< draft-ietf-lpwan-coap-static-context-hc-01.txt		draft-ietf-lpwan-coap-static-context-hc-02.txt >
	lpwan Working Group A. Minaburo		lpwan Working Group A. Minaburo
	Internet-Draft Acklio		Internet-Draft Acklio
	Intended status: Informational L. Toutain		Intended status: Informational L. Toutain
	Expires: September 11, 2017 Institut MINES TELECOM ; IMT Atlantique		Expires: March 10, 2018 Institut MINES TELECOM ; IMT Atlantique
	March 10, 2017		September 06, 2017
	LPWAN Static Context Header Compression (SCHC) for CoAP		LPWAN Static Context Header Compression (SCHC) for CoAP
	draft-ietf-lpwan-coap-static-context-hc-01		draft-ietf-lpwan-coap-static-context-hc-02
	Abstract		Abstract
	This draft discusses the way SCHC header compression can be applied		This draft defines the way SCHC header compression can be applied to
	to CoAP headers in an LPWAN flow regarding the generated traffic.		CoAP headers. CoAP header structure differs from IPv6 and UDP
	CoAP protocol differs from IPv6 and UDP protocols because the CoAP		protocols since the CoAP Header is flexible header with a variable
	Header has a flexible header due to variable options. Another		number of options themself of a variable length. Another important
	important difference is the asymmetric format in the header		difference is the asymmetry in the header information used for
	information used in the request and the response packets. This draft		request and response messages. This draft takes into account the
	shows that the Client and the Server do not uses the same fields and		fact that a thing can play the role of a CoAP client, a CoAP client
	how the SCHC header compression can be used.		or both roles.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on September 11, 2017.		This Internet-Draft will expire on March 10, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2017 IETF Trust and the persons identified as the		Copyright (c) 2017 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
			Table of Contents
			1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
			2. CoAP Compressing . . . . . . . . . . . . . . . . . . . . . . 3
			3. Compression of CoAP header fields . . . . . . . . . . . . . . 4
			3.1. CoAP version field (2 bits) . . . . . . . . . . . . . . . 4
			3.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 5
			3.3. CoAP token length field . . . . . . . . . . . . . . . . . 5
			3.4. CoAP code field . . . . . . . . . . . . . . . . . . . . . 6
			3.5. CoAP Message ID field . . . . . . . . . . . . . . . . . . 8
			3.6. CoAP Token field . . . . . . . . . . . . . . . . . . . . 9
			4. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 9
			4.1. CoAP option Content-format field. . . . . . . . . . . . . 9
			4.2. CoAP option Accept field . . . . . . . . . . . . . . . . 10
			4.3. CoAP option Max-Age field, CoAP option Uri-Host and Uri-
			Port fields . . . . . . . . . . . . . . . . . . . . . . . 11
			5. CoAP option Uri-Path and Uri-Query fields . . . . . . . . . . 11
			5.1. CoAP option Proxy-URI and Proxy-Scheme fields . . . . . . 12
			5.2. CoAP option ETag, If-Match, If-None-Match, Location-Path
			and Location-Query fields . . . . . . . . . . . . . . . . 13
			6. Other RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 13
			6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 13
			6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 13
			6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 13
			7. Protocol analysis . . . . . . . . . . . . . . . . . . . . . . 13
			8. Examples of CoAP header compression . . . . . . . . . . . . . 14
			8.1. Mandatory header with CON message . . . . . . . . . . . . 14
			8.2. Complete exchange . . . . . . . . . . . . . . . . . . . . 16
			9. Normative References . . . . . . . . . . . . . . . . . . . . 17
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
			CoAP [rfc7252] is an implementation of the REST architecture for
			constrained devices. Gateway between CoAP and HTTP can be easily
			built since both protocols uses the same address space (URL), caching
			mechanisms and methods.
			Nevertheless, if limited, the size of a CoAP header may be too large
			for LPWAN constraints and some compression may be needed to reduce
			the header size.
	[I-D.toutain-lpwan-ipv6-static-context-hc] defines a header		[I-D.toutain-lpwan-ipv6-static-context-hc] defines a header
	compression mechanism for LPWAN network based on a static context.		compression mechanism for LPWAN network based on a static context.
	Where the context is said static since the element values composing		The context is said static since the element values composing the
	the context are not learned during the packet exchanges but are		context are not learned during the packet exchanges but are
	previously defined. The context(s) is(are) known by both ends before		previously defined. The context(s) is(are) known by both ends before
	transmission.		transmission.
	A context is composed of a set of rules (contexts) that are		A context is composed of a set of rules (contexts) that are
	referenced by Rule IDs (identifiers). A rule describes the header		referenced by Rule IDs (identifiers). A rule contains an ordered
	fields with some associated Target Values (TV). A Matching Operator		list of the header fields containing a field ID (FID) and its
	(MO) is associated to each header field description. The rule is		position when repeated, a direction indicator (DI) (upstream,
	selected if all the MOs fit the TVs. In that case, a Compression		downstream and bidirectional) and some associated Target Values (TV)
			which are expected in the message header. A Matching Operator (MO)
			is associated to each header field description. The rule is selected
			if all the MOs fit the TVs. In that case, a Compression
	Decompression Function (CDF) associated to each field defines the		Decompression Function (CDF) associated to each field defines the
	link between the compressed and decompressed value for each of the		link between the compressed and decompressed value for each of the
	header fields.		header fields.
	This draft discusses the way SCHC can be applied to CoAP headers, how		This document describes how the rules can be applied to CoAP flows. Compression of the
	to extend MOs to match a specific element when several fields of the		CoAP header may be done in conjunction with the above layers or independantly.
	same type are presented in the header. It also introduces the notion
	of bidirectional or unidirectional (upstream and downstream) fields.
	2. CoAP Compressing		2. CoAP Compressing
	CoAP [RFC7252] is an implementation of the REST architecture for		CoAP differs from IPv6 and UDP protocols on the following
	constrained devices. Gateway between CoAP and HTTP can be easily
	built since both protocols uses the same address space (URL), caching
	mechanisms and methods.
	Nevertheless, if limited, the size of a CoAP header may be too large
	for LPWAN constraints and some compression may be needed to reduce
	the header size. CoAP compression is not straightforward. Some
	differences between IPv6/UDP and CoAP can be highlighted. CoAP
	differs from IPv6 and UDP protocols in the following
	aspects:		aspects:
	o IPv6 and UDP are symmetrical protocols. The same fields are found		o IPv6 and UDP are symmetrical protocols. The same fields are found
	in the request and in the response, only position in the header		in the request and in the response, only location in the header
	may change (e.g. source and destination fields). A CoAP request		may vary (e.g. source and destination fields). A CoAP request is
	is different from an response. For example, the URI-path option		different from an response. For example, the URI-path option is
	is mandatory in the request and is not found in the response.		mandatory in the request and is not found in the response, request
			may contain an Accept option and the response a Content-format
			option.
