Talk:Comparison of synchronous and asynchronous signalling
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The description of "synchronous transmission" provided in the article is inconsistent with various physical synchronous interfaces, e.g., SMPTE-310M. While a synchronizing signal is required (and provided) to receive the transmission, it need not travel "on another wire" -- the actual synchronizing signal can be embedded within the synchronous signal.
From SMPTE/EBU Task Force for Harmonized Standards for the Exchange of Program Material as Bitstreams[1]:
"Synchronous transmission" describes a transmission technique that requires a common clock signal (or timing reference) between two communicating devices to coordinate their transmissions. This common reference can be embedded within the signal, or can physically travel along with the signal on a similar or different medium.
"Asynchronous transmission" describes any transmission technique that does not require a common clock between the two communicating devices, but instead derives timing signals from special bits or characters (e.g. start/stop bits, flag characters) in the data stream itself. The essential characteristic of time-scales or signals such that their corresponding significant instants do not necessarily occur at the same average rate.
Perhaps confusing the issue are cases of non-linear signals, e.g., when compressed video is carried, wherein the video time base has an asynchronous relationship to the interface clocks.
- I'm confused. When I read that SMPTE/EBU document, I see the same definition for "asynchronous transmission", but I don't see any definition in that document for "synchronous transmission".
- Instead I see:
- Synchronous: A term used to describe a transmission technique that requires a common clock signal (or timing reference) between two communicating devices to coordinate their transmissions.
- ...
- E.3.3.3. Synchronization: Streaming data requires timing synchronization between the transmitters and receiver(s). This timing synchronization may be achieved through either the recovery of timing references embedded within the stream, or through the distribution of a system-wide clock to all participating devices.
- ...
- That document does talk a lot about embedding timing reference in the data stream.
- But I don't see anywhere that it defines that as "synchronous".
- I'm also going to argue that the "timing synchronization" mentioned can be achieved through timing references embedded within a asynchronous transmission stream.
- I can't find even one place where that document uses the phrase "common reference can be embedded within the signal".
- Therefore, I think "single wire synchronous transmission" should really be better classified as "asynchronous".
- If you expand the definition of "synchronous" to include not only two-signal protocols but also single-signal protocols, then what is left for the word "asynchronous" to describe?
- --68.0.124.33 (talk) 03:26, 7 May 2008 (UTC)
