unit 5 - fundamentals of computer networks Flashcards
what is the internet?
the internet is a group of interconnected networks
what is the world wide web?
- information system of interlinked webpages and other resources
- accessed from web browsers; chrome, safari, edge
- makes use of HTTP to send and receive data
- the world wide web is one of the many services that make use of the internet
what is a WAN?
WIDE AREA NETWORK
- any network in which the computers communicate via resources of a third party network such as BT
- usually covers a wide geographic area - can connect networks at remote locations
uses cables, telephone lines, satellites or radiowaves to connect two or more remote locations
who uses a WAN?
organisations such as universites and school which have different locations; large, multi-national companies, goverments, research organisations
what is an example of a WAN?
the internet
what is a LAN?
LOCAL AREA NETWORK
- wires/cables and a main server
- smaller geographical area, usually just one site/location
who uses a LAN?
operates on a single site like a school or hotel who use their own cabling system
what is a PAN?
PERSONAL AREA NETWORK
- any network that connects computer devices near to a person
- usually carried out with bluetooth
what uses a PAN?
bluetooth speakers/headphones, connecting smart phones to cars
advantages of using networks
- computers can share resources such as printers
- files can be accessed through any computer in the network
- data is easy to back up as it is stored centrally on the server
disadvantages of networks
- purchasing the network hardware is expensive
- managing a large network is complicated
- viruses may be able to infiltrate the network and infect every computer
what is an IP address?
INTERNET PROTOCOL ADDRESS
- routes the individual packets from one IP address to another
- every computer in the world has an internet protocol address
- they are four 8-bit numbers separated by dots
what is a circuit switching network?
- when you make a telephone call, a dedicated connection is set up between you and that one person - works for calls but there aren’t enough lines for the billions of people sending data via the internet - solved by packet switching
what is packet switching?
- files are broken up in to equal data packets and each packet is given a header
- the packets will flow through the internet via different routes
- each packet is marked with a packet number so it can then be put back together by the receiver - the recipient then re-orders them
- each packet is checked for errors
what is contained in a packet header?
- the IP address it is going to
- the IP address it has come from
- sequence of the packets
- number of packets in communication
- error checking data
what is a data packet?
a small chunk of data
how are packets reassembled?
the recipient re-orders them by packet number and each packet is checked for errors
what is a node?
computers/servers on a network
what is a NIC?
NETWORK INTERFACE CARD
- built into every every networked device (wired and wireless)
- most modern phones and computers have the NIC incorporated into their motherboards
- provides a computer with a dedicated, full-time connection to a network
what is a MAC address?
MEDIA ACCESS CONTROL
- identifies a device to other devices on the same local network
- assigned to each NIC by the manufacturer
- a device may have more then one MAC address if it has both an ethernet and wifi connection
- smartphones have two: for wifi and bluetooth
- every unique device has a unique MAC address - 2^46 possible addresses
what is the difference between an IP and MAC address?
- IP - the geographical location of a device can be determined by its IP address. if you change location the IP address will change
- MAC - the MAC address of an NIC is unique and never changes
what is a router?
- looks at the destination of the packets of data and sends them to the network that is the closest to their destination
- home router will route packets within the home LAN and the internet
what is a switch?
- switches connect each node (computer) in a network and they know all the MAC addresses
- when a packet arrives, they send it to the correct computers
what is a hub?
will send the data to all the connected computers
what is wireless transmission?
uses radiowaves for communication but is susceptible to interference from objects and other devices
what is a wireless network?
- they connect using wifi
- broadcast using radiowaves
what is a WAP/AP?
WIRELESS ACCESS POINT
- a device that allows wireless devices to connect to a wired network using wifi
- usually connects to a router via a wired network
what is a wireless NIC?
- built into every networked device capable of connecting to a wired network
- eg. wireless devices: PCs, smartphones, wireless speakers
advantages of wireless networks
- no need to lay cables
- easy to connect new devices
- devices can be portable within the range of the access point
disadvantages of wireless networks
- less reliable than wired networks
- connection can be very slow if many devices try to use the same AP
- connection speed reduces further from the access point
- can be less secure than wired
what is a topology?
the way in which parts of a system/network are connected
what are the two types of topologies for networks and LANs?
star and bus
what is a star topology?
computers and other devices (nodes) are all connected to a central switch
advantages of a star topology
- faster data transfer to the hub as each wire isn’t shared with other computers
- if one cable fails the others aren’t affected
disavantages of a star topology
- requires additional hardware such as the central switch and network cables
- if the central switch fails the whole network goes down
what is a bus topology?