			Even when a field is "symmetric" (i.e. found in both directions)
			the values carried are different. For instance the Type field
			will contain a CON value in the request and a ACK or RST value in
			the response. Exploiting the asymmetry in compression will allow
			to send no bit in the compressed request and a single bit in the
			answer. Same behavior can be applied to the CoAP Code field (O.OX
			code are present in the request and Y.ZZ in the answer).
	o CoAP also obeys to the client/server paradigm and the compression		o CoAP also obeys to the client/server paradigm and the compression
	rate can be different if the request is issued from a LPWAN node		rate can be different if the request is issued from a LPWAN node
	or from an non LPWAN device. For instance a Thing (ES) aware of		or from an non LPWAN device. For instance a Thing (ES) aware of
	LPWAN constraints can generate a 1 byte token, but a regular CoAP		LPWAN constraints can generate a 1 byte token, but a regular CoAP
	cleint will certainly send a larger token to the Thing.		client will certainly send a larger token to the Thing. SCHC
			compression will not modify the values to offer a better
			compression rate. Nevertheless a proxy placed before the
			compressor may change some field values to offer a better
			compression rate and maintain the necessary context for
			interoperability with existing CoAP implementations.
	o In IPv6 and UDP header fields have a fixed size. In CoAP, Token		o In IPv6 and UDP header fields have a fixed size. In CoAP, Token
	size may vary from 0 to 8 bytes, length is given by a field in the		size may vary from 0 to 8 bytes, length is given by a field in the
	header. More systematically, the CoAP options are described using		header. More systematically, the CoAP options are described using
	the Type-Length-Value. When applying SCHC header compression, the		the Type-Length-Value. When applying SCHC header compression.
	token size is not known at the rule creation, the sender and the
	receiver must agree on its compressed size.
	o The options type in CoAP is not defined with the same value. The
	Delta TLV coding makes that the type is not independent of
	previous option and may vary regarding the options contained in
	the header.
	2.1. CoAP behavior
	A LPWAN node can either be a client or a server and sometimes both.
	In the client mode, the LPWAN node sends request to a server and
	expects an answer or acknowledgements. Acknowledgements can be at 2
	different levels:
	o In the transport level, a CON message is acknowledged by an ACK
	message. A NON confirmable message is not acknowledged at all.
	o In REST level, a REST request is acknowledged by an "error" code.
	The [RFC7967] defines an option to limit the number of
	acknowledgements.
	Note that acknowledgement can be optimized and a REST level
	acknowledgement can be used as a transport level acknowledgement.
	2.2. CoAP protocol analysis
	CoAP header format defines the following fields:
	o version (2 bits): this field can be elided during the SCHC
	compresssion
	o type (2 bits). It defines the type of the transport messages, 4
	values are defined, regarding the type of exchange. If only NON
	messages are sent or CON/ACK messages, this field can be reduced
	to 0 or 1 bit.
	o token length (4 bits). The standard allows up to 8 bytes for a
	token. If a fixed token size is chosen, then this field can be
	elided. If some variation in length are needed then 1 or 2 bits
	could be enough for most of LPWAN applications.
	o code (8 bits). This field codes the request and the response
	values. In CoAP these values are represented in a more compact
	way then the coding used in HTTP, but the coding is not optimal.
	o message id (16 bits). This value of this header field is used to
	acknowledge CON frames. The size of this field is computed to
	allow the anticipation (how many frames can be sent without
	acknowledgement). When a value is used, the [RFC7252] defines the
	time before it can be reused without ambiguities. This size
	defined may be too large for a LPWAN node sending or receiving few
	messages a day.
	o Token (0 to 8 bytes). Token header field is used to identify
	active flows. Regarding the usage for LPWAN (stability in time
	and limited number), a short token (1 Byte or less) can be enough.
	o options are coded using delta-TLV. The delta-T depends on
	previous values, length is encoded inside the option. The
	[RFC7252] distinguishes repeatable options that can appear several
	times in the header. Among them we can distinguish:
	* list options which appear several time in the header but are
	exclusive such as the Accept option.
	* cumulative options which appear several times in the header but
	are part of a more generic value such as Uri-Path and Uri-
	Query. In that case, some elements may not change during the
	Thing lifetime and other may change at each request. For
	instance CoMi [I-D.ietf-core-comi] defines the following path
	/c/X6?k="eth0", where the first path element "c" does not
	change, the second element can vary over time with a different
	length (it represents the base64 enconding of a SID) and the
	query string can also vary over time.
	For a given flow some value options are stable through time.
	Observe, ETag, If-Match, If-None-Match and Size varies in each
	message.
	The CoAP protocol must not be altered by the compression/
	decompression phase, but if no semantic is attributed to a value, it
	may be changed during this phase. For instance, the compression
	phase may reduce the size of a token but must maintain its unicity.
	The decompressor will not be able to restore the original value but
	the behavior will remain the same. If no special semantic is
	assigned to the token, this will be transparent. If a special
	semantic is assigned to the token, its compression may not be
	possible.
	3. SCHC rules for CoAP header compression
	This draft refines the rules definition by adding the direction of
	the message, from the Thing point of view (uplink, downlink or
	bidirectional). It does not introduce new Machting Operator or new
	Compression Decompression Function, but add some possibility to check
	one particular element when several of them are present at the same
	time.
	A rule can contain CoAP and IPv6/UDP entries. In that case, IPv6/UDP
	entries are tagged bidirectional.
	3.1. Directional Rules
	By default, an entry in a rule is bidirectional which means that it
	can be applied either on the uplink or downlink headers. By
	specifying the direction, the LC will take into account the specific
	field only if the direction match.
	If the Thing is a client, the URI-Path option is only present on
	request and not on the response. Therefore, the exact matching
	principle to select a rule cannot apply.
	Some options are marked unidirectional, the value (uplink or
	downlink) depends of the scenario. A Uri-Path option will be marked
	uplink if the Thing acts as a client and downlink if the Thing acts
	as a server. If the Thing acts both as client and server, two
	different rules will be defined.
	3.2. Matching Operator
	The Matching Operator behavior has not changed, but the value must
	take a position value, if the entry is repeated :
	FID TV MO CDF
	URI-Path foo equal 1 not-sent		By sending compressed field information following the rule order,
	URI-Path bar equal 2 not-sent		SCHC offers a serialization/deserialization mechanism. Since a
			field exists to indicate the token length there is no ambiguity.
