Signal Theory

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AS and A Level Computer Science

Anas Patel                Assignment 1

BTEC National Certificate

for

IT Practitioners

Unit 8

Communication Technologies

Assignment 1

In this assignment I am going to describes different types of communication devices. For example Switches, Routers, etc. Then I am going to explain the principles of signal theory. After this I will look at difference methods of electronic communication and transmission used.

Communication Devices

Switches – These are mainly used for local area networks (LAN). The reason behind this is that they can be used to bridge a lot of computers together. They do look like hubs but they can vary in speed. They are more intelligent due to the fact that they can send out packets from a set port. There is advantage of using a network switch, they can be used with an Ethernet cable or a fibre optic cable and they still will work perfectly fine. When connecting a router or a server in an LAN or WAN network it is slightly easier because you would just need one cable which would mostly need to a fibre optic cable, so you can get the maximum rate of transfer speed.

Routers – They are mainly used for connecting one network to another. They are meant for handling information and forwarding to another network connected to the router. You can either connect using wireless or a cable. Normally an Ethernet cable is used to connect the computer networks. 

Hubs – Also known as a concentrator or a multiport repeater. Used in a star or a hierarchical network setup to connect the station or the cable segments. There are two main types of hubs: passive & active. Active takes the incoming traffic, amplifies the signal and then forwards it all the ports. In a passive hub it simply divides the incoming traffic and forwards it. A hub can be used to manage and allow individual port configuration and traffic. Hubs operate on the physical layer of the OSI model and they are protocol transparent. This means that they do have the ability to set upper layer protocols such as IP, IPX or a MAC addresses. Hubs just extend them do not control the broadcast or collision domains.

Bridges – Used to increase the performance of a network by dividing it into separate collision domains. Even though they are more intelligent than hubs due to the fact that they operate at the Data Link layer of the OSI model, they still are not able to control the upper layer protocols. On a separate segment they store the MAC addressing table of all nodes. Basically it takes the incoming frames and checks the destined MAC address and lookups it up against the store MAC addressing table and decides what to do. If the frame is comes from the same port as the destined port than it simply discards the frame. If the destined location is not known than it will be flooded throughout the outgoing ports and segments.

Repeaters –One of the less complex hardware of the networking world, because it basically runs at the physical layer of an OSI model, so it is not aware of the frame formats and upper layer protocols. Repeater basically is used to expand a LAN network over large distance regenerating a signal. When using a repeater remember the 5-4-3 rule which means that a maximum distance between two hosts on the same network is 5. Use only maximum of 4 repeaters in a network and only 3 segments can be populated.

Gateways – Very intelligent devices, they work at the Transport Layer protocol. This is higher than the Upper Layer protocol. This means that can manage and control IP, IPX and MAC addressing. They allow IPX/SPX clients to IP/TCP uplink network to connect to the internet. A gateway in simple terms is like a post office. All the information is sent to it and then as a post office knows the number of houses in the area in the same way a gateway would know all the ports and direct it there.

Cell Phones – It is a piece of device which is used by a lot of people. It is a portable version and more advanced version of a normal home phone. It lets you voice calling, text messaging, the some other advanced phones even allow video calling and internet browsing. Cell phone is a full duplex device therefore you can connect it to your computer and use it as a modem even though it would be very slow. The newer released phones are somewhere near capable of the proper modem speeds.

DCE & DTE devices – Data Communication Equipment (DCE) is basically equipment which allows communication with a Data Terminal Equipment (DTE). In another words DTE ends the communication line and a DCE provides the path of communication. An example of an DCE is an modem and a computer is a DTE.

Fax Machine – A device which allows you to send paper copies using PSTN lines to other people. It can also be used to send memos and other information as well. It uses the phone line to transmit the data that is sent. A fax machine has a sensor to read the data and the end of it. It will encode the black and white that it picks on the paper and moves it to the receiving end. It will compress the data before transmitting it. As soon as it receives the data it decodes and decompresses the data so it can arrange it in the way that it scanned it from the original document. There are a lot of things in a fax machine that allow it to do its function. It consists of a source projecting a light beam, a rotating cylinder and a photo electric cell. It also has paper feed like a printer.

E-Mail – Email also which is the short form for electronic mail. You can use e-mail to stay in contact with your friend/family even colleagues. It does it by finding out the person you want to email he’s email address and then you will send him an email and click send and then that person will receive it.

Signal Theory

When talking about signal theory data is represented by digital format which is dependent on binary or base 2 principles. Analogue and digital frequencies are used for transmitting signals along a medium link. Analogue records the waveform as they are. Digital on the other hand turns the analogue signals normally to sets of number. Analogue signals can have varying amplitude and frequency. Amplitude analyzes the loudness of the signal and Frequency determines the pitch of the signal. “Pitch” mostly used to refer to low and high notes. If the frequency is lowered than you get a low note and if the opposite is applied than you get a high note. Bit is a binary digit which represents value of 0 which is normally off and 1 which is normally on. Bit can also be referred to as a electrical pulse which is generated by the inner clock in the control unit or data register. Bit can also be used for digital electronics which is another system that uses digital signals. Manipulation of a bit within the memory of a computer can be kept in a steady level on a storage device as a magnetic tape or disc.

Byte which is made up of 8 bits is a unit measurement used for information stored on a computer.

Synchronous & Asynchronous Communication

To sum up synchronous communication it is when interaction with data takes place it is done in real time. On the other hand asynchronous or delayed communication is when any data which is archived or stored and accessed later. It is important to choose the most effective delivery mode because it directly impacts the level of interaction that is going to take place.

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Synchronous

It does not use start or stop bits but instead it synchronizes the transmission speed with receiving and sending end of transmission using the clock signals specifically built for each of the components. After this constant streams of data are transmitted between two sources. Because no start or stop bits are involved data transmission is faster, but more problems occur because if latency takes into effect then the synchronization clock will be out of timing therefore the receiving node will get the wrong timings that have been acknowledged in the protocol sending and receiving data. If this happens ...

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Signal Theory
Document Details
  • Word Count
    6197
  • Page Count
    15
  • Level
    AS and A Level
  • Subject
    Computer Science
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