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syncronise multiple ADCs over an Ethernet network?

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Yansi:
mansaxel,  do NOT and NEVER timestamp all samples. That is completely impractical nonsense, that will not have any benefit.

Both AES67 and Ravenna (both interoperable, routable) use RTP as the transport.  For 1ms chunks, you send RTP packets containing 48 samples of data, timestamped as a whole, including a packet series number.

See https://tools.ietf.org/html/rfc3550 for details about RTP transport.

FenTiger : Of course time stamp of only the first sample in a packet is sufficient.

And because AES67 is also paywalled, I suggest using the Ravenna audio standard, which is even superior (and interoperable) with AES67. https://www.ravenna-network.com/

mansaxel:

--- Quote from: Yansi on December 09, 2019, 10:24:42 am ---mansaxel,  do NOT and NEVER timestamp all samples. That is completely impractical nonsense, that will not have any benefit.

--- End quote ---

I can see what you mean. And yes, in a system where sample frequency is very tightly controlled (like audio), it is sufficient to stamp at intervals of "ptime".
In a more general case, where samples are perhaps taken at more interrupted intervals, the time stamp becomes more crucial.


--- Quote from: Yansi on December 09, 2019, 10:24:42 am ---Both AES67 and Ravenna (both interoperable, routable) use RTP as the transport.  For 1ms chunks, you send RTP packets containing 48 samples of data, timestamped as a whole, including a packet series number.

See https://tools.ietf.org/html/rfc3550 for details about RTP transport.

FenTiger : Of course time stamp of only the first sample in a packet is sufficient.

And because AES67 is also paywalled, I suggest using the Ravenna audio standard, which is even superior (and interoperable) with AES67. https://www.ravenna-network.com/

--- End quote ---

The service location in Ravenna suffers from several of the problems in Dante too. Plain AES67 is so much a subset of Ravenna specs that one can use Ravenna to build AES67 ;-).  Andreas at ALC Networks was very much involved in both Ravenna (of course) and AES67.


/Måns, working at a SMPTE member who is not an AES member. The paywall pain is obvious.

rstofer:

--- Quote from: FenTiger on December 09, 2019, 08:40:19 am ---Is it really important to timestamp every sample?

I'd have thought it would be OK for each packet to contain the timestamp of its first sample, and then the others can be assumed to follow at regular intervals.

--- End quote ---

At least for TCP, packets can, and will, arrive out of order.  Maybe one of the other protocols avoids this but I don't see how considering the vagaries of ethernet transmission.

FenTiger:
Yes, but the samples within a packet won't be reordered. One timestamp per packet is all that's needed to reorder them.

(Also, a single Ethernet hop won't reorder packets unless you're detecting drops and doing retransmission somehow.)

Yansi:

--- Quote from: rstofer on December 09, 2019, 04:00:07 pm ---
--- Quote from: FenTiger on December 09, 2019, 08:40:19 am ---Is it really important to timestamp every sample?

I'd have thought it would be OK for each packet to contain the timestamp of its first sample, and then the others can be assumed to follow at regular intervals.

--- End quote ---

At least for TCP, packets can, and will, arrive out of order.  Maybe one of the other protocols avoids this but I don't see how considering the vagaries of ethernet transmission.

--- End quote ---

TCP is a high level protocol used to NOT get out of order or missing packets. You probably meant UDP/IP.

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