lpwan Working Group A. Minaburo Internet-Draft Acklio Intended status: Standards Track L. Toutain Expires:August 6, 202113 March 2022 Institut MINES TELECOM; IMT AtlantiqueFebruary 02,9 September 2021 Data Model for Static Context Header Compression (SCHC)draft-ietf-lpwan-schc-yang-data-model-04draft-ietf-lpwan-schc-yang-data-model-05 Abstract This document describes a YANG data model for the SCHC (Static Context Header Compression) compression and fragmentation rules. 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 onAugust 6, 2021.13 March 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents(https://trustee.ietf.org/license-info)(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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. SCHC rules . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1. Compression Rules . . . . . . . . . . . . . . . . . . . . 3 2.2. Identifier generation . . . . . . . . . . . . . . . . . . 4 2.3. Field Identifier . . . . . . . . . . . . . . . . . . . .3 2.3.5 2.4. Field length . . . . . . . . . . . . . . . . . . . . . .5 2.4.7 2.5. Field position . . . . . . . . . . . . . . . . . . . . .6 2.5.8 2.6. Direction Indicator . . . . . . . . . . . . . . . . . . .6 2.6.8 2.7. Target Value . . . . . . . . . . . . . . . . . . . . . .7 2.7.9 2.8. Matching Operator . . . . . . . . . . . . . . . . . . . .8 2.7.1.10 2.8.1. Matching Operator arguments . . . . . . . . . . . . .9 2.8.11 2.9. Compression Decompression Actions . . . . . . . . . . . .10 2.8.1.11 2.9.1. Compression Decompression Action arguments . . . . . 123. Rule definition2.10. Fragmentation rule . . . . . . . . . . . . . . . . . . . 12 2.10.1. Fragmentation mode . . . . . . . . . . . . . . . . . 123.1. Compression rule2.10.2. Fragmentation Header . . . . . . . . . . . . . . . . 13 2.10.3. Last fragment format . . . . . . .14 3.1.1. Compression context representation.. . . . . . . . . 143.1.2.2.10.4. Acknowledgment behavior . . . . . . . . . . . . . . 16 2.10.5. Fragmentation Parameters . . . . . . . . . . . . . . 18 2.10.6. Layer 2 parameters . . . . . . . . . . . . . . . . . 19 3. Rule definition . . . . . . . . . . . . . . . . . . .15. . . . 19 3.1. Compression rule . . . . . . . . . . . . . . . . . . . . 21 3.2. Fragmentation rule . . . . . . . . . . . . . . . . . . .1623 3.3. YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . 26 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . .2428 5. Security considerations . . . . . . . . . . . . . . . . . . .2428 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .2428 7. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .2428 8. Normative References . . . . . . . . . . . . . . . . . . . .4150 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .4251 1. Introduction 2. SCHC rules SCHC is a compression and fragmentation mechanism for constrained networks defined in [RFC8724]. It is based on a static context shared by two entities at the boundary this constrained network. Draft [RFC8724] providesana non formal representation of the rules used either for compression/decompression (or C/D) or fragmentation/ reassembly (or F/R). The goal of this document is to formalize the description of the rules to offer:o* the same definition on both ends, even if the internal representation is different.o* an update the other end to set up some specific values (e.g. IPv6 prefix, Destination address,...)o* ... This document defines a YANG module to represent both compression and fragmentation rules, which leads to common representation for values for all the rules elements. SCHC compression is generic, the main mechanismdo no refersdoes not refer to a specific protocol. Any header field is abstracted through an ID, a position, adirectiondirection, and a value that can be a numerical value or a string. [RFC8724] and[I-D.ietf-lpwan-coap-static-context-hc][RFC8824] specifies fields for IPv6, UDP, CoAP and OSCORE. [I-D.barthel-lpwan-oam-schc]decribesdescribes ICMPv6 headercompression.compression and [I-D.ietf-lpwan-schc-compound-ack] includes a new fragmentation behavior. SCHC fragmentation requires a set of common parameters that are included in a rule. These parameters are defined in [RFC8724]. 2.1. Compression Rules [RFC8724] proposesana non formal representation of the compression rule. A compression context for a device is composed of a set of rules. Each rule contains information to describe a specific field in the header to be compressed. +-----------------------------------------------------------------+ | Rule N | +-----------------------------------------------------------------+| | Rule i || +-----------------------------------------------------------------+|| | (FID) Rule 1 ||| |+-------+--+--+--+------------+-----------------+---------------+||| ||Field 1|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act|||| |+-------+--+--+--+------------+-----------------+---------------+||| ||Field 2|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act|||| |+-------+--+--+--+------------+-----------------+---------------+||| ||... |..|..|..| ... | ... | ... |||| |+-------+--+--+--+------------+-----------------+---------------+||/ ||Field N|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act||| |+-------+--+--+--+------------+-----------------+---------------+|/ | | \-----------------------------------------------------------------/ Figure 1: Compression Decompression Context 2.2. Identifier generation Identifier used un the SCHC YANG Data Model are from the identityref statement to ensure to be globally unique and be easily augmented if needed. The principle to define a new type based on a group of identityref is the following: * define a main identity ending with the keyword base-type. * derive all the identity used in the Data Model from this base type. * create a typedef from this base type. The example (Figure 2) shows how an identityref is created for RCS algorithms used during SCHC fragmentation. // -- RCS algorithm types identity rcs-algorithm-base-type { description "identify which algorithm is used to compute RSC. The algorithm also defines the size if the RSC field."; } identity rcs-RFC8724 { base rcs-algorithm-base-type; description "CRC 32 defined as default RCS in RFC8724."; } typedef rcs-algorithm-type { type identityref { base rcs-algorithm-base-type; } description "type used in rules"; } Figure 2: Principle to define a type based on identityref. 2.3. Field Identifier In the process of compression, the headers of the original packet are first parsed to create a list of fields. This list of fields is matched against the rules to find the appropriate one and apply compression. The link between the list given by the parsed fields and the rules is done through a field ID. [RFC8724] do not state how the field ID value can be constructed. In examples, identification is done through a string indexed by the protocol name (e.g. IPv6.version, CoAP.version,...). The current YANG Data Model includes fields definitions found in [RFC8724], [RFC8824], and [I-D.barthel-lpwan-oam-schc]. Using the YANG model, each field MUST be identified through a global YANG identityref. A YANG field ID for the protocol always derives from thefield-id-base-fid-base-type. Then an identity for each protocol is specified using the naming convention fid-<<protocol name>>-base- type. All possible fields for this protocol MUST derive from the protocol identity. The naming convention is "fid" followed by the protocol name and the field name. If a field has to be divided into sub-fields, the field identity serves as a base. The full field-id definition is found in Section 7. The example Figure23 givessomethe first field ID definitions.Note that some field IDs can be splitted is smaller pieces. ThisA type isthe casedefined for"fid-ipv6-trafficclass-ds"IPv6 protocol, and"fid-ipv6-trafficclass-ecn" which are a subset of "fid-ipv6-trafficclass-ds".each field is based on it. Note that the DiffServ bits derives from the Traffic Class identity. identityfield-id-base-typefid-base-type { description "Field IDwith SID";base type for all fields"; } identity fid-ipv6-base-type { base fid-base-type; description "Field IP base type for IPv6 headers described in RFC 8200"; } identity fid-ipv6-version { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 version field from RFC8200"; } identity fid-ipv6-trafficclass { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Traffic Class field from RFC8200"; } identity fid-ipv6-trafficclass-ds { basefield-id-base-type;fid-ipv6-trafficclass; description "IPv6 Traffic Class field from RFC8200, DiffServ field from RFC3168"; }identity fid-ipv6-trafficclass-ecn { base field-id-base-type; description "IPv6 Traffic Class field from RFC8200, ECN field from RFC3168"; }... Figure2:3: Definition of identityref for field IDsFigure 2 gives some examples of field ID identityref definitions. The base identity is field-id-base-type, and field id are derived for