more cables involved especially at long distances.
Prone to skewing which means the bits need to wait for others to catch up.
Bit Rate vs Baud Rate
Bit Rate: The amount of bits transferred per second.
Baud Rate: The rate at which the signal changes.
Bandwidth
The range of signal frequencies that a medium (i.e. copper, optical fibre) can transmit.
The greater the bandwidth, the greater the potential bit rate.
Latency
A general term used to explain the time delay that occurs when any component within a computer system is responding to an instruction.
Parity Bit
A bit is added to a group of bits used for error checking.
Odd Parity
Set to a 1 or 0 to make the total number of ‘1’ bits including the parity bit equal to an odd value.
Even Parity
Set to a 1 or 0 to make the total number of ‘1’ bits including the parity bit equal to an even value.
Synchronous Transmission
Synchronous means occurring the same time/having the same speed.
Which means two devices which are communicating will synchronise their transmission signals by their internal clocks.
If not synchronised then data could be lost during transmission.
Asynchronous Transmission
It does not need permanent synchronisation with sender’s and receiver’s system clocks.
Instead it only synchronises for the duration of the transmission by sending additional bits of information called start and stop bits.
