draft-ietf-lpwan-coap-static-context-hc-08.txt		draft-ietf-lpwan-coap-static-context-hc-09.txt
	lpwan Working Group A. Minaburo		lpwan Working Group A. Minaburo
	Internet-Draft Acklio		Internet-Draft Acklio
	Intended status: Standards Track L. Toutain		Intended status: Standards Track L. Toutain
	Expires: November 30, 2019 Institut MINES TELECOM; IMT Atlantique		Expires: January 7, 2020 Institut MINES TELECOM; IMT Atlantique
	R. Andreasen		R. Andreasen
	Universidad de Buenos Aires		Universidad de Buenos Aires
	May 29, 2019		July 06, 2019
	LPWAN Static Context Header Compression (SCHC) for CoAP		LPWAN Static Context Header Compression (SCHC) for CoAP
	draft-ietf-lpwan-coap-static-context-hc-08		draft-ietf-lpwan-coap-static-context-hc-09
	Abstract		Abstract
	This draft defines the way SCHC header compression can be applied to		This draft defines the way SCHC header compression can be applied to
	CoAP headers. The CoAP header structure differs from IPv6 and UDP		CoAP headers. The CoAP header structure differs from IPv6 and UDP
	protocols since CoAP		protocols since CoAP uses a flexible header with a variable number of
	uses a flexible header with a variable number of options themselves		options, themselves of variable length. The CoAP protocol is
	of variable length. The CoAP protocol is asymmetric in its message		asymmetric in its message format: the format of the packet header in
	format, the format of the header packet in the request messages is		the request messages is different from that in the response messages.
	different from that in the response messages. Most of the		Most of the compression mechanisms have been introduced in
	compression mechanisms have been introduced in
	[I-D.ietf-lpwan-ipv6-static-context-hc], this document explains how		[I-D.ietf-lpwan-ipv6-static-context-hc], this document explains how
	to use the SCHC compression for CoAP.		to use the SCHC compression for CoAP.
	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 https://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 November 30, 2019.		This Internet-Draft will expire on January 7, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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
	(https://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
	skipping to change at page 2, line 28 ¶		skipping to change at page 2, line 25 ¶
	2. SCHC Compression Process . . . . . . . . . . . . . . . . . . 3		2. SCHC Compression Process . . . . . . . . . . . . . . . . . . 3
	3. CoAP Compression with SCHC . . . . . . . . . . . . . . . . . 4		3. CoAP Compression with SCHC . . . . . . . . . . . . . . . . . 4
	4. Compression of CoAP header fields . . . . . . . . . . . . . . 6		4. Compression of CoAP header fields . . . . . . . . . . . . . . 6
	4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 6		4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 6
	4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 6		4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 6
	4.3. CoAP code field . . . . . . . . . . . . . . . . . . . . . 6		4.3. CoAP code field . . . . . . . . . . . . . . . . . . . . . 6
	4.4. CoAP Message ID field . . . . . . . . . . . . . . . . . . 6		4.4. CoAP Message ID field . . . . . . . . . . . . . . . . . . 6
	4.5. CoAP Token fields . . . . . . . . . . . . . . . . . . . . 7		4.5. CoAP Token fields . . . . . . . . . . . . . . . . . . . . 7
	5. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 7		5. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 7
	5.1. CoAP Content and Accept options. . . . . . . . . . . . . 7		5.1. CoAP Content and Accept options. . . . . . . . . . . . . 7
	5.2. CoAP option Max-Age field, CoAP option Uri-Host and Uri-		5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields . . . . 7
	Port fields . . . . . . . . . . . . . . . . . . . . . . . 8
	5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 8		5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 8
	5.3.1. Variable length Uri-Path and Uri-Query . . . . . . . 8		5.3.1. Variable length Uri-Path and Uri-Query . . . . . . . 8
	5.3.2. Variable number of path or query elements . . . . . . 9		5.3.2. Variable number of path or query elements . . . . . . 9
	5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme		5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme
	fields . . . . . . . . . . . . . . . . . . . . . . . . . 9		fields . . . . . . . . . . . . . . . . . . . . . . . . . 9
	5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path		5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path
	and Location-Query fields . . . . . . . . . . . . . . . . 9		and Location-Query fields . . . . . . . . . . . . . . . . 9
	6. Other RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 10		6. Other RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 9
	6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 10		6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 10		6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 10
	6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 10		6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 10
	6.4. Time Scale . . . . . . . . . . . . . . . . . . . . . . . 10		6.4. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 10
	6.5. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 11		7. Examples of CoAP header compression . . . . . . . . . . . . . 11
	7. Examples of CoAP header compression . . . . . . . . . . . . . 12		7.1. Mandatory header with CON message . . . . . . . . . . . . 11
	7.1. Mandatory header with CON message . . . . . . . . . . . . 12		7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 12
	7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 13		7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 16
	7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 17		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27		9. Security considerations . . . . . . . . . . . . . . . . . . . 26
	9. Security considerations . . . . . . . . . . . . . . . . . . . 27		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27		11. Normative References . . . . . . . . . . . . . . . . . . . . 26
	11. Normative References . . . . . . . . . . . . . . . . . . . . 27		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
	1. Introduction		1. Introduction
	CoAP [rfc7252] is an implementation of the REST architecture for		CoAP [rfc7252] is an implementation of the REST architecture for
	constrained devices. Although CoAP was designed for constrained		constrained devices. Although CoAP was designed for constrained
	devices, the size of a CoAP header may still be too large for LPWAN		devices, the size of a CoAP header may still be too large for the
	constraints and some compression may be needed to reduce the header		constraints of Low Power Wide Area Networks (LPWAN) and some
	size.		compression may be needed to reduce the header size.
