3. Networking

All Past Paper Questions: https://docs.google.com/document/d/1vNZHDwmVpjr_FtfKK6hSrniGD02bbcCwLTdDMDe65Q4/edit?usp=sharing

Questions left out:

p3-ch2-pg71
p3-ch2-pg85
p3-ch2-pg89
p3-ch7-pg15

Data Terms

bit rate
- description
  - number of bits transmitted per unit of time
  - units: Kbps (kilobits per second)
  - measure of how fast data can be sent from one device to another
- how its measured physically?
  - Start video streaming a file of known size
  - Use software to capture video traffic
  - Select video stream from captured traffic and calculate bits per second.
- factors affecting it
  - bandwidth available (on communication channel)
  - level of SNR ratio (signal to noise ratio)
  - number of signal levels used to represent data

Network Classification

LAN

WAN

Comparisons

LAN vs WAN
- LAN
  - small geographical area
  - high data transfer speeds
  - uses Ethernet / Token Ring technologies
  - connect together into bigger LANs using fiber optic cabling
  - owned by one organization (usually)
  - fewer errors raised (when transmitting data)
  - fewer congestion problems
  - use Layer 1 or Layer 2 devices
    - eg: switches,
    - bridges,
    - hubs,
    - repeaters, etc...
- WAN
  - uses ATM / Frame Relay
  - connect together using public telecommunication systems
  - has collective ownership
  - use Layer 3 devices
    - eg: routers
    - multi layer switches

Network Models

TCP/IP Model

OSI Model

Packet Switching

how a video is streamed
- computer requests stream
- NIC on server determines dst address for file
- Video file is converted into packets (by NIC on server)
- NIC on server uses packet switching
- packets contain details of dst address
- Packets are sent from network (server's LAN) to router
- Router compares packet dst IP with routing table
- Router chooses next hop to send packets
  - (based on routing table)
- Applies QOS (quality of service) rules to prioritise the packets
  - (of the streamed video)
- Sends packets to next router
- Next router does the same thing
  - and passes on the packet
- user's Router receives packets from the internet routers
- and transfers to laptop viewing video
- Dynamic routing tables of routers may be updated to ensure QOS for streaming

Circuit Switching

Frame Relay

why
- supports high speed data transmission
- connectionless service
  - each packet through network
  - contains address information
- can use virtual circuits
  - they appear permanent to users
- multiplexing of virtual circuits to share network bandwidth
- can only detect errors at Data Link layer
  - so, no flow control
- faulty frames dropped
  - no request for re-transmission
- supports variable frame sizes
- operated at Physical layer and Data Link Layer
  - so, can be used for internet
- no error control
  - so it requires less reliable method
  - for transmission
advantages
disadvantages
- frames delivered unreliably
  - have to be retransmitted if sender is aware (to resend)
  - frames may go missing
    - no acknowledgement from recieving packets
  - packets may not be delivered in same order as sent
  - no flow control
    - cannot stop data transmission
    - if network is congested
    - so, data is lost
  - data is lost if frame doesnt get re-transmitted

Comparisons

TCP/IP vs OSI model
- similarities
- differences

Hardware

Routers

stuff
- in L3 (network layer) of OSI model
- used in WANs
- connect two (or more) networks together
- connects devices to internet
- do not use data frames
  - (deals with data packets, not ethernet frames)
- work with IP addresses (packets)
- can dynamically change route (for shortest path)
- carries out NAT (network address translation)
- does routing decisions between networks
- have own broadcast domain
- store routing data in 'routing tables'
- contains WAP in same physical unit (AIO)
- mostly does packet switching only
routing
- static
  - stuff (compared to dynamic)
    - created by network admins
    - does not (automatically) consider network conditions
    - routes are fixed
    - routing tables are not updated
    - routing table does not time out
  - how?
    - Routes entered into database
      - by network admin
    - Entries are fixed
      - (not reconfigured automatically)
      - Defines fixed routes
        
        for packets
        
        to take from the router
    - forwarding table created
      - by the routing algorithm
      - when choosing the next hop
    - Defines route of exit point from router
    - As fail-safe if dynamic routing does not provide a route
    - Can transfer routing information from one router to another
- dynamic
  - stuff (compared to static)
    - generated by algorithms
    - creates routing table
      - by considering real-time logical network layouts
    - can adjust to changing network conditions
    - routing changes shared between routers
    - can limit number of hops
    - have limited time-to-live data
      - cuz table will be updated
  - how?
    - Routing protocols create a table of routing information from real-time logical network layouts
    - Created automatically
      - Using many protocols to determine 'best' route
    - Routing information shared with other routers (automatically)
      - to discover changes in networks
    - to limit the number of 'hops' that a packet can take
    - after TTL (time-to-live), table will be updated
    - Packets forwarded via different routes
    - Packets can be routed around network issues
    - Allow as many routes as possible to be kept open.
- static vs dynamic routing
  - similarities
    - used in routers
    - to determine next hop to send packet
    - algorithms create a 'forwarding table'
      - (routing table)
      - when choosing the next route
      - its stored in non-volatile memmory
        
