INTERNET GATEKEEPERS (THE HINDU)

• Data on the Web can be imagined as a train of discrete packets with transaction details stamped on each of them — source, destination, nature of information and data payload.
• Firewalls can be software programs or hardware network equipment, performing packet filtering to increase security, screen web traffic and, in extreme cases, censoring information.
• Filtering a specific type of traffic can be accomplished by writing rules to either drop/accept/forward packets from communication ports. 
• Communication ports can be perceived as numbered, dedicated lanes in the Internet for carrying traffic of designated type.
• Web traffic, which is primarily HTTP (Hyper Text Transfer Protocol)-based, is carried on port 80 from the web server, HTTPS (the secure variant) runs on port 443. Likewise, File Transfer Protocol (FTP) transacts data on port 21 and other services.
• Software firewalls, which are capable of basic packet filtering, are inherent to most operating systems, to help users keep their computers safe.
• Hardware firewalls are dedicated network equipment capable of performing basic switching and routing of data packets. The equipment performs filtering of packets at a local area network (LAN) level, where hundreds of computers may be connected.
• The Great Firewall of China, the metaphor for Internet censorship in China, is implemented not by a single device but a whole network of complex firewall mechanisms