Computer networks, connections and protocols

network

• A network is two of more devices connected together with the purpose of sharing resources

What are the advantages of having a network

• Users can share resources such as printers and connection to the internet 

• Users can access their files from any computer on the network

• Communication can be made easier via email and social networks

• Users can share files and folders easily such as central databases and spreadsheets

• Servers can be used to provide centralised backups, updates and security

What are the disadvantages of having a network?

• There is an increased security risk to data 

• Malicious software can infiltrate the network and render it unusable

• Servers and switches can provide a central point of failure, resulting in users not being able to complete tasks using their computer

• Factors can impact the performance of the network such as the number of users and data on the network at one time

What is a local area network?

• A local area network (LAN) is a network which has a small geographical area (under 1 mile)

• All of the hardware is owned by the company/organisation/household using it

• LANs will use unshielded twisted pair (UTP) cable, fibre optic cable or wireless connections (Wi-Fi)

What is a wide area network?

• A wide area network (WAN) is a network which has a large geographical area (over 1 mile)

• They are a collection of LANs joined together

• The computers on a WAN are connected via routers

• The hardware used to connect the networks together is not all owned by the company/organisation/household using it.

• Telephone lines owned by telecommunication companies are an example

• WANs will use fibre optic cable, telephone lines and satellite to connect the LANs together

A travel agent has offices in two sites that are 10 miles apart. Describe the difference between a LAN and a WAN [2]

1 mark per bullet 

• LAN is small geographical area

• WAN is over a large geographical area 

or 

• LAN (usually) has its own/dedicated infrastructure

• WAN uses external / shared infrastructure or hardware

What are the factors that affect network performance

• Number of Users

• Bandwidth

• Latency

• Error Rate

• Transmission Media

Number of users

• This is how many users are on the network at the same time

• Too many users can cause the network to slow down if there is not enough bandwidth for all of the data being sent and received

Bandwidth

• Bandwidth is the amount of data that can be sent and received at any given time

• Measured in bits per second (bit rate)

• A smaller bandwidth means that less data can be sent and the network can slow down, potentially to the point of becoming unusable

Latency

• Latency is the delay between data being sent and received

• If there is a big delay between the two, more data will be on the network causing collisions

• This can lead to even more packets of data being sent as the error rate has increased

Error rate

• Error rate is the measure of how many packets of data do not reach their destination

• An increased error rate occurs in less reliable connections - a poor wireless signal would be a contributing factor to an increased error rate

Transmission media

• Transmission media is the type of cable used in wired connections

• Wired connections offer a higher bandwidth than wireless connections 

• The main options for transmission media are unshielded twisted pair and fibre-optic

• Fibre optic has a higher bandwidth than copper cabling as well as faster transfer speeds

Worked Example

A university has a LAN (Local Area Network). The LAN allows access by both wired and wireless devices. Users have reported that the network sometimes runs very slowly. 

(i) Explain why the number of devices using the network at the same time can affect the performance of the network [3]

(ii) Identify one other factor that can affect the performance of the network [1]

How to answer this question

• To answer this question there must be an answer with an explanation of its impact

• An example answer that would score full marks

  • More devices accessing the network at one time would result in the network performing slower because the bandwidth would be split between them [1]

  • The impact of this would mean that there is less bandwidth for each device, slowing down how fast data could be sent and received [1]

  • Having more users/devices means that there is more data being sent and received [1]

Answers

(i)1 mark each to a maximum of 3

• Slower transmission of data // less data can be transmitted at the same time // the transmission rate decreases // time to send/receive increases

• More devices mean more data is being transmitted at a time

• Bandwidth will be split between all the devices sending data // each device uses some of the bandwidth

  • this means that there is less bandwidth for each device 

• Devices have to wait longer before they can transmit // increased latency

• If the maximum bandwidth is used then devices cannot transmit

• Central device/switch/router has to handle more requests and may run slower

• More collisions are likely) // higher error rate

  • This means more data has to be retransmitted

• Loss of more packets

  • This means more data has to be retransmitted

(ii) 1 mark

• Bandwidth

• Interference // with example

• Wired // wireless // transmission medium

• Type/amount of data being transmitted

• Central hardware performance // with example

  • e.g. router/switch

• Error rate

• Distance between nodes

• Topology // physical layout

• Wireless repeaters

What is a network model?