        (of router hardware)
    - provides default route for packet
      - if no route can be determined
QOS
- quality of service
- for video streaming
  - set router's QOS configuration to prioritise video stream
  - use traffic shaping configuration to prioritise video stream
  - configure specific ports for video service
  - intelligent QOS with prioritise in a pre-determined order
    - (only in new routers)
    - order:
      - voice
      - video
      - application traffic
      - print services
      - file downloads

Hubs

stuff 1 (compared to Routers)
- broadcast all received data
- to all devices on the network
- do not store information about devices
- can reduce network performance
  - will use all available bandwidth

Switches

stuff 1 (compared to Routers)
- used in LANs
- all ports in switch has same broadcast domain
- store data in a CAM (content addressable memmory) table with MAC addresses
- usually wired only
- can configure to do
  - circuit switching
  - message switching
  - packet switching
stuff 2 (compared to Hubs)
- examine data packets
- to determine where to send them
- store information about MAC addresses of devices
- more efficient (bandwidth usage)
  - as they do not self data to all devices
- lower latency
  - eg: can ehance gaming
types
- L2 switch
  - in L3 (data link layer) of OSI model
  - connects nodes in same network
- L3 switch
  - in L3 (network layer) of OSI model
  - can connect two networks
  - deals with frames & also packets
  - work with MAC addresses (frames)
  - faster at connecting segments/routes
role and
- Connects devices together
  - more than devices to a single cable connection
- process packets from
  - end-user devices (eg: laptop)
  - and intermediary devices (eg: switches)
- Forward packets to destination device.
operation
- Operates at data link layer (Layer 2)
- Creates table in memory
  - Content Addressable Memory
  - has MAC addresses and ports
    - (of recieved network frames)
- uses MAC address
  - (not IP address)
  - in Ethemet frame
- Compares with stored table of MAC addresses
- Sends frame to known port
- Unknown frames are sent to all ports

NIC

network interface card
how it works
- circuitry between computing device and transmission medium
- Each NIC has a MAC address
  - unique
  - 48 bits
  - in Headecimal
- for high speed data transmission (cabled)
- Uses the OSI model
  - to send signals at the physical layer,
  - transmit data packets at the network layer
  - and operate as an interface at the TCP/IP layer.
- Data
  - from CPU and sends to destination
- Translates data
  - to form so can send in cable
  - from cable into form useable by
  - Converted to/from parallel structure from/to linear structure
- Uses interrupts
  - tell CPU
  - ready to receive data for sending
- Polled by CPU
  - to determine if NIC has data
  - for it to deal with
- CPU moves data to/from NIC to memory
- Uses DMA
  - to transfer data to/from main memory
    - (via system bus)
  - independent of CPU
- Prepares data for transmission
  - in form of frames
- Process bits from the physical layer and pass to next layer.

WAP

wireless access point
description (short)
- connects portable devices to a cabled network (over WiFi)
roles Allow Wi-Fi connections from devices Connected to the wired network (LAN by ethernet) devices can be mobile secure access using password
limitations
- limited connection distance
- signal affected by
  - Obstacles
    - can reduce connectivity (inbetween WAP and device )
  - type of antenna in use
  - presence of other wireless devices
    - (transmitting on the same frequencies)
  - Weather conditions
  - Power output
- less bandwidth (vs wired)
  - 350 Mbits/s vs 1000 Mbits/s (Gigabit)
- multiple devices -> increases congestion
- Security is based on encryption
  - adds overhead to packets processing
- devices that can connect to a WAP is limited
- Unsecured WAP allows access to anyone within range
- less secure
  - can easily intercept traffic
- can slow down workflow is password is forgotten
- faraday cages in building structures
  - will not allow users inside it to connect
how to improve security?
- Hide SSID (service set identifier)
  - "Hidden Network"
    - SSID doesnt appear
    - asks for SSID before connecting
  - provides limited protection
- Filter MAC addresses to only allow known devices
  - Ensure WAP is not issuing IP addresses to unknown devices
- Use encryption
  - (between WAP and client device)
  - use up-to-date encryption protocol
    - eg: WPA3
  - dont use old protocols
    - WEP (Wired Equivalent Privacy)
    - TKIP (Temporal Key Integrity Protocol)
  - requires user to enter a 'network key'
    - (password)
    - atleast use 14 characters
how data transferred from LAN to WAP
- Uses radio waves
  - frequency ranges: 2.4GHz / 5GHz
  - frequency bands: 900 MHz and 3.6 GHz
- frames are modulated onto carrier wave
- Spread spectrum used for higher power levels
- Two channels used for full duplex exchange of data
  - (most WiFi is half-duplex)
- WiFi network uses SSID to identify itself
- Access point and device must be connected to same WiFi network
- Data is encrypted during transmission
- Devices must use IEEE 802.11 standards
  - IEEE 802.11 has variants
  - a/b/g/n/ac(/ad/ah/aj/ax/ay/az)
- 14 channels on 2.4 GHz
  - which are 5 MHz spaced

Comparisons

switch vs router
- similarities
  - used in LAN
  - handles data packets
  - have multiple data ports
  - conenct to multiple devices
  - send data to specific devices
  - provide high transmission rates
  - can work in full duplex mode
  - can work in broadcat, multicast and unicast
hub vs switch
- similarities
  - allows multiple devices to connect to a network
  - devices can form a LAN
  - send the packets to other devices
  - can transfer data to all devices (on a network)