it. The naming convention is "fid" followed by the protocol name and the field name. The yang model in annex (see Section 7) gives the full definition of the field ID for [RFC8724], [I-D.ietf-lpwan-coap-static-context-hc], and [I-D.barthel-lpwan-oam-schc].The type associated to this identity isfield-id-typefid-type (cf. Figure3)4) typedeffield-id-typefid-type {description "Field ID generic type.";type identityref { basefield-id-base-type;fid-base-type; } description "Field ID generic type."; } Figure3:4: Type definition for field IDs2.3.2.4. Field length Field length is either an integer giving the size of a field in bits or a specific function. [RFC8724] defines the "var" function which allows variable length fields in byte and[I-D.ietf-lpwan-coap-static-context-hc][RFC8824] defines the "tkl" function for managing the CoAP Token length field. The naming convention is "fl" followed by the function name. identityfield-length-base-typefl-base-type { description"used"Used to extend field length functions"; } identity fl-variable { basefield-length-base-type;fl-base-type; description"residue"Residue length in Byte issent";sent defined in for CoAP in RFC 8824 (cf. 5.3)"; } identity fl-token-length { basefield-length-base-type;fl-base-type; description"residue"Residue length in Byte issent";sent defined in for CoAP in RFC 8824 (cf. 4.5)"; } Figure4:5: Definition of identityref forfield ILengthField Length As for field ID, field length function can be defined asaan identityref as shown in Figure4. Therefore5. Therefore, the type for field length is a union between an integer giving in bits the size of the length and the identityref (cf. Figure5).6). typedeffield-length-typefl-type {description "Field length either a positive integer giving the size in bits or a function defined through an identityref.";type union { type int64; /* positive length in bits */ type identityref { /* function */ basefield-length-base-type;fl-base-type; } } description "Field length either a positive integer giving the size in bits or a function defined through an identityref."; } Figure5:6: Type definition for field LengthThe naming convention is fl followed by the function name as defined in SCHC specifications. 2.4.2.5. Field position Field position is a positive integer which gives the position of a field, the default value is 1, but if the field is repeated several times, the value is higher. value 0 indicates that the position is not important and is nottaken into accountconsidered during the rule selection process. Field position is a positive integer. The type is an uint8.2.5.2.6. Direction Indicator The Direction Indicator(DI)(di) is used to tell if a field appears in both direction (Bi) or only uplink (Up) or Downlink (Dw). identitydirection-indicator-base-typedi-base-type { description"used"Used to extend field length functions"; } identity di-bidirectional { basedirection-indicator-base-type;di-base-type; description "Direction Indication of bidirectionality";directionality in RFC 8724 (cf. 7.1)"; } identity di-up { basedirection-indicator-base-type;di-base-type; description "Direction Indication ofupstream";upstream defined in RFC 8724 (cf. 7.1)"; } identity di-down { basedirection-indicator-base-type;di-base-type; description "Direction Indication ofdownstream";downstream defined in RFC 8724 (cf. 7.1)"; } Figure6:7: Definition of identityref for direction indicators Figure67 gives the identityref for Direction Indicators. The naming convention is "di" followed by the Direction Indicator name. The type is "direction-indicator-type" (cf. Figure7).8). typedefdirection-indicator-typedi-type { type identityref { base di-base-type; } description"direction"Direction in LPWAN network, up when emitted by the device, down when received by the device, bi when emitted or received by the device.";type identityref { base direction-indicator-base-type; }} Figure7:8: Type definition for direction indicators2.6.2.7. Target Value The Target Valuemayis a list of binary sequences of any length, aligned on the left. Figure 9 gives the definition of a single element of a Target Value. In the rule, this will beeitherused as astringlist, with position as a key. The highest position value is used to compute the size of the index sent in residue for LSB CDA. The position allows to specify several values: * For Equal and LSB, a single value is used, such as for the equal orbinary sequence.LSB CDA, the position is set to 0. * Formatch- mapping,match-mapping, several of these values can be contained in a Target Value field. In the data model, this is generalized by adding a position, which orders the list of values.By default the position is set to 0. The leaf "value" is not mandatory to represent a non existing value in a TV.Position values must start from 0 and be contiguous. groupingtarget-values-structtv-struct { description"defines"Define the target value element.Can be either an arbitrary binary or ascii element. All target values are considered asAlways amatching lists. Position is usedbinary type, strings must be converted toorder values, by default position 0 is used when containing a single element.";binary. field-id allows the conversion to the appropriate type."; leaf value { typeunion { typebinary;type string; }} leaf position { type uint16; description "If only one element position is 0, otherwise position is the matching list.";type uint16;} } Figure8:9: Definition of target valueFigure 8 gives the definition of a single element of a Target Value. In the rule, this will be used as a list, with position as a key. The highest position value is used to compute the size of the index sent in residue. 2.7.2.8. Matching Operator Matching Operator (MO) is a function applied between a field value provided by the parsed header and the target value. [RFC8724] defines 4MO.MO as listed in Figure 10. identitymatching-operator-base-typemo-base-type { description"used"Used to extend Matching Operators with SID values"; } identity mo-equal { basematching-operator-base-type;mo-base-type; description"RFC 8724";"Equal MO as defined RFC 8724 (cf. 7.3)"; } identity mo-ignore { basematching-operator-base-type;mo-base-type; description"RFC 8724";"Ignore MO as defined RFC 8724 (cf. 7.3)"; } identity mo-msb { basematching-operator-base-type;mo-base-type; description"RFC 8724";"MSB MO as defined RFC 8724 (cf. 7.3)"; } identity mo-matching { basematching-operator-base-type;mo-base-type; description"RFC 8724";"match-mapping MO as defined RFC 8724 (cf. 7.3)"; } Figure9:10: Definition of identityref for Matching Operator The naming convention is "mo" followed by the MO name. The type is "matching-operator-type" (cf. Figure10)11) typedefmatching-operator-typemo-type { type identityref { base mo-base-type; } description "Matching Operator (MO) to compare fields values with target values";type identityref { base matching-operator-base-type; }} Figure10:11: Type definition for Matching Operator2.7.1.2.8.1. Matching Operator arguments Some Matching Operator such as MSB can take some values. Even if currently LSB is the only MO takes only one argument, in the future some MO may require several arguments. They are viewed as a list of target-values-type.2.8.2.9. Compression Decompression Actions Compression Decompression Action (CDA) identified the function to use either for compression or decompression. [RFC8724] defines 6 CDA. Figure 13 gives some CDA definition, the full definition is in Section 7. identitycompression-decompression-action-base-type;cda-base-type { description "Compression Decompression Actions"; } identity cda-not-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"not-sent CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-value-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"value-sent CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-lsb { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"LSB CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-mapping-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724"; } identity cda-compute-length { base compression-decompression-action-base-type; description "RFC 8724"; } identity cda-compute-checksum { base compression-decompression-action-base-type; description "RFC 8724"; } identity cda-deviid { base compression-decompression-action-base-type; description "RFC 8724"; } identity cda-appiid { base compression-decompression-action-base-type; description "RFC 8724";"mapping-sent CDA as defines in RFC 8724 (cf. 7.4)"; } .... Figure11:12: Definition of identityref for Compresion Decompression Action Thetypenaming convention is"comp-decomp-action-type" (cf. Figure 12)"cda" followed by the CDA name. typedefcomp-decomp-action-typecda-type { type identityref { base cda-base-type; } description "Compression Decompression Action to compression or decompress a field.";type identityref { base compression-decompression-action-base-type; }} Figure12:13: Type definition for Compresion Decompression Action2.8.1.2.9.1. Compression Decompression Action arguments Currently no CDA requires arguments, but the future some CDA may require several arguments. They are viewed as a list of target- values-type. 2.10. Fragmentation rule Fragmentation is optional in the data model and depends on the presence of the "fragmentation" feature. Most of parameters for fragmentation are defined in Annex D of [RFC8724]. Since fragmentation rules work for a specific direction, they contain a mandatory direction. The type is the same as the one used in compression entries, but the use of bidirectional is forbidden. 