To see the relationship between the E-carrier system, the T-carrier system, and DS0 multiples, see Digital Signal X.
E1 (or E-1) is a European digital transmission format devised by the ITU-TS and given the name by the Conference of European Postal and Telecommunication Administration (CEPT). It's the equivalent of the North American T-carrier system format. E2 through E5 are carriers in increasing multiples of the E1 format.
The E1 signal format carries data at a rate of 2.048 million bits per second and can carry 32 channels of 64 Kbps * each. E1 carries at a somewhat higher data rate than T-1 (which carries 1.544 million bits per second) because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal. E1 and T-1 can be interconnected for international use.
E2 (E-2) is a line that carries four multiplexed E1 signals with a data rate of 8.448 million bits per second.
E3 (E-3) carries 16 E1 signals with a data rate of 34.368 million bits per second.
E4 (E-4) carries four E3 channels with a data rate of 139.264 million bits per second.
E5 (E-5) carries four E4 channels with a data rate of 565.148 million bits per second.
* In international English outside the U.S., the equivalent usage is "kbps" or "kbits s-1."
Echelon is an officially unacknowledged U.S.-led global spy network that operates an automated system for the interception and relay of electronic communications. Monitored transmissions are said to include up to 3 billion communications daily, including all the telephone calls, e-mail messages, faxes, satellite transmissions, and Internet downloads of both public and private organizations and citizens worldwide. Led by the U.S. National Security Agency (NSA ), Echelon is operated collaboratively by the intelligence agencies of the United States, the United Kingdom, Australia, Canada, and New Zealand. The organization's name originated as the code name for the system component responsible for intercepting satellite communications.
Echelon collects information through an extensive system of radio antennae and satellites that monitor satellite communications and sniffer devices that collect Internet communications from data packets. Some sources claim that the organization employs underwater devices to tap into transcontinental fiber optic phone cables. According to the ACLU, Echelon gathers huge volumes of data indiscriminately, and then filters out useful information through artificial intelligence (AI) technology. The system is also said to involve voice recognition, language translation, and keyword searching to select messages to study in their entirety.
According to recent reports, Echelon enabled intelligence gatherers to learn several months prior to the World Trade Center strike that some sort of large-scale action was planned, although the details were insufficient to avert it.deit is not clear how much detail was learned. While Echelon is clearly considered an asset by the intelligence community , some organizations and individuals are made uneasy by claims that the organization monitors well-intentioned endeavors, such as Amnesty International. The Scientific and Technical Options Assessment program office (STOA) of the European Parliament recently commissioned two reports looking into Echelon. These reports found: that the organization exists; that it routinely intercepts both personal and business communications, in probable contravention of human rights; and that stringent encryption practices should be followed to protect against Echelon's transgressive invasions of privacy.
As counter-terrorist activity intensifies following the events of September 11, 2001, Echelon activity is also considered likely to intensify.
EGB - Exterior Gateway Protocol:
See Exterior Gateway Protocol
Encryption is the conversion of data into a form, called a ciphertext, that cannot be easily understood by unauthorized people. Decryption is the process of converting encrypted data back into its original form, so it can be understood.
The use of encryption/decryption is as old as the art of communication. In wartime, a cipher, often incorrectly called a "code," can be employed to keep the enemy from obtaining the contents of transmissions. (Technically, a code is a means of representing a signal without the intent of keeping it secret; examples are Morse code and ASCII.) Simple ciphers include the substitution of letters for numbers, the rotation of letters in the alphabet, and the "scrambling" of voice signals by inverting the sideband frequencies. More complex ciphers work according to sophisticated computer algorithms that rearrange the data bits in digital signals.
In order to easily recover the contents of an encrypted signal, the correct decryption key is required. The key is an algorithm that "undoes" the work of the encryption algorithm. Alternatively, a computer can be used in an attempt to "break" the cipher. The more complex the encryption algorithm, the more difficult it becomes to eavesdrop on the communications without access to the key.
Encryption/decryption is especially important in wireless communications. This is because wireless circuits are easier to "tap" than their hard-wired counterparts. Nevertheless, encryption/decryption is a good idea when carrying out any kind of sensitive transaction, such as a credit-card purchase online, or the discussion of a company secret between different departments in the organization. The stronger the cipher -- that is, the harder it is for unauthorized people to break it -- the better, in general. However, as the strength of encryption/decryption increases, so does the cost.