• A network model is the logical structure of the network

• It defines how the network will operate on top of the physical network structure (Star or Mesh)

What is a Client-Server model?

• 
  

• A client is a computer on the network, these connect to the server via a switch

• A server is a computer on a network which often has a single purpose, for example

  • Managing access to the Internet

  • Managing printing

  • Providing email services

  • Providing backups

  • Controlling security

• Servers are often more powerful than the client machines

• Servers are seen as more significant than the client machines and can require specialist hardware and software

• A network which uses a server is called a client-server model

• Most companies, organisations and schools will use a client-server network model

advanatges of client-server

Managing backups of the network is easier as it is done from one central point

Updating and installing new software can be done centrally instead of having to log on to each machine

Security of files can be managed easily

Disadvantages of client server

Servers can be expensive to purchase, setup and maintain

A specialist network manager would be required as servers require specialist IT knowledge

Servers can be a single point of failure, meaning all users would lose access to the network if the server fails

What is a Peer-to-Peer model?

• A peer is a computer on a network which is equal to all other computers

• Each peer on the network

  • Often have their own printer attached

  • Will provide access to their own files

  • Is responsible for their own backups

  • Is responsible for their own security

  • Is responsible for carrying out their own backups

• A network with no server providing services is a peer-to-peer network

• Most homes will have a peer-to-peer network model

advantages peer to peer

Very easy to set up and maintain

Very cheap to set up because there is no expensive hardware to purchase

No specialist knowledge or staff are required to run the network

Disadvantages of peer to peer

Users will need to manage their own backups

Users will need to manage their own software updates

The network can be less secure

What hardware is needed to make up a local area network?

• 
  

• Network hardware is a selection of essential components that enable the connectivity and communication of devices within computer networks

• You need to understand the purpose of the following network hardware:

  • Router

  • Wireless access point (WAP)

  • Switch

  • Network interface card (NIC)

  • Transmission media

What is a router?

• The router is responsible for routing data packets between different networks

• An example of data the router can direct is, sending internet traffic to the right devices in your home

• The router connects networks together, local area networks (LAN) to the wider internet which is a type of wide area network (WAN)

• The router can manage and prioritise data traffic, which can help to keep connections stable

• The router will assign IP addressed to the devices on the networ

What is a wireless access point (WAP)?

• The Wireless Access Point (WAP) allows wireless devices to connect to a local area network (LAN)

• The WAP connects to a Switch or Hub via an Ethernet cable

• The WAP range is limited so the use of multiple Wireless Access Points can be used for complete coverage or a home/business

What is a switch?

• A Switch allows multiple wired devices to connect to a local area network (LAN)

• The Switch is an active device, which means it can inspect network data and route it to the correct device, thus reducing traffic on the network

• A Switch can contain extra Software to allow administration/configuration

What is a network interface card (NIC)?

• 
  

• The Network Interface Card (NIC) is required for a computer to connect to a network

• A NIC can be both wired and wireless and allows your computer to send and receive data over a network

What is transmission media?

• Transmission media is the phrase used to describe the method of connecting a wired network

• There are 3 main types of transmission media used

  • Unshielded Twisted Pair (UTP)

  • Coaxial (Copper)

  • Fibre Optic

Unshielded twisted pair (UTP)

• 
  

• A Twisted Pair cable is made up of insulated pairs of copper wires twisted around each other

• Twister Pair is Low Bandwidth and more affordable than the other two cables, so is commonly found in Local Area Networks (LAN)

Coaxial

• A coaxial cable is a medium bandwidth and more expensive than UTP

• Coaxial cables are used to connect large-scale networks such as telephone networks and digital cable/satellite television

Fibre optic

• A Fibre Optic cable, unlike the other two, is unaffected by electrical noise, making it the fastest in terms of data transfer

• Fibre Optic is High Bandwidth and the most expensive

• Fibre Optic is commonly used for high data volume networks and long-distance connections such as between cities/countries

One piece of network hardware is a router. State 3 tasks carried out by a router. [3]

To answer the question you must simply identify 3 tasks a router does.

