| lpwan Working Group | A. Minaburo |
| Internet-Draft | Acklio |
| Intended status: Standards Track | L. Toutain |
| Expires: August 31, 2020 | Institut MINES TELECOM; IMT Atlantique |
| February 28, 2020 |
Data Model for Static Context Header Compression (SCHC)
draft-ietf-lpwan-schc-yang-data-model-02
This document describes a YANG data model for the SCHC (Static Context Header Compression) compression and fragmentation rules.
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This Internet-Draft will expire on August 31, 2020.
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.
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SCHC is a compression and fragmentation mechanism for constrained networks defined in [I-D.ietf-lpwan-ipv6-static-context-hc] it is based on a static context shared by two entities at the boundary this contrained network. Draft [I-D.ietf-lpwan-ipv6-static-context-hc] provides an abstract 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:
This document defines a YANG module to represent both compression and fragmentation rules, which leads to common representation and values for the elements of the rules. SCHC compression is generic, the main mechanism do no refers to a specific fields. A field is abstractedh through an ID, a position, a direction and a value that can be a numerical value or a string.
[I-D.ietf-lpwan-ipv6-static-context-hc] and [I-D.ietf-lpwan-coap-static-context-hc] specifies fields for IPv6, UDP, CoAP and OSCORE.
Fragmentation requires a set of common parameters that are included in a rule.
[I-D.ietf-lpwan-ipv6-static-context-hc] proposes an abstract 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
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 again the rules to find the appropriate one and apply compression. The link between the list given by the parsed fields and the rules is doen through a field ID. [I-D.ietf-lpwan-ipv6-static-context-hc] do not state how the field ID value can be constructed. In the given example, it was given through a string indexed by the protocol name (e.g. IPv6.version, CoAP.version,…).
Using the YANG model, each field can be identified through a global YANG identityref. A YANG field ID derives from the field-id-base-type. Figure 2 gives some field ID definitions. Note that some field IDs can be splitted is smaller pieces. This is the case for “fid-ipv6-trafficclass-ds” and “fid-ipv6-trafficclass-ecn” which are a subset of “fid-ipv6-trafficclass-ds”.
identity field-id-base-type {
description "Field ID with SID";
}
identity fid-ipv6-version {
base field-id-base-type;
description "IPv6 version field from RFC8200";
}
identity fid-ipv6-trafficclass {
base field-id-base-type;
description "IPv6 Traffic Class field from RFC8200";
}
identity fid-ipv6-trafficclass-ds {
base field-id-base-type;
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";
}
...
identity fid-coap-option-if-match {
base field-id-base-type;
description "CoAP option If-Match from RFC 7252";
}
identity fid-coap-option-uri-host {
base field-id-base-type;
description "CoAP option URI-Host from RFC 7252";
}
...
Figure 2: Definition of indentityref for field IDs
Figure 2 gives an example 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 gives the full definition of the field ID for [I-D.ietf-lpwan-ipv6-static-context-hc] and [I-D.ietf-lpwan-coap-static-context-hc].
The type associated to this identity is field-id-type (cf. Figure 3)
typedef field-id-type {
description "Field ID generic type.";
type identityref {
base field-id-base-type;
}
}
Figure 3: Definition of indentityref for field IDs
Field length is either an integer giving the size of a field in bits or a function. [I-D.ietf-lpwan-ipv6-static-context-hc] defines the “var” function which allows variable length fields in byte and [I-D.ietf-lpwan-coap-static-context-hc] defines the “tkl” function for managing the CoAP Token length field.
identity field-length-base-type {
description "used to extend field length functions";
}
identity fl-variable {
base field-length-base-type;
description "residue length in Byte is sent";
}
identity fl-token-length {
base field-length-base-type;
description "residue length in Byte is sent";
}
Figure 4: Definition of indetntyref for field IDs
As for field ID, field length function can be defined as a identityref as shown in Figure 4.