			For options, the rule indicates also the expected options found
			the int CoAP header. Therefore only the length is needed to
			recognise an option. The length will be send using the same CoAP
			encoding (size less than 12 are directly sent, higher values uses
			the escape mechanisms defined by [rfc7252]). Delta Type is
			omitted, the value will be recovered by the decompressor. This
			reduce the option length of 4, 12 or 20 bits regarding the
			orignial size of the delta type encoding in the option.
	Figure 1: Position entry.		o In CoAP headers a field can be duplicated several times, for
			instances, elements of an URI (path or queries) or accepted
			formats. The position defined in a rule, associated to a Field
			ID, can be used to identify the proper element.
	For instance, the rule Figure 1 matches with /foo/bar, but not /bar/		3. Compression of CoAP header fields
	foo.
	The position is added after the natural argument of the MO, for		This section discusses of the compression of the different CoAP
	example MSB (4,3) indicates a most significant bit matching of 4 bits		header fields. These are just examples. The compression should take
	in a field located in position 3.		into account the nature of the traffic and not only the field values.
			Next chapter will define some compression rules for some common
			exchanges.
	3.3. Compressed field length		3.1. CoAP version field (2 bits)
	When the length is not clearly indicated in the rule, the value		This field is bidirectional and can be elided during the SCHC
	length must be sent with the field data, which means for CoAP to send		compression, since it always contains the same value. It appears
	directly the CoAP option where the delta-T is set to 0.		only in first position.
	For the CoMi path /c/X6?k="eth0" the rule can be set to:		FID Pos DI TV MO CDF
			ver 1 bi 1 equal not-sent
	FID TV MO CDF		3.2. CoAP type field
	URI-Path c equal 1 not-sent		This field can be managed bidirectionally or unidirectionally.Several
	URI-Path ignore 2 value-sent		strategies can be applied to this field regarding the values used:
	URI-Query k= MSB (16, 1) value-sent
	Figure 2: CoMi URI compression		o If the ES is a client or a Server and non confirmable message are
			used, the transmission of the Type field can be avoided:
	Figure 2 shows the parsing and the compression of the URI. where c is		* Pos is always 1,
	not sent. The second element is sent with the length (i.e. 0x02 X 6)
	followed by the query option (i.e. 0x08 k="eth0").
	[[NOTE we don't process URI with a multiple number of path element		* DI can either be "uplink" if the ES is a CoAP client or
	??]].		"downlink" if the ES is a CoAP server, or "bidirectional"
	4. Application to CoAP header fields		* TV is set to the value,
	This section lists the different CoAP header fields and how they can		* MO is set to "equal"
	be compressed.
	4.1. CoAP version field		* CDF is set to "not-sent".
	This field is bidirectional.		FID Pos DI TV MO CDF
			type 1 bi NON equal not-sent
	This field contains always the same value, therefore the TV may be 1,		o If the ES is either a client or a Server and confirmable message
	the MO is set to "equal" and the CDF is set to "not-sent"		are used, the DI can be used to elide the type on the request and
			compress it to 1 bit on the response. The example above shows the
			rule for a ES acting as a client, directions need to be reversed
			for a ES acting as a server.
	4.2. CoAP type field		FID Pos DI TV MO CDF
			type 1 up CON equal not-sent
			type 1 dw {0:ACK, 1:RST} match-mapping mapping-sent
	This field is bidirectional or undirectional.		o Otherwise if the ES is acting simultaneously as a client and a
			server and the rule handle these two traffics, Type field must be
			sent uncompressed.
	Several strategies can be applied to this field regarding the values		FID Pos DI TV MO CDF
	used:		type 1 bi ignore send-value
	o if only one type is sent, for example NON message, its		3.3. CoAP token length field
	transmission can be avoided. TV is set to the value, MO is set to
	"equal" and CDF is set to "not-sent".
	o if two values are sent, for example CON and ACK and RST is not		This field is bi-directional.
	used, this field can be reduced to one bit. TV is set to a
	matching value {CON: 0, ACK: 1}, MO is set to match-mapping and
	CDF is set to mapping-sent.
	o It is also possible avoid transmission of this field by marking it		Several strategies can be applied to this field regarding the values:
	unidirectional. In one direction, the TV is set to CON, MO is set
	to "equal" and CDF is set to "not-sent". On the other direction,
	the TV is set to ACK, the MO is set to "equal" and the CDF is set
	to "not-sent".
	o Otherwise TV is not set, MO is set to "ignore" and CDF is set to		o no token or a wellknown length, the transmission can be avoided.
	"value-sent".		A special care must be taken, if CON messages are acknowledged
			with an empty ACK message. In that case the token is not always
			present.
	4.3. CoAP token length field		FID Pos DI TV MO CDF
			TKL 1 bi value ignore send-value
	This field is bi-directional.		o If the length is changing from one message to an other, the Token
			Length field must be sent. If the Token length can be limited,
			then only the least significant bits have to be sent. The example
			below allows values between 0 and 3.
	Several strategies can be applied to this field regarding the values:		FID Pos DI TV MO CDF
			TKL 1 bi 0x0 MSB(2) LSB(2)
	o no token or a wellknown length, the transmission can be avoided.		o otherwise the field value has to be sent.
	TV is set to the length, the MO is set to "equal" and CDF is set
	to "not-sent"
	o The length is variable from one message to another. TV is not		FID Pos DI TV MO CDF
	set, MO is set to "ignore" and CDF is set to "value-sent". The		TKL 1 bi ignore value-sent
	size of the sent value must be known by ends. The size may be 4
	bits. The receiver must take into account this value to retrieve
	the token. A CoAP proxy may be used before the compression to
	reduce the field size.
	4.4. CoAP code field		3.4. CoAP code field
	This field is unidirectional. The client and the server do not use		This field is bidirectional, but compression can be enhanced using
	the same values.		DI.
	The CoAP code field defines a tricky way to ensure compatibility with		The CoAP Code field defines a tricky way to ensure compatibility with
	HTTP values. Nevertheless only 21 values are defined by [RFC7252]		HTTP values. Nevertheless only 21 values are defined by [rfc7252]
	compared to the 255 possible values. So, it could efficiently be		compared to the 255 possible values.
	coded on 5 bits. The number of code may vary over time, some new
	codes may be introduced or some applications use a limited number of
	values.