Answer

1 mark each to max 3 e.g.

• Receive packets

• Forward/send packets

• Maintain a routing table 

• Identify the most efficient path to the destination / correct IP / correct location

• Assign IP addresses to nodes / devices

• Converts packets from one protocol to another

What is the Internet?

• he Internet is a collection of networks spanning the whole world

• The Internet is the most well-known Wide Area Network (WAN)

• The Internet is used to provide connectivity and is different from the World Wide Web, which is the collection of webpages you access via a web browser

What is a domain name system?

• The Domain Name System (DNS) can be thought of as the Internet's equivalent to a phone book

• It is essentially a directory of domain names and is used to translate human-readable domain names to the numeric  IP addresses that computers use

• When you type a URL into your browser, the DNS translates the domain name into its associated IP address so your computer can connect to the server hosting the website

• Without DNS, we would have to remember the IP address of every site we want to visit

• When a domain is newly registered, or a server changes its IP address, the DNS record for that domain needs to be updated in what's known as DNS propagation

How does DNS work?

1. URL Entry: The user enters the URL (web address) of a website into the web browser

2. DNS Query: The web browser sends a query to a DNS server (usually hosted by your ISP) to translate the URL into an IP address

3. DNS Resolver: The DNS resolver checks its cache to see if it has the IP address for the requested domain. If not, it sends the request to the DNS root servers

4. Root Server Query: The root server directs the resolver to a Top-Level Domain (TLD) server (like .com, .org) based on the extension of the URL

5. TLD Server Query: The TLD server then provides the resolver with the IP address of the domain's authoritative DNS server

6. Retrieve IP Address: DNS server responds with the IP address for the requested domain

7. Request the Web Page: The web browser sends an HTTP or HTTPS request to the IP address it received

8. Server Response: The server at the given IP address processes the request and sends back the data for the web page (HTML, CSS, JavaScript, etc.)

9. Render the Web Page: The web browser renders the received data into the web page that you see

What are web servers?

• Web servers are dedicated servers that store web pages/websites and other resources

• They have a dedicated IP address to ensure that users can access them 24/7

• The most common web servers in use are

  • Hosting websites

  • Dealing with client requests

What are clients?

• Clients are end-users who make requests of web servers

• For example, a client requests a webpage

  • The user will request the website by typing in the URL into their web browser

  • The request will be sent to their local ISP DNS

  • The DNS will return the IP address of that URL: 104.18.1.107

  • The client machine will then send a GET request to the web server

  • Save My Exams webserver will then return the webpage/resource to the client's web browser

  • More details about this process are above under the heading of 'DNS'

What is hosting?

• Hosting is the storing of websites, files and other content on servers

• The servers need to be accessible by potentially thousands of users and they need to be available 24/7

• The servers must be reliable and secure from any form of attack

• The IP address for the server must remain the same so that users can access the website whenever they want

• Servers are set up with the single purpose of serving these files in this manner and in a safe and secure way

What is the cloud?

• The cloud is a collection of servers which are used to store data, applications and files over the internet

Advantages of the cloud

Content in the cloud can be accessed anytime and from anywhere

Users can use any device to access their content

Users have a large storage capacity available to them

Low cost / free to set up and use

Responsibility for backups and security is with the cloud service provider

Users can easily collaborate

disadvantages of the cloud

Accessing content and software is only possible when the user has an internet connection

Expanding capacity can become expensive if using it across a business

Vulnerable to security threats such as data leaks and photo leaks

It is not thoroughly clear to users who is the owner of the data once it is uploaded to a cloud service

Keyword

Internet

LAN

WAN

DNS

URL

ISP

Internet	A collection of LANs connected together spanning the whole world (WAN)
LAN	A collection of computers connected in a small geographical area using its own hardware
WAN	A collection of LANs connected together
DNS	Domain Name System: A directory of domain names (URLs) and their corresponding IP addresses
URL	Uniform Resource Locator: The web address typed into a web browser
ISP	Internet Service Provider: the company that provides internet services to you

What is a network topology?

