The Cable Center

This glossary of cable and telecommunications terms is intended to enhance your understanding of this dynamic industry. We are able to present this information with the generous help of CableLabs - consult their website for the most up-to-date information about cable technology.

0 - 9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Radio Frequency (RF)
Analog electrical signals sent over the cable. Conventional (broadcast) television and radio, as well as cable TV, deliver RF signals to your television/radio. RF is quickly becoming yesterday’s news to many cable TV providers who are installing fiber-optic lines that will replace today’s cables. Or in cable television systems, this refers to electromagnetic signals in the range 5 to 1000 MHz.

Radio Frequency (RF) Interference
Undesired signals received by a user; those signals that miss their desired user become interference energy to users in the same or adjacent cells.

Ranging
The process by which a cable modem learns its distance from the headend. Ranging is a continual process, due to the expansion and contraction of cable that occurs during the day.

Raster
The scanned (illuminated) area of the cathode ray picture tube.

Real-time Protocol/Real-time Control Protocol (RTP/RTCP)
The Internet Engineering Task Force (IETF) specification for audio and video signal management. Allows applications to synchronize and spoil audio and video information. Refer to www.ietf.org.

Reboot
The act of reloading the operating system of a computer, usually by resetting the power to the computer with the power switch, or selecting Start/Shutdown/Restart in Windows.

Rebuild
The physical upgrade of a cable system, often involving the replacement of amplifiers, power supplies, passive devices and sometimes the cable, strand, hardware and subscriber unit.

Receiver
Electronic device which can convert electromagnetic waves into either visual or aural signals, or both. For cable television, usually the subscriber’s television set.

Receiver Isolation
The attenuation between any two receivers connected to the system.

Record Keeping Server (RKS)
In a PacketCable network, the RKS is responsible for accepting partial billing information generated by a distributed set of PacketCable elements and correllating this information into a single coherent record that describes the resources used during the service.

Reflection Coefficient
Ratio of reflected wave to incident wave.

Reflections or Echoes
In video transmission this may refer either to a signal or to the picture produced. In a signal it is either waves reflected from structures or other objects or waves which are the result of impedance or other irregularities in the transmission medium. In a picture, “Echoes” observed in the picture produced by the reflected waves.

Regional Bell Operating Company (RBOC)
RBOC comprises the U.S. local carriers created in the 1982 Consent Degree to break up AT&T. Seven were formed to serve as parent companies for the 22 then-existing Bell Operating Companies.

Registration, Admission, and Status (RAS)
RAS Channel is an unreliable channel used to convey the RAS messages and bandwidth changes between two H.323 entities.

Remote Access Dial-In User Service (RADIUS)
An internet protocol (IETF RFC 2138 and RVC 2139) originally designed for allowing users dial-in access to the internet through remote servers. Its flexible design has allowed it to be extended well beyond its original intended use.

Remote Method Invocation (RMI)
A Java programming feature that allows a program running on one computer to access the objects and methods of another Java program running on a separate computer.

Repeater
A repeater is a network device that repeats signals from one cable onto one or more other cables, while restoring signal timing and waveforms.

Reprovision
The term given to the process of resetting a cable modem by removing its entry from the cable router, then adding it back on to re-establish the connection.

Request for Comments (RFC)
A technical policy document of the Internet Engineering Task Force (IETF); these documents can be accessed on the World Wide Web at http://www.ietf.org/.

Resident Application
A resident application is an application that is saved on the host device and may be run at any time. Resident applications, such as the monitor application or EPG, are typically responsible for host device control.

Residential Gateway
A part of the Access Network which adds network functionality and multiplexes difference services. The gateway must perform the basic functions of media translation and address translation.

Resistance
The opposition that a substance offers to the flow of electric current.

Resistor
An electronic component that is deliberately designed to have a specific amount of resistance.

Resolution
A measure of picture resolving capabilities of a television system determined primarily by bandwidth, scan rates and aspect ratio. Relates to fineness and details perceived.

Resolution (Horizontal)
The amount of resolvable detail in the horizontal direction in a picture. It is usually expressed as the number of distinct vertical lines, alternately black and white, which can be seen in three-quarters of the width of the picture. This information usually is derived by observation of the vertical wedge of a test pattern. A picture which is sharp and clear and shows small details has good, or high, resolution. If the picture is soft and blurred and small details are indistinct it has poor, or low, resolution. Horizontal resolution depends upon the high-frequency amplitude and phase response of the pickup equipment, the transmission medium and the picture monitor, as well as the size of the scanning spots.

