The use of statistical multiplexing to cram multiple digitally compressed video streams onto a distribution network is an example of variable bit rate usage. Because different compressed channels contain varying amounts of motion, a statmux can alter how those channels are carried on the network, allocating more room to high-action content, and less to talking head/low action content. Thus, the bit rate varies.
Usage: When capacity varies with regard to user requirements, variable bit rate techniques are used to move the data over a network.
VDSL involves the placement of fiber as close as possible to homes, terminated in a unit that links to short twisted pair runs to homes.
Virtual channels are interspersed among the many hundreds of digitally compressed channels that a cable or satellite provider nests in its digital tier. They are tunable, either from an electronic program guide, or by channel surfing. To some extent, virtual channels are the digital equivalent of analog channels that use a character generator to show a scrolling display of community information, real estate listings, or school information.
But, because they are digital, and require backing by a real-time hosting infrastructure, virtual channels tend to look better than their analog counterparts, and are much easier to refresh with up-to-the-minute information. Virtual channels, as a whole, will spawn new brands, or protect existing brands.
Since the first edition of this dictionary (2000), two big technological shifts happened, to strengthen the core workings of VOD. First was the advancement of Gigabit Ethernet corridors between servers, and QAM modulators. That let operators centralize video storage, and send it to hubs over notably inexpensive, Gig-E paths.
Second was the desire, among cable providers, for suppliers to separate the storage part of their gear, from the streaming part. Storage and streaming, after all, grow at different rates. Theres the move to 3,000 hours of storage, from 1,500, which is a totally different decision than whether to add more streams, because more types of VOD could mean more live viewing sessions.
As a direct result of those technology shifts, the supplier marketplace for VOD continues to grow new entrants. Some have newer or less expensive ways to store VOD titles; others have newer or faster ways to stream VOD titles.
Strategically, VOD is often contrasted with digital video recorders, in the sense of “why both?” Although both techniques allow customers to apply VCR-like features to stored material, there is a relatively important distinction between VOD and DVR. It is this: With DVRs, consumers must first select a show, before it can be “taped” and viewed later. With VOD, the title can be retrieved at any time, without having to first select it.
That means VOD and DVR are probably more complementary than they are competitive with one another. Combined, they work in tandem to further both the “anytime” and the “anything” parts of TV viewing.
Rather, voice service is a lower-cost alternative to primary line/lifeline phone service, with a target market of “additional lines” purchased for use by teenagers or for otherwise non-lifeline use. Synonymous with “Internet voice.”
For most cable providers, winning with voice-over-IP (VoIP) is capturing residential phone revenues, preferably without ever having to buy entry or exit passage on the public phone network built and serviced by incumbent telcos. Some MSOs, like Time Warner Cable, initially opted to quicken their pace to the VoIP market by partnering with seasoned telephony experts Sprint and MCI, in TWC’s case.
The partnerships were designed to outsource certain aspects of making VoIP into a business. That means customer provisioning, or what it takes to port a new customer onto the cable VoIP network. Also PSTN provisioning, or the physical hand-off of a call from a cable VoIP customer to the public switched telephone network. Standard voice services, like directory assistance, operator assistance, and information. Life critical services, like CALEA and 911. Long distance. Rate center connectivity, or using established links into the many rate centers that populate a metropolitan market (a mid-sized city can have as many as 30).
Outside of the “back office” partnerships, VoIP requires equipment. Ingredient number one: The 1.1 upgrade to the Data Over Cable Services Interface Specification (DOCSIS). Thats the CableLabs cable modem specification that offers “quality of service,” or QoS (pronounced as the letters: Q-oh-S). In short, QoS offers a way to “stripe” voice packets to stand out as high-priority, isochronous traffic that requires low latency.
Ingredient number two: A VoIP-ready cable modem termination system, or CMTS. Anyone offering cable modem service already owns and operates CMTS gear, because it is the necessary “other end” of each cable modem. The CMTS is usually located at the headend.
Adding VoIP to the data services mix usually requires a CMTS upgrade. Doing lifeline VoIP, so that the phone works when the power is out, will probably require a whole new CMTS — the so-called “forklift upgrade.”
Ingredient number 3: A “multimedia terminal adapter,” or “MTA.” This is the box that straps to the side of the house, or gets installed inside. Picture a cable modem with RJ-11 jacks on it — and because it does both data and phone, it shaves deployment costs for homes that want both services.
And then the servers. Lots of servers. Cable VoIP essentially duplicates, in software, the way in which calls are made on analog, telco-delivered networks. To do that, you need a lot of software firepower: To look up destination numbers, to issue dial and ring tone commands, to dole out messages (“the number you dialed is busy,” etc.).
Most of the cable VoIP ingredients are laboriously described in the CableLabs PacketCable specification series. Heres a simplified version of how it works:
Customers get a box — the MTA. The phones in the house are linked into it. Say customer Jane decides to make a call. She picks up the phone.
Unbeknownst to her, an off-hook indicator zips through the MTA, along the upstream, IP path, to the CMTS. The CMTS recognizes the activity as specific to the Jane’s MTA. It alerts a call management server (CMS) that she needs to make a call. The server acknowledges by giving Jane a dial tone.
Jane dials. The dialed digits traverse the same IP upstream path, again through the CMTS, again to the call management server. The server consults a built-in lookup table, to see what it knows about the dialed number: Is it within this cable system? Is it outside the system?
If within the cable system, the call server alerts the destination MTA, via the cable plant, of an incoming call, and instructs it to ring. When the dialed party answers, the call server assures dialer and dialee are hooked up, then retreats. Before it leaves, it tells the MTAs to let it know when the call ends.
If the dialed call is intended for a destination outside of its zone, the call server hands the call to a signaling gateway for completion. The gateway is a device that moves calls over the public phone network, and ultimately over a managed, private, cable backbone, to the destination.
Jane completes the call, and hangs up. The CMS notes the duration of the call, and hands the usage information to a records server, which in turn links to a billing system. And so on, for every VoIP call — it has to work as well for one as it does for millions, so scale matters, too.
Continuing with the bowling ball analogy: If it does actually roll off the dining room table and begin to fall, the process of falling — the speed, or velocity — is analogous to the flow of electrical energy (the current). That flow is measured in Amperes, or Amps.
The potential (voltage) of such a large, heavy object falling off a relatively high surface, multiplied by the speed at which it falls (amperage) is measured in watts.
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