Glossary
A coded representation of a presentation unit. In the case of compressed audio, an access unit is an Audio Access Unit. In the case of compressed video, an access unit is the coded representation of a picture.
Any technique enabling the receiver to automatically identify and reject messages that have been altered deliberately or by channel errors.
The rate at which the compressed bitstream is delivered from the channel to the input of a decoder.
A code in which parity bits are added to the message bits.
A bit in a coded bitstream is byte-aligned if its position is a multiple of 8-bits from the first bit in the stream.
A nonforgeable, tamper-proof way of certifying the validity and, therefore, protecting the integrity of published public keys. Digital certificates are issued, verified, and revoked by a certifying authority, which can be any trusted party for central administration.
A digital medium that stores or transports a bitstream.
A data element as represented in its encoded form.
In a coded bitstream, the ratio of the information bits to the total bits.
A reduction in the number of bits used to represent an item of data.
The control mechanisms, data structures, and commands that provide for selective access and denial of specific services. Conditional access (CA) systems use signal security, which is any technology, such as encryption, that can prevent a signal from being received by anyone except authorized users.
An operation in which the bit rate is constant from the start to the finish of the compressed bitstream.
The frequency varying key used to decrypt a service. Control words are delivered in ECMs.
The art or process of writing or deciphering secret code.
Cyclic Redundancy Code (CRC) check:
A way to verify the correctness of data.
An item of data before encoding and after decoding.
data encryption standard (DES):
A block ciphering technique described in a U.S. government standard (FIPS PUB 46-2) used for privacy protection. It is probably the best-known and most widely used crypto-algorithm in the world. As a secret-key, symmetric system, it requires the exchange of secret encryption keys between users.
The decoded reconstruction of a compressed bitstream.
An embodiment of a decoding process.
The process-defined MPEG standard that reads an input-coded bitstream and outputs decoded pictures or audio samples.
decoding time stamp (DTS) [system]:
A field that may be present in a PES packet header that indicates the time in which an access unit is decoded in the system target decoder.
Selects which of the four possible subcarrier phases was transmitted. It produces a 2-bit digital output.
An electronic “passport” that only one entity can produce, but all others can verify with the sender’s public key. Digital signatures provide an unambiguous confirmation of the identity of the sender of a message. With digital signatures, messages from unauthorized sources can be rejected and authorized messages cannot be repudiated by the sender.
A digital storage or transmission device or system.
The subsidiary of Hughes Electronics that provides the service of the same name.
The first commercial communication satellite. Developed by Hughes Aircraft Company for COMSAT. Its official name is INTELSAT I.
The process by which one or more compressed bitstreams are manipulated to produce a new compressed bitstream. Conforming edited bitstreams must meet the requirements defined in the MPEG standard.
elementary stream (ES) [system]:
A generic term for one of the coded video, coded audio, or other coded bitstreams.
Elementary Stream Clock Reference (ESCR):
A time stamp in the PES Stream from which decoder timing is derived.
An embodiment of an encoding process.
A process, not specified in the MPEG standard, that reads a stream of input pictures or audio samples and produces a valid coded bitstream as defined in the MPEG standard.
Transforms digital data into a format that is unintelligible without the proper key for decryption. Sometimes known as “scrambling” when applied to a digital service. The design of the algorithm and the key length employed will determine the strength of the cryptographic protection. Encryption can be used both for service denial/access and message privacy.
The use of a pseudorandom generator technique to ensure that the bitstream does not contain runs of the same type of bit.
Data structures transmitted within messages having cryptographic protections that authorize reception of a service at a set-top terminal. Entitlements may be delivered in EMMs via the MPEG 2 Transport Stream or via ‘out of band’ communication channels.
entitlement control message (ECM):
Messages containing systemwide information that “unlocks” an encrypted service by transmitting control words. Each ECM, which is unique for each service, enables cryptographic partitioning so that different service providers can selectively grant access to their own services.
entitlement management message (EMM):
Messages that are individually addressed to or sent by specific receivers that allow delivery of secure and authenticated authorizations and supports nonrepudiation of service orders. RSA’s public key cryptography typically will be used for EMM transmission.
Variable length lossless coding of the digital representation of a signal to reduce redundancy.
A collection of Elementary Streams with a common time base, an associated start time, and an associated end time.
fast forward playback [video]:
The process of displaying a sequence or parts of a sequence of pictures in display-order faster than real time
Federal Communications Commission (FCC):
The U.S. government agency responsible for regulating communications.
Methods used in a signal to identify the source decoder, thereby providing a mechanism to detect and trace unauthorized copying of material.
When used in the clauses defining the coded bitstream, indicates that the value shall never be used. This is usually to avoid emulation of start codes.
Use of parity bits and codes to reduce transmission errors.
Hughes Electronics satellite family that is the basis for the DBS satellites.
Integrated Receiver Decoder (IRD):
The indoor part of a DBS receiving unit.
Rules, which describe what governs the motion of bodies orbiting the Earth, developed by Johannes Kepler.
One of the levels in the data hierarchy of the Video and Systems specifications defined in Parts 1 and 2 of the MPEG 2 standard.
Part of a receiver’s outdoor unit that amplifies an incoming Ku signal and then downconverts it into L-Band.
Consists of a pack header followed by zero or more packets. It is a layer in the system coding syntax.
Contiguous bytes of data from an Elementary Stream present in a packet.
Consists of a header followed by a number of contiguous bytes from an elementary data stream. It is a layer in the system coding syntax.
packet identifier (PID) [system]:
A unique integer value used to associate Elementary Streams of a program in a single or multiprogram Transport Stream.
Packetized Elementary Stream (PES) [system]:
The data structure used to carry Elementary Stream data. It consists of a PES packet header followed by PES packet payload.
