Internet DRAFT - draft-toutain-schc-sid-allocation
draft-toutain-schc-sid-allocation
schc Working Group A. Minaburo
Internet-Draft Consultant
Intended status: Standards Track L. Toutain
Expires: 8 January 2024 Institut MINES TELECOM; IMT Atlantique
7 July 2023
SCHC Sid Allocation
draft-toutain-schc-sid-allocation-01
Abstract
YANG SID (Schema Item iDentifier) is a method to identify YANG items
in constrained environments. The YANG Data Model for SCHC needs to
use smaller values and reduce the distance between two sections to
minimize deltas' size and assure header compression performance.
Keeping compact values for SCHC can be done when data and identity
are differentiated.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 January 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. SCHC YANG Data Model . . . . . . . . . . . . . . . . . . . . 2
2.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Recommendation for SID values . . . . . . . . . . . . . . . . 5
4. SID value impact . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Administrative process . . . . . . . . . . . . . . . . . 8
5. Normative References . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Set of Rules . . . . . . . . . . . . . . . . . . . . 9
Appendix B. SID Allocation . . . . . . . . . . . . . . . . . . . 9
Appendix C. Security Considerations . . . . . . . . . . . . . . 10
Appendix D. IANA Considerations . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
RFC9363 defines a YANG Data Model for SCHC rules.
[I-D.ietf-core-sid] specifies the process for SID allocation and
management. This document discuss of the SID allocation for RFC9363
to minimize the rule representation.
2. SCHC YANG Data Model
The version @2023-01-18 of the SCHC YANG Data Model published in the
RFC 9363 contains 136 SIDs (92 for identities, 2 for features and 42
for data). [I-D.ietf-core-sid] indicates that the SID range for the
YANG Data Model specified in RFC is between 1000 and 59 000 and that
the maximum request pool SHOULD NOT exceed 1000. The draft also
gives some pre allocated values.
Since SIDs will be used either to represent unique identity contained
in the data model and also leaves (data) forming this data model, it
could be wise to distinguish between identifiers and data.
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Data structures are delta encoded and included as a CBOR element, the
size depends on the value. Deltas between -24 and +23 are encoded on
a single byte. Deltas between -256 and +255 use 2 bytes and larger
values corresponding to the RFC SID range will be encoded into 3
bytes. To optimize the CORECONF representation delta should be
smaller as possible for the more frequent leaves.
On the other hand identities are included in the CORECONF
representation and for the RFC SID range the size is constant and
equal to 3 bytes.
2.1. Example
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CORECONF
{5095: {1: [{4:
[{1: 5015,
5: 5018,
6: 5068,
7: 4,
8: 1,
9: 5083,
13: [{1: 0, 2: h'06'}]},
{1: 5015,
5: 5018,
6: 2000003,
7: 8,
8: 1,
9: 5083,
13: [{1: 0, 2: h'00'}]}]
}]}
}
RESTCONF
{"ietf-schc:schc": {"rule": [{"entry":
[{"comp-decomp-action": "ietf-schc:cda-not-sent",
"direction-indicator": "ietf-schc:di-bidirectional",
"field-id": "ietf-schc:fid-ipv6-version",
"field-length": 4,
"field-position": 1,
"matching-operator": "ietf-schc:mo-equal",
"target-value": [{"index": 0, "value": "Bg=="}]},
{"comp-decomp-action": "ietf-schc:cda-not-sent",
"direction-indicator": "ietf-schc:di-bidirectional",
"field-id": "ietf-schc-oam:fid-icmpv6-type",
"field-length": 8,
"field-position": 1,
"matching-operator": "ietf-schc:mo-equal",
"target-value": [{"index": 0, "value": "gA=="}]} ]
}]}
}
Figure 1
The example in Figure 1 gives a CORECONF structure transposed the
CBOR diagnostic notation and its equivalent in RESTCONF with JSON.
For readability and compactness, this example is edited and do not
encode a full rule as defined in RFC9363.
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The default SID numbering produced by pyang is used, starting from
5000 for SCHC Data Model defined in RFC9363 and 2000000 for an
experimental module for OAM.
We can see the delta encoding. The first SID 5095 represents "ietf-
schc:schc". "/ietf-schc:schc/rule" which is coded with a +1 since SID
5096 has been assigned. "/ietf-schc:schc/rule/entry" is coded with a
delta of 4. Then a list of Field Description follows. +1 represents
the leaf "ietf-schc:schc/rule/entry/comp-decomp-action" and the value
assigned to that key contains the SID of "ietf-schc:cda-not-sent"
identity.
Note that the second element contains a "field-id" belonging to the
"ietf-schc-oam" module and the associate SID is 2000003.
