Networks Flashcards
Define
network.
an arrangement of two or more computers that are connected together for the purpose of sharing resources and data
What are some advantages of a
network?
(5)
they allow multiple users to:
- share data files with each other
- share hardware devices (e.g. printers, speakers)
- share an internet connection and internet services (e.g. www and email)
- communicate with each other (e.g. email, messaging)
- work together using web-based software (e.g. shared calendars, virtual meetings)
What is the
internet?
the world’s largest public WAN, a global system of interconnected networks, linking together billions of digital devices worldwide
What are some characteristics of
LANs?
- geographic area?
- ownership?
- security?
- speed?
- cost?
- topology?
- type of addressing?
- hardware forwarding packets?
- small
- private individuals
- more secure
- slower cables but many less users
- cheaper as there is less hardware required
- bus or star or mesh
- MAC addressing
- switch
What are some characteristics of
WANs?
- geographic area?
- ownership?
- security?
- speed?
- cost?
- topology?
- type of addressing?
- hardware forwarding packets?
- large
- businesses and organisations
- less secure
- faster cables but shared amongst millions of connections
- more expensive
- partial mesh
- IP addressing
- router
What is a
node?
a device on a network
What is a
network topology?
how different nodes on a network connect to one another
What does a
bus topology consist of?
(3 key points)
- all the nodes on the network are connected to a single cable, known as the backbone
- messages are sent along the cable in the form of electronic signals
- a terminator at each end absorbs signals that have reached the end of the cable (preventing them from bouncing back and causing interference)
What are the advantages of a
bus topology?
(3)
- relatively inexpensive to install since very little cabling is needed
- if one node fails, the rest can still communicate with each other
- easy to add extra devices to the network
What are the disadvantages of a
bus topology?
(3)
- if the cable is cut or damaged the whole network stops functioning
- the more devices that are added, the more collisions will occur and the slower the network will run
- all nodes on the network ‘see’ all data traffic (this may be a security risk)
What is an example of a use of a
bus topology?
small, short-term networks
What does a
star network consist of?
(2 key points)
- every node is connected to a central node (likely a switch)
- all data traffic passes through the central node, which is responsible for routing to its destination
What are the advanatges of a
star topology?
(5)
- if one node goes down, the rest of the network will continue functioning
- a damaged cable doesn’t stop the network from working, just the device connected to it
- data traffic is only sent to the intended recipient and not passed through any other nodes (making it secure)
- it is easy to locate faults
- nodes can be added and removed without having to take the entire network offline
What are the disadvantages of a
star topology?
(3)
- if the central node fails, then the rest of the network stops functioning
- network performance and maximum number of nodes depends on the capacity of the central node
- a lot of cabling is required, making it difficult and expensive to set up
What is an example of a use of a
star topology?
home networks
What does a
mesh network consist of?
(2 key points)
- each node is connected to multiple other nodes eith by cable or wirelessly
- communication in peer-to-peer (P2P) as there is no central controlling device
What are the advantages of a
mesh network?
(4)
- very fault tolerant - if one node fails, messages are rerouted
- nodes can be added and removed without having to take the entire network offline
- very scalable, any number of additional nodes can be added
- very high performance
What is the disadvantage of
mesh networks?
a wired mesh network is difficult and expensive to install
What is the
structure of the internet?
(4 levels)
- Every device connected to the internet is part of a network.
- Local networks connect to the internet via a Point of Presence (POP) (provided by an Internet Service Provider (ISP)).
- The ISP’s network is connected to a high-level network owned by a major telecommunication company (BT in the UK).
- Network Access Points (NAPs) interconnect the internet backbones to form a worldwide network.
What are some examples of
Internet Service Providers?
(3)
- Virgin Media
- BT
- Sky
What do
routers do?
(2)
- forward data from one network to another across the internet from source to destinatinon
- keep each other up to date about traffic conditions in their part of the network, so that data can be routed away form congested areas
What is
IP?
and what does it stand for?
a set of rules governing data transfer on the internet
internet protocol
What do
IP addresses do?
uniquely identify devices on a network
What does an
IPv4 address look like?
13.255.182.0
(each of the four bytes is expressed as a decimal number between 0 and 255 separated by dots)
What does an
IPv6 address look like?
fd2a:1450:4013:c01:0:0:0:5e
(eight 16-bit hexadecimal numbers separated by colons)
Why was
IPv6 introduced?
