A user agent is a client A client is an application or system that accesses a remote service on another computer system, known as a server, by way of a network. The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing application implementing a network protocol In computing, a protocol is a set of rules which is used by computers to communicate with each other across a network. A protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, used in communications within a client–server distributed computing system. The term most notably refers to applications that access the World Wide Web The World Wide Web, abbreviated as WWW and commonly known as the Web, is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them by using hyperlinks. Using concepts from earlier hypertext systems, British, but other systems, such as the Session Initiation Protocol The Session Initiation Protocol is an IETF-defined signaling protocol, widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP). The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media (SIP), use the term user agent to refer to both end points of a communications session.[1]
Web user agents range from Web browsers A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to to search engine A web search engine is designed to search for information on the World Wide Web. The search results are usually presented in a list of results and are commonly called hits. The information may consist of web pages, images, information and other types of files. Some search engines also mine data available in databases or open directories. Unlike crawlers A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner or in an orderly fashion. Other terms for Web crawlers are ants, automatic indexers, bots, or Web spiders, Web robots, or—especially in the FOAF community—Web scutters (spiders), as well as mobile phones A mobile phone is an electronic device used for full duplex two-way radio telecommunications over a cellular network of base stations known as cell sites. Mobile phones differ from cordless telephones, which only offer telephone service within limited range through a single base station attached to a fixed land line, for example within a home or, screen readers A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen . This interpretation is then re-presented to the user with text-to-speech, sound icons, or a Braille output device. Screen readers are a form of assistive technology (AT) potentially useful to people who are blind, visually and braille The Braille system is a method that is widely used by blind people to read and write. Braille was devised in 1821 by Louis Braille, a blind Frenchman. Each Braille character or cell is made up of six dot positions, arranged in a rectangle containing two columns of three dots each. A dot may be raised at any of the six positions to form sixty-four browsers used by people with disabilities. When a user agent operates, it typically identifies itself, its application type, operating system An operating system is the software on a computer that manages the way different programs use its hardware, and regulates the ways that a user controls the computer. Operating systems are found on almost any device that contains a computer with multiple programs—from cellular phones and video game consoles to supercomputers and web servers. Some, software vendor, or software revision, by submitting a characteristic identification string In mathematical logic, more precisely in the theory of formal languages, and in computer science, a string is a sequence of symbols that are chosen from a set or alphabet.[citation needed] to its operating peer. In the HTTP The Hypertext Transfer Protocol is an Application Layer protocol for distributed, collaborative, hypermedia information systems and SIP protocols, this is transmitted in a header field User-Agent. Bots Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the Internet. Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human alone. The largest use of bots is in web spidering, in which an automated, such as Web crawlers, often also include a URL In computing, a Uniform Resource Locator is a Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it. In popular usage and in many technical documents and verbal discussions it is often incorrectly used as a synonym for URI,. The best-known example of a URL is the " and/or e-mail address An e-mail address identifies an email box to which e-mail messages may be delivered. An e-mail address on the modern Internet looks like, for example, jsmith@example.com and is usually read as "jsmith at example dot com". Many earlier e-mail systems used different address formats so that the Webmaster A webmaster , also called a web architect, web developer, site author, website administrator, or (informally) webmeister, and sometimes heard in tongue-in-cheek feminine form web mistress, is a person responsible for maintaining one or many websites. The duties of the webmaster may include ensuring that the web servers, hardware and software are can contact the operator of the bot.
Contents |
User agent identification
Some user agents identify their software as part of the client–server conversation. In HTTP and SIP, the identity is transmitted via the User-Agent request header, as described by RFC 1945. This string is then used by the communications partner to characterize the client and optionally select suitable content or operating parameters for session. For example, this may be used to provide properly formatted content for desktop computers A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator. This is in contrast to the batch processing or time-sharing models which allowed large expensive mainframe and for smartphones A smartphone is a mobile phone that offers more advanced computing ability and connectivity than a contemporary basic 'feature phone'. Smartphones and feature phones may be thought of as handheld computers integrated within a mobile telephone, but while most feature phones are able to run applications based on platforms such as Java ME or BREW, a.
The user agent string is one of the criteria by which Web crawlers may be excluded from accessing certain parts of a Web site using the Robots Exclusion Standard The Robot Exclusion Standard, also known as the Robots Exclusion Protocol or robots.txt protocol, is a convention to prevent cooperating web spiders and other web robots from accessing all or part of a website which is otherwise publicly viewable. Robots are often used by search engines to categorize and archive web sites, or by webmasters to (robots.txt file).
