Data Model for Static Context Header Compression (SCHC)

Introduction SCHC is a compression and fragmentation mechanism for constrained networks defined in . It is based on a static context shared by two entities at the boundary of the constrained network. provides a 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: the same definition on both ends, even if the internal representation is different. an update of the other end to set up some specific values (e.g. IPv6 prefix, Destination address,...) ... 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 rules SCHC is a compression and fragmentation mechanism for constrained networks defined in . It is based on a static context shared by two entities at the boundary of the constrained network. provides a 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: the same definition on both ends, even if the internal representation is different. an update of the other end to set up some specific values (e.g. IPv6 prefix, Destination address,...) ... 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 mechanism does not refer to a specific protocol. Any header field is abstracted through an ID, a position, a direction, and a value that can be a numerical value or a string. and specify fields for IPv6, UDP, CoAP and OSCORE. SCHC fragmentation requires a set of common parameters that are included in a rule. These parameters are defined in . The YANG model allows to select the compression or the fragmentation using the feature command.

Compression Rules proposes a 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.

Identifier generation Identifier used in 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 () shows how an identityref is created for RCS algorithms used during SCHC fragmentation.

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 rule and apply compression. 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 , . Using the YANG model, each field MUST be identified through a global YANG identityref.
A YANG field ID for the protocol always derives from the 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 . The example gives the first field ID definitions. A type is defined for IPv6 protocol, and each field is based on it. Note that the DiffServ bits derives from the Traffic Class identity.

The type associated to this identity is fid-type (cf. )

Field length Field length is either an integer giving the size of a field in bits or a specific function. defines the "var" function which allows variable length fields in byte and defines the "tkl" function for managing the CoAP Token length field. The naming convention is "fl" followed by the function name.

Field ID, field length function can be defined as an identityref as shown in . Therefore, the type for field length is a union between an integer giving in bits the size of the length and the identityref (cf. ).

Field position Field position is a positive integer which gives the position of a field, the default value is 1, and incremented at each repetition. value 0 indicates that the position is not important and is not considered during the rule selection process. Field position is a positive integer. The type is an uint8.

Direction Indicator The Direction Indicator (di) is used to tell if a field appears in both direction (Bi) or only uplink (Up) or Downlink (Dw).

gives the identityref for Direction Indicators. The naming convention is "di" followed by the Direction Indicator name. The type is "di-type" (cf. ).

Target Value The Target Value is a list of binary sequences of any length, aligned on the left. 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 for LSB CDA. The position allows to specify several values: For Equal and LSB, a single value is used, such as for the equal or LSB CDA, the position is set to 0. For match-mapping, several of these values can be contained in a Target Value field. Position values must start from 0 and be contiguous.

Matching Operator Matching Operator (MO) is a function applied between a field value provided by the parsed header and the target value. defines 4 MO as listed in .

The naming convention is "mo" followed by the MO name. The type is "mo-type" (cf. )

Matching Operator arguments They are viewed as a list of tv-struct.

Compression Decompression Actions Compression Decompression Action (CDA) identified the function to use either for compression or decompression. defines 6 CDA. gives some CDA definition, the full definition is in .

The naming convention is "cda" followed by the CDA name.

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.

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 . 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.

Fragmentation mode 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. give the definition for identifiers from these three modes.

The naming convention is "fragmentation-mode" followed by the fragmentation mode name.

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. ): 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 , its size is defined by the rule.

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. defines a single algorithm based on Ethernet CRC computation. The identity of the RCS algorithm is shown in .

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 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.

The naming convention is "all1-data" followed by the behavior identifier.

Acknowledgment behavior A cknowledgment fragment header goes in the opposite direction of data. The header is composed of (see ): 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?

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. ) define the acknowledgment behavior.

The naming convention is "ack-behavior" followed by the algorithm name.

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 ). 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 ), 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 ). maximum-packet-size gives in bytes the larger packet size that can be reassembled. The are defined as unsigned integer, see .

Layer 2 parameters The data model includes two parameters needed for fragmentation: l2-word-size: 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 .