Wired

data transferring
- unencrypted
- less subjected to interference
- cannot easily intercept
- no need credentials to connect
- requires device to be physically connected
  - so, less portable

Copper Cables

why
- Can use long runs of cable
  - less signal loss
- Greater tensile strength
- no harm from electrical interference
- no harm from environmental changes
- Can provide very high bandwidth
advantages
disadvantages
- Difficult to setup
- Loss of signal at joins.
- cannot bend too much
  - not very flexible
  - (if bent beyond their limited physical arc, they will break)
- Special test equipment required
- susceptible to physical damage
  - eg: being cut / broken
- Data transmission losses occur
  - when wrapped around curves
  - with small radius.
- expensive than wireless
- cannot provide high bandwidth like fibre optics

Fiber Optic Cables

Wireless

why less secure (in LAN)
- might be unencrypted
- easier to intercept (than wired connections)
- Access points can be 'spoofed'
- access points broadcast SSID (network ID) to public.
data transferring
- slow speeds
- high latency
- need recognition of connection between devices
- requires connection to be encrypted
- requires user to input credentials
- encrypted data is easier to intercept (even if no meaning)
- easier & cheaper to install
- signal interference from other devices
- more portability to client devices
advantages
- internet (radio signals) around home
- can control devices remotely / portably
- multiple wireless handsets to use one wired landline
- can use wireless doorbells
- communication without disruption
- can be used in historic buildings (without network wires)
- multiple devices connect to centralaccess points so
- easy sharing of printers, files, etc...
- mobility / portability of devices
- can use of (discrete) hearing aids
  - so, high volumes doesnt disturb others
- remote control of household appliances
  - eg: smart home devices (IoT)
  - eg: like CCTVs
disadvantages
- subjected to interference
  - from electronic devices
  - microwave ovens
  - fridges
  - so, unreliable
- security issues if not set up properly

Microwave Transmissions

how
- Uses beam of electromagnetic waves
- Uses line-of sight between antennae
- Uses frequencies: 300 MHz to 300 GHz
  - (wavelength 10cm to 1mm)
- Uses parabolic dishes
  - with (horn) antennae
  - to provide 'spot' beams
- Uses multiple antennae
  - to send/receive signals
  - (if sending/receiving simultaneously)
- Data is modulated
  - onto carrier wave
  - using OFDM (orthogonal frequency-division multiplexing) / OFDMA (orthogonal frequency-division multiple access)
- Pulsed transmission of waves
advantages
- directional antennae
  - increased performance
  - low power usage
  - point directly at each other
    - can use same frequencies
    - (as neighbouring transmissions)
    - without interference
- Narrow microwave beams do not interfere (with other equipment)
- Small antennae means more portable
  - e.g. portable radio systems
- large bandwidth
  - carry more data
disadvantages
- tall antennae
  - difficult to install
- Line of sight required
  - antenna cannot be 'over horizon' (earth curvature)
  - (limited to 50-80 km)
  - else,
    - obstacles will interfere
    - Unable to penetrate obstacles
    - causes interference
  - so position antennas intrusively
- atmospheric conditions can degrade signal
  - (weather)
  - 'Rain fade' absorbs microwaves by weather
  - dust / smoke / high-pollen-counts because signal scatters (by particles)
  - Solar events
- ?? can be intercepted behind official antenna (eg: by space satellite) ??
uses
- phone systems (3G, 4G, 5G)
- WiFi systems (in LAN)
- communication between base station and satellites
  - + uplink and downlink satellites
- used for TV / radio
  - to transmit programs from outside the studio
  - (broadcasts)
  - instead of using expensive satellite links
- used to carry cellular data between stations
  - to provide backbone to carrier system
- for short-range indoor communications
- to link remote telephone exchanges to main exchanges without using cobber/fibre-optic cabling

WiFi

stuff
- asymmetrical
  - one central point to many remote devices
- uses a central access point (usually)
- covers wider area
- complex to establish a connection
  - requires a lot of authentication and encryption stuff
how WiFi connection is established
- User selects Wi-Fi connection (SSID)
  - (from list of available connections)
- Connection to a WAP (in a router) (1st)
  - which is wired into the LAN
- Uses radio waves
  - frequencies in the 2.4/5 GHz range
  - to carry data packets
- Wi-Fi uses frames
  - uses Wi-Fi protocols
  - working at data link layer of TCP/IP stacks
  - (to carry data over radio waves)
- WAP sends beacon frames at intervals to announce its SSID
- Smartphone sends authentication frames (probe frames)
  - to WAP
  - requesting connection.
- WAP responds with authentication credentials
- User input of authentication credentials to establish security
  - encryption for data exchange, eg:
    - WPA2 (and variants)/
    - TKIP protocols/
  - using 128/256 bit keys for encryption
- error control used between smartphone and WAP when maintain connection
- User data
  - encapsulated within data frames
  - using Wi-Fi protocols
using public wifi
- advantages
  - low cost / free
  - attracts more customers
  - allows mobile connections, so, more productive
  - convenient when travelling
  - avoids use of data allowance in mobile phone networks
- disadvantages
  - unreliable connections
  - some services might be restricted
    - eg: torrenting
  - might insert advertisements
  - may require authentication/verification with personal details
  - can be intercepted by others
    - subjected to MITM attacks
    - might inject malware code
    - personal data can be stolen
      - and used for fraudulent activities
  - might limit bandwidth unless extra fees paid

