1.3 Computer networks, connections and protocols Flashcards
LANs
Local Area Networks. A single network that is geographically confined to one building or site
-Located within a single building - home, office, uni campus, school, etc.
Standalone computer
Computers that aren’t connected to any networks
Hardware needed to connect standalone computers into a LAN
-NIC (Network Interface Card)
-WAP (Wireless Access Point)
-Switch
-Router
-Transmission media
NIC
Network Interface Card - an internal piece of hardware that is required for the computer to connect to a network
-includes a MAC address - used when sending data across a LAN
MAC address
Media Access Control address
A unique number that identifies the actual device that is connected to the internet or network.
-No two MAC addresses are the same
-in a device’s NIC
-used to route frames on a local area network
WAP
Wireless Access Point. Provides a link between wireless and wired networks. Creates a wireless LAN that allows WiFi-enabled devices to connect to a wired network.
-may be a separate device or built into another device (e.g. router)
Data packet
A file that has to be broken up into small chunks of data in order to be transmitted over a network
WAP compared with wired connections
–More convenient
–Less bandwidth
–Security is more an issue
Switch
A switch used to connect devices together on a LAN
-receives data packets from a connected node, reads the destination address in the packet header and forwards data to its destination
-generate a list of MAC addresses of all devices connected to it when it receives data, must scan for matching destination address before sending
-alternative - hub: less secure as it forwards a copy of received data to all connected nodes
Router
Used to transfer data packets between networks.
Router - process of sending data
-receives incoming data packets from one network and analyses the packet header to determine the destination IP address
-It then looks up the IP address in a routing table (routing table of known networks) to determine the next network where the packet should be sent
-The router then forwards the packet to the appropriate network or device
Transmission Media
Physical media that can be used to transmit data. E.g twisted copper cable, fibre optic, etc.
Copper cables
-also known as UTP/ ethernet cables
-Made up of four ‘twisted pair’ copper wires enclosed in a plastic sleeve with a standard plug in the end.
-Data carried through cables by electrical signals
Fibre optic cable
For high bandwidth connections and cover high distances and less interference
-use light to transmit data
-the backbone of the Internet
-more expensive than ethernet cables
WAN
Wide Area Network. Connects two or more LANs that are in different geographical locations. It extends over a large geological area.
-E.g. The Internet - largest WAN - no single organisation owns it
Pros of networking
-Users can share files to other networks
-Users can access their files from any device on their networks
-servers can control security, software updates, back up
-communication with others
Cons of networking
-increased security risks to data -malware/ viruses can be spread easily between computers
-computers may run more slowly if there is a lot of data travelling on the network
Factors affecting performance of networks
-Bandwidth
-no. of users
-error rates
-latency (delay)
Bandwidth
More bandwidth –> faster
Bandwidth - the amount of data that can be sent and received successfully in a given time
-measure of quantity
-measured in bits per second
No. of users - affects performance
Too many users/ devices on the same networks can cause the network to slow down as it has to be shared by everyone
Transmission errors - performance of networks
-Inevitably there will be times when devices try to communicate with each other at the same time
-Their signals collide with each other and the transmission fails
-The greater the number of devices on a network, the more chance of a collision occurring, and the longer it takes to transmit a message
Latency
The delay from transmitting data to receiving it
-The larger the network, the longer it takes
-Every switch, cable, router is adding latency
What effects wireless performance
Radio interference
-if at the same frequency, lowers wi-fi performance
Physical layout
-blocked by walls, signals get weaker further away
Limited connections
-Limits how many people can use the connections
Wire vs wireless - cost
Wireless is cheaper as it only needs a WAP.
Wired needs to install cables into a building.
Wire vs wireless - no. of people
Wireless limits a no. of people to connect at one time
Wired allows 100s of people to login at the same time but they need to be plugged in
Wire vs wireless - radio interference
Wired not affected, wireless affected
Wire vs wireless - security
Wired has excellent security as computer needs to be physically connected to the network
Wireless not as secure as data that is transmitted has to be encrypted first.
