1.3.1 Networks and topologies

What is a LAN?

• local area network

• a network over a small geographical area such as a single site

• the network infrastructure is usually owned and managed by the organisation

What is a WAN?

• wide area network

• a network over a large geographical area such as multiple sites, towns, cities countries or continents

• requires third party connections such as phone lines and satellite

What is the role of a client in a client-server network?

• a less powerful computer that relies on servers to provide and manage data

• they have no control over the network as a whole or over individual computers

• to send requests to a server, wait for a response, and then receive the response

What is the role of a server in a client-server network?

• a more powerful computer that manages and stores files (provides services) to client computers on the network

• to wait for requests from clients, to perform the request and to send a response back to the client

What are the advantages and disadvantages of a client-server network?

advantages

• can be controlled centrally from the server which also backs up all software and file servers as well as controls security

• hardware, software and resources can be shared across the network (e.g printers, applications and files)

• allows for improved scalability - works well with a large network

disadvantages

• all users are reliant on the central server for files so if there is a fault with it, files cannot be accessed

• servers are expensive

• hard to manage and maintain - IT technicians needed

• malware can spread quickly across the network

What are the roles of computers in a peer to peer (P2P) network?

• there is no central server so data is shared directly between systems and all computers have equal status

• each requests and performs tasks on the network - serve each other

• all responsible for providing data

What are the advantages and disadvantages of a peer to peer network?

advantages

• for a small network it is easier and cheaper to set up - new computers easily added - no dedicated equipment like a server needed and no specialist staff

• direct communication - optimal for quickly sharing files between systems, especially media files

• computers are not dependent on a single server

• if a computer goes down, only its files are lost

disadvantages

• no central device to manage backups or security so it must be performed on each individidual computer - less secure

• decreased scalabilty and ability to manage beyond a few computers - doesn’t work well with a large network

• files on individual computers may be hard to locate as each user is responsible for their own filing so it may be unorganised

How does bandwidth affect network performance?

• it is the max amount of data that can be transmitted in a network’s transmission media at a time

• bandwidth of the medium is shared between all connected devices

• as the number of devices increases, bandwidth per device decreases - devices must wait longer before they can transmit (increased latency) so the network is slower and the transmission rate decreases

• if maximum bandwidth is being used, no more transmission can happen at that time

How does the number of collisions (error rate) affect network performance?

• when devices try to communicate with each other at the same time, the signals collide

• the transmission fails and the signal must be re sent which slows the network

• more devices connected - more collisions likely - loss of more packets - more data has to be retransmitted - high error rate

What are all of the factors that affect network performance?

• the bandwidth available

• number of users at the same time

• error rate

• interference

• distance between nodes

• type and amount of data to transfer

• transmission medium

• toplogy

• central hardware performance

When is a client-server network used?

• best suited to organisations with many computers, or to situations where many computers need access to the same information. Many schools use this type of model.

When is a peer to peer network used?

• best suited to smaller organisations that have fewer computers, or where fewer computers need access to the same data.

What is the role of a wireless access point?

• to provide a link between wireless and wired networks

• creates a wireless LAN that allows wifi enabled devices to connect to a wired network

• e.g a wifi or bluetooth hotspot

• may be a seperate device or built into another device such as a router

What is the role of a router?

• to transmit data packets between networks from router to router

• receive data packets and use the IP address in the packet header to determine the most appropriate route for transmission

• it stores the IP address of each computer connected to it

• assigns IP addresses to nodes

• maintains a routing table

What is the role of a switch?

• to connect devices together on a LAN

• recieves data packets from a connected node, reads the destination address in the packet header and forwards the data directly to its destination

• keeps/records a list of the MAC addresses of all devices connected to it when it receives data

• scans for a matching destination address before sending the data packets directly to one of the connected computers

What is an alternative to a switch?

hub

• forwards a copy of the received data to all connected nodes

• less secure

• slower - unneccessary signals are sent

What is the role of a network interface controller/card?

• internal piece of hardware (embedded on the motherboard) required for a device to connect to a network

• includes a MAC address which is used when sending data across a LAN

• ethernet cable plugged into it to allow data to be exchanged between the device and the network

What is transmission media?

• the communication channel along which data signals are transferred

• can be wired or wireless

• type used afffects performance

What are the advantages and disadvantages of copper cables?

• use electricity

advantages

• tried and trusted technology

• relatively inexpensive

disadvantages

• signal affected by electric
  and magnetic fields

• low bandwidth

• heavy, trailing cables

What are the advantages and disadvantages of fibre optics?

