Networks

Networks

1. topologies

   • Bus
     • A single cable connects all the computers/printer/servers.
     • Terminators are attached to each of the cable
     • advantages
       • Cheap to install
   • Ring
     • each computer is connected to the other.
     • no risk of collision
     • it is simple and cheap, but has a high risk of failure.
   • Star
     • All computers are connected to a central switch or hub.
     • A switch checks the address of the message and directs it to the correct computer
     • A hub directs every message to every computer on the network, and leaves it up to the computer to accept or reject it
     • advantages.
       • Fast – no data collisions (no computers trying to transmit on the same cable) Reliable – a broken cable won’t take out the whole network Easy to identify faults – a good switch can cut the connection to a malfunctioning device
     • disadvantage
       • Expensive to set up (needs a lot of cabling, and a central switch or hub) The whole network depends on the switch or hub, if this fails, the network fails It is possible to overload a switch if too much data is passing through it, causing slowdowns
   • Mesh
     • Large, global networks (like the Internet) use a mesh topology A full mesh has every computer connected to every other computer
     • A full mesh is only realistic for a small network Large networks (like the Internet) use a partial mesh, where each device is connected to one or more other devices In a mesh network there are multiple possible paths between any two devices
     • advantages
       • Almost impossible to break – if any node goes down, an alternative route is available
     • disadvanteges
       • Very complex, as route-finding is necessary to decide path for data Many redundant connections that may rarely be used
   • hardware
     • WAP?NIC
       • A WAP (no, not that) is a Wireless Access Point A NIC is a Network Interface Card They are the two devices needed to create a wireless network The WAP (still not that) is a wireless hub, and router which transmits and receives wireless signals The NIC plugs into a computer to receive and transmit signals from and to the WAP (seriously, not that)
         • A Wireless Access Point is a device that creates a wireless network and allows other devices to connect
         • A Network Interface Card is a device that joins the network (wired or wireless) and connects to a computer or other device
     • router
       • A router is a device that enables a whole network to join a new network as if it is one device
       • A router stores the addresses of computers on its network and transfers their data to devices on other networks
     • bridge/gateway
       • Bridges and Gateways are used to connect two networks together A bridge connects two networks of the same type A gateway connects two networks of different types
       • A bridge connects together two networks that use the same base protocols A gateway connects together two networks that use different base protocols
     • hub/switch
       • Hubs are considerably cheaper than switches, as they require very little processing Switches are more secure than hubs, as packets don’t get sent to unnecessary computers Hubs are slower than switches, as there is more chance of collision, since all the connections are used for every packet
       • A switch routes packets round a network by analysing them and sending them to the device they are addressed to A hub routes packets round a network by blindly sending them to every device it’s connected to
     • broadband router
       • Most of you will have a broadband router at home, probably provided by BT, Sky, PlusNet or something similar These devices are actually a switch, gateway, router and wireless access point all in one BT calls it’s device the “Home Hub”, which is annoying, since a hub is pretty much the only device it doesn’t contain.

2. Lan/Wan

   • LAN
     • local are network is a network within a single organisation of area. usualy using a star topology
   • WAN
     • a wide area network is a network that spans a large are , usualy using a mesh topology.