User agent spoofing
The popularity of various Web browser products has varied through out the Web's history, and this has influenced the design of Web sites in such a way that Web sites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the World Wide Web Consortium The World Wide Web Consortium is the main international standards organization for the World Wide Web (abbreviated WWW or W3) (W3C) or the Internet Engineering Task Force The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite. It is an open standards organization, with no formal membership or membership requirements. All participants and managers are (IETF). Web sites often include code to detect browser version to adjust the page design sent according to the user agent string received. This may mean that less-popular browsers are not sent complex content, even though they might be able to deal with it correctly or, in extreme cases, refused all content.[2] Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content.
Other HTTP client programs, like download managers A download manager is a computer program dedicated to the task of downloading possibly unrelated stand-alone files from (and sometimes to) the Internet for storage. This is unlike a World Wide Web browser, which is mainly intended to browse web pages, composed of a multitude of smaller files, where error-free moving of files for permanent storage and offline browsers, also have the ability to change the user agent string.
Spam bots and Web scrapers often use fake user agents.
At times it has been popular among Web developers to initiate Viewable With Any Browser campaigns,[3] encouraging developers to design Web pages that work equally well with any browser.
A result of user agent spoofing may be that collected statistics of Web browser usage The usage share of web browsers is the percentage of visitors to a group of websites that use a particular web browser. For example, when it is said that Internet Explorer has 52% usage share, it means that some version of Internet Explorer is used by 52% of visitors that visit a given set of sites is inaccurate.
User agent sniffing
The term user agent sniffing refers to the practice of Web sites showing different content when viewed with a certain user agent. On the Internet, this will result in a different site being shown when browsing the page with a specific browser. A useful example of this is Microsoft Exchange Server Microsoft Exchange Server is the server side of a client-server, collaborative application product developed by Microsoft. It is part of the Microsoft Servers line of server products and is used by enterprises using Microsoft infrastructure solutions. Exchange's major features consist of electronic mail, calendaring, contacts and tasks; support 2003's Outlook Web Access feature. When viewed with Internet Explorer 6 (or newer), more functionality is displayed compared to the same page in any other browser, because other browsers could not render the same content.[citation needed] User agent sniffing is mostly considered poor practice, since it encourages browser-specific design and penalizes new browsers with unrecognized user agent identifications. Instead, the W3C recommends creating HTML markup that is standard,[citation needed] allowing correct rendering in as many browsers as possible, and to test for specific browser features rather than particular browser versions or brands.[4]
Web sites specifically targeted towards mobile phones, like NTT DoCoMo NTT Docomo, Inc. is the predominant mobile phone operator in Japan. The name is officially an abbreviation of the phrase, "do communications over the mobile network", and is also from a compound word dokomo, meaning "everywhere" in Japanese. Docomo provides phone, video phone (FOMA and Some PHS), i-mode (internet), and mail (i-'s I-Mode NTT DoCoMo's i-mode is a mobile internet service popular in Japan. Unlike Wireless Application Protocol or WAP, i-mode encompasses a wider variety of internet standards, including web access, e-mail and the packet-switched network that delivers the data. i-mode users have access to various services such as e-mail, sports results, weather forecast, or Vodafone Vodafone Group plc is a global telecommunications company headquartered in Newbury, United Kingdom. It is the world's largest mobile telecommunications company measured by revenues and the world's second largest measured by subscribers (behind China Mobile) with 347 million proportionate subscribers as at 30 June 2010. It operates networks in 31's Vodafone Live! Vodafone live! is the brand name for the multimedia portal service of mobile phone operator Vodafone, which was initially developed by Japan's J-Phone under the J-Sky brand. Vodafone acquired J-Phone including J-Sky in 2001–2002 and changed the name from J-Sky to Vodafone Live! in 2003 portals, often rely heavily on user agent sniffing, since mobile browsers A mobile browser, also called a microbrowser, minibrowser or wireless internet browser , is a web browser designed for use on a mobile device such as a mobile phone or PDA. Mobile browsers are optimized so as to display Web content most effectively for small screens on portable devices. Mobile browser software must be small and efficient to often differ greatly from each other. Many developments in mobile browsing have been made in the last few years,[when?] while many older phones that do not possess these new technologies are still heavily used. Therefore, mobile Web portals will often generate completely different markup code depending on the mobile phone used to browse them. These differences can be small, e.g., resizing of certain images to fit smaller screens, or quite extensive, e.g., rendering of the page in WML Wireless Markup Language, based on XML, is a markup language intended for devices that implement the Wireless Application Protocol specification, such as mobile phones, and preceded the use of other markup languages now used with WAP, such as HTML/XHTML (which are gaining in popularity as processing power in mobile devices increases) instead of XHTML XHTML is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML), the language in which web pages are written.