2.10.1. Fragmentation mode [RFC8724] defines 3 fragmentation modes: * No Ack: this mode is unidirectionnal, no acknowledgment is sent back. * Ack Always: each fragmentation window must be explicitly acknowledged before going to the next. * Ack on Error: A window is acknowledged only when the receiver detects some missing fragments. Figure 14 give the definition for identifiers from these three modes. identity fragmentation-mode-base-type { description "Fragmentation mode"; } identity fragmentation-mode-no-ack { base fragmentation-mode-base-type; description "No Ack of RFC 8724."; } identity fragmentation-mode-ack-always { base fragmentation-mode-base-type; description "Ack Always of RFC8724."; } identity fragmentation-mode-ack-on-error { base fragmentation-mode-base-type; description "Ack on Error of RFC8724."; } typedef fragmentation-mode-type { type identityref { base fragmentation-mode-base-type; } description "type used in rules"; } Figure 14: Definition of fragmentation mode identifer The naming convention is "fragmentation-mode" followed by the fragmentation mode name. 2.10.2. Fragmentation Header A data fragment header, directly following the rule ID can be sent on the fragmentation direction. The direction is mandatory and must be up or down. bidirectional is forbidden. The SCHC header may be composed of (cf. Figure 15): * a Datagram Tag (Dtag) identifying the datagram being fragmented if the fragmentation applies concurrently on several datagrams. This field in optional and its length is defined by the rule. * a Window (W) used in Ack-Always and Ack-on-Error modes. In Ack- Always, its size is 1 and depends on the rule in Ack-on-Error. This field is not need in No-Ack mode. * a Fragment Compressed Number (FCN) indicating the fragment/tile position on the window. This field is mandatory on all modes defined in [RFC8724], its size is defined by the rule. |-- SCHC Fragment Header ----| |-- T --|-M-|-- N --| +-- ... -+- ... -+---+- ... -+--------...-------+~~~~~~~~~~~~~~~~~~~~ | RuleID | DTag | W | FCN | Fragment Payload | padding (as needed) +-- ... -+- ... -+---+- ... -+--------...-------+~~~~~~~~~~~~~~~~~~~~ Figure 15: Data fragment header from RFC8724 2.10.3. Last fragment format The last fragment of a datagram is sent with an RCS (Reassembly Check Sequence) field to detect residual transmission error and possible losses in the last window. [RFC8724] defines a single algorithm based on Ethernet CRC computation. The identity of the RCS algorithm is shown in Figure 16. // -- RCS algorithm types identity rcs-algorithm-base-type { description "Identify which algorithm is used to compute RSC. The algorithm defines also the size if the RSC field."; } identity rcs-RFC8724 { base rcs-algorithm-base-type; description "CRC 32 defined as default RCS in RFC8724."; } typedef rcs-algorithm-type { type identityref { base rcs-algorithm-base-type; } description "type used in rules"; } Figure 16: type definition for RCS The naming convention is "rcs" followed by the algorithm name. For Ack-on-Error mode, the All-1 fragment may just contain the RCS or can include a tile. The parameters defined in Figure 17 allows to define the behavior: * all1-data-no: the last fragment contains no data, just the RCS * all1-data-yes: the last fragment includes a single tile and the RCS * all1-data-sender-choice: the last fragment may or may not contain a single tile. The receiver can detect if a tile is present. // -- All1 with data types identity all1-data-base-type { description "Type to define when to send an Acknowledgment message"; } identity all1-data-no { base all1-data-base-type; description "All1 contains no tiles."; } identity all1-data-yes { base all1-data-base-type; description "All1 MUST contain a tile"; } identity all1-data-sender-choice { base all1-data-base-type; description "Fragmentation process choose to send tiles or not in all1."; } typedef all1-data-type { type identityref { base all1-data-base-type; } description "Type used in rules"; } Figure 17: type definition for RCS The naming convention is "all1-data" followed by the behavior identifier. 2.10.4. Acknowledgment behavior A cknowledgment fragment header goes in the opposite direction of data. The header is composed of (see Figure 18): * a Dtag (if present). * a mandatory window as in the data fragment. * a C bit giving the status of RCS validation. In case of failure, a bitmap follows, indicating received fragment/tile. The size of the bitmap is given by the FCN value. NOTE: IN THE DATA MODEL THERE IS A max-window-size FIELD TO LIMIT THE BITMAP SIZE, BUT IS NO MORE IN RFC8724! DO WE KEEP IT? |--- SCHC ACK Header ----| |-- T --|-M-| 1 | +-- ... -+- ... -+---+---+~~~~~~~~~~~~~~~~~~ | RuleID | DTag | W |C=1| padding as needed (success) +-- ... -+- ... -+---+---+~~~~~~~~~~~~~~~~~~ +-- ... -+- ... -+---+---+------ ... ------+~~~~~~~~~~~~~~~ | RuleID | DTag | W |C=0|Compressed Bitmap| pad. as needed (failure) +-- ... -+- ... -+---+---+------ ... ------+~~~~~~~~~~~~~~~ Figure 18: Acknowledgment fragment header for RFC8724 For Ack-on-Error, SCHC defined when acknowledgment can be sent. This can be at any time defined by the layer 2, at the end of a window (FCN All-0) or at the end of the fragment (FCN All-1). The following identifiers (cf. Figure 19) define the acknowledgment behavior. // -- Ack behavior identity ack-behavior-base-type { description "Define when to send an Acknowledgment message"; } identity ack-behavior-after-All0 { base ack-behavior-base-type; description "Fragmentation expects Ack after sending All0 fragment."; } identity ack-behavior-after-All1 { base ack-behavior-base-type; description "Fragmentation expects Ack after sending All1 fragment."; } identity ack-behavior-always { base ack-behavior-base-type; description "Fragmentation expects Ack after sending every fragment."; } typedef ack-behavior-type { type identityref { base ack-behavior-base-type; } description "Type used in rules"; } Figure 19: bitmap generation behavior The naming convention is "ack-behavior" followed by the algorithm name. For Ack-onError, [RFC8724] allows a single bitmap in an acknowledment fragment, and [I-D.ietf-lpwan-schc-compound-ack] proposes to acknowledge several windows on a single ack fragment. The following identifiers (cf. Figure 20) define the behavior. identity bitmap-format-base-type { description "Define how the bitmap is defined in ACK messages."; } identity bitmap-RFC8724 { base bitmap-format-base-type; description "Bitmap as defined in RFC8724."; } identity bitmap-compound-ack { base bitmap-format-base-type; description "Compound Ack."; } typedef bitmap-format-type { type identityref { base bitmap-format-base-type; } description "type used in rules"; } Figure 20: bitmap generation behavior The naming convention is "bitmap" followed by the algorithm name. 2.10.5. Fragmentation Parameters The state machine requires some common values to handle fragmentation: * retransmission-timer gives in seconds the duration before sending an ack request (cf. section 8.2.2.4. of [RFC8724]). If specified, value must be higher or equal to 1. * inactivity-timer gives in seconds the duration before aborting (cf. section 8.2.2.4. of [RFC8724]), value of 0 explicitly indicates that this timer is disabled. * max-ack-requests gives the number of attempts before aborting (cf. section 8.2.2.4. of [RFC8724]). * maximum-packet-size gives in bytes the larger packet size that can be reassembled. The are defined as unsigned integer, see Section 7. 2.10.6. Layer 2 parameters The data model includes two parameters needed for fragmentation: * l2-word-size: [RFC8724] base fragmentation on a layer 2 word which can be of any length. The default value is 8 and correspond to the default value for byte aligned layer 2. A value of 1 will indicate that there is no alignment and no need for padding. * maximum-packet-size: defines the maximum size of a uncompressed datagram. By default, the value is set to 1280 bytes. They are defined as unsigned integer, see Section 7. 3. Rule definition A rule is either a C/D or an F/R rule. A rule is identified by the rule ID value and its associated length. The YANG grouping rule-id- type defines the structure used to represent a rule ID. Length of 0 is allowed to represent an implicit rule.