14 Communication Revision for A2 Computer Science by Inqilab Patel

14.1 Protocols
Show understanding of why a protocol is essential for communication between computers
Show understanding of how protocol implementation can be viewed as a stack, where each layer has its own functionality
Show understanding of the TCP/IP protocol suite Four Layers (Application, Transport, Internet, Link)
Show understanding of protocols (HTTP, FTP, POP3, IMAP, SMTP, BitTorrent) and their purposes
14.2 Circuit switching, packet switching
Show understanding of circuit switching
Show understanding of packet switching
Protocols:
Protocols are agreed set of rules to be followed during data transmission.
Modern computers are designed with communication in mind. At a basic level, computers may need to communicate with peripherals such as a printer, or to send messages to other computers, which may be connected across a local area network (such as in a business, or a school), a mobile phone cellular network, or the internet.
Before one computer can communicate with another, there must be a set of agreed rules in place that manage how the communication is to take place. These rules are known collectively as a protocol. Computers use rules, and these form the protocols that are used for computer communication.
Protocols need to specify several aspects of communication, for example:
• the communication medium to be used, such as wired or wireless
• the transmission type, such as duplex or simplex
• whether the handshake is hardware or software in nature
• the method of error checking to be used
• the bit rate
• the character set that will be used.
Why protocols are needed?
• Protocols set a standard for communication.
• Protocols enable communication compatibility between devices even they are from different manufacturers or working on different platforms.
If two devices were sending messages to each other but using different protocols, they would not be able to communicate properly. Modern computers are designed with communication in mind. At a basic level, computers may need to communicate with peripherals such as a printer, or to send messages to other computers, which may be connected across a local area network (such as in a business, or a school), a mobile phone cellular network, or the internet.
The protocols allow messages to be transmitted in a structured, specific manner, so that the receiving device is able to process the data sent from the sending device. Protocols therefore make sure that communication between any two devices is successful. Different communication protocols exist to specify rules for different types of communication, for example:
HTTP/HTTPS, FTP, SMTP, POP3, IMAP, TCP, IP, DNS, bitTorrent
1 Hyper Text Transfer Protocol (HTTP) – handles transmission of web pages from a website to user’s computer. This makes use of hyperlinks (rules for the transferring of data over the internet). HTTP is a client/server protocol: request messages are sent out to the web servers which then send web pages. HTTP protocols define the format of the messages sent and received.
• File Transfer Protocol (FTP) – handles transmission of files across a network. It is used when transferring files from one computer/device to another via the internet or other networks.
It is like HTTP and SMTP, but FTP’s only task is the application protocol for the transfer of files over a network. Web browsers can be used to connect to an FTP address in a way like HTTP, for example, ftp://inqilabpatel.com
Additional features of FTP include
• ftp server – is the central computer that stores files to be downloaded.
• anonymous ftp – this allows a user to access files without the need to identify themselves to the ftp server.
• ftp commands – a user can send commands/instructions that are to be carried on ftp server. For example, delete, close, rename, cd (change directory on a remote machine).
• Simple Mail Transfer Protocol (SMTP) – handles email transmission, used to send from client to email server and from one email server to another server.
• Post Office Protocol (POP-3) – handles downloading email from email server in user computer. POP3 downloads the email from a server to a single computer, then deletes the email from the email server. It is used when user has a dedicated device for email and wants to access email off-line.
• Internet Message Access Protocol (IMAP) – handles receiving of emails. IMAP is used when user is working across multiple devices, but email is available online only.
• TCP – handles communication over the internet, it breaks down a file into packets to be transmitted and reassembles receiving packets into file. TCP is also connection-orientated since it establishes an end-to-end connection between two host computers using handshakes. For this last reason, TCP is often referred to as a host-to-host transmission protocol.
• IP – handles communication over the internet, it attaches sender and destination IP address in data packets.
• Domain Name System
• bitTorrent –