• A network topology is the physical structure of the network

• It defines how the network hardware will be arranged to create the network

• Different network models (PS2P/Client-Sever) can be used on a topology

What is a star topology?

• A star topology has a central switch which all other devices connect to

• A switch is an intelligent device which ensures that traffic only goes to the intended device

• A star topology is commonly seen in most homes, businesses, organisations and schools

What are the advantages of a star topology?

If any single cable stops working, the rest of the network will continue to work

This is important because in other topologies if a cable was broken, all computers on the network would stop working which would have a negative impact on learning in schools and businesses completing their daily tasks

What are the disadvantages of a star topology?

• The central switch is a single point of failure

• This means that if the switch stops working, all of the devices connected to it will not be able to connect to the network or any of its facilities and resources

What is a mesh topology?

• A mesh topology allows all computers to be connected to all other computers

• This is known as a full mesh network topology

• LANs can make use of mesh networks however, they are more commonly seen in IoT devices such as wearable technology and smart home devices

What are the advantages of a full mesh topology?

• If any single cable stops working, the rest of the network will continue to work as the data can find a different route to get to its destination

• In the example below you can see that one cable has been marked as not working and that that data can simply use an alternate route

What are the disadvantages of a full mesh topology?

• The topology requires a lot of hardware, cables and switches to set up

• This means there is a higher cost for setting up the network

• Adding new devices is not as easy as in a star topology, making it more challenging to scale the network

What is a partial mesh topology?

• A partial mesh topology is very similar to a full mesh, with the difference being that each device is not connected to every other device directly

• This means 

  • Less cables and hardware are required

  • Multiple routes still exist between devices

  • It is a compromise solution to reduce the amount of hardware needed

• The diagram below is an example of how the backbone structure of the Internet appears

To connect devices to a network, there are two main options:

• 
  Wired

• Wireless

What is a wired network?

• A wired network is a network where physical cables are used to join devices together and transmit data

• Computers can be connected to networks using many different types of wires to transmit data

• The most common type of cable in a local area network (LAN) is Ethernet

What is Ethernet?

• Ethernet is a wired networking standard to carry electrical signals between devices

• Ethernet is common in most offices and homes to connect devices such a desktop computers & servers

• Ethernet uses twisted pair cables to allow duplex communication

advantages of ethernet

Speed - Fast data transfer

Security - Better physical security

Range - High (up to 100m), less susceptible to interference

Disadvantages of ethernet

Portability - Can't move easily, location is limited by physical cable

Cost - Need more cables to add a new device

Safety - Cables can be trip hazards, need routing along walls, under floors

Worked Example

A school has a LAN (Local Area Network)

The LAN allows access by both wired and wireless devices. 

The wired connection is an Ethernet connection. Ethernet is considered a standard.

Explain why Ethernet is a standard [2

• Ethernet is used by (mostly) all manufacturers // Ethernet is used in many devices

• ...to allow compatibility with other devices

• Ethernet has a high bandwidth

• Ethernet has inbuilt security

• Ethernet is a proven/reliable connection

• Ethernet is low cost for purchase/installation/maintenance (compared to other wired connections) 

What is a wireless network?

• A wireless network is a network where connections are made using radio waves to transmit data through the air

• The most common types of wireless connections are:

  • Wi-Fi

  • Bluetooth

What is Wi-Fi?

• Wireless fidelity (Wi-Fi) is a common standard for wireless networks

• Wi-Fi is common in most homes and offices to connect devices such as laptops, tablets & smart phones

• Using Wi-Fi, devices communicate with a wireless access point (WAP), which can be a standalone device or built into a router or switch Wireless fidelity (Wi-Fi) is a common standard for wireless networks

• Wi-Fi is common in most homes and offices to connect devices such as laptops, tablets & smart phones

• Using Wi-Fi, devices communicate with a wireless access point (WAP), which can be a standalone device or built into a router or switch 

Advantages wi-fi

Portability - Easy to move around, location is only limited by range

Cost - Less expensive to setup and add new devices

Compatibility - Most devices are manufactured with a built in Wi-Fi adapter

Disadvantages of wi-fi

Speed - Slower data transfer than Ethernet

Security - Less secure than Ethernet

Range - Relies on signal strength to the WAP, signals can be obstructed (up to 90m)

What is Bluetooth?

