Knowledge

Concept of computer networking

Purpose

    • Sharing resources and data between computer systems. Including data storage, printers and other devices.
    • Enables the exchange to take place between personal computers and the server software

Computer Networks: Crash Course Computer Science #28

Advantages of Computer Networks

    • Ease of use / Productivity
    • Collaboration
    • Web Conference / Online meeting

Disadvantages of Computer Networks

    • Additional cost
    • Security
    • Training

Types of transmission media

Optic fibre

  • Consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signals.
  • Each strand, is as thin as a human hair
  • Inside the cable an insulating glass cladding and a protective coating surround each optical fibre
  • Capability of carrying significantly more signals than wire cables
  • Faster data transmission
  • Less susceptible to noise (Interference) from other devices such as a copy machine
  • Better security for signals during transmission because they are less susceptible to noise
  • Smaller size (Thinner and lighter weight)

Wired

Physical and logical connections

Twisted- pair cable

- Consists of one or more twisted pair wires bundled together

- Each twisted pair wire consists of two separate insulated copper wires that are twisted together

- The wires are twisted together to reduce noise

- Noise is an electrical disturbance that can degrade communications

Fiber- optic cable

- Consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signal

- Each strand, called an optical finer, is as thin as a human hair

- Inside the fiber optical cable, an insulating glass cladding and a protective coating surround each optical fiber

Wireless

  • More convenient than installing cables
  • Businesses use wireless transmission media in locations where it is impossible to install cables
  • Types of wireless transmission media used in communications include;
    • infrared, Broadcast radio, Cellular radio, microwaves, communication satellites

The concept of transmission rates

 

Network topologies for local area network (LAN)

Wired star

https://www.lifewire.com/computer-network-topology-817884

(Wired) star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch (or hub on older networks) which acts as a conduit to transmit messages. In star topology, every host is connected to a central switch.

Example

The IT team at a school sets up a computer lab classroom to connect to the client server network using a (wired) star network. In the classroom, there is one switch and each computer is physically connected to the switch. If a new computer is to be added or removed, this can be done without disrupting the network to the other computers.

    • All computers and devices (nodes) on the network connect to a central device, forming a star
    • Two types of devices that provide a common central connection point for nodes on the network are a hub and a switch
    • All data that transfers from one node to another passes through the hub/switch
    • Star networks are fairly easy to install and maintain
    • Nodes can be added to and removed from the network with little or no disruption to the network
    • If one node fails, only that node is affected
    • If the hub/switch fails, the entire network is inoperable until the device is repaired

Advantages

Reliability: If one node or its connection breaks it doesn’t affect the other computers and their connections.

Ability to add/remove computers: Devices can be added or removed without disturbing the network

Disadvantages

Cost: An expensive network layout to install because of the amount of cables needed

Single point of failure: The central hub is a single point of failure for the network.

Wikimedia Foundation (2017). Star network. Retrieved 11 October, 2017, from https://en.wikipedia.org/wiki/Star_network   .

Wireless

A wireless network is a computer network that uses wireless data connections between network nodes.

Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Wireless telecommunications networks are generally implemented and administered using radio communication. This implementation takes place at the physical level (layer) of the OSI model network structure.

Through a Wireless AccessPoint

There is a central device called an  ‘access point’ to which all client computers connect. This access point provides interconnectivity between clients and also sometimes between the wireless and wired network

Ad-Hoc

No central device, just a number of computers connected together through their wireless network adapters/

Wikimedia Foundation (2017). Wireless network. Retrieved 11 October, 2017, from https://en.wikipedia.org/wiki/Wireless_network  .

Creately (2017). Network Diagram. Retrieved October 17, 2017,  from at https://au.pinterest.com/pin/464011567831173778/  .

Advantages

Mobility: With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc. More and more businesses are also offering free Wi-Fi access.

Fast setup: If your computer has a wireless adapter, locating a wireless network can be as simple as clicking “Connect to a Network” — in some cases; you will connect automatically to networks within range.

Cost: Setting up a wireless network can be much more cost effective than buying and installing cables.

Expandability: Adding new computers to a wireless network is as easy as turning the computer on (as long as you do not exceed the maximum number of devices).

Disadvantages

Security: Wireless networks are much more susceptible to unauthorized use. If you set up a wireless network, be sure to include maximum security. You should always enable WEP (Wired Equivalent Privacy) or WPA (Wi-Fi Protected Access), which will improve security and help to prevent virtual intruders and freeloaders.

Interference: Because wireless networks use radio signals and similar techniques for transmission, they are susceptible to interference from lights and electronic devices.

Inconsistent connections: How many times have you hears “Wait a minute, I just lost my connection?” Because of the interference caused by electrical devices and/or items blocking the path of transmission, wireless connections are not nearly as stable as those through a dedicated cable.

Power consumption: The wireless transmitter in a laptop requires a significant amount of power; therefore, the battery life of laptops can be adversely impacted. If you are planning a laptop project, be sure to have power plugs and/or additional batteries available.

Speed: The transmission speed of wireless networks is improving; however, faster options (such as gigabit Ethernet) are available via cables. In addition, if set up a wireless network at home, and you are connecting to the Internet via a DSL modem (at perhaps 3 Mbps), your wireless access to the Internet will have a maximum of 3 Mbps connection speed.

Technology to Business (2017). Wireless LANs advantages and disadvantages. Retrieved 11 October, 2017, from https://technologytobusiness.wordpress.com/2011/03/03/wireless-lans-advantages-and-disadvantages/ .

Client server

Client server networks form the structure of most modern computer Local Area Networks (LANs). One or more computers act as a server and the other computers on the network request services from the server. The server controls access to the hardware, software and other resources on the network and provides a centralised storage area for programs, data and information. The clients are other computers and mobile devices on the network that rely on the server for its resources.

