1.3 - Networks and topologies

Completed flashcard set

What is a network?

Give advantages and disadvantages for networking

A network is more than one computer system connected together allowing for communication and sharing of resources

Advantages:

• Sharing of resources:

  • Folders and files can be stored on a file server so they can be accessed by authorised users from any computer on a network

  • Peripheral devices can be shared

  • Internet connection can be shared

• Centralised management:

  • User accounts can be stored centrally on a server, meaning that users can log into any device on the network and access their account

  • Security can be managed centrally, ensuring all devices are up to date

  • Software (eg. security software (antimalware), applications) can be downloaded and distributed across a network, rather than having to install it individually

  • All files can be backed up centrally

Disadvantages:

• Network infrastructure is expensive

• Managing a large network is complicated

• Malware may be able to infiltrate the network and infect every computer

Describe the two types of networks and given common examples for each

• LAN (local area network)

  • Computer systems situated geographically close together

  • The network infrastructure is usually owned and managed the network owner (usually a single person or organisation)

Examples:

• Home network

• School network

• Office network

• Library/ cafe

Usually covers one building.

• WAN (wide area network)

  • Computer systems situated geographically far away/ distant from each other

  • WAN’s often use third party communication channels

Examples:

• The internet

• National bank network

• International supermarket chain network

Explain the factors that affect the performance of networks

• Bandwidth

  • Bandwidth is the maximum amount of data that can be transferred over a network in a given time (usually Mbps)

  • If a network has a high bandwidth, large amounts of data can be sent and received at the same time, so things load faster.

  • If bandwidth is low, data has to queue until there is enough bandwidth for it to be sent, causing slow transfer speeds and buffering.

  • Bandwidth is shared between users

• Transmission media: wired/wireless

  • Wired is faster and more reliable (as it uses a direct, stable connection, avoiding wireless interference and signal loss due to distance of obstacles), whereas wireless are slower as they are affected by interference

• Number of users

  • The bandwidth is shared between users on a network; the more users, the less available bandwidth per person, so each user will not be able to send/ receive as much data across the network per given time, so the data will have to queue until there is sufficient bandwidth, causing slow transfer speeds.

• Interference

  • Wireless networks send data using radio wave signals; interference occurs when those radio waves are weakened or disrupted

  • Walls/ objects can absorb or block radio waves, weakening the signal; a weaker signal means data may be lost so data may have to be resent, slowing the network

  • Other devices that use radio wave signals can cause their signals to overlap with the wireless computer system’s signals, causing data packets to become corrupted so data must be resent (binary data has been altered)

• Latency

  • Latency is the time taken/ time delay between the transmission of data and when it is received at its destination.

• Amount of data being transferred

  • If the amount of data being transferred is greater than the available bandwidth, packets will have to queue to be sent, causing slow transfer speeds

Describe the different roles of computers in a client-server and peer-to-peer network and give the advantages and disadvantages for both

Client-server network:

• Client: A computer which requests services or resources provided by the server

• Server: A powerful computer that manages and responds to requests from clients by providing services or resources required by any of the clients

Advantages:

• Data backup, software updates and security can be controlled centrally on the sever (eg. downloading and deploying anti-malware to all clients, controlling access levels)

• Hardware, software and resources can be shared across the network

• The network allows for improved scalability, as more clients can easily be added to the central server

Disadvantages:

• All clients are dependent on the central server, so if a fault occurs with the server, the whole network will go down

• Malware (eg. viruses) can be spread quickly across the network

• IT technicians may be required to manage and maintain the network; servers can be expensive

Peer-to-peer network:

Data is shared directly between computer systems without requiring a central server.

• Peers: all peers have equal status and the same role in the network, so all are equally responsible for providing data.

Advantages:

• Easy and simple to set up

• Clients are not dependent on a server

• Doesn’t need expensive IT technicians or a server

Disadvantages:

• Data backup, software updates and security are not centrally controlled, so must be done individually for each computer

• Poor security as each computer manages its own security (may have irresponsible users that cause virus’ to spread)

• Less suitable for large networks, as it is may become difficult to connect every computer system to each other

Describe how data is transferred across networks

Data transmission is the process of sending data from one device to another over a network.