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. Three types of rules are defined in : Compression: a compression rule is associated to the rule ID. No compression: nothing is associated to the rule ID. Fragmentation: fragmentation parameters are associated to the rule ID. Fragmentation is optional and feature "fragmentation" should be set.

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.

Compression rule A compression rule is composed of entries describing its processing (cf. ). An entry contains all the information defined in with the types defined above. The compression rule described is defined by compression-content. It defines a list of compression-rule-entry, indexed by their field id, position and direction. The compression-rule-entry element represent a line of the table . Their type reflects the identifier types defined in Some controls are made on the values: target value must be present for MO different from ignore. when MSB MO is specified, the matching-operator-value must be present

Fragmentation rule A Fragmentation rule is composed of entries describing the protocol behavior. Some on them are numerical entries, others are identifiers defined in . The definition of a Fragmentation rule is divided into three sub-parts: parameters such as the the fragmnetation-mode, the l2-word-size and the direction. Since Fragmentation rules are always defined for a specific direction, the value must be must be either di-up or di-down (bi-bidirectional is not allowed). parameters defining the Fragmentation header format (dtag-size, w-size, fcn-size and rcs-algorithm). Protocol parameters for timers (inactivity-timer, retransmission-timer) or behavior (maximum-packet-size, max-interleaved-frames, max-ack-requests). If these parameters are specific to a single fragmentation mode, they are regrouped in a choice structure dedicated to that Fragmentation mode. If some parameters can be find in several modes, typically ACK-Always and ACK-on-Error. They are defined in a common part and a when statement indicates which modes are allowed.

YANG Tree

IANA Considerations This document has no request to IANA.

Security considerations This document does not have any more Security consideration than the ones already raised on

Acknowledgements The authors would like to thank Dominique Barthel, Carsten Bormann, Alexander Pelov.

