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 This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference 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. Minaburo & Toutain Expires 8 January 2024 [Page 1] Internet-Draft SCHC Sid Allocation July 2023 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. 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. Minaburo & Toutain Expires 8 January 2024 [Page 2] Internet-Draft SCHC Sid Allocation July 2023 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 Minaburo & Toutain Expires 8 January 2024 [Page 3] Internet-Draft SCHC Sid Allocation July 2023 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. Minaburo & Toutain Expires 8 January 2024 [Page 4] Internet-Draft SCHC Sid Allocation July 2023 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. Minaburo & Toutain Expires 8 January 2024 [Page 5] Internet-Draft SCHC Sid Allocation July 2023 * 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. Minaburo & Toutain Expires 8 January 2024 [Page 6] Internet-Draft SCHC Sid Allocation July 2023 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 Minaburo & Toutain Expires 8 January 2024 [Page 7] Internet-Draft SCHC Sid Allocation July 2023 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, . [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, . Minaburo & Toutain Expires 8 January 2024 [Page 8] Internet-Draft SCHC Sid Allocation July 2023 [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, . [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, . [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [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, . [RFC9363] Minaburo, A. and L. Toutain, "A YANG Data Model for Static Context Header Compression (SCHC)", RFC 9363, DOI 10.17487/RFC9363, March 2023, . 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} Minaburo & Toutain Expires 8 January 2024 [Page 9] Internet-Draft SCHC Sid Allocation July 2023 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 Minaburo & Toutain Expires 8 January 2024 [Page 10]