#1 April 10, 2017 21:49:31

mkirk
Registered: 2016-03-09
Posts: 48
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Timing of ACK responses for Simple Repeated and Source Routed messages?

Can you confirm that the ACK (module-to-host) messages:
0xAA - simple repeated and
0xAC - source routed
are sent when the respective message TTL has expired?

Or are these ACK messages sent to the host after the initial message packet transmission is completed from the source radio, i.e. not waiting for TTL expiration?

For Source Routed, does it depend on the CCA/Retry mode?

I am wondering if the host has to compute TTL and wait to send a new message or can use the ACK from the radio as the indication that the TTL has expired.

Thanks.

Edited mkirk (April 10, 2017 21:58:58)

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#2 April 17, 2017 13:40:17

SupportEngineer
Registered: 2016-03-11
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Timing of ACK responses for Simple Repeated and Source Routed messages?

Hello,

The host needs to calculate the TTL timer.

Regards,
Laird/LSR

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#3 April 17, 2017 15:43:04

mkirk
Registered: 2016-03-09
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Timing of ACK responses for Simple Repeated and Source Routed messages?

OK, thanks. But my observation for a broadcast Simple Repeated packet received by 3 repeater radios were being echoed back to the originating radio (host port) before the host ACK message was sent.
This implies the originating radio is delaying the ACK by at least 3 repeat cycles. With additional testing, I could add more repeaters and stagger the repeat cycles to see if this trend continues.

Example (payload AA AA AA AA AA , max repeats = 3, max repeaters = 10, address 0x1285)

Source message: 01 0E 2A 00 FF FF 18 AA AA AA AA AA A1 04

Received packets at originating radio (1 repeat cycle, 3 repeaters)
01 1B AB 00 00 00 00 00 00 FF 18 A1 1B FF FF 85 12 35 12 FF AA AA AA AA AA C7 04 ( repeater 1235,TS3, RC1)
01 1B AB 00 00 00 00 00 00 FF 18 A1 2B FF FF 85 12 95 12 FF AA AA AA AA AA 37 04 ( repeater 1295, TS5, RC1)
01 1B AB 00 00 00 00 00 00 FF 18 A1 3B FF FF 85 12 90 12 FF AA AA AA AA AA 42 04 ( repeater 1290, TS7, RC1)
01 06 AA 18 C9 04 (ACK of simple repeat message to host).

Same source message, 3 repeated packets, 2 repeat cycles
01 1B AB 00 00 00 00 00 00 FF 18 A1 1B FF FF 85 12 35 12 FF AA AA AA AA AA C7 04 (repeater 1235 TS3, RC1)
01 1B AB 00 00 00 00 00 00 FF 18 A1 2B FF FF 85 12 95 12 FF AA AA AA AA AA 37 04 (repeater 1295 TS5, RC1)
01 1E AB 00 00 00 00 00 00 FF 18 A2 3B FF FF 85 12 35 12 90 12 FF FF AA AA AA AA AA 8C 04 (repeater 1290 TS7, RC2)
01 06 AA 18 C9 04 (ACK of simple repeat message to host)

Same source message, 3 repeated packets, 3 repeat cycles
01 1B AB 00 00 00 00 00 00 FF 18 A1 2B FF FF 85 12 95 12 FF AA AA AA AA AA 37 04 (repeater 1295 TS5, RC1)
01 1E AB 00 00 00 00 00 00 FF 18 A2 3B FF FF 85 12 95 12 90 12 FF FF AA AA AA AA AA EC 04 (repeater 1290 TS7, RC2)
01 21 AB 00 00 00 00 00 00 FF 18 A3 1B FF FF 85 12 95 12 90 12 35 12 FF FF FF AA AA AA AA AA 16 04 (repeater 1235 TS3, RC3)
01 06 AA 18 C9 04 (ACK of simple repeat message to host)

So in all 3 cases, the ACK is not sent to the host until the repeat cycles have completed.
I don't have exact timing on the message arrivals and have not extended the test past 3 repeat cycles.

Edited mkirk (April 17, 2017 15:45:04)

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#4 April 17, 2017 17:11:47

mkirk
Registered: 2016-03-09
Posts: 48
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Timing of ACK responses for Simple Repeated and Source Routed messages?

I did some measurements of the serial port delays. The computed TTL for this message is about 244ms (no security, broadcast packet).

The originating radio shows the ACK for the simple repeated packet is sent about 278ms to 300ms after the Tx message. This delay is greater than the TTL. Also, this delay is not dependent on the number of repeat cycles (1, 2 or 3), So I think the ACK is delayed by the TTL in the originating radio.

Edited mkirk (April 17, 2017 18:06:37)

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#5 April 17, 2017 18:02:36

SupportEngineer
Registered: 2016-03-11
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Timing of ACK responses for Simple Repeated and Source Routed messages?

Hello,

I did some digging and found the related formulas below.

•TTL = ((Max # of Repeaters x Max # of Repeats) +1) x Slot Time.
•Slot Time = Guard Band Time + Transmit Time
•Transmit Time = ((Mac OH + LSR OH + Security OH + Payload) x (8 bits per byte / Data Rate)

These may help confirm your findings. There was another case of similar nature in the following link below.

https://www.lsr.com/forumtopic/4490/

Please let me know if these help and clarify what you are seeing.

Best Regards,
Laird/LSR

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#6 April 17, 2017 18:07:56

mkirk
Registered: 2016-03-09
Posts: 48
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Timing of ACK responses for Simple Repeated and Source Routed messages?


After some additional tests, I don't think there is any correlation to the delay. I increased and decreased the Maximum Repeaters for these radios and the ACK timing did not change. Specifically, when I went to the maximum of 15 repeaters and 7 repeats, the TTL was around 800 ms, but the response delay from the radio was still around 270ms to 300 ms.

Thanks for the additional feedback. I will need to add code to the host controller to handle the TTL now.

Regards,
Mike

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