	[I-D.ietf-lpwan-ipv6-static-context-hc] defines a header compression		[I-D.ietf-lpwan-ipv6-static-context-hc] defines a header compression
	mechanism for LPWAN network based on a static context. The context		mechanism for LPWAN network based on a static context. The context
	is said static since the field description composing the Rules are		is said static since the field description composing the Rules are
	not learned during the packet exchanges but are previously defined.		not learned during the packet exchanges but are previously defined.
	The context(s) is(are) known by both ends before transmission.		The context(s) is(are) known by both ends before transmission.
	A context is composed of a set of rules that are referenced by Rule		A context is composed of a set of rules that are referenced by Rule
	IDs (identifiers). A rule contains an ordered list of the fields		IDs (identifiers). A rule contains an ordered list of the fields
	descriptions containing a field ID (FID), its length (FL) and its		descriptions containing a field ID (FID), its length (FL) and its
	position (FP), a direction indicator (DI) (upstream, downstream and		position (FP), a direction indicator (DI) (upstream, downstream and
	bidirectional) and some associated Target Values (TV). Target Value		bidirectional) and some associated Target Values (TV). Target Value
	indicates the value that can be expected. TV can also be a list of		indicates the value that can be expected. TV can also be a list of
	values. A Matching Operator (MO) is associated to each header field		values. A Matching Operator (MO) is associated to each header field
	description. The rule is selected if all the MOs fit the TVs for all		description. The rule is selected if all the MOs fit the TVs for all
	fields. In that case, a Compression/Decompression Action (CDA)		fields of the incoming packet. In that case, a Compression/
	associated to each field defines the link between the compressed and		Decompression Action (CDA) associated to each field defines how the
	decompressed value for each of the header fields. Compression		compressed and the decompressed values are computed out of each
	results mainly in 4 actions: send the field value, send nothing, send		other, for each of the header fields. Compression mainly results in
	less significant bits of a field, send an index. Values sent are		one of 4 actions: send the field value, send nothing, send some least
	called Compression Residues and follows the rule ID.		significant bits of the field or send an index. Values sent are
			called Compression Residues and follow the rule ID in the transmitted
			message.
			The compression rules define a generic way to compress and decompress
			the fields. If the device is modified, for example, to introduce new
			functionalities or new CoAP options, the rules must be updated to
			reflect the evolution. There is no risk to lock a device in a
			particular version of CoAP.
	2. SCHC Compression Process		2. SCHC Compression Process
	The SCHC Compression rules can be applied to CoAP flows. SCHC		The SCHC Compression rules can be applied to CoAP flows. SCHC
	Compression of the CoAP header MAY be done in conjunction with the		Compression of the CoAP header MAY be done in conjunction with the
	above layers (IPv6/UDP) or independently. The SCHC adaptation layers		lower layers (IPv6/UDP) or independently. The SCHC adaptation layers
	as described in [I-D.ietf-lpwan-ipv6-static-context-hc] may be used		as described in [I-D.ietf-lpwan-ipv6-static-context-hc] may be used
	as shown in Figure 1.		as shown in Figure 1.