• Bluetooth is another common standalone for wireless networks

• Bluetooth is common in most homes and offices to connect devices such as headphones, controllers, keyboards & mice

• Bluetooth is used typically for a direct connection between two device

advantages of bluetooth

Compatibility - Ideal for personal devices and ad-hoc connections

Power - Very low power consumption

disadvantages of bluetooth

Speed - Very slow transfer speeds

Security - Data can be intercepted by anyone in range

Range - Very short range (10m)

Worked Example

Dave has set up a new travel agency and needs you to set up a network for the shop. There will be four workstations for staff to book new holidays and take payments from clients, and each member of staff will also be issued with a tablet so they can show customers different destinations and hotels. Staff will use their PCs to phone customers and suppliers using headsets.

Describe how different types of network connection could be set up to support the new business [6]

Answer

• The workstations should be connected using Ethernet [1] because they won’t need to be moved, this will allow for fast transfer speeds and it is more secure than Wi-Fi for sending customer data [1]

• The tablets should be connected using Wi-Fi [1] so they can be moved around without cables and the signals won’t have to go through walls [1]

• The headsets should be connected through Bluetooth [1] so that staff don’t get tangled in wires and they can connect just to their own workstation rather than needing full access to the network [1]

encryption

• Encryption is a method of scrambling data before being transmitted across a network in order to protect the contents from unauthorised access

why is encryption important for wireless networks

• While encryption is important on both wired and wireless networks, it's even more critical on wireless networks due to the data being transmitted over radio waves, making it easy to intercept

How is wireless data encrypted?

• Wireless networks are identified by a 'Service Set Identifier' (SSID) which along with a password is used to create a 'master key'

• When devices connect to the same wireless network using the SSID and password they are given a copy of the master key

• The master key is used to encrypt data into 'ciphertext', before being transmitted

• The receiver uses the same master key to decrypt the cipher text back to 'plaintext' 

• To guarantee the security of data, the master key is never transmitted

• Without it, any intercepted data is rendered useless

• Wireless networks use dedicated protocols like WPA2 specifically designed for Wi-Fi security

how is wired data encrypted

• Wired networks are encrypted in a very similar way to a wireless network, using a master key to encrypt data and the same key to decrypt data

• Encryption on a wired network differs slightly as it is often left to individual applications to decide how encryption is used, for example HTTPS

Worked Example

A bank does not use encryption when data is transmitted through the network.

Give two reasons why the bank should use encryption [2]

How to answer this question

• Answer must be 'why' the bank should use encryption and NOT just what encryption is. Give examples in your answer

Answer

• Customer data cannot be understood if intercepted // The data will be meaningless

• So that only authorised users can access the confidential material // protect confidential/personal/user/bank data

• To follow legislation/Data Protection Act

What is an IP address?

• An IP (Internet Protocol) address is a unique identifier given to devices which communicate over the Internet (WAN)

• IP addresses are dynamic, they can change

• IP addresses make it possible to deliver data to the right device

• A device connecting to a network will be given an IP address, if it moves to a different network then the IP address will change

IPv4

• Internet Protocol version 4 is represented as 4 blocks of denary numbers between 0 and 255, separated by full stops

• Each block is one byte (8 bits), each address is 4 bytes (32 bits)

• IPv4 provides over 4 billion unique addresses (2³²), however, with over 7 billion people and countless devices per person, a solution was needed

• IPv6

• Internet Protocol version 6 is represented as 8 blocks of 4 hexadecimal digits, separated by colons

• Each block is 2 bytes (16 bits), each address is 16 bytes (128 bits)

• IPv6 could provide over one billion unique addresses for every person on the planet (2¹²⁸)

What is a MAC address?

