Broadband glossary: il glossario della banda larga

Definitions for Common Broadband Terms
Term list
ATM  |  CLEC  |  DVR  |  DOCSIS  |  HDTV  |  HFC  |  IP   |  LEC   |  LAN  |  MDU  |  MMDS  |  MPEG
MSO  |  NOC  |  PoP  |  POTS  |  PVR  |  QAM  |  RBOC  |  SOHO  |  SONET  |  USB  |  VOD  |  VoIP
Definitions

ATM (asynchronous transfer mode) – A standardized communications protocol, based on high-speed packet switching, where data are transmitted in chunks of 53-byte packets – five bytes reserved as a “header,” to indicate destination and to hold other housekeeping information, and the remaining 48 bytes composing the actual data payload. ATM was designed to carry many different types of data (voice, video and literally anything digitized), as well as to aptly handle time-sensitive traffic, like voice – where any delays in transmission would foul up how a phone conversation sounds. The original principle was one of “divide and conquer” – as in breaking large data files into the smallest possible size – 53 bytes – for uniformity and ease of handling. The “asynchronous” in ATM refers to an allowance, within the protocol’s parameters, for differences in time between a sender clock and a receiver clock.

CLEC (competitive local exchange carrier) – A term that entered the telecom lexicon as a result of the Telecommunications Act of 1996, and describes companies that target select regions to provide a choice in providers of local, long distance, data communication, and video services. The companies either lease or build their own telecommunications lines, both wired and wireless, and vie against incumbent local exchange carriers (ILECs), once known as “Baby Bells,” and interexchange carriers (IXCs), like AT&T and MCI.

DVR [or PVR] (digital [or personal] video recorder) – A consumer electronics device used to capture, store and play digitally encoded video to a television set or monitor. DVRs incorporate microprocessors capable of transforming analog video streams into MPEG-2 video, housing the encoded material on an enclosed hard disk, and just as quickly turning it back into an analog stream that can be heard and seen through an ordinary television set. Why bother? Because once the DVR has coaxed a TV signal into the malleable form of digital code, the DVR can work various wonders upon the signal, such as allowing viewers to pause or rewind what appears to be a live TV feed. In fact, the user is manipulating a recording of content that was, seconds ago, captured to the disk. DVRs also allow users to record and store requested television programs from a range of selection criteria, such as the name of a program, a favorite actor or genre.

DOCSIS (data over cable service interface specification) – A formal specification and testing process to assure that cable modems manufactured by different suppliers can interoperate with associated headend equipment made by different suppliers, regardless of which cable service provider uses the gear.

HDTV (high-definition television) – A digital television standard promising four times the picture resolution of today’s installed base of analog TVs. HDTV, standardized by the Advanced Television Systems Committee in 1996, doubles both vertical and horizontal resolution in today’s analog, NTSC-based displays, and adds CD-quality, digital sound.

HFC (hybrid fiber-coax) – The modern descriptor of how a cable television network is constructed, with a blend (hybrid) of fiber-optic cables and coaxial cable. Fibers extend outward from the headend in north-south-east-west directions, then join, at nodes, to coaxial cables that carry signals the rest of the way, to connected homes.

IP (Internet protocol) – The language of the Internet, used by data communications equipment to converse in such a manner that all of the pieces in the chain of Internet-related communications know where and how to send information.

It is also an acronym that does not transfer gracefully into spoken language. Example (say this aloud): “It seems like IP everywhere.”

Yet, it does seem like IP everywhere. Internet protocol is the language of cable modems, DSL modems, and even some digital video applications (such as the advanced digital cable boxes that contain a DOCSIS or other IP-based communications path). Voice-grade and carrier-class telephony is headed toward IP.
Mostly, IP puts addresses on packets of data. In a high-speed data network, for example, cable modems and DSL users are identified by their IP addresses.

LEC (local exchange carrier) – A company that provides local telephone service to businesses and residences. Also called Independent Local Exchange Carriers (ILECs), regional Bell operating companies (RBOCs), Baby Bells, and telcos. In the United States today, the five main LECs are SBC Communications, Qwest, Ameritech, BellSouth, and Verizon.

LAN (local area network) – The linking of multiple personal computers and peripheral devices like printers, scanners and servers, so as to share information and resources. LANs came into existence in the early 1980s; now, few organizations exist without them.

There are two main factors of a LAN: the transmission medium and the topology. Together, these dictate the type of data that can be sent, its speed, and the types of applications that can be shared and used by multiple, connected PCs.

LAN topologies run a gamut, and are named to reflect their logical shape: Examples include “ring,” “star,” “bus,” and “tree.” To some extent, the cable network itself is a large LAN.

MDU (multiple dwelling unit) – A term referring to residential housing complexes, such as apartment buildings, condominiums, or townhouses.

MMDS (multichannel multipoint distribution system) – An over-the-air technique for sending video and data signals from an origination point, over terrestrial microwave antennas, to multiple receivers. MMDS operators license spectrum in the 2.5-2.7 GHz range, using transmitters that can launch signals in a 30-70 kilometer radius. Using MPEG-2 digital video compression and 64 QAM (Quadrature Amplitude Modulation), MMDS operators can offer roughly 200 video channels, or about 1 Gbps of available bandwidth.
MMDS, also known as wireless cable, has historically been a reasonable way to serve rural areas with more channels than residents are otherwise able to see. Because housing densities are typically low – a farm every five or so miles, perhaps – wired cable providers have been hard-pressed to make the economics work. Wireless techniques fit the bill.

