| 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)
draft-toutain-lpwan-schc-yang-data-model-00
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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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:
The field identifier is used to identify a specific field. It is viewed as an uint32.
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.
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.
/***********************************************/
/* 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.
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.
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.
The authors would like to thank Michel Veillette, Alexander Pelov, Antoni Markovski for their help on COMI/CoOL and YANG.
| [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. |