Encryption strength notations
Web browsers created in the United States, such as Netscape Navigator Netscape Navigator and Netscape are the names for the proprietary web browser popular in the 1990s, the flagship product of the Netscape Communications Corporation and the dominant web browser in terms of usage share, although by 2002 its usage had almost disappeared. This was partly due to the increased usage of Microsoft's Internet Explorer web and Internet Explorer Windows Internet Explorer , is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. It has been the most widely used web browser since 1999, attaining a peak of about 95% usage share during 2002 and 2003 with IE5 and IE6, use the letters U, I, and N, to specify the encryption In cryptography, encryption is the process of transforming information using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information (in cryptography, referred to as ciphertext). In many contexts, the word encryption strength in the user agent string. Until the United States government allowed encryption with keys longer than 40 bits to be exported, in 1996, vendors shipped various browser versions with different encryption strengths. "U" stands for "USA" (for the version with 128-bit encryption), "I" stands for "International" — the browser has 40-bit encryption and can be used anywhere in the world — and "N" stands (de facto) for "None" (no encryption).[5] Following the lifting of export restrictions, most vendors supported 256-bit encryption.
See also
- Robots Exclusion Standard The Robot Exclusion Standard, also known as the Robots Exclusion Protocol or robots.txt protocol, is a convention to prevent cooperating web spiders and other web robots from accessing all or part of a website which is otherwise publicly viewable. Robots are often used by search engines to categorize and archive web sites, or by webmasters to
- Web crawler A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner or in an orderly fashion. Other terms for Web crawlers are ants, automatic indexers, bots, or Web spiders, Web robots, or—especially in the FOAF community—Web scutters
- Wireless Universal Resource File (WURFL) WURFL stands for Wireless Universal Resource FiLe. It is part of a FOSS community effort focused on the problem of presenting content on the wide variety of wireless devices. The WURFL itself is an XML configuration file which contains information about device capabilities and features for a variety of mobile devices. Device information is
- User Agent Profile (UAProf)
- List of user agents for mobile phones
- Apache Mobile Filter
References
- ^ RFC 3261, SIP: Session Initiation Protocol, IETF, The Internet Society (2002)
- ^ Burstein complaining "... I've been rejected until I come back with Netscape"
- ^ "Viewable with Any Browser" campaign
- ^ Clary, Bob (10 February 2003). "Browser Detection and Cross Browser Support". Mozilla Developer Center. Mozilla Mozilla is a term used in a number of ways in relation to the now-defunct Netscape Communications Corporation and its related application software, including the Mozilla.org group and its successor the Mozilla Foundation. https://developer.mozilla.org/en/Browser_Detection_and_Cross_Browser_Support. Retrieved 2009-05-30.
- ^ Zawinski, Jamie (1998-03-28). "user-agent strings (obsolete)". mozilla.org. http://www-archive.mozilla.org/build/user-agent-strings.html. Retrieved 2010-01-08.
External links
Categories: Clients Categories: Network-related software | Application layer protocols | Distributed computing architecture | HTTP headers
Thu, 08 Jul 2010 09:43:25 GMT+00:00
Boosh News (press release) (blog) SIP end points are usually IP telephones or soft phone clients running on top of some ordinary computing hardware (referred as user agent clients in the ...
463px x 657px | 53.40kB
[source page]
con nosotros enviandonos la informacion sin espacios lo que supone un considerable de ahorro en los datos transmitidos y por lo tanto un considerable ahorro para nuestros bolsillos Algunas reflexiones Realizar una aplicacion Web para dispositivos moviles es una tarea relativamente complicada debido a diversos factores resolucion de la pantalla ancho de banda
rapunzel
ue, 31 Aug 2010 17:03:00 GM
Fairy Tale of Allerleirauh: of Cover-Ups and Urged Silence. (Illustration Tatjana Hauptmann, Das Grosse Maerchenbuch, Diogenes Verlag). Grimm's Fairy Tale No. 65: Allerleirauh. There once lived a king, whose wife had golden hair. ...