MPEG (Moving Pictures Expert Group) – The entity shepherded jointly by the International Standards Organization (ISO) and the International Electrotechnical Commission, which develops video compression standards. Its first effort was MPEG-1, which came out in 1991. In general, without MPEG compression, video information, when digitized, carries about the same characteristics (in terms of size) as it did in analog. But when digitized, video is ripe for a type of data compression realized by removing the picture elements that are the same from one frame of the video to the next. A common example given in describing video compression is a scene in which the only thing moving is an airplane, flying by. With compression, the first frame of background scenery is kept. Each frame of video that follows is marked – “same as the last one.” The airplane’s movement thus becomes the only element that needs attention.

MSO (multiple system operator) – A cable provider that owns more than one system or group of systems. MSOs include AT&T Broadband, Time Warner Cable, Cox Communications, Comcast Corp., Charter Communications, Adelphia Communications, and others. It used to be that there were hundreds of MSOs. Heavy consolidation in the late 1990s created an environment where the top eight MSOs, along with DBS providers, controlled 80 percent of the U.S. cable subscribers.

NOC (network operating center) – The physical location in which communications services are monitored for health, outages, bandwidth usage, and other back-office functions. Today, most major MSOs allocate resources or align with turnkey providers of NOC services, so that they can anticipate and quickly pinpoint outages and potential outages before their customers are affected.

PoP (point of presence) – A physical spot, usually a building, within a data or telecommunications network where signals are picked up and dropped off. The term itself came from the common carrier world, and is most commonly expressed as a word: “pop.” Generally speaking, long distance carriers own the PoPs, and use them to help other communications providers move their traffic on and off the long-haul network.

In that sense, the carrier building is the point. The entities that need to hop traffic on and off local cable, telco or wireless networks are the presence. Traditional local exchange carriers – Qwest, BellSouth, Verizon, etc. – own PoPs, too, and lease space out to alternative DSL providers.
Cable, in its open access work, will also need to provide PoPs: places where third-party ISPs connect up to the cable plant.

POTS – Acronym for Plain Old Telephone Service

PVR or [DVR] (personal [or digital] video recorder) – A consumer electronics device used to capture, store and play digitally encoded video to a television set or monitor. PVRs incorporate microprocessors capable of transforming analog video streams into MPEG-2 video, housing the encoded material on an enclosed hard disk, and just as quickly turning it back into an analog stream that can be heard and seen through an ordinary television set. Why bother? Because once the PVR has coaxed a TV signal into the malleable form of digital code, the PVR can work various wonders upon the signal, such as allowing viewers to pause or rewind what appears to be a live TV feed. In fact, the user is manipulating a recording of content that was, seconds ago, captured to the disk. PVRs also allow users to record and store requested television programs from a range of selection criteria, such as the name of a program, a favorite actor or genre.

QAM (quadrature amplitude modulation) – A method for printing digital signals onto a carrier for transportation from one place, such as a cable headend, to another, such as a home.
Even though the technique is called quadrature amplitude modulation, it also involves the use of phase modulation. What happens, loosely is this: Digital bits are grouped into symbols, which are then imprinted onto a carrier by manipulating two transmission characteristics: amplitude (power) and phase (frequency shape). The advantage is the ability to stuff twice as much information into the transmission channel.

RBOC (regional Bell operating companies) – The four (formerly seven) local telephone companies that came into existence after AT&T was forced to divest itself of its (at the time) 22 local telephone companies. (They’re also known as Baby Bells.) The 22 AT&T companies were geographically clumped into what was, at the time, Nynex, Bell Atlantic, BellSouth, Ameritech, U S West, Southwestern Bell, and Pacific Bell. Now, Nynex owns Bell Atlantic; U S West’s name is Qwest; Southwestern Bell owns Pacific Bell and Ameritech.

SOHO – Acronym for Small office/Home office

SONET (synchronous optical network) – A standardized set of high-speed, digital backbone parameters, such as transmission speed (OC-1 through OC-768 and higher), and interfaces among multiple equipment suppliers. In cable systems, SONET techniques usually happen after the headend-to-subscriber side of the network, but on the high-speed fiber backbone side.

USB (universal serial bus) – A standardized way to plug peripherals into a PC, and the technology that gave rise to the term “plug and play.” A cable modem outfitted with a USB connector, for example, can easily plug into a USB receptacle on the back of a PC, and the PC’s owner doesn’t have to deal with popping the hood, installing a network interface card, and potentially bungling everything up. Technically, USB is an input/output bus technology developed for PC and Macintosh computers, running data at about 12 Mbps.

VOD (video-on-demand) – A method of providing television programs that respond to viewer-initiated commands similar to those associated with VCRs.

A VOD program demands a unique connection between one viewer’s television and one provider’s machinery. For the duration of a VOD session, or the period of time in which a viewer has access to a VOD program, the viewer effectively rents a unique slice of network bandwidth that is devoted only to that user. In most instances, viewers can summon programs at will; impose VCR-like commands on the program stream (pause, rewind, fast forward); and, depending on the licensing arrangements provided by cable TV or broadband service provider, enjoy access to the supplied movie or video content for a period of 24 hours or longer. Most VOD architectures plant the content itself in giant video servers tied to a two-way network, although there are other models, such as personal video recorder systems that capture program feeds in home-based servers, making them available for on-demand viewing later.

VoIP (voice-over IP) – The technologies and business practices that let residential and business customers make telephone calls using the Internet infrastructure, instead of the traditional telephone network. Cable VoIP essentially duplicates, in software, the way in which calls are made on today’s analog, telco-delivered network.

 

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