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.
spectrum reuse—CATV’s most fundamental concept. Historically, the over-the-air spectrum has been assigned to many purposes other than that of carrying TV signals. This has resulted in an inadequate supply of spectrum to serve the needs of viewers. Cable can reuse spectrum that is sealed in its aluminum tubes.
subscriber unit (SU)—An alternate term for cable access router. See cable access router.
upstream—The set of frequencies used to send data from a subscriber to the headend.
