Communications and Network Flashcards
What is serial transmission?
- Bits sent one after the other over a single wire from source to destination
What is parallel transmission?
Multiple bits are sent simultaneously over parrallel wires drom source to destination
What is skew?
- Problem in parrallel transmission
- Each individual wire has slightly different properties
- Meaning different travel speeds when sends bits
- Meaning parrallel is only suitable over short distances (motherboard)
Why would you want to use serial over parrallel
- Skew means parallel wires are unreliable over short distances
- Serial is reliable over longer distances
- Serial is cheaper sinse there is only one less complex cable compared to parallel
- Crosstalk can occur bettween parrallel wires where there can be interference between lines leading to corruption which increases with signal
- Serial sufferes from little freqeuncy interference meaning it can carry higher frequencies meaning more data can be carried
What is synchronous transmission?
- Data transferrred at regular intervals
- Sunchronised by a clock pulse signal
- Parallel communication makes use of synchronous transmission
- Useful for real time data
What is asynchronous transmission?
- Each bit is sent speratly as soon as ready
- Each character set is paired with a parity bit and a start and stop bit
- Allows for reciver to know when new data has arrived providing a ga between sets of bits delaying the next.
What is latency?
The time delay before some component in a computer system responds to an instruction
- Home device
- Satelite
- Server
What is protocals?
- A set of rules for communication between devices
- Both devices need to use the same protocol to communicate
Controls for : - Transmission speed and method
- Error checking method
- Data transmission format
What is bit and baud rate?
Bit rate is the numebr of bits that are transferred between devices in one second
BAud rate is the number of times a signal in a commnications channel changes state
How do you increase transmission rate?
- Increase baud rate
- If there is more than two voltage states to encode binary
- The bitrate would be different compared to the baud rate
- As more frequencies can be produced
How do you calculate bit rate of a channel
Bit rate of a channel (Bits per second) = Baud rate x number of bits per signal
What is bandwidth?
The measure of the maximum capacity of a given communication channel
- The higher the bandwidth the greater the volum of data transmission
- AKA data transfer rate
What is a network topology? + List the different topologies
The wat a network and its connected devices are connected
- Bus topology
- Star topology
- Mesh topology
What is the advantages of bus topology
- Cheap to install
- Does not require additional harware beyond the main cable
- Easy to add more devices to the network
What is the disadvantages of the bus topology?
- If the main cables the whole network goes down
- Performance degrades heavily with more devices
- Security is poor as all computers can see all data transmission
What is the advantages of the star topology?
- If a single cable fails the issue is isolated
- Easy to add new devices
- Consistent performance even under heavy load
- Less likely to have data collisions
What is the disadvantages with the star topology?
- Can be costly to setup and install due to alot of caballing
- If central node goes down the whole network goes down
How do physical and logical topologies work together?
- Physical topologies would pyhsically connect devices together
- A bus topology protocal could be installed on one of the computers in the network
- Allowing for that computer to see transmission of data on the network
What is client server model
- All devices are connected to a central server
- Personal files, software
- Server is a point of failure
What is a peer to peer model?
- No central server
- No single point of failure
- Each computer acts as a client and server
- Good for internet sharing
- If one computer goes down then those files are inaccesible to the other devices on the network
What is WIFI + advatages
- A common standard for wireless network
- Cheap and easy to install and maintain
- Can transfer and handle concorrunt data and users
What are the components for wireless networking?
- Wireless network card
- WAP
- Modem + Router
- Internet
What is SSID’s
- Service set identifier (Wifi name)
- Has to be used by all devices which want to connect to the network
- Automatically broacast to any wireless device within range of the WAP
- Can be hidden and requires a password
What does CSMA/CA and RTS/CTS stand for?
Carrier sense multiple access with collision avoidence
Request to send/clear to send
Why does overlap occur?
- Multiple channels are used by multiple people
- Causing traffic within that channel
- When devices are sending requests.
What is CSMA/CA without RTS/CTS
- Data you want to send is put into a packet
- Is the channel idle? (device to wifi network)
- NO = Wait YES = Move on
- Then is transmitted across the network
How does CSMA/CA with RTA/CTS
- Packet assembled
- Is channel idle (Device to netowork)
- No=Wait Yes=Request to send (RTS)
- Then waits for Clear to Send Signal
- No=Wait Yes=Transmit Data
Why do we use CSMA/CA with RTS/CTS
- Hidden node problem
- Devices can be out of range of each other but are in range of WAP
- So they cannot communicate causing collisions
- RTS/CTS is where the WAP double checks for the devices
What is the internet?
- Intercontinenctal fibre optic lines
- Allowing for large amounts of data
- Collection of domain name server routers
- Mapping webaddresses to ip addresses
What are Routers
- Recives packets on a networks
- FOrwards to correct destination on network
- Uses algorithm to determine best method to decide on best route to the destination device on the network
What are gateways?