• When sending data across a network, files are broken down into smaller parts called data packets

  • Each packet contains a portion of the data along with a packet header.

  • The packet header contains:

    • Destination IP address

    • Source IP address

    • Sequence number of the packet

    • Number of packets in the entire data

    • Error checking data

• Routers receive packets and use the IP address in the packet header to determine the best, most efficient route to send the data; packets are sent individually and may take different routes to reach their destination

• Data is transmitted from router to router across the network towards the destination

• The destination device receives the data packets and as the packet may arrive out of order, the device uses the packet’s header to put them in the correct order and reassembles them back into the original file

• If any packets are missing or have been corrupted, they will be re-transmitted

Name network hardware and explain their purposes

• Wireless access points

• Routers

• Switches (and hubs)

• NIC

• Transmission media

• Wireless access points

  • Provides a link between wired and wireless networks

  • Receives data from a network via its physical connection and then converts this data into radio waves which are then transmitted. It also receives radio waves and converts this data back and transmits it via its physical connection.

• Routers

  • Used to transfer data packets by using the destination IP address in the packet’s header to determine the best route to transmit data, transferring data from router to router across a WAN

  • A router stores the IP address of each computer connected to it on the network and uses a routing table to calculate the quickest and shortest route to transfer data

• Switches

  • A switch is used to connect devices together on a LAN

  • Receives packets from a device on the LAN, reads the destination address in the packet header and forwards it directly to its destination.

  • A switch generates a list of all of the MAC addresses of the devices connected to it when it receives data and must scan for a matching destination address before sending

An alternative to a switch is a hub, however a hub is slower and less secure as it forwards a copy of the received data to all connected nodes (not just directly to the destination).

• NIC (Network interface card)

  • Internal piece of hardware required for a computer to connect to a network

  • Each NIC has a unique MAC address, which enables the device to be identified on the network, allowing it to send and receive data on the network

  • It converts data from the computer into signals that can be transmitted over the network and receives data from the network and converts it back into data that the computer can use

• Transmission medium

  • Ethernet cables

  • Fibre optic cables (very fast, but more expensive and fragile)

  • Coaxial cables (older, slower, affected by electromagnetic interference)

The communication channel on which data is sent over affects network performance

What is the internet?

A global network of interconnected networks

What’s a URL?

Uniform resource locator

It is the address of a resource (the web page) on the internet.

It tells the browser the location of the server hosting the web page and the path to the resource.

What is the DNS?

The DNS (domain name system) is a system of servers and rules that translate human-readable domain names into their corresponding IP addresses.

The IP address tells devices the location of the web server where the website is hosted.

Explain how a user searches and receives a web page

• The user enters the URL (uniform resource locator) into the web browser

• The browser extracts the domain name from the URL

• The browser acts as a client and sends a DNS lookup request/ query to the local DNS server to get the domain name’s corresponding IP address

• The DNS server checks if it holds an IP address corresponding to the domain name, and if it does the DNS server returns the IP address to the browser

• The IP address tells the browser the location of the web server where the website is hosted

• The browser then sends a request to the web server of the IP address for the web page

• The web server processes the request and responds by sending back the web page data

• The browser receives the web page data and displays it

What is the DNS, whats a DNS server and how does it work?

The domain name service is a system that translates URLs into IP addresses; it is made up of multiple domain name servers.

A DNS server stores a list of domain names and the corresponding IP addresses of the location of the web server where the web site is stored.

• A web browser send a DNS lookup request/ query to the local DNS server.

• The local DNS server will check if it holds an IP address corresponding to that domain name, and if it does it will return the IP address to the web browser

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

• If the IP address is found, it is passed on to DNS servers lower in the hierarchy until it is passed to the local DNS server and then returned to the web browser

• If not found, an error is returned and the web browser displays this error

What is the cloud? Give advantages and disadvantages for using the cloud

The cloud refers to storing and accessing data and software through networks of servers over the internet.