Example

When a student accesses the SEQTA with a web browser (the client), the client initiates a request to the instance of the SEQTA web server. The student's login credentials are  stored in a database, and the web server accesses the database server as a client. An application server interprets the returned data by applying the application's business logic, and provides the output to the web server. Finally, the web server returns the result to the client web browser for display.

In each step of this sequence of client–server message exchanges, a computer processes a request and returns data. This is the request-response messaging pattern. When all the requests are met, the sequence is complete and the web browser presents the data to the customer.

Wikimedia Foundation (2017). Client-server model. Retrieved 11 October, 2017, from https://en.wikipedia.org/wiki/Client%E2%80%93server_model .

Advantages

1)  Centralization : Unlike P2P, where there is no central administration, here in this architecture there is a centralized control. Servers help in administering the whole set-up. Access rights and resource allocation is done by Servers.

2)  Proper Management : All the files are stored at the same place. In this way, management of files becomes easy. Also it becomes easier to find files.

3) Back-up and Recovery possible : As all the data is stored on server its easy to make a back-up of it. Also, in case of some break-down if data is lost, it can be recovered easily and efficiently. While in peer computing we have to take back-up at every workstation.

4) Upgradation and Scalability in Client-server set-up : Changes can be made easily by just upgrading the server. Also new resources and systems can be added by making necessary changes in server.

5)  Accessibility : From various platforms in the network, server can be accessed remotely.

6)  As new information is uploaded in database , each workstation need not have its own storage capacities increased (as may be the case in peer-to-peer systems). All the changes are made only in central computer on which server database exists.

7)  Security : Rules defining security and access rights can be defined at the time of set-up of server.

Disadvantages

1)  Congestion in Network :Too many requests from the clients may lead to congestion, which rarely takes place in P2P network. Overload can lead to breaking-down of servers. In peer-to-peer, the total bandwidth of the network increases as the number of peers increase.

2)  Client-Server architecture is not as robust as a P2P and if the server fails, the whole network goes down. Also, if you are downloading a file from server and it gets abandoned due to some error, download stops altogether. However, if there would have been peers, they would have provided the broken parts of file.

3) Cost : It is very expensive to install and manage this type of computing.

4) You need professional IT people to maintain the servers and other technical details of network.

ianswer4u.com (2017). Client Server Network : Advantages and Disadvantages. Retrieved 11 October, 2017, from http://www.ianswer4u.com/2011/05/client-server-network-advantages-and.html#axzz4vAgSoUNt  .

Peer-to-peer

A peer-to-peer network is a simple, inexpensive network that typically connects fewer than 10 computers. Each computer is called a peer because it has equal responsibilities and capabilities, sharing hardware, data or information with other peers (computers) on the network. Each computer stores files on its own storage devices, has its own operating system and application software.  All computers on the network share any peripheral devices attached to any computer. In a peer-to-peer network, each computer may not necessarily be physically connected to every other computer.

Some common examples of peer-to-peer networks include:

  • Bitcoin
  • BitTorrent

Example

Students decided to meet each other after school for a LAN party. Each student brings around their PC to the person who is hosting the party. They connect their computers together in a string using ethernet cables and allocate IP addresses. The students then play a multiplayer game which they have installed on their own computers. The student who is hosting the party has a printer connected to her computer so they all print out their results on her printer.

Example

A person uses a  file peer-to-peer file sharing network to share media between their computers via the internet such as BitTorrent. The person finds the file and the packets are downloaded directly from other users computers (via the internet). Sharing of media files for which copyright is not owned is illegal, and a number of file peer-to-peer services have been taken to court in the US.

Advantages

Network operating system not required: No need for a network operating system

Does not need an expensive server:  Individual workstations are used to access the files

No need for specialist staff: Such as network technicians because each user sets their own permissions as to which files they are willing to share.

Much easier to set up: Does not need specialist knowledge

No disruption to network if computer fails: It just means that those files aren't available to other users at that time.

Disadvantages

Slow performance: Because each computer might be being accessed by others it can slow down the performance for the user

Cannot be centrally backed up: Files and folders cannot be centrally backed up

No shared file storage: Files and resources are not centrally organised into a specific 'shared area'. They are stored on individual computers and might be difficult to locate if the computer's owner doesn't have a logical filing system.

No way to protect against viruses: Ensuring that viruses are not introduced to the network is the responsibility of each individual user.

Little to no security: There is little or no security besides the permissions. Users often don't need to log onto their workstations.

 

Network components for internet connection for a small business

Server

A server controls access to the hardware, software and other resources on the network and provides a centralised storage area for programs, data and information.

Router

A router connects multiple computers or other routers together and transmit data to its correct destination on a network. To prevent unauthorised users from accessing files and computers, many routers are protected by a built in firewall, called a hardware firewall. Some Routers, also support wireless communications, eliminating the need for a separate wireless access point in a wifi network

Network interface card (NIC)

A network interface card (NIC) enables a computer or device that does not have built in networking capability to access a network. The network card coordinates the transmission and receipt of data, instructions and information to and from the computer or device containing the network card.

Switch

A switch provides a central point for cables in a network. Larger networks typically use a Switch, while older networks use a hub. Some switches include a router. They receive data from many directions and then forward it to one or more destinations.

Modem

A modem sends and receives data and information to and from a digital line. Three types of digital modems are ISDN, DSL and cable modems. These typically include built in WiFi connectivity. Some mobile users have a wireless modem that uses cell phone network to connect to the internet wirelessly from a notebook computer.

Skills

Design a suitable LAN topology