YANG Module

file ietf-schc@2022-02-15.yang module ietf-schc { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-schc"; prefix schc; organization "IETF IPv6 over Low Power Wide-Area Networks (lpwan) working group"; contact "WG Web: WG List: Editor: Laurent Toutain Editor: Ana Minaburo "; description " 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 RFC 8724 and RFC8824. Include compression, no compression and fragmentation rules. This module is a YANG model for SCHC rules (RFc 8724). RFC 8724 describes compression rules 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 describe some operations in fields. This data model applies to both compression and fragmentation."; revision 2022-02-15 { description "Initial version from RFC XXXX "; reference "RFC XXX: Data Model for Static Context Header Compression (SCHC)"; } feature compression { description "SCHC compression capabilities are taken into account"; } feature fragmentation { description "SCHC fragmentation capabilities are taken into account"; } // ------------------------- // Field ID type definition //-------------------------- // generic value TV definition identity fid-base-type { description "Field ID base type for all fields"; } identity fid-ipv6-base-type { base fid-base-type; description "Field ID base type for IPv6 headers described in RFC 8200"; } identity fid-ipv6-version { base fid-ipv6-base-type; description "IPv6 version field from RFC8200"; } identity fid-ipv6-trafficclass { base fid-ipv6-base-type; description "IPv6 Traffic Class field from RFC8200"; } identity fid-ipv6-trafficclass-ds { base fid-ipv6-trafficclass; description "IPv6 Traffic Class field from RFC8200, DiffServ field from RFC3168"; } identity fid-ipv6-trafficclass-ecn { base fid-ipv6-trafficclass; description "IPv6 Traffic Class field from RFC8200, ECN field from RFC3168"; } identity fid-ipv6-flowlabel { base fid-ipv6-base-type; description "IPv6 Flow Label field from RFC8200"; } identity fid-ipv6-payloadlength { base fid-ipv6-base-type; description "IPv6 Payload Length field from RFC8200"; } identity fid-ipv6-nextheader { base fid-ipv6-base-type; description "IPv6 Next Header field from RFC8200"; } identity fid-ipv6-hoplimit { base fid-ipv6-base-type; description "IPv6 Next Header field from RFC8200"; } identity fid-ipv6-devprefix { base fid-ipv6-base-type; description "corresponds to either the source address or the destination address prefix of RFC 8200. Depending if it is respectively an uplink or a downklink message."; } identity fid-ipv6-deviid { base fid-ipv6-base-type; description "corresponds to either the source address or the destination address prefix of RFC 8200. Depending if it is respectively an uplink or a downklink message."; } identity fid-ipv6-appprefix { base fid-ipv6-base-type; description "corresponds to either the source address or the destination address prefix of RFC 8200. Depending if it is respectively a downlink or an uplink message."; } identity fid-ipv6-appiid { base fid-ipv6-base-type; description "corresponds to either the source address or the destination address prefix of RFC 8200. Depending if it is respectively a downlink or an uplink message."; } identity fid-udp-base-type { base fid-base-type; description "Field ID base type for UDP headers described in RFC 768"; } identity fid-udp-dev-port { base fid-udp-base-type; description "UDP source or destination port from RFC 768, if uplink or downlink communication, respectively."; } identity fid-udp-app-port { base fid-udp-base-type; description "UDP destination or source port from RFC 768, if uplink or downlink communication, respectively."; } identity fid-udp-length { base fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-udp-checksum { base fid-udp-base-type; description "UDP length from RFC 768"; } identity fid-coap-base-type { base fid-base-type; description "Field ID base type for UDP headers described in RFC 7252"; } identity fid-coap-version { base fid-coap-base-type; description "CoAP version from RFC 7252"; } identity fid-coap-type { base fid-coap-base-type; description "CoAP type from RFC 7252"; } identity fid-coap-tkl { base fid-coap-base-type; description "CoAP token length from RFC 7252"; } identity fid-coap-code { base fid-coap-base-type; description "CoAP code from RFC 7252"; } identity fid-coap-code-class { base fid-coap-code; description "CoAP code class from RFC 7252"; } identity fid-coap-code-detail { base fid-coap-code; description "CoAP code detail from RFC 7252"; } identity fid-coap-mid { base fid-coap-base-type; description "CoAP message ID from RFC 7252"; } identity fid-coap-token { base fid-coap-base-type; description "CoAP token from RFC 7252"; } identity fid-coap-option-if-match { base fid-coap-base-type; description "CoAP option If-Match from RFC 7252"; } identity fid-coap-option-uri-host { base fid-coap-base-type; description "CoAP option URI-Host from RFC 7252"; } identity fid-coap-option-etag { base fid-coap-base-type; description "CoAP option Etag from RFC 7252"; } identity fid-coap-option-if-none-match { base fid-coap-base-type; description "CoAP option if-none-match from RFC 7252"; } identity fid-coap-option-observe { base fid-coap-base-type; description "CoAP option Observe from RFC 7641"; } identity fid-coap-option-uri-port { base fid-coap-base-type; description "CoAP option Uri-Port from RFC 7252"; } identity fid-coap-option-location-path { base fid-coap-base-type; description "CoAP option Location-Path from RFC 7252"; } identity fid-coap-option-uri-path { base fid-coap-base-type; description "CoAP option Uri-Path from RFC 7252"; } identity fid-coap-option-content-format { base fid-coap-base-type; description "CoAP option Content Format from RFC 7252"; } identity fid-coap-option-max-age { base fid-coap-base-type; description "CoAP option Max-Age from RFC 7252"; } identity fid-coap-option-uri-query { base fid-coap-base-type; description "CoAP option Uri-Query from RFC 7252"; } identity fid-coap-option-accept { base fid-coap-base-type; description "CoAP option Accept from RFC 7252"; } identity fid-coap-option-location-query { base fid-coap-base-type; description "CoAP option Location-Query from RFC 7252"; } identity fid-coap-option-block2 { base fid-coap-base-type; description "CoAP option Block2 from RFC 7959"; } identity fid-coap-option-block1 { base fid-coap-base-type; description "CoAP option Block1 from RFC 7959"; } identity fid-coap-option-size2 { base fid-coap-base-type; description "CoAP option size2 from RFC 7959"; } identity fid-coap-option-proxy-uri { base fid-coap-base-type; description "CoAP option Proxy-Uri from RFC 7252"; } identity fid-coap-option-proxy-scheme { base fid-coap-base-type; description "CoAP option Proxy-scheme from RFC 7252"; } identity fid-coap-option-size1 { base fid-coap-base-type; description "CoAP option Size1 from RFC 7252"; } identity fid-coap-option-no-response { base fid-coap-base-type; description "CoAP option No response from RFC 7967"; } identity fid-coap-option-oscore-flags { base fid-coap-base-type; description "CoAP option oscore flags (see RFC 8824, section 6.4)"; } identity fid-coap-option-oscore-piv { base fid-coap-base-type; description "CoAP option oscore flags (see RFC 8824, section 6.4)"; } identity fid-coap-option-oscore-kid { base fid-coap-base-type; description "CoAP option oscore flags (see RFC 8824, section 6.4)"; } identity fid-coap-option-oscore-kidctx { base fid-coap-base-type; description "CoAP option oscore flags (see RFC 8824, section 6.4)"; } //---------------------------------- // Field Length type definition //---------------------------------- identity fl-base-type { description "Used to extend field length functions."; } identity fl-variable { base fl-base-type; description "Residue length in Byte is sent as defined in for CoAP in RFC 8824 (cf. 5.3)."; } identity fl-token-length { base fl-base-type; description "Residue length in Byte is sent as defined in for CoAP in RFC 8824 (cf. 4.5)."; } //--------------------------------- // Direction Indicator type //--------------------------------- identity di-base-type { description "Used to extend direction indicators."; } identity di-bidirectional { base di-base-type; description "Direction Indication of bi directionality in RFC 8724 (cf. 7.1)."; } identity di-up { base di-base-type; description "Direction Indication of uplink defined in RFC 8724 (cf. 7.1)."; } identity di-down { base di-base-type; description "Direction Indication of downlink defined in RFC 8724 (cf. 7.1)."; } //---------------------------------- // Matching Operator type definition //---------------------------------- identity mo-base-type { description "Used to extend Matching Operators with SID values"; } identity mo-equal { base mo-base-type; description "Equal MO as defined RFC 8724 (cf. 7.3)"; } identity mo-ignore { base mo-base-type; description "Ignore MO as defined RFC 8724 (cf. 7.3)"; } identity mo-msb { base mo-base-type; description "MSB MO as defined RFC 8724 (cf. 7.3)"; } identity mo-match-mapping { base mo-base-type; description "match-mapping MO as defined RFC 8724 (cf. 7.3)"; } //------------------------------ // CDA type definition //------------------------------ identity cda-base-type { description "Compression Decompression Actions."; } identity cda-not-sent { base cda-base-type; description "not-sent CDA as defines in RFC 8724 (cf. 7.4)."; } identity cda-value-sent { base cda-base-type; description "value-sent CDA as defines in RFC 8724 (cf. 7.4)."; } identity cda-lsb { base cda-base-type; description "LSB CDA as defines in RFC 8724 (cf. 7.4)."; } identity cda-mapping-sent { base cda-base-type; description "mapping-sent CDA as defines in RFC 8724 (cf. 7.4)."; } identity cda-compute-length { base cda-base-type; description "compute-length CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-compute-checksum { base cda-base-type; description "compute-checksum CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-deviid { base cda-base-type; description "deviid CDA as defines in RFC 8724 (cf. 7.4)"; } identity cda-appiid { base cda-base-type; description "appiid CDA as defines in RFC 8724 (cf. 7.4)"; } // -- type definition typedef fid-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 */ base fl-base-type; } } description "Field length either a positive integer giving the size in bits or a function defined through an identityref."; } typedef di-type { type identityref { base di-base-type; } description "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 { base mo-base-type; } description "Matching Operator (MO) to compare fields values with target values"; } typedef cda-type { type identityref { base cda-base-type; } description "Compression Decompression Action to compression or decompress a field."; } // -- 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 RFC8724."; } 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"; } // -- Ack behavior identity ack-behavior-base-type { description "Define when to send an Acknowledgment ."; } 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-by-layer2 { base ack-behavior-base-type; description "Layer 