Author Topic: Retry Time for Missed Packets  (Read 394 times)

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Offline wxnerd

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Retry Time for Missed Packets
« on: June 10, 2024, 07:41:35 AM »
I know when a packet is not received, it will retry. But for how long? In other words, how long does the ISS store missed packets that the console has not yet received? I know if several packets are missed, the console goes to "R" for resync and after 10 minutes goes to "L" for Lost connection. But does the ISS store the missed packets for that whole potential 10 minutes that it's trying to resync?

Reason I ask is because I noticed my console went to "R" during a downpour and stayed that way for about 4 or 5 minutes. Then the "X" returned and instantly my rain total jumped several tenths of an inch. Obviously, this wasn't just a couple seconds worth of rain; It had to be part (or all) of the missed data accumulated over that couple minute outage.

Not exactly sure how the communication works, but I'm assuming once the console receives a packet, it sends some kind of "packet received" response back to the ISS; Otherwise, the ISS keeps resending the same packets until it gets that "received" response or until a given amount of time elapses and/or the ISS runs out of local storage space.

Offline johnd

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Re: Retry Time for Missed Packets
« Reply #1 on: June 10, 2024, 08:40:58 AM »
The ISS sends packets about every 2.5 seconds. AFAIK there is no storage of packets at the ISS - a lost packet is a lost packet. And no packet acknowledgement at all

There is a small counter for the rainfall on the ISS and it is the counter value that is sent in the rainfall packet.. So that's how it can jump in the way you describe.
« Last Edit: June 10, 2024, 09:00:19 AM by johnd »
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Offline wxnerd

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Re: Retry Time for Missed Packets
« Reply #2 on: June 10, 2024, 09:24:07 AM »
There is a small counter for the rainfall on the ISS and it is the counter value that is sent in the rainfall packet.. So that's how it can jump in the way you describe.

Interesting! So when does the counter "reset"? Curious as to how long I can retrieve a lost rain total after the fact.

Offline johnd

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Re: Retry Time for Missed Packets
« Reply #3 on: June 10, 2024, 11:12:18 AM »
Interesting! So when does the counter "reset"? Curious as to how long I can retrieve a lost rain total after the fact.

It's not documented anywhere publicly AFAIK. And TBH I cannot remember exactly, but a number in the 70's sticks in my head, maybe 75. So it would go from 0-0.75" before resetting for a 0.01" gauge. But TBH also this explanation never feels right to me - I would have expected it to be a binary number like 64 or 128. So I think the principle of this explanation is right but the exact number may be wrong. Someone else who has played with receiving the ISS messages may have a better number than me.

And so there is not a duration in time over which the rainfall can catch up. It all depends how much it has been raining. If the counter resets then the previous batch of rainfall will be lost.
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Offline wxnerd

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Re: Retry Time for Missed Packets
« Reply #4 on: June 10, 2024, 12:00:55 PM »
So I guess the "daily rain" is determined by when the console receives the data. Example, I disconnect console now (June 10) and it rains 0.12" later today. I reconnect the console tomorrow (June 11) and that 0.12"  will show up as June 11th rain, even though it fell on June 10th.

Offline mcrossley

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Re: Retry Time for Missed Packets
« Reply #5 on: June 10, 2024, 06:01:27 PM »
Interesting! So when does the counter "reset"? Curious as to how long I can retrieve a lost rain total after the fact.

It's not documented anywhere publicly AFAIK. And TBH I cannot remember exactly, but a number in the 70's sticks in my head, maybe 75. So it would go from 0-0.75" before resetting for a 0.01" gauge. But TBH also this explanation never feels right to me - I would have expected it to be a binary number like 64 or 128. So I think the principle of this explanation is right but the exact number may be wrong. Someone else who has played with receiving the ISS messages may have a better number than me.

And so there is not a duration in time over which the rainfall can catch up. It all depends how much it has been raining. If the counter resets then the previous batch of rainfall will be lost.
It uses 7 bits for the rain counter in the radio packet, so you would think it will reset every 128 tips. I haven't gone through log files to check though.
Mark

Offline Mattk

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Re: Retry Time for Missed Packets
« Reply #6 on: Yesterday at 01:06:42 AM »
It is not logical that the rain counter resets (as such) otherwise rainfall could obviously be lost. It would be workable if it was a FiFo type counter/register? 

