UTS Internet Programming Lecture 1 The Internet
Internet Domains
A domain is a group of computers that are associated by either their geographical location, or their business type. A domain name is a string of characters that represent the numeric IP address of an Internet site. It solves the Internet addressing problem. There are more than 200 top-level domains, such as: .au - Australia, .us - United States, .uk - United Kingdom There are also world wide generic domains, such as: .edu - educational sites .com - commercial sites .gov - government sites .org - non-profit sites
True
A protocol defines what is to be communicated, how it is to be communicated and when it is to be communicated.
website
A web site is defined by a URL for a particular web server. HTML tags containing HREF attributes within a particular web page point to other websites. HREF attributes are found in tags such as A, MAP etc. Links are uni-directional. Links can have 4 kinds of destinations:- Location in the same document. (Anchor) Document on the same web site (relative URL) Document on another web site (absolute URL) A program that results in a web page (e.g. PHP script, CGI script, Java Server Page)
OSI
Application - Allows access to network resources Presentation - Encrypts, translate and compresses data Session - Establishes, manages and terminates sessions Transport - Provides reliable process-to-process message delivery and error recovery Network - Moves data from source computer to destination computer Data - Organises bits into frames Physical - Transmits bits li.e electrical pulses over a medium through defined physical interfaces The lower layers provide services for the upper layers. The lower layers aremore hardware oriented than the upper ones. The very bottom layer (Physical) is solely concerned with the physical and electrical properties of interfaces.
TCP/IP Model
Application - This layer provides the same services as the Application; Presentation and Session Layers in the OSI Model Transport - This layer is responsible for source to destination delivery of an entire message Internet - This layer is responsible for the transmission of individual parts of a message (packets) from source to destinations Network Access - These protocols are not part of TCP/IP strictly speaking. However TCP/IP supports most common protocols at this level including ethernet, FDDI, etc.
WWW Basics
Client-Server Architecture (inherited from Internet) Standard Protocol Engine Standard Format for information presentation Extended interface to other programs eg. Scripts written in PHP,Perl,JSP (Java Server Pages) or ASP
False
Does the internet provide a way for local computers and local networks to communicate and share services and resources?
WWW Security
For Web-aware systems, security is a prime problem. There are 2 general problems:- Web-server (database) Security - Firewalls, File Permissions and access control lists. Communication Security. Encrypting data being transferred and authenticating it.
W3C
Founded in 1994 by Tim Berners-Lee, the inventor of the concepts of URLs, HTTP and HTML. The W3C is responsible for the official standards for HTML, XHTML, XML and CSS. Website is at http://www.w3.org/ W3C consults closely with other organisations such as the IETF and Apache Foundation in the formulation of standards.
send email
What is SMTP used to do?
Layered Protocols
Global Data Communications are implemented through several levels. There is an internationally ratified standard (model) setting out that defines the worldwide internet communication in seven layers and how they relate to each other. This is the famous OSI (Open Systems Interconnect) Model. An alternative and ( simpler) model is the TCP/IP Model. In this course we focus on application layer of protocols, which are built on the top of the TCP/IP protocol stack.
supported by browsers
HTML (Hypertext Markup Language) is a universal document formatting system for information presentation in web pages. HTML allows for the inclusion of Javascript in Web pages. The inclusion of Javascript and Java Applets as client-side features of the World Wide Web assists the production of more versatile web pages.
HTTP Protocol
HTTP functions as a request-response protocol in the client-server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body. A web browser is an example of a user agent (UA). Other types of user agent include the indexing software used by search providers (web crawlers), voice browsers, mobile apps, and other software that accesses, consumes, or displays web content.
Hypertext
Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text. HTTP is the protocol to exchange or transfer hypertext. The standards development of HTTP was coordinated by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), culminating in the publication of a series of Requests for Comments (RFCs). The first definition of HTTP/1.1, the version of HTTP in common use, occurred in RFC 2068 in 1997, although this was obsoleted by RFC 2616 in 1999.
Domain Names
IP addresses uniquely identify hosts. However, remembering IP addresses is fairly tedious for human beings. In order to overcome this problem, the Domain Name is used. The Domain Name system is a way of associating IP addresses and textual Domain Names with each other. Every time a web page (e.g. www.smh.com.au) is requested by your browser, the domain name smh.com.au must be translated into an IP address. To do this the browser sends the domain name (in this case www.smh.com.au) to a Domain Name Server (DNS). The DNS matches the domain name with the right IP address (32 bits) and returns it to browser. The browser then sends out a request to the host computer at the IP address (203.26.51.42) it has obtained from the DNS.
IPv6
Internet Protocol version 6 (IPv6) is a version of the Internet Protocol (IP) that is designed to succeed Internet Protocol version 4 (IPv4). It was developed by IETF in 1998. While IPv4 allows 32 bits addressing, and can therefore support (4,294,967,296) addresses, IPv6 uses 128-bit addresses, so the new address space supports 2128 (or 3.4×1038) addresses. This expansion allows for many more devices and users on the internet as well as extra flexibility in allocating addresses and efficiency for routing traffic.