Therefore the type for field length is a union between an integer giving in bits the size of the length and the identityref (cf. Figure 5).
typedef field-length-type {
type union {
type int64; /* positive length */
type identityref { /* function */
base field-length-base-type;
}
}
}
Figure 5: Definition of indetntyref for field IDs
The naming convention is fl followed by the function name as defined in SCHC specifications.
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 not taken into account during the rule selection process.
Field position is a positive integer. The type is an uint8.
The Direction Indicator (DI) is used to tell if a field appears in both direction (Bi) or only uplink (Up) or Downlink (Dw).
identity direction-indicator-base-type {
description "used to extend field length functions";
}
identity di-bidirectional {
base direction-indicator-base-type;
description "Direction Indication of bi directionality";
}
identity di-up {
base direction-indicator-base-type;
description "Direction Indication of upstream";
}
identity di-down {
base direction-indicator-base-type;
description "Direction Indication of downstream";
}
Figure 6: Definition of identityref for direction indicators
Figure 6 gives the identityref for Direction Indicators.
The type is “direction-indicator-type” (cf. Figure 7).
typedef direction-indicator-type {
type identityref {
base direction-indicator-base-type;
}
}
Figure 7: Definition of identityref for direction indicators
Target Value may be either a string or binary sequence. For 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.
grouping target-values-struct {
leaf value {
type union {
type binary;
type string;
}
}
leaf position {
type uint16;
}
}
Figure 8: Definition of target value
Figure 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.
Matching Operator (MO) is a function applied between a field value provided by the parsed header and the target value. [I-D.ietf-lpwan-ipv6-static-context-hc] defines 4 MO.
identity matching-operator-base-type {
description "used to extend Matching Operators with SID values";
}
identity mo-equal {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-ignore {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-msb {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-matching {
base matching-operator-base-type;
description "SCHC draft";
}
Figure 9: Definition of Matching Operator identity
the type is “matching-operator-type” (cf. Figure 10)
typedef matching-operator-type {
type identityref {
base matching-operator-base-type;
}
}
Figure 10: Definition of Matching Operator type
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.
Compresion Decompression Action (CDA) idenfied the function to use either for compression or decompression. [I-D.ietf-lpwan-ipv6-static-context-hc] defines 6 CDA.
identity compression-decompression-action-base-type;
identity cda-not-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-value-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-lsb {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-mapping-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-compute-length {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-compute-checksum {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-deviid {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-appiid {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
Figure 11: Definition of Compresion Decompression Action identity
The type is “comp-decomp-action-type” (cf. Figure 12)
typedef comp-decomp-action-type {
type identityref {
base compression-decompression-action-base-type;
}
}
Figure 12: Definition of Compresion Decompression Action type
Currently no CDA requires argumetns, but the future some CDA may require several arguments. They are viewed as a list of target-values-type.
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.
// Define rule ID. Rule ID is composed of a RuleID value and a Rule ID Length
grouping rule-id-type {
leaf rule-id {
type uint32;
description "rule ID value, this value must be unique combined with the length";
}
leaf rule-length {
type uint8 {
range 0..32;
}
description "rule ID length in bits, value 0 is for implicit rules";
}
}
// 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";
uses rule-id-type;
choice nature {
case fragmentation {
uses fragmentation-content;
}
case compression {
uses compression-content;
}
}
}
}
Figure 13: Definition of a SCHC Context
To access to a specfic 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 identify though a version id.
A compression rule is composed of entries describing its processing (cf. Figure 14). An entry contains all the information defined in Figure 1 with the types defined above.
