4.9 - Communication and Networking Flashcards
Serial Data Transmission
Data is sent via an interface, one bit at a time.
+ Very high rates of data transfer
+ Reliable over long distances
+ Higher net rate of data transfer
+ Smaller and less complex
+ Cheaper
Parallel Data Transmission
Multiple bits sent simultaneously over multiple wires. Used in RAM and other ICs.
- Each wire has slightly different properties, causing skew.
- Reliable over short distances.
- Interference between wires (crosstalk).
Bit Rate
Rate of data transfer
Baud Rate
Rate of signal change on a transmission medium
Equation for bit rate
Bit Rate = Baud rate * bits per signal
Bandwidth
Range of frequencies that can be carried by a transmission medium. Directly proportional to bit rate.
Latency
Delay between transmission of first bit and last bit recieved.
Synchronous Data Transmission
Data is transferred at regular intervals, per clock pulse. Allows for a constant and reliable data stream, often used in parallel transmissions (e.g. inside computer).
Asynchronous Data Transmission
Data transferred byte-by-byte. Each character is proceeded by a start bit and preceeded by a stop bit.
Protocol
Rule for communication between devices.
LAN
Local Area Network.
A collection of devices within a single building or site connected together.
Bus Topology
A single main cable that all devices are connected to.
Star Topology
Central node that all devices are connected to by their own link.
Logical Topology
The path the data travels in, rather than the physical layout of a network.
MAC Address
Unique 48-bit address to identify a device. Written in HEX.
Benefits of a Bus Topology
Cheaper than star topology.
Drawbacks of a Bus Topology
Will fail if the main cable fails.
Performance will decrease under heavy load.
Not ideal security, as every computer has access to every transmission.
Benefits of a Star Topology
Easy to locate faults.
Performs consistently.
No data collisions.
More secure as transmissions are only sent to the central device.
Easy to install new devices.
Drawbacks of a Star Topology
More expensive due to quantity of cabling required.
Will fail if the central device fails.
Client-Server Network
Every client is connected to a powerful central server and can hold their own files (although these are also stored on the central servers).
Peer-to-peer Network
Computers are connected to each other over a LAN or a WAN.
Benefits of a Client-Server Network
Good security as access rights controlled by central server.
Centralised control over backups, updates, printers, etc.
Easy to share resources across the network.
Drawbacks of a Client-Server Network
Expensive installation.
Professional IT staff required.
Benefits of a Peer-to-Peer Network
Cheap to set up.
Users can share resources.
Easy to maintain.
Drawbacks of a Peer-to-Peer Network
Widely used for piracy.
No centralised control.
WiFi
LAN technology that allows wireless connections.
Requirements for WiFi
Router
Wireless Access Point
Wireless Network Adaptor
Wireless Access Point
Allows WiFi-enabled devices to connect to a network.
Wireless Network Adaptor
Small component of a device that allows it to connect to WiFi.
WPA2
WiFi Proteced Access 2.
Encrypts transmissions.
SSID
Service Set Identifier.
CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance.
Protocol for data transmission on a wireless network.
Frame
Consists of data being sent and other info such as the header.
RTS/CTS
Request to Send / Clear to Send.
Used to check if a reciever is ready to recieve.
ISP
Internet Service Provider
URL
Uniform Resource Locator.
Address of a resource on the internet.
Contents of a URL
Protocol, host, domain name, folder, file.
TLD
Top-level domain (e.g. .com, .uk, .org)
DNS
Domain Name Service.
Stores each IP address so it knows where to find each resource.
FQDN
Fully-qualified domain name.
Includes host server name, domain name, TLDs.
Internet registries
5 global companies that have databases that hold records of all domain names.
Data Packet
Small chunk of data to be transmitted across a network.
Contents of a data packet
Header, payload and sometimes trailer.
Data Packet Header
Contains info such as sender/destination socket addresses, protocol, TTL.
TTL
Time to live.
Time until packet is destroyed.
Router
Connects multiple networks together.
Gateway
Translates between protocols.
Firewall
Hardware/software method of preventing unauthorised access to a network.
Aspects of a firewall
Packet filters.
Stateful inspection.
Proxy servers.
Packet Filter
Examins socket address to decide whether to allow/deny the packet access to the network.
