YANG module for LPWAN Static Context Header Compression (SCHC)

defines a compression technique for LPWA network based on static context. The context is known by both ends. A context contains an ordered list of rules (cf. ). Each rule is a vector of entries. Each entry is composed of a field descriptor, a prescribed matching value, a matching rule for the compression side, a matching rule for the decompression side and a compression/decompression action function.

A value may be associated for each field in a rule. The value's type depends of 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. gives its definition.

Note that as defined in , ESprefix and LCprefix can be of 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 the compressed or uncompressed header. defines three operators: equal: the rule's value must be equal to the packet header value for a specific field. lsb(L): this operator compare the most significant bits. The operator takes one argument representing the length of least significant bit part, which will be ignored during the matching but sent if the rule matches. ignore: there is no check for this field.

represents the matching operator type definition.

defines some actions functions. Action functions tell how to compress and inversely how to decompress the field. They are defined in

Each rule's row is defined by several leaves, composed of: a field name that can be used for debugging purpose, a field position which will be used as a key, a field value containing the value that will be compared, two matching operators for rule selection: one for compression and the other for decompression, an action function to compress/uncompress the field. defines the format.

This lead to the generic rule definition, represented .

A context is defined by a set of rules identified through a rule-id. Each rule contains a set of field definitions identified through a field position. gives the yang definition of this module.

Specific modules can be defined based on the same principle. represents the module defined in .

Each field is specifically defined with some default values.

COMI/CoOL defines a management function set adapted to constrained networks. In the generic format, the keys to access a field (referenced as field-SID) are the rule-id and the field-pos. Therefore to modify one value for a specific rule and a specific field, a iPATCH will be used as defined in

For a specific context, only the rule-id has to be specified in the iPATH methods since each field has its own sid value.

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