Asynchronous Serial Interface, or ASI, is a method of carrying an MPEG Transport Stream (MPEG-TS) over 75-ohm copper coaxial cable or optical fiber. [1] It is popular in the television industry as a means of transporting broadcast programs from the studio to the final transmission equipment before it reaches viewers sitting at home.
The ASI standard is maintained by CENELEC, the European Committee for Electrotechnical Standardization, and is part of the collection of standards known as Digital Video Broadcast, or DVB.
ASI carries MPEG data serially as a continuous stream with a constant rate at or less than 270 megabits per second, depending on the application. It cannot run faster than this, which is the same rate as SDI [2] and also the rate of a DS4 telecommunications circuit which is typically used to transport the stream over commercial telephone/telecommunications digital circuits (Telco). The MPEG data bits are encoded using a technique called 8B/10B which stands for 8-bit bytes mapped to 10-bit character codes. Encoding maintains DC balance and makes it possible for the receiving end to stay synchronized. When on 75-ohm coaxial cable, ASI is terminated with BNC male connectors on each end. Electrically, the coaxial standard specifies an output voltage of 800 millivolts peak-to-peak, while the receiver must be able to operate from a voltage anywhere from 200 mV to 880 mV. [3] [4] ASI is electrically identical to and has the same bit rate as standard definition SDI. [5] When ASI is on optical fiber, it is multimode fiber. [6]
There are two data transmission packet sizes commonly seen by the ASI interface and the cable carrying it: the 188 byte packet and the 204 byte packet, the fundamental building blocks of the MPEG Transport Stream. The 188 byte format is by far the most common packet size, used by the vast majority of transmissions. When optional Reed–Solomon error correction data are included, a format primarily developed by Cable Television industry, the packet grows an extra 16 bytes to 204 bytes total. [note 1]
ASI has one purpose only: the transmission of an MPEG Transport Stream (MPEG-TS), [7] [8] and MPEG-TS is the only standard protocol universally used for real-time transport of broadcast audio and video media today. Even when tunneled over IP, MPEG-TS is the lowest-common-denominator of all long-distance audio and video transport. In the US, it can be broadcast to homes as the ATSC Transport Stream; in Europe, it is broadcast to homes as the DVB-T Transport Stream. All broadcast satellite transmissions see it as the DVB-S Transport Stream. It is usually made up of one or more television channels with accompanying audio, sometimes with additional audio-only or data transmission channels. When that composite data transmission path, asynchronous but formatted data, travels through space as RF, it is usually called DVB-S, DVB-T, or ATSC. But when carried on coaxial cable, unmodulated, it is called an ASI signal.
It is a one-way transmission, similar to RS-232 asynchronous data—a stream of raw but formatted zeros and ones—designed to primarily travel through coaxial cable at speeds that range from 6-200 megabits per second. Though 270 megabits per second is the rate of the underlying available bandwidth, Transport Streams, and therefore ASI transmissions, usually top out at around 200 megabits per second.
A Transport Stream, and thereby ASI when over coax, can carry one or multiple SD, HD or audio programs that are already compressed, as opposed to an uncompressed SD-SDI (270 Mbit/s) or HD-SDI (1.485 Gbit/s). An ASI signal can be at varying transmission speeds and is completely dependent on the user's engineering requirements. For example, an ATSC (US digital standard for broadcasting) has a specific bit rate of 19.392658 Mbit/s. Null characters, represented by the ASCII comma, are used to pad the transmission to that rate should the media itself not require the entire bitstream.
Generally, the ASI signal is the final product of video and audio compression for distant delivery, internal distribution, or broadcast to the public, as is today's digital television and cable.. Though it is codec agnostic and can carry any kind or data, It most often carries MPEG2 (H.262 video with MPEG-1 Layer II audio) or MPEG4 (H.264 video with MPEG-4 Part 14 audio), ready for transmission to a television or radio broadcast transmitter, microwave system or other device. Sometimes it is also converted to fiber, RF or the "SMPTE 310" format: (a synchronous version of ASI developed by Harris specifically for the 19+ megabit per second ATSC-transmitter input feed).
By far, in the television industry the term ASI refers to its use on coaxial cable, not optical fiber, and even though the standard itself also maintains its use on fiber, whenever ASI is mentioned the meaning is almost always coaxial cable. ASI is also sometimes referred to as DVB-ASI or TS-ASI. [9]
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth. While MPEG-2 is not as efficient as newer standards such as H.264/AVC and H.265/HEVC, backwards compatibility with existing hardware and software means it is still widely used, for example in over-the-air digital television broadcasting and in the DVD-Video standard.