3. Recommendation for SID values
The SCHC YANG Data Model defined in RFC 9363 will probably be
augmented, to include for instance access control data. To keep a
compact representation, delta values must be kept as small as
possible. The LPWAN working group should not use the automatic SID
numbering and provide a more optimal allocation scheme for
augmentation of the SCHC YANG Data Model.
A first recommendation is to avoid merging data and identity in order
to limit the delta encoding. The distance between these two sections
can be 255 SID to allow deltas on 2 bytes.
The second recommendation is to leave some unused SID around SCHC
rules to allow augmentation.
4. SID value impact
To study the impact of SIDs size and delta size, we will take three
scenarii, which cover the original Data Model defined in [RFC9363]
and some augmentations, rules regarding these scenarii are listed in
the annex:
* sor-9363 contains only parameters defined in [RFC9363] with IPv6,
UDP and CoAP fields. This is a set of 7 rules: 2 for compression
and 5 for fragmentation.
* sor-oam adds to the previous set of rules, a compression rule for
ICMP messages. This add new identities for ICMPv6 fields, but the
rule structure is not modified.
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* sor-oam+ac augments to the previous set of rule with access
control nodes. This requires an augmentation with Access Control
DM and includes new nodes in the rule Data Model.
For this three group of Set of Rule, we applied four different
allocation methods for the SIDs:
* SIDs are located in the million range for the 3 YANG modules (1000
000 for basic model based on RFC9363, 2 000 000 for OAM and 3 000
000 for Access Control),
* SIDs are located in the IETF range (5000:500, 5500:50, 6000:50)
and in the alphabetical order,
* SIDs are manually allocated regarding their frequency occurrences
in the rule,
* tens of the main used SID for RFC9363 are allocated in the IESG
range (CDA: compute, LSB, Match Mapping, not sent, value-send, MO:
equal, ignore, match, MSB, and bidirectional).
The following table shows the results:
+------------+------------+------------+------------+------------+--------+
| | million | IETF | IETF | IESG | JSON |
| | | separate | grouped | (dream) | |
+------------+------------+------------+------------+------------+--------+
| sor-9363 | 2194 | 1740 (-454)| 1721 (-19) | 1586 (-135)| 15388 |
+------------+------------+------------+------------+------------+--------+
| sor-oam | 2841 | 2265 (-576)| 2243 (-22) | 2064 (-179)| 19871 |
+------------+------------+------------+------------+------------+--------+
| sor-oam+ac | 2925 | 2321 (-604)| 2271 (-50) | 2092 (-179)| 20686 |’
+------------+------------+------------+------------+------------+--------+
Figure 2: Size in Bytes SID allocations strategies
The most important result, is the factor 10 between CBOR and JSON
(without indentation) size which proves the efficiency of encoding. 2
kilo-byte of information to represent 8 rules (3 compression and 5
fragmentation rules).
The IETF-grouped has a impact on the rule size, even when no
augmentation is perform. This is the case for rfc9363 compatible
rules and OAM addition. Figure Figure 3 shows the alphabetical order
allocation with pyang.
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5095 data /ietf-schc:schc
5096 data /ietf-schc:schc/rule
5097 data /ietf-schc:schc/rule/ack-behavior
5098 data /ietf-schc:schc/rule/direction
5099 data /ietf-schc:schc/rule/dtag-size
5100 data /ietf-schc:schc/rule/entry
5101 data /ietf-schc:schc/rule/entry/comp-decomp-action
5102 data /ietf-schc:schc/rule/entry/comp-decomp-action-value
5103 data /ietf-schc:schc/rule/entry/comp-decomp-action-value/index
5104 data /ietf-schc:schc/rule/entry/comp-decomp-action-value/value
5105 data /ietf-schc:schc/rule/entry/direction-indicator
5106 data /ietf-schc:schc/rule/entry/field-id
5107 data /ietf-schc:schc/rule/entry/field-length
5108 data /ietf-schc:schc/rule/entry/field-position
5109 data /ietf-schc:schc/rule/entry/matching-operator
5110 data /ietf-schc:schc/rule/entry/matching-operator-value
5111 data /ietf-schc:schc/rule/entry/matching-operator-value/index
5112 data /ietf-schc:schc/rule/entry/matching-operator-value/value
5113 data /ietf-schc:schc/rule/entry/target-value
5114 data /ietf-schc:schc/rule/entry/target-value/index
5115 data /ietf-schc:schc/rule/entry/target-value/value
5116 data /ietf-schc:schc/rule/fcn-size
5117 data /ietf-schc:schc/rule/fragmentation-mode
5118 data /ietf-schc:schc/rule/inactivity-timer
------ 23 delta limit
5119 data /ietf-schc:schc/rule/inactivity-timer/ticks-duration
5120 data /ietf-schc:schc/rule/inactivity-timer/ticks-numbers
5121 data /ietf-schc:schc/rule/l2-word-size
5122 data /ietf-schc:schc/rule/max-ack-requests
5123 data /ietf-schc:schc/rule/max-interleaved-frames
5124 data /ietf-schc:schc/rule/maximum-packet-size
5125 data /ietf-schc:schc/rule/rcs-algorithm
5126 data /ietf-schc:schc/rule/retransmission-timer
5127 data /ietf-schc:schc/rule/retransmission-timer/ticks-duration
5128 data /ietf-schc:schc/rule/retransmission-timer/ticks-numbers
5129 data /ietf-schc:schc/rule/rule-id-length
5130 data /ietf-schc:schc/rule/rule-id-value
5131 data /ietf-schc:schc/rule/rule-nature
5132 data /ietf-schc:schc/rule/tile-in-all-1
5133 data /ietf-schc:schc/rule/tile-size
5134 data /ietf-schc:schc/rule/w-size
5135 data /ietf-schc:schc/rule/window-size
Figure 3: Alphabetical order of SIDs
"Rule-id-value", "rule-id-length", "rule-nature" present in all rules
have a delta higher than 23. On the other hand, other elements such
are matching-operator-value or comp-decomp-action-value which are not
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present in all rules have a smaller delta. Figure {#Allocation}
gives the manual SID allocation used in this document. This lead to
a reduction of about 20 bytes (a mean of 5 bytes for the 8 rules in
the example) when no augmentation is perform. In case of
augmentation with the last example including access control, this
leads to 50 bytes.
