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.