// DefineThree types of rules are defined in [RFC8724]: * Compression: a compression rule is associated to the rule ID.Rule ID* No compression: nothing iscomposed of a RuleID valueassociated to the rule ID. * Fragmentation: fragmentation parameters are associated to the rule ID. Fragmentation is optional anda Rule ID Lengthfeature "fragmentation" should be set. grouping rule-id-type { leafrule-idrule-id-value { type uint32; description"rule"Rule ID value, this value must be unique combined with the length"; } leafrule-lengthrule-id-length { type uint8 { range0..32;"0..32"; } description"rule"Rule ID length in bits, value 0 is for implicit rules"; } description "A rule ID is composed of a value and a length in bit"; } // SCHC table for a specific device. container schc {leaf version{ type uint64; mandatory false; description "used as an indication for versioning"; }list rule { key"rule-id rule-length";"rule-id-value rule-id-length"; uses rule-id-type; choice nature { case fragmentation { if-feature "fragmentation"; uses fragmentation-content; } case compression { uses compression-content; } case no-compression { description "RFC8724 allows a rule for uncompressed headers"; } description "A rule is either for compression, no compression or fragmentation"; } description "Set of rules compression, no compression or fragmentation rules identified by their rule-id "; } description "a SCHC set of rules is composed of a list of rule which are either compression or fragmentation"; } } Figure13:21: Definition of a SCHC Context To access to a specific rule, rule-id and its specific length is used as a key. The rule is either a compression or a fragmentation rule. Each context can be identified though a version id. 3.1. Compression rule A compression rule is composed of entries describing its processing (cf. Figure14).22). An entry contains all the information defined in Figure 1 with the types defined above.3.1.1. Compression context representation.The compression rule described Figure 1 isassociated to a rule ID. The compression rule entry isdefinedin Figure 14. Each column in the table is either representedby compression- content. It defines aleaf or a list. Note that Matching Operators and Compression Decompression actions can have arguments. They are viewed a orderedlist ofstringscompression-rule-entry, indexed by their field id, position andnumbers asdirection. The compression-rule-entry element represent a line of the table Figure 1. Their type reflects the identifier types defined in Section 2.1 Some controls are made on the values: * targetvalues.value must be present for MO different from ignore. * when MSB MO is specified, the matching-operator-value must be present grouping compression-rule-entry { description "These entries defines a compression entry (i.e. a line) as defined in RFC 8724 and fragmentation parameters. +-------+--+--+--+------------+-----------------+---------------+ |Field 1|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act| +-------+--+--+--+------------+-----------------+---------------+ An entry in a compression rule is composed of 7 elements: - Field ID: The header field to be compressed. The content is a YANG identifer. - Field Length : either a positive integer of a function defined as aYANGYANF id. - Field Position: a positive (and possibly equal to 0) integer. - Direction Indicator: a YANG identifier giving the direction. - Target value: a value against which the header Field is compared. - Matching Operator: a YANG id giving the operation,parametersparamters may be associated to that operator. - Comp./Decomp. Action: A YANG id giving the compression or decompression action,parametersparamters may be associated to that action. "; leaf field-id { type schc:fid-type; mandatory true; description "Field ID, identify a field in the header with a YANGidentityref."; mandatory true; type schc:field-id-type;refenceid."; } leaf field-length { type schc:fl-type; mandatory true; description "Field Length in bit or through a function defined as a YANGidentityref"; mandatory true; type schc:field-length-type;referenceid"; } leaf field-position { type uint8; mandatory true; description"field"Field position in the header is a integer. If the field is not repeated in the header the value is 1, and incremented for each repetition of the field. Position 0 means that the position is not important and order may change when decompressed";mandatory true; type uint8;} leaf direction-indicator { type schc:di-type; mandatory true; description "Direction Indicator, a YANGidentityrefreferenceid to say if the packet isbidirectionnal,bidirectional, up or down";mandatory true; type schc:direction-indicator-type;} listtarget-valuestarget-value { key "position"; uses tv-struct; description"a"A list of value to compare with the header field value. If target value is a singleton, position must be 0. For matching-list, should be consecutive position values starting from 1.";key position; uses target-values-struct;} leaf matching-operator { type schc:mo-type; must "../target-value or derived-from-or-self(., 'mo-ignore')" { error-message "mo-equal, mo-msb and mo-match-mapping require target-value"; description "target-value is not required for mo-ignore"; } must "not (derived-from-or-self(., 'mo-msb')) or ../matching-operator-value" { error-message "mo-msb requires length value"; } mandatory true;type schc:matching-operator-type;description "MO: Matching Operator"; } list matching-operator-value { keyposition;"position"; usestarget-values-struct;tv-struct; description "Matching Operator Arguments, based on TV structure to allow several arguments. In RFC 8724, only MSB define a single argument: length in bits "; } leaf comp-decomp-action { type schc:cda-type; mandatory true;type schc:comp-decomp-action-type;description "CDA: Compression Decompression Action"; } list comp-decomp-action-value { keyposition;"position"; usestarget-values-struct;tv-struct; description "CDA Arguments, based on TV structure to allow several arguments. In RFC 8724, no argument is defined for CDA"; } }Figure 14: Definition of a compressiongrouping compression-content { list entry3.1.2. Rule definition A{ key "field-id field-position direction-indicator"; uses compression-rule-entry; description "A compression rule is a list ofentries. grouping compression-content {rule entry describing each header field. An entry is identifed through a field-id, its position in the packet and its direction"; } description"define"Define a compression rule composed of a list of entries.";list entry { key "field-id field-position direction-indicator"; uses compression-rule-entry; }} Figure15:22: Definition of a compressionrule To identify a specificentryField ID, position and direction are needed.3.2. Fragmentation ruleParameters for fragmentation are defined in Annex D of [RFC8724]. Figure 16 gives the first elements found in this structure. It starts with a direction. Since fragmentation rules work for a specific direction, they contain a mandatory direction. The typeA Fragmentation rule is composed of entries describing thesame as the one used in compressionprotocol behavior. Some on them are numerical entries,but the use of bidirectionnal is forbidden.others are identifiers defined in Section 2.10. Thenext elements describe size of SCHC fragmentation header fields. Onlydata model defines some relations between theFCN size is mandatory and valueentries: * direction must behighereither up orequal to 1.down (not bidirectional). * W size is only needed for Ack Always and Ack on Error modes. grouping fragmentation-content { description "This grouping defines the fragmentation parameters for all the modes (No Ack, Ack Always and Ack on Error) specified in RFC 8724."; leaf l2-word-size { type uint8; default "8"; description "Size in bit of the layer 2 word"; } leaf direction { must "derived-from-or-self(., 'di-up') or derived-from-or-self(., 'di-down')" { error-message "direction for fragmentation rules is up or down"; } type schc:direction-indicator-type; mandatory true; description"should"Should be up or down, bi directionnal isforbidden."; mandatory true;forbiden."; } leafdtagsizedtag-size { type uint8; default "0"; description"size"Size in bit of the DTag field"; } leafwsizew-size { when "not(derived-from(../fragmentation-mode, 'fragmentation-mode-no-ack'))"; type uint8; description"size"Size in bit of the window field"; } leaffcnsizefcn-size { typeuint8 { range 1..max; }uint8; mandatory true; description"size"Size in bit of the FCN field";mandatory true;}... Figure 16: Definition of a fragmentation parameters, SCHC header RCS algorithm is defined (Figure 17), by default with the CRC computation proposed in [RFC8724]. The algorithms are identified through an identityref specified in the SCHC Data Model and with the type RCS-algorithm-type (Figure 18). ...leafRCS-algorithmrcs-algorithm { typeRCS-algorithm-type;rcs-algorithm-type; defaultschc:RFC8724-RCS;"schc:rcs-RFC8724"; description"Algoritm"Algorithm used for