In recent years, a controversy has arisen over so-called strong encryption. This refers to ciphers that are essentially unbreakable without the decryption keys. While most companies and their customers view it as a means of keeping secrets and minimizing fraud, some governments view strong encryption as a potential vehicle by which terrorists might evade authorities. These governments, including that of the United States, want to set up a key-escrow arrangement. This means everyone who uses a cipher would be required to provide the government with a copy of the key. Decryption keys would be stored in a supposedly secure place, used only by authorities, and used only if backed up by a court order. Opponents of this scheme argue that criminals could hack into the key-escrow database and illegally obtain, steal, or alter the keys. Supporters claim that while this is a possibility, implementing the key escrow scheme would be better than doing nothing to prevent criminals from freely using encryption/decryption.
ENUM is a standard adopted by the Internet Engineering Task Force (IETF) that uses the domain name system (DNS) to map telephone numbers to Web addresses or uniform resource locators (URL). The goal of the ENUM standard is to provide a single number to replace the multiple numbers and addresses for an individual's home phone, business phone, fax, cell phone, and e-mail. The ENUM standard is a joint effort of Telecordia and Verisign. Every toll-free call in the United States depends on Telecordia software. Verisign is the leader in translating over 24 million .com, .NET, and .org domain names on the Internet. Verisign is also a leader in Internet security.
Ethernet is a network standard of communication using either coaxial or twisted pair cable. The most widely used for of LAN communication, Ethernet typically runs at 10 megabytes per second, though newer systems use 100 Mbps, or ever gigabit of transfer.
Ethernet is the IEEE standard 802.3. It has several different flavors, with the original Ethernet designed with 10base5. The "10" stands for 10 megabytes per second. Base is the Baseband communications it uses. The "5" stands for a maximum distance of 500 meters to communicate with. Original Ethernet used coaxial wiring, while newer versions use twisted-pair cabling. There are several flavors of Ethernet, including 10Base2 (10 Mbps, 200 meters), 10BaseT (10 Mbps, 100 meters, twisted-pair), and 100BaseT (100 Mbps, 100 meter, twisted-pair).
Exabyte - EB:
An exabyte (EB) is a large unit of computer data storage, two to the sixtieth power bytes. The prefix exa means one billion billion, or one quintillion, which is a decimal term. Two to the sixtieth power is actually 1,152,921,504,606,846,976 bytes in decimal, or somewhat over a quintillion (or ten to the eighteenth power) bytes. It is common to say that an exabyte is approximately one quintillion bytes. In decimal terms, an exabyte is a billion gigabytes.
In information technology, extensible describes something, such as a program, programming language, or protocol, that is designed so that users (or later designers) can extend its capabilities. Extensibility can be a primary reason for the system, as in the case of the Extensible Markup Language (XML), or it may be only a minor feature. Approaches to extensibility include facilities (sometimes called hooks) for allowing users to insert their own program routines, the ability to define new data types, and the ability to define new formatting markup tags.
Extensible Hypertext Markup Language - XHTML:
As the World Wide Web Consortium (W3C) describes it, XHTML (Extensible Hypertext Markup Language) is "a reformulation of HTML 4.0 as an application of the Extensible Markup Language (XML )." For readers unacquainted with either term, HTML is the set of codes (that's the "markup language") that a writer puts into a document to make it displayable on the World Wide Web. HTML 4 is the current version of it. XML is a structured set of rules for how one might define any kind of data to be shared on the Web. It's called an "extensible" markup language because anyone can invent a particular set of markup for a particular purpose and as long as everyone uses it (the writer and an application program at the receiver's end), it can be adapted and used for many purposes - including, as it happens, describing the appearance of a Web page. That being the case, it seemed desirable to reframe HTML in terms of XML. The result is XHTML, a particular application of XML for "expressing" Web pages.
XHTML is, in fact, the follow-on version of HTML 4. You could think of it as HTML 5, except that it is called XHTML 1.0. In XHTML, all HTML 4 markup elements and attributes (the language of HTML) will continue to be supported. Unlike HTML, however, XHTML can be extended by anyone that uses it. New elements and attributes can be defined and added to those that already exist, making possible new ways to embed content and programming in a Web page. In appearance, an XHTML file looks like a somewhat more elaborate HTML file.