Wire vs wireless - building layout
Wired not affected
Wireless signal affected by walls, floors
Wire vs wireless - portability
Wired is not portable. Computer needs to have a network socket available
Wireless very portable.
Client-server model
Clients make requests to a server, server manages request and responds. Server controls network security, backups, can be upgraded to manage high demand.
Pros of client-server model
-network controlled centrally from the server to easily backup data and update software
-hardware, software, resources can be shared across the network - application, files
-more clients can be easily added to the central server
Cons of client-server model
-large amounts of traffic congestion causes the network to slow down
-if fault occurs with the server, the whole network will fail
-IT technicians may be required to manage and maintain the network
-malware can spread quickly across the network
Peer to peer model
Data shared directly between systems without requiring a central server.
-Each computer is equally responsible for providing data
-optimal for sharing files that can then be downloaded
Pros of peer to peer model
-simpler network to set up
-not dependent on a server
-good for quickly sharing files between systems
Cons of peer to peer model
-no central device to manage security or backups. They must be performed on each individual system
-computer performance decreases with more devices connected to the network, especially if other machines are slower
The Internet
A collection of interconnected networks spanning the world. Most well known Wan.
URL
Uniform Resource Locator - unique numerical combination that represents a specific network to access a connected device
IP address
Internet Protocol - a unique identification number given to every device that is connected to the internet
-represents the unique location on which you are connected to the internet
-allows data to be sent and received between devices
What does an IP address look like
e.g. 12.123.12.123
Two types of IP addresses
-Static IP addresses - never changes, permanent
-Dynamic IP addresses - temporary, assigned to the device every time it accesses the internet
DNS
Domain Name System - Translate a web address into a correct IP addresses for the server/ service you requested.
-DNS servers store a list of domain names and a list of corresponding IP addresses where the website is stored
Process of going to a website through URL
- Domain name is typed into the browser
- Query sent to local DNS server for the corresponding IP address of the domain name
- Local DNS server will check if it holds an IP address corresponding to that domain name.
- If it does it passes the IP address to your browser
- Browser connects to the IP address of the server and accesses the website
Types of web hosting
-Local hosting
-External hosting
Local hosting
-Set up your PC as a web server and allow others to connect to it and access web files you store
–saves money
–useful for your own use/ local network users
External hosting
-Where you pay a web hosting company to host your website on one of their servers
–provide you with:
-hard disk space on their server to host your site
-ensure your site is running and available at all times
-provide bandwidth, maintenance, security, technical help
Two types of external hosting
-shared web hosting
-dedicated server
Shared web hosting
Where many sites are hosted on the same web server. Costs of running server is shared between all of the users - saves money
-Cons - share the same resources (e.g. Ram, bandwidth)
Dedicated server
Where the website is hosted on its own server. Used by companies who have a lot of website traffic.
-Pros - faster, dedicated, support from web hosts
- backups, patches carried out on a daily basis
-Cons - expensive
The cloud
Network of servers that can be accessed over the internet
-Online website hosting, online file and media storage, streaming services, online backups
Advantages of the cloud
-Access data from any device with an internet connection
-documents and files can be worked on simultaneously by different people
-store large files online, reduce the storage needed on home devices
-work automatically backed up
Disadvantages of the cloud
-can’t access if no internet connection/ forget password
-many services have a cost
-risk of online hackers
Types of network topologies
-Star network topology
-Full mesh network topology
Star network
Each computer system is connected into a central switch and transfers its data packets there
-switch looks at destination address and transfers packets directly to the intended computer
Advantages of a star network
-secure - data packets are sent directly to and form the hub/ switch in the centre
-new systems can be attached directly to central switch
-transfer speeds are fast - minimal network collisions
Disadvantages of a star network
-extra hardware is required to be purchased, installed and maintained
