The Logical And Physical Topologies

Published Date: 02 Nov 2017

Local Area Network(LAN)-It's a network mostly found at home or small offices, most of the network uses Ethernet connection, although some might use WiFi access too. The purpose of the LAN is to share and exchange information.

Wide Area Network(WAN)- This type of network is consisted of a group of LAN networks. Most of the WANs are created by one organisation . for instance: we have Uxbridge college which has two campuses. Uxbridge campus and Hayes campus uses WAN to connect them together.

Internet-Knows as (world wide web) it's a very big network of devices connected together which exchanges information and data. The most common protocol which is used is TCP/IP (transmission control protocol / Identification Protocol) Internet contains a lot of LANs and WANs which could be just used at home or in business and school/universities. When internet has began the main idea of it was to communicate and exchange documents and it was only available for the military purposes. Now "internet" is a one big database, we can find everything in internet now days starting from books and finish on movies, games and social networking.

WAN Technologies

-Frame Relay

-MPLS

-ATM

Personal Area Network (PAN)- it is an network which is organised by a person, most of the times it is used for personal purposes and transferring files between devices. although the network is used by a mobile and PDA devices in most cases.

Logical and physical topologies-Logical topologies is the way how the user is connected to the interface and physical is the actual cabling and the layout of the cables. Physical topologies are presented with a diagrams of how the cables are placed, although we have many physical topologies;

Star Network: Devices are connecting to the central unit which is a hub or a router this is a good example of home network, where computers are connecting to the central unit like router to gain access to the internet. In star network we use Ethernet cable to connect computer to the hub.http://upload.wikimedia.org/wikipedia/commons/thumb/6/66/NetworkTopology-Star.png/220px-NetworkTopology-Star.png

As all technologies has a good point and bad points I have to mention them :

The main advantage of star network is that offers the data to flow fast.

Another good point is we can easily connect new devices into the network, and failure of one device does not affect the others.

The bad points are if the router or hub meets a failure then the whole network will lose access to the internet. Also the network might have limited capacity it depends on the hub or switch, how many devices can be connected. Most of the hubs and routers are expensive which is increasing the cost of the network.

Bus Network; The whole network of computers is connected to the bus, which is used for exchanging data between the devices. The bus uses coaxial cable which has to be terminated on the both sides in order to eliminate signal from reflecting.http://upload.wikimedia.org/wikipedia/commons/thumb/4/47/BusNetwork.svg/220px-BusNetwork.svg.png

It is a easy solution for a small network as this type of network will not handle a very high amount of traffic. It can be easily expanded, but only one device can send data at time. It limits it selves for a certain number of computers.

The big disadvantages is that the cable fault will disable the whole network.

Ring Network: Is a type of network where the devices are connected together in a circle, where the data is send through all of them to its destination. If a device wants to send a data it need to request a token. After one device is finished with transmitting data it passes the token to the other which can send data. http://upload.wikimedia.org/wikipedia/commons/thumb/d/db/NetworkTopology-Ring.png/220px-NetworkTopology-Ring.png

The token allows to lower the traffic in the network as only one device sends the data at time.

In case of breaking the cable the data will flow in the opposite direction.

It has a better performance under the heavy traffic than the bus network.

the disadvantage is that the number of devices in the ring decides about the speed of sent data.

Mesh Network: In this type of network we have all devices connected together. It is a secured network because if computer 1 send information to computer 2 the data which is being sent is secured and only addressed computer can read that data or message. In order to make computers identify themselves in network they all need to obtain IP address (identification Protocol). This type of network gives several advantages. http://blog.networksaremadeofstring.co.uk/wp-content/uploads/2012/06/527px-FullMeshNetwork.svg_.png

Main advantage is that if one computer brakes it doesn't affect the others or the network.

Also this type of network is sending messages through other computers, so if there is too much traffic on one of the path it uses the different one to get to its destination. Also if one path is broken it uses another one.

The disadvantage is that this type of network requires a lot of cabling.

Network access methods

Token passing- It's a method of connection which enables to send data by simple passing the token a good example of token passing is a ring network where computers are connected in the circle. When one device is carrying the token this means that the device is allowed to send data. Once the data is send the device passes token to another device in order to allow this device to send data.