RCS"; }... Figure 17: Definition of a fragmentation parameters, RCS algorithm identity RCS-algorithm-base-type { description "identify which algorithm is used to compute RSC. The algorithm defines also the size if the RSC field."; } identity RFC8724-RCS { description "CRC 32 defined as default RCS in RFC8724."; base RCS-algorithm-base-type; } typedef RCS-algorithm-type { type identityref { base RCS-algorithm-base-type; } } Figure 18: Definition of identityref for RCS Algorithm Figure 19 gives the parameters used by the state machine to handle fragmentation: o maximum-window-size contains the maximum FCN value that can be used. o retransmission-timer gives in seconds the duration before sending an ack request (cf. section 8.2.2.4. of [RFC8724]). If specifed, value must be higher or equal to 1. o inactivity-timer gives in seconds the duration before aborting (cf. section 8.2.2.4. of [RFC8724]), value of 0 explicitly indicates that this timer is disabled. o max-ack-requests gives the number of attempts before aborting (cf. section 8.2.2.4. of [RFC8724]). o maximum-packet-size gives in bytes the larger packet size that can be reassembled. ...leaf maximum-window-size { type uint16; description"by"By default 2^wsize -2";1"; } leaf retransmission-timer { type uint64 { range1..max;"1..max"; } description"duration"Duration in seconds of the retransmission timer"; // Check the units } leaf inactivity-timer { type uint64; description"duration"Duration is seconds of the inactivity timer, 0 indicates the timer is disabled"; // check units } leaf max-ack-requests { type uint8 { range1..max;"1..max"; } description"the"The maximum number of retries for a specific SCHC ACK."; } leaf maximum-packet-size { type uint16; default1280;"1280"; description "When decompression is done, packet size must not strictly exceed this limit in Bytes"; }... Figure 19: Definition of a fragmentation state machine parameters Figure 20 gives information related to a specific compression mode: fragmentation-mode MUST be set with a specific behavior. Identityref are given Figure 21. For Ack on Error some specific information may be provided: o tile-size gives in bits the size of the tile; If set to 0 a single tile is inserted inside a fragment. o tile-in-All1 indicates if All1 contains only the RCS (all1-data- no) or may contain a single tile (all1-data-yes). Since the reassembly process may detect this behavior, the choice can be left to the fragmentation process. In that case identityref all1- data-sender-choice as to be specified. All possible values are given Figure 21. o ack-behavior tells when the fragmentation process may send acknowledgments. When ack-behavior-after-All0 is specified, the ack may be sent after the reception of All-0 fragment. When ack- behavior-after-All1 is specified, the ack may be sent after the reception of All-1 fragment at the end of the fragmentation process. ack-behavior-always do not impose a limitation at the SCHC level. The constraint may come from the LPWAN technology. All possible values are given Figure 21. ...leaf fragmentation-mode { type schc:fragmentation-mode-type; mandatory true; description"which"Which fragmentation mode is used (noAck, AckAlways, AckonError)";mandatory true;} choice mode { case no-ack; case ack-always; case ack-on-error { leaf tile-size { type uint8; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description"size"Size in bit of tiles, if not specified or set to 0: tile fills the fragment."; } leaf tile-in-All1 { type schc:all1-data-type; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description "When true, sender and receiver except a tile in All-1 frag"; } leaf ack-behavior { type schc:ack-behavior-type; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description "Sender behavior to acknowledge, after All-0, All-1 or when the LPWAN allows it (Always)"; }} } ... Figure 20: Definition of a fragmentation specific information // -- FRAGMENTATION TYPE // -- fragmentation modes identity fragmentation-mode-base-type { description "fragmentation mode"; } identity fragmentation-mode-no-ack { description "No Ack of RFC 8724."; base fragmentation-mode-base-type; } identity fragmentation-mode-ack-always { description "Ack Always of RFC8724."; base fragmentation-mode-base-type; } identity fragmentation-mode-ack-on-error { description "Ack on Error of RFC8724."; base fragmentation-mode-base-type; } typedef fragmentation-mode-typeleaf bitmap-format { typeidentityref { base fragmentation-mode-base-type; } } // -- Ack behavior identity ack-behavior-base-type { description "defineschc:bitmap-format-type; whento send an Acknowledgment message"; } identity ack-behavior-after-All0 { description "fragmentation expects Ack after sending All0 fragment."; base ack-behavior-base-type; } identity ack-behavior-after-All1 { description "fragmentation expects Ack after sending All1 fragment."; base ack-behavior-base-type; } identity ack-behavior-always {"derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; default "schc:bitmap-RFC8724"; description"fragmentation expects"How the bitmaps are included in the Ackafter sending every fragment."; base ack-behavior-base-type; } typedef ack-behavior-type { type identityref { base ack-behavior-base-type; } } // -- All1 with data types identity all1-data-base-type { description "type to define when to send an Acknowledgment message"; } identity all1-data-no { description "All1 contains no tiles."; base all1-data-base-type;message."; }identity all1-data-yes { description "All1 MUST contain a tile"; base all1-data-base-type;}identity all1-data-sender-choice {description"Fragmentation process choose to send tiles or not in all1."; base all1-data-base-type; } typedef all1-data-type { type identityref { base all1-data-base-type;"RFC 8724 defines 3 fragmentation modes"; } }Figure 21: Specific types for Ack On Error mode ##3.3. YANG Tree module:schcietf-schc +--rw schc +--rwversion? uint64 +--rwrule*[rule-id rule-length][rule-id-value rule-id-length] +--rwrule-idrule-id-value uint32 +--rwrule-lengthrule-id-length uint8 +--rw (nature)? +--:(fragmentation) {fragmentation}? | +--rw l2-word-size? uint8 | +--rw directionschc:direction-indicator-typeschc:di-type | +--rwdtagsize?dtag-size? uint8 | +--rwwsize?w-size? uint8 | +--rwfcnsizefcn-size uint8 | +--rwRCS-algorithm? RCS-algorithm-typercs-algorithm? rcs-algorithm-type | +--rw maximum-window-size? uint16 | +--rw retransmission-timer? uint64 | +--rw inactivity-timer? uint64 | +--rw max-ack-requests? uint8 | +--rw maximum-packet-size? uint16 | +--rw fragmentation-mode schc:fragmentation-mode-type | +--rw (mode)? | +--:(no-ack) | +--:(ack-always) | +--:(ack-on-error) | +--rw tile-size? uint8 | +--rw tile-in-All1? schc:all1-data-type | +--rw ack-behavior? schc:ack-behavior-type | +--rw bitmap-format? schc:bitmap-format-type +--:(compression) | +--rw entry* [field-id field-position direction-indicator] | +--rw field-idschc:field-id-typeschc:fid-type | +--rw field-lengthschc:field-length-typeschc:fl-type | +--rw field-position uint8 | +--rw direction-indicatorschc:direction-indicator-typeschc:di-type | +--rwtarget-values*target-value* [position] | | +--rw value?unionbinary | | +--rw position uint16 | +--rw matching-operatorschc:matching-operator-typeschc:mo-type | +--rw matching-operator-value* [position] | | +--rw value?unionbinary | | +--rw position uint16 | +--rw comp-decomp-actionschc:comp-decomp-action-typeschc:cda-type | +--rw comp-decomp-action-value* [position] | +--rw value?unionbinary | +--rw position uint16 +--:(no-compression) Figure2223 4. IANA Considerations This document has no request to IANA. 5. Security considerations This document does not have any more Security consideration than the ones already raised on [RFC8724] 6. Acknowledgements The authors would like to thank Dominique Barthel, Carsten Bormann, Alexander Pelov. 7. YANG Module <code begins> fileschc@2020-02-28.yangietf-schc@2021-08-17.yang moduleschc{ietf-schc { yang-version"1";1.1; namespace"urn:ietf:lpwan:schc:rules-description";"urn:ietf:params:xml:ns:yang:ietf-schc"; prefix"schc";schc; organization "IETF IPv6 over Low Power Wide-Area Networks (lpwan) working group"; contact "WG Web: <https://datatracker.ietf.org/wg/lpwan/about/> WG List: <mailto:p-wan@ietf.org> Editor: Laurent Toutain <mailto:laurent.toutain@imt-atlantique.fr> Editor: Ana Minaburo <mailto:ana@ackl.io>"; description"Generic" Copyright (c) 2021 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. ************************************************************************* Generic Data model for Static Context Header Compression Rule for SCHC, based on draft-ietf-lpwan-ipv6-static-context-hc-18. Include compression rules and fragmentation rules. This module is a YANG model for SCHC rules (RFc 8724). RFC 8724 describes a rule in a abstract way through a table. |-----------------------------------------------------------------| | (FID) Rule 1 | |+-------+--+--+--+------------+-----------------+---------------+| ||Field 1|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act|| |+-------+--+--+--+------------+-----------------+---------------+| ||Field 2|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act|| |+-------+--+--+--+------------+-----------------+---------------+| ||... |..