Networks

Networks

1. LAN

   • local area network
     • small geographical area
     • all hardware is owned by the organisation that owns it
     • either wired - Ethernet cables - or wireless - wifi
   • will have them at businesses, schools or universities
   • a lot of homes have a LAN to connect devices
     • e.g. PCs, tablets etc
   • why LAN?
     • Sharing files is easier - access same files and work collaboratively
       • and copy files between machines
     • internet connection can be shared with every device on it
     • can update computers all at once
     • instant communication - instant messages - cheap and easy
     • user accounts can be stored centrally, so users csn log in from any device on the network

2. WAN

   • connects LANS
   • wide area network
   • e.g. a business often has a office in 3 different countries and would need a WAN
   • organisations hire infrastructure - communication lines - from telecommunication companies
     • WAN is a lot more expensive than LAN
   • may be set up using copper or fibre telephone lines, satellite links or radio links
   • internet is biggest WAN

3. performance of networks

   • bandwidth is the amount of data that can be transferred at a given time
     • the greater the bandwidth, the better the network can perform
   • available bandwidth is shared between users of network
     • to many users or heavy use may cause congestion and slow network
     • you can limit bandwidth available to individual users to stop this
   • wired connections are normally more reliable and faster
     • fibre optic cables are better than copper cables
     • wireless depends on signal quality so if affected by range of device
       • amount of interference and physical obstructions affects this
   • choice of hardware other than cables and network topology affects it too

4. hardware

   • NICS, SWITCHES AND ROUTERS
     • network interface controller(NIC) is internal
       • allows device to connect to network
       • built into motherboard
       • for wired and wireless connection
     • switches connect devices on LAN
       • receive data in frames (unit) from one device and transmit data so another device of the network with the correct MAC address
     • router are for transmitting data between networks
       • always connected to at least two different networks
       • directing data in units called packets to destination
       • can be used in homes or offices to connect LAN to internet
         • most routers in homes are all-in-one with router, switch and WAP
   • cables
     • Ethernet cables are used to connect devices in LAN
       • most common are CAT 5e and CAT 6
         • twisted pair cables, containing 4 copper wires, twisted together to reduce internal interference
     • coaxial cables are made of a single copper wire with a plastic layer for insulation
       • also metallic mesh to shield from outside interferences
     • fibre optic cables transmit data as light
       • high performance - expensive - and don't suffer from interference
         • transmit over very large distance without loss of signal quality
   • wireless uses radio waves to transmit data
     • you need a WAP (wireless access point)
       • which is like a switch that allows devices to connect wirelessly
     • NOT A HOTSPOT
       • a hotspot is a location you can connect to a WAP
     • devices need wireless capability
       • normally built in
       • can use a USB dongle - HDMI dongles are popular iv TVs
   • WIFI is the standard to wireless networks
     • uses two radio frequency bands - 2.4GH and 5GHz
       • 2.5GHz has a greater range and better at getting through walls and obstructions
       • 5GHz is faster over small distances
     • the bands are spilt into numbered channels that each cover a small frequency range
       • have the 2.4GHz overlap
     • affected by interference using adjacent channels
       • to avoid problems only certain channels that are spaced tend to be used
       • 5GHz band has non-overlapping channels so less chance of interference

5. client server and peer-to-peer networks

   • client servers are managed by the server and connect clients
     • files and software are stored centrally on the server
     • client send requests and server processes and responds
     • server stores user profiles, passwords and access information
       • may request password before doing request or is may deny a request if not the right access level
     • most uses of internet work of this
       • websites hosted of web serves
       • web browsers are client programs and send requests to web servers
         • web servers fulfil requests for thousands of clients
     • pros
       • easy to keep track of files - central
         • easy to install and update software
         • easy to manage network security
       • easy for backups
       • reliable and always on
     • cons
       • expensive and need IT specialists to set up
       • server dependence - if server goes down then all clients go down
       • can become to overloaded if all using it at once