Dual Ring
This consists of 2 identical rings, which are linked to its inside/outside partner. The rings themselves are not physically joined but the nodes are at points.
This topology uses the same ideas as ring, but the spare ring of nodes are present should an error occur! They work as two independent rings, of which, only one at a time is used.
Irregular
There is no set pattern in the position of nodes and links in this network. The nodes can have different numbers of cables leading into and from them. Networking like this can be found in badly run businesses.
Mesh
This is known as a complete topology as every node is directly linked to every other node. They all each have their own direct connection! This creates redundant connections as only one is needed to retrieve data and there is x amount of possibilities.
Cellular - Wireless
This consists of circular areas where a central node is found in the centre. Each cell works for wireless communication, using electromagnetic waves. This technology is found in mobile phones and satellite links. There is no need for installation of cabling, but devices or nodes must be within the right distance.
The different types of communication media
Shielded twisted pair – STP
This communication media uses both shielding and protection techniques. It consists of an outer jacket with a shield within, which holds four strands of shielding with another 4 pairs of wires in holding 150 Ohm cables.
This media reduces electrical noise within the cable and outside of it (cross talk). Although it is used for many networks, it is more expensive and harder to install than UTP.
Screened twisted pair - ScTP
This is a hybrid of STP, but in addition it is screened to primarily add strength and to minimise the interference that might be found with the original STP.
Unshielded twisted pair – UTP
UTP consists of four-pair wire medium. Each of the separate copper wires within the UTP cable is individually covered by insulating material. The idea behind this cable is to insulate the copper wires with many layers which will decrease the cancellation effect and other decreases in signal quality.
Coaxial - Thicknet and Thinnet
This media is very cheap and is often referred to ‘cheaper net’. It is very easy to install, which is one of the main factors to why it is cheap overall. However, because of the outer copper jacket in the cable the electrical materials must be kept grounded or poor signals will occur. For this reason Coaxial is not used very much in networks!
The difference between Thicknet and Thinnet is that Thicknet is physically larger and thicker in shape than Thinnet. This can enable larger amounts of copper wire to pass through the coaxial cable.
Coaxial cable consists of a hollow outer cylinder that surrounds a single inner wire made of copper for the centre and a metallic foil to cover and act as a shield to prevent outside interference.
Fibre optical cable
This medium is capable of conducting modulated light signals. But with this relatively new technology comes the extra cost, in both installation and maintenance. This form of cable is by far the most efficient as it cannot lose signal strength as it doesn’t consist of electrical transmissions; instead the signals are sent in bits and converted into beams of light. This form isn’t considered as wireless as light fibres are still needed to guide the transmissions.
Science behind the transmission of data across different types of network
Analogue Signals - The principal feature of analogue signals is that they are continuous. Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency and phase. Analogue signals are wavy in character. They have a continuous varying voltage versus time graph. Typically found in nature and used widely in telecommunication
Digital Signals - Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they can distinguish between just two values, 0 and 1, or off and on.
The signals have discrete or jumpy voltage versus time graph and they are typically found in recent technology
Communication Channels
A communication channel refers to the various methods that I particular media can be used for. In this case it is the difference methods in which a network can be connected to each other. This can be determined by the requirements of the network and therefore the type of media chosen. The communication channel is a crucial part of the of the communication network.
How carrier waves are manipulated to carry data using encoding and modulation
Carrier waves can be altered in such ways so that they hold data but in different forms depending on what is appropriate for the media and the receiving node. This is done by encoding, which means the converting of 1’s and 0’s into something real and physical.
Modulation is the process by which the characteristics of electrical signals are transformed to represent information. Types of modulation include Amplitude, Frequency and Phase modulation. All of these types of modulations are described in greater detail below. This means taking a wave and changing, or modulating it so that it carries information
There are different types of carrier methods used the main ones are Broadband and Baseband
Broadband – This is a transmission system that ‘multiplexes’ multiple independent signals onto one cable. As discussed earlier on, multiplexing allows multiple logical signals to be transmitted simultaneously across a single physical channel. Broadband means that any channel having a ‘bandwidth’ greater than a voice-grade channel is classified as broadband. Within LAN terminology, a coaxial cable would be used on which analogue signalling be used across it. Broadband is also referred to as wideband
Baseband – This is where only one carrier frequency is used. Ethernet is an example of a baseband network. This technology is the opposite of broadband, as it supports significantly less than what broadband is capable of and therefore has different uses and purposes, which is also why it is called narrowband
Multiplexing
Multiplexing is a scheme that allows multiple logical signals to be transmitted simultaneously across a single physical channel. It is the process which is used to combine multiple signals (analogue or digital) for transmission over a single line or media. The most common type of multiplexing combines several low-speed signals for transmission over a single high-speed connection, however there are two types;
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Time division multiplexing - Signals from different sources can be sent over one cable by multiplexing. This multiplexing involves sending signals from a source in batches of time
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Frequency division multiplexing - Uses different frequencies to carry data over a the cable
Demultiplexing however, is the process of separating the multiple input streams that have been multiplexed into a common physical signal back into multiple output streams.
Manchester Encoding – This is slightly different to the other carrier methods, as Manchester encoding does just that, encodes, which means that all the bits of data are represented by voltages and is the process that converts 1’s and 0’s into something physical. Manchester encoding is a digital coding scheme, used by such standards as IEEE 802.3 and Ethernet. The encoding is used and a 1 is denoted by a high level during the first half of the bit time.
Manchester encoding is more immune to noise and is better at remaining synchronized. In Manchester encoding the voltage that is on the copper wire or whatever form it is, has the bits encoded as transitions.
Non return to zero (NRZ) – These signals maintain constant voltage levels with no signal transitions (no return to a zero-voltage level) during a bit interval.
However,
Non return to zero inverted (NRZI) signals maintain constant voltage levels with no signal transitions (no return to a zero-voltage level), which is the same but interpret the presence of data at the beginning of a bit interval as a signal transition and the absence of data as no transition.
Discuss the following encoding and definitions
Amplitude Modulation – The amplitude is the maximum value of an analogue or a digital waveform. This is normally seen on a graph and can be identified as the distance the line is compared from one point to another. This modulation technique is where information is conveyed through the amplitude of the carrier signal.
Frequency Modulation – This is the modulation technique in which signals of different frequencies represent different data values.
Phase Modulation - Process by which the characteristics of electrical signals are transformed to represent information. As the name suggests the phase, or beginning and ending points of the wave is varied to carry the message
