Communication Methods

Parallel Vs Serial

Serial Data Transmission

In serial data transmission each bit is sent one after another by varying the line voltage between 0 & 5 volts for each bit, for two way communication a return wire is required. Serial Data Transmission is commonly used in USB and crossover cables.

Uses

Long distance communication

Advantages

Only need one signal path per way, can be used to route over telecommunications, saves cost of cabling

Disadvantages

Signal strength degrades over distance, so repeaters and so on required

Parallel Data Transmission

Each binary word is transmitted as one, with a signal path for each bit, additional signal paths for Return, Ready/Busy, & one strobe wire are required Ready/Busy is the status of the receiver, strobe wire used after signal placed onto wires on Strobe receiver will set Busy & read after read the receiver sets Ready.

Uses

Short distance data communication

Advantages

Offers faster transmission when compared to Serial

Disadvantages

Skew can easily affect data transmission, leading to errors

Baud Rate

Frequency at which a signal can change (ie from 0 to 5 volt), a baud signal of one changes once per second

Bit Rate

Number of bits transmitted per second, bit rate does not equal Baud rate if more than one bit is sent per time, 2 bits can be sent each time with more voltage levels.

Bandwidth

How fast data can be transmitted over a transmission media without significant reduction in strength greater bandwidth means greater the data rate can be sent there is a direct relationship between bit rate and bandwidth. The greater the bandwidth of the transmission system, the higher is the bit rate that can be transmitted over that system. On a cable, bandwidth is measured in Mhz, network Cable has 500 Mhz bandwidth which means 500 million cycles per second more cycles = more data.

Latency

It is the time delay between initiation and the first effect, WAN latency due to distance eg: between ground stations and satellites

Propagation Latency

Time taken to pass through a logic gate

Transmission Latency

Time taken to pass through a medium

Processing Latency

Time taken to pass around a network

Protocols

Is a set of agreed:

• Rules
• Codes
• Signals

That allow the transfer of data from one system to another And consists of:

• Handshake
• Message
• Goodbye