Wired and Wireless Networks

Wired and Wireless Networks

1. Topologies

   • Definition: a way of describing the layout of a network
   • Types
     • Star: a topology in which all devices have their own cabling connected to a central device.
       • Advantage: fast. if one breaks, the whole network is still fine.
       • Disadvantage: The cabling is very expensive.
     • Ring: in which all devices are connected to each other in a loop
       • Advantage: cheaper cabling.
       • Disadvantage: if one cable breaks, the network is down. also queues can form .
     • Bus: All devices are connected together on a main cable.
       • Advantage: very cheap
       • Disadvantage: quite slow, if one cable breaks the whole network is down.
     • Mesh
       • pentagram
       • expensive bc of cabling
       • dont need addition hardware or server

2. Protocols

   • Definition: a set of rules governing communication between devices.
   • HTTP protocol: HTTP (hypertext transfer protocol) is used for accessing and receiving web pages in the form of HTML files on the Internet
   • HTTPS: (secure protocol) encrypts the information so that it cannot be understood if it is hacked
   • Ftp(file transfer protocol):Used for sending or retrieving files to or from a remote server or computer Works just like Windows’ File Explorer
   • POP and IMAP: These email retrieval protocols fetch message data and attachments from your remote mail server POP will download entire messages to your local device and 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 This means other devices checking the same mailbox will also see the messages
   • SMTP (Simple Mail Transfer Protocol) Email protocol used for transferring email between remote email servers Client email software sends message to outgoing mail server Mail server contacts destination mail server to pass on email using SMTP
   • TCP/IP protocol TCP (Transmission Control Protocol) Breaks up messages sent over the Internet into small chunks called packets Reassembles the packets at the other end Detects errors Resends lost messages IP protocol Routes the individual packets
   • The TCP/IP protocol stack The protocol stack defines four layers in which different protocols operate to pass data packets across a network The four layers are divisions of network functionality, each carrying out different roles: Application layer Transport layer Network layer Link layer

3. Layers

   • Application
     • The network applications you are using operate on the Application layer The application selects the correct protocol to use depending on which application it is and what you are trying to do
     • Which application protocol would be selected by: A browser connecting to a banking website? An email program used to send a message? File transfer software used to upload files to a website?
   • Transport
     • The Transport layer creates the connection between two computers, or ‘hosts’
     • The two computers agree the communication settings and the size of the packets they will send and receive Data is then divided up into packets and numbered e.g. 1 of 6 Packets are reassembled by the recipient’s Transport layer Lost packets are resent
   • Network
     • Routers operate on the Network layer
     • Destination addresses are written on to the packets ready for transmission Which layer uses the TCP protocol? Why? Which layer operates using the IP protocol? Why?
   • Link
     • The Link layer is the physical hardware that connects the two hosts such as the NIC and the cabling

4. The Internet

   • Packet switching
     • Suppose you want to send a file of 3Mb across the Internet The file is broken up into data “packets” of 512 bytes Each packet is given a header containing The IP (Internet Protocol) address it is going to The IP address it has come from The sequence number of the packet The number of packets in the whole communication Error checking data
   • WAN
     • A WAN uses cables, telephone lines, satellites and radio waves to connect, usually spread over a wide geographical area 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