Word of the Day : Bit Stuffing

bit stuffing

Bit stuffing is the insertion of one or more bits into a transmission unit as a way to provide signaling information to a receiver. The receiver knows how to detect and remove or disregard the stuffed bits.

For example, the timing or bit rate of T-carrier system signals is constantly synchronized between any terminal device and an adjacent repeater or between any two repeaters. The synchronization is achieved by detecting the transition in polarity for 1 bits in the data stream. (T-1 signalling uses bipolar signaling, where each successive bit with a value of 1 is represented by voltage with a reverse polarity from the previous bit. Bits with a value of 0 are represented by a no-voltage time slot.) If more than 15 bits in a row are sent with a 0 value, this "lull" in 1 bits that the system depends on for synchronization may be long enough for two end points to become out of synchronization. To handle this situation (the sequence of more than 15 0 bits), the signal is "stuffed" with a short, unique bit pattern (which includes some 1 bits) that is recognized as a synchronization pattern. The receiving end removes the stuffed bits and restores the bit stream to its original sequence.

In another example of bit stuffing, a standard HDLC packet begins and ends with 01111110. To make sure this sequence doesn't appear again before the end of the packet, a 0 is inserted after every five consecutive 1s.

Bit stuffing is defined by some to include bit padding, which is the addition of bits to a tranmission to make the transmission unit conform to a standard size, but is distinct from bit robbing, a type of in-band signaling.

Word of the Day : WYSIWYP

WYSIWYP (what you see is what you print)

WYSIWYP (what you see is what you print) is the ability of an application program, such as a word processor, to generate print versions of content that match what the user sees on the screen. The WYSIWYP feature is intended to resolve a problem that has plagued users of word processors ever since computers replaced typewriters: printouts often differ from their on-screen counterparts.

A printout from a program with WYSIWYP should have the same layout, resolution and colors as the onscreen version. However, the success of WYSIWYP may depend, to some extent, on user hardware and associated software.

The term is a variation on WYSIWYG (what you see is what you get) and is pronounced similarly: "whizzy-whip."

Word of the Day : WS-Transaction (WS-TX)

WS-Transaction (WS-TX)

WSTx (Web Services Transaction) is a set of XML markup specifications designed to permit the use of open, standard protocols for secure, reliable transactions across the Web. Three constituent standards were approved in April 2007:

• WS-Coordination
• WS-AtomicTransaction
• WS-BusinessActivity

The standards were created to accommodate two typical transaction patterns involving multiple, distributed software components and services:

1. Individual atomic transactions that represent the building blocks for more complex transactions among peers and partners

2. Web-based interactions that result in the exchange of goods, information, or services, usually called business activities.

WS-coordination refers to the mechanisms whereby atomic transactions may be composed into complete business activities, and thus also provides the glue that ties the overall WSTx environment together.

WSTx standards are overseen by a technical committee of the same name at OASIS. The technical committee is staffed with vendors and users of Web services technologies. On its Web pages, the committee describes its agenda as: "...to define a set of protocols to coordinate the outcomes of distributed application actions." Vendors involved in the WSTx committee include Adobe, BEA Systems, Fujitsu, Hitachi, IBM, Microsoft, Oracle, SAP and TIBCO, among numerous others.

Word of the Day : Electromagnetic fields

An electromagnetic field, sometimes referred to as an EM field, is generated when charged particles, such as electrons, are accelerated. All electrically charged particles are surrounded by electric fields. Charged particles in motion produce magnetic fields. When the velocity of a charged particle changes, an EM field is produced.

Electromagnetic fields were first discovered in the 19th century, when physicists noticed that electric arcs (sparks) could be reproduced at a distance, with no connecting wires in between. This led scientists to believe that it was possible to communicate over long distances without wires. The first radio transmitters made use of electric arcs. These "spark transmitters" and the associated receivers were as exciting to people in the early 20th century as the Internet is today. This was the beginning of what we now call wirelesscommunication.

Electromagnetic fields are typically generated by alternating current (AC) in electrical conductors. The frequencyof the AC can range from one cycle in thousands of years (at the low extreme) to trillions or quadrillions of cycles per second( at the high extreme). The standard unit of EM frequency is the hertz, abbreviated Hz.Larger units are often used. A frequency of 1,000 Hz is onekilohertz(kHz); a frequency of 1,000 kHz is one megahertz (MHz); a frequency of 1,000 MHz is one gigahertz (GHz).

