Communication Basics and Networks

Parallel Transmission

Uses a number of wires to send a number of bits simultaneously
The more wires, the more data can be sent
Used primarily for buses
As this uses more wires it can be more expensive
Interference between the wires degrades the signal over long distances
Timing- can't guarentee that each signal on each wire will arrive at the receiver at exactly the same time
This is known as synchronisation and becomes more difficult with the number of wires

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A measure of the capacity of the channel down which the data is being sent- measured in hertz (Hz)
The range is the difference between the upper and lower frequencies used for a transmission channel
As the range of frequencies increases so does the amount of data that can be transmitted within the same time frame.

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The rate at which data is actually being transmitted
Measured in bits per second
There is obviously a link between bandwidth and bit rate- as the bandwidth increases so does the bit rate etc.

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Another term used to express the speed at which data can be sent
One baud represents one electronic state change per second- this can be a voltage, frequency or phase change, for example.
It is possible to send more than one bit per state change

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The time delay that occurs when transmitting data between devices.
Propagation Latency- amount of time it takes for a logic gate within a circuit to transmit data
Transmission Latency- amount of time it takes to pass through a particular communication medium. Fibre latency < Copper Latency.
Processing Latency- amount of time it takes data to pass around a network depending on how many servers or devices it has to pass through
Ping Test (example)- sends a packet to a destination on the net and see how long it takes to get back.

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Asynchronous Transmission- data is transmitted between two devices that do not share a common clock
It does not require the permanent synchronisation of the sender's and receiver's clock
It only synchronises for the duration of the transmission by sending additional bits of information called start and stop bits

Synchronous Transmission- The sending and receiving devices are completely in time with each other.
The devices share a common clock
Once synchronised, the two devices can send and receive data without further information (primarily to resynchronise)

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