	+------+------------------------------+-----------+		+------+------------------------------+-----------+
	| Code | Description | Mapping |		| Code | Description | Mapping |
	+------+------------------------------+-----------+		+------+------------------------------+-----------+
	| 0.00 | | 0x00 |		| 0.00 | | 0x00 |
	| 0.01 | GET | 0x01 |		| 0.01 | GET | 0x01 |
	| 0.02 | POST | 0x02 |		| 0.02 | POST | 0x02 |
	| 0.03 | PUT | 0x03 |		| 0.03 | PUT | 0x03 |
	| 0.04 | DELETE | 0x04 |		| 0.04 | DELETE | 0x04 |
	| 0.05 | FETCH | 0x05 |		| 0.05 | FETCH | 0x05 |
	skipping to change at page 8, line 39 ¶		skipping to change at page 7, line 39 ¶
	| 4.13 | Request Entity Too Large | 0x15 |		| 4.13 | Request Entity Too Large | 0x15 |
	| 4.15 | Unsupported Content-Format | 0x16 |		| 4.15 | Unsupported Content-Format | 0x16 |
	| 5.00 | Internal Server Error | 0x17 |		| 5.00 | Internal Server Error | 0x17 |
	| 5.01 | Not Implemented | 0x18 |		| 5.01 | Not Implemented | 0x18 |
	| 5.02 | Bad Gateway | 0x19 |		| 5.02 | Bad Gateway | 0x19 |
	| 5.03 | Service Unavailable | 0x1A |		| 5.03 | Service Unavailable | 0x1A |
	| 5.04 | Gateway Timeout | 0x1B |		| 5.04 | Gateway Timeout | 0x1B |
	| 5.05 | Proxying Not Supported | 0x1C |		| 5.05 | Proxying Not Supported | 0x1C |
	+------+------------------------------+-----------+		+------+------------------------------+-----------+
	Figure 3: Example of CoAP code mapping		Figure 1: Example of CoAP code mapping
	Figure 3 gives a possible mapping, it can be changed to add new codes		Figure 1 gives a possible mapping, it can be changed to add new codes
	or reduced if some values are never used by both ends.		or reduced if some values are never used by both ends. It could
			efficiently be coded on 5 bits.
			Even if the number of code can be increase with other RFC,
			implementations may use a limited number of values, which can help to
			reduce the number of bits sent on the LPWAN.
			The number of code may vary over time, some new codes may be
			introduced or some applications use a limited number of values.
			The client and the server do not use the same values. This asymmetry
			can be exploited to reduce the size sent on the LPWAN.
	The field can be treated differently in upstream than in downstream.		The field can be treated differently in upstream than in downstream.
	If the Thing is a client an entry can be set on the uplink message		If the Thing is a client an entry can be set on the uplink message
	with a code matching for 0.0X values and another for downlink values		with a code matching for 0.0X values and another for downlink values
	for Y.ZZ codes. It is the opposite if the thing is a server.		for Y.ZZ codes. It is the opposite if the thing is a server.
	4.5. CoAP Message ID field		If the ES always sends or receives requests with the same method, the
			Code field can be elided. The entry below shows a rule for a client
			sending only GET request.
			FID Pos DI TV MO CDF
			code 1 up GET equal not-sent
			If the client may send different methods, a matching-list can be
			applied. For table Figure 1, 3 bits are necessary, but it could be
			less if fewer methods are used. Example below gives an example where
			the ES is a server and receives only GET and POST requests.
			FID Pos DI TV MO CDF
			code 1 dw {0:0.01, 1:0.02}match-mapping mapping-sent
			The same approach can be applied to responses.
			3.5. CoAP Message ID field
	This field is bidirectional.		This field is bidirectional.
	Message ID is used for two purposes:		Message ID is used for two purposes:
	o To acknowledge a CON message with an ACK.		o To acknowledge a CON message with an ACK.
	o To avoid duplicate messages.		o To avoid duplicate messages.
	In LPWAN, since a message can be received by several radio gateway,		In LPWAN, since a message can be received by several radio gateway,
	some LPWAN technologies include a sequence number in L2 to avoid		some LPWAN technologies include a sequence number in L2 to avoid
	duplicate frames. Therefore if the message does not need to be		duplicate frames. Therefore if the message does not need to be
	acknowledged (NON or RST message), the Message ID field can be		acknowledged (NON or RST message), the Message ID field can be
	avoided. In that case TV is not set, MO is set to ignore and CDF is		avoided.
	set to "not-sent". The decompressor can generate a number.
	[[Note; check id this field is not used by OSCOAP .]]		FID Pos DI TV MO CDF
			Mid 1 bi ignore not-sent
			The decompressor must generate a value.
			[[Note; check id this field is not used by OSCOAP .]]
	To optimize information sent on the LPWAN, shorter values may be used		To optimize information sent on the LPWAN, shorter values may be used
	during the exchange, but Message ID values generated a common CoAP		during the exchange, but Message ID values generated a common CoAP
	implementation will not take into account this limitation. Before		implementation will not take into account this limitation. Before
	the compression, a proxy may be needed to reduce the size. In that		the compression, a proxy may be needed to reduce the size.
	case, the TV is set to 0x0000, MO is set to "MSB(l)" and CDF is set
	to "LSB(16-l)", where "l" is the size of the compressed header.
	Otherwise if no compression is needed the TV is not set, MO is set to		FID Pos DI TV MO CDF
	ignore and CDF is set to "not-sent".		Mid 1 bi 0x0000 MSB(12) LSB(4)
	4.6. CoAP Token field		Otherwise if no compression is possible, the field has to be sent
			FID Pos DI TV MO CDF
			Mid 1 bi ignore value-sent
			3.6. CoAP Token field
	This field is bi-directional.		This field is bi-directional.
	Token is used to identify transactions and varies from one		Token is used to identify transactions and varies from one
	transaction to another. Therefore, it is usually necessary to send		transaction to another. Therefore, it is usually necessary to send
	the value of the token field on the LPWAN network. The optimization		the value of the token field on the LPWAN network. The optimization
	will occur by using small values.		will occur by using small values.
	Common CoAP implementations may generate large tokens, even if		Common CoAP implementations may generate large tokens, even if
	shorter tokens could be used regarding the LPWAN characteristics. A		shorter tokens could be used regarding the LPWAN characteristics. A
	proxy may be needed to reduce the size of the token before		proxy may be needed to reduce the size of the token before
	compression.		compression.
	Otherwise the TV is not set, the MO is set to ignore and CDF is set		The size of the compress token sent is known by a combination of the
	to "value-sent".		Token Length field and the rule entry. For instance, with the entry
			below:
	The decompression may know the length of the token field from the		FID Pos DI TV MO CDF
	token length field.		tkl 1 bi 2 equal not-sent
			token 1 bi 0x00 MSB(12) LSB(4)
	4.7. CoAP option Content-format field.		The uncompressed token is 2 bytes long, but the compressed size will
			be 4 bits.
