1.3 Exchanging data

• What does the application layer do

  Provides interface between user applications and network
• What does the transport layer do


  establishes end to end connection

  splits data into packets

  adds header with: sequence number, source and destination port

  (if not UDP)

  requests lost packets
• What does the Internet layer do

  Adds source and destination IP to the header

  Adds time to live to the header
• What does the link layer do

  Adds the MAC addresses of the source and destination IP
• What protocols act in the transport layer

  UDP

  TCP
• What protocols act in the application layer

  FTP

  SMTP

  DNS

  HTTP(S)

  POP
• What protocols act in the network layer

  IP
• What protocols act in the link layer

  Ethernet

  ARP
• Packet routing

  Router checks if destination IP matches, if not sends to next router on best path towards web server

  (TTL reduces by one)
• What are the routing table protocols

  Routing Information Protocol (RIP)

  Open Shortest Path First (OSPF)

  Border Gateway Protocol (BGP)
• What does the routing table do

  Routers automatically exchange up to date information with each other to find best path
• Benefits of layering like TCP/IP

  Decomposes a large problem into smaller problems that are easier to solve

  Assists in protocol design, must work with layer above and below (not all)

  Prevents technology changing in one layer affecting all layers
• What does the DNS do and how

  Translates the names into IP addresses (names i.e com, co.uk, www)

  Partitions memorable names with dots
• Benefits of DNS

  Allows the IP address to change but the Domain Name to stay the same

  Allows for unique names
• What is a protocol

  A protocol is a set of rules for communication between two devices
• Type and description of protocol standards

  De jure: regulation by official bodies

  De facto: rise up through popular use, for example font choice
• Why are standards important

  Form the building blocks for product development by establishing consistent protocols

  Without standards only hardware and software from same provider would be compatible
• Why are protocols important

  Allows devices to communicate by ensuring all devices follow the same rules and therefore interpret data in the same way
• What is a LAN


  Geographically small area (School, building)

  Equipment is owned by company using it
• What is a WAN


  Geographically large area (continents)

  Connects LANs together using third party equipment (e.g BT)
• What is a hub


  Piece of network equipment that sends all incoming data to all connected ports
• What is a switch


  Piece of network equipment that sends incoming data to the intended recipient using MAC addresses
• What is a Wireless Access Point


  Piece of network equipment that connects to a switch and allows WIFI devices to connect to the network
• What is a Network Interface Card


  Piece of network equipment that connects the device and the network
• What is a router

  a network device that forwards data packets between networks
• What is a repeater 


  network device that amplifies and regenerates an incoming signal
• What threats are there and their relevant security types(cybersecurity)

  Confidentiality - keeping data private (phishing, hacking)

  Integrity - Preventing data modification (SQL injection, MMA)

  Availability - Keeping network services running (Ransomware, DDOS)
• What is a proxy server

  A server that sits between a device and the firewall, keeping the clients IP address hidden.
• Facts of lossy compression

  Some data is permanently removed during compression

  Provides more compression than lossless

  Popular where data removal is not noticeable (audio)
• Facts of lossless compression

  All original data can be recovered when uncompressed

  Used with text

  Not normally applied to video
• What is dictionary encoding

  Lossless method used for text

  Any data matching a value in a lookup table is substituted with a value with fewer bits
• What is run-length encoding

  Lossless compression for images

  Replaces sequences or identical data with code indicating the data and the number of repetitions
• Benefits of compression

  Reduces storage space needed

  Reduces data usage and wait times to download
• What are the two types of encryption

  Symmetric

  Asymetric
• Facts of symmetric encryption


  Same key is used to encrypt and decrypt the message

  Both sender and recipient must know the key

  Symmetric encryption is faster as it uses less complicated mathematical operations

  Key exchange is the weak point
• How asymmetric encryption works

  Two keys public and private are used

  Someone sends a message to you encrypted with your public key

  Can only be decrypted with the private key which only you have access to
• Pros and Cons of asymmetric encryption

  More robust

  Additional security of authentication

  Slow because complex mathematically
• What is a hash

  An algorithm who's output is called a digest

  The digest can not be reverted back to the original value. A collision is a situation when two distinct pieces of data have the same hash
• How can hashing be used to detect tampering

  Hash the original data

  Send it across the network with the original data

  On the other side of the network use the same hash, if the two digests do not equal the data has been tampered with
• Uses of hashing

  Tamper detection

  Searching and storing arrays