Asynchronous serial interface

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.

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.

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).

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..

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).

The ASI output of a DVB Integrated Receiver/Decoder (IRD). It carries the entire MPEG transport stream being received from a DVB satellite feed entering the RF input (far left side in picture).