CSMA(Carrier Sense Multiple Access)- This type of network access is used mostly on the shared networks. When devices connects to the network is has to listen before transmitting, because only one person can transmit information at the time although all the devices connected to the network has equal access to speak when network is not in use. There are some chances that there could be collision when two devices uses the network at the same time. In that case the transmission will stop for a certain amount of time and after that time transmission will be resumed. But there is a bad point as well, because if we have too much collisions going on in the network the waiting time radically increases and the performance of the networks is going down.

Network models

TCP/IP-(transmission control protocol/ internet protocol)Is the protocol which is responsible of data flowing from the computer to the internet. This includes downloads, emails, chat rooms, IP protocol holds address of the data where it needs to be transmitted.

Peer to Peer-It's a type of network where all computer are linked together and they share files in between them. this type of network don't require server or hub, because computer in the network are just sending files straight from their own hard disk drives.

Network protocols and standards:

Apple Talk- This protocol was developed by apple which was build under the OSI model which made it very easy and compatible to use with other devices. The thing which made it so good at that time was that it automatically assign it selves with an IP number from the router or hub.

UDP-(User Datagram Protocol)- This type of the protocol is used to send datagram which are a short messages which can be exchanged by servers. This kind of protocol is not negotiating the speed of the transfer as well as it doesn't check the data in search of errors. So for instance if we are sending data this protocol just sends it there is no connection and we are not sure if the data has arrived or not and if arrived in what order it arrived.

FDDI-(Fibre Distributed Data Interface)-This type of the protocol is in use in fibre optic local area networks, which is used most of the times in the ring network. This has quite longer range that a standard LAN it can reach up to 200 kilometres.

Wireless technologies

Bluetooth- It’s wireless technology for exchanging data over a short distance using radio transmission.

Versions and transfer Rates

Version 1.0- 24kb/s

Version 1.1-124kb/s

Version 1.2-328kb/s

Version 2.0- max-2.1mb/s + EDR (Enhanced Data Rate)= 3.1Mb/s

Version 3.0 +HS (high speed) - 24Mb/s (3MB/s)

Version 3.1 + HS (High Speed) (5MB/s)

Bluetooth Technology is used in many mobile devices and computers. Bluetooth is used by mobile phones to send files and applications, it’s also used to connect hands free kits. Laptops uses Bluetooth to transfer files around, sometimes to connect to the internet. Tom Tom devices also use Bluetooth technology to connect mobile phones for hands free and many other devices . Some of the remote controls also use Bluetooth. There are different Protocols which allows Bluetooth to be use to connect to the internet.

Wi-Fi- It’s a connection which uses radio waves which allows devices to exchange data. WiFis now used in every laptop and mobile phone in order to connect to the internet. Devices are connecting to hotspot which is exchanging data with devices and allow them to surf internet. As every good thing has a disadvantage this connections gives us a security issue. All the data is sent wirelessly so it can be easily overtaken by someone with bad intensions. WiFi uses WEP and WPA-PSK encryption to code the data so it would not get into improper hands.

Infrared- Is short connection which uses laser to transfer data. This is mostly used in remote controllers. The disadvantage of infrared is that works over short distance and if anything stands between a remote and TV it will not work.

Application layer protocols types:

SMTP-(Simple Mail Transfer Protocol) This protocol is mainly used by the software which is designed to sent emails. This protocol helps servers exchanges the mails. However this protocols is only used to send messages.

FTP-(File Transfer Protocol) It is used to transfer data in the internet, for instance when we are downloading any movies or music this downloads are enabled by FTP protocol. Most of the browsers has embedded FTP client in it, so we don't need to download special software for downloads

DNS- When we type in the browser website it goes to the DNS server it checks the IP of the website and redirect us to the webpage. Sometimes when IP address is not found on one DNS server it directs to another one. If the IP is still not found we get the message DNS server not found.

HTTP-(Hyper Text Transfer Protocol) is used to transfer data from the computer to the WWW (world wide web) servers.

Network Devices:

Work stations- It is a higher specification computer designed, for purposes different than using it at home. It usually has larger amount of RAM (Random Access Memory) installed and better processor and graphic card in order to handle more complicated operation. For instance Graphics designers might use workstation because they have to use computer to design and edit graphics. Standard computer would not handle those operation, that's why we need workstations.