2 defines when to send an Ack."; } 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 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."; } // -- 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. RCS is 4 byte-long"; } typedef rcs-algorithm-type { type identityref { base rcs-algorithm-base-type; } description "type used in rules."; } // -------- RULE ENTRY DEFINITION ------------ grouping tv-struct { description "Define the target value element. Always a binary type, strings must be converted to binary. field-id allows the conversion to the appropriate type."; leaf value { type binary; description "Target Value"; } leaf position { type uint16; description "If only one element position is 0, otherwise position is the the position in the matching list."; } } 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 referenceid."; } leaf field-length { type schc:fl-type; mandatory true; description "Field Length in bit or through a function defined as a YANG referenceid."; } leaf field-position { type uint8; mandatory true; description "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"; } leaf direction-indicator { type schc:di-type; mandatory true; description "Direction Indicator, a YANG referenceid to say if the packet is bidirectional, up or down"; } list target-value { key "position"; uses tv-struct; description "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."; } 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 need 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; description "MO: Matching Operator"; } list matching-operator-value { key "position"; uses 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; description "CDA: Compression Decompression Action."; } list comp-decomp-action-value { key "position"; uses 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 { 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 fragmentation-mode { type schc:fragmentation-mode-type; mandatory true; description "which fragmentation mode is used (noAck, AckAlways, AckonError)"; } leaf l2-word-size { type uint8; default "8"; description "Size in bit of the layer 2 word"; } leaf direction { type schc:di-type; must "derived-from-or-self(., 'di-up') or derived-from-or-self(., 'di-down')" { error-message "direction for fragmentation rules are up or down."; } mandatory true; description "Should be up or down, bi directionnal is forbiden."; } // SCHC Frag header format leaf dtag-size { type uint8; default "0"; description "Size in bit of the DTag field (T variable from RFC8724)."; } leaf w-size { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error') or derived-from(../fragmentation-mode, 'fragmentation-mode-ack-always') "; type uint8; description "Size in bit of the window field (M variable from RFC8724)."; } leaf fcn-size { type uint8; mandatory true; description "Size in bit of the FCN field (M variable from RFC8724)."; } leaf rcs-algorithm { type rcs-algorithm-type; default "schc:rcs-RFC8724"; description "Algoritm used for RCS. The algorithm spedifies the RCS size"; } // SCHC fragmentation protocol paramters leaf maximum-packet-size { type uint16; default "1280"; description "When decompression is done, packet size must not strictly exceed this limit in Bytes."; } leaf window-size { type uint16; description "By default, if not specified 2^w-size - 1. Should not exceed this value. Possible FCN values are between 0 and window-size-1."; } leaf max-interleaved-frames { type uint8; default "1"; description "Maximum of simultaneously fragmented frames. Maximum value is 2^dtag-size. All DTAG values can be used, but only max-interleaved-frames must be active."; } leaf inactivity-timer { type uint64; description "Duration is seconds of the inactivity timer, 0 indicates the timer is disabled."; } leaf retransmission-timer { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error') or derived-from(../fragmentation-mode, 'fragmentation-mode-ack-always') "; type uint64 { range "1..max"; } description "Duration in seconds of the retransmission timer."; } leaf max-ack-requests { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error') or derived-from(../fragmentation-mode, 'fragmentation-mode-ack-always') "; type uint8 { range "1..max"; } description "The maximum number of retries for a specific SCHC ACK."; } choice mode { case no-ack; case ack-always; case ack-on-error { leaf tile-size { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; type uint8; description "Size in bit of tiles, if not specified or set to 0, tile fills the fragment."; } leaf tile-in-All1 { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; type schc:all1-data-type; description "When true, sender and receiver except a tile in All-1 frag."; } leaf ack-behavior { when "derived-from(../fragmentation-mode, 'fragmentation-mode-ack-on-error')"; type schc:ack-behavior-type; description "Sender behavior to acknowledge, after All-0, All-1 or when the LPWAN allows it (Always)."; } } 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 { leaf rule-id-value { type uint32; description "Rule ID value, this value must be unique combined with the length."; } leaf rule-id-length { type uint8 { range "0..32"; } description "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 { list rule { key "rule-id-value rule-id-length"; uses rule-id-type; choice nature { case fragmentation { if-feature "fragmentation"; uses fragmentation-content; } case compression { if-feature "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."; } }

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