Wired And Wireless Networks

Wired And Wireless Networks

1. The Internet

   • Circuit Switching Network
     • When youn make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call
     • For internet there aren't enough lines for the billions of users to use Circuit Switching Networks.
       • So instead we use Packet Switching
         • Files are broken down into "packets" which are small bits of data that are sent across the internet.
           • They are then reassembled at the recepents comuputer
           • Each "packet" is given a header containing.....
             • The IP address it is going to
             • The IP address it has come from
             • The sequence number of the packet ie 5th
             • The number of total packets
             • Error checking data
           • Packets travel by the fastest possible route not the shortest distance
             • When the recpient gets there packets they are reasembled and checks the packets for errors
               • corrupt packets are requested to be resent
                 • any packets not acknowledged after a set time interval will be automatically resent
   • The internet is a collection of inter-connected networks.
   • The internet is a Wide Area Network | WAN
     • Any network in which the computers communicate using resources supplied by a “third party carrier”, such as British Telecom, is a WAN
     • A WAN uses cables, telephone lines, satellites and radio waves to connect, usually spread over a wide geographical area
   • In 1969, there were 4 internet connected networks. In 2012 2.1 billion people were internet users
   • IP Adsressing
     • IPv4 Adressing
       • every network in the world has a separate, unique address.
       • There are almost no more IPv4 addresses left so IPv6 adresses are replacing them
     • Every computer and other device connected to the Internet has an IP address
   • Hard Ware
     • The Router
       • The router is used to send each packet through the internet using the quickest route
     • Network Interface Cards
       • built into every networked device
       • MAC addressing
         • a Media Access Control is assigned to each Network Interface Card by the manufacturer
         • your computer may have more than 1 MAC address e.g 1 for ethernet and 1 for wireless
         • a MAC address looks like this: 3B:14:E6:39:0A:2C
         • Ther are 281,474,976,710,656 possible different MAC addresses possible
           • enough for 40,000 NIC per person
         • The ROLE of the MAC address
           • The actual geographical location (e.g your house) of a networked device is determined by it IP adress
             • so if you take your laptop to another part of town or a different country is IP address will change.
           • The MAC address is used to identify the device
           • When you request a web page, each router along the way uses the MAC address of the next router to send the data packet on the next leg of its journey
     • Domain Name System Technology
       • The role of DNS technology
         • it takes names such as www.google.co.uk
           • then translates it into an IP address
             • e.g. www.google.co.uk = 74.125.131.94
       • DNS Servers
         • There are 13 DNS "root" servers worldwide which keep a complete database of all names and IP addresses
           • smaller DNS servers hold smaller parts of the database
             • When a DNS server receives a request not in its database, it will pass the request on to another server until it reaches one with the matching name and IP address
               • Lower level DNS servers are owned by ISPs

2. LANs

   • What is a LAN
     • LAN stands for Local Area Network
     • A LAN operates on a single site such as a school or small business using their own cabling systems
   • Advantages and Disadvantages of Networking
     • Advantages
       • Sharing resources such as printers saves money
       • You can access your files from any computer in the network
       • Data is easy to back up as it is stored centrally on the server
     • Disadvantages
       • purchasing the network hardware is expensive
       • Managing a large network is complicated
       • Viruses may be able to infiltrate the network and infect every computer
   • Network Topolgies
     • Networks can be set up in different ways
     • Star Topology
       • Advantages
         • Fast data transfer as there are fewer data collisions
         • If one cable fails the other workstations are not affected
       • Disadvantages
         • Requires additional hardware such as the central switch
         • If the central device fails the whole network goes down
     • Mesh Topolgy
       • Nodes act as routers for data in order to relay and propagate data in the network
       • Partial mesh network model usually used, often in conjunction with star topologies to create larger networks
       • Wireless mesh networks
         • Wireless mesh networks have enormous potential to provide Wi-Fi solutions for entire organisations, cities or even countries
           • Only one node needs a wired Internet connection – no other cabling or infrastructure is required
           • The more nodes that use the network, the more the signal can travel
           • A node within broadcast distance of three other nodes, will have triple the standard bandwidth
           • As the distance between one node and another is halved, signal strength becomes four times stronger
       • Advantages and disadvantages
         • Advantages
           • No single point of failure – It is a self-healing network
           • Expansion and modification can be done without disrupting the network
           • Data can be transmitted from different devices simultaneously
         • Disadvantages
           • Can involve redundant connections
           • Expensive to install cabling if using wired connections
           • Network maintenance and administration is difficult
   • Network Hardware
     • A Network Interface Card (NIC) in your computer or device
     • A router or switch, which provides access to a local area network
     • A modem may also be combined with the router in a single device
     • Routers, Hubs and Switches
       • Router: Sends data packets on their way in the best direction
       • Hub: Central, multi-plug adaptor for computers and printers in a network. When a packet of data is received, it broadcasts the packet to all devices on the network
       • Switch: Smart multi-plug adaptor only sends packets to the intended recipient, using its MAC address. Reduces network traffic and increases speed

3. Ethernet

   • Ethernet Cable
     • The Ethernet networking standard uses twisted pair cabling or fibre optics
   • Ethernet Protocols
     • ‘Ethernet’ refers to a family of standard local networking ‘protocols’ or rules
       • It describes how devices should format data ready for transmission between computers on the same network
         • nodes will wait until the connection is quiet before attempting to ‘speak’ or transmit
           • Two nodes attempting to transmit simultaneously will stop and each wait a random period before reattempting
   • Ethernet transmission
     • Ethernet systems divide data into frames, similar to Internet packets
     • Each frame contains source and destination addresses and error checking data
     • Frames are broadcast to all nodes – only the intended recipient will open the frame. Others will be discarded
     • Frames which are detected to contain transmission errors are dropped or resent

4. Virtual Netowrks

   • Logical segments of a larger physical network (e.g. the Internet) are configured to behave as though they are part of a separate, and much smaller network
   • Transmission is encrypted since data is travelling across a space used by others

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