IT Tutorials For Beginners: September 2015

Tutorial : Communication Media

What is communication media?

Communication media is the term used for the delivering and receiving data or information.

Two forms of communication media:

Analog telecommunications
Examples: radio, telephonic and television broadcasts.

Digital telecommunications
Example: Computer networking and telegraphy.

Data communication media includes:

Coaxial cable is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield.

Advantages:

o Has a higher bandwidth than twisted pairs (400-600mHz).

o Less vulnerable to interference compared to the twisted pair.

Disadvantages:

o Can be tapped easily.

o It has a high attenuation rate which means there is a huge reduction in the strength of the signal over a distance. This means that when used over long distances it can become costly.

o It is quite bulky.

Where it is used today?

Computers/Tv’s/Video Game systems – no security is needed and it only has to be used over short distances while still having a faster than average bandwidth.

Communication Satellites is a satellite placed in orbit around the earth to relay television, radio, and telephone signals.

Advantages:

o Mobile communication is easily achieved because of its flexibility to interconnect mobile vehicles.

o The quality of the transmitted signals is better than a fibre cable as the sending and receiving of information is independent on the distance.

o Satellite relay is wide area broadcast where point to multi-point communication is possible.

Disadvantages:

o Time delay which reduces the efficiency of satellites in data transmission and long file transfer.

o Overcrowding of available bandwidth due to the low of antenna gains.

o High atmosphere losses, above 30GHz, limits the carrier frequency.

Fibre optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves.

Advantages:

o They are not affected by EMI and RFI which means essentially the signal loss is much lower than other mediums like copper wiring. This also means that data can travel longer distances before signal regeneration is needed i.e. 200 km’s compared to copper cables which can only cover up to 5 km’s.

o Optical signals can carry a lot more data than normal electrical signals. For instance optical fibers have a bandwidth of up to 2 gigabytes per second.

o Fiber optic is also a lot safer because it can’t be hacked as easily as other mediums in terms of tapping because data isn’t sent electronically it is sent using light signals.

Disadvantages:

o The only downside to fiber optic cables is the fact that it costs a lot more than general copper cables.

o Another disadvantage is that fiber optic cables can’t be blended too much otherwise they’d lose some light reflecting properties,

o Fiber optic cables can also be damaged easier than copper cables and also cost a lot to be repaired.

o Installation has to be done by highly skilled installers with special tools.

Where it is used today?

Military- used for missile launches and radar system because a lot of heavy copper wiring can be replaced by a single pen sized fiber optic cable while still being able to withstand harsh environments and providing more security.

Microwave transmission is the process of transmitting information or energy by microwaves.

Advantages:

o Relatively low costs.

o Able to transmit large quantities of data due to high operating frequencies.

o Wide bandwidth.

Disadvantages:

o Signals do not pass through objects.

o Affected by any interference that degrades, obstructs or interrupts the performance of microwave signals.

Where it is used today?

Radio repeater, transmitter station, wireless energy transfer.

Twisted pairs:

Advantages:

o It is Cheap and easily available.

o The cables are flexible and light

o A specialist doesn’t need to be brought in because it can be easily installed.

Disadvantages:

o Vulnerable to interference and noise.

o For analog, repeaters are needed for every 5-6 km

o For digital, repeaters are needed every 2-3km.

o Bandwidth is much lower than fiber or other mediums (300Hz).

Where it is used today?

Telephone, CATV, 1000BASE-TX in the same cable and 40GBASE-T Ethernet.

When it comes to communication media another important aspect is choosing the right type of cable to send and receive information. Different cables offer different bandwidth, sizes and costs. The aim is to choose a cable that is the most beneficial and cost effective.

Some factors to consider are:

Cost: you need to think about how much you are willing to spend and the repercussions for instance paying extra now for fiber optic could mean it is less expensive in the future when it comes to maintenance or someone trying to hack into the cables.

Security: you need to think about security concerns when choosing a type of cable for instance if the data being sent and received isn’t sensitive then a medium like a coaxial cable can be used but if the data is sensitive then a safer alternative needs to be used like fiber optic which is highly secure because it is harder to tap.

