MiniSEED packet size

[Richard]

Hi,

Sorry for a slightly off topic question but you are the people who will know.

I'm writing a report on earthquake early warning, where the smallest packet size possible for transmission from a digitiser to the acquisition is  important when considering latency.

All modern digitisers seem to use MiniSEED as one of their possible protocols.  Does anyone know, please, what limitation the protocol itself puts on packet size (as opposed to limitations of the digitisers )?  As far as I can tell from the documentation, if you turn compression off, there is no real limit, but this cannot be true.  Has anyone tried pushing the size right down?

How small a packet could slink2ew cope with please?

Thank you,

Richard.

[Paul Friberg]

For some digitizers we have seen folks use 128byte sized MSEED packets (64 byte header, 64 bytes of uncompressed data). This is the smallest allowable...and that has worked to reduce latency feeding into Earthworm.

Paul

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Paul Friberg   p.fr...@isti.com
CEO/Seismologist
ISTI==Instrumental Software Technologies, Inc.
Phone +1.518.602.0001  

[Mitchell M Withers (mwithers)]

Which also means half your bandwidth is consumed by overhead so you better have a big enough pipe to handle it.

Mitch

Interim Director
Center for Earthquake Research and Information (CERI)
University of Memphis
Memphis, TN 38152
901-678-4940

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Subject: Re: [Earthworm Forum] MiniSEED packet size

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For some digitizers we have seen folks use 128byte sized MSEED packets (64 byte header, 64 bytes of uncompressed data). This is the smallest allowable...and that has worked to reduce latency feeding into Earthworm.

Paul

On Thu, Feb 2, 2023 at 1:42 AM Richard <r...@bgs.ac.uk<mailto:r...@bgs.ac.uk>> wrote:
Hi,

Sorry for a slightly off topic question but you are the people who will know.

I'm writing a report on earthquake early warning, where the smallest packet size possible for transmission from a digitiser to the acquisition is important when considering latency.

All modern digitisers seem to use MiniSEED as one of their possible protocols. Does anyone know, please, what limitation the protocol itself puts on packet size (as opposed to limitations of the digitisers )? As far as I can tell from the documentation, if you turn compression off, there is no real limit, but this cannot be true. Has anyone tried pushing the size right down?

How small a packet could slink2ew cope with please?

Thank you,

Richard.

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Paul Friberg p.fr...@isti.com<mailto:p.fr...@isti.com>

CEO/Seismologist
ISTI==Instrumental Software Technologies, Inc.
Phone +1.518.602.0001

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[Richard Luckett - BGS]

Paul, Mitch,

Thank you. That is very useful. Yes, bandwidth is another topic...

Richard.

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[Alexandru Marmureanu]

Hello Richard,

My name is Alexandru Marmureanu and i worked a lot in EWS research for Vrancea (Romania) earthquakes (http://ews.infp.ro/).  We use 35 stations for EWS in the Vrancea area. The peculiarity of Vrancea is that there are deep events (down to 200km)

I have several observations on your questions:

1. In the initial EWS that we designed we used 1-second data packets for data. Custom software was written by me / or existed in Earthworm.  I have some papers on this, but when i look back they seem waste of my time :) 

2. Now we use 512 miniseed data packets for a very simple reason.... When an earthquake is at 120 km depth we receive about 15 P phases in 2 seconds. We use only 6 P phases for the initial magnitude and location.... This is mainly caused by two things: a) Deep events P phases come more or less in this time window at the surface; b) when there is "movement" the time window/span of a data packet is smaller (eg. only noise a packet can contain 6 seconds at 100 sps/ and during an earthquake around 1.5-3 seconds of acceleration data). So when you have a big number of stations at the surface, statistically it doesn't matter if it is miniseed or 1 packet/second.

3. I think that this is similar at crustal events.. The time shrinking of miniseed is valid and if you have enough stations it will be ok. 

There are some workarounds to change the data packet size (recompiling acquisition software or use acquisition software/digitisers that fill with 0 data in miniseed datapackets.)..

Cheers,

Alexandru Marmureanu

mar...@infp.ro

National Institute for Earth Physics, Romania

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[Richard Luckett - BGS]

Hello Alexandru,

 

Thank you for your observations.  I have read some of your papers and the Romanian system is included in our report.

 

I understand that it many cases latency due to packet size is not going to make a lot of difference but at the moment we’re dealing with principals. I had noticed that a couple of the digitisers give you the chance to zero pad packets but the same ones also allow you to set the number of frames per packet, which seems more efficient?  Maybe that is needed for other acquisition systems.

 

Regards,

 

Richard.

 

From: earthwo...@googlegroups.com <earthwo...@googlegroups.com> On Behalf Of Alexandru Marmureanu
Sent: Thursday, February 2, 2023 4:42 PM
To: earthwo...@googlegroups.com
Subject: Re: [Earthworm Forum] MiniSEED packet size

 

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[Alexandru Marmureanu]

Hello,

I hope that I understood correctly your question.

If you use 200 samples / second the packet time width will be smaller than for 100 samples/second.  So the 512 bytes are filled much faster :)

This will increase bandwidth....   

Regards,

Alexandru

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