The compression rule described Figure 1 is associated to a rule ID. The compression rule entry is defined in Figure 14. Each column in the table is either represented by a leaf or a list. Note that Matching Operators and Compression Decompression actions can have arguments. They are viewed a ordered list of strings and numbers as in target values.
grouping compression-rule-entry {
leaf field-id {
mandatory true;
type schc-id:field-id-type;
}
leaf field-length {
mandatory true;
type schc-id:field-length-type;
}
leaf field-position {
mandatory true;
type uint8;
}
leaf direction-indicator {
mandatory true;
type schc-id:direction-indicator-type;
}
list target-values {
key position;
uses target-values-struct;
}
leaf mo {
mandatory true;
type schc-id:matching-operator-type;
}
list mo-value {
key position;
uses target-values-struct;
}
leaf cda {
mandatory true;
type schc-id:comp-decomp-action-type;
}
list cda-value {
key position;
uses target-values-struct;
}
}
Figure 14: Definition of a compression entry
A compression rule is a list of entries.
grouping compression-content {
list entry {
key "field-id field-position direction-indicator";
uses compression-rule-entry;
}
}
Figure 15: Definition of a compression rule
To identify a specific entry Field ID, position and direction are needed.
Parameters for fragmentation are defined in Annex D of [I-D.ietf-lpwan-ipv6-static-context-hc]. Two new types are defined for Ack on Error acknowlement behavior (ack-behavior-type) and the RCS algorithm (RCS-algorithm-type).
grouping fragmentation-content {
leaf direction {
type schc-id:direction-indicator-type;
description "should be up or down";
}
leaf dtagsize {
type uint8;
description "size in bit of the DTag field";
}
leaf wsize {
type uint8;
description "size in bit of the window field";
}
leaf fcnsize {
type uint8;
description "size in bit of the FCN field";
}
leaf RCS-algorithm {
type RCS-algorithm-type;
default schc-id:RFC8724-RCS;
description "Algoritm used for RCS";
}
leaf maximum-window-size {
type uint16;
description "by default 2^wsize - 1";
}
leaf retransmission-timer {
type uint64;
description "duration in seconds of the retransmission timer"; // Check the units
}
leaf inactivity-timer {
type uint64;
description "duration is seconds of the inactivity timer"; // check units
}
leaf max-ack-requests {
type uint8;
}
leaf maximum-packet-size {
type uint16;
mandatory true;
default 1280;
description "When decompression is done, packet size must not strictly exceed this limit in Bytes";
}
choice mode {
case no-ack;
case ack-always;
case ack-on-error {
leaf tile-size {
type uint8;
description "size in bit of tiles";
}
leaf tile-in-All1 {
type boolean;
description "When true, sender and receiver except a tile in All-1 frag";
}
leaf ack-behavior {
type schc-id:ack-behavior-type;
mandatory true;
}
}
}
}
Figure 16: Definition of a fragmentation rule
module: schc
+--rw schc
+--rw version? uint64
+--rw rule* [rule-id rule-length]
+--rw rule-id uint32
+--rw rule-length uint8
+--rw (nature)?
+--:(fragmentation)
| +--rw direction? schc-id:direction-indicator-type
| +--rw dtagsize? uint8
| +--rw wsize? uint8
| +--rw fcnsize? uint8
| +--rw RCS-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 (mode)
| +--:(no-ack)
| +--:(ack-always)
| +--:(ack-on-error)
| +--rw tile-size? uint8
| +--rw tile-in-All1? boolean
| +--rw ack-behavior schc-id:ack-behavior-type
+--:(compression)
+--rw entry* [field-id field-position direction-indicator]
+--rw field-id schc-id:field-id-type
+--rw field-length schc-id:field-length-type
+--rw field-position uint8
+--rw direction-indicator schc-id:direction-indicator-type
+--rw target-values* [position]
| +--rw value? union
| +--rw position uint16
+--rw mo schc-id:matching-operator-type
+--rw mo-value* [position]
| +--rw value? union
| +--rw position uint16
+--rw cda schc-id:comp-decomp-action-type
+--rw cda-value* [position]
+--rw value? union
+--rw position uint16
Figure 17
This document has no request to IANA.
This document does not have any more Security consideration than the ones already raised on [I-D.ietf-lpwan-ipv6-static-context-hc]
The authors would like to thank Dominique Barthel, Carsten Bormann, Alexander Pelov.
Currently the data model is split into two parts. The first one is dedicated to SCHC identifiers and the second one contains the rules definition. The goal is to allow some stabilities in the rule identifiers if new SCHC identfiers are added. When the model will be stable, these two files will be merged.