Bluetooth

stuff 1 (vs WiFi)
- to be used upto 8 devices
- doesnt use a central access point (usually)
- symmetrical
  - two devices
- covers short range connections
- more affected by obstacles
- simple to establish a connection
- has low bandwidth
- less harm from electromagnetic interference than WiFi
- less secure than WiFi
- uses less power
- shorter range
- restricted by solid barriers (eg: walls)
stuff 2 (vs NFC)
- working distance: 100m
  - (devices must be kept very close)
- sets up in 6 seconds
- bitrate: 2.1Mbits
- requires PIN
- one-to-one connection (peer-to-peer)
- new technology (doesnt support older devices)
stuff 3 (compared to infra red)
- uses radio frequency: 2.4GHz
- can use multiple channels
  - (spread spectrum technology)
- can travel through walls (but signal will deteriorate)
- free standard
- high bandwidth (compared to IR)
how Bluetooth connection is established
- turn on both devices
- ensure within range (both should find eachother)
- set one device to search for other
- device is discovered/found
- device required password/user-response
  - eg: pressing a button
  - or confirming a one-time code
- password confirmed by both devices
- devices are paired
- frequencies+channels to be used are decided
advantages
- free to use
- many devices support it
- uses less power (than e.g. WiFi)
  - saved phone battery life
- Easy to pair devices
  - no need passwords
- Connections are 'remembered'
  - so simple to repeat
- It is wireless (so, convenient)
- Can connect through obstacles (usually)
- Has greater range than infra-red connections
- It is short range
  - signals hard to intercept
  - so, more secure
disadvantages
- can hack Connection of idle devices
- short range only
- slow when sending large files
- low bandwidth
  - compared to e.g. WiFi/cable connections
- only 8 devices at max
  - (can connect to 7 devices at once ONLY)
- Can lose connection due to interference / obstacles
- Can receive viruses

Infra-red

for data transmission
stuff (compared to bluetooth)
- uses wavelength: 20 to 400THz
- less susceptible to interference
- requires line of sight
- limited to 10m
  - depends on power of IR source
- can only use with 1 other device
- usually need proprietary equipment
- IR bandwidth is limited
  - depends on on/off pulses of data
- can setup personal area network (PAN)

NFC

near field communication
uses
- to make contactless payments
- identify user in ticketing systems
- in social networking for sharing images
  - (between close devices)
- exchange personal details
  - eg: bussiness card
- unlock doors with smart locks
stuff (vs Bluetooth)
- working distance: <20cm
- sets up in <0.1 seconds
  - (quicker than bluetooth)
- bitrate: 400kbps (lower)
- uses less power
- can be used to activate passive tags
- automatic connection

Cellular Networks

structure
- base stations
  - in a cell
  - for wireless connection
  - to end user
- central switched network
  - handles voice calls & text messages
- packet switched network
  - handles mobile data
- public switched telephone network (PSTN)
  - for connection
  - into global telephone networks
why no interference
- use frequency multiplex division (to share frequencies)
- Spread spectrum technology allows multiple connections on same frequencies
- Multiple input and multiple output (MIMO)
  - using multiple transmit/receive antenna
  - to increase data flow
- Antennae from base stations directional to avoid
  - so, no interference to other towers
- Adjacent cells use different frequencies from neighbouring cells
- wireless frequencies
  - are re-used by cells
  - distant from each other
  - to increase capacity
  - (where ranges of frequencies are limited)

5G, 4G, 3G

5G
- feaures (suitable for large networks)
  - large connection capacity
    - upto a million devices per km²
  - very high bandwidth (data transfer)
    - even allows use UHD video on demand
  - very low latencies (fast responses)
  - seamless handover between base stations
  - use 'beam-forming' techniques
    - by base stations
    - to improve connections to specific devices
- advantages
  - (most stuff in features section above)
  - may gradually replace land-line connections (for internet connections)
- disadvantages
  - reduced coverage
    - need more cell towers
    - more expensive
  - shortage of radio frequencies
  - can interfere with existing radio spectrum
  - new devices required to acecss 5G
  - new technology required to implement 5G
  - potential for cyber attacks
  - low latency
    - can control devices remotely, in real time
  - high infrastructure costs
4G
- stuff
  - use only packet switching
3G

Comparisons

4G vs 3G
- higher bandwidth
  - due to higher range of frequencies
  - due to use of MIMO
    - (multiple input and multiple output)
    - using multiple transmit/recieve antenna
    - to increase use of transmission channels
  - connections use frequency multiplex division to share
  - due to use of spread spectrum technology
    - to allow multiple connections
    - on same set of frequencies
  - gives
    - faster download speeds
    - more buffering capacity
    - content loads faster
- handovers between base stations are smoother
  - less interruptions
- use only packet switching
  - allows packets to be multiplexed
  - so, increased rate of data flow
bluetooth vs infra-red
- bluetooth
- infra-red