			4. CoAP options
			4.1. CoAP option Content-format field.
	This field is unidirectional and must not be set to bidirectional in		This field is unidirectional and must not be set to bidirectional in
	a rule entry. It is used only by the server to inform the client		a rule entry. It is used only by the server to inform the client
	about of the payload type and is never found in client requests.		about of the payload type and is never found in client requests.
	If the value is known by both sides, the TV contains that value and		If single value is expected by the client, the TV contains that value
	MO is set to "equal" and the CDF is set to "not-sent".		and MO is set to "equal" and the CDF is set to "not-sent". The
			examples below describe the rules for an ES acting as a server.
	Otherwise the TV is not set, MO is set to "ignore" and CDF is set to		FID Pos DI TV MO CDF
	"value-sent"		content 1 up value equal not-sent
	A mapping list can also be used to reduce the size.		If several possible value are expected by the client, a matching-list
			can be used.
	4.8. CoAP option Accept field		FID Pos DI TV MO CDF
			content 1 up {0:50,1:41} match-mapping mapping-sent
			Otherwise the value can be sent.The value-sent CDF in the compressor
			do not send the option type and the decompressor reconstruct it
			regarding the position in the rule.
			FID Pos DI TV MO CDF
			content 1 up ignore value-sent
			4.2. CoAP option Accept field
	This field is unidirectional and must not be set to bidirectional in		This field is unidirectional and must not be set to bidirectional in
	a rule entry. It is used only by the client to inform of the		a rule entry. It is used only by the client to inform of the
	possible payload type and is never found in server response.		possible payload type and is never found in server response.
	The number of accept options is not limited and can vary regarding		The number of accept options is not limited and can vary regarding
	the usage. To be selected a rule must contain the exact number about		the usage. To be selected a rule must contain the exact number about
	accept options with their positions.		accept options with their positions. Since the order in which the
			Accept value are sent, the position order can be modified. The rule
			below
	if the accept value must be sent, the TV contains that value, MO is		FID Pos DI TV MO CDF
	set to "ignore x" where "x" is the accept option's position and CDF		accept 1 up 41 egal not-sent
	is set to value-sent. Since the value length is not known, it must		accept 2 up 50 egal not-sent
	be sent as a CoAP TLV with delta-T set to 0.
	Otherwise the TV is not set, MO is set to "equal x" where x is the		will be selected only if two accept options are in the CoAP header if
	accept option's position and CDF is set to "not-sent"		this order.
	[[note: it could be more liberal and do not provide the same order		The rule below:
	after decompression]]
	4.9. CoAP option Max-Age field		FID Pos DI TV MO CDF
			accept 0 up 41 egal not-sent
			accept 0 up 50 egal not-sent
			will accept a-only CoAP messages with 2 accept options, but the order
			will not influence the rule selection. The decompression will
			reconstruct the header regarding the rule order.
			Otherwise a matching-list can be applied to the different values, in
			that case the order is important to recover the appropriate value and
			the position must be clearly indicate.
			FID Pos DI TV MO CDF
			accept 1 up {0:50,1:41} match-mapping mapping-sent
			accept 2 up {0:50,1:61} match-mapping mapping-sent
			accept 3 up {0:61,1:71} match-mapping mapping-sent
			Finally, the option can be explicitly sent.
			FID Pos DI TV MO CDF
			accept 1 up ignore value-sent
			4.3. CoAP option Max-Age field, CoAP option Uri-Host and Uri-Port
			fields
	This field is unidirectional and must not be set to bidirectional in		This field is unidirectional and must not be set to bidirectional in
	a rule entry. It is used only by the server to inform of the caching		a rule entry. It is used only by the server to inform of the caching
	duration and is never found in client requests.		duration and is never found in client requests.
	If the duration is known by both ends, the TV is set with this		If the duration is known by both ends, value can be elided on the
	duration, the MO is set to "equal" and the CDF is set to "not-sent".		LPWAN.
	Otherwise the TV is not set, the MO is set to "ignore" and the CDF is		A matching list can be used if some wellknown values are defined.
	set to "value-sent". Since the value length is not known, it must be
	sent as a CoAP TLV with delta-T set to 0.		Otherwise the option length and value can be sent on the LPWAN.
	[[note: we can reduce (or create a new option) the unit to minute,		[[note: we can reduce (or create a new option) the unit to minute,
	second is small for LPWAN ]]		second is small for LPWAN ]]
	4.10. CoAP option Uri-Host and Uri-Port fields		5. CoAP option Uri-Path and Uri-Query fields
	This fields are unidirectional and must not be set to bidirectional		This fields are unidirectional and must not be set to bidirectional
	in a rule entry. They are used only by the client to access to a		in a rule entry. They are used only by the client to access to a
	specific server and are never found in server response.		specific resource and are never found in server response.
	For each option, if the value is known by both ends, the TV is set		The Matching Operator behavior has not changed, but the value must
	with this value, the MO is set to "equal" and the CDF is set to "not-		take a position value, if the entry is repeated :
	sent".
	Otherwise the TV is not set, the MO is set to "ignore" and the CDF is		FID Pos DI TV MO CDF
	set to "value-sent". Since the value length is not known, it must be		URI-Path 1 up foo equal not-sent
	sent as a CoAP TLV with delta-T set to 0.		URI-Path 2 up bar equal not-sent
	4.11. CoAP option Uri-Path and Uri-Query fields		Figure 2: Position entry.
	This fields are unidirectional and must not be set to bidirectional		For instance, the rule Figure 2 matches with /foo/bar, but not /bar/
	in a rule entry. They are used only by the client to access to a		foo.
	specific resource and are never found in server response.
	Path and Query option may have different formats. Section 3.2 gives		When the length is not clearly indicated in the rule, the value
	some examples.		length must be sent with the field data, which means for CoAP to send
			directly the CoAP option with length and value.
	If the URI path as well as the query is composed of 2 or more		For instance for a CoMi path /c/X6?k="eth0" the rule can be set to:
	elements, then the position must be set in the MO parameters.
	If a Path or Query element is stable over the time, then TV is set		FID Pos DI TV MO CDF
	with its value, MO is set to "equal x" where x is the position in the		URI-Path 1 up c equal not-sent
	Path or the Query and CDF is set to "not-sent".		URI-Path 2 up ignore value-sent
			URI-Query 1 up k= MSB (16) LSB
	Otherwise if the value varies over time, TV is not set, MO is set to		Figure 3: CoMi URI compression
	"ignore x" where x is the position in the Path or in the Query and
	CDF is set to "value-sent". Since the value length is not known, it		Figure 3 shows the parsing and the compression of the URI. where c is
	must be sent as a CoAP TLV with deltaT set to 0.		not sent. The second element is sent with the length (i.e. 0x2 X 6)
			followed by the query option (i.e. 0x05 "eth0").