<code begins> file schc-id@2020-02-28.yang
module schc-id{
yang-version "1";
namespace "urn:ietf:lpwan:schc:schc-id";
prefix "schc-id";
description
"Identifiers used in SCHC data model.";
revision 2020-02-28 {
description "Add fragmentation identifiers";
}
revision 2020-02-11 {
description "Clean up";
}
revision 2020-01-07 {
description "First version of the SCHC identifiers";
}
// -------------------------
// Field ID type definition
//--------------------------
// generic value TV definition
identity field-id-base-type {
description "Field ID with SID";
}
identity fid-ipv6-version {
base field-id-base-type;
description "IPv6 version field from RFC8200";
}
identity fid-ipv6-trafficclass {
base field-id-base-type;
description "IPv6 Traffic Class field from RFC8200";
}
identity fid-ipv6-trafficclass-ds {
base field-id-base-type;
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";
}
identity fid-ipv6-flowlabel {
base field-id-base-type;
description "IPv6 Flow Label field from RFC8200";
}
identity fid-ipv6-payloadlength {
base field-id-base-type;
description "IPv6 Payload Length field from RFC8200";
}
identity fid-ipv6-nextheader {
base field-id-base-type;
description "IPv6 Next Header field from RFC8200";
}
identity fid-ipv6-hoplimit {
base field-id-base-type;
description "IPv6 Next Header field from RFC8200";
}
identity fid-ipv6-devprefix {
base field-id-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 {
base field-id-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 {
base field-id-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 {
base field-id-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-dev-port {
base field-id-base-type;
description "UDP length from RFC 768";
}
identity fid-udp-app-port {
base field-id-base-type;
description "UDP length from RFC 768";
}
identity fid-udp-length {
base field-id-base-type;
description "UDP length from RFC 768";
}
identity fid-udp-checksum {
base field-id-base-type;
description "UDP length from RFC 768";
}
identity fid-coap-version {
base field-id-base-type;
description "CoAP version from RFC 7252";
}
identity fid-coap-type {
base field-id-base-type;
description "CoAP type from RFC 7252";
}
identity fid-coap-tkl {
base field-id-base-type;
description "CoAP token length from RFC 7252";
}
identity fid-coap-code {
base field-id-base-type;
description "CoAP code from RFC 7252";
}
identity fid-coap-code-class {
base field-id-base-type;
description "CoAP code from RFC 7252";
}
identity fid-coap-code-detail {
base field-id-base-type;
description "CoAP code from RFC 7252";
}
identity fid-coap-mid {
base field-id-base-type;
description "CoAP message ID from RFC 7252";
}
identity fid-coap-token {
base field-id-base-type;
description "CoAP token from RFC 7252";
}
identity fid-coap-option-if-match {
base field-id-base-type;
description "CoAP option If-Match from RFC 7252";
}
identity fid-coap-option-uri-host {
base field-id-base-type;
description "CoAP option URI-Host from RFC 7252";
}
identity fid-coap-option-etag {
base field-id-base-type;
description "CoAP option Etag from RFC 7252";
}
identity fid-coap-option-if-none-match {
base field-id-base-type;
description "CoAP option if-none-match from RFC 7252";
}
identity fid-coap-option-observe {
base field-id-base-type;
description "CoAP option Observe from RFC 7641";
}
identity fid-coap-option-uri-port {
base field-id-base-type;
description "CoAP option Uri-Port from RFC 7252";
}
identity fid-coap-option-location-path {
base field-id-base-type;
description "CoAP option Location-Path from RFC 7252";
}
identity fid-coap-option-uri-path {
base field-id-base-type;
description "CoAP option Uri-Path from RFC 7252";
}
identity fid-coap-option-content-format {
base field-id-base-type;
description "CoAP option Content Format from RFC 7252";
}
identity fid-coap-option-max-age {
base field-id-base-type;
description "CoAP option Max-Age from RFC 7252";
}
identity fid-coap-option-uri-query {
base field-id-base-type;
description "CoAP option Uri-Query from RFC 7252";
}
identity fid-coap-option-accept {
base field-id-base-type;
description "CoAP option Max-Age from RFC 7252";
}
identity fid-coap-option-location-query {
