Computer Networks Flashcards
What is a computer network?
A connected network of computers (or printers, phones and other devices)
Why do we have computer networks?
To share data (documents, images, videos and so on)
How are devices connected in a computer network?
Wires or waves
Name three types of networks.
LAN (or WLAN) -Local
MAN - Metropolitan
WAN - Wide
WLAN
Wireless Local Area Network
MAN
Metropolitan Area Network - eg between universities or hospitals in a large city
WAN
Wide Area Network - Spans more than 30 miles, made up of multiple MANs. The Internet is the most known WAN.
Parts of a network
Nodes - the connected devices
Communications media - How data is transferred (wires or waves)
What is a server?
A special computer accessible to many users.
What is a webserver?
Webservers are special servers accessible to anyone (with an internet connection), very powerful, a lot of memory.
What is a request?
A message sent to a webserver requesting something (files)
What is a client?
A device used to access the Internet. Recives file or data from server.
What is a host?
The server, sends the file or data to the client.
What component is needed in a computer to access the internet?
NIC - Network Interface Card
What is a protocol?
A set of rules governing communication - format and order.
What three parts are in this URL:
http://www.website.com/file.html
http:// - protocol
www.website.com - server name
/file.html - file
What is network topology?
It describes different ways to lay out a network.
Name 4 network topologies.
Bus
Ring
Star
Mesh
What defines a bus network?
1 main cable and a terminator at each end to absorb signal. Cheap but breaks easily.
What defines a ring network?
Each node connected to the next. Data hits each node until it reaches its destination. More common to use two rings with inverse data flow.
What defines a star network?
All nodes connected to central node (router). Easy to expand, most common(?) like a WLAN. If central node breaks it all breaks.
What defines mesh network?
All nodes connected to all nodes. Built in protection, data always has alternate routes. Very expensive, lots of communications media.
What layers are in the OSI - model?
- Application
- Presentation
- Session
- Transport
- Network
- Data link
- Physical
OSI - model
Open Systems Interconnection - model
Application layer?
The software that the user is looking at
Presentation layer?
OS, letters and numbers (what we can understand)
Session layer?
Conversation between two computers (getting data from a web server for example)
Transport layer?
A packet is a chunk of data, packets are delivered reliably, in the proper order and according to how the protocol needs it
Network layer?
Determines best route for data (routers are involved on this layer)
Data link layer?
NIC’s/checking for errors in data
Physical layer?
Cable/fiber optics - any electric signals involved
What does a modem do?
Connects your network to internet service provider.
What 3 things does a router do?
- Connects via ethernet cable to modem.
- Decides the route that the data is going to take.
- Join networks together, your network with the internet for example.
What does a switch do?
Give more ports in router for devices. Can be managed / unmanaged. Managed switch gives more settings and control.
What does a repeater do?
Boost a weak network signal. Not only for WiFi. 100m is max for ethernet cable, use wired repeater. Switches also work as repeaters.
What two parts are in a IP address?
Network id,
Host id
What decides what part of an IP address is host / network?
Subnet mask
What two problems are solved by subnet mask?
Networks can be different sizes
No ip addresses are wasted
DHCP
Dynamic Host Configuration Protocol
What does DHCP do?
Assigns IP adresses in a network to connected devices.
What does a device do when first connecting to a network?
Send out ‘discover message’ from default IP 0.0.0.0
What happens when the router hears a ‘discover message’?
Router looks through all IP adresses available in the network. Offers the first available to the new device - the computer requests it - router sends “Ack”.
DNS
Domain name system
What does the DNS do?
Translate domain names like www.google.com to IP addresses - and back.