	A Mapping list can be used to reduce size of variable Paths or		A Mapping list can be used to reduce size of variable Paths or
	Queries. In that case, to optimize the compression, several elements		Queries. In that case, to optimize the compression, several elements
	can be regrouped into a single entry. Numbering of elements do not		can be regrouped into a single entry. Numbering of elements do not
	change, MO comparison is set with the first element of the matching.		change, MO comparison is set with the first element of the matching.
	For instance, the following Path /foo/bar/variable/stable can leads		FID Pos DI TV MO CDF
	to the rule defined Figure 4.		URI-Path 1 up {0:"/c/c", equal not-sent
			1:"/c/d"
	FID TV MO CDF		URI-Path 3 up ignore value-sent
			URI-Query 1 up k= MSB (16) LSB
	URI-Path {"/foo/bar":1, match-mapping 1 mapping-sent
	"/bar/foo":2}
	URI-Path ignore 3 value-sent
	URI-Path stable equal 4 not-sent
	Figure 4: complex path example		Figure 4: complex path example
	4.12. CoAP option Proxy-URI and Proxy-Scheme fields		For instance, the following Path /foo/bar/variable/stable can leads
			to the rule defined Figure 4.
			5.1. CoAP option Proxy-URI and Proxy-Scheme fields
	These fields are unidirectional and must not be set to bidirectional		These fields are unidirectional and must not be set to bidirectional
	in a rule entry. They are used only by the client to access to a		in a rule entry. They are used only by the client to access to a
	specific resource and are never found in server response.		specific resource and are never found in server response.
	If the field value must be sent, TV is not set, MO is set to "ignore"		If the field value must be sent, TV is not set, MO is set to "ignore"
	and CDF is set to "value-sent. A mapping can also be used.		and CDF is set to "value-sent. A mapping can also be used.
	Otherwise the TV is set to the value, MO is set to "equal" and CDF is		Otherwise the TV is set to the value, MO is set to "equal" and CDF is
	set to "not-sent"		set to "not-sent"
	4.13. CoAP option ETag, If-Match, If-None-Match, Location-Path and		5.2. CoAP option ETag, If-Match, If-None-Match, Location-Path and
	Location-Query fields		Location-Query fields
	These fields are unidirectional.		These fields are unidirectional.
	These fields values cannot be stored in a rule entry. They must		These fields values cannot be stored in a rule entry. They must
	always be sent with the request.		always be sent with the request.
	[[Can include OSCOAP Object security in that category ]]		[[Can include OSCOAP Object security in that category ]]
	5. Other RFCs		6. Other RFCs
	5.1. Block		6.1. Block
	Block option should be avoided in LPWAN. The minimum size of 16		Block option should be avoided in LPWAN. The minimum size of 16
	bytes can be incompatible with some LPWAN technologies.		bytes can be incompatible with some LPWAN technologies.
	[[Note: do we recommand LPWAN fragmentation since the smallest value		[[Note: do we recommand LPWAN fragmentation since the smallest value
	of 16 is too big?]]		of 16 is too big?]]
	5.2. Observe		6.2. Observe
	[RFC7641] defines the Observe option. The TV is not set, MO is set		[rfc7641] defines the Observe option. The TV is not set, MO is set
	to "ignore" and the CDF is set to "value-sent". SCHC does not limit		to "ignore" and the CDF is set to "value-sent". SCHC does not limit
	the maximum size for this option (3 bytes). To reduce the		the maximum size for this option (3 bytes). To reduce the
	transmission size either the Thing implementation should limit the		transmission size either the Thing implementation should limit the
	value increase or a proxy can be used limit the increase.		value increase or a proxy can be used limit the increase.
	Since RST message may be sent to inform a server that the client do		Since RST message may be sent to inform a server that the client do
	not require Observe response, a rule must allow the transmission of		not require Observe response, a rule must allow the transmission of
	this message.		this message.
	5.3. No-Response		6.3. No-Response
	[RFC7967] defines an No-Response option limiting the responses made		[rfc7967] defines an No-Response option limiting the responses made
	by a server to a request. If the value is not by both ends, then TV		by a server to a request. If the value is not by both ends, then TV
	is set to this value, MO is set to "equal" and CDF is set to "not-		is set to this value, MO is set to "equal" and CDF is set to "not-
	sent".		sent".
	Otherwise, if the value is changing over time, TV is not set, MO is		Otherwise, if the value is changing over time, TV is not set, MO is
	set to "ignore" and CDF to "value-sent". A matching list can also be		set to "ignore" and CDF to "value-sent". A matching list can also be
	used to reduce the size.		used to reduce the size.
	6. Examples of CoAP header compression		7. Protocol analysis
			8. Examples of CoAP header compression
	6.1. Mandatory header with CON message		8.1. Mandatory header with CON message
	In this first scenario, the LPWAN compressor receives from outside		In this first scenario, the LPWAN compressor receives from outside
	client a POST message, which is immediately acknowledged by the		client a POST message, which is immediately acknowledged by the
	Thing. For this simple scenario, the rules are described Figure 5.		Thing. For this simple scenario, the rules are described Figure 5.
	rule id 1		rule id 1
	+-------------+------+---------+-------------+-----+----------------+		+-------------+------+---------+-------------+-----+----------------+
	| Field |TV |MO |CDF |dir | Sent |		| Field |TV |MO |CDF |dir | Sent |
	+=============+======+=========+=============+=====+================+		+=============+======+=========+=============+=====+================+
	|CoAP version | 01 |equal |not-sent |bi | |		|CoAP version | 01 |equal |not-sent |bi | |
	|CoAP Type | |ignore |value-sent |bi |TT |		|CoAP Type | |ignore |value-sent |bi |TT |
	|CoAP TKL | 0 |equal |not-sent |bi | |		|CoAP TKL | 0 |equal |not-sent |bi | |
	|CoAP Code | ML1 |match-map|matching-sent|bi | CC CCC |		|CoAP Code | ML1 |match-map|matching-sent|bi | CC CCC |
	|CoAP MID | 0000 |MSB(7 ) |LSB(9) |bi | M-ID |		|CoAP MID | 0000 |MSB(7 ) |LSB(9) |bi | M-ID |
	|CoAP Uri-Path| path |equal 1 |not-sent |down | |		|CoAP Uri-Path| path |equal 1 |not-sent |down | |
	+-------------+------+---------+-------------+-----+----------------+		+-------------+------+---------+-------------+-----+----------------+
	Figure 5: CoAP Context to compress header without token		Figure 5: CoAP Context to compress header without token
	The version and Token Length fields are elided. Code has shrunk to 5		The version and Token Length fields are elided. Code has shrunk to 5
	bits using the matching list (as the one given Figure 3: 0.01 is		bits using the matching list (as the one given Figure 1: 0.01 is
	value 0x01 and 2.05 is value 0x0c) Message-ID has shrunk to 9 bits to		value 0x01 and 2.05 is value 0x0c) Message-ID has shrunk to 9 bits to
	preserve alignment on byte boundary. The most significant bit must		preserve alignment on byte boundary. The most significant bit must
	be set to 0 through a CoAP proxy. Uri-Path contains a single element		be set to 0 through a CoAP proxy. Uri-Path contains a single element
	indicated in the matching operator.		indicated in the matching operator.