Satellite Communication

how it works?
- Satellite remains in orbit
  - follows rotation over Earth
  - appears stationary over target area
- Multiple satellites
  - can be arranged in constellation
  - each covering of small area of surface
  - can cover areas farthest from equator
  - target specific areas of Earth
- Satellite can use spot beams
  - to target specific areas
  - provides high bandwidth
- Ground stations
  - maintain permanent (microwave) links
  - with satellites
  - Both uplink and downlink connections
  - via dish antenna
- User
  - has dish with transceiver
  - via LNB pointed at satellite
  - dish needs to be line of sight
  - eg: dish in Southern hemisphere northerly direction.
- MORE STUFF -> (for full marks)
- Ground (gateway) stations
  - have internet connection
  - relay user internet data to from satellite
  - convert data carried by satellite signals to/from IP packets
- Satellite
  - serves to receive, amplify and re-transmit signal
  - (without processing of data)
- User
  - has satellite modem
  - to modulate/demodulate data
  - between local IP packets
    - and satellite link signals.
advantages
- Satellites are in geostationary orbit
  - so ground stations for uplink
  - can point directly at them
  - so less power needed
- Receiving dishes
  - can point directly at satellite
  - for less fluctuation (in signal)
- Low/medium orbit satellites
  - provide low latency connections
  - with high speeds
- Physical connections not required
  - so access can be from anywhere
- No need ground-based infrastructure
- aircraft/ships can use to access internet
- Coverage can be optimised for high bandwidth
disadvantages
- Satellites in geostationary orbit are
  - c. 18 000 km high
  - so signal has to travel c. 36 000 km
  - resulting in delay
    - high latency (worse than dial-up)
    - SSL may not succeed
    - TCP protocols may break
- Interference by weather conditions
  - can reduce signal quality
- Must be line of sight to satellite
- Reflections reduce signal quality
  - by phase cancellation effects.
broadcast from satellite to TV
- Satellite is in geostationary orbit
  - appears to be at fixed point above
- be at correct height
  - 37 000 km above equator
- Satellite has
  - ransmitting dish pointed at Earth.
  - has transponder(s)
    - which receives and transmits
    - signals (to/from) Earth.
    - use different frequencies.
      - set range: 4—8 and 12—18 GHz range
- Horizontal & vertical signal polarisation
  - to increase capacity.
- TV signal may be encrypted
  - to prevent viewing without paying
- High definition signals with multi-channel sound requires more bandwidth.
- Receiving dish on Earth
  - pointed at the satellite in line of sight.
  - has LNB (Low Noise Block) at antenna
    - to amplify signal
    - allows use of cheaper cable to receiver.
- Receiver
  - decodes signal into pictures and sounds
  - decrypts the encrypted TV signal (paid).

Networking Models

Client-Server

explanation
- all files in a centralized server
- only one copy has to be maintained
- files can be mirrored to other servers
  - for increased performance
  - without the need to copy to each device in use
- disaster recovery is easy + quick
  - can quickly recovery backups
- servers can be updated (easily scalable)
  - without upgrading user devices
- data shared across different devices
- data can be accessed from different locations
  - (as long as the device is in the same network)
  - (or by using a VPN tunnel)
- data can be queried from DBMS (SQL or No-SQL database)
  - regardless of interface
- better data security
- server can perform authentication before returning data

Peer to Peer

advantages
- No centralised system
- so failure of one device does not affect others
- Access to files is local/faster
- more productive to users
- No need network operating systems
- as its stores own files
- Less knowledge to setup
- less technicians needed
- No central records of access are stored
- so can be used for piracy
- easy scaling
  - without performance impact
disadvantages
- Files not centrally organised
- difficult to locate specific files
- high Risk of malware
  - each peer/node is responsible for their own security
- Security is lower as not centrally deployed
- no central Backup systems
  - user's responsibility to backup
- document templates may exist in different versions
- hard to be consistent
- Files cannot be checked before download
- security issued
  - no central control over access
  - Remote access can be insecure
- one device down = affect others
  - that portion of files is lost

