BTEC ICT Revision - Teach Me Computing
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Html is made up of tags. The majority of them will be in pairs. Some of the most common tags are shown below. Tags What does this mean? <b> Bold <i> Italic <p> Paragraph <img> Image <a href> Hyperlink <li> List <ul> bullet A page will be set out like the following. <html> <body> </body> </html> Web Crawlers/Spiders are the same thing. These are small automated programs(or bots) that carry out processes all the time without Human involvement. They are constantly moving around the internet, finding new pages. When they find a new page they log it in an indexed database which the search engines will use to populate results. Packet switching is the process of data being broken into packets to be sent through a network and then reassembled at the other end. This method is used on the internet. See diagram page 22 in revision booklet. Voip uses CODECs at either end to encode and decode data. So Mr Cole records a message using a webcam and microphone. This is converted(encoded) into digital data which is then broken down into packets and sent across the internet. Once it reaches the other end it is reassembled into it a complete digital form, and the decoded so the person can view the video and sound. Simplex Full duplex Data goes in one direction at a time (Remote) Signals go in both directions at the same time (Smartphone) Half Duplex Signals go in both directions but don’t transmite at the same time (printer) Parallel connection means simultaneous transmission of N bits. These bits are sent simultaneously over N different channels (a channel being, for example, a wire, a cable or any other physical medium). The parallel connection on PC-type computers generally requires 10 wires. Benefit Faster as more bits are transferred per second Limitation Overall short distance (maximum of a 5 meter cable) In a serial connection, the data are sent one bit at a time over the transmission channel. However, since most processors process data in parallel, the transmitter needs to transform incoming parallel data into serial data and the receiver needs to do the opposite. Benefit Good over large distances Limitation Complex as the data has to be broken into individual bits Pop – Point of Presence NAP – Network Access Point Takes data from the TCP (Transmission Control Protocol) Organises it into packets Routes it across the network and puts the packets back in the correct order at the other end. FTP – File Transfer Protocol Takes data from the users application Passes it to the internet protocol. (The reverse happens at the other end) IP – Internet Protocol Different networks interconnect, such as your home network connecting the internet. TCP – Transmission Control Protocol Is an access point to the internet. An ISP may have several PoPs to allow good access to the internet. FTP is the protocol which allows files to be transferred between two computers or devices. It is usually used to download or upload large files to a server. HTTP – HyperText transfer Protocol It is a protocol that allows you to request web pages and download them to our computers. Emaail is known as a STORE and FORWARD System. POP3, IMAP and SMTP are all communication protocols used when sending and receiving emails. SMTP Simple Mail Transfer Protocol ‘Push’ pushes the mail from the server to the client. POP3 Post office Protocol 3 ‘pull’ pulls the mail from the server to client when requested. IMAP Internet Used for Message Access webmail protocol See Page 26 – revision guide See page 27 revision guide
