Data Model for Static Context Header Compression (SCHC)Acklio1137A avenue des Champs Blancs35510 Cesson-Sevigne CedexFranceana@ackl.ioInstitut MINES TELECOM; IMT Atlantique2 rue de la ChataigneraieCS 1760735576 Cesson-Sevigne CedexFranceLaurent.Toutain@imt-atlantique.frlpwan Working GroupThis document describes a YANG data model for the SCHC (Static Context Header Compression)
compression and fragmentation 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 this constrained network.
Draft provides an 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 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 do no refers
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 specifies fields for IPv6, UDP, CoAP and OSCORE. decribes ICMPv6 header compression.SCHC fragmentation requires a set of common parameters that are included in a rule. These parameters are defined in . proposes an 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.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. 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,…).Using the YANG model, each field MUST be identified through a global YANG identityref. A YANG field ID derives from the field-id-base-type. 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”. 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 ) gives the full definition of the field ID for , , and .The type associated to this identity is field-id-type (cf. )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.As for field ID, field length function can be defined as a 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. ).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). gives the identityref for Direction Indicators.The type is “direction-indicator-type” (cf. ).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. 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.Matching Operator (MO) is a function applied between a field value provided by the parsed header and the target value. defines 4 MO.the type is “matching-operator-type” (cf. )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.Compression Decompression Action (CDA) identified the function to use either for compression or decompression.
defines 6 CDA.The type is “comp-decomp-action-type” (cf. )Currently no CDA requires arguments, 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.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.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 associated to a rule ID. The compression
rule entry is defined in . 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.A compression rule is a list of entries.To identify a specific entry Field ID, position and direction are needed.Parameters for fragmentation are defined in Annex D of . 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 type is the same as the one used in compression entries, but the use of bidirectionnal is
forbidden.The next elements describe size of SCHC fragmentation header fields. Only the FCN size is mandatory
and value must be higher or equal to 1.RCS algorithm is defined (), by default with the CRC computation proposed in .
The algorithms are identified through an identityref specified in the SCHC Data Model and with the type RCS-algorithm-type (). gives the parameters used by the state machine to handle fragmentation:maximum-window-size contains the maximum FCN value that can be used.retransmission-timer gives in seconds the duration before sending an ack request (cf. section 8.2.2.4. of ). If specifed, 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. gives information related to a specific compression mode: fragmentation-mode MUST be set with a specific behavior. Identityref are given .For Ack on Error some specific information may be provided:tile-size gives in bits the size of the tile; If set to 0 a single tile is inserted inside a fragment.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 .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 .## YANG TreeThis document has no request to IANA.This document does not have any more Security consideration than the ones already raised on The authors would like to thank Dominique Barthel, Carsten Bormann, Alexander Pelov. file schc@2020-02-28.yang
module schc{
yang-version "1";
namespace "urn:ietf:lpwan:schc:rules-description";
prefix "schc";
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.
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.";
revision 2020-06-15 {
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";
}
revision 2020-01-07 {
description "First version of the YANG model";
}
// -------------------------
// 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 class from RFC 7252";
}
identity fid-coap-code-detail {
base field-id-base-type;
description "CoAP code detail 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-oscore-flags {
base field-id-base-type;
description "CoAP option oscore flags (see draft schc coap, section 6.4)";
}
identity fid-coap-option-oscore-piv {
base field-id-base-type;
description "CoAP option oscore flags (see draft schc coap, section 6.4)";
}
identity fid-coap-option-oscore-kid {
base field-id-base-type;
description "CoAP option oscore flags (see draft schc coap, section 6.4)";
}
identity fid-coap-option-oscore-kidctx {
base field-id-base-type;
description "CoAP option oscore flags (see draft schc coap, section 6.4)";
}
identity fid-icmpv6-type {
base field-id-base-type;
description "ICMPv6 field (see draft OAM)";
}
identity fid-icmpv6-code {
base field-id-base-type;
description "ICMPv6 field (see draft OAM)";
}
identity fid-icmpv6-checksum {
base field-id-base-type;
description "ICMPv6 field (see draft OAM)";
}
identity fid-icmpv6-identifier {
base field-id-base-type;
description "ICMPv6 field (see draft OAM)";
}
identity fid-icmpv6-sequence {
base field-id-base-type;
description "ICMPv6 field (see draft OAM)";
}
/// !!!!!!! See future CoAP extentions
//----------------------------------
// 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 "RFC 8724";
}
identity mo-ignore {
base matching-operator-base-type;
description "RFC 8724";
}
identity mo-msb {
base matching-operator-base-type;
description "RFC 8724";
}
identity mo-matching {
base matching-operator-base-type;
description "RFC 8724";
}
//------------------------------
// CDA type definition
//------------------------------
identity compression-decompression-action-base-type;
identity cda-not-sent {
base compression-decompression-action-base-type;
description "RFC 8724";
}
identity cda-value-sent {
base compression-decompression-action-base-type;
description "RFC 8724";
}
identity cda-lsb {
base compression-decompression-action-base-type;
description "RFC 8724";
}
identity cda-mapping-sent {
base compression-decompression-action-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";
}
// -- type definition
typedef field-id-type {
description "Field ID generic type.";
type identityref {
base field-id-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 {
type int64; /* positive length in bits */
type identityref { /* function */
base field-length-base-type;
}
}
}
typedef direction-indicator-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.";
type identityref {
base direction-indicator-base-type;
}
}
typedef matching-operator-type {
description "Matching Operator (MO) to compare fields values with target values";
type identityref {
base matching-operator-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 {
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-type {
type identityref {
base fragmentation-mode-base-type;
}
}
// -- Ack behavior
identity ack-behavior-base-type {
description "define when to 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 {
description "fragmentation expects Ack after 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;
}
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;
}
}
// -- 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 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;
}
}
// -------- RULE ENTRY DEFINITION ------------
grouping target-values-struct {
description "defines the target value element. Can be either an arbitrary
binary or ascii element. All target values are considered as a matching lists.
