chapter 2 - networks Flashcards
benefits of networking
- share resources eg printers which reduces cost
- share files/ data
- data can be backed up centrally
- managers can manage the network eg apply access rights
- can communicate
- licences to run software on a single network is often cheaper than on many computers
drawbacks of networking
- expensive hardware
- expensive / hard to manage
- if on device breaks eg file server it affects the whole network
- malware can affect the whole network
MAC address
- 48bit hexadecimal separated into 6 bytes
- physical hardware address and is unique
- assigned to NIC by manufacturer
- identifies devices
what is an ISP
provides access to the internet eg EE vodaphone
internet browser
accesses the internet via an app eg bing
LAN vs WAN
- LAN is over a smaller physical area whereas WAN is over a many different locations
- individual vs shared ownership
- faster vs slower
- twisted pair cable/wifi vs fibre optic
LAN +
+ expense of installing software on individual PCs could be reduced
+ file server can be connected to allow sharing
+ can share resources eg printers reducing cost and allowing higher quality resources to be brought
+ office can become paper less
WAN +
+can run a ‘job’ on a remote comp that required the application software
+ data archive stored on a remote computer that could be accessed
+ a message could be transmitted electronically to a user on a remote comp
IP address
- assigned by the router
- identifies the device on the network
- can change if location changes
internet vs www
internet is the hardware that the www runs on
www is the software that runs on the internet
eg email - uses www to open web browser and email account but internet at acc send to different computers
client server model
where a client runs an application provided by a server on a network -
- uses separate servers and client computers
- users can access files which are stored on servers
- server supplies resources and client consumes them
- used to share data
thin client
choses an application to run on a server and only provides input and receives output from the server - doesn’t process on the client
thick client
carries out some of the processing itself
thin client +/-
+cheaper to expand
+all devices linked to server
+ server offers protection against hacking and malware
-reliant on the server - if it breaks
-higher start up costs – more complex – powerful servers needed
thick client +/-
+ more robust
+ clients have more control
-data integrity - since many clients access same data
-less secure
- each client needs to update data individually
peer to peer model
- each node is connected to the other nodes = status
- each responsible for own security
- users access data from each other - act as provider and consumer
Used for - smaller less secure networks where workstation based applications are needed - for connectivity
server definition
- provide functions
– have dedicated roles and run software to perform dedicated tasks eg file servers, windows server, web servers
– client requests service server provides
frame/packet
unit of transfer containing the data, address and control info
peer to peer +/ -
+ avoids congestion on the network when many clients are downloading files at the same time
+ parts of a file can be downloaded separately
+ the parts are available from more than one host
- less secure
- no central backup
- all comps have to be on to share files - might not always be available
client- server +
+ allows an organisation to control downloading and use of some files
+ files can be better protected from malware attacks because the files are stored on one server which can be scanned using anti virus software
bus topology
central main cable
+ cheap to install
+ even if one node fails test function
- if cable fails no data can be transmitted
- increased traffic down central backbone
- poor security as all computers can see transmissions along shared cable
star topology
central switch
+ if cable fails other computers aren’t affected
+ easy to add new computers
+ less traffic as its isolated between computers
+ no data collisions
- costly to install - extra hardware
- if central node fails so does whole network
point to point topology
- one comp to one comp
- Transmission can be simplex or duplex
- Message is unicast
+ simple
neg- only 2 comps
mesh topology
Each comp has a point to point connection to another comp - direct links - can act as relays passing packets towards the destination
- Transmission is duplex
- Messages are unicast, multicast or broadcast
+ easy to see where faults are
+ broken links don’t affect other nodes
- lots of cabling
- complex set up
hybrid topology
collection of connected LANs where they have diff topologies or supporting technologies
+ large volumes of traffic
+ east to see where faults are
+ good for large networks
network topologies
- point to point
- bus
- mesh
- star
- hybrid
public cloud
-client and company are separate entities eg google docs, one drive
not owned by companies using it
private cloud
- Storage provided by a dedicated environment behind a company firewall
- client and storage provider are integrated / same and operate as a single entity
cloud storage +
+ files can be accessed at any time (with internet access) by any device
+ no need to carry an external storage device with you (heavy) - less stuff on hard drive
+ remote back up - adds security
+ data can be recovered
+almost unlimited storage capacity
+ cheap - some are free
cloud storage -
-if no internet/slow - cant download data/files
-costs can be high if large storage capacity required - can build up if have a subscription model (long term costs)
-expensive to pay for the necessary high download/ upload limits (high bandwidth) from the ISP
-trust in third party company to not lose data/ have a failure
modes to send data ( ways) - transmission
- Simplex - one way
- half duplex - data flows either way but not simultaneously
- full duplex - simultaneous data flow both ways
how to send data (who to) - message type
