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ARINC 818

Glossary

8b/10b encoding: The IBM-patented encoding method used by ARINC 818 for encoding 8-bit data bytes to 10-bit transmission characters to improve the physical signal. This encoding is also used by Fibre Channel, Gigabit Ethernet, 10 Gigabit Ethernet, ATM transmission, and other interfaces.

64b/66b encoding: This alternate encoding will be used in extremely high-speed ARINC 818-2 applications: 14.025 Gb/s (16 times the protocol base rate), 21.0375 Gb/s (24x), and 28.05 Gb/s (32x).

ARINC 818 video frame structure
ARINC 818 video frame terms

Active image area: The image visible on a display, with all special characters stripped off and vertical and horizontal blanking areas removed.

ADVB frame: For transmission, one video frame is broken down into multiple ADVB frames, each of which includes a payload limited to 2112 bytes. For example, an XGA image has 3 bytes/pixel and 1024 pixels per line, a total of 3072 bytes. Thus it requires two ADVB frames per line, each including a payload of 1536 bytes. An ADVB frame may contain several rows of video data or less than a single row.

ADVB frame structure
ADVB frame details

ARINC 818-2: ARINC Specification 818-2 is the current version of ARINC 818, published in December 2013. ARINC 818-2 standardized innovations in prior custom ARINC 818 implementations, enabling compression, encryption, greater speed, and other features.

Beginning running disparity: ARINC 818 ordered sets are comprised of four 8b10b codes. Therefore they are the 40 bits after 8b10b encoding. In the same way that there are two possible 10-bit codes based on the current running disparity, there are two possible 40-bit codes that can represent an ordered set. ARINC 818 only permits one of these 40-bit possibilities on the link. This is the 40-bit code that occurs when you begin with running disparity negative. The other other possibility, when you begin with running disparity positive, is not permitted in ARINC 818. See also, Running displarity.

Container: One container holds a complete Video frame, including the container header and various objects representing ancillary data, audio, and video. By grouping video, audio, and ancillary data into relatively large data sets to be transported as a unit, the container is an optimal transmission tool.

ADVB container components
The container and its relationship to the video frame and ADVB frames

Container objects: Four object types are defined within ARINC 818. Object 0 carries header data; Object 1 carries audio data (but this isn't usually used); Object 2 carries video data; and Object 3 also carries video data, but is only used for interlaced video.

CRC: Cyclic Redundancy Code. The term CRC applies to algorithms based on polynomial division. The essential mathematical operation in the calculation of a CRC is binary division, and the remainder from the division determines the CRC. CRCs cannot, however, be safely relied upon to verify data integrity.

FC-AV: Fibre Channel–Audio Video is an older standard (ANSI INCITS 356-2002). It defines a container system that provides a framework onto which various digital audio/video formats can be mapped. Each of its implementations is unique. ARINC 818 built on FC-AV, moving toward more standardized but still extremely flexible systems.

Frame: This term is potentially ambiguous when used alone in an ARINC 818 context. Instead, specify Video frame or ADVB frame. See Containter illustration above.

Horizontal blanking: This is adopted from analog systems. After scanning a horizontal row, from left to right, the electron beam of a cathode ray tube (CRT) needed time to move from right back to left to begin to scan the next line. The time needed was the horizontal blanking. In the digital world, the horizontal blanking is not as necessary, but most systems retain it. The horizontal blanking is controlled by inserting idle ordered sets.

Horizontal scan direction: Adopted from CRT technology, a line is draw left to right.

Horizontal sync: Indicates the start of the row timing within the video frame.

ICD (interface control document): An ICD is required to define parameters for each ARINC 818 implementation. By providing for interoperability of system components, it enables the extreme flexibility of ARINC 818. An ICD defines physical medium, connector type, link speed, pixel dimensions, color model, scan (e.g., progressive), frame rate, synchronization and sigmentation class, and detailed timing parameters.

Ordered sets: These sets are pre-defined 4-byte sequences that define special control characters—for example, a start-of-frame (SOF) or end-if-frame (EOF) ordered set.

Payload: In an ARINC818 fiber channel frame, the data immediately following the header and preceding the CRC in the footer is known as payload or video payload. See illustration "ADVB frame details" above.

Partial imaging in ARINC 818
Partial imaging

Region of Interest (ROI): ARINC 818-2 accommodates vertical and horizontal banding and tiling, which can be used to give special characteristics to a region of interest within a video frame. For example, a region of interest can have a higher frame rate than the frame as a whole.

Running disparity: The cumulative number of ones minus the cumulative number of zeros that have been transmitted on the ARINC 818 serial link. Each byte of data feed to the 8b/10b encoder will have two possible 10-bit output codes. Typically these codes will be one with 6 ones and 4 zeros and one with 4 ones and six zeros. (Another possibility is a neutral code with 5 ones and 5 zeros, which does not effect the running disparity.) For each input byte, the 8b/10b encoder will chose the 10-bit code that keeps the running disparity between -1 and +1. See also, Beginning running disparity.

Special Characters: When using 8b/10b encoding, there are two types of characters: data characters and special characters. When a character is converted from eight bits to ten bits, the serializer must be told if a byte is data or a special character by asserting a given pin on the serializer. Common special characters are: K28.0, K28.1, K28.2, K28.3, K28.4, K28.5, K28.6, K28.7, K23.7, K27.7, K29.7, and K30.7. These can be used to indicate start of frame, end of frame, start of line, end of line, idle, or other control characters.  The special character K28.5 is used as the first character of all ARINC 818 ordered sets.

Vertical sync: Indicates start of a video frame—that is, start of the image container. See the Video frame components diagram above.

Vertical blanking: Like Horizontal blanking, this term comes from analog technology. The time required to reposition the electron beam from the lower right hand corner, to the upper left hand corner is the vertical blanking. In the digital world, the vertical blanking is the time between video frames. For example, if transmitting at a rate of 30Hz, a new video frame will be sent every 1/30 of a second. If the entire time needed to transmit the frame is 1/60 of a second, another 1/60 of a second is left over before beginning the transmission of the next video frame. This leftover time is the vertical blanking inserted between each video frame. The vertical blanking is accomplished by inserting idle characters.

Vertical scan direction: Adopted from CRT technology, lines are drawn from top to bottom.

Video frame: In the video world, a frame is considered to be all the payload information needed to describe an image. This is not equivalent to a container in the ARINC818 world. The video world frame should not be confused with the  ARINC818 world frame (aka Fiber Channel Frame (FCF), ADVB Frame, ARINC818 Frame). See the Video frame components diagram above.