	Figure 6 shows the time diagram of the exchange. A LPWAN Application		Figure 6 shows the time diagram of the exchange. A LPWAN Application
	Server sends a CON message. Compression reduces the header sending		Server sends a CON message. Compression reduces the header sending
	only the Type, a mapped code and the least 9 significant bits of		only the Type, a mapped code and the least 9 significant bits of
	Message ID. The receiver decompresses the header. .		Message ID. The receiver decompresses the header. .
	skipping to change at page 14, line 37 ¶		skipping to change at page 15, line 30 ¶
	+-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+--------+		+-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+--------+
	| | |1|2| 0|2.05| 0x0034 |		| | |1|2| 0|2.05| 0x0034 |
	v v +-+-+--+----+--------+		v v +-+-+--+----+--------+
	Figure 6: Compression with global addresses		Figure 6: Compression with global addresses
	The message can be further optimized by setting some fields		The message can be further optimized by setting some fields
	unidirectional, as described in Figure 7. Note that Type is no more		unidirectional, as described in Figure 7. Note that Type is no more
	sent in the compressed format, Compressed Code size in not changed in		sent in the compressed format, Compressed Code size in not changed in
	that example (8 values are needed to code all the requests and 21 to		that example (8 values are needed to code all the requests and 21 to
	code all the responses in the matching list Figure 3)		code all the responses in the matching list Figure 1)
	rule id 1		rule id 1
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	| Field |TV |MO |CDF |dir| Sent |		| Field |TV |MO |CDF |dir| Sent |
	+=============+======+=========+=============+===+================+		+=============+======+=========+=============+===+================+
	|CoAP version | 01 |equal |not-sent |bi | |		|CoAP version | 01 |equal |not-sent |bi | |
	|CoAP Type | CON |equal |not-sent |dw | |		|CoAP Type | CON |equal |not-sent |dw | |
	|CoAP Type | ACK |equal |not-sent |up | |		|CoAP Type | ACK |equal |not-sent |up | |
	|CoAP TKL | 0 |equal |not-sent |bi | |		|CoAP TKL | 0 |equal |not-sent |bi | |
	|CoAP Code | ML2 |match-map|matching-sent|dw |CCCC C |		|CoAP Code | ML2 |match-map|mapping-sent |dw |CCCC C |
	|CoAP Code | ML3 |match-map|matching-sent|up |CCCC C |		|CoAP Code | ML3 |match-map|mapping-sent |up |CCCC C |
	|CoAP MID | 0000 |MSB(5) |LSB(11) |bi | M-ID |		|CoAP MID | 0000 |MSB(5) |LSB(11) |bi | M-ID |
	|CoAP Uri-Path| path |equal 1 |not-sent |dw | |		|CoAP Uri-Path| path |equal 1 |not-sent |dw | |
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	ML1 = {CON : 0, ACK:1} ML2 = {POST:0, 2.04:1, 0.00:3}		ML1 = {CON : 0, ACK:1} ML2 = {POST:0, 2.04:1, 0.00:3}
	Figure 7: CoAP Context to compress header without token		Figure 7: CoAP Context to compress header without token
	6.2. Complete exchange		8.2. Complete exchange
	In that example, the Thing is using CoMi and sends queries for 2 SID.		In that example, the Thing is using CoMi and sends queries for 2 SID.
	CON		CON
	MID=0x0012 | |		MID=0x0012 | |
	POST | |		POST | |
	Accept X | |		Accept X | |
	/c/k=AS |------------------------>|		/c/k=AS |------------------------>|
	| |		| |
	| |		| |
	skipping to change at page 16, line 7 ¶		skipping to change at page 16, line 36 ¶
	rule id 3		rule id 3
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	| Field |TV |MO |CDF |dir| Sent |		| Field |TV |MO |CDF |dir| Sent |
	+=============+======+=========+=============+===+================+		+=============+======+=========+=============+===+================+
	|CoAP version | 01 |equal |not-sent |bi | |		|CoAP version | 01 |equal |not-sent |bi | |
	|CoAP Type | CON |equal |not-sent |up | |		|CoAP Type | CON |equal |not-sent |up | |
	|CoAP Type | ACK |equal |not-sent |dw | |		|CoAP Type | ACK |equal |not-sent |dw | |
	|CoAP TKL | 1 |equal |not-sent |bi | |		|CoAP TKL | 1 |equal |not-sent |bi | |
	|CoAP Code | POST |equal |not-sent |up | |		|CoAP Code | POST |equal |not-sent |up | |
	|CoAP Code | 0.00 |equal |not-sent |dw | |		|CoAP Code | 0.00 |equal |not-sent |dw | |
	|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM |		|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
	|CoAP Token | |ignore |send-value |up |TTTTTTTT |		|CoAP Token | |ignore |send-value |up |TTTTTTTT |
	|CoAP Uri-Path| /c |equal 1 |not-sent |dw | |		|CoAP Uri-Path| /c |equal 1 |not-sent |dw | |
	|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |		|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |
	|CoAP Content | X |equal |not-sent |up | |		|CoAP Content | X |equal |not-sent |up | |
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	rule id 4		rule id 4
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	| Field |TV |MO |CDF |dir| Sent |		| Field |TV |MO |CDF |dir| Sent |
	+=============+======+=========+=============+===+================+		+=============+======+=========+=============+===+================+
	|CoAP version | 01 |equal |not-sent |bi | |		|CoAP version | 01 |equal |not-sent |bi | |
	|CoAP Type | CON |equal |not-sent |dw | |		|CoAP Type | CON |equal |not-sent |dw | |
	|CoAP Type | ACK |equal |not-sent |up | |		|CoAP Type | ACK |equal |not-sent |up | |
	|CoAP TKL | 1 |equal |not-sent |bi | |		|CoAP TKL | 1 |equal |not-sent |bi | |
	|CoAP Code | 2.05 |equal |not-sent |dw | |		|CoAP Code | 2.05 |equal |not-sent |dw | |
	|CoAP Code | 0.00 |equal |not-sent |up | |		|CoAP Code | 0.00 |equal |not-sent |up | |
	|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM |		|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
