H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks. H.323 was originally promoted as a way to provide consistency in audio, video and data packet transmissions in the event that a local area network (LAN) did not provide guaranteed service quality (QoS ). Although it was doubtful at first whether manufacturers would adopt H.323, it is now considered to be the standard for interoperability in audio, video and data transmissions as well as Internet phone and voice-over-IP (VoIP) because it addresses call control and management for both point-to-point and multipoint conferences as well as gateway administration of media traffic, bandwidth and user participation.
H.323, which describes how multimedia communications occur between terminals , network equipment and services, is part of a larger group of ITU recommendations for multi-media interoperability called H.3x. The latest of these recommendations, H.248, is a recommendation to provide a single standard for the control of gateway devices in multi-media packet transmissions to allow calls to connect from a LAN to a Public Switched Telephone Network (PSTN), as well as to other standards-based terminals. This recommendation was announced in August 2000, by the ITU-TU Study Group 16 and the Megaco Working Group of the Internet Engineering Task Force (IETF).
Hacker is a term used by some to mean "a clever programmer" and by others, especially journalists or their editors, to mean "someone who tries to break into computer systems."
1) Eric Raymond, compiler of The New Hacker's Dictionary , defines a hacker as a clever programmer. A "good hack" is a clever solution to a programming problem and "hacking" is the act of doing it. Raymond lists five possible characteristics that qualify one as a hacker, which we paraphrase here:
* A person who enjoys learning details of a programming language or system
* A person who enjoys actually doing the programming rather than just theorizing about it
* A person capable of appreciating someone else's hacking
* A person who picks up programming quickly
* A person who is an expert at a particular programming language or system, as in "UNIX hacker"
Raymond deprecates the use of this term for someone who attempts to crack someone else's system or otherwise uses programming or expert knowledge to act maliciously. He prefers the term cracker for this meaning.
2) Journalists or their editors almost universally use hacker to mean someone who attempts to break into computer systems. Typically, this kind of hacker would be a proficient programmer or engineer with sufficient technical knowledge to understand the weak points in a security system. For more on this usage, see cracker.
In an ideal cellular telephone network, each end user's telephone set or modem (the subscriber's hardware) is always within range of a base station. The region covered by each base station is known as its cell. The size and shape of each cell in a network depends on the nature of the terrain in the region, the number of base stations, and the transmit/receive range of each base station. In theory, the cells in a network overlap; for much of the time, a subscriber's hardware is within range of more than one base station. The network must decide, from moment to moment, which base station will handle the signals to and from each and every subscriber's hardware.
Each time a mobile or portable cellular subscriber passes from one cell into another, the network automatically switches coverage responsibility from one base station to another. Each base-station transition, as well as the switching process or sequence itself, is called handoff. In a properly functioning network, handoff occurs smoothly, without gaps in communications and without confusion about which base station should be dealing with the subscriber. Subscribers to a network need not do anything to make handoff take place, nor should they have to think about the process or about which base station is dealing with the signals at any given moment.
Half-Duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. For example, on a local area network using a technology that has half-duplex transmission, one workstation can send data on the line and then immediately receive data on the line from the same direction in which data was just transmitted. Like full-duplex transmission, half-duplex transmission implies a bidirectional line (one that can carry data in both directions).
In telephone communication, Handshaking is the exchange of information between two modems and the resulting agreement about which protocol to use that precedes each telephone connection. You can hear the handshaking in those crunching and other sounds when you make a dial-out call from your computer.
Since the modems at each end of the line may have different capabilities, they need to inform each other and settle on the highest transmission speed they can both use. At higher speeds, the modems have to determine the length of line delays so that echo cancellers can be used properly. The most common modem standards are briefly described in our V.xx page.
HiperLAN is a set of wireless local area network (WLAN) communication standards primarily used in European countries. There are two specifications: HiperLAN/1 and HiperLAN/2. Both have been adopted by the European Telecommunications Standards Institute (ETSI).
The HiperLAN standards provide features and capabilities similar to those of the IEEE 802.11 wireless local area network (LAN) standards, used in the U.S. and other adopting countries. HiperLAN/1 provides communications at up to 20 Mbps in the 5-GHz range of the radio frequency (RF) spectrum. HiperLAN/2 operates at up to 54 Mbps in the same RF band. HiperLAN/2 is compatible with 3G (third-generation) WLAN systems for sending and receiving data, images, and voice communications. HiperLAN/2 has the potential, and is intended, for implementation worldwide in conjunction with similar systems in the 5-GHz RF band.
Also see 802.11.
A Honey Pot is a computer system on the Internet that is expressly set up to attract and "trap" people who attempt to penetrate other people's computer systems. (This includes the hacker, cracker, and script kiddy.) To set up a honey pot, it is recommended that you:
* Install the operating system without patches installed and using typical defaults and options
* Make sure that there is no data on the system that cannot safely be destroyed
* Add the application that is designed to record the activities of the invader
Maintaining a honey pot is said to require a considerable amount of attention and may offer as its highest value nothing more than a learning experience (that is, you may not catch any hackers).