Resolution (Vertical)
The amount of resolvable detail in the vertical direction of a picture. It is usually expressed as the number of distinct horizontal lines, alternately black and white, which can be seen in a test pattern. Vertical resolution is primarily fixed by the number of horizontal scanning lines per frame. Beyond this, vertical resolution depends on the size and shape of the scanning spots of the pickup equipment and picture monitor and does not depend upon the high-frequency response or bandwidth of the transmission medium or picture monitor.

Resource reSerVation Protocol (RSVP)
An Internet protocol used for negotiating end-to-end IP quality of service (QoS) within the network. In a PacketCable-based network, RSVP can be used to negotiate QoS on the cable access network. Or IETF resource reservation setup protocol for IP networks.

Response Time
The length of time between the occurrence of an event and the response of an instrument or circuit to that event.

Return channel
A return channel refers to the communications mechanism that provides connection between OpenCable and a remote server.

Return Loss
The parameter describing the attenuation of a guided wave signal (e.g., via a coaxial cable) returned to a source by a device or medium resulting from reflections of the signal generated by the source.

Return Path
The term used to describe traffic and paths that go from the subscriber to the headend. Also known as Upstream, or Reverse Path.

Reuse/Frequency Reuse
The utilization of frequency (channels) more than once in a wireless network; equated primarily with the basic cellular grid design, where each cell uses each channel once within its boundaries and is insulated from other cells using that frequency to allow for anticipated interference; due to the shortcomings of conventional transmission techniques, frequency reuse in adjacent cells has been largely implausible until the recent development of spatial processing technology, which can enable same-cell frequency reuse.

Revenue generating unit (RGU)
Commonly referred to one additional cable subscription unit. For example, a customer who signs up for digital video and high-speed Internet access is counted as two RGUs, because the customer is signing up for two subscriptions.

Reverse Channel
The direction of signal flow toward the headend, away from the subscriber; equivalent to upstream.

Reverse Path Forwarding
A technique where a router receives a packet, then floods the packet out on all paths, except the path on which it received the packet.

R-F Pattern
A term sometimes applied to describe a fine herringbone pattern in a picture. May also cause a slight horizontal displacement of scanning lines resulting in a rough or ragged vertical edge of the picture. Caused by high-frequency interference.

Right-Click
Using the secondary mouse button (usually the right button) to open context menus.

Ring
A network topology in which the nodes are connected in a closed loop. Data is transmitted from node to node around the loop, always in the same direction.

Ringing
An oscillatory transient occurring in the output of a system as a result of a sudden change in input. Results in close-spaced multiple reflections, particularly noticeable when observing test patterns, equivalent square waves, sine-squared signal, or any fixed objects whose reproduction requires frequency components approximating the cutoff frequency of the system.

Rivest Cipher 4 (RC4)
A variable length stream cipher. Optionally used to encrypt the media traffic in PacketCable.

RJ-11 Jack/Connector
An RJ-11 connector is the small, modular plug used for most analog telephones. It has six pin slots in the head, but usually only two or four of them are used.

RJ-45 Jack/Connector
An RJ-45 connector is similar in appearance to a modular RJ-11 connector, but is wider and has eight-pin slot positions instead of six. RJ-45 connectors are used to connect ISDN S/T Interfaces and for 10-Base-T, 100Base-T, or 1000Base-T Ethernet cabling.

Roadblocking
The practice of stripping commercials in designated time periods across multiple cable channels. Can be an effective method for catching channel surfers.

Roll-Off
A gradual attenuation of gain-frequency response at either or both ends of the transmission pass band.

Root Private Key
The private signing key of the highest-level Certification Authority. It is normally used to sign public key certificates for lower-level Certification Authorities or other entities.

Root Public Key
The public key of the highest level Certification Authority, normally used to verify digital signatures generated with the corresponding root private key.

Router
Routers are special network devices used to connect one recognized computer network to another. Routers work like a postal worker; they examine the To addresses of network messages they are given and use part of the address like a zip code to figure out which computer network to send it to. Once a router has figured out which network the message should go to, it sends the message to another router, which repeats the process until the last router in the chain sends it directly to the computer listed in the destination address. Most WANs use routers to connect one LAN location to another.

Routing Information Protocol (RIP)
A protocol of the Internet Engineering Task Force (IETF) for exchanging routing information about Internet Protocol (IP) networks and subnets.

RSA
A public-key, or asymmetric, cryptographic algorithm that is used to provide the services of authentication and encryption. RSA stands for the three inventors of the algorithm; Rivest, Shamir, Adleman.

RSA Key Pair
A public/private key pair created for use with the RSA cryptographic algorithm.