BitTorrent

description
- peer-to-peer file sharing
- web seeding to allow use of HTTP sources
- provide RSS feeds
  - via 'broadcatching'
  - (for content distribution)
- Used to
  - stream videos
  - transfer large files using minimum bandwidth
  - ?? social media to distribute updates to servers ??
how it works
- Peers share processing power without a central server
- Nodes work as both client and server for other nodes
- Nodes can connect undstructured or in structured topology
- Unstructured mode
  - robust when nodes join/drop frequently
  - but finding a file is more difficult
- Structured mode is organised
  - (using hash tables)
  - and files can be found easily
- Peer-to-peer software run on /node
  - Software queries other nodes to find file
    - Search request
      - has 'time to live' (TTL)
      - after which it ceases to search
      - propagates from queried nodes to others
    - When found,
      - software downloads from node to node
    - Other nodes can copy downloaded file from each node
- fragments of file can be copied from different nodes at once,
  - increasing speed.
how it works? (old)
- source computers are used without a central server
- BitTorrent client required on internet-connected computer
  - to implement BitTorrent protocol
    - works well over low-bandwidth connections
- BitTorrent descriptor file is used to describe file being distributed
- BitTorrent node set up with use of descriptor file and file to be distributed
- Node becomes seed for download
- Files made available to others for download by connection to other peers
- File is divided into small segments
- Segment becomes available to other peers as it is downloaded
- original (source) seed is relieved of load
- Every segment protected by a cryptographic hash
  - used to detect changes
  - to ensure file integrity
- Segments downloaded in random order
  - and re-ordered by BitTorrent client.
why its insecure
- Nodes more susceptible to remote attack
- IP address is clearly visible to others so
  - (so, easy for hackers to target)
- can use IP to steal user data
- resulting in fraud / blackmail
- Malicious code can edit routing tables of nodes
- responses to requests can contain malicious code
- so, we download malware instead of original resource
- Authors are unknown
  - so, may contain trojans/malware/stealers
- Sections of files can be replaced with malware
- Downloaded Bit Torrent files
  - stored by default in folder along with other user data
  - risking exposing the data to others
- session can be left open unintentionally
- Bit Torrent traffic is not encrypted by default
  - UDP and TCP ports used
    - might be subjected to monitoring by ISP
  - so, use VPN
- piracy (of copyrighted materials) give rise to legal issues

Tunnelling

why
- set up VPN
  - (allows data to be private)
- data can be be kept secure when working remotely
  - (eg: working from home)
- can circumvent firewall rules
  - to allow access to internal network
  - by data carried in packets
- can use foreign' protocols on networks
  - (when its not supported)
  - e.g. use of IPv6 on IPv4 networks.
how? (to tunnel over the internet)
- data broken into small packets
  - (for transmission over IP network)
- IP packets encapsulated by tunnelling protocol (L2TP)
- IP packet sent over internet (public communication channels)
- data is encrypted using SSH / IPSec
- packets are decapsulated and unencrypted at destination

VPN

evaluvate
- Encrypts all data (secure)
  - protects privacy of user
- changing the user IP address
  - allows users to browse internet anonymously
  - prevents tracking of activity by ISP, trakcets, etc...
- can configure to block advertisements
- can bypass geo-restrictions
  - access material from other countries
  - eg: journalists looking for news
  - movies, music, etc...
- to bypass censorship (imposed by ISPs or countries)
- can bypass ISP bandwidth
- may be illegal in some countries (might lead to prosecution)
- reduce performance and increase letency/ping
- may collect data and sell to third party (data brokers)
- can be difficult to set up
- ?? need latest OS to use VPN ??
- Some sites may block VPN
- can be configured to allow an extranet to be set allowing remote access to a private network

Cloud Computing

meaning
- ...
Storing data on remote servers
Servers maintained by third-party (companies)
Accessed via web browser
Can use VPN for secure connection.
servers can be accessed from anywhere (with internet access).
Resources shared between clients and provider (seamlessly).
dynamically changed by provider
many service models exist eg,
- providing infrastructure/
- providing software
- providing the 'computing platform'
- providing development environment
impact
- cheap maintenance costs
  - no need servers, IT staff
- large storage for cheap
- performance is monitored by provider
- Productivity is increased
- invest in reliable internet.
- dynamic Scalability
  - requirements met quickly
- Resources expanded and contracted as required
- unexpected costs when resources exceed
- no full control of their data.
- Data may not be stored in the same jurisdiction
  - laws difficult to comply with
- expensive service provision
storing data in cloud
- meaning
  - store in network of servers
  - accessed over internet
  - Access available from any (remote) device
  - data may be managed by third parties
  - managed by a cloud storage provider.
- security issues
  - Data not under our direct control
  - depends on third party for security
    - cannot trust third party companies with our data
  - Data is susceptible to cyber-attack
    - as only accessible over intemet
    - as multiple copies of data (buckups)
    - attack to servers
      - e.g. DOS attacks
      - uses all server resources
  - Data accessible to government check / subpoenas
  - data loss, may result in legal issues
    - could storage provider is responsible
  - Data is difficult permanently
    - already in cloud
    - already had multiple copies (backup)
  - not standardised across all companies
    - if a company using cloud storage
    - they might not be able to change supplier
  - cannot access data without internet (while offline)

Bit Streaming

describe
- contiguous sequence of bits
- sent/recieved serially
- over a communications network

Real Time

stuff
- from a live source
- cannot be accessed later

On Demand

stuff
- from a pre-recorded video
- can be streamed at any time

Protocols

Also at:

DHCP

describe
- a network manaqement protocol
- Automatically assigns
  - a network configuration to a device
  - an IP address
  - a gateway address
  - a subnet mask
- Creates a database
  - to avoid addressing conflicts

UDP

describe
- Sends data (in datagrams) using lP
- Provides
  - checksums
  - port numbers for source/destination
  - (of datagram)
- Connectionless communication
- No reporting of lost packets (to sender)
- Used when delivery of datagrams is not important
- Avoids processing overheads
  - (of error checking)
- No handshaking
- No guarantee of delivery/
- No order of datagrams
- No error checking.
packet header
- four fields of 2 bytes
- source port field used to reply if needed
- dst port used to specify reciever port number
- dst port is always required
- header + data field
  - (in bytes)
  - used for error checking
- length of header (8 bytes minimum)
- checksum field
  - results of calculations
  - to be used to check errors
  - optional in IPv4
    - set to 0 if not calculated
  - required in IPv6
advantages
disadvantages
- no acknowledgement after recieving packet
- not sure if packet lost or recieved
- provides for ordering of packets so there is no tracking of messages
- no congestion control
  - so these have to be separately
  - carried at application level
- Reciever must handle lack of handshake
  - of data
  - increasing complexy/overheads.