Hosting (also known as Web site hosting, Web hosting, and Webhosting) is the business of housing, serving, and maintaining files for one or more Web site s. More important than the computer space that is provided for Web site files is the fast connection to the Internet. Most hosting services offer connections on T-carrier system lines. Typically, an individual business hosting its own site would require a similar connection and it would be expensive. Using a hosting service lets many companies share the cost of a fast Internet connection for serving files.
A number of Internet access providers, such as America Online, offer subscribers free space for a small Web site that is hosted by one of their computers. Geocities is a Web site that offers registered visitors similar free space for a Web site. While these services are free, they are also very basic.
A number of hosting companies describe their services as virtual hosting. Virtual hosting usually implies that their services will be transparent and that each Web site will have its own domain name and set of e-mail addresses. In most usages, hosting and virtual hosting are synonyms. Some hosting companies let you have your own virtual server, the appearance that you are controlling a server that is dedicated entirely to your site.
Dedicated hosting is the provision of a dedicated server machine that is dedicated to the traffic to your Web site. Only very busy sites require dedicated hosting. Many companies purchase their own servers and place them on a site that provides fast access to the Internet. This practice is called colocation.
htm is sometimes used as a short form of the file name suffix for an HTML file. For example, the file for our definition of computer might be named "computer.htm" instead of "computer.html". The main advantage is that it's one character shorter. The disadvantage is that it's not quite as easy to recognize as an HTML file. Prior to wide-spread use of Windows 95 and later systems, there was another reason to prefer the three-character suffix rather than the four-character. Certain operating systems, such as Windows 3.1 and OS/2 used the original DOS operating system naming conventions, in which names were limited to eight characters and suffixes to three characters. So it was safer to create file names and suffixes that met this "8.3" limitation. (For example, if you created an HTML page coding hypertext links to your other pages based on a four-character suffix (".html") system and then moved that page to a Web server that only allowed a three-character suffix, your file name suffixes would all be shortened and your links would no longer work. And if you created links with the three-character suffix and moved it to a server that always required four-character suffixes for HTML files, you would be in trouble again.)
Today, the operating systems most people are likely to create HTML pages on and serve them from are all operating systems (such as Windows 95/98/NT, Mac OS, and UNIX-based systems) that support longer file names and suffixes. So if you were building a new Web site, you would most likely use the four-character html suffix for clarity (unless you preferred the brevity of the three-character suffix) because you could know that you could safely use either suffix - as long as the suffixes in your links and your file names matched.
However, if you have an existing Web site that started out using the three-character suffix, you may prefer to leave everything as it is. If you do move to a server that requires a four-character suffix for server consistency, you could do a search-and-replace at that time.
HTML - Hyper Text Make Up Language:
See Hypertext Markup Language.
HTTP - Hypertext Transfer Protocol:
See Hypertext Transfer Protocol.
Hyper Text Make Up Language - HTML:
Hypertext Markup Language (HTML) is the set of markup symbols or codes inserted in a file intended for display on a World Wide Web browser page. The markup tells the Web browser how to display a Web page's words and images for the user. Each individual markup code is referred to as an element (but many people also refer to it as a tag). Some elements come in pairs that indicate when some display effect is to begin and when it is to end.
HTML is a formal Recommendation by the World Wide Web Consortium (W3C ) and is generally adhered to by the major browsers, Microsoft's Internet Explorer and Netscape's Navigator, which also provide some additional non-standard codes. The current version of HTML is HTML 4.0 . However, both Internet Explorer and Netscape implement some features differently and provide non-standard extensions. Web developers using the more advanced features of HTML 4 may have to design pages for both browsers and send out the appropriate version to a user. Significant features in HTML 4 are sometimes described in general as dynamic HTML. What is sometimes referred to as HTML 5 is an extensible form of HTML called Extensible Hypertext Markup Language (XHTML).
Hypertext Transfer Protocol - HTTP:
The Hypertext Transfer Protocol (HTTP) is the set of rules for exchanging files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. Relative to the TCP/IP suite of protocols (which are the basis for information exchange on the Internet), HTTP is an application protocol.
Essential concepts that are part of HTTP include (as its name implies) the idea that files can contain references to other files whose selection will elicit additional transfer requests. Any Web server machine contains, in addition to the HTML and other files it can serve, an HTTP daemon, a program that is designed to wait for HTTP requests and handle them when they arrive. Your Web browser is an HTTP client, sending requests to server machines. When the browser user enters file requests by either "opening" a Web file (typing in a Uniform Resource Locator) or clicking on a hypertext link, the browser builds an HTTP request and sends it to the Internet Protocol address indicated by the URL. The HTTP daemon in the destination server machine receives the request and, after any necessary processing, the requested file is returned.