base field-id-base-type;
description "CoAP option Location-Query from RFC 7252";
}
identity fid-coap-option-block2 {
base field-id-base-type;
description "CoAP option Block2 from RFC 7959";
}
identity fid-coap-option-block1 {
base field-id-base-type;
description "CoAP option Block1 from RFC 7959";
}
identity fid-coap-option-size2 {
base field-id-base-type;
description "CoAP option size2 from RFC 7959";
}
identity fid-coap-option-proxy-uri {
base field-id-base-type;
description "CoAP option Proxy-Uri from RFC 7252";
}
identity fid-coap-option-proxy-scheme {
base field-id-base-type;
description "CoAP option Proxy-scheme from RFC 7252";
}
identity fid-coap-option-size1 {
base field-id-base-type;
description "CoAP option Size1 from RFC 7252";
}
identity fid-coap-option-no-response {
base field-id-base-type;
description "CoAP option No response from RFC 7967";
}
identity fid-coap-option-end-option {
base field-id-base-type;
description "CoAP End Option from RFC 7967";
}
//----------------------------------
// Field Length type definition
//----------------------------------
identity field-length-base-type {
description "used to extend field length functions";
}
identity fl-variable {
base field-length-base-type;
description "residue length in Byte is sent";
}
identity fl-token-length {
base field-length-base-type;
description "residue length in Byte is sent";
}
//---------------------------------
// Direction Indicator type
//---------------------------------
identity direction-indicator-base-type {
description "used to extend field length functions";
}
identity di-bidirectional {
base direction-indicator-base-type;
description "Direction Indication of bi directionality";
}
identity di-up {
base direction-indicator-base-type;
description "Direction Indication of upstream";
}
identity di-down {
base direction-indicator-base-type;
description "Direction Indication of downstream";
}
//----------------------------------
// Matching Operator type definition
//----------------------------------
identity matching-operator-base-type {
description "used to extend Matching Operators with SID values";
}
identity mo-equal {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-ignore {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-msb {
base matching-operator-base-type;
description "SCHC draft";
}
identity mo-matching {
base matching-operator-base-type;
description "SCHC draft";
}
//------------------------------
// CDA type definition
//------------------------------
identity compression-decompression-action-base-type;
identity cda-not-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-value-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-lsb {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-mapping-sent {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-compute-length {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-compute-checksum {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-deviid {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
identity cda-appiid {
base compression-decompression-action-base-type;
description "from SCHC draft";
}
// -- type definition
typedef field-id-type {
description "Field ID generic type.";
type identityref {
base field-id-base-type;
}
}
typedef field-length-type {
type union {
type int64; /* positive length */
type identityref { /* function */
base field-length-base-type;
}
}
}
typedef direction-indicator-type {
type identityref {
base direction-indicator-base-type;
}
}
typedef matching-operator-type {
type identityref {
base matching-operator-base-type;
}
}
typedef comp-decomp-action-type {
type identityref {
base compression-decompression-action-base-type;
}
}
// -- fragmentation types
identity ack-behavior-base-type {
description "type to define when to send an Acknowledgment message";
}
identity ack-behavior-after-All0 {
description "fragmentor expect Ack after sending All0 fragment.";
base ack-behavior-base-type;
}
identity ack-behavior-after-All1 {
description "fragmentor expect Ack after sending All1 fragment.";
base ack-behavior-base-type;
}
identity ack-behavior-after-Always {