	^ +------------+ ^ +------------+ ^ +------------+		^ +------------+ ^ +------------+ ^ +------------+
	| | CoAP | | | CoAP | inner | | CoAP |		| | CoAP | | | CoAP | inner | | CoAP |
	| +------------+ v +------------+ x | OSCORE |		| +------------+ v +------------+ x | OSCORE |
	| | UDP | | DTLS | outer | +------------+		| | UDP | | DTLS | outer | +------------+
	| +------------+ +------------+ | | UDP |		| +------------+ +------------+ | | UDP |
	| | IPv6 | | UDP | | +------------+		| | IPv6 | | UDP | | +------------+
	v +------------+ +------------+ | | IPv6 |		v +------------+ +------------+ | | IPv6 |
	| IPv6 | v +------------+		| IPv6 | v +------------+
	+------------+		+------------+
	Figure 1: rule scope for CoAP		Figure 1: rule scope for CoAP
	Figure 1 shows some examples for CoAP architecture and the SCHC		Figure 1 shows some examples for CoAP architecture and the SCHC
	rule's scope. A rule can cover all headers from IPv6 to CoAP, in		rule's scope.
	which case SCHC C/D is performed at the device and at the LPWAN
	boundary. If an end-to-end encryption mechanisms is used between the		In the first example, a rule compresses all headers from IPv6 to
	device and the application, CoAP MAY be compressed independently of		CoAP. In this case, SCHC C/D is performed at the device and at the
	the other layers. The rule ID and the compression residue are		LPWAN boundary.
	encrypted using a mechanism such as DTLS. Only the other end can
	decipher the information.		In the second example, an end-to-end encryption mechanisms is used
			between the device and the application. CoAP is compressed
			independently of the other layers. The rule ID and the compression
			residue are encrypted using a mechanism such as DTLS. Only the other
			end can decipher the information.
	Layers below may also be compressed using other SCHC rules (this is		Layers below may also be compressed using other SCHC rules (this is
	out of the scope of this document). OSCORE		out of the scope of this document).
	[I-D.ietf-core-object-security] can also define 2 rules to compress
	the CoAP message. A first rule focuses on the inner header and is		In the third example, OSCORE [I-D.ietf-core-object-security] is used.
	end to end, a second rule may compress the outer header and the		2 rulesets are used to compress the CoAP message. A first ruleset
	layers below. SCHC C/D for inner header is done by both ends, SCHC		focuses on the inner header and is end to end, a second ruleset
	C/D for outer header and other headers is done between the device and		compresses the outer header and the layers below. SCHC C/D for inner
	the LPWAN boundary.		header is done by both ends, and SCHC C/D for outer header and other
			headers is done between the device and the LPWAN boundary.
	3. CoAP Compression with SCHC		3. CoAP Compression with SCHC
	CoAP differs from IPv6 and UDP protocols on the following aspects:		CoAP differs from IPv6 and UDP protocols on the following 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 the location in the		in the request and in the response, with the value of some fields
	header may vary (e.g. source and destination fields). A CoAP		being swapped on the return path (e.g. source and destination
	request is different from a response. For example, the URI-path		fields). A CoAP request is intrinsically different from a
	option is mandatory in the request and is not found in the		response. For example, the URI-path option is mandatory in the
	response, a request may contain an Accept option and the response		request and is not found in the response, a request may contain an
	a Content option.		Accept option and the response a Content option.
	[I-D.ietf-lpwan-ipv6-static-context-hc] defines the use of a		[I-D.ietf-lpwan-ipv6-static-context-hc] defines the use of a
	message direction (DI) in the Field Description, which allows a		message direction (DI) in the Field Description, which allows a
	single Rule to process message headers differently in both		single Rule to process message headers differently depending of
	directions.		the direction.
	o Even when a field is "symmetric" (i.e. found in both directions)		o Even when a field is "symmetric" (i.e. found in both directions)
	the values carried in each direction are different. Combined with		the values carried in each direction are different. Combined with
	a matching list in the TV, this allows reducing the range of		a matching list in the TV, this allows reducing the range of
	expected values in a particular direction and therefore reduce the		expected values in a particular direction and therefore reduce the
	size of the compression residue. For instance, if a client sends		size of the compression residue. For instance, if a client sends
	only CON request, the type can be elided by compression and the		only CON request, the type can be elided by compression and the
	answer may use one single bit to carry either the ACK or RST type.		answer may use one single bit to carry either the ACK or RST type.
	The same behavior can be applied to the CoAP Code field (0.0X code		The same behavior can be applied to the CoAP Code field (0.0X code
	are present in the request and Y.ZZ in the answer). The direction		are present in the request and Y.ZZ in the answer). The direction
	skipping to change at page 5, line 25 ¶		skipping to change at page 5, line 30 ¶
	direction.		direction.
	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, the length being given by a field		size may vary from 0 to 8 bytes, the length being given by a field
	in the header. More systematically, the CoAP options are		in the header. More systematically, the CoAP options are
	described using the Type-Length-Value.		described using the Type-Length-Value.
