Signal Theory On Communication Methods Computer Science Essay

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Leased Line - A leased line is a dedicated line that is connected by fibre optic cabling and can be used to link 2 or more buildings together. The main advantage of having a leased line is that it is very secure to use especially when sending important data across the network. Also the leased line has its own dedicated bandwidth available to use for everyone and an internet connection will be used on top of it. The only disadvantage of a leased line is that it is very expensive and if the line goes down then the whole network will go down with it.

VPN - The internet is a public network so anything can be seen when data is being sent across, this is where a VPN comes into use. A Virtual Private Network is a secure network that can be used to connect computers from any location this is done by using your existing internet connection and then providing login credentials to authenticate onto the virtual private network. The big advantage of a VPN is that the packets are encrypted inside another packet, only users connected to VPN can encrypt/decrypt. This is to prevent hackers using packet sniffers to sniff packets on the network especially when important information is being transmitted across the network.

P2 Signal theory on communication methods

Modem - A modem also known as a modulator and demodulator converts an analogue signal into a digital signal down a telephone cable, this then connects to the local telephone exchange to make connections to the outside world. This is what is generally used for an internet connection.



Analogue Waveform

Wave forms

Wave forms are used to represent an electronic signal when being carried across a form of transmission medium. In the diagram above there is an analogue signal at the top and a digital signal at the bottom.

Purpose of a cable

A cable is used to transfer data over a network, data is sent in the form of an electrical signal down the cable. An RJ-45 Ethernet cable is mostly used for connecting a modem to a network card installed in the computer and a RJ-11 telephone cable is used to connect the modem to a telephone socket.

RJ-45 Ethernet Connector

RJ-45 Ethernet socket

RJ-11 Modem Connector

Cable Connectors

Each cable must have its own connector to be able to connect to an interface. E.g. an Ethernet cable needs a RJ-45 connector to be able to connect to a modem or network interface card. A telephone cable requires a RJ-11 connector to be able to connect a modem to a telephone socket.

Data Transfer

The data changes into an electronic signal and passes through the connector into the cable, the wire may be an ordinary copper wire or a type of optical fiber.

Direction of Travel

When the data travels across the transmission medium, it travels in the direction the cable is going and may be simplex, half duplex or full duplex. Most modern network devices now use full duplex. The Manchester code is in place to determine how the data travels by using 0's and 1's as a change of voltage in the medium.


Simplex means the data can only travel in one direction

Half Duplex

Half Duplex means the data can travel in both directions but not at the same time.

Full Duplex

Full Duplex means the data can travel in both directions at the same time.

A VPN can use a variety of connections to connect to the network, it can go through a copper cable and then through a fibre optic cable and then maybe through a copper connection again, the fastest link is the slowest link. Here below I have described the 2 communication methods

Copper cable - When data is transmitted over the network, it is a digital signal being represented electronically and is made out of bits and bytes and made into a packet structure. If the connection is ADSL it is an asynchronous digital subscriber line, the data is sent in a timing that is encoded in the packets and is calculated by the bit rate of the connection. A wire does not have any sense of error correction, this is done at the send/receiving ends by using protocols such as TCP, checksums are also in place to detect errors, when data is sent the computer will do a mathematical calculation using an algorithm and the data will be assigned a string of numbers and letters. When the data is received and if the string of letters and numbers are exactly the same then no errors were detected during transmission. Copper cabling also has a limit to how far it can travel at approximately 100 metres, once it travels any further than that the signal will degrade. This is known as attenuation and will have to be connected to a booster box such as a switch to extend the signal. There may also be noise which will cause the signal to degrade noise is usually generated from other electronic devices.

Fibre Optic Cable - A Fibre optic cable transfer's data by sending signals of light across the cable. The signal can be sent over a long range which is useful for travelling through a geographic location. The electrical signal is first converted into a light signal and is then sent, at the receiving end the light signal is converted back to an electrical signal. Fibre optic cables have less chance of attenuation, crosstalk and noise as they only travel in straight lines. The maximum distance a fibre optic cable can travel is up to 2 km but some types of fibre optic cables can travel up to 70km.

Wireless - Wireless is sending data using electromagnetic signals without using any wires. This is mostly used for laptops which can be carried around for portable use. The quality of the signal is determined by how close you are to the wireless router. It is hard to determine the signal when you are further away but as you travel more further away the signal degrades. The signal can pass through walls but the signal heavily degrades.