A method to adjust the average length of an audio frame in time to the duration of the corresponding PCM samples by conditionally adding a slot to the audio frame.
The bytes that follow the header bytes in a packet. For example, the pay-load of a Transport Stream packet includes the PES_packet_header and its PES_packet_data_bytes, pointer_field and PSI sections, or private_data, but a PES_packet_payload consists of only PES_packet_data_bytes. The Transport Stream packet header and adaptation fields are not payload.
An abbreviation for Packetized Elementary Stream.
Consists of PES packets, all of whose payloads consist of data from a single Elementary Stream and all of which have the same stream_id. Specific semantic constraints apply.
Methods used to thwart piracy and prevent unauthorized access to crucial elements of a CA system. In a set-top terminal, a secure microprocessor supports nonvolatile storage of keys and authorizations, and assures a protected environment for decryption and encryption, authentication, and access control logic.
Any impersonation, unauthorized browsing, falsification or theft of data, or disruption of service or control information in a network.
presentation time stamp (PTS) [system]:
A field that may be present in a PES packet header indicating the time that a presentation unit is presented in the system target decoder.
presentation unit (PU) [system]:
A decoded Audio Access Unit or a decoded picture.
The decryption (reception) or the encryption (signature) component of an asymmetric key set.
A collection of Elementary Streams with a common timebase and intended for synchronized presentation.
Program Clock Reference (PCR) [system]:
A time stamp in the Transport Stream from which decoder timing is derived.
Program Specific Information (PSI) [system]:
Consists of normative data that is necessary for the demultiplexing of Transport Streams and the successful regeneration of programs. One case of PSI, the nonmandatory Network Information Table, is privately defined.
Specific rules, procedures, or conventions relating to the format and timing of data transmission between two devices. For broadband networks, international standards such as MPEG, DVB, and DA VIC define appropriate protocols.
Algorithms that encrypt and decrypt by using asymmetric (different), yet mathematically linked keys. Each security module is assigned a pair of keys: The encryption key is “public” and does not require distribution by secure means. The decryption, or ‘private,’ key cannot be discovered through knowledge of the public key or its underlying algorithm. Public key algorithms can apply to one or more of the following: key distribution, encryption, authentication, or digital signature.
Quadrature (Quaternary) Phase Shift Keying (QPSK):
A modulation technique that has four possible states for each transmitted symbol. Provides two bits per symbol.
A model that predicts the amount of rain in various parts of the world. Important because Ku and Ka bands have significant rain attenuation.
The shape of the base band filter used to reduce the sidelobes of the QPSK signal.
The process of beginning to read and encode the coded bitstream at an arbitrary point.
A nonbinary block code frequently used as the outer code in a concatenated coding system.
Regional Administrative Radio Council (RARC):
A regional version of WARC.
Easily changing a CA system to plug security breaches or to introduce technological advances.
Denial that a specific event has taken place. In a broadband network, the event could be an order for products or services, or for their cancellation.
When used in the clauses defining the coded bitstream, indicates that the value may be used in the future for ISO-defined extensions. All reserved bits shall be set to '1'.
The power-out versus power-in curve for a TWT-A or other power amplifier.
The key that encrypts and decrypts in symmetric algorithms. To prevent interception by unauthorized users, secret keys must be distributed by secure means. Secret keys are good for high-speed data streams, such as content (service) scrambling. DES and DVB Superscrambling are popular secret-key algorithms.
A specially shaped antenna that transmits more energy into one area than others. This is usually done to normalize the effects of rain.
The technology used to prevent reception of a service without authorization.
An insertable credit card-sized device with imbedded processor(s) that provide EMM and ECM functions and a means of secure electronic storage. A smart card can be programmed to decrypt messages, verify messages and digital signatures, and create digital signatures for outgoing messages. Most smart-card implementations are based on the ISO Standard 7816.
A single nonmultiplexed stream of samples before compression coding.
Unique 32-bit codes that are embedded in the coded bitstream. They are used for several purposes, including identifying some of the layers in the coding syntax. Start codes consist of a 24-bit prefix (0x0000001) and an 8-bit stream_id as discussed in Chapter 7.
A first-in first-out buffer at the input of system target decoder for storage of compressed data from Elementary Streams before decoding.
A coded still picture consists of a video sequence containing one coded picture that is intracoded. This picture has an associated PTS. The presentation time of succeeding pictures, if any, is later than that of the still picture by at least two picture periods.
The first geosynchronous communication satellite. It was developed by Hughes Aircraft Company for NASA.
System Clock Reference (SCR) [system]:
A time stamp in the Program Stream from which decoder timing is derived.
A data structure that carries information summarizing the system characteristics of the multiplexed stream.
The effective temperature of the receiver that determines the noise part of the signal-to-noise ratio (SNR).
system target decoder (STD) [system]:
A hypothetical reference model of a decoding process used to describe the semantics of a multiplexed bitstream.
Time Division Multiplex (TDM):
The combining of multiple services into a single bitstream.
A term that indicates the time of an event.
The subsystem on a satellite that receives the Earth-transmitted signal, translates its frequency, amplifies it, and retransmits it to Earth.
Transport Stream packet header [system]:
A data structure used to convey information about the Transport Stream payload.
A security enhancement of single-DES encryption that employs three successive processing-DES block operations. Different versions use either two or three unique DES keys. This enhancement is considered to be highly invulnerable to all known cryptographic attacks.
The part of an IRD that selects a particular transponder.
An operation in which the bit rate varies with time during the decoding of a compressed bitstream.
World Administrative Radio Council (WARC):
Quadrennial meetings held by the ITU that establish world communication regulations.
XPD (Cross-Polarization Discrimination):
The discrimination against the undesired signal of the opposite polarization than the one desired.