• use light

advantages

• very fast data transmission

• low loss of signal over distance

• not affected by magnetic or
  electric fields

• require very little power

• more difficult to intercept than copper cables

disadvantages

• high investment cost

• need for expensive optical
  transmitters and receivers

What are the advantages and disadvantages of wireless
transmission?

• uses radio waves

advantages

• allows devices to be used
  anywhere provided there is a
  signal

• no need for trailing wires (safer)

• easier to add devices to a
  network

disadvantages

• data transmission rate less
  than that of wired systems

• signal can be blocked by
  objects or walls

• increased risk of security issues -

  • data can be intercepted easily

    and without network owners

    knowing

What is a network topology?

• the layout of computer systems (nodes) on a LAN

• star and mesh

What is a star topology?

• nodes are connected to each other through a central switch through which all communication passes

What are the advantages and disadvantages of a star topology?

advantages

• improved security - data packets sent directly to and from the switch in the centre and not necessarily all devices

• new nodes can be added directly and easily to the central switch - network will not need to be shut down to modify it

• if an attached node or cable fails, the rest of the network is not affected - only that single node is

• faster data transfer speeds - data goes to intended recipient directly with minimal collisions - higher performance

disadvantages

• requires additional hardware which is expensive and needs to be maintained

• single point of failure - if the central device fails, the whole network will become unusable until fixed

What is a mesh toplogy?

• no central connection point - each node is directly connected to at least one other node

• each acts as a router to relay data

• full mesh - each node is connected to every other node

What are the advantages and disadvantages of a mesh toplogy

advantages

• if one cable or node fails, the data packets can take an alternative route - no single point of failure

• many possible connections allow data transmission from multiple devices simultaneously - can withstand large amounts of data traffic - messages more likely to get through and do so quickly

• modification and expansion can be done without disrupting the entire network

disadvantages

• large amount of cabling and hardware needed in a full mesh especially - expensive to install and maintain - difficult to maintain

• may involve redundant connections (those that will never be needed)

Where is a star toplogy found?

• smaller businesses

• schools

• wireless home networks

Where is a mesh toplogy found?

• large organisations that require reliable communication

• e.g military or emergency services

What are the advantages and disadvantages of using networks over having stand alone computers?

advantages

• file sharing

• hardware sharing

• communication - email, chat, video etc

• roaming access - sign in to any computer on the network and be able to access your files

• centralised maintenance and updates - network managers can apply software updates across a network, removing the need for individual users to do it

• centralised security - anti-virus software and firewalls can be implemented across a network, helping to protect user files from risks

• user monitoring

• levels of access - different users can be given different access rights.

disadvantages

• cost - additional equipment is needed

• require management by technical staff

• malware can easily spread across an improperly secured network

• hacking once a device is connected to another device, it is possible that data may be accessed without the device owner's permission

What is the internet?

• a worldwide collection of interconnected computer networks

What is web hosting?

• a service offered by companies that will host web pages and files

• a website must be hosted (stored) on a web server to be able to be accessed by others on the internet

How does web hosting work?

• web server responds to the web browser (client’s) request to display a web page

• processes the request by preparing the web page and returns it to the web browser

• displayed to the user through the broswer

What are the advantages of web hosting?

advantages

• web hosts have far more bandwidth - can serve more users

• able to monitor their equipment 24/7

• web hosts will back up sites remotely - individuals don’t have to

What is the domain name system?

• every web page has a domain name - easy to remember - and a unique IP address for the device that the web page is stored on

• a DNS server stores a list of domain names and a list of corresponding IP addresses

• 13 DNS root servers worldwide - contain a complete list of all domain names and their IP addresses

What are the steps taken to display a web page?

• domain name typed into browser

• query is sent to the local DNS server - it will check if it holds the corresponding IP address. if it does, it passes it to your browser

• browser then connects to the IP address of the server and accesses the website - displays it to user

• if the local DNS server does not hold the IP address, the query is passed to another DNS server at a higher level

• if found, the address is passed down to servers lower in the hierarchy until it reaches the local DNS server and then the browser

What is the cloud?

• a set of servers working together to deliver a service over the internet

• software as a service

• purposes include running applications, storing data and processing

• data stored on large servers owned by a hosting company

What are the advantages and disadvantages of cloud storage?

advantages

• huge capacity and ability to upgrade your subscription easily for as much extra storage as you need

• free for a certain amount of storage

• access can be granted to another user and people can work on a file simultaneously

• can be accessed from anywhere on demand with an adequete internet connection

• no need for a powerful computer to store data

• back ups are supposed to be done by the service provider

disadvantages

• unusable without a good enough internet connection

• slower to access as the data has to be sent over the internet rather than local storage device

• no guarantee that data is being backed up

• personal data will be stored on another company’s servers - admin of that system have access - data protection risk