Design for Future: you need to think about the future when dealing which communication media so you need to think about using a cable that can support a higher bandwidth then the bare minimum so if more is expected you don’t have to pay for additional installations.

The Video below shows how communications media works hand-in-hand with networking:

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Tutorial : Network Topologies

What is a network topology?

A topology describes the arrangement of the network, which includes all the nodes (components), and their connecting lines.

A network geometry is split into two categories: physical topology and logical (Signal) topology.

The physical topology of a network is the actual physical layout of the devices which are connected in that network. The following are the most common physical topologies:

In a bus network topology, every node is connected to a main cable which runs throughout the topology, with terminators placed on the ends to prevent damage in the topology. Should a component connected in the bus network fail, the other components will operate as normal, however, should the main connector fail, all components in the network will not function.

In a Star network topology, every node in the network is indirectly connected to every other node in the network generally via a hub, server, or central computer. Should any component (other than the central connector) in a star network topology fail, only that component will not work, the other components will resume operation as normal, however should the central connector fail, all components in the network will be affected . The star network topology acts as a client server network connection.

Every node in the ring network topology is connected to the nodes next to it in a closed loop configuration. The ring topology is one of the simplest and cheapest network topologies to set up. It is also the most insecure network topologies. Should one of the nodes or connectors in this network fail, all the components will be affected.

The “token ring” is often thought by many to be an actual topology, but it is actually a protocol which is used in both the star and ring network topologies. This protocol works by attaching a signal to a figurative “token” as it travels between nodes in the network.

Mesh Topology

A mesh network topology is a topology which connects one node in a network to every other node in a network (As seen in the illustration above, the blue lines show how the one node is connected to every other node in the network).

The above image is an example of a full mesh topology. A full mesh topology connects one node DIRECTLY to all other nodes in the network. In a partial mesh topology the nodes are often connected to hubs which are connected to other hubs which relay and indirect connection from one node to all other nodes in the network.

A mesh network acts as a Peer-to-Peer network, it is also the most secure network topology as if one node fails, all the other nodes will continue to operate as normal. The mesh network is also the most expensive network to set up.

Here is one of the more uncommon network topologies:

Hierarchical Topology

The hierarchical network topology is designed to help create a network in separate layers. Each layer has specific tasks which it must perform which means that it is very important to choose the right components for each layer. The hierarchical topology is usually divided into the following layers:

Core Layer: usually made up of hubs/switches and with high-speed cabling (fiber optic cables). The core layer is considered to be the backbone of the network.

Distribution Layer: this layer is usually made up of switches and LAN-based routers, and it is responsible for ensuring that the packets are properly routed in the network.

Access Layer: Usually referred to as the desktop layer. This layer is tasked with connecting client nodes in a network and ensuring that the packets are delivered to the end user.

Logical (or signal) topology refers to the nature in which a topology operates. In most cases, the logical topology is the same as the physical topology, but this is not always true.

For example, a network topology may for instance have the physical topology of a star, but in terms of the logically topology it may operate as a bus, or even a ring network.

Why do we use network topologies?

There are many reasons to use network topologies, some of which are as follows:

Network topologies make communication between devices on the same network easier.

Many business’ use network topologies to save on hardware and software costs.

Easier sharing of data – most network topologies have a centralized administration system, which can access all the data needed from the other nodes on the network.

Reduces data duplication and the risk of data corruption.

How do the above reasons help us?

It is easier for a node on the network to access, communicate or get data from other nodes on the network.

You save on hardware costs because the computers/nodes on the network can share peripheral devices connected in the network. This means that there isn’t a need for every individual node to have its own printer, scanner or other peripheral devices.

The administrator can access the data from all nodes from a single node on the network.

Data corruption and data duplication is prevented as the same files are uploaded to a network, and therefore if they are copied, or downloaded, the data will not be duplicated, nor can it become corrupted.

The following video on network topologies might assist you in your studies of the topic:

For more information on the Bus, star, ring and mesh network topology click here.

Click here for more about the hierarchical topology as a whole.

Click here for more about the layers of the hierarchical topology.

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