The wavelength of an EM field is related to the frequency. If the frequency f of an EM wave is specified in megahertz and the wavelength w is specified in meters (m), then in free space, the two are related according to the formula:

w = 300/f

For example, a signal at 100 MHz (in the middle of the American FM broadcast band) has a wavelength of 3 m, or about 10 feet. This same formula applies if the frequency misgiven in gigahertz and the wavelength is specified in millimeters (mm). Thus, a signal at 30 GHz would have a wavelength of 10 mm, or a little less than half an inch.

The realm of EM field energy is called the electromagnetic radiation spectrum. In theory, this extends from arbitrarily long wavelengths to arbitrarily short wavelengths, or, as engineers sometimes imprecisely quip, "from DC to light."

Word of the Day : Dogfood

Dogfood is an expression that means "to use the product or service that you are trying to sell."

Dogfood can be used as a noun, as in the sentence "A company that eats its own dog food sends the message that it considers its own products to be the best on the market." Or it can be used as a verb, as in the sentence "We need to dogfood this product before we roll it out to the public."

The expression was inspired by an advertising campaign for commercial dog food from the 1970's where actor Lorne Greene told consumers "And when it comes to feeding my own dog, I know there isn't a better dog food than Alpo." The message to the consumer was that the product spokesman thought Alpo was so good that he used it himself.

According to Paul Vick, Microsoft's tech lead for Visual Basic Development, dogfood is part of the company culture at Microsoft because:

1) It proves to customers that Microsoft believes in their products.
2) It helps flush out bugs, because dogfooding involves beta (or pre-beta) software.
3) It makes Microsoft employees suffer the same bugs and design flaws that they inflict on users, thereby providing incentive to fix them.
4) It's a valuable reality check that the product is actually as good as Microsoft says it is.
5) Because Microsoft is such a large company, dogfooding an enterprise-level product can flush out problems that could not otherwise be found prior to full-scale rollout at launch.
6) It allows Microsoft developers to learn how their products actually work, which may not be exactly how developers think they work.

Word of the Day : Deep packet inspection (DPI)

Deep packet inspection (DPI)

Deep packet inspection (DPI) is an advanced method of packet filtering that functions at the application layer of the OSI (Open Systems Interconnection) reference model. The use of DPI makes it possible to find, identify, classify, reroute or block packets with specific data or code payloads that conventional packet filtering, which examines only packet headers, cannot detect.

Using DPI, communications service providers can allocate available resources to streamline traffic flow. For example, a message tagged as high priority can be routed to its destination ahead of less important or low-priority messages or packets involved in casual Internet browsing. DPI can also be used for throttled data transfer to prevent P2P (peer-to-peer) abuse, improving network performance for most subscribers. The security implications of DPI are widespread because the technology makes it possible to identify the originator or recipient of content containing specific packets, a capability that has sparked concern among advocates of online privacy.

DPI has at least three significant limitations. First, it can create new vulnerabilities as well as protect against existing ones. While effective against buffer overflow attacks, denial of service attacks and certain types of malware, DPI can also be exploited to facilitate attacks in those same categories. Second, DPI adds to the complexity and unwieldy nature of existing firewalls and other security-related software. DPI requires its own periodic updates and revisions to remain optimally effective. Third, DPI can reduce computer speed because it increases the burden on the processor. Despite these limitations, many network administrators have embraced DPI technology in an attempt to cope with a perceived increase in the complexity and widespread nature of Internet-related perils.

Numerous companies, including such major players as Alcatel, Cisco, Ericsson, IBM, Microsoft, Nokia and Symantec have begun to aggressively market DPI technology as components of hardware and software firewalls.

Word of the Day : Fast Infoset (FI)

Fast Infoset (FI)

Fast Infoset (FI) is a standard that can serve as an alternative to XML (Extensible Markup Language) document formatting. The FI specification, which was approved by the ITU (International Telecommunication Union) in May 2005 and published in March 2007, is designed to provide more efficient serialization than XML.

Documents in XML format can be converted to FI format and vice-versa without loss of content. In a simplified sense, FI documents resemble compressed XML documents. However, Fast Infoset optimizes the speed with which ASN.1 binary encoding is generated and processed and minimizes the file size. The FI specification defines encoding for an XML infoset, a data model consisting of up to 11 components known as:

• Document information items
• Document type declaration information items
• Character information items
• Notation information items
• Namespace information items
• Element information items
• Attribute information items
• Processing instruction information items
• Unexpanded entity reference information items
• Comment information items
• Unparsed entity information items.

The FI specification is also known as ITU-T Rec. X.891 and ISO-IEC 24821-1.