Advantages: To quote the W3C again, the advantages are "extensibility and portability."
Extensibility means that as new ideas for Web communication and presentation emerge, they can be implemented without having to wait for the next major version of HTML and browser support. New tags or attributes can be defined to express the new possibilities and, assuming some program at the receiving end can understand and act on them, new things may happen on your Web page that never happened before. Specific sets of extensions for XHTML are planned for mathematical expressions, vector graphics, and multimedia applications.
If extensibility is likely to lead to more complicated pages and larger programs, the portability advantage means that Web pages can now be made simpler than they were before so that small devices can handle them. This is important for mobile devices and possibly household devices that contain microprocessors with embedded programming and smaller memories. XHTML defines several levels of possible markup complexity and each document states its level of complexity at the beginning. Programs in microdevices might expect XHTML-coded files that state the simplest level of complexity so that they could be handled by a small program and memory.
Differences and Distinctive Features: You can find out more by reading the specification and tutorials, but here are some distinctive features of XHTML and differences between HTML 4:
* XHTML requires strict adherence to coding rules. Notably, it requires that you use closing as well as opening elements (this is known as well-formed syntax ) and that all elements be in lower case. HTML was much less rigorous about notation and browsers tended to be even more forgiving.
* This means that XHTML files will tend to be "busier" than HTML. However, they won't necessarily be harder to read because rigor may force more order in coding. In addition, the major editing and file creation tools will probably lay out pages for easier readability.
* XHTML would seem to encourage a more structured and conceptual way of thinking about content and, combined with the style sheet, a more creative way of displaying it.
* XHTML will make it easier for people to dream up and add new elements (and develop browsers or other applications that support them).
Extensible Markup Language - XML:
XML (Extensible Markup Language) is a flexible way to create common information formats and share both the format and the data on the World Wide Web, intranets, and elsewhere. For example, computer makers might agree on a standard or common way to describe the information about a computer product (processor speed, memory size, and so forth) and then describe the product information format with XML. Such a standard way of describing data would enable a user to send an intelligent agent (a program) to each computer maker's Web site, gather data, and then make a valid comparison. XML can be used by any individual or group of individuals or companies that wants to share information in a consistent way.
XML, a formal recommendation from the World Wide Web Consortium (W3C), is similar to the language of today's Web pages, the Hypertext Markup Language (HTML). Both XML and HTML contain markup symbols to describe the contents of a page or file. HTML, however, describes the content of a Web page (mainly text and graphic images) only in terms of how it is to be displayed and interacted with. For example, the letter "p" placed within markup tags starts a new paragraph. XML describes the content in terms of what data is being described. For example, the word "phonenum" placed within markup tags could indicate that the data that followed was a phone number. This means that an XML file can be processed purely as data by a program or it can be stored with similar data on another computer or, like an HTML file, that it can be displayed. For example, depending on how the application in the receiving computer wanted to handle the phone number, it could be stored, displayed, or dialed.
XML is "extensible" because, unlike HTML, the markup symbols are unlimited and self-defining. XML is actually a simpler and easier-to-use subset of the Standard Generalized Markup Language (SGML ), the standard for how to create a document structure. It is expected that HTML and XML will be used together in many Web applications. XML markup, for example, may appear within an HTML page.
Early applications of XML include Microsoft's Channel Definition Format (CDF), which describes a channel , a portion of a Web site that has been downloaded to your hard disk and is then is updated periodically as information changes. A specific CDF file contains data that specifies an initial Web page and how frequently it is updated. Another early application is ChartWare, which uses XML as a way to describe medical charts so that they can be shared by doctors. Applications related to banking, e-commerce ordering, personal preference profiles, purchase orders, litigation documents, part lists, and many others are anticipated.
Exterior Gateway Protocol - EGP:
Exterior Gateway Protocol (EGP) is a protocol for exchanging routing information between two neighbor gateway hosts (each with its own router ) in a network of autonomous systems. EGP is commonly used between hosts on the Internet to exchange routing table information. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen. Each router polls its neighbor at intervals between 120 to 480 seconds and the neighbor responds by sending its complete routing table. EGP-2 is the latest version of EGP. A more recent exterior gateway protocol, the Border Gateway Protocol (BGP), provides additional capabilities. Also see Interior Gateway Protocol (IGP).