6. Networking

6. Networking

1. Local Area Networks (LANs) are a collection of computers and peripheral devices connected together on a single site, i.e school

   • Benefits
     • Sharing Resources
       • Sharing files and folders so that they can be accessed anywhere on the network
       • Sharing peripheral devices
       • Sharing an internet connection
     • Communication
       • Using email to communicate with colleagues
       • Using message systems to chat whilst you are working on other things
       • Transferring files between computers
     • Centralised Management
       • User profiles and security can be managed centrally
       • Software can be distributed across the network instead of having to install it on every machine
       • Users can use any PC and still access their own files
       • Centralised backup of all files
   • Network Topologies
     • Bus Network, computers are connected to a single back bone cable . All computers share the cable to transmit to each other, can result in problems if theres lots of traffic
       • Advantages
         • Easy and inexpensive to install
         • Easy to add new computers
       • Disadvantages
         • If the main cable fails then the whole network goes down
         • Performance slows down as the amount of traffic increases
     • Ring Network, Computers are connected to adjacent computers in a ring . Computers take it turns to transmit, controlled by passing a token around the ring. Computers can only transmit when they have the token
       • Advantages
         • Not dependant on a central computer like a star network
         • Token passing protocol is simple and reliable
         • Consistent performance even when there is a lot of traffic
       • Disadvantages
         • A single link failure disrupts the entire network
     • Star network, all computers have their own cable connecting then to the central computer which controls the network. This is usually a switch or server
       • Advantages
         • If a cable fails only one station is affected
         • Consistent performance even when a network has heavy traffic
         • Easy to add new computers
         • More secure
       • Disadvantages
         • Can be costly to install due to cabling
         • If the central computer fails then the whole network goes down
       • Used in most classrooms/ offices. Computers are star wired to a hub or switch nearby. The room may look like a bus network but the ducting has cabling for each computer
         • A hub is a hardware device that provides connectivity to a LAN cable. A multiport box that has connection to the LAN from one side and several computers on the other
         • A switch is similar to a hub but has built in intelligence to direct traffic to the correct place
   • Peer to peer, a method of organising devices in a network where devices are all of equal status rather then having specialised roles . Each computer can access resources on another computer assuming access rights have been granted
     • Suitable for small networks
     • Easy to set up and maintain
     • Each computer must be backed up centrally
     • No dependency on a server
   • Each computer must have a network Card (NIC to connect to the LAN
   • Client server, a method of organising devices in a network where some computers have specialised roles , servers. The server provides resources and service to the other computers known as clients. Management of the network and shared resources/ files is centralised at the server
     • Managed by a central powerful computer called a server
     • Client computers communicate via a central server
     • There may be other computers that act as email servers, print servers and web servers
     • Not practical for smaller networks because it would not be cost effective to have someone to manage the network, usually a network manager
     • Back ups done from central server

2. Wide Area Network (WAN) is a collection of computers and networks connected over a geographically remote area

   • Geographically remote does not mean that networks have to be miles apart, but is more to do with what separates the sites, i.e. if a motorway separates 2 sites then they would need to be connected with a WAN
     • WANs use hire infrastructure to connect the LANs together
     • Use routers to make up the network. IP is the protocol used between these routers

3. How devices communicate on a Network

   • They follow rules called protocols, which govern everything from how the communication will start, to the transmission speed and how the bits will be delivered
   • Internet protocol (IP) how computers and routers communicate on the internet
   • MAC Addresses are unique reference numbers. Each NIC will have a MAC address so that data knows where it should be delivered MAC addresses are only used to address devices inside a LAN
   • Packets are the small chunks a message on the LAN is broken down into. The packets have the MAC address of the destination device . The destination will see all the traffic on the LAN but only pick up the packets with its MAC address on them, can be compared to a luggage conveyor belt in an airport

4. The Internet

   • Internet protocol
     • Each device on the internet must have a unique IP address so it can communicate over the WAN
   • When searching on the internet people use domain names to search for their desired website. Each website has a unique IP address. The domain name, i.e. www.bbc.co.uk must then be translated into the correct IP address. This is done because human are bad at remembering numbers
     • The Domain Name System Server (DNS) has a database of domain names and IP addresses so it can translate
       • There are lots of DNS servers on the internet that communicate with each other and update each others data
       • Advantages,
         • Humans do not need to remember or type in numerical addresses
         • If the IP address changes at some point the DNS servers can update the database so that the humans can still use the same domain name
   • Hyper Text Transfer Protocol (HTTP) is the protocol used to request and deliver webpages
     • Added to the front of the domain name you type in a browser
   • Packet switching on the internet
     • Messages are split into packets, to get from one device to another. At each router the IP protocol decides which way to send each packet. The router has to know the sources and the destination device to make appropriate routing decisions. The packets could get out of sequence so contain a packet sequence number so the message can be reconstructed.
   • Connecting to the internet
     • Modems, cheapest and slowest form of connection, only 56kb/s so no longer are popular
       • Uses the telephone network to create a connection from your PC to the internet
       • The telephone network is analogue and is designed for voice traffic. The modem converts to digital signal from a computer into analogue signal and visa versa
       • If on the internet you can not use your phone which can be problematic
     • Local router usually wireless for all devices to connect to
       • Can be connected by fibre optic cable
       • Can be connected by using the phone line cable but uses broadband technology
         • Uses a wholly digital signal unlike a modem