Cisco uBR900 Series Configuring page 136

Glossary
headend—Central distribution point for a CATV system. Video signals are received here from
satellite (either co-located or remote), frequency converted to the appropriate channels, combined
with locally originated signals, and rebroadcast onto the HFC plant. For a CATV data system, the
headend is the typical place to create a link between the HFC system and any external data networks.
HFC—Hybrid fiber-coaxial (cable network). Older CATV systems were provisioned using only
coaxial cable. Modern systems use fiber transport from the headend to an optical node located in the
neighborhood to reduce system noise. Coaxial cable runs from the node to the subscriber. The fiber
plant is generally a star configuration with all optical node fibers terminating at a headend. The
coaxial cable part of the system is generally a trunk-and-branch configuration.
host—Any end-user computer system that connects to a network. In this document, the term host
refers to the computer system connected to the LAN interface of the cable access router.
ingress noise—Over-the-air signals that are inadvertently coupled into the nominally closed coaxial
cable distribution system. Ingress noise is difficult to track down and intermittent in nature.
MAC layer—Media Access Control sublayer. Controls access by the cable access router to the
CMTS and to the upstream data slots.
MCNS—Multimedia Cable Network System Partners Ltd. A consortium of cable companies
providing service to the majority of homes in the United States and Canada. This consortium has
decided to drive a standard with the goal of having interoperable cable access routers.
MSO—Multiple System Operator. A cable service provider that operates in more than one
geographic area, thus having multiple headend facilities.
narrowband—A single RF frequency.
NTSC—National Television Systems Committee. A United States TV technical standard, named
after the organization that created the standard in 1941. Specifies a 6 MHz-wide modulated signal.
PAL—Phase Alternating Line. The TV system used in most of Europe, in which the color carrier
phase definition changes in alternate scan lines. Utilizes an 8 MHz-wide modulated signal.
QAM—Quadrature Amplitude Modulation. A method of modulating digital signals onto a
radio-frequency carrier signal in which the value of a symbol consisting of multiple bits is
represented by amplitude and phase states of the carrier. QAM is a modulation scheme mostly used
in the downstream direction (64-QAM, 256-QAM). 16-QAM is expected to be usable in the
upstream direction. Numbers indicate number of code points per symbol. The QAM rate or the
number of points in the QAM constellation can be computed by 2 raised to the power of <number
of bits/symbol>. For example, 16-QAM has 4 bits per symbol, 64-QAM has 6 bits per symbol, and
256-QAM has 8 bits per symbol.
QPSK—Quadrature Phase-Shift Keying. A digital modulation method in which there are 2 data bits
represented with each baud symbol.
ranging—The process of acquiring the correct timing offset such that the transmissions of a cable
access router are aligned with the correct mini-slot boundary.
RF—Radio frequency. The portion of the electromagnetic frequency spectrum from 5 MHz to
approximately 860 MHz.
SECAM—TV system used in France and elsewhere, utilizing an 8 MHz-wide modulated signal.
SID (Service ID)—A number that defines (at the MAC sublayer) a particular mapping between a
cable access router (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth
allocation and class-of-service management.
Signal-to-Noise—S/N (also SNR). The difference in amplitude between a baseband signal and the
noise in a portion of the spectrum.
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