description "fragmentor expect Ack after sending every fragment.";
base ack-behavior-base-type;
}
typedef ack-behavior-type {
type identityref {
base ack-behavior-base-type;
}
}
// -- fragmentation 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 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;
}
}
}
<code ends>
Figure 18
<code begins> file schc@2020-02-28.yang
module schc{
yang-version "1";
namespace "urn:ietf:lpwan:schc:rules-description";
prefix "schc";
import schc-id {
prefix "schc-id";
}
description
"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.";
revision 2020-02-28 {
description "Add Fragmentation parameters";
}
revision 2020-01-23 {
description "Modified TV with binary and union";
}
revision 2020-01-07 {
description "First version of the YANG model";
}
// -------- RULE DEFINITION ------------
grouping target-values-struct {
leaf value {
type union {
type binary;
type string;
}
}
leaf position {
type uint16;
}
}
grouping compression-rule-entry {
leaf field-id {
mandatory true;
type schc-id:field-id-type;
}
leaf field-length {
mandatory true;
type schc-id:field-length-type;
}
leaf field-position {
mandatory true;
type uint8;
}
leaf direction-indicator {
mandatory true;
type schc-id:direction-indicator-type;
}
list target-values {
key position;
uses target-values-struct;
}
leaf mo {
mandatory true;
type schc-id:matching-operator-type;
}
list mo-value {
key position;
uses target-values-struct;
}
leaf cda {
mandatory true;
type schc-id:comp-decomp-action-type;
}
list cda-value {
key position;
uses target-values-struct;
}
}
grouping fragmentation-content {
leaf direction {
type schc-id:direction-indicator-type;
description "should be up or down";
}
leaf dtagsize {
type uint8;
description "size in bit of the DTag field";
}
leaf wsize {
type uint8;
description "size in bit of the window field";
}
leaf fcnsize {
type uint8;
description "size in bit of the FCN field";
}
leaf RCS-algorithm {
type RCS-algorithm-type;
default schc-id:RFC8724-RCS;
description "Algoritm used for RCS";
}
leaf maximum-window-size {
type uint16;
description "by default 2^wsize - 1";
}
leaf retransmission-timer {
type uint64;
description "duration in seconds of the retransmission timer"; // Check the units
}
leaf inactivity-timer {
type uint64;
description "duration is seconds of the inactivity timer"; // check units
}
leaf max-ack-requests {
type uint8;
}
leaf maximum-packet-size {
type uint16;
mandatory true;
default 1280;
description "When decompression is done, packet size must not strictly exceed this limit in Bytes";
}
choice mode {
mandatory true;
case no-ack;
case ack-always;
case ack-on-error {
leaf tile-size {
type uint8;
description "size in bit of tiles";
}
leaf tile-in-All1 {
type boolean;
description "When true, sender and receiver except a tile in All-1 frag";
}
leaf ack-behavior {
type schc-id:ack-behavior-type;
mandatory true;
}
}
}
}
grouping compression-content {
list entry {
key "field-id field-position direction-indicator";
uses compression-rule-entry;
}
}
// Define rule ID. Rule ID is composed of a RuleID value and a Rule ID Length
grouping rule-id-type {
leaf rule-id {
type uint32;
description "rule ID value, this value must be unique combined with the length";
}
leaf rule-length {
type uint8 {
range 0..32;
}
description "rule ID length in bits, value 0 is for implicit rules";
}
}
// 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";
uses rule-id-type;
choice nature {
case fragmentation {
uses fragmentation-content;
}
case compression {
uses compression-content;
}
}
}
}
}
<code ends>
Figure 19
| [I-D.ietf-lpwan-coap-static-context-hc] | Minaburo, A., Toutain, L. and R. Andreasen, "LPWAN Static Context Header Compression (SCHC) for CoAP", Internet-Draft draft-ietf-lpwan-coap-static-context-hc-12, December 2019. |
| [I-D.ietf-lpwan-ipv6-static-context-hc] | Minaburo, A., Toutain, L., Gomez, C., Barthel, D. and J. Zuniga, "Static Context Header Compression (SCHC) and fragmentation for LPWAN, application to UDP/IPv6", Internet-Draft draft-ietf-lpwan-ipv6-static-context-hc-24, December 2019. |
| [RFC7252] | Shelby, Z., Hartke, K. and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014. |