List of Terms
6
Cisco IOS Release 12.0(5)T
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.