• A MAC (Media Access Control) address is a unique identifier given to devices which communicate over a local area network (LAN)

• MAC addresses are static, they can never change

• MAC addresses make it possible for switches to efficiently forward data to the intended recipient

• Any device that contains a Network Interface Card (NIC) has a MAC address assigned during manufacturing

• A device connecting to a local network already has a MAC address, if it moves to a different network then the MAC address will stay the same

• A MAC address is represented as 12 hexadecimal digits (48 bits), usually grouped in pairs

• The first three pairs are the manufacturer ID number (OUI) and the last three pairs are the serial number of the network interface card (NIC)

Worked Example

Computers in a network can be identified using both IP addresses and MAC addresses.

Describe two differences between IP addresses and MAC addresses [2]

Answer

• IP address is dynamic/can change // MAC address is static/cannot change

• IP address is used to communicate on a WAN/Internet // MAC address is used to communicate on a LAN

What is a standard?

• A computing standard is a set of guidelines that when used with different hardware and software allows them to work with each other (compatibility) and allow data exchange (interoperability)

• Standards outline the broad guidelines and protocols focus on specific procedures

what do standards give

• Standards give manufacturers and software developers the ability to create hardware and software that will function together

where are standards not used

• Countries that use different plug sockets and devices that use different charger cables are examples of where standards are not used

examples of computer standards are:

• HTML - A standard for creating websites that allows them to be viewed on the World Wide Web (WWW) using web browser software

• Ethernet - A standard for wired network cables that allows the network to function

• USB - A standard that defines the physical connector used for connecting peripheral devices to computers

• Wi-Fi  - A standard that allows wireless devices to communicate on a local area network (LAN) 

What is a protocol?

• A protocol is a set of rules that govern communication on a network

different types of protocols

• TCP/IP

• HTTP

• HTTPS

• FTP

• POP,

• IMAP

• SMTP

What is TCP/IP?

• TCP/IP is two protocols, transmission control protocol (TCP) and internet protocol (IP) that combined allow communication over the internet (WAN)

• TCP is responsible for making sure communication between two routers is error free

• IP is responsible for making sure data is delivered to the right device on a wide area network (WAN)

HTTP

• Hypertext Transfer Protocol (HTTP) allows communication between clients and servers for website viewing

• HTTP allows clients to receive data from the sever (fetching a webpage) and send data to the server (submitting a form, uploading a file)

HTTPS

• HTTPS works in the same way as HTTP but with an added layer of security. All data sent and received using HTTPS is encrypted

• HTTPS is used to protect sensitive information such as passwords, financial information and personal data

What is FTP?

• File Transfer Protocol (FTP) allows sending and receiving files between computers

• Uploading and downloading files to/from a web server is often completed using FTP

• FTP offers greater efficiency and support for bulk transfers and large files such as resuming interrupted transfers

• FTP clients are software applications that use the FTP protocol to make the process easier for users

POP, IMAP & SMTP

• A family of protocols that handle sending and receiving of email across the internet (WAN)

What is SMTP?

• Simple Mail Transfer Protocol (SMTP) is a protocol that allows communication between an email sender and the email server, and between different email servers using the internet

• In the diagram above, SMTP is used to transfer the senders email to their email providers server and SMTP is used to transfer the email to the recipients email server

What is POP?

• Post Office Protocol (POP) is a protocol for downloading emails to a device from an email server

• Once the email has been retrieved it is removed from the server

What is IMAP?

• Internet Message Access Protocol (IMAP) is a protocol for downloading emails to a device from an email server

• Once the email has been retrieved, a copy is retained on the mail server

advantages of POP

• Frees up storage space on email servers

• Faster on slow connections

disadvantages of POP

• Only access emails from the device they're downloaded to

• Emails deleted on the server once downloaded

advantages of IMAP

• View and manage emails from any device with internet access

• Changes made on one device are synchronised on all connected devices

disadvantages of IMAP

• Server storage space can limit amount of retained emails

• Requires internet access to view emails

Worked Example

Protocols are used to transmit data through the network and over the internet.

Define what is meant by a ‘network protocol’. [1]

Answer

• A set of rules for communication

Worked Example

TCP/IP is one example of a protocol.

Give the name of one appropriate protocol for each task in the table [3]

Answer