- computers and other devices are all conected to a central coaxial cable
- terminators are placed at each end to absorb signals and to prevent them reflecting down the cable
advantages of a bus topology
- less cable so cheaper to install
- easier to add more devices as they only need to connect to the central cable
disadvantages of a bus topology
- single cable shared by many devices so there may be ‘collisions’ of data if sent at the same time
- if cable is damaged, whole network fails
- any device can view all data on the cable: creating a security risk
what additional hardware is required to connect a stand alone computer to a LAN?
- NIC in the device
- switch/hub that connects together all the devices on the LAN
- modem required to connect to the internet (usually combined with a router to form one device)
- router needed to route packets towards their destination
- WAP connects the wireless devices to a network
what is ethernet?
a family of standard local networking ‘protocols’
- describes how devices should format data for transition between nodes on the same network
- nodes wait until the connection is quiet before attempting to transmit
- two nodes attempting to transmit simultaneously will stop and each wait a random period before reattempting
what is ethernet transmission?
- divides data in to frames and each frame contains source and destination addresses and error checking data
- frames are broadcast to all nodes but only the inteded recipient opens the frame (so the rest is discarded)
- frames which are detected to have errors are dropped or resent
what kind of cables are used ethernet?
- star: twisted copper cables
- bus: coaxial cable
advantages + disadvantages of using a copper cable
+ adequate speed for low bandwidth applications
+ low cost cable, with cheaper equipment
- signals affected by electrical interference
- significant loss of signal over distance - usually 100m
advantages + disadvantages of using a fibre optic cable
+ very fast connection with a greater bandwidth
+ signals travel as light waves so cannot be attracted by stray EM signals
+ less loss of signal strength - usually 1km +
- higher cabling and equipment cost
advantages + disadvantages of using a fibre optic cable
+ very fast connection with a greater bandwidth
+ signals travel as light waves so cannot be attracted by stray EM signals
+ less loss of signal strength - usually 1km +
- higher cabling and equipment cost
what is bluetooth?
a wireless method of connecting devices together over a short distance
- radiowaves at 2.4GHz
- devices usually with 10m of each other
how does pairing work?
- persistent link made between the two devices so that data can now be communicated between the devices
- device can ask for a passkey in order to pair it - greater layer of security
- passkeys entered only once and then the device is remembered
what are network security methods?
methods which improve the network’s level of security
what are two network security methods?
authentication, encryption
what is authentication?
checking that the cimputer and user are allowed to access content
- commonly done using a username and password
what is encryption?
encoding of data so that it can no longer be easily understood [converting plaintext to ciphertext]
why do people use encryption?
- any data that is transmitted over a network can be intercepted (read and understood) unless measures such as encryption are taken against it
- data can’t be read easily
what is plaintext?
the original message to be encrypted
what is ciphertext?
the encrypted message
what is a key?
a sequence of numbers used to encrypt or decrypt data, often using a mathematical formula
what is the encryption algorithm?
the formula for encrypting plaintext
- two inputs: plaintext and a secret key
what are the two encryption techniques?
private key, public key
what is private key?
a single key is used to encrypt and decrypt a message and data must be given to the recipient of your message to decrypt the data [SYMMETRIC]
what is public key?
two keys are used - a public key to encrypt and a private key to decrypt, which is more secure because you never have to send or reveal your decryption key [ASYMMETRIC]
what is the caesar shift cipher?
- each letter is replaces by a letter n positions further on in the alphabet
- n is the key to encrypt AND decrypt the message [symmetric encryption]
- the most basic and insecure type of encryption
- shift → 3 means each letter of the code has been shifted to 3 letters ahead of it
why is encryption used in networks?
wifi, ethernet and fibre optic cables are also vulnerable to eavesdroppers as signals can be listened to from a distance
what are the three wireless encryption standards?
WEP, WPA, HTTPS
what is WEP?
WIRED EQUIVALENT PRIVACY
- older method of encryption that should no longer be used to protect home router
what is WPA?
WIFI PROTECTED ACCESS
why is HTTPS used as a mode of encryption?
should be used for websites as it encrypts data sent to and received from the site
what is strong and weak encryption?
