Networks Flashcards
Exchanging data
What is protocol
A set of rules for communication between devices
They allow different devices to make sense of the data they receive and transmit.
What is meant by layering
The principle of dividing a complex problem into separate, independent sub-problems
How can packets travel across the internet
Each packet has layers of further data added to it
What are some of the features of layering
- Allows for the creation and maintenance of parts of a system without having to take into account the whole system
- Networks use layering with protocols
- Protocols on each layer communicate only with the layers above and below.
What does the transmission control protocol/ Internet protocol (TCP/IP) stack consist of
- Application layer
- Transport layer
- Internet layer
- Link layer
What is the purpose of the application layer (TCP/IP stack)
It specifies what protocol needs to be used to relate the application that’s being sent.
- For example, if the application is a browser then it would select a protocol
Examples - HTTP, HTTPS, IMAP
What is the purpose of the transport layer (TCP/IP stack)
Establish an end-to-end connection
between the source and recipient computer.
Splits data up into packets and labels them with:
- packet number, the total number of packets the original data was split
up into and the port number being used for communication.
- If any packets get lost, the transport layer requests retransmission of these
lost packets.
Examples - TCP
What is the purpose of the network layer (TCP/IP stack)
Concerned with providing links across different network types.
- Adds the source and destination IP addresses (socket address)
(router operates at this level)
What is the purpose of the Link layer (TCP/IP stack)
Passes data to the physical network.
- connection between the network devices (adds the MAC address identifying the NIC of the source and destination computers )
Example - Wi-Fi, ethernet
How is a packet sent across a network
Encapsulating the data
- The packet is sent down the stack, starting with the application protocol, and each protocol adds its own additional necessary data.
Decapsulating the data
- Once the data has arrived at its destination it is passed back up the stack and each protocol removes relevant data
What is a URL
Uniform resource locator
- The main part of the website address e.g. hodder.co.uk
We use them because they are easier to remember than an IP address
What is the purpose of a domain name server (DNS)
Converts URLs to IP addresses
- The system uses a series of servers that act like address books, matching URLs to their IP addresses.
How does the DNS work
(long answer)
- First, your computer checks the local cache to see if the IP address has previously been found
- If it doesn’t have a copy of the IP address, it checks one of the root servers. (root servers are the highest level of servers in the DNS that hold the locations of all the top-level domain servers)
- If the root server doesn’t have a copy it points to a server matching the top-level domain (TLD) such as .com, .uk or .org
- These may point to the second-level domains (e.g. .co.uk)
- finally comes the authoritative name server that holds the IP addresses of the server being sought. This is sent back to the browser so it can visit the site
Once the address is found, as it gets passed back to each server the address is cached so it can be found more quickly next time
What is a LAN
Local area network
- Networks over a small geographical area
- Their infrastructure is owned by the organisation that uses it, and the organisation is also responsible for its upkeep
What is a WAN
Wide area network
- Network over a large geographical area
- Consists of interconnected LANs
- The internet can be considered a WAN
What is circuit switching
A pathway for the data is set up in advance of communication and then the data is sent across it. The pathways are closed after transmission. (provides an exclusive dedicated channel)
Usually used for live broadcasts eg. a phone call
What are the three stages of circuit switching
- connection established
- data transferred
- connection released
What is packet switching
Packages of data are sent across a network. They may take different routes and are reassembled by the receiver.
What is a data packet
Data is broken down into chunks called packets when sent across a network.
What does a data packet contain
Header
- Source address and Destination address
- Packet sequence number (the order of the packet in the sequence)
- Protocol (the type of protocol being used)
Payload
- The actual data being sent
Trailer
- Checksum (used for error checking )
- End packet maker (denotes the end of the packet)
How does packet switching work
- Packets are sent across a network by whichever routes are available or most efficient
- They may arrive in a different order to which they are sent
- The receiver uses the sequence number to reassemble them into the original message
What is good about packet switching
- It doesn’t tie up large chunks of the network, making it perform better for multiple users
- It is also part of what makes the Internet reliable; if one route is unavailable, there is always others
(redundancy boosting reliablilty)
define hacking
The process of gaining unauthorised access to a computer system
what is a firewall
Software that can inspect and block incoming and outgoing network data
What is a proxy
A server that sits between a network and the internet, through which internet data requests are made
How do firewalls work
usually hardware devices but can be implemented as software
- Inspect data entering and leaving the network
- Can block these packets according to a set of rules
- Can be configured to restrict access to certain sites or file types
What are the functions of a proxy
- Catching
- Logging and monitoring traffic
- Security
- Privacy
Describe catching (functions of a proxy) LA
- Once a proxy receives a request for a file or website from the internet, a copy is stored on a proxy
- Every subsequent person who requests the same file can get their copy directly from the proxy
This is quicker for the users and keeps bandwidth being used on the internet connection
However, the file or website on the proxy might get out of date
Describe logging and monitoring traffic (functions of a proxy )
A proxy can monitor data going into a network. They can keep logs of all traffic in and out
Describe how a proxy provides security (functions of a proxy)
External users are unable to see or access devices inside the network - their only contact is with the proxy
Describe does a proxy provides privacy (functions of proxy)
Proxies can be external to a network and used to fetch web pages
As far as the website is concerned, the request comes from the proxy and therefore it is the proxy’s IP address that is logged on the website, not the user’s.
What is Encryption
The process of making data unreadable to a third party. It has to be decrypted to be read.
What are the two ways encryption can be used on a network
- Stored data can be encrypted
So it cannot be read by anyone who may gain unauthorised access to a private network - During transmission
This is crucial especially if transmission is taking place across public communication channels or using wireless tech.
What is a client-server model
This is when high-end computers (one or sometimes many) act as servers that provide services to users or clients.
Give 4 examples of services provided to a user (client-server)
- File storage and access
- Printing
- Internet access
- Security features such as logins and audit trails
4 advantages of a client-server model
- client computers don’t need to be powerful do can be cheaper
- It makes it easier to make data and software accessible from anywhere in the network
- Banks of servers can be combined to make best use of their potential
- Separate functionality can be devolved to virtual servers or physical servers
What is a virtual server
A server that exists as a virtual machine, rather than a physical device dedicated to the task
What is a peer-to-peer network
When each computer on the network has an equal status
3 advantages of a peer-to-peer network
- Cheap way of implementing a network
- Popular way on the internet to pass files between users without the need to go through servers
- Useful way to make use of distributed computing to promote collaborative working
What is distributed computing
A collection of computers working together on a single task
What is the HTTP
Hypertext Transfer Protocol
- Used for web page rendering, an encrypted version
HTTS is also becoming common
What is the TCP/IP
Transmission Control Protocol/ Internet protocol
- This is a networking protocol used in the routing of packets through networks
What is the POP3 and IMAP
Post Office Protocol
Internet Message Access protocol
- Mailing protocols, used for email access
What is the FTP
File transfer protocol
- Used for the transmission of files over networks
