Specifications

List of Terms

Bridging and Routing Features for the Cisco uBR904 Cable Modem 3

DHCP—Dynamic Host Conﬁguration Protocol. This protocol provides a mechanism for allocating

IP addresses dynamically so that addresses can be reused when hosts no longer need them.

DOCSIS—Data Over Cable Service Interface Speciﬁcation. Deﬁnes technical speciﬁcations for

equipment at both subscriber locations and cable operators’ headends.

Downstream—The set of frequencies used to send data from a headend to a subscriber.

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 modem.

MAC layer—Media Access Control sublayer. Controls access by the cable modem 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 modems.

MSO—Multiple Service Operator. A cable service provider that also provides other services such

as data and/or voice telephony.

QAM—Quadrature Amplitude Modulation. A method of modulating digital signals onto a

radio-frequency carrier signal involving both amplitude and phase coding. QAM is a modulation

scheme mostly used in the downstream direction (QAM-64, QAM-256). QAM-16 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>.

QPSK—Quadrature Phase-Shift Keying. A method of modulating digital signals onto a

radio-frequency carrier signal using four phase states to code two digital bits.

Ranging—The process of acquiring the correct timing offset such that the transmissions of a cable

modem are aligned with the correct mini-slot boundary.

SID (Service ID)—A number that deﬁnes (at the MAC sublayer) a particular mapping between a

cable modem (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth

allocation and class-of-service management.

Subscriber Unit (SU)—An alternate term for cable modem. See cable modem.

Upstream—The set of frequencies used to send data from a subscriber to the headend.

Platforms

The Cisco uBR904 cable modem is a standalone device; it works in conjunction with the

Cisco uBR7246 universal broadband router.