|..|..| ... | ... | ... || |+-------+--+--+--+------------+-----------------+---------------+| ||Field N|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act|| +-------+--+--+--+------------+-----------------+---------------+|| |-----------------------------------------------------------------| This module proposes a global data model that can be used for rule exchanges or modification. It proposes both the data model format and the global identifiers used to describes some operations in fields. This data model applies both to compression and fragmentation."; revision2020-06-152021-08-17 { description"clean up and add descriptions, merge schc-id to this file"; } revision 2020-02-28 { description "Add Fragmentation parameters"; } revision 2020-01-23 { description "Modified TV with binary and union";"Initial version from RFC XXXX "; reference "RFC XXX: Data Model for Static Context Header Compression (SCHC)"; }revision 2020-01-07feature fragmentation { description"First version of"Fragmentation is usually required only at theYANG model";transportation level."; } // ------------------------- // Field ID type definition //-------------------------- // generic value TV definition identityfield-id-base-typefid-base-type { description "Field IDwith SID";base type for all fields"; } identity fid-ipv6-base-type { base fid-base-type; description "Field IP base type for IPv6 headers described in RFC 8200"; } identity fid-ipv6-version { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 version field from RFC8200"; } identity fid-ipv6-trafficclass { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Traffic Class field from RFC8200"; } identity fid-ipv6-trafficclass-ds { basefield-id-base-type;fid-ipv6-trafficclass; description "IPv6 Traffic Class field from RFC8200, DiffServ field from RFC3168"; } identity fid-ipv6-trafficclass-ecn { basefield-id-base-type;fid-ipv6-trafficclass; description "IPv6 Traffic Class field from RFC8200, ECN field from RFC3168"; } identity fid-ipv6-flowlabel { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Flow Label field from RFC8200"; } identity fid-ipv6-payloadlength { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Payload Length field from RFC8200"; } identity fid-ipv6-nextheader { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Next Header field from RFC8200"; } identity fid-ipv6-hoplimit { basefield-id-base-type;fid-ipv6-base-type; description "IPv6 Next Header field from RFC8200"; } identity fid-ipv6-devprefix { basefield-id-base-type;fid-ipv6-base-type; description "correspond either to the source address or the desdination address prefix of RFC 8200. Depending if it is respectively a uplink or an downklink message."; } identity fid-ipv6-deviid { basefield-id-base-type;fid-ipv6-base-type; description "correspond either to the source address or the desdination address prefix of RFC 8200. Depending if it is respectively a uplink or an downklink message."; } identity fid-ipv6-appprefix { basefield-id-base-type;fid-ipv6-base-type; description "correspond either to the source address or the desdination address prefix of RFC 768. Depending if it is respectively a downlink or an uplink message."; } identity fid-ipv6-appiid { basefield-id-base-type;fid-ipv6-base-type; description "correspond either to the source address or the desdination address prefix of RFC 768. Depending if it is respectively a downlink or an uplink message."; } identity fid-udp-base-type { base fid-base-type; description "Field IP base type for UDP headers described in RFC 768"; } identity fid-udp-dev-port { basefield-id-base-type;fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-udp-app-port { basefield-id-base-type;fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-udp-length { basefield-id-base-type;fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-udp-checksum { basefield-id-base-type;fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-coap-base-type { base fid-base-type; description "Field IP base type for UDP headers described in RFC 768"; } identity fid-coap-version { basefield-id-base-type;fid-coap-base-type; description "CoAP version from RFC 7252"; } identity fid-coap-type { basefield-id-base-type;fid-coap-base-type; description "CoAP type from RFC 7252"; } identity fid-coap-tkl { basefield-id-base-type;fid-coap-base-type; description "CoAP token length from RFC 7252"; } identity fid-coap-code { basefield-id-base-type;fid-coap-base-type; description "CoAP code from RFC 7252"; } identity fid-coap-code-class { basefield-id-base-type;fid-coap-code; description "CoAP code class from RFC 7252"; } identity fid-coap-code-detail { basefield-id-base-type;fid-coap-code; description "CoAP code detail from RFC 7252"; } identity fid-coap-mid { basefield-id-base-type;fid-coap-base-type; description "CoAP message ID from RFC 7252"; } identity fid-coap-token { basefield-id-base-type;fid-coap-base-type; description "CoAP token from RFC 7252"; } identity fid-coap-option-if-match { basefield-id-base-type;fid-coap-base-type; description "CoAP option If-Match from RFC 7252"; } identity fid-coap-option-uri-host { basefield-id-base-type;fid-coap-base-type; description "CoAP option URI-Host from RFC 7252"; } identity fid-coap-option-etag { basefield-id-base-type;fid-coap-base-type; description "CoAP option Etag from RFC 7252"; } identity fid-coap-option-if-none-match { basefield-id-base-type;fid-coap-base-type; description "CoAP option if-none-match from RFC 7252"; } identity fid-coap-option-observe { basefield-id-base-type;fid-coap-base-type; description "CoAP option Observe from RFC 7641"; } identity fid-coap-option-uri-port { basefield-id-base-type;fid-coap-base-type; description "CoAP option Uri-Port from RFC 7252"; } identity fid-coap-option-location-path { basefield-id-base-type;fid-coap-base-type; description "CoAP option Location-Path from RFC 7252"; } identity fid-coap-option-uri-path { basefield-id-base-type;fid-coap-base-type; description "CoAP option Uri-Path from RFC 7252"; } identity fid-coap-option-content-format { basefield-id-base-type;fid-coap-base-type; description "CoAP option Content Format from RFC 7252"; } identity fid-coap-option-max-age { basefield-id-base-type;fid-coap-base-type; description "CoAP option Max-Age from RFC 7252"; } identity fid-coap-option-uri-query { basefield-id-base-type;fid-coap-base-type; description "CoAP option Uri-Query from RFC 7252"; } identity fid-coap-option-accept { basefield-id-base-type;fid-coap-base-type; description "CoAP option Max-Age from RFC 7252"; } identity fid-coap-option-location-query { basefield-id-base-type;fid-coap-base-type; description "CoAP option Location-Query from RFC 7252"; } identity fid-coap-option-block2 { basefield-id-base-type;fid-coap-base-type; description "CoAP option Block2 from RFC 7959"; } identity fid-coap-option-block1 { basefield-id-base-type;fid-coap-base-type; description "CoAP option Block1 from RFC 7959"; } identity fid-coap-option-size2 { basefield-id-base-type;fid-coap-base-type; description "CoAP option size2 from RFC 7959"; } identity fid-coap-option-proxy-uri { basefield-id-base-type;fid-coap-base-type; description "CoAP option Proxy-Uri from RFC 7252"; } identity fid-coap-option-proxy-scheme { basefield-id-base-type;fid-coap-base-type; description "CoAP option Proxy-scheme from RFC 7252"; } identity fid-coap-option-size1 { basefield-id-base-type;fid-coap-base-type; description "CoAP option Size1 from RFC 7252"; } identity fid-coap-option-no-response { basefield-id-base-type;fid-coap-base-type; description "CoAP option No response from RFC 7967"; } identity fid-coap-option-oscore-flags { basefield-id-base-type;fid-coap-base-type; description "CoAP option oscore flags (see draft schc coap, section 6.4)"; } identity fid-coap-option-oscore-piv { basefield-id-base-type;fid-coap-base-type; description "CoAP option oscore flags (see draft schc coap, section 6.4)"; } identity fid-coap-option-oscore-kid { basefield-id-base-type;fid-coap-base-type; description "CoAP option oscore flags (see draft schc coap, section 6.4)"; } identity fid-coap-option-oscore-kidctx { basefield-id-base-type;fid-coap-base-type; description "CoAP option oscore flags (see draft schc coap, section 6.4)"; } identity fid-icmpv6-base-type { base fid-base-type; description "Field IP base type for UDP headers described in RFC 768"; } identity fid-icmpv6-type { basefield-id-base-type;fid-icmpv6-base-type; description "ICMPv6 field (see draft OAM)"; } identity fid-icmpv6-code { basefield-id-base-type;fid-icmpv6-base-type; description "ICMPv6 field (see draft OAM)"; } identity fid-icmpv6-checksum { basefield-id-base-type;fid-icmpv6-base-type; description "ICMPv6 field (see draft OAM)"; } identity fid-icmpv6-identifier { basefield-id-base-type;fid-icmpv6-base-type; description "ICMPv6 field (see draft OAM)"; } identity fid-icmpv6-sequence { basefield-id-base-type;fid-icmpv6-base-type; description "ICMPv6 field (see draft OAM)"; }/// !!!!!!! See future CoAP extentions//---------------------------------- // Field Length type definition //---------------------------------- identityfield-length-base-typefl-base-type { description"used"Used to extend field length functions"; } identity fl-variable { basefield-length-base-type;fl-base-type; description"residue"Residue length in Byte issent";sent defined in for CoAP in RFC 8824 (cf. 5.3)"; } identity fl-token-length { basefield-length-base-type;fl-base-type; description"residue"Residue length in Byte issent";sent defined in for CoAP in RFC 8824 (cf. 4.5)"; } //--------------------------------- // Direction Indicator type //--------------------------------- identitydirection-indicator-base-typedi-base-type { description"used"Used to extend field length functions"; } identity di-bidirectional { basedirection-indicator-base-type;di-base-type; description "Direction Indication of bidirectionality";directionality in RFC 8724 (cf. 7.1)"; } identity di-up { basedirection-indicator-base-type;di-base-type; description "Direction Indication ofupstream";upstream defined in RFC 8724 (cf. 7.1)"; } identity di-down { basedirection-indicator-base-type;di-base-type; description "Direction Indication ofdownstream";downstream defined in RFC 8724 (cf. 7.1)"; } //---------------------------------- // Matching Operator type definition //---------------------------------- identitymatching-operator-base-typemo-base-type { description"used"Used to extend Matching Operators with SID values"; } identity mo-equal { basematching-operator-base-type;mo-base-type; description"RFC 8724";"Equal MO as defined RFC 8724 (cf. 7.3)"; } identity mo-ignore { basematching-operator-base-type;mo-base-type; description"RFC 8724";"Ignore MO as defined RFC 8724 (cf. 7.3)"; } identity mo-msb { basematching-operator-base-type;mo-base-type; description"RFC 8724";"MSB MO as defined RFC 8724 (cf. 7.3)"; } identity mo-matching { basematching-operator-base-type;mo-base-type; description"RFC 8724";"match-mapping MO as defined RFC 8724 (cf. 7.3)"; } //------------------------------ // CDA type definition //------------------------------ identitycompression-decompression-action-base-type;cda-base-type { description "Compression Decompression Actions"; } identity cda-not-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"not-sent CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-value-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"value-sent CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-lsb { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"LSB CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-mapping-sent { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"mapping-sent CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-compute-length { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"compute-length CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-compute-checksum { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"compute-checksum CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-deviid { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"deviid CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-appiid { basecompression-decompression-action-base-type;cda-base-type; description"RFC 8724";"appiid CDA as defines in RFC 8724 (cf. 7.4)"; } // -- type definition typedeffield-id-typefid-type { type identityref { base fid-base-type; } description "Field ID generic type."; } typedef fl-type { type union { type int64; /* positive length in bits */ type identityref { /* function */ basefield-id-base-type;fl-base-type; } }typedef field-length-type {description "Field length either a positive integer giving the size in bits or a function defined through an identityref.";type union} typedef di-type { typeint64; /* positive length in bits */ typeidentityref {/* function */basefield-length-base-type; }di-base-type; }} typedef direction-indicator-type {description"direction"Direction in LPWAN network, up when emitted by the device, down when received by the device, bi when emitted or received by the device."; } typedef mo-type { type identityref { basedirection-indicator-base-type;mo-base-type; }} typedef matching-operator-type {description "Matching Operator (MO) to compare fields values with target values"; } typedef cda-type { type identityref { basematching-operator-base-type;cda-base-type; }} typedef comp-decomp-action-type {description "Compression Decompression Action to compression or decompress a field.";type identityref { base compression-decompression-action-base-type; }} // -- FRAGMENTATION TYPE // -- fragmentation modes identity fragmentation-mode-base-type { description "fragmentation mode"; } identity fragmentation-mode-no-ack { base fragmentation-mode-base-type; description "No Ack of RFC 8724.";base fragmentation-mode-base-type;} identity fragmentation-mode-ack-always { base fragmentation-mode-base-type; description "Ack Always of RFC8724.";base fragmentation-mode-base-type;} identity fragmentation-mode-ack-on-error { base fragmentation-mode-base-type; description "Ack on Error of RFC8724.";base fragmentation-mode-base-type;} typedef fragmentation-mode-type { type identityref { base fragmentation-mode-base-type; } description "type used in rules"; } // -- Ack behavior identity ack-behavior-base-type { description"define"Define when to send an Acknowledgment message"; } identity ack-behavior-after-All0 { base ack-behavior-base-type; description"fragmentation"Fragmentation expects Ack after sending All0 fragment.";base ack-behavior-base-type;} identity ack-behavior-after-All1 { base ack-behavior-base-type; description"fragmentation"Fragmentation expects Ack after sending All1 fragment.";base ack-behavior-base-type;} identity ack-behavior-always { base ack-behavior-base-type; description"fragmentation"Fragmentation expects Ack after sending every fragment.";base ack-behavior-base-type;} typedef ack-behavior-type { type identityref { base ack-behavior-base-type; } description "Type used in rules"; } // -- All1 with data types identity all1-data-base-type { description"type"Type to define when to send an Acknowledgment message"; } identity all1-data-no { base all1-data-base-type; description "All1 contains no tiles.";base all1-data-base-type;} identity all1-data-yes { base all1-data-base-type; description "All1 MUST contain a tile";base all1-data-base-type;} identity all1-data-sender-choice { base all1-data-base-type; description "Fragmentation process choose to send tiles or not in all1.";base all1-data-base-type;} typedef all1-data-type { type identityref { base all1-data-base-type; } description "Type used in rules"; } // -- RCS algorithm types identityRCS-algorithm-base-typercs-algorithm-base-type { description"identify"Identify which algorithm is used to compute RSC. The algorithmdefinesalso defines the size if the RSC field."; } identityRFC8724-RCSrcs-RFC8724 { base rcs-algorithm-base-type; description "CRC 32 defined as default RCS in RFC8724."; } typedef rcs-algorithm-type { type identityref { baseRCS-algorithm-base-type;rcs-algorithm-base-type; } description "type used in rules"; } // --- Bitmap format identity bitmap-format-base-type { description "Define how the bitmap is defined in ACK messages."; } identity bitmap-RFC8724 { base bitmap-format-base-type; description "Bitmap as defined in RFC8724."; } identity bitmap-compound-ack { base bitmap-format-base-type; description "Compound Ack."; } typedefRCS-algorithm-typebitmap-format-type { type identityref { baseRCS-algorithm-base-type;bitmap-format-base-type; } description "type used in rules"; } // -------- RULE ENTRY DEFINITION ------------ groupingtarget-values-structtv-struct { description"defines"Define the target value element.Can be either an arbitrary binary or ascii element. All target values are considered asAlways amatching lists. Position is usedbinary type, strings must be converted toorder values, by default position 0 is used when containing a single element.";binary. field-id allows the conversion to the appropriate type."; leaf value { typeunion { typebinary;type string; }} leaf position { type uint16; description "If only one element position is 0, otherwise position is the matching list.";type uint16;} } grouping compression-rule-entry { description "These entries defines a compression entry (i.e. a line) as defined in RFC 8724 and fragmentation parameters. +-------+--+--+--+------------+-----------------+---------------+ |Field 1|FL|FP|DI|Target Value|Matching Operator|Comp/Decomp Act| +-------+--+--+--+------------+-----------------+---------------+ An entry in a compression rule