Stateful Inspection
Examins packet payload to decide whether to allow/deny the packet.
Proxy Servers
Intercept data packets in order to disguise their origin/destination.
Encryption
Scrambling of data into ciphertext using a key.
Ciphertext
Scrambled data that is uninterpretable without a key.
Symetric Encryption
Using the same key to encrypt and decrypt.
Asymetric (Public Key) Encryption
Using 2 separate, unrelated keys to encrypt and decrypt.
If A encrypts data using B’s public key, who can decrypt and and with what?
B can decrypt using B’s private key.
Public Key
Avaliable to all.
Private Key
Avaliable to one user only.
Digital Signature
Used to verify the authenticity of a transmission.
Digital Certificate
Used to authenticate the sender of a transmission.
How are digital signatures used to verify a message’s authenticity? (9 Steps)
- Digest produced from the message using a hash function.
- Digest encrypted using the sender’s private key. This is the digital signature.
- Signature added to the original message.
- Whole thing encoded by public key encryption (i.e. using reciever’s public key).
On recieve… - Decrypt with reciever’s private key.
- Separate message from signature.
- Decrypt signature with sender’s public key.
- Run the same hash function on the decrypted signature.
- Compare decrypted digest with newly generated digest.
TCP
Transmission Control Protocol
IP
Internet Protocol
Application Layer
Selects the necessary protocol for data transmission.
Transport Layer
Uses TCP to establish a connection with the recipient. Splits data into packets, each with a sequence number, total number of packets and port.
Network Layer
Adds origin/destination IP to form the socket addresses. Routers operate on this level.
Link Layer
Physical connection between different nodes on a network. Adds the MAC addresses from the origin/destination NICs.
Why do the MAC addresses of packets change after each ‘hop’?
The packet passes through a new node, so MACs must change to reflect that.
FTP
File Transfer Protocol
HTTP(S)
Hypertext Transfer Protocol (Secure)
SSH
Secure Shell
POP3
Post Office Protocol v3
IMAP
Internet Message Access Protocol (keeps emails on server).
SMTP
Simple Mail Transfer Protocol.
Port 20/21
Commonly used for FTP.
Port 22
Commonly used for SSH.
Port 23
Commonly used for Telnet.
Port 25
Commonly used for SMTP.
Port 80/8080
Commonly used for HTTP.
Port 113
Commonly used for POP3.
Port 143
Commonly used for IMAP.
Port 443
Commonly used for HTTPS.
IPv4
Dotted decimal address format that uses 32 bits (4 bytes).
IPv6
128 bits, expressed in hexadecimal.
2 parts of IPv4
Network ID
Host ID
Classful IPs
Use different classes to determine the length of each part of the IPv4 address. Class A has 1 byte for network ID, class C has 3 bytes for network ID.
Classless IPs
Number of bits in the subnet mask is specified (e.g. 122.324.654.211/24)
Subnet Mask
Separates network/host IDs once bitwise ANDed with the IP.
Subnet
Segment of large network with a unique identifier in the IP.
Public IP
Routable.
Accessible from any computer in the world.
Private IP
Non-routable.
Accessible on the LAN only. Requires NAT to access other resources/be accessed.
DHCP
Dynamic Host Configuration Protocol.
Dynamically assigns IPv4s as and when they are requested.
Used on LANs and WANs.
NAT
Translates and forwards data between routable and non-routable addresses.
Port Forwarding
Allows external devices to communicate with those on a LAN.
Client-server Model
A client requests data from a server and then recieves a reponse from the server.
API
Application Programming Interface
Group of protocols that instruct applications how to interact with each other.
REST
Representational State Transfer
Way of designing an API that uses HTTP requests for clients to interact with a database.
JSON
JavaScript Object Notation
Compared to XML…
- easier to read
- more compact
- easier to create
- easier and quicker to parse
XML
Extensible Markup Language
Compared to JSON…
- more flexible structure
- wider range of data types
Websocket Protocol
Defines an API that allows for a full duplex connection between client and server (data can be sent at any time). Reduces packet header size.
CRUD
Create, retrieve, update, delete.
Fundamental operations of a DBMS
Thick-client
Handles all processing and storage on the client machine.
Thin-client
Server does all processing, storage, etc.
