Wired and Wireless Networks

Wired and Wireless Networks

1. Protocols and layers

   • A set of Rules is called a protocol
   • HTTP and HTTPS protocol
     • HTTP is used for accessing and receiving web pages in the form of HTML files on the Internet
       • Hyper Text Transfer Protocol
       • This protocol requests the web server to upload the requested web page to the user's browser for viewing.
     • The HTTPS encrypts the information so that it cannot be understood if it is hacked
       • Secure version of HTTP
       • Websites like facebook might require this because if it doesn't full conversations between people could be leaked
   • FTP (File Transfer Protocol)
     • Used for sending or retrieving files from a remote server or computer
   • POP and IMAP
     • Email retrieval Protocols fetch message data and attachments from your remote mail server
     • POP will download entire messages to your local device and then it will delete them from the server.
     • IMAP will only download the message header until the message is opened and will leave the message on the server
   • SMTP
     • Protocol used for transferring email between remote email servers
   • TCP/IP protocol
     • TCP (Transmission Control Protocol)
       • Breaks up the file into small packets. Reassembles them and checks for errors. If any packets missing it will request for a resend
     • IP protocol
       • routes individual packets
     • TCP/IP Protocol Stack
       • Has four layers each with its own set of rules to pass data along
       • Application Layer. Transport Layer. Network Layer. Link Layer
       • The application will determine the correct protocol to use to communicate
       • The Application Layer
         • Network Applications.
         • Would see which protocol to use and then pass it on to the transport layer
       • Transport Layer
         • Makes connection between two hosts
         • The two computers agree the communication settings and the size of the packets they will send and receive
       • Network Layer
         • Operate on routers
         • Destination Addresses are written on to the packets
       • Data link layer
         • The link layer is the physical hardware that connects the two hosts such as the NIC and the cabling

2. Local Area Networks

   • LAN
   • Operates on a single site such as a school o small business using thier own cabelng systems
   • you can save money by sharing printers and having files backed up on a centeral server
     • can be accessed from anywhere
   • Topologies
     • Star
       • Fast data transfer
       • If one cable fails others aren't affected
       • Requires additionall hardware
     • Mesh
       • Nodes act as routers
       • Partial mesh networks often used with conjunction
       • The internet is a giant mesh network.
       • Wireless mesh networks
         • Only one node requires an internet connection
         • The more nodes use the network the more signal it will have
       • Self healing network
   • Network Hardware
     • Network Interface Card
     • A router or a switch
       • Sends packets in the right direction and if it is a switch it will make this more efficient
     • A modem may also be combined
   • Ethernet Protocols
     • Describes how devices should format the data ready for transmission between computers on the same network
     • Two nodes attempting to transmit simultaneously will stop and wait a random period before starting again
   • Virtual networks
     • 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

3. The Internet

   • The internet is a WAN
   • A collection of inter-connected networks
   • A Wide Area Network
     • Any network where the computers communicate using resources supplied by a “third party carrier”, such as British Telecom
     • A WAN uses cables, telephone lines, satellites and radio waves to connect
     • Usually spread over a wide geographical area
   • IPv4 Adressing
     • Every network has a seperate and unique address
     • There are so many computers that the IPv4 addresses are running out.
     • A new IPv6 System is slowly replacing the IPv4 System
   • Circuit Switching Network
     • When making a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call.
       • Circuit Switching
     • Would not work on the internet due to the amount of people sending files all the time
     • Packet Switching
       • A file is broken up into "packets" of 512 bytes.
         • Each packet will contain the same number of bytes and is marked with the packet number and the total number of packets in the transmission
       • Each packet is given a header containing.
         • The IP Address it is going to. The IP it has come from. The number of packets in the whole communication. Error checking data
       • Any packets lost will be resent.
   • IP addressing
     • Every computer and device has an IP address.
     • Packets are labelled with the senders and the destination IP addresses
     • Packets are sent across the internet separately via different routes and put back together at the end
     • IP can change
   • Domain Name System
     • DNS lets you type in to the URL bar things like www.google.com
     • Translates web addresses into an IP address
     • There are 13 DNS "root" servers worldwide which keep a complete database of all names and IP addresses
       • Other DNS servers lower down the hierarchy hold parts of the database
     • When a DNS server receives a request that it doesn't have it will pass on the request to another server until it reaches one with the matching name and IP address
       • Lower level DNS servers are owned by ISPs
   • Network Interface Cards
     • Built into every networked device
       • Wired or wireless
   • MAC addressing
     • A Media Access Control (MAC) address is assigned to each Network Interface Card (NIC)
       • eg. 3B:14:E6:39:0A:2C  
     • A mac address is unique and doesn't change.
     • There are 2 to the power of 48 possible addresses.
     • A mac Address is assigned to a NIC so if you go on holiday it will stay the same.

4. Wired and Wireless Networking

   • Client server Model
     • The server is a powerful computer which provides services or resources required by any of the clients
     • A client is a computer which requests the services or resources provided by the server
     • A file server holds all the data files and the databases and manages backups
     • A web server may host the school’s external website
     • The client sends requests to the server.
     • The server waits for requests from a client Acknowledges the request The server may need to pass the request The requested data is sent back to the client
     • Client server Networking
       • A central server is used to manage security Some files are held on the central server Some processing tasks are performed by the server Clients issue requests to the server for services such as email, file storage, backup and printing Suitable for many different types of organisation, small and large Can require specialist IT staff to administer the network
       • Data can be backed up centerally
       • Security is better
       • Useres can log on from anywhere
   • A P2P (Peer to Peer)
     • Has no centeral server
     • Suitable for small companies
     • Can communicate with each other without going through a server
     • If a computer is switched off data cannot be retrieved
     • Easy to setup
     • Can share printers, routers, and modems and other hardware
     • No special software required
     • Viruses can be easily transferred
     • Data recovery and backup cannot be done centerally
   • Peer-to-peer on a WAN
     • P2P can be used to share files
     • Can be used for illegal distribution of files
   • Hosting
     • Internet host is a company (often an ISP) that is able to store your files and make them available to you or others from other Internet-connected computers
     • Cloud
       • Enables coumputers to access files or services from a externall network
       • Backing up isnt crucial
       • More vulnerable to hacking