- Broadcast - one to all communication
- multicast - one source to many destinations
- Unicast - one to one communication
twisted pair cable
eg connect telephone handsets to telephone lines
- cheapest
- lowest bandwidth
- affected by attenuation
- most affected by interference - uses lots of, thinner wires with less insulation
- more need for repeaters
can be unshielded or shielded (commercially used to cancel out interference)
coaxial cable
eg used by cable television companies in MANs
- higher cost
- higher bandwidth - as its thicker
- most affected by attenuation
- less affected by interference
- more repeaters needed
fibre optic cable
uses pulses of light not electricity
can be single or multi mode
doesnt bend due to mirrors being used
eg long distance cabling
- highest cost
- highest bandwidth
- least affected by attenuation
- least affected by interference
- less repeaters needed
single vs multi mode
single
- uses a single mode light source
- smaller central core so less reflection
- can travel faster/further
eg CATV or telecommunications
multi
- works for multi mode light source
- construction causes higher light reflections in core- work best in shorter distances
eg LAN
radio waves
used by bluetooth and WiFi
uses spread spectrum freq hopping - picks one channel and if that channel is being used picks another
bluetooth
- sends radio waves at 79 frequencies (channels)
- 2.45GHz freq
- devices automatically detect and connect to each other (each device uses a diff channel so they don’t interfere)
used for multiple close devices - slow speed - low bandwidth
WiFi
- also uses spread spectrum freq hopping
- has faster data transfer
- better range
- better security
- accesses internet via WAP
microwaves
For most applications microwaves are best as they have a better bandwidth than radiowaves
infrared
- highest bandwidth and best at focussing directionally
- but most attenuation, needs repeaters most, worst penetration
- mainly used for indoors as it cannot escape and cause interference elsewhere (benefit)
satellite
- Transmitted between antennae
- uses microwaves and radio waves
+ Enable long distance communication
+ less interference
+ compensates for the curvature of the earth so can communicate globally - Can be transmission delays due to greater distances which cause technical problems
wired +/-
+ more reliable/ stable - less interference
+ data transfer is faster - no dead spots
+ overall cheaper in spite of need for hardware
- devices aren’t mobile
- trip hazard / fire risk from cables
wireless +/-
+ easier to expand
+ increase mobility
- increased interference
- less data security (easy to intercept data)
- slower transmission
- signals can be stopped by thick walls
cabling on LANs
nowadays mostly twisted pair cables and fibre optic becoming more common
bridge
- connects two segments of a LAN ( that use the same protocols) so they can function as one LAN
- stores the network address for the end-systems in the two segments it connects
repeater
- a device which connects two cables and provides a full strength signal (over long distances signals become attenuated ao this reduces that by generating a new full strength sigbal) to the second cable
- can be used to extend a bus by connecting two bus cables - and boosts all signals to prevent dead spots in the WiFi zone
hubs with repeaters negatives
- collisions may occur and are not resolved - one way to deal with this is to use jamming signals however this reduces performance
- they are unable to manage delivery paths and security
hub
- can have a number of devices connected to them so are used to connect devices to form a LAN
- takes a data packet recieved at a port and sends the data to every computer in the network
- not secure and wasteful use of bandwidth
switch
- a connecting device that can send a unicast message
- central device on a star network
- can direct communication to a specific-end system
+ More efficient than hubs as they check the data packets received and works out its address and sends data only to the appropriate computer - more secure
router
- routes data between different networks to the appropriate switch eg joins LANs to WANs
- can take data and format it into different protocols to be used on different networks
NIC
- component used to identify the end system
- has a unique network address
- contains MAC address
WAP
- connecting device in a WiFi LAN - provided the system has a WNIC installed
server
- a system providing a service of end-systems
- provides functions – has dedicated roles and runs software to perform dedicated tasks eg file servers, windows server, web servers
– client requests service server provides
gateway
- acts as an entrance to a network – converts packets to different protocols
ethernet
- The dominant LAN protocol
- Originally used on a bus configuration
- Used CSMA/CD to minimise the effect of collisions
- Modern version is switched
Made up of: - a node eg any device on the LAN
- medium - a path used by the LAN devices eg Ethernet cable
- Frame- data is transmitted in frames - made up of source address and destination address (MAC + IP)
how does ethernet reduce collisions
- Uses broadcast transmissionn so data can be sent at the same time causing collisions
- Uses **CSMA/CD **
- when a collision is detected the node stops transmitting a frame - transmits a ‘jam’ signal - then waits for a random time interval before trying to resend the frame
PSTN
public switched telephone network
- cables used to connect devices/LANs between towns/cities
- Changed from copper to fibre optic (faster broadband)
- Always open even so can always be used
- Remains active during power cut - have separate power source
- Use circuit switching - connection is maintained for the duration of the call
ethernet conflicts
- it is possible for IP addresses to conflict
- may occur is devices on the same network have been given the same IP address - most likely on LANS with dynamic IP and static
- can be resolved by restarting the router - so IP will be reassigned