Offline johnd

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Re: Retry Time for Missed Packets
« Reply #7 on: Yesterday at 05:24:27 AM »
It is not logical that the rain counter resets (as such) otherwise rainfall could obviously be lost. It would be workable if it was a FiFo type counter/register?

Mark may well have looked into this more than I have, but I've always imagined that the console firmware knows what the maximum value for the counter is (whether it's 75 or 127** or whatever) and if it detects that a new value is lower than the previous saved value then it will make the appropriate adjustment  to the running rainfall total and reset the previous value.

Maybe I'm missing something, but I can't envisage how a FIFO buffer would work. AFAIK the only rainfall value that's passed from ISS to console is the current counter value for the number of bucket/spoon tips, ie an integer between 0 and 127 (or whatever the top value is). How would this be compatible with a FIFO buffer?

**A 7-bit value (0-127) value for the number of rainfall tips would make a lot more sense. Maybe whoever gave me this information from Davis only half-remembered the true value and gave me a number in the 70's rather than the more credible 7-bit value.
« Last Edit: Yesterday at 05:43:15 AM by johnd »
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Offline mcrossley

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Re: Retry Time for Missed Packets
« Reply #8 on: Yesterday at 10:21:08 AM »
It "resets" in the sense that it wraps around from 127 to 0, but it's a circular counter. From 126 to 1 would be 3 tips. You only "miss"counts if you miss over 127 counts.
Mark

Offline wxnerd

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Re: Retry Time for Missed Packets
« Reply #9 on: Yesterday at 11:44:59 AM »
It "resets" in the sense that it wraps around from 127 to 0, but it's a circular counter. From 126 to 1 would be 3 tips. You only "miss"counts if you miss over 127 counts.

So if I'm understanding correctly, the number of temporarily-missed tips that I can recover later depends on how close the counter's current position is to 127.....Thus, if the counter happens to be currently at position 120, the console loses connection and it starts raining,  then I can only recover the full amount during lost connection if the added rain was 0.07" or less. If I get 0.08" during that lost connection period, then my console will display 0.01" when it resumes connection....On the other hand, if the counter happens to be at position 50 when I lose connection and it starts raining, then I can recover the full amount up to 0.77"...At 0.78", the console would report 0.01" when connection is resumed in this case.

If I'm correct on this, then by knowing the position of the counter before and after the rain, I could manually calculate the total. Say, if I know the counter is at 120 when the rain starts and it's at 5 when the rain ends, then my total would be 0.13" (7 tips to get to 127 position plus 6 more tips to get to 5 position = 13 tips total or 0.13" on a 0.01" calibrated gauge)

But how do i find the current position of the counter? Is the number displayed on the physical counter inside the rain gauge? Or can the counter position be displayed in the console diagnostic menus?

Offline mcrossley

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Re: Retry Time for Missed Packets
« Reply #10 on: Yesterday at 12:19:33 PM »
Forget zero, it can count up to 128, so you have to exceed that to lose counts. The radio counter is not visible anywhere.
Mark

Offline johnd

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Re: Retry Time for Missed Packets
« Reply #11 on: Yesterday at 03:00:33 PM »
Say, if I know the counter is at 120 when the rain starts and it's at 5 when the rain ends, then my total would be 0.13" (7 tips to get to 127 position plus 6 more tips to get to 5 position = 13 tips total or 0.13" on a 0.01" calibrated gauge)

But how do i find the current position of the counter? Is the number displayed on the physical counter inside the rain gauge? Or can the counter position be displayed in the console diagnostic menus?

Don't worry about it, the console firmware should calculate this automatically. (ie it should remember the last counter reading received and recognise if the counter was near the top of its range.) The only problem happens if the ISS has not been transmitting for an extended period during which a large amount of rain fell, ie if the counter would have reset more than once. The console can only account for a single reset of the counter AFAIK.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
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Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.