TCP

describe
- Sends data (in datagrams) using lP
- Provides
  - checksums
  - port numbers for src/dst
  - (of datagram)
- Connection-oriented communication
  - (point to point)
- Reporting to sender of lost packets
- Establishes how data is transferred over network
- Handshaking is carried out to establish connection.
- Manages flow control
- Used when delivery of datagrams is important
- Error checking.

FTP

file transfer protocol
for sharing files to/from server

HTTP

hyper text transfer protocol
for accessing web pages

HTTPS

hyper text transfer protocol secure
learn more at: Chapter 4 - Security
for secure data transfer

SMTP

simple mail transfer protocol
to send emails

IMAP

Internet Message Access Protocol
to recieve emails

POP3

post office protocol 3
to recieve emails

SSH

secure shell
for secure access to a server

SFTP

secure file transfer protocol
for secure method of uploading data to a server

SMB

Server Message Block (used by Samba)
for transferring files to a file server

TELNET

teletype network
to connect computers to a switch/router

Applications

Forums

advantages Accessible from anywhere Interaction between experts from different areas is possible Can develop a group opinion moderated comments can increase reliability
disadvantages
difficult to maintain (when discussing medical issues)
unable to verify accuracy of comments.
Comments added at any time.
No non-verbal clues about participants.
Can become little more than a group chat about symptoms with no focus.
?? Posting of the same comment multiple times can cause reliability of data issues ??

Blogs

to adversite bussiness
- advantages
  - can increase bussiness
  - encourages feedback
  - repeat visitors
  - can analyze data from blog to learn more about customers
  - ensure to alert customers regularly
  - easy to setup
  - can be started by anyone
- disadvantages
  - can be continually updated
  - hard to follow bad written content
    - often written alone
  - can be inconsistent in details
  - might not show up in search results
  - maybe misleading to customers
  - if blog not updated
    - income may fall
    - we get negative feedback
how to social engineer
- pg73

Micro Blogs

advantages
- specific Topics
- reflects real time activities
- Use short sentences
  - for users who don't have the patience to go through longer blog posts
- Can be impromptu
- no need to construct passages
- Takes less time for blogger
- Use video links (no embeds)
  - can only open if like
  - or if device is powerful
disadvantages
- may not be long lived
- small Word count
- overloads reader with information
  - information unfolds quickly
- leads to crucial information being overlooked
- difficult to customised pages.

Proxy Server

evaluvate
- intermediate gateway between client and websites
  - so, websies cannot log activity of user
  - cannot log IP
    - so, cannot determine geolocation
    - keeps clients identity secure + private
  - can do access control
  - can filter out unwanted stuff
  - can cache frequenly used websites
    - reduced internet usage
    - but user may recieve outdated info
    - user will not know and will use old data
  - can encrypt web requests from client (enforce HTTPS)
  - can provide VPN services (for remote access)
    - eg: students remotely accessing school network
  - high latency (as all traffic goes through the body)

Printer Server

explanation
- Accept print jobs from client devices
- Manage print job to printer
- Queue print jobs (if printer is busy)
- management of print queues
- quota of print jobs
- can enforce admin policies
- Allow authentication
  - water-marking of print jobs.

Web Server

explanation
- store html documents (on secondary storage devices)
- store media/scripts/stylesheets associated with HTML documents
- process incoming network requests
- use HTTP(S) to receive/deliver communications
- provides server-side script services (for dynamic web pages)

FTP Server

how it works
- uses file transfer protocol
- between server and client
- FTP addresses being with ftp://
  - (to indicate the protocol required to transfer)
- server listens for USER and PASS commands
  - (username and password)
- FTP uses port 21 (by default)
- active mode
  - uses port 21
  - for connection with client
- passive mode is used
  - if client is behind a firewall
  - (if unable to recieve incoming TCP connections)
  - sets up different port (for c-s data connections)
- USER and PASS are not encrypted (by default)
  - encrypted in
    - SFTP (Secure FTP - over SSH)
    - uses port 22 (ssh)
- server sends acknowledgement
  - to client
  - if valid credentials
  - and session is opened
- anonymous access can download, but not upload
- server allows checkpoints
  - so, downloads can be resumed (if interrupted)

E-Mail

explanation
- Manage email accounts
- Host domains for provision of email accounts
- Send email using Simple Mail Transfer Protocol/SMTP
- Receive email using Intemet Message Access Protocol (IMAP) / POP3
- uses store and forward model.
having own mail server
- advantages
  - can provide custom email
  - only to be used for bussiness
  - can have more emails at no extra cost
  - company can control email policy
    - authorization
  - company has more control over email
  - more secure, as we own the data
  - can archive emails
    - eg: for later reference, for legal requirements
  - can be filtered/scanned for malware
    - before delivered to employee
  - can set a max size for sender
- disadvantages
  - complex to configure
  - need experts to setup
    - expensive
  - hard to maintain
  - SMTP services of email from own server are prihibited on ISP accounts
    - extra costs
  - hard to avoid blacklists
    - eg: for bad DNS listing
how emails are sent and recieved (basic)
- Mail server provides email services to email client
- Email client sends request to server
- Server sends a response to email client
- Email client logs-in to mail server
- Rules for requests are determined by protocols
  - eg: SMTP, IMAP, POP3
- Messages are transferred between client and server
  - (from emails stored on server).

