SLR 21 - networks and the internet Flashcards
What is a topology ?
Refers to the structure of a network
What are the two types of topology?
- physical and logical
What is a physical network topology?
- refers to the actual architecture of a network
- the two types are star and bus
How is a physical star topology connected?
- each client in a network has its own direct connection to the central hub
- the hub receives packets from all clients and is responsible for correctly delivering them to recipients
- a serve can be connected in the same way the clients are connected to the central hub
What are the advantages of a physical star topology?
- packets are sent through a direct connected to recipient (other clients can’t see them)
- its easy to add and remove clients from a network
- collisions don’t occur because each cable communicates for one device
- the rest of the network wont be affected if one cable fails
What are the disadvantages a physical star topology?
- if the central hub fail, all communication over the network is stopped
- expensive to install because of the amount of cables
What is a physical bus topology?
- clients are connected to a single main cable called the backbone
- a terminator is placed at either end of the backbone
- a server could be connected to the backbone like a star another computer
What are the advantages of a physical bus topology?
- there is no central hub, so network failure is less likely
- its less expensive as less cabling is required
What are the disadvantages of a physical bus topology?
- packets sent through the shared backbone (clients can see all the packets not intended for them)
- there is a risk of collisions
- the entire network becomes unusable
What is a logical network topology?
a logical network topology refers to the flow of data packets in a network
What is the process of a logical bus versus a logical star?
- logical bus delivers packets to all clients
- logical star delivers packets only to their recipient
- stars can act like buses and vice versa e.g., a set up is physically a star but sends data to every device in the network
What is a host?
- A device on a network that provides services
- the server and the clients can be hosts
What is a client server network?
- servers are connected in the same way as clients but are more powerful
- clients request services from the server and they respond to the client by providing a service
Why would schools use a client server?
- it allows for central management
- it can improve security
How does a peer to peer network work?
- services are provided by the clients themselves
- every client has an equal status
Disadvantage of peer to peer:
- all clients providing service must be running for the network to be fully operational
- e.g., client managing data storage breaks and no one can pen their file
Advantage of peer to peer:
- is more cost effective as there is no need for a powerful server
- much easier to set up and maintain
What do large file sharing networks use
- use peer-to-peer networking to provide high
performance services without the requirement for a server
What is WiFi?
it is a local area wireless technology that connected devices together using WAPs, that is based on international standards
How does WiFi work?
any wireless device meets specific standards allowing interoperability and backward compatibility
What was formed in 1999?
the WIFI Alliance was formed to establish international standards for interoperability and backward compatibility
What does connecting to a wireless network require? where can this be found?
- a wireless network adapter
- most computers come with integrated n the mother board
What is a station?
the combination of a computer and the interface controller
what do stations share?
a single radio frequency communication channel, which they tune to the frequency of in order to pick up transmissions
What receives transmissions ?
all the stations within the range of the wireless access point
How does the WAP connect to the internet?
WAP usually connects to a router, but it can also be integral part of the router
What do you use to secure a wireless network?
- WPA (Wi-Fi Protected Access)
- Wi-Fi Protected Access II (WPA2)
What is WPA2?
- it is built into wireless network interface cards
- it provides strong encryption of data transmissions
- it has a new 128-bit key being generated for each packet sent
What does SSID stand for and what is it?
- SSID = Service Set Identification (the informal name for a network)
- e.g., Home223
- the purpose is to name the network so you can identify it as your computer will be in range of several networks
What an you do to the SSID?
You can disable the broadcast of your SSID from others looking to connect to a named network
What is a whitelist?
- uses MAC addresses to control who is allowed on networks
- addresses are assigned to every wireless device by their manufacturer and are unique to that device
- blacklists ca also be used to block specific devices from connecting to a network
What is CSMA/CA?
- (Carrier Sense Multiple Access/Collision Avoidance) is a protocol for the carrier transmission in wireless local are networks
What is CSMA/CA used for?
it avoids collisions in data networks caused when multiple devices communicate simultaneously
What does a device do when its ready to transmit?
- it listens to its communication channel to check whether it is idle
- if so, the data is transmitted
- if not, the device waits for a random period of time before checking the channel again
What can be used to increase the time period a device will wait between each channel check?
an exponential backoff algorithm
What is a hidden node?
it’s when a node can communicate with a (WAP), but cannot directly communicate with other nodes that are communicating with it - they cant see each other.
What protocol deal with hidden nodes? how.
- Request to send/clear to send (RTS/CTS)
- Its an additional step in the CSMA process
- when the channel is idle it sends a ‘request to send’ to the server
- If its clear the server responds with a ‘clear to send’ message