	[I-D.ietf-lpwan-ipv6-static-context-hc] offers the possibility to		[I-D.ietf-lpwan-ipv6-static-context-hc] offers the possibility to
	define a function for the Field Length in the Field Description.		define a function for the Field Length in the Field Description.
	o In CoAP headers, a field can be present several times. This is		o In CoAP headers, a field can appear several times. This is
	typical for elements of an URI (path or queries). The position		typical for elements of a URI (path or queries).
	defined in a rule, associated to a Field ID, can be used to
	identify the proper instance.
	[I-D.ietf-lpwan-ipv6-static-context-hc] allows a Field ID to		[I-D.ietf-lpwan-ipv6-static-context-hc] allows a Field ID to
	appears several times in the rule, the Field Position (FP) removes		appears several times in the rule, the Field Position (FP)
	ambiguities for the matching operation.		identifies the proper instance, thereby removing the ambiguity of
			the matching operation.
	o Field sizes defined in the CoAP protocol can be too large		o Field sizes defined in the CoAP protocol can be too large
	regarding LPWAN traffic constraints. This is particularly true		regarding LPWAN traffic constraints. This is particularly true
	for the message ID field or Token field. The MSB MO can be used		for the message ID field or Token field. The MSB MO can be used
	to reduce the information carried on LPWANs.		to reduce the information carried on LPWANs.
	o CoAP also obeys the client/server paradigm and the compression		o CoAP also obeys the client/server paradigm and the compression
	ratio can be different if the request is issued from an LPWAN		ratio can be different if the request is issued from an LPWAN
	device or from an non LPWAN device. For instance a Device (Dev)		device or from a non LPWAN device. For instance a Device (Dev)
	aware of LPWAN constraints can generate a 1 byte token, but a		aware of LPWAN constraints can generate a 1 byte token, but a
	regular CoAP client will certainly send a larger token to the Dev.		regular CoAP client will certainly send a larger token to the Dev.
	SCHC compression will not modify the values to offer a better		The SCHC compression-decompression process does not modify the
	compression rate. Nevertheless, a proxy placed before the		values. Nevertheless, a proxy placed before the compressor may
	compressor may change some field values to offer a better		change some field values to allow SCHC achieving a better
	compression ratio and maintain the necessary context for		compression ratio, while maintaining the necessary context for
	interoperability with existing CoAP implementations.		interoperability with existing CoAP implementations.
	4. Compression of CoAP header fields		4. Compression of CoAP header fields
	This section discusses the compression of the different CoAP header		This section discusses the compression of the different CoAP header
	fields.		fields.
	4.1. CoAP version field		4.1. CoAP version field
	This field is bidirectional and MUST be elided during the SCHC		This field is bidirectional and MUST be elided during the SCHC
	compression, since it always contains the same value. In the future,		compression, since it always contains the same value. In the future,
	if new versions of CoAP are defined, new rules will be defined to		if new versions of CoAP are defined, new rules will be defined to
	avoid ambiguities between versions.		avoid ambiguities between versions.
	4.2. CoAP type field		4.2. CoAP type field
	[rfc7252] defines 4 types of messages: CON, NON, ACK and RST. The		[rfc7252] defines 4 types of messages: CON, NON, ACK and RST. The
	last two are a response to the first two. If the device plays a		last two are a response to the first two. If the device plays a
	specific role, a rule can exploit these properties with the mapping		specific client or server role, a rule can exploit these properties
	list: [CON, NON] for one direction and [ACK, RST] for the other		with the mapping list: [CON, NON] for one direction and [ACK, RST]
	direction. Compression residue is reduced to 1 bit.		for the other direction. The compression residue is reduced to 1
			bit.
	The field SHOULD be elided if for instance a client is sending only		The field SHOULD be elided if for instance a client is sending only
	NON or CON messages.		NON or only CON messages.
	In any case, a rule MUST be defined to carry RST to a client.		In any case, a rule MUST be defined to carry RST to a client.
	4.3. CoAP code field		4.3. CoAP code field
	The compression of the CoAP code field follows the same principle as		The compression of the CoAP code field follows the same principle as
	for the CoAP type field. If the device plays a specific role, the		that of the CoAP type field. If the device plays a specific role,
	set of code values can be split in two parts, the request codes with		the set of code values can be split in two parts, the request codes
	the 0 class and the response values.		with the 0 class and the response values.
	If the device only implements a CoAP client, the request code can be		If the device only implements a CoAP client, the request code can be
	reduced to the set of requests the client is able to process.		reduced to the set of requests the client is able to process.