In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the payload. Control information provides data for delivering the payload. Typically, control information is found in packet headers and trailers.
Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) of the European Telecommunications Standardisé Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU).
DigiCipher 2, or simply DCII, is a proprietary standard format of digital signal transmission and it doubles as an encryption standard with MPEG-2/MPEG-4 signal video compression used on many communications satellite television and audio signals. The DCII standard was originally developed in 1997 by General Instrument, which then became the Home and Network Mobility division of Motorola, then bought by Google in Aug 2011, and lastly became the Home portion of the division to Arris.
DVB-T, short for Digital Video Broadcasting — Terrestrial, is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in Singapore in February, 1998. This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing modulation. It is also the format widely used worldwide for Electronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point. It is also used in the US by Amateur television operators.
Digital Video Broadcasting - Cable (DVB-C) is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/digital video stream, using a QAM modulation with channel coding. The standard was first published by the ETSI in 1994, and subsequently became the most widely used transmission system for digital cable television in Europe, Asia and South America. It is deployed worldwide in systems ranging from the larger cable television networks (CATV) down to smaller satellite master antenna TV (SMATV) systems.
Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that standard, is used mostly in the United States, Mexico, Canada, and South Korea. Several former NTSC users, in particular Japan, have not used ATSC during their digital television transition, because they adopted their own system called ISDB.
An integrated receiver/decoder (IRD) is an electronic device used to pick up a radio-frequency signal and convert digital information transmitted in it.
Serial digital interface (SDI) is a family of digital video interfaces first standardized by SMPTE in 1989. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s.
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the Digital Video Broadcasting Project, an international industry consortium, and ratified by ETSI in March 2005. The standard is based on, and improves upon DVB-S and the electronic news-gathering system, used by mobile units for sending sounds and images from remote locations worldwide back to their home television stations.
A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel.
Datacasting is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital terrestrial television, but may also be applied to digital signals on analog TV or radio. It generally does not apply to data which is inherent to the medium, such as PSIP data which defines virtual channels for DTT or direct broadcast satellite systems; or to things like cable modem or satellite modem, which use a completely separate channel for data.
MPEG transport stream or simply transport stream (TS) is a standard digital container format for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data. It is used in broadcast systems such as DVB, ATSC and IPTV.
1080p is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vertically; the p stands for progressive scan, i.e. non-interlaced. The term usually assumes a widescreen aspect ratio of 16:9, implying a resolution of 2.1 megapixels. It is often marketed as Full HD or FHD, to contrast 1080p with 720p resolution screens. Although 1080p is sometimes informally referred to as 2K, these terms reflect two distinct technical standards, with differences including resolution and aspect ratio.
A Technology and Engineering Emmy Award is given by the National Academy of Television Arts and Sciences (NATAS) for outstanding achievement in technical or engineering development. An award can be presented to an individual, a company, or to a scientific or technical organization for developments and/or standardization involved in engineering technologies which either represent so extensive an improvement on existing methods or are so innovative in nature that they materially have affected the transmission, recording, or reception of television. The award is determined by a special panel composed of highly qualified, experienced engineers in the television industry.
In television technology, Active Format Description (AFD) is a standard set of codes that can be sent in the MPEG video stream or in the baseband SDI video signal that carries information about their aspect ratio and other active picture characteristics. It has been used by television broadcasters to enable both 4:3 and 16:9 television sets to optimally present pictures transmitted in either format. It has also been used by broadcasters to dynamically control how down-conversion equipment formats widescreen 16:9 pictures for 4:3 displays.
Packetized Elementary Stream (PES) is a specification in the MPEG-2 Part 1 (Systems) and ITU-T H.222.0 that defines carrying of elementary streams in packets within MPEG program streams and MPEG transport streams. The elementary stream is packetized by encapsulating sequential data bytes from the elementary stream inside PES packet headers.
ATSC-M/H is a U.S. standard for mobile digital TV that allows TV broadcasts to be received by mobile devices.
The Digital Signal 4/NA (DS4/NA) in telecommunications, is a 139.264-Mbit/s aggregate-multiplexed signal, equivalent to 3 Digital Signal 3s or 2,016 Digital Signal 0s.
Astra is a professional software to organize digital broadcasting service for TV operators and broadcasters, internet service providers, hotels, etc. Astra is an acronym for "advanced streaming application".