Network Working Group A. Minaburo
Internet-Draft Acklio
Intended status: Informational L. Toutain
Expires: September 12, 2019 Institut MINES TELECOM ; IMT Atlantique
March 11, 2019

Data Model for Static Context Header Compression (SCHC)


This document describes a YANG data model for the SCHC (Static Context Header Compression). A generic module is defined, that can be applied for any headers and also a specific model for the IPv6 UDP protocol stack is also proposed. Note that this draft is a first attempt to define a YANG data module for SCHC, more work is needed to use all the YANG facilities.

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1. Introduction

SCHC [I-D.ietf-lpwan-ipv6-static-context-hc] defines a compression technique for LPWAN networks based on static context. The context contains a list of rules (cf. Figure 1). Each rule contains itself a list of field descriptions composed of a field identifier (FID), a field length (FID), a field position (FP), a field direction (DI), a target value (TV), a matching operator (MO) and a Compression/Decompression Action (CDA).

  |                      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

The goal of this document is to provide an YANG data model to represent SCHC Compression and Fragmentation rules, to allow management over a LPWAN network. The main constraints are:

2. YANG types

2.1. Field Identifier

The field identifier is used to identify a specific field. It is viewed as an uint32.

2.2. Target Value field

    typedef lpwan-types {
      type union {
        type uint8;
        type uint16;
        type uint32;
        type uint64;
        type inet:ipv6-prefix;
        type string;

Figure 2: Value types

A value may be associated for each field in a rule. The value's type depends on the field. It can be an integer, a prefix, a string, or any other type carried by the field. The LPWA-types regroups all the possibles values. Figure 2 gives its definition. [I-D.ietf-lpwan-ipv6-static-context-hc], Dev and App Prefixes can be of type inet:ipv6-prefix-type, but this type derives from ASCII characters, a binary representation such as uint64 will be more compact.

2.3. Matching Operators

A matching operator is used to check the field value stored in the rule against the value contained in the header field. If there is no matching the rule is not selected. Two instances of matching operator are defined to allow the rule selection from informations contained either in the compressed header or the uncompressed header. The SCHC document [I-D.ietf-lpwan-ipv6-static-context-hc] defines four operators:

    /* Matching operator type         */
    typedef matching-operator-type {
        type enumeration {
            enum equal;
            enum ignore;
            enum msb;
            enum match-mapping;

Figure 3: Matching operators

Figure 3 represents the Matching Operator type definition.

2.4. Compression Decompression Actions

	/* Compression-Decompression action type       */
	typedef compression-decompression-action-type {
			type enumeration {
				enum not-sent;
				enum value-sent;
				enum lsb;
				enum mapping-sent;
				enum compute-length;
				enum compute-checksum;
				enum esiid-did;
				enum laiid-did;

Figure 4: Action functions

The SCHC document [I-D.ietf-lpwan-ipv6-static-context-hc] defines some compression decompression actions (CDA). The CDA tells how to compress and decompress the field. They are defined in Figure 4. they are coded the same way as MO.

3. Generic rule definition

	grouping rule-entry {
		leaf field-id {
			type int32;
			description "Field ID unique value representing the Field";
		leaf field-length {
		        type uint8;
			description "size in bits of the field";

		leaf field-position {
			type uint8;
			description "For repeated fields, we need to be able to 
			             distinguish between successive occurences";

		leaf direction {
        	     type direction-type;
		list target-values {
		     key tv-key;
		     leaf tv-key {
		        type int8;
		     leaf target-value {
			type lpwan-types;
		     description "Target Values can be a list of value, for 
		                  match-mapping. For other MO, only one entry is specified";  
		leaf matching-operator {
      		     type matching-operator-type;

		leaf matching-operator-parameter {
      		     type lpwan-types;
		     description "If the matching operator requires a parameter 
		                  (for example lsb or msb), the value is provided here.";

		leaf compression-decompression-action {
      		     type compression-decompression-action-type;

		leaf compression-decompression-action-parameter {
      		     type lpwan-types;
		     description "If the matching operator requires a parameter 
		                  (for example lsb or msb), the value is provided here.";

Figure 5: Action functions

Each rule's row is defined by several leaves, composed of: Figure 5 defines the format.

4. YANG static context model

  grouping compression-rule {
    leaf rule-id {
	    type uint8;
            description "The number of the context rule that should be applied.";
    leaf rule-id-length {
    	    type uint8;

    list rule-fields {
      key "field-id field-position direction";
      uses rule-entry;


Figure 6: YANG definition of the generic module

This lead to the generic rule definition, represented Figure 7. It defines a set of rules.

module: ietf-lpwan-schc-rule
  +--rw rule-id?          uint8
  +--rw rule-id-length?   uint8
  +--rw rule-fields* [field-id field-position direction]
     +--rw field-id                                      int32
     +--rw field-length?                                 uint8
     +--rw field-position                                uint8
     +--rw direction                                     direction-type
     +--rw target-values* [tv-key]
     |  +--rw tv-key          int8
     |  +--rw target-value?   lpwan-types
     +--rw matching-operator?                            m.-o.-type
     +--rw matching-operator-parameter?                  lpwan-types
     +--rw compression-decompression-action?             c.-d.-a.-type
     +--rw compression-decompression-action-parameter?   lpwan-types

Figure 7: Generic module tree


SID        Assigned to
---------  --------------------------------------------------
60000      node /rule-fields
60001      node /rule-fields/compression-decompression-action
60002      node /rule-fields/compression-decompression-action-parameter
60003      node /rule-fields/direction
60004      node /rule-fields/field-id
60005      node /rule-fields/field-length
60006      node /rule-fields/field-position
60007      node /rule-fields/matching-operator
60008      node /rule-fields/matching-operator-parameter
60009      node /rule-fields/target-values
60010      node /rule-fields/target-values/target-value
60011      node /rule-fields/target-values/tv-key
60012      node /rule-id
60013      node /rule-id-length

File ietf-lpwan-schc-rule@2016-10-31.sid created
Number of SIDs available : 100
Number of SIDs assigned : 14

Figure 8: Example of SID allocation

Figure 7. Figure 8 gives a simple allocation for SID value. SID values from 100 to 113 are used for /generic-rules/context-rules/rule-fields/field-compression-decompression-action. SID value from 1009 to 1012 are used in /generic-rules/context-rules/rule-fields/field-matching-operator.

5. Acknowledgement

The authors would like to thank Michel Veillette, Alexander Pelov, Antoni Markovski for their help on COMI/CoOL and YANG.

6. Normative References

[I-D.ietf-core-comi] Veillette, M., Stok, P., Pelov, A. and A. Bierman, "CoAP Management Interface", Internet-Draft draft-ietf-core-comi-04, November 2018.
[I-D.ietf-lpwan-ipv6-static-context-hc] Minaburo, A., Toutain, L., Gomez, C., Barthel, D. and J. Zuniga, "LPWAN Static Context Header Compression (SCHC) and fragmentation for IPv6 and UDP", Internet-Draft draft-ietf-lpwan-ipv6-static-context-hc-18, December 2018.

Authors' Addresses

Ana Minaburo Acklio 1137A Avenue des Champs Blancs 35510 Cesson-Sevigne Cedex, France EMail:
Laurent Toutain Institut MINES TELECOM ; IMT Atlantique 2 rue de la Chataigneraie CS 17607 35576 Cesson-Sevigne Cedex, France EMail:

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