Manchester Code

The Manchester Code is used in transmission of data to ensure a stable constant voltage is being transmitted down the line directly to the clock rate. When there is a change of voltage in the line the binary is encoded into a signal representing this means the synchronisation between the receivers and the transmitters becomes easier. When the data is sent down a cable it is represented in a different format instead of 0'S and 1's. This makes it easier than using binary encoding.

Choice of Transmission Media for this purpose

Copper Cable - Copper cable is used for Ethernet and is also used in the telephone lines connected to the phone exchange, this is typically used for an ADSL internet connection. This is recommended but the internet speed is limited. The wires are usually twisted to prevent any crosstalk occurring. The price of Ethernet is very cheap and is widely used and all modems, switches and routers can be connected with Ethernet. I have chosen copper cable because it is widely available and is cheap and easy to produce.

Task 2

Communication Methods that could be used;

Leased Line - A leased line can be used to connect the school to an internet provider, a well known provider for educational facilities is known as JANET (Joint Academic Network) this is a large network for educational facilities only. This is linked by a dedicated leased line.

Transmission Method

A leased line will use a fibre optic cable to link the network, a subscription fee is required for a leased line which is very expensive but it is well worth it. You have your own dedicated bandwidth and a secure line. This is an example of hiring a leased line for internet connectivity.

Cost's from £299 a month.

A leased line is highly recommended for dedicated bandwidth and security; this may be used for sending large files across from one site to another with no delay.

P7 the nature of Internet Communication

When the user connects to the internet, the modem sends a signal to the telephone exchange using the plain old telephone system (POTS) through copper cabling in telephone wires underground. At the telephone exchange this is where your internet service provider will be and they handle all the incoming connections and route them out to other networks throughout the globe, this is known as the internet.

When the user enters a web address e.g. the DNS server translates the name into a number known as an IP address, the IP address of the website is but we don't have to enter this number, this is what DNS is for. A connection is then established to the HTTP server and automatically downloads HTML files to display the website in the web browser.

Requirements for Connection to ISP

PC or Internet Ready Device

Modem or Network Interface Card (NIC)

ADSL or Cable Modem

Email client

Internet Browser

Subscription with an Internet Service Provider (ISP)

Network Cable (Ethernet cable, modem cable for ADSL, coaxial for cable internet)

Firewall for security (Built in router)

First off you need a personal computer or a device that is ready to connect to the internet.

A network interface card (NIC) is required to connect to the internet; this is used to connect your computer to a modem these are mostly integrated into the motherboard these days. A subscription with your Internet Service Provider (ISP) is required for an internet connection. A modem is required to make a connection to the internet, your ISP will usually supply you with a modem to allow you to connect to the internet, this may be either a ADSL or Cable Modem depending on your ISP, but they are both the same but speeds may be different, ADSL uses a telephone line and Cable uses coaxial wires underground.

A network cable is required to connect your computer to a modem and a telephone cable will be required to connect an ADSL modem to a phone line, or a coaxial cable to connect a cable modem to the internet.

An internet browser is required to view websites on the internet, most computers will have a web browser pre installed known as Microsoft Internet Explorer, there are alternate web browsers to choose from such as Safari, Opera, Mozilla Firefox and Google Chrome.

An email client is required to access your email account by connecting to a mail server. Your ISP will usually supply you with an email account, Most computers will have an email client pre installed called Microsoft Outlook Express.

Router for security, most modems now have the router built in to ensure security and saves taking up space with devices. A software firewall is now usually built into the router and can use Network Address Translation (NAT). It is still advisable to have an antivirus installed on the computer.

The availability of the connection will be reliable and the connection will not drop so this ensures a connection 24/7. The performance of the internet connection will vary on what internet service provider is chosen. Most internet service providers will provide a connection of up to 8 Mbps downstream these days. But if you constantly use the connection and download a lot of data the provider may throttle your internet connection to slow it down to reduce usage. Modems can go faster than the designated speed your ISP is providing but the ISP cap your modem with a configuration file to go no higher than the allocated downstream and upstream speeds.

M2 Network Situations

Wired - A wired connection is using a network interface card (NIC) and is connected using an Ethernet cable, the Ethernet cable may then be connected to a switch or a router. The switch or router is then connected to a modem (however modern routers may have the modem integrated) which then connects to the outside world known as the internet through underground telephone wires.

Wireless - Wireless is sending data using electromagnetic signals without using any wires. This is mostly used for laptops which can be carried around for portable use. The quality of the signal is determined by how close you are to the wireless router. It is hard to determine the signal when you are further away but as you travel more further away the signal degrades. The signal can pass through walls but the signal heavily degrades.