Position is used to order values, by default position 0 is used when containing
a single element.";
leaf value {
type union {
type binary;
type string;
}
}
leaf position {
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 {
description "Field ID, identify a field in the header with a YANG refenceid.";
mandatory true;
type schc:field-id-type;
}
leaf field-length {
description "Field Length in bit or through a function defined as a YANG referenceid";
mandatory true;
type schc:field-length-type;
}
leaf field-position {
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";
mandatory true;
type uint8;
}
leaf direction-indicator {
description "Direction Indicator, a YANG referenceid to say if the packet is bidirectionnal,
up or down";
mandatory true;
type schc:direction-indicator-type;
}
list target-values {
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.";
key position;
uses target-values-struct;
}
leaf matching-operator {
mandatory true;
type schc:matching-operator-type;
}
list matching-operator-value {
key position;
uses target-values-struct;
}
leaf comp-decomp-action {
mandatory true;
type schc:comp-decomp-action-type;
}
list comp-decomp-action-value {
key position;
uses target-values-struct;
}
}
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;
}
}
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 direction {
type schc:direction-indicator-type;
description "should be up or down, bi directionnal is forbiden.";
mandatory true;
}
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";
mandatory true;
}
leaf RCS-algorithm {
type RCS-algorithm-type;
default schc:RFC8724-RCS;
description "Algoritm used for RCS";
}
leaf maximum-window-size {
type uint16;
description "by default 2^wsize - 1";
}
leaf retransmission-timer {
type uint64 {
range 1..max;
}
description "duration in seconds of the retransmission timer"; // Check the units
}
leaf inactivity-timer {
type uint64;
description "duration is seconds of the inactivity timer, 0 indicates the timer is disabled"; // check units
}
leaf max-ack-requests {
type uint8 {
range 1..max;
}
description "the maximum number of retries for a specific SCHC ACK.";
}
leaf maximum-packet-size {
type uint16;
default 1280;
description "When decompression is done, packet size must not strictly exceed this limit in Bytes";
}
leaf fragmentation-mode {
type schc:fragmentation-mode-type;
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;
description "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;
description "When true, sender and receiver except a tile in All-1 frag";
}
leaf ack-behavior {
type schc:ack-behavior-type;
description "Sender behavior to acknowledge, after All-0, All-1 or when the
LPWAN allows it (Always)";
}
}
}
}
// 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;
}
}
}
}
}
]]>SCHC: Generic Framework for Static Context Header Compression and FragmentationThis document defines the Static Context Header Compression and fragmentation (SCHC) framework, which provides both a header compression mechanism and an optional fragmentation mechanism. SCHC has been designed with Low-Power Wide Area Networks (LPWANs) in mind.SCHC compression is based on a common static context stored both in the LPWAN device and in the network infrastructure side. This document defines a generic header compression mechanism and its application to compress IPv6/UDP headers.This document also specifies an optional fragmentation and reassembly mechanism. It can be used to support the IPv6 MTU requirement over the LPWAN technologies. Fragmentation is needed for IPv6 datagrams that, after SCHC compression or when such compression was not possible, still exceed the Layer 2 maximum payload size.The SCHC header compression and fragmentation mechanisms are independent of the specific LPWAN technology over which they are used. This document defines generic functionalities and offers flexibility with regard to parameter settings and mechanism choices. This document standardizes the exchange over the LPWAN between two SCHC entities. Settings and choices specific to a technology or a product are expected to be grouped into profiles, which are specified in other documents. Data models for the context and profiles are out of scope.LPWAN Static Context Header Compression (SCHC) for CoAPThis draft defines how to compress the Constrained Application Protocol (CoAP) using the Static Context Header Compression (SCHC). SCHC is a header compression mechanism adapted for Constrained Devices. SCHC uses a static description of the header to reduce the header's redundancy and size. While RFC 8724 describes the SCHC compression and fragmentation framework, and its application for IPv6/UDP headers, this document applies SCHC for CoAP headers. The CoAP header structure differs from IPv6 and UDP since CoAP uses a flexible header with a variable number of options, themselves of variable length. The CoAP protocol messages format is asymmetric: the request messages have a header format different from the one in the response messages. This specification gives guidance on applying SCHC to flexible headers and how to leverage the asymmetry for more efficient compression Rules.OAM for LPWAN using Static Context Header Compression (SCHC)With IP protocols now generalizing to constrained networks, users expect to be able to Operate, Administer and Maintain them with the familiar tools and protocols they already use on less constrained networks. OAM uses specific messages sent into the data plane to measure some parameters of a network. Most of the time, no explicit values are sent is these messages. Network parameters are obtained from the analysis of these specific messages. This can be used: * To detect if a host is up or down. * To measure the RTT and its variation over time. * To learn the path used by packets to reach a destination. OAM in LPWAN is a little bit trickier since the bandwidth is limited and extra traffic added by OAM can introduce perturbation on regular transmission. Two scenarios can be investigated: * OAM coming from internet. In that case, the NGW should act as aThe Constrained Application Protocol (CoAP)The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.