[child-supervision] mechanism to inform interval from child to parent

[abtink]

This commit contains changes to child supervision feature. It adds a new mechanism for a child to inform its desired supervision interval to its parent. A new optional MLE TLV is added with type 27 and value of uint16_t indicating the supervision interval in seconds. This TLV is included in MLE Child ID Request and MLE Child Update Request (sent from the child). The parent can echo back this TLV in the corresponding responses to indicate that it supports supervision. This commit changes the parent implementation to track the supervision interval per child.

This change allows backward compatibility: If the parent does not support child supervision, it ignores the new TLV in the MLE messages and the child would fall back to periodically exchanging MLE Child Update Request with parent. If the child does not support supervision and/or does not indicate its desired child supervision interval, the parent will fall back to use the configured default interval.

This commit also updates the OT public APIs along with the related CLI commands:

• API now allows the supervision interval to be set on a child.
• New field in otChildInfo to indicate the child's supervision interval.
• New counter is added to track the number of supervision check timeouts failures on a child (intended for testing and debugging).

This commit adds a test test_child_supervision to cover behavior of child supervision and its new behaviors.

---

This is related to SPEC-1046.

[size-report[bot]]

Size Report of OpenThread

Merging #7993 into main(0491c8ff2c060e84f9ab4dee631e390914e6cd35).

name	branch	text	data	bss	total
ot-cli-ftd_1.1	main	469320	776	63556	533652
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	+/-	+1688	0	+280	+1968
ot-cli-mtd_1.1	main	389448	776	53844	444068
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	+/-	+888	0	+24	+912
ot-ncp-ftd_1.1	main	443740	776	58912	503428
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	+/-	+1512	0	+280	+1792
ot-ncp-mtd_1.1	main	367460	776	49208	417444
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	+/-	+536	0	+24	+560
ot-rcp_1.1	main	60156	564	19964	80684
	#7993	60156	564	19964	80684
	+/-	0	0	0	0
libopenthread-cli-ftd.a_1.1	main	52480	0	7868	60348
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libopenthread-cli-mtd.a_1.1	main	44229	0	7860	52089
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libopenthread-ftd.a_1.1	main	243428	20	38246	281694
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libopenthread-mtd.a_1.1	main	178303	20	28542	206865
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libopenthread-ncp-ftd.a_1.1	main	31481	0	5852	37333
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	+/-	+182	0	0	+182
libopenthread-ncp-mtd.a_1.1	main	26433	0	5852	32285
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libopenthread-rcp.a_1.1	main	8992	0	4988	13980
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libopenthread-radio.a_1.1	main	18053	0	174	18227
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ot-cli-ftd_1.3	main	491320	776	73036	565132
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ot-cli-mtd_1.3	main	404384	776	55068	460228
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ot-ncp-ftd_1.3	main	464668	776	68384	533828
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ot-ncp-mtd_1.3	main	380932	776	50424	432132
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ot-rcp_1.3	main	62516	564	20532	83612
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libopenthread-cli-ftd.a_1.3	main	55381	0	7868	63249
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libopenthread-cli-mtd.a_1.3	main	46531	0	7860	54391
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libopenthread-ftd.a_1.3	main	261497	20	47182	308699
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libopenthread-mtd.a_1.3	main	189720	20	29222	218962
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libopenthread-ncp-ftd.a_1.3	main	33319	0	5852	39171
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libopenthread-ncp-mtd.a_1.3	main	27797	0	5852	33649
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libopenthread-rcp.a_1.3	main	9158	0	4988	14146
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libopenthread-radio.a_1.3	main	18938	0	206	19144
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[codecov[bot]]

Codecov Report

Merging #7993 (7f73cd4) into main (ccf8ea6) will decrease coverage by 0.23%. The diff coverage is n/a.

:exclamation: Current head 7f73cd4 differs from pull request most recent head 26ebb1e. Consider uploading reports for the commit 26ebb1e to get more accurate results

@@            Coverage Diff             @@
##             main    #7993      +/-   ##
==========================================
- Coverage   85.41%   85.18%   -0.24%     
==========================================
  Files         511      511              
  Lines       70410    70988     +578     
==========================================
+ Hits        60144    60469     +325     
- Misses      10266    10519     +253     

Impacted Files	Coverage Δ
src/core/mac/mac_types.cpp	75.22% <0.00%> (-15.40%)	:arrow_down:
src/core/mac/data_poll_handler.hpp	88.23% <0.00%> (-11.77%)	:arrow_down:
src/core/thread/link_metrics_tlvs.hpp	91.95% <0.00%> (-8.05%)	:arrow_down:
src/core/meshcop/timestamp.cpp	87.23% <0.00%> (-4.44%)	:arrow_down:
src/core/mac/mac_links.cpp	79.01% <0.00%> (-3.49%)	:arrow_down:
src/core/thread/csl_tx_scheduler.cpp	94.07% <0.00%> (-2.95%)	:arrow_down:
src/core/thread/link_metrics.cpp	91.90% <0.00%> (-2.94%)	:arrow_down:
src/cli/cli.cpp	78.90% <0.00%> (-2.08%)	:arrow_down:
src/core/api/dns_api.cpp	75.00% <0.00%> (-2.05%)	:arrow_down:
src/core/thread/router_table.cpp	93.28% <0.00%> (-1.63%)	:arrow_down:
... and 116 more

[AlanLCollins]

@abtink , is there a specific problem/issue that triggered adding this new feature?

[jwhui]

@abtink , is there a specific problem/issue that triggered adding this new feature?

@AlanLCollins , there is some background at https://openthread.io/guides/build/features/child-supervision

To provide an energy-efficient mechanism for a sleepy end device (SED) to verify that it is still connected to its parent router (listed in the parent router's child table), enable the Child Supervision feature.

The Thread Specification requires an SED to periodically perform an MLE Child Update Request and Response exchange with its parent router to verify connectivity. Child Supervision is an alternate solution for verification of SED-router connectivity that places the burden of message transmission on the parent router instead of on the energy-constrained SED.

Note: Most 802.15.4 radios generate an AUTO ACK in response to a received MAC frame. An SED cannot solely rely on the 802.15.4 ACKs it receives from a parent router as an indication that it is still connected to that router and listed in its child table.

[abtink]

@abtink , is there a specific problem/issue that triggered adding this new feature?

@AlanLCollins This is related to SPEC-1046. The idea is to add mechanism in Thread spec (new TLV) to allow child to specify what supervision interval it wants.