A LAN is recommended for a small basic home or office network

In a local area network it is best to use a wired Ethernet connection to ensure a reliable high speed connection any device can be easily added to the network such as printers, external hard drives. Users may need to use the internet regularly and to do their work they may have to upload it onto a server on the LAN for the teachers to mark it or print it. The users cannot afford to have interference in the network and any other disruptions to the network such as slow traffic and long distance.


A Wide Area Network is a small geographical location which may consist of many types of connections such as wired, wireless, fibre optic connections.

A WAN is recommended for a company as they need reliability; more than one type of connection, security; server with roles and policies in place and a router with a firewall for monitoring incoming and outgoing connections, high speed internet access; this may be achieved from a leased line.

Task 3

D3 Transfer of Data over Wired and Wireless Networks

Possibly the slowest of all networks is the mobile network which uses WAP GPRS which has speeds ranging up to 128 kbps however this has been replaced by a newer form of mobile internet communication known as 3G which theoretically has speeds of up to 384 kbps, this is the slowest methods of wireless communication. High speeds methods of wireless communication is known as 802.11 Wireless; this operates at frequencies 2.4, 3.6 and 5 GHz, this has theoretical speeds of up to 54 mbps however a newer protocol has been developed known as 802.11N which has theoretical speeds of up to 144 Mbps.

Ethernet is the most common of all wired networks, this consists of a cable that can reach up to 100 metres before the signal attenuates; the standard Category 5 Ethernet cable can reach speeds of up to 100 Mbps however the new Category 6 Ethernet cable can reach speeds of up to 1 Gbps.

Currently the fastest of them all is Fibre Optic; this is a cable that consists of glass covered in cladding and coating that transfers pulses of light down the cable, The maximum distance a fibre optic cable can travel is up to 2 km but some types of fibre optic cables can travel up to 70km. The highest speed a fibre optic cable can transfer at is up to almost 100 Gbps.

Copper Ethernet Cabling and Wireless Compared


Ethernet - Ethernet cables are very cheap to buy and can be easily used to extend the schools extension LAN. Ethernet cables can be bought for a few pence.

Wireless - Wireless is still expensive to buy, wireless routers need to be purchased which start from £20+. Wireless receivers will then need to be purchased which will also cost £20+ unless you are using laptop which has wireless built in. You can also get USB wireless devices that can connect via a USB port.


Ethernet - Copper Ethernet cables are available almost anywhere, the copper wires are also in telephone lines which are found in walls and under floors. The only downside is if you are in a listed building which will prevent you making holes in the wall to pass the cables through.

Wireless - Wireless is only available when a wireless signal is in range depending on the location of the wireless access point, the signal can pass through walls and floors but the signal heavily degrades, to get the best performance it is ideal to be within a small distance of the wireless access point.


Ethernet - Ethernet is very reliable as long as the cable doesn't travel any longer than 100 metres before it has to be connected to a repeater otherwise the cable will suffer from attenuation which causes the signal to degrade. The wires inside a cable are twisted to prevent any crosstalk occurring.

Wireless - Wireless is reliable when in a suitable range. Wireless signals can be a problem when other electronic devices are in range such as microwaves as these can jam the wireless signal.

Health and Safety

Ethernet - Ethernet cables must be tucked away in safe places to prevent people from tripping over them, this is a health and safety risk.

Wireless - Wireless uses no wires so there is no risk of tripping over any cables but the wireless signal does emit RF signals which can lead to radiation, but this is very little.


Ethernet - Anyone can take an Ethernet cable plugged into a device and plug it into a device of their own, hackers may carefully plug an Ethernet cable into the schools router and hide it away and leave it trailing outside which will allow them to gain access to a network. Also the signals emitted from Ethernet cables can be picked up from clever sniffing devices. People can cut the wires and attach a box in the middle of the connection to also link their own devices to.

Wireless - Wireless has its own method of security to access the network; it can have encryption set so the users wanting to connect must enter an encryption key to allow them to authenticate the connection. WEP, WPA and WPA-PSK is the most common methods of encryption, they can either use 64 bit or 128 bit encryption. 128 bit encryption is recommended. WEP has been proved insecure so it is advisable to not use this method of encryption.


Ethernet - The performance of an Ethernet cable is very good; a CAT5 cable can reach up to 100 Mbps whilst a CAT6 cable can reach up to 1 Gbps. As long as the cable is less than 100 metres it will perform at the theoretical speed before the cable attenuates.

Wireless - The performance of wireless varies on the distance you are between the wireless access point and the receiver. 802.11b can perform up to 11 Mbps, 802.11a and 802.11g can perform up to 54 Mbps. 802.11n can possibly reach up to 300 Mbps.