Organisation Framework
Internet Society (ISOC) Internet Engineering Task Force (IETF) World Wide Web Consortium (W3C) Apache Software Foundation Web Hypertext Application Working Group (WHATWG)
Unix
Most web servers run under a variety of Unix systems e.g. Linux, Solaris, HP Unix, etc. Unix has its own built-in system of file permissions. The Unix file system divides users into three classes. The owner of the file, the owners group, and the rest of the world. In addition, there are three types of permissions for every file. These are read access, write access and execute access. The first Laboratory class will go into this in more detail.
NNTP
Network News Transfer Protocol (NNTP) is used for serving Usenet Posts.
Apache
Non-profit organisation responsible for the most widely used Web Server (provided as open source). Also involved in various other open source projects. Frequently consulted by the IETF and W3C for input into the development of new standards.
SSL
Pages using this security technology have URLs beginning with "https". SSL uses RSA to authenticate the server and optionally authenticate the browser. RSA is the most commonly used public key encryption algorithm. Allows authenticated and encrypted communication. SSL runs "above" TCP/IP but "below" application protocols such as HTTP. Both client & server must be SSL enabled.
Protocol
What is a set of rules that govern data communication?
Web Security
Secure Sockets Layer (SSL). (You can identify when SSL is being used as the protocol in the URL is HTTPS). The latest version of SSL is known as TLS (Transport Layer Security).
TCP/IP
TCP/IP is the fundamental data communication protocol of Internet and WWW. TCP/IP (Transmission Control Protocol/Internet Protocol) is a set of communication rules used to route data packets across the Internet. The use of a protocol standard enables computers with different Operating Systems to communicate with each other. PCs using Windows, Unix, Linux, Mac OS, as well as other less well known Operating Systems all use TCP/IP to connect to the Internet.
True
Telnet is used to login to a remote machine for remote administration of Unix computers.
HTTP Protocol
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.
Internet Gateways
The Internet is a global network of networks connecting millions of users worldwide via many computer networks. It uses a common addressing system and communication protocol (TCP/IP) The connections between different networks are called gateways Gateways serve to transfer data worldwide.
Client-Server Model
The Internet works in a client-server model. The resources of the internet - information and services are provided through host computers known as servers. The server is a computer system that may contain such things as emails, file downloading service (ftp) or web pages. A customer (client) acting at the Application Level accesses these resources via a client program (e.g. a web browser) which uses TCP/IP to deliver information or files.
three layers
The Structural Layer - responsible for web page content. Consists of HTML or XHTML. The Presentation Layer - responsible for how the content is presented. Consists of CSS (Cascading Style Sheets) which are referenced from the Markup Layer and the Behaviour Layer Behavioural Layer - responsible for handling events and user interaction with the web page. Consists of javascript code.
Standard Protocol Engine
The major protocol used on the World Wide Web is HTTP (Hypertext Transfer Protocol). The client (browser) and the Web Server conduct their transactions using HTTP. HTTP 1.0 is a stateless Protocol. Once a request has been made and replied to, the transaction is completed. The Web server has no memory of the transaction. HTTP was designed as a document retrieval protocol only, so it is a relatively simple protocol.
Firewalls
The most popular technique to protect an internal server from unauthorized access is by means of a firewall. A firewall consists of screening routers and proxy servers. The routers filter IP packages according to a set of rules set up by the system administrator. TCP/IP Packets can be rejected, accepted, or forwarded to a computer inside the network protected by the firewall.
ISOC and IETF
The peak body governing the Internet is the Internet Society (ISOC) ISOC is an international non-profit organisation formed in 1992 to provide support for the standards setting process. Subsidiary organisations include the Internet Architecture Board (IAB), the Internet Engineering Task Force (IETF) and the Internet Research Task Force. Requests for Comments (RFCs) are memoranda issued by the IETF. Many RFCs become binding standards.
IP Address
Under the TCP/IP scheme, all internet hosts (i.e. computers connected on the network) are identified by a unique IP Address. The IP Address is a 32 bit binary number. e.g 10000001 00110100 00000110 00000000 this is usually represented as 4 bytes e.g. 129 . 52 . 6 . 0 That can therefore support 232 (4,294,967,296) addresses In many cases (e.g. browsing the web), we do not use Internet Addresses directly, instead we use Domain Names.
File Transfer Protocol
What does FTP stand for?
Hypertext Transfer Protocol
What does HTTP stand for?
Hypertext Transfer Protocol Secure
What does HTTPS stand for?
Internet Message Access Protocol
What does IMAP stand for?
Post Office Protocol
What does POP3 stand for?
Simple Mail Transfer Protocol
What does SMTP stand for?
send and retrieve files
What is FTP used for?
retrieve webpages
What is HTTP used to do?
retrieve email
What is POP3 used to?
ssh
What is used to login to a remote machine for remote administration of Unix computers, but data is encrypted. ssh stands for secure shell?
global computer
What kind of network is the internet?
World Wide Web
World Wide Web is an on-line global information source allowing users to locate and view multimedia-based documents on almost any subject worldwide. Invented by Tim Berners-Lee WWW is one of the most significant creations of humankind. Why? Applications will be no longer running on "stand-alone" PCs Today's applications can be written and run on hundreds of millions of computers