Instant Messaging

advantages
- simple to setup
- accessible any time
- accessible with any device
  - no need specific hardware
- gives real-time communication
  - (enables fast responses)
- cheaper than using telephone-systems (for long distances)
- can keep record of conversations
- less disruptive to employee workflow
- can increase productivity
  - can have simultaneous IM connections
  - to text with multiple people
  - in the same time
- can use along-side video conferencing
- group chats
- custom-written apps more secure than emails
  - specially using: end-to-end encryption
disadvantages

Other

types of transmission media (for UHD TV)
- 25 megabits/sec bandwidth needed
  - might not be available to everyone
- Satellite signals might provide it.
  - less channels
  - (unless more satellites brought to service)
- Wireless/mobile networks have restricted bandwidth
  - not enough for UHD
- 5G will make UHD available
  - but new phones needed
- Copper cable networks
  - bandwidth 100 Mbit/s (Cat 5) to 1 Gbit/s (Cat 6)
  - can provide ultra HD.
  - limited distance
    - bandwidth reduces over distance
- Fibre optic cables
  - can provide high bandwidth (10 Gbit/s).
  - expensive
  - FTC (Fibre to cabinet) may provide UHD to more homes.
  - allows much longer cable
    - (low installation costs)
  - long distances from exchange to home.

video streaming, viewing resolution affected, p3-ch2-pg71
- The more available bandwidth on the connection the higher quality of video that can be streamed
- Use of a 3G connection to the intemet limits video/streaming to low bit rate of 400 Kb/s
- Buffers not filled completely so video pauses/stops/jerky if frames not received fast enough
- Provides video of 320 x 240 pixels without apparent stuttering/buffering/stop-start issues
- This will be a poor video/low definition video as seen on the 1024 x 576 screen
- Use of a 4G connection with higher bandwidth of c. 15Mbit/s allows video with higher bitrates to be viewed properly
- This is 1024 x 576 is possible and this is HD quality
- Highest bit rates of 19/ 30 Mbit/s allowing resolutions of up to 1920 x 1080 pixels
- Available/can be streamed over Wi-Fi (IEEE 802.1 g) wireless connections....
- Which have a maximum of 54 Mbit/s
- 1920 x 1080 pixels will have to be downscaled for viewing on the smartphone screen
- Which may lead to artefacts and loss of quality.

Data Terms​

Network Classification​

LAN​

WAN​

Comparisons​

Network Models​

TCP/IP Model​

OSI Model​

Packet Switching​

Circuit Switching​

Frame Relay​

Comparisons​

similarities​

differences​

Hardware​

Routers​

Hubs​

Switches​

NIC​

WAP​

Comparisons​

Wired​

Copper Cables​

Fiber Optic Cables​

Wireless​

Microwave Transmissions​

WiFi​

Bluetooth​

Infra-red​

NFC​

Cellular Networks​

5G, 4G, 3G​

Comparisons​

Satellite Communication​

Networking Models​

Client-Server​

Peer to Peer​

BitTorrent​

Tunnelling​

VPN​

Cloud Computing​

Bit Streaming​

Real Time​

On Demand​

Protocols​

DHCP​

UDP​

TCP​

FTP​

HTTP​

HTTPS​

SMTP​

IMAP​

POP3​

SSH​

SFTP​

SMB​

TELNET​

Applications​

Forums​

Blogs​

Micro Blogs​

Proxy Server​

Printer Server​

Web Server​

FTP Server​

E-Mail​

Instant Messaging​

Other​

Data Terms

Network Classification

LAN

WAN

Comparisons

Network Models

TCP/IP Model

OSI Model

Packet Switching

Circuit Switching

Frame Relay

Comparisons

similarities

differences

Hardware

Routers

Hubs

Switches

NIC

WAP

Comparisons

Wired

Copper Cables

Fiber Optic Cables

Wireless

Microwave Transmissions

WiFi

Bluetooth

Infra-red

NFC

Cellular Networks

5G, 4G, 3G

Comparisons

Satellite Communication

Networking Models

Client-Server

Peer to Peer

BitTorrent

Tunnelling

VPN

Cloud Computing

Bit Streaming

Real Time

On Demand

Protocols

DHCP

UDP

TCP

FTP

HTTP

HTTPS

SMTP

IMAP

POP3

SSH

SFTP

SMB

TELNET

Applications

Forums

Blogs

Micro Blogs

Proxy Server

Printer Server

Web Server

FTP Server

E-Mail

Instant Messaging

Other