Servers-We have many types of servers. Server it selves it's a hardware which has a special operating system to serve others (clients). It also depends what type of server we are talking about. There are web servers, file servers etc.. For instance web server is used to store web pages. So when we are creating web page, we are renting a space on the server and place the page over there. When we type the address in the browser, there is a request sent to the server. The server extracts the page and sends it to us. File server work similarly, therefore when request is sent , the server sends a file through FTP protocol, it could be any file like; photos, music, movies etc. Servers also needs to have high performance hardware in them as it serves a lot of clients.

Interconnection Devices:

Router- It's a device used in networking, It's like a traffic manager as it has to choose the best and faster way to send data. Routers bases the route on the IP protocol in order to select the best way to deliver the packet/ piece of data. Also in routers we have a routing table where the information about different routes are stored, this information can be shared with other routers within the network.

Switch- It's a device in the LAN(Local Area Network) where all the devices are connected to it in order to gain access to the internet. Switch is a similar device to network hub, but it is constructed way much better that hub, because if there is a message for a specific device it recognise the MAC address of a connected device and passes the message to it. Hub are different in way that the message goes to whole network instead of selected device. We can also connect a printer to the switch. To summarise switch offers faster connections and better performance in compare to hub, but unlike switches are more expensive than hubs.

Connectors and cabling:

Category 5- This type of cable is an Ethernet cable which is used in networking to exchange the data between devices. There are different types of cat5 cables like:

Unshielded twisted pair (UTP)-

It is made of one or more twisted pairs of cables. The cables are twisted in order to reduce electrical noise; it is cheaper than STP because unshielded. The transfer speed is 100Mb/s. It is one of the cheapest cables used in telephonic and broadband industry. The maximum length is 100m.

Shielded twisted pair (STP)

Is the same kind of cable but is in the shield and grounded in order reduce electrical noise and interference. Each twisted pair is foiled to reduce interference from radiation and microwaves. This kind of cable is a bit more expensive than UTP and is harder to lay it out. Transfer rate is the same as UTP 100Mb/s

Coaxial- It’s a cable which is in use in many years for cable television. It is very cheap cable, but it takes much space. The data is transmitted by sending electro-magnetic waves down its core. Maximum cable length is 500m. Coaxial cable was replaced in IT industry by twisted pair because it is easier to install and more flexible.

Fibre Optic- Fibre optic cables are using light to form electromagnetic wave to transfer data, that’s why they are very fast but expensive. It can be used for a long distance which is an advantage.

Software:

Network Operating System- There are different types of network operating system on the market now days. The most popular and common one is Windows Server. Operating system for server differs from traditional operating system for PC. Windows 7 is a operation system for home use like; word processing, gaming etc.. Server version of operating system are created to manage the network in a easier way, it has some extended security and network features.

Virus Check- this software is used to protect our computer from viruses. All antivirus needs to update the database regularly because everyday hackers release new virus. Antivirus is scanning our computer for viruses all the time in background if he founds virus it gives us information and ask what should he do with it we have 3 options

Quarantine- if we select quarantine the virus will be locked in the cage so he is still on the computer but locked and doesn't harm our computer

Delete- If we select delete option virus will be permanently deleted from the computer.

Ignore – If we select ignore program will just ignore it and carry on scanning.

So far we have different types of viruses;

Trojan horse-When the virus is installed on the computer it opens the port so the person gets full access of our computer and can do whatever he likes. This is very dangerous because we might lose all the data and worse thing if we store our bank details on the computer we might get hacked into our account.

Worm-this types of virus is installed on the computer and duplicate it selves. Each of this worms use some memory of the computer, so If we get more and more of them the computer will slow down and finally crash.

Spyware-this type of virus as it names says "spy" hackers use it to gather information from the potential victim. Virus is installed on the computer when we download software or anything from internet. Virus takes the information from the computer and sends it to the person who creates it. There is a problem when we use our bank card online and store information on the computer because spyware will take that information and send this may effect that we may be a victim of a fraud.

Firewall- It's a piece of software mostly built into operating system or sometimes piece of hardware. Most of the decent and new operating system do have it. Firewall works in a way that it block or allow incoming traffic from the internet by analyzing the data or checking the source of that packet. by source I mean the IP of the sender and location.