IPv4 allows more than 4 billion devices to be uniquely identified. This is no longer anywhere near sufficient.
What is the purpose of
IP addresses?
(2)
- facilitate routing across the Internet
- provide a sender & destination unique addressing scheme
this is temporarily allocated to devices whilst they are connected to the Internet/ a WAN
What information is stored in the
metadata of a packet?
(5)
- IP address of source
- IP address of destination
- sequence number of packet
- total number of packets
- checksum
How do
routers send packets to their destination?
(4)
- The router inspects the packet header to find the destination address.
- It then uses a routing table to determine where to send the packet next. (It is likely that a packet will be forwarded from one router to another several times before reaching its destination.)
- If there is congestion on one route, the next packet to arrive will be sent a different way to avoid it.
- Once a packet arrives at its destination, the checksum formula is applied to the data. If the generated checksum does not match, the destination will request the packet to be resent from the source.
Packets may arrive at their destination via different routes may be out of sequence on arrival.
Define
speed.
the transfer rate of data from source to destination
Define
range.
and give its unit.
the maximum distance a signal can travel before becoming disrupted
metres, m
Define
latency.
and give its unit.
the length of time it takes between a transmission being sent and received
Ms (higher is worse)
Define
bandwidth.
and give its units.
the maximum transfer rate of data from source to destination
bits per second, bps (higher is better)
What equation links
file size, time and bandwidth?
file size = time x bandwidth
Define
protocol.
a set of rules that allow devices to communicate
What are the most common forms of
wired transmission media?
- copper wire
- fibre optic cable
What does an
unshielded twisted pair copper wire consist of?
four pairs of thin copper wires covered in plastic insulation that are twisted together to help reduce interference
What does a
fibre optic cable consist of?
one or more very thin strands of glass, surrounded by several layers of protective material, encased in an outer sheath
What are the key characteristics of a
copper wire?
- how it works?
- range?
- speed?
- latency?
- uses?
- transmits data as electrical pulses
- short (up to 100m)
- up to 10Gbps
- high (suceptible to interference)
- connecting computers and other devices on a LAN
What are the key characteristics of a
fibre optic cable?
- how it works?
- range?
- speed?
- latency?
- uses?
- transmits data as pulses of light
- large (can transmit data over long distances with no loss of signal strength)
- high - up to 100Gbps
- low (less subject to interference
- connecting LANs together to form WANs
What are the characteristics of
wired networks?
- installation?
- flexibility?
- reliability?
- security?
- range?
- bandwidth?
- latency?
- time-consuming and disruptive, can present a trip hazard
- not flexible - the number of NAPs and their locations have to be determined at the outset, expanding or changing the LAN once it is up and running will require additional cabling
- reliable and delivers a consistent speed - because it is less susceptible to interference
- very secure - data can only be accessed by devices that are physiclly attached to the network, not easy to intercept or eavesdrop
- can transmit data over long distances and between different buildings on the same site
- fast - up to 10Gbps per connection
- low
What are the characteristics of
wireless networks?
- installation?
- flexibility?
- reliability?
- security?
- range?
- bandwidth?
- latency?
- less time-consuming and disruptive to install (than wired)
- very flexible
- performance can be inconsistent because WiFi signals are subject to interference
- less secure - data needs to be encrypted to prevent eavsdropping or interception
- theoretical range of 100m (but physical objects and interference can obstruct the signal)
- slower (than wired)
- high
What does
HTTP stand for?
and what is it used for?
Hyper Text Transfer Protocol
requests and responses between web browser & web servers
What does
HTTPS stand for?
and what is it used for?
Hyper Text Transfer Protocol Secure
encryption communication between browser & web server
What does
FTP stand for?
and what is it used for?
File Transfer Protocol
sending and receiving files over the internet
What does
SMTP stand for?
and what is it used for?
simple mail transfer protocol
sending emails
What does
IMAP stand for?
and what is it used for?
Internet Mail Access Protocol
reading/receiving emails
this leaves the email on the mail server
What does
POP3 stand for?
and what is it used for?
Post Office Protocol
reading/receiving emails
this deletes the email off the mail server