	|CoAP Token | |ignore |send-value |dw |TTTTTTTT |		|CoAP Token | |ignore |send-value |dw |TTTTTTTT |
	|COAP Accept | X |equal |not-sent |dw | |		|COAP Accept | X |equal |not-sent |dw | |
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	alternative rule:		alternative rule:
	rule id 4		rule id 4
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	| Field |TV |MO |CDF |dir| Sent |		| Field |TV |MO |CDF |dir| Sent |
	+=============+======+=========+=============+===+================+		+=============+======+=========+=============+===+================+
	|CoAP version | 01 |equal |not-sent |bi | |		|CoAP version | 01 |equal |not-sent |bi | |
	|CoAP Type | ML1 |equal |match-sent(1)|bi |t |		|CoAP Type | ML1 |match-map|match-sent |bi |t |
	|CoAP TKL | 1 |equal |not-sent |bi | |		|CoAP TKL | 1 |equal |not-sent |bi | |
	|CoAP Code | ML2 |equal |match-sent(1)|up | cc |		|CoAP Code | ML2 |match-map|match-sent |up | cc |
	|CoAP Code | ML3 |equal |match-sent(2)|dw | cc |		|CoAP Code | ML3 |match-map|match-sent |dw | cc |
	|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM |		|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
	|CoAP Token | |ignore |send-value |dw |TTTTTTTT |		|CoAP Token | |ignore |send-value |dw |TTTTTTTT |
	|CoAP Uri-Path| /c |equal 1 |not-sent |dw | |		|CoAP Uri-Path| /c |equal 1 |not-sent |dw | |
	|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |		|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |
	|CoAP Content | X |equal |not-sent |up | |		|CoAP Content | X |equal |not-sent |up | |
	|COAP Accept | x |equal |not-sent |dw | |		|COAP Accept | x |equal |not-sent |dw | |
	+-------------+------+---------+-------------+---+----------------+		+-------------+------+---------+-------------+---+----------------+
	ML1 {CON:0, ACK:1} ML2 {POST:0, 0.00: 1} ML3 {2.05:0, 0.00:1}		ML1 {CON:0, ACK:1} ML2 {POST:0, 0.00: 1} ML3 {2.05:0, 0.00:1}
	ML4 {NULL:0, k=AS:1, K=AZE:2}		ML4 {NULL:0, k=AS:1, K=AZE:2}
	7. Normative References		9. Normative References
	[I-D.ietf-core-comi]
	Stok, P., Bierman, A., Veillette, M., and A. Pelov, "CoAP
	Management Interface", draft-ietf-core-comi-00 (work in
	progress), January 2017.
	[I-D.toutain-lpwan-ipv6-static-context-hc]		[I-D.toutain-lpwan-ipv6-static-context-hc]
	Minaburo, A. and L. Toutain, "LPWAN Static Context Header		Minaburo, A. and L. Toutain, "LPWAN Static Context Header
	Compression (SCHC) for IPv6 and UDP", draft-toutain-lpwan-		Compression (SCHC) for IPv6 and UDP", draft-toutain-lpwan-
	ipv6-static-context-hc-00 (work in progress), September		ipv6-static-context-hc-00 (work in progress), September
	2016.		2016.
	[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol		[rfc7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
	(IPCP)", RFC 1332, DOI 10.17487/RFC1332, May 1992,
	<http://www.rfc-editor.org/info/rfc1332>.
	[RFC3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
	Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
	K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
	Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
	Compression (ROHC): Framework and four profiles: RTP, UDP,
	ESP, and uncompressed", RFC 3095, DOI 10.17487/RFC3095,
	July 2001, <http://www.rfc-editor.org/info/rfc3095>.
	[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
	"Transmission of IPv6 Packets over IEEE 802.15.4
	Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
	<http://www.rfc-editor.org/info/rfc4944>.
	[RFC4997] Finking, R. and G. Pelletier, "Formal Notation for RObust
	Header Compression (ROHC-FN)", RFC 4997,
	DOI 10.17487/RFC4997, July 2007,
	<http://www.rfc-editor.org/info/rfc4997>.
	[RFC5225] Pelletier, G. and K. Sandlund, "RObust Header Compression
	Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and
	UDP-Lite", RFC 5225, DOI 10.17487/RFC5225, April 2008,
	<http://www.rfc-editor.org/info/rfc5225>.
	[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
	Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
	DOI 10.17487/RFC6282, September 2011,
	<http://www.rfc-editor.org/info/rfc6282>.
	[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
	Application Protocol (CoAP)", RFC 7252,		Application Protocol (CoAP)", RFC 7252,
	DOI 10.17487/RFC7252, June 2014,		DOI 10.17487/RFC7252, June 2014,
	<http://www.rfc-editor.org/info/rfc7252>.		<https://www.rfc-editor.org/info/rfc7252>.
	[RFC7641] Hartke, K., "Observing Resources in the Constrained		[rfc7641] Hartke, K., "Observing Resources in the Constrained
	Application Protocol (CoAP)", RFC 7641,		Application Protocol (CoAP)", RFC 7641,
	DOI 10.17487/RFC7641, September 2015,		DOI 10.17487/RFC7641, September 2015,
	<http://www.rfc-editor.org/info/rfc7641>.		<https://www.rfc-editor.org/info/rfc7641>.
	[RFC7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.		[rfc7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.
	Bose, "Constrained Application Protocol (CoAP) Option for		Bose, "Constrained Application Protocol (CoAP) Option for
	No Server Response", RFC 7967, DOI 10.17487/RFC7967,		No Server Response", RFC 7967, DOI 10.17487/RFC7967,
	August 2016, <http://www.rfc-editor.org/info/rfc7967>.		August 2016, <https://www.rfc-editor.org/info/rfc7967>.
	Authors' Addresses		Authors' Addresses
	Ana Minaburo		Ana Minaburo
	Acklio		Acklio
	2bis rue de la Chataigneraie		2bis rue de la Chataigneraie
	35510 Cesson-Sevigne Cedex		35510 Cesson-Sevigne Cedex
	France		France
	Email: ana@ackl.io		Email: ana@ackl.io
End of changes. 106 change blocks.
	371 lines changed or deleted		341 lines changed or added
This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/