4.9

4.9

1. Communication

   • TRANSMISSIONS
     • Parallel Transmission
       • Advantages
         • faster, more transferred bits per cycle
       • Disadvantages
         • less reliable over long distances, more costly
       • Description
         • each bit is sent at the same time on different channels
       • used for short distance
     • Serial Transmissions
       • Advantages
         • easier set up, cheaper hardware, better over distances, less wire bulk
       • Disadvantages
         • only one bit per cycle
       • Description
         • transmission where bits are sent on the same stream one after the other
       • used for peripherals and longer distances
     • Synchronous Transmission
       • transmission accompanied by a clock system to sychronise transmission
     • Asynchronous Transmission
       • transmission synchronised by start/stop bits in transmission medium
     • Latency
       • time between transmission start and transmission effect, time for bit to be transmitted.
     • Protocols
       • the set of rules that govern how a transmisson should be carried out, normally decided by either the transmitting machine or recieving machine
     • Rates
       • Bit
         • number of transmitted bits per second
       • Baud
         • number of signal changes a wire can handle beofre signal warps
       • Bandwidth
         • maximum bit rate 0f a transmission (capacity of a transmittor)

2. topologies

   • bus topology
     • all computers connect by a single cable, all clients and servers also connect by it
     • advantages:easy installation,cheap, no extra equipment needed
     • disadvantagesfaults can level the network, only suitable for small networks
   • ring topology
     • computers are connected in a ring, data travels one way around the ring
     • advantages all that apply to bus, plus fewer collisions than bus
     • faults may also level server, also more difficult to make additions to the network.
   • star topology
     • all machines connect to a hub which directs data
       • most servers today are star but implement bus protocols
     • advantages: quick, reliable,easy to make additions, faults don't level
     • disadvantages: expensive, main hub requires maintenance, requires many cables + hub.

3. networks

   • client server
     • computers fill different roles, servers handle either file distribution, internet distribution or webpage distribution, computers send requests to servers, servers must be powerful
   • peer to peer
     • computer equality has been achieved, computers can request and serve data, shared load , no servers
       • great for data distribution , terrible for databases

4. wireless networks

   • multiple bands are used to minimze collisions
     • 2.4 is only used band by non-priority networks
       • csma ca and cd are used to avoid collisions
         • CA sends a data pack and if it gets through continues, otherwisewaits a random amount of time then retries
         • CD uses a received signal to handle cleared data
       • only true wireless network security is WPA,uses encryption that requires a key.

5. The Internet

   • internet is a network of networks, Internet is the global internet and has all the important services now
     • Similar to many star networks, can connect two computers anywhere now.
   • packet switching is used, data split into packets packets take different routes round the net and are reassembled at the destination.
     • a pack contains three components: header ( ip addresses, number and protocols) the payload (data) and trailer ( end data)
     • Routers direct packets to their destination by reading the ip address
     • gateways connect different networks types by stripping the header and footer and reformatting it
   • each internet accessible server has an ip address
     • Ip addresses have 4 billion unique addresses., gateways translate internal/exteranl IPs.
       • Domain names are used for simplicity such as BBC.co.uk or flylo.co.uk.com.org.net.ccm.com
         • A global register is used to determine countries IP addresses

6. Internet dangers.

   • Malware can abuse/gain access to systems using human error, exploiting poor code , or through poor practice
     • human error uses deceptive methods such as trojan horses or mimicry of actual software
     • Some malware can use coding mistakes such as SQL injections
     • People keep obsolete prevention methods
   • There are multiple tools and techniques used to prevent
     • The firewall can prevent malware from entering a system from banned IPS or unrecognised machines
     • An antivirus scans files for suspicious code or signatures and can delete or quarantine, needs frequent updating
     • Encryption makes data/communications unreadable
       • Private key uses an identical key to encrypt and decrypt, the key must be shared in advance
       • Public key uses different keys for encryption and decryption, each computer shares their public keys and use their private keys to decrypt
     • Certificates/signatures are used to show downloads are truthful. Upon download the certificate is decrypted, tampered data will not be accurate