Aims
| Social Media 2011 | History of the Internet | Internet Explained |
| Invention of World Wide Web | World Wide Web in Plain English | The Gamified World |
Write an account of the development of the internet. Your account should include key dates, terms and acronyms:
It would be hard to remember many IP addresses and it is far more convenient to have a more memorable name to act as an alias for a number up to 12 digits long. The domain name system (DNS) provides a system of substituting a name for an IP address e.g. bbc.co.uk. The DNS is a hierarchical system of names and abbreviations.
A fully qualified domain name (FQDN) is a complete address that uniquely identifies a host e.g. 196.120.70.123 or mail.abc.yorks.sch.uk.
.uk is a top-level domain name, as are .com, .net, .de and so on.
.sch is a second-level domain name (includes all schools); .yorks is third-level and abc (the actual school) is fourth-level. mail is the name of the server with a unique IP address.
DNS servers translate FQDNs into IP addresses.
A uniform resource locator (URL) is a target for a hyperlink. It specifies the server, the access method and the location in the server. A URL includes the protocol e.g. http, https, ftp; the domain name; and the path on the server - see the address in the URL bar in your browser for this page.
A uniform resource identifier (URI) is a higher level category of identifier that includes URLs and uniform resource names (URN). The W3C and IETF say that URLs should be called URIs.
An internet registry is a list of registered domain names. Each major domain e.g. .co.uk has its own registry. Internet registrars are responsible for registering internet domains.
An internet service provider (ISP) is an organisation that sells people access to the internet e.g BT, Virgin.
The client and server are software processes. Servers wait for requests from clients and may read or write information sent by the client. The client starts the communication by issuing a request: the server sits and listens for requests.
A protocol is a set of rules and agreed signals to control communication between systems. The internet uses the TCP/IP protocol stack. The word stack is used because networking protocols are usually arranged in layers. The OSI model has 7 layers while TCP/IP has 4; the 4 levels of the TCP/IP stack correspond with one or more of the OSI model layers.
This handles details of the networking or data commnications application e.g. browser. Protocols here include ftp, smtp and http.
This handles host-to-host communication. It enables applications to establish a connection between two hosts. It splits data into packets. It ensures a reliable flow of data between the hosts that are communicating. It detects errors and retransmits packets if they occur. It reassembles incoming packets into data for applications.
Hosts run many processes at a time. TCP sends data from processes to the IP layer and has to decide which part of the IP layer to send the data to. This is the job of TCP ports, which provide an additional element in an IP address. TCP assigns different port numbers to different applications. Well known port numbers include: FTP: 20 & 21; Telnet: 23; SMTP: 25; www: 80 & 8080; POP3: 110.
Servers accept multiple simultaneous connections from clients.
The combination of an IP address and a port is called a socket. The connection between two sockets, one on each host, provides bi-dierctional communication between applications.
This layer adds source and destination addresses to the packets handed to it from the transport layer. It also receives incoming packets from the link layer, which it passes on the TCP layer.
This layer contains communication technologies for a local network e.g. Ethernet, Appletalk. It adds source and destination hardware addresses to packets (MAC address on the NIC). The packets can then find their way across the physical link of the network infrastructure to the next point in the chain of connections - this is often a router rather than a host.
A client sends a request to a server and the server responds with a message. The response may contain many forms of data, one of the most common of which is a page written in HTML. Other data includes images, sound and video. TCP establishes a connection between client and server, along which the http request and response messages can flow.
The simplest request mesasge uses GET, which fetches the default web page from a server. An HTML file is a text file that is interpreted by the browser and rendered into the form defined by the author. An HTML page may make use of CSS, either embedded in the HTML or in an external file. An HTML file may also make use of a client-side scripting language such as Javascript or VBScript. When the response is complete the connection between server and host is broken.
This is HTTP over Secure Sockets Layer. This was originally developed by Netscape to provide encryption and decryption services over HTTP so that sensitive data could be transmitted safely between hosts. It uses a protocol layer (SSL) underneath the HTTP application layer. HTTPS uses port 443 rather than 80.
File Transfer Protocol allows file exchange between hosts. One host runs an FTP client while the other runs an FTP server. FTP servers use two ports: 20 for data and 21 for commands.
Telnet is a protocol that allows remote management of another host. It allows the reading of email and web pages on the remote host and file management such as creating folders and deleting files - in fact any operation, as if the remote computer were the user's own. It uses port 23.
Simple Mail Transfer Protocol is a simple text-based protocol that is used to send email. It is used mainly to send mail between servers with outgoing mail part 25 and new mail on 587. The Post Office Protocol is used by clients to retrieve mail stored on a server. IMAP (Internet Message Access Protocol) is also used by clients to access email. The original SMTP specification did not require user authentication and so was vulnerable to hacking and spamming; changes have improved this but it is still not secure against attacks. SMTP can utilise the SSL layer, when it is called SMTPS, though this is not an official protocol.
| Inside Facebook | IM | |
| Online games (ESA) | Future Internet |
| Mikko Hypponen:Fighting Viruses | Cracking Stuxnet | |
Does it set the people free?
Whom does the internet affect?