Manual allocation allows also to use some other space, the last
scenario takes 10 values (1%) from the IESG space for the most
frequent identity.
4.1. Administrative process
The allocation process proposed in [I-D.ietf-core-sid] is slightly
enhanced:
* the SCHC WG requests IANA for a larger pool of SIDs than
originally needed for a single Data Model (for instance 500 SIDs)
* the SCHC WG MAY request IESG review for a small amount of SIDs
* the WG manages the space as presented in Appendix B.
* If a module is validated by the WG and request a WG allocation,
the SID are allocated in the space and a sid file is issue for
this module.
The result is a better allocation of the space, [I-D.ietf-core-sid]
proposes a minimum of 50 SIDs per module, but looking at the existing
models, the effective number is smaller. Using a common pool, allows
a better utilization.
5. Normative References
[I-D.ietf-core-sid]
Veillette, M., Pelov, A., Petrov, I., Bormann, C., and M.
Richardson, "YANG Schema Item iDentifier (YANG SID)", Work
in Progress, Internet-Draft, draft-ietf-core-sid-20, 1
March 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-core-sid-20>.
[I-D.ietf-lpwan-schc-compound-ack]
Zúñiga, J. C., Gomez, C., Aguilar, S., Toutain, L.,
Cespedes, S., and D. S. W. L. Torre, "SCHC Compound ACK",
Work in Progress, Internet-Draft, draft-ietf-lpwan-schc-
compound-ack-17, 4 April 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lpwan-
schc-compound-ack-17>.
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[I-D.ietf-lpwan-schc-yang-data-model]
Minaburo, A. and L. Toutain, "A YANG Data Model for Static
Context Header Compression (SCHC)", Work in Progress,
Internet-Draft, draft-ietf-lpwan-schc-yang-data-model-21,
9 October 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-lpwan-schc-yang-data-model-21>.
[I-D.toutain-lpwan-access-control]
Minaburo, A., Toutain, L., and I. Martinez, "SCHC Rule
Access Control", Work in Progress, Internet-Draft, draft-
toutain-lpwan-access-control-01, 20 February 2023,
<https://datatracker.ietf.org/doc/html/draft-toutain-
lpwan-access-control-01>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/rfc/rfc8341>.
[RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static
Context Header Compression (SCHC) for the Constrained
Application Protocol (CoAP)", RFC 8824,
DOI 10.17487/RFC8824, June 2021,
<https://www.rfc-editor.org/rfc/rfc8824>.
[RFC9363] Minaburo, A. and L. Toutain, "A YANG Data Model for Static
Context Header Compression (SCHC)", RFC 9363,
DOI 10.17487/RFC9363, March 2023,
<https://www.rfc-editor.org/rfc/rfc9363>.
Appendix A. Set of Rules
{::include sor-9363.json}
Figure 4: SoR only referenced by RFC9363
{::include sor-oam.json}
Figure 5: SoR including OAM compression
{::include sor-oam+ac.json}
Figure 6: SoR including Access Control
Appendix B. SID Allocation
{::include Classeur2.csv}
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Figure 7: Manual SID allocation
Appendix C. Security Considerations
TBD
Appendix D. IANA Considerations
TBD
Authors' Addresses
Ana Minaburo
Consultant
Rue de Rennes
35510 Cesson-Sevigne
France
Email: anaminaburo@gmail.com
Laurent Toutain
Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Laurent.Toutain@imt-atlantique.fr
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