Usage: The cable viewpoint is that every last-mile distribution method, with the possible exception of fixed wireless, is narrowband, meaning that the alternatives cannot yet adequately or economically handle the simultaneous transmission of living-room quality digital video, high-speed Internet access, and phone.
Further, the “NCTAs mission is to advance the public policies of the cable television industry before Congress, the executive branch, the courts and the American public. Working with state cable associations, NCTA also presents the industry’s interests to organizations representing state and local policy makers. NCTA hosts the industry’s annual trade show, which typically features more than 300 exhibiting companies and attracts more than 30,000 attendees.
The NCTA is overseen by a board of directors populated by the CEOs of cable and member companies; a variety of working committees address specific issues. The organization itself is staffed by about 85 individuals, in departments including: Association Affairs (with subcategories handling cable signal theft and rural system issues), communications, government relations, industry affairs/administration, legal, program network policy, public affairs, and science/technology. Web site: www.ncta.com.
Usage: Most cable providers segment capital expenditures for plant into three categories: New built/line extension, rebuild, and upgrade.
In its early iterations, NGNA was a fairly heavily guarded topic amongst its participants. It began as a way to collate industrial mindsets around “all-digital,” or, the migration to wholly digital networks. Another tenet was to shift, as entirely as possible, away from proprietary technologies. And, the MSOs wanted to provide focus to the supplier community about advanced codecs, OCAP, alternative two-way signal paths, and open conditional access. Elements of DOCSIS 3.0 and M-CMTS also grew out of NGNA. Two areas were specifically excluded: Plant, and back office functions, like billing and device/service provisioning.
In Spring of 2004, NGNA was “closed” as a separate, privately-held company, and its contents shifted to CableLabs for development.
Usage: A rule of thumb in NID design is to enable at least four lines of residential phone service per unit.
The first time you walk into a NOC, you’re likely to be struck by the Star Wars-ness of it. (If for no other reason than this: If youve been invited into a NOC, it’s usually to instill in you that very sense.) Heads-up displays line the upper portion of the walls, showing detailed maps of plant layout and links to other networks. In most cases, NOCs have the ability to drill down to individual components within the plant, showing inputs, outputs and performance statistics (Am I healthy? Am I getting overloaded? Have I died?). Blinking colors show alarm areas. Employees sit at banks of computers, busily attending to network health needs.
In local area networks, nodes are connected devices — individual PCs, printers, scanners — identifiable by their individual MAC (media access control) address.
Usage: Most cable HFC networks are designed to handle between 500-1000 homes per node.
What’s needed to split a node is another node: Double the optoelectronics, halve the number of home sharing bandwidth, the logic goes. The (circa 2005) rule of thumb on node-splitting: One person, half a day, about $1,000.
The IEEE defines noise as “unwanted disturbances superposed upon a useful signal that tend to obscure its information content.” Cable engineers use a more strict definition, classifying noise as “thermal,” meaning it is both unpredictable, and doesnt repeat.
Thermal noise is a function of HFC transmission characteristics and bandwidth-per-channel, and is usually expressed in decibels relative to microvolts (mV), or dBmV. When designing cable systems, engineers calculate the minimum thermal noise power figure, expressed as “the noise floor.” The noise floor in cable systems is generally recognized to exist at (-) 59 dBmV.
In general, when the noise floor rises, signals degrade or slow down (in the case of some digital transmission systems.) This is no different than driving on a heavily pocked and pitted road. It makes you slow down. The potholes, in this case, are the noise. On a smooth road — no potholes, no noise — you can go faster. Same idea.
Noise is also an element in two of the most commonly used design parameters in cable systems: The carrier-to-noise ratio (also known as “C/N” and “CNR”) and the signal-to-noise ratio (also known as “S/N” and “SNR.”) Carrier-to-noise ratio quantifies noise figures of individual amplifiers, input levels to each amplifiers, and the number of amplifiers in cascade, to come up with an end-of-line “budget” of acceptable CNR. SNR measures noises as a function of signal level, and is also used to calculate an end-of-line “budget” of acceptability.
Noise is particularly prevalent in the 5-40 MHz spectral area used by cable operators to send signals from homes to the headend. Here, two other types of noise enter the discussion: Impulse noise, generated by random bursts of unwanted electricity, and ingress, which happens when signals leak into a section of coaxial cable.
If noise predictably repeats, noise cancellation filters can be used to remove it. Usually, this is done by sampling the slice of noise, then inverting it by 180 degrees, and adding it to the original signal containing the noise.
In digital transmissions, some noise can be corrected through a technique known as “forward error correction.” Reed-Solomon encoding is one example of a forward error correction technique, which lets the receive end detect and fix mistakes to data packets, caused by noise, without requiring the transmitter to resend the packets.
Nonetheless, NVOD is an outgrowth of digital video compression, and works by reserving a chunk of spectrum such that the same movie can be ordered in 15-minute increments, making it more of a stagger-cast. Although NVOD doesnt generally include rewind, fast-forward or pause features (those come with VOD), the staggered start times let consumers wander away, then catch the movie at the next scheduled start time.
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