Cloud services run on remote servers hosted in off-site data centres maintained by third parties; data is stored on large servers owned by the hosting company.

Advantages:

• Data can be accessed from anywhere in the world where there is an internet connection

• Data can be shared with other people in different locations, allowing remote collaboration

• Data is usually automatically backed up on the cloud provider’s servers

• Users don’t have to purchase and maintain their own personal servers or storage

• Easy to increase storage by upgrading subscription

Disadvantages:

• You are dependent on having an internet connection to access data

• Security risks as data is stored on external servers which could potentially be accessed by a hacker

• Ongoing cost, subscriptions

What are network collisions?

• A network collision occurs when devices attempt to send data at the same time on the same network segment

• When this occurs, data packets interfere with each other, causing errors

• Devices must stop, wait a random time and resend the data which slows down network performance

Describe the different types of network topologies and give their advantages and disadvantages

Star network:

• Each computer system is connected to a central device (usually hub or switch) and transfers their data packets there; the central device looks at the destination address in the packet header and transfers the packets to the intended computer

Advantages

• If one cable/ computer system fails, the other workstations are not affected

• New computer systems can be added

• Transfer speeds are fast as there are minimal network collisions

Disadvantages

• Can be costly to install as there is lots of cabling and extra hardware (central device)

• If the central device fails, the entire network goes down

Mesh network:

• Each computer system is connected to every other computer system; data packets are transferred to the destination address along the quickest path, travelling from node to node

• If a pathway is broken, there are many alternative pathways that the data packets can take

Advantages

• If one cable or computer system fails, the data packets can take alternative routes to reach the destination address

• Can withstand large amounts of data traffic due to large number of systems, connections and therefore alternative routes

• Don’t have to pay for and maintain expensive central device

Disadvantages

• Because of large amounts of cables, network can be expensive to install and maintain

• Difficult to expand and add new devices as it means creating many new connections, which takes time and planning

Give the advantages and disadvantages for wired and wireless connections

Wired:

• Restricted movement

• Highest bandwidth, so better network performance/ faster transmission of large amounts of data

• More secure (as people need to be physically close to and have a physical connection to access the network)

• Less interference

Wireless:

• Freedom of movement

• Lower bandwidth, so worse network performance

• Less secure (people can intercept radio wave signals without being physically close to the network)

• More interference

What is Ethernet?

A wired technology used to connect devices together on a LAN using cables

What is Wi-Fi?

Wi-Fi is a family of wireless networking protocols that use radio waves to allow devices to connect to a LAN, which can provide access to the internet if the LAN is connected to an ISP through a router.

What is Bluetooth?

Bluetooth is a short-range wireless technology that allows devices to directly communicate with each other using radio waves.

Bluetooth devices typically have built-in radio antennas so they can send and receive signals from other Bluetooth devices.

Compare Ethernet, WiFi and Bluetooth

These are all standards.

Ethernet:

• Highest bandwidth, so better network performance/ faster transmission of large amounts of data

• Lowest amount of interference

• No mobility

• More secure

Wireless:

• Bluetooth directly connects two devices together wirelessly, whereas WiFi connects multiple devices together wirelessly by connecting them to a LAN

• Bluetooth has lower bandwidth, WiFi has greater bandwidth (wireless connections have a lower bandwidth than wired)

• Bluetooth has less interference (frequency hopping), WiFi has more interference (radio wave signals from multiple devices can overlap and interfere with each other)

• Bluetooth usually only works over a short distance, whereas WiFi works over a longer distance

Describe what encryption is

• Encryption is the process of converting plaintext (original data)

• into ciphertext (encrypted message)

• using an encryption algorithm (the method for encryption the plaintext),

• so that data cannot be understood by individuals without access to the key (a sequence of lettters, numbers and other characters used to encrypt or decrypt data).

Encryption is performed so attackers cannot understand information if the data is intercepted.

What are standards? Name some

Standards provide rules that allow hardware and software to interact, exchange data and interpret signals the same way across different manufacturers or producers.

• Ethernet

• WiFi

• Bluetooth

What is a protocol?

