Signal Theory

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Signal Theory
Introduction-

In this report I will be writing about Signal Theory and all of its aspects, this involves talking about how data is transferred over a network, what a packet is and what information it contains, asynchronous and synchronous transmission, errors that data may encounter and what protocols are in place to avoid this from happening.

Digital Signalling Methods-

When data is sent over a network, it can either be through a wired or a wireless technology. The data is sent over a network using electric pulses.

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Amplitude-

Amplitude is the strength or loudness of the signal whilst transferring data over a network, the higher the amplitude is the stronger the network signal will be. Therefore, the lower the amplitude is the weaker the signal would be concluding that a stronger amplitude would travel a greater distance and transfer data at a quicker rate.

In other technologies amplitude has different meanings, radio and microwaves use the same transmission method, radio waves signalling distance would be measured by metres or millimetres. Microwaves would wirelessly transfer over kilometres with power readings differing between MHz and GHz.

Telephone cables and data cables both rely on electrical currents, telephone cables can handle up to +/- 50 volts switching between a positive and negative current, this is called an alternative current. Standard data cables can only handle +/- 5 volts, if the is exceeded then it could damage components inside your computer.

When dealing with light technologies like fibre optic, the strength of the signal all depends on the brightness of the light or laser source. Light can travel much faster than any other source and can cover greater distances, but at the same time is much more expensive.

Frequency-

Frequency is the rise and fall of the signal, it moves from zero upwards then cycles back round, a low frequency would only transmit a small amount of cycles per second where a high frequency can transmit billions of cycles per second. This however requires a high amplitude aswell.

Bandwidth-

Bandwidth is defined as the quantity of data that can be send through a data transmission medium over a specified period of time, it is usually displayed from slow to fast:

• Bits per second (bps)

• Kilobits per second (Kbps)

• Mega bits per second (Mbps)

• Giga bits per second (Gbps)

Bandwidth can come with some restrictions and priority issues. A sector of a network using video streaming, downloads or VOIP would be allocated more bandwidth by the network manager. Areas of the network using email, IM or just web browsing would be allocated low bandwidth for low priority tasks.

Data

When data is transferred it is represented in a digital format based on binary principles. The smallest form of data is a bit or a binary digit these are represented by either a 1 or 0. When bits are brought together they make up more useful clusters of data, for example: 8 bits form a byte.

Packets

In networking data has to be bunched together into suitable packages for transport. The format of a packet can change depending on what type of network you are on but a data packet is used to describe the package.

A packet at the minimum should contain: Source address, destination address, data and error control.

The source address is sent so the receiver knows who has sent the packet. The destination address is required to make sure the packet is sent to the right destination. The data is the actual information or message being sent. Error control is added to the packet to help identify any problems with the data after it has been received.

Asynchronous and synchronous transmission-

Asynchronous transmission consists of two devices, but the second device must acknowledge the transfer of data before the first device will send anything else, this is because there is no synchronization between...
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