- strong when the useful lifetime of the encrypted data is less than the time taken to break the code
- weak when the code may be broken in time to use the information but it wouldn’t be worth the effort
how does a firewall work?
- separates a trusted network from an untrusted one (the internet)
- data is sent around a network in small packets and these packets are checked to see their destination and where they came from
- packets that don’t match filtering rules are dropped - therefore packets from malicious computers can be detected
where can firewall be run?
- can be run on dedicated hardware or as software
1) can be built into hardware as a dedicated unit
2) built into other devices such as a home wifi router
what does a firewall do?
- constantly monitors incoming and outgoing network traffic
- decides whether to allow or block traffic based on the set security rules
- prevents many possible ways that an attacker may gain access to a network
- can block certain malicious computers by filtering packets from a certain IP address
- port blocking: can prevent access to certain ports on the network
what is MAC address filtering?
can block a specific device or only allow approved devices via their MAC addresses
- MAC is a unique hex numver assigned to to all NICs
- a wireless router can be configured to block access to specific devices identified by their MAC address
what is a protocol?
a set of rules that governs transmission of data.
what is HTTP?
HYPERTEXT TRANSFER PROTOCOL
- accessing and reviewing web pages via the internet - writen in html - protocol requests a webpage from server and then it reponds
what is HTTPS?
secure HTTP
encrypts the information so it can’t be understood by an eavesdropper
- used by bank websites, online shops and social networks
what is FTP?
FILE TRANSFER PROTOCOL
used for sending or receiving files to or from an FTP server
eg. a graphical interface
what is POP?
POST OFFICE PROTOCOL
- downloads every new message to the local device, meaning they are no longer available on the server
what is IMAP?
INTERNET MESSAGE ACCESS PROTOCOL
- they leave the messages on the server and can be accessed by multiple devices - only removed if deleted by the user
what is SMTP?
SIMPLE MAIL TRANSFER PROTOCOL
- software sends email to SMTP server used - the mail server relays this message via ‘mail relays’ - email arrives at destination server
used by email softwares: outlook, gmail
what is TCP?
TRANSMISSION CONTROL PROTOCOL
- breaks up messages sent over the internet into small packets - reassembles the packets at the other end - detects errors//resends lost messages
what is UDP?
USER DATAGRAM PROTOCOL
- maintains an open data connection to send a stream of packets, without checking that the packets are correctly sent
used in online gaming, video streaming
how are emails sent?
email sent to a mail server (via SMTP) → forwarded by other SMTP → stored at its destination mail server → user’s computer uses POP or IMAP to access the email
what is the TCP/IP protocol stack?
four layers which enable communication on the internet
in which order do the layers work to SEND data?
application → transport → internet → link layer
in which order do the layers work to receive data?
link → internet → transport → application
1) link layer removes MAC address + passes packets up to the internet layer
2) internet layer removes the IP addresses + passes the packets up to transport layer
3) transport layer reassembles packets + passes it to application layer
4) application layer uses the correct protocol to correctly display the data
what does the application layer do? and which protocols function here?
- applications such as email clients and web browsers create data to send in this layer
- SMTP, FTP, HTTP
what does the transport layer do? and which protocols function here?
- creates the connection between two host computers - the two agree the communication settings and the size of packets to be sent and received - data then divided into packets and given a packet number - packets reassembled by transport layer + lost packets resent
what does the transport layer do? and which protocols function here?
- creates the connection between two host computers - the two agree the communication settings and the size of packets to be sent and received - data then divided into packets and given a packet number - packets reassembled by transport layer + lost packets resent
TCP, UDP
what does the internet layer do? and which protocols function here?
- responsible for routing packets - the source and destination are wriiten on the packets for transmission
routers, IP
what does the link layer do? and which protocols function here?
- where the physical hardware is located: NIC (network interface card), cables + wifi, OS device drivers
MAC (media access control), ethernet, wifi, OS device drivers work here
what are the advantages of layers?
- layers are self contained - the functionality of one layer won’t affect the other
- provides interoperability between providers and systems as different hardware or software operates on a particular layer
- senders and receivers using different software and hardware can communicate using the same layer protocols
what is the difference between TCP and UDP?
UDP does not check each packet and maintains an open connection
what is the difference between POP and IMAP?
POP downloads the message from the server so it isnt there anymore whereas IMAP downloads only a copy of the message from the server so that the same email can be accessed from multiple devices