is composed of 7 elements: - Field ID: The header field to be compressed. The content is a YANG identifer. - Field Length : either a positive integer of a function defined as a YANF id. - Field Position: a positive (and possibly equal to 0) integer. - Direction Indicator: a YANG identifier giving the direction. - Target value: a value against which the header Field is compared. - Matching Operator: a YANG id giving the operation, paramters may be associated to that operator. - Comp./Decomp. Action: A YANG id giving the compression or decompression action, paramters may be associated to that action. "; leaf field-id { type schc:fid-type; mandatory true; description "Field ID, identify a field in the header with a YANG refenceid.";mandatory true; type schc:field-id-type;} leaf field-length { type schc:fl-type; mandatory true; description "Field Length in bit or through a function defined as a YANG referenceid";mandatory true; type schc:field-length-type;} leaf field-position { type uint8; mandatory true; description"field"Field position in the header is a integer. If the field is not repeated in the header the value is 1, and incremented for each repetition of the field. Position 0 means that the position is not important and order may change when decompressed";mandatory true; type uint8;} leaf direction-indicator { type schc:di-type; mandatory true; description "Direction Indicator, a YANG referenceid to say if the packet isbidirectionnal,bidirectional, up or down";mandatory true; type schc:direction-indicator-type;} listtarget-valuestarget-value { key "position"; uses tv-struct; description"a"A list of value to compare with the header field value. If target value is a singleton, position must be 0. For matching-list, should be consecutive position values starting from 1.";key position; uses target-values-struct;} leaf matching-operator { type schc:mo-type; must "../target-value or derived-from-or-self(., 'mo-ignore')" { error-message "mo-equal, mo-msb and mo-match-mapping require target-value"; description "target-value is not required for mo-ignore"; } must "not (derived-from-or-self(., 'mo-msb')) or ../matching-operator-value" { error-message "mo-msb requires length value"; } mandatory true;type schc:matching-operator-type;description "MO: Matching Operator"; } list matching-operator-value { keyposition;"position"; usestarget-values-struct;tv-struct; description "Matching Operator Arguments, based on TV structure to allow several arguments. In RFC 8724, only MSB define a single argument: length in bits "; } leaf comp-decomp-action { type schc:cda-type; mandatory true;type schc:comp-decomp-action-type;description "CDA: Compression Decompression Action"; } list comp-decomp-action-value { keyposition;"position"; usestarget-values-struct;tv-struct; description "CDA Arguments, based on TV structure to allow several arguments. In RFC 8724, no argument is defined for CDA"; } } grouping compression-content {description "define a compression rule composed of a list of entries.";list entry { key "field-id field-position direction-indicator"; uses compression-rule-entry; description "A compression rule is a list of rule entry describing each header field. An entry is identifed through a field-id, its position in the packet and its direction"; } description "Define a compression rule composed of a list of entries."; } grouping fragmentation-content { description "This grouping defines the fragmentation parameters for all the modes (No Ack, Ack Always and Ack on Error) specified in RFC 8724."; leaf l2-word-size { type uint8; default "8"; description "Size in bit of the layer 2 word"; } leaf direction { must "derived-from-or-self(., 'di-up') or derived-from-or-self(., 'di-down')" { error-message "direction for fragmentation rules are up or down"; } typeschc:direction-indicator-type;schc:di-type; mandatory true; description"should"Should be up or down, bi directionnal is forbiden.";mandatory true;} leafdtagsizedtag-size { type uint8; default "0"; description"size"Size in bit of the DTag field"; } leafwsizew-size { when "not(derived-from(../fragmentation-mode, 'fragmentation-mode-no-ack'))"; type uint8; description"size"Size in bit of the window field"; } leaffcnsizefcn-size { type uint8; mandatory true; description"size"Size in bit of the FCN field";mandatory true;} leafRCS-algorithmrcs-algorithm { typeRCS-algorithm-type;rcs-algorithm-type; defaultschc:RFC8724-RCS;"schc:rcs-RFC8724"; description "Algoritm used for RCS"; } leaf maximum-window-size { type uint16; description"by"By default 2^wsize - 1"; } leaf retransmission-timer { type uint64 { range1..max;"1..max"; } description"duration"Duration in seconds of the retransmission timer"; // Check the units } leaf inactivity-timer { type uint64; description"duration"Duration is seconds of the inactivity timer, 0 indicates the timer is disabled"; // check units } leaf max-ack-requests { type uint8 { range1..max;"1..max"; } description"the"The maximum number of retries for a specific SCHC ACK."; } leaf maximum-packet-size { type uint16; default1280;"1280"; description "When decompression is done, packet size must not strictly exceed this limit in Bytes"; } leaf fragmentation-mode { type schc:fragmentation-mode-type; mandatory true; description "which fragmentation mode is used (noAck, AckAlways, AckonError)";mandatory true;} choice mode { case no-ack; case ack-always; case ack-on-error { leaf tile-size { type uint8; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description"size"Size in bit of tiles, if not specified or set to 0: tile fills the fragment."; } leaf tile-in-All1 { type schc:all1-data-type; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description "When true, sender and receiver except a tile in All-1 frag"; } leaf ack-behavior { type schc:ack-behavior-type; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; description "Sender behavior to acknowledge, after All-0, All-1 or when the LPWAN allows it (Always)"; } leaf bitmap-format { type schc:bitmap-format-type; when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; default "schc:bitmap-RFC8724"; description "How the bitmaps are included in the Ack message."; } } description "RFC 8724 defines 3 fragmentation modes"; } } // Define rule ID. Rule ID is composed of a RuleID value and a Rule ID Length grouping rule-id-type { leafrule-idrule-id-value { type uint32; description"rule"Rule ID value, this value must be unique combined with the length"; } leafrule-lengthrule-id-length { type uint8 { range0..32;"0..32"; } description"rule"Rule ID length in bits, value 0 is for implicit rules"; } description "A rule ID is composed of a value and a length in bit"; } // SCHC table for a specific device. container schc {leaf version{ type uint64; mandatory false; description "used as an indication for versioning"; }list rule { key"rule-id rule-length";"rule-id-value rule-id-length"; uses rule-id-type; choice nature { case fragmentation { if-feature "fragmentation"; uses fragmentation-content; } case compression { uses compression-content; } case no-compression { description "RFC8724 allows a rule for uncompressed headers"; } description "A rule is either for compression, no compression or fragmentation"; } description "Set of rules compression, no compression or fragmentation rules identified by their rule-id "; } description "a SCHC set of rules is composed of a list of rule which are either compression or fragmentation"; } } <code ends> Figure2324 8. Normative References [I-D.barthel-lpwan-oam-schc] Barthel, D., Toutain, L., Kandasamy, A., Dujovne, D., and J. C. Zuniga, "OAM for LPWAN using Static Context Header Compression (SCHC)",draft-barthel-lpwan-oam-schc-02 (workWork inprogress),Progress, Internet-Draft, draft-barthel-lpwan-oam-schc-02, 2 November2020. [I-D.ietf-lpwan-coap-static-context-hc] Minaburo, A.,2020, <https://www.ietf.org/archive/id/draft-barthel-lpwan-oam- schc-02.txt>. [I-D.ietf-lpwan-schc-compound-ack] Zuniga, J. C., Gomez, C., Aguilar, S., Toutain, L., Cespedes, S., andR. Andreasen, "LPWAN Static Context Header Compression (SCHC) for CoAP", draft-ietf- lpwan-coap-static-context-hc-18 (work in progress), January 2021.D. Wistuba, "SCHC Compound ACK", Work in Progress, Internet-Draft, draft-ietf-lpwan-schc-compound- ack-00, 9 July 2021, <https://www.ietf.org/archive/id/ draft-ietf-lpwan-schc-compound-ack-00.txt>. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <https://www.rfc-editor.org/info/rfc7252>. [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.Zuniga,Zúñiga, "SCHC: Generic Framework for Static Context Header Compression and Fragmentation", RFC 8724, DOI 10.17487/RFC8724, April 2020, <https://www.rfc-editor.org/info/rfc8724>. [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/info/rfc8824>. Authors' Addresses Ana Minaburo Acklio 1137A avenue des Champs Blancs 35510 Cesson-Sevigne Cedex France Email: ana@ackl.io 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