- Recives packets on a network and sends to correct address
- Able to deal with packets using different protocals between devices
- First strips header data from header info leaving raw data and then uses a new header format needed for a destination network
What is a packet
- A bundle of data
- Wrapped up in addtional information
- For destination information
- Error checking
What is packet switching?
- Network Interface Card (NIC) recive a message to send out data
- NIC splits the message up into equaly sized packets and number with them + Calculates each packet
- Packets are routed to ISP + Checks for packet errors
- Packes are routed to next node (speed and selection is effected by bandwith and conjestion)
- Packets arrive at the ISP of the destination computer
- Destination computer and TCP re-orders the packets into the correct sequence
- Protocal bits are stripped from packets and origonal data is passed to the application needing it
What is the protocals you have to know?
- TCP/IP
- FTP
- SMTP (POP3,IMAP)
- HTTP,HTTPS
What is FTP used for?
- File transport system
- Used for transfering files across networks
- Ports 20,21
What is the TCP/IP protocols
- Transfer Control Protocol / Internet Protocol
- Four layers of network protocals (application, transport, network, link)
What is the stucture of the URL
What are interet registers?
- Five org that governed by Internet coporationn for assigned names and numbers
- Hold database of all domain names
How are domain names organised?
- Domain names are structured into a hierachy fashion
- Smaller domains appearing lower down
- When written outyou go from bottom up
What are the steps in loading a website?
- URL request by brower from user www.codekuma.co.uk/index.js
- Browerser extracts FQDN and sends to DNS server
- Local DNS server maps the FQDN to an IP and returns to brower
- If DNS lookup table doesnt have the FQDN it passes the request to a regional DNS which has larger lookup table
- If the regional DNS doesnt have the IP then the request is sent to the NSPand DNS which has even bigger tabels and is garenteed to have the address and is sent to user and to local ISP for future
- GET request is sent to webserver
- File returend to browser from server
How do firewalls work?
- Filter communication into and out of a server
- Can be software or hardware or both
- Rules are set on the network like blacklists and whitelists
- Statefull packet insepction peaks into incoming packets and checks for patterns like virus
How do proxies work?
- Pyhsical computer between a network anda known source (webserver)
- All traffic passes in and out of a network
- Uses blacklists and whitelists and caches websites
- Ensures there is no single connection other than itself to the internet
What are the steps inasymetric encryption
- Public keys are exchanged between two people
- Person 1 uses Person 2’s public key to encrpt message
- Person 1 also uses thier private key to encrpt again creating a combined key
- Person 2 can then use thier own private key and Person 1’s public key to decrypt the message
What are the steps in using digital signatures?
- Hash function used on plaintext to produce a message digest which changes if message changes
- Craig uses private key to encrypt digital signature and attaches to plaintext message
- This is then encrypted using Daves pulic key and send to Dave
- Encrypted message is decrypted by using Dave using his private key
- Digital signiture is then extracted and decrypted using daves public key giving a message digest
- Message digest then is regenerated applying hash function to plaintext mesage
- Compare decrypted digest to regenerated digest to see if the message came from craig and is unchanged
How can you protect against malware?
What is a routable IP adress?
- IP adresses assigned to devices connected to internet
- Assigned by IANA ensuring te are unique and identified on a world wide scale
What are non-routable IP addresses?
- Assingned internally to devices on a private network
- Routers or global internet will reject them as they are in the private range
- Non-routable as no router will forward them on
What is NAT?
- Network address translation
- Responsible for converting IP addresses as they pass over the boundry between public and private address spaces
- Via a router which has a public and private IP
What are the steps in NAT and Port Forwarding?
- Computer on local network sends request to router with source and destination IP
- Router then stores computer IP in the NAT translaion table and create a random port number and attaches onto router public IP
- Request is sent to webserver from router with its own public IP and the given destination IP
- Reponse is sent from the webserver to the route with the destination and source
- Router then forwards the data to the private address of the computer in the network
What is an API?
- Application programming interface
- Set of protocols which define how two applications that can interact with each other
What is the websocket protocol?
- Modern API used for communication with a webserver
- Provides a modern, always open,bidirectional ,fast, real time interaction communication stream
- Saves transmission time, bandwidth speed and cost
- Used in games and instant messaging
What is a REST API?
- Respresentational state transfer
- Client sends HTTPS request to webserver
- Allows for javascript to send a call a HTTPS request to server on webserver to database server (Where SQL quieries are sent)
- And a JSON or XML reponses given to the web server
- Webserver then passes on response to client browser
What are the different HTTP request methods and the related CRUD and SQL database function?
What is Thick-client computing?
- Majority of processing and storage on client
- Little processing and storage done on server
What is thin-client computing
- Very little processing and stroage done on client
- Majority of processin and storage done on server