A set of rules that define how devices communicate with each other on a network.

What is IP addressing? Describe the format of IP addresses

• Every device on a network is assigned an IP (internet protocol) address, which is a unique numerical code

• IP addresses can be dynamic, so they can change

IP addressing allows devices to be identified on a network and thus allows devices to send and receive data in the form of data packets; supports routing of data across networks.

There are two types of IP addressing: IPv4, IPv6

IPv4:

• Four 8 bit segments of denary values (eight bits can give from 0 - 255 in denary); therefore (4 × 8) 32 bit address represented in denary

• The four segments are separated by full stops

Eg. 145.13.218.102

IPv6:

• Eight 16 bit segments of hexadecimal (four hexadecimal values 0000-FFFF), therefore (8 × 16) 128 bit address represented in hexadecimal

• The eight segments are separated by colons

Eg. 736E:1029:A4B3:902D:77B2:72FF:AE62:0912

Summary:

IPv4 smaller, IPv6 bigger

IPv4: four of eight of denary, full stops

IPv6: (double that) eight of sixteen of hexadecimal, colons

What is MAC addressing? Describe the format of MAC addresses

• Every networked device is assigned a unique MAC address, which is a unique hexadecimal number assigned to the NIC inside of the networked device

• MAC addresses cannot change as they were assigned during manufacturing

MAC addresses uniquely identify physical devices on a LAN, allowing data to be transmitted and received by the correct devices.

Format of MAC address:

• Six 8 bit pairs in hexadecimal, therefore (6×8), 48 bit address

• Separated by dashes

Eg. 19-C2-D1-47-AA-38

Describe the format of IP addresses and MAC addresses

IP: IPv4, IPv6

IPv4:

• Four 8 bit segments

• Denary

• Separated by full stops

IPv6:

• Eight 16 bit segments

• Hexadecimal (0000-FFFF)

• Separated by colons

MAC addresses:

• Six 8 bit pairs

• Hexadecimal (00-FF)

• Separated by dashes)

Describe the TCP/IP protocols

TCP (transmission control protocol):

• Defines how messages are broken up into packets and reassembled at destination

• Detects errors and resends lost packets

Allows packets to be sent and received between computer systems

IP (internet protocol):

• Defines the location of a device on the internet

• Addresses the packets with their source and destination IP addresses to allow individual packets to be routed from source to destination via routers

Allows devices to be identified on a network and packets to be addressed and routed so that they can be transmitted across networks and be received at the correct destination device.

Describe the HTTP and HTTPS protocols

Hypertext transfer protocol/ secure

HTTP:

• Used to make a request for a web page; the server returns the page or an error code if there was a problem with the request

HTTPS:

• Used to make an encrypted request for a web page; the server returns the encrypted web page or an error code if there was a problem with the request

Describe the FTP protocol

File transfer protocol

FTP:

• It is used to transfer files across a network; used to upload or download files

Describe the email protocols

POP (post office protocol), IMAP (internet messaging access protocol), SMTP (simple mail transfer protocol)

SMTP:

• Used to send an email to an email server; the server returns whether the email could or could not be delivered

POP:

• Downloads emails from the server to the device

• Deletes the emails from the server after downloading

• After emails have been downloaded, they are no longer stored on the server and instead are stored locally on the device

This means that emails are now only downloaded on that specific device, so cannot be accessed from other devices even with the same email account. These emails can be accessed offline.

IMAP:

• Stores emails on a server but synchronises devices with the email server

• So users are able to view and manipulate emails as if they were stored locally

• Emails remain on the server

Emails can be accessed from multiple devices as IMAP synchronises devices with the email server.

How are layers used in protocols? What are their benefits?

A layer is a division of network functionality - each layer provides a specific function to assist the transmission of data.

Benefits:

• Layers are self-contained, so they allow different developers to work on a specific aspect of the network at a time, without needing to know how the rest of the layers function

• Easier to identify errors in the network

• Changes in one layer (eg. improvements) do not impact other layers

• Each layer uses specific protocols, so using layers ensures that the protocols are applied in a specific order