-if central system fails, whole network will be unusable
Full mesh network topologies
Every device connected to every other device
-data packets transferred to the destination address along the quickest path
4 Advantages of full mesh network topology
-robust network. If one path fails, there is another to reach the destination address
-can handle very high data traffic rates
-data packets can be sent simultaneous
-devices can join/ leave the network without affecting the overall network
Disadvantages of full mesh network topology
-becomes impractical topology for wired networks as so many cables would be needed
-expensive - many switches and cables
Two modes of connections
-Ethernet (wired) - wires used for communicating on a wired LAN
-Wi-fi (wireless networks)-common standard for wireless networks
Advantage of ethernet
-provides reliable, error free, fast communication between two points
2 Disadvantages of ethernet
-user location is limited by the need for a physical cable connection
-set-up relies on cables, ports, physical hardware - so it is costly
5 Advantages W-Fi
-users are free to move around
-users can share files and other resources with other devices that are connected without needing cables
-less costly - no need to lay cables through walls
-not limited by the number of ports
-instant transfer of information of social media is made much easier
Bluetooth
Ideal for connecting personal devices e.g. headphones
Disadvantages of Bluetooth
-very short range, around 10 meters
-low power consumption compared to wi-fi
Encyrption
Wireless networks broadcasts data, so it must be encrypted in order for it to be secure and no one but the intended viewer can see it
-text (plaintext)
-encryption key
-encrypted message (cipher text)
-decryption key
-text
Encryption key
Piece of information used by software algorithm to encrypt data and allow data to be readable again (decryption)
What does a MAC address look like
-12 digits in 6 pairs, separated by colons (48 bit hex numbers)
e.g. 00:0a:95:9d:68:16
Two versions of IP addresses
-IPv4
-IPv6
IPv4
IPv4 - 32 bits
-written as 4 numbers separated by full stops
-each number can be between 0-255
e.g. 193.74.211.63
-around 4 billion possible addresses
IPv6
-not enough IP addresses in IPv4 as there are more and more connected devices
-same as IPv4, but with 128 bits (16 bytes)
-encoded as 8 groups of 4 hexadecimal digits separated by colons
e.g. 49cd:c92d:dabb:469f:003c:4877:f44b:5441
-340, trillion, trillion trillion combinations approx
Standards
Set of specifications for hardware and software that makes it possible for manufactures to create products and services which are compatible with each other
-without standards most devices wouldn’t be able to successfully interact or communicate
Examples of standards
Character sets - a standard set of binary codes which different devices can use to represent characters
use of HTML - a standard in use for displaying of web pages in browsers
Types of Protocols
-TCP/IP
-HTTP/HTTPS
-FTP
-SMTP
-POP
-IMAP
TCP/ IP
TCP (Transmission Control Protocol) - provides an error free transmission between two routers
IP (Internet Protocol) - routes packets across a WAN
Make up the TCP/ IP protocol stack
-foundation of communication over the Internet
HTTP/ HTTPS
HTTP (Hypertext Transfer Protocol) - way for a client and server to send and receive requests, and to deliver HTML web pages
-protocol used so people can receive the web page in your browser
HTTPS (Hypertext Transfer Protocol (Secure)) - effectively the same as HTTP except it adds in encryption and authentication
-Should be used on the web when a website needs to deal with sensitive information such as passwords or bank account details
FTP
File Transmission Protocol - protocol used for sending files between computers, normally on a wide area network (WAN)
POP/ IMAP/ SMTP
Three popular protocols used in conjunction with mail servers to deal with emails
SMTP
Simple Mail Transfer Protocol - transfers outgoing emails from one server to another
POP
Post Office Protocol - retrieves emails from a mail server. Removes it from server and transfer to your device
IMAP
Internet Message Access Protocol - when an email is retrieved, it leaves the original copy of the email on the server, allowing synchronicity between devices
Layers
Transferring data between two points on a WAN (or a LAN) is a very complex operation
-the concept of layers is to divide the complex task of networking into smaller, simpler tasks that work with each other
Process of layers
-the hardware/ software for each layer has a defined responsibility
-each layer provides a service to the layer above it but it does not need to consider what other layers do
-a layer is self contained and can be removed or changed without affecting any other layers
Advantages of layers
-reduces complexity of the problem into manageable sub-problems
-devices can be manufactured to operate at a particular layer
-products from different vendors will work together