	All the response codes MUST be compressed with a SCHC rule.		All the response codes MUST be compressed with a SCHC rule.
	4.4. CoAP Message ID field		4.4. CoAP Message ID field
	This field is bidirectional and is used to manage acknowledgments.		This field is bidirectional and is used to manage acknowledgments.
	The server memorizes the value for a EXCHANGE_LIFETIME period (by		The server memorizes the value for a EXCHANGE_LIFETIME period (by
	skipping to change at page 8, line 5 ¶		skipping to change at page 7, line 48 ¶
	These fields are both unidirectional and MUST NOT be set to		These fields are both unidirectional and MUST NOT be set to
	bidirectional in a rule entry.		bidirectional in a rule entry.
	If a single value is expected by the client, it can be stored in the		If a single value is expected by the client, it can be stored in the
	TV and elided during the transmission. Otherwise, if several		TV and elided during the transmission. Otherwise, if several
	possible values are expected by the client, a matching-list SHOULD be		possible values are expected by the client, a matching-list SHOULD be
	used to limit the size of the residue. If is not possible, the value		used to limit the size of the residue. If is not possible, the value
	has to be sent as a residue (fixed or variable length).		has to be sent as a residue (fixed or variable length).
	5.2. CoAP option Max-Age field, CoAP option Uri-Host and Uri-Port		5.2. CoAP option Max-Age, Uri-Host and Uri-Port fields
	fields
	These fields is unidirectional and MUST NOT be set to bidirectional		These fields are unidirectional and MUST NOT be set to bidirectional
	in a rule entry. It is used only by the server to inform of the		in a rule entry. They are used only by the server to inform of the
	caching duration and is never found in client requests.		caching duration and is never found in client requests.
	If the duration is known by both ends, the value can be elided on the		If the duration is known by both ends, the value can be elided on the
	LPWAN.		LPWAN.
	A matching list can be used if some well-known values are defined.		A matching list can be used if some well-known values are defined.
	Otherwise these options SHOULD be sent as a residue (fixed or		Otherwise these options SHOULD be sent as a residue (fixed or
	variable length).		variable length).
	skipping to change at page 10, line 37 ¶		skipping to change at page 10, line 29 ¶
	[rfc7967] defines a No-Response option limiting the responses made by		[rfc7967] defines a No-Response option limiting the responses made by
	a server to a request. If the value is known by both ends, then TV		a server to a request. If the value is known by both ends, then TV
	is set to this value, MO is set to "equal" and CDA is set to "not-		is set to this value, MO is set to "equal" and CDA 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 CDA to "value-sent". A matching list can also be		set to "ignore" and CDA to "value-sent". A matching list can also be
	used to reduce the size.		used to reduce the size.
	6.4. Time Scale		6.4. OSCORE
	The time scale [I-D.toutain-core-time-scale] option allows a client
	to inform the server that it is in a constrained network and that
	message ID MUST be kept for a duration given by the option.
	If the value is known by both ends, then TV is set to this value, MO
	is set to "equal" and CDA is set to "not-sent".
	Otherwise, if the value is changing over time, TV is not set, MO is
	set to "ignore" and CDA to "value-sent". A matching list can also be
	used to reduce the size.
	6.5. OSCORE
	OSCORE [I-D.ietf-core-object-security] defines end-to-end protection		OSCORE [I-D.ietf-core-object-security] defines end-to-end protection
	for CoAP messages. This section describes how SCHC rules can be		for CoAP messages. This section describes how SCHC rules can be
	applied to compress OSCORE-protected messages.		applied to compress OSCORE-protected messages.
	0 1 2 3 4 5 6 7 <--------- n bytes ------------->		0 1 2 3 4 5 6 7 <--------- n bytes ------------->
	+-+-+-+-+-+-+-+-+---------------------------------		+-+-+-+-+-+-+-+-+---------------------------------
	|0 0 0|h|k| n | Partial IV (if any) ...		|0 0 0|h|k| n | Partial IV (if any) ...
	+-+-+-+-+-+-+-+-+---------------------------------		+-+-+-+-+-+-+-+-+---------------------------------
	| | |		| | |
	skipping to change at page 12, line 4 ¶		skipping to change at page 11, line 29 ¶
	This draft recommends to implement a parser that is able to identify		This draft recommends to implement a parser that is able to identify
	the OSCORE Option and the fields it contains.		the OSCORE Option and the fields it contains.
	Conceptually, it discerns up to 4 distinct pieces of information		Conceptually, it discerns up to 4 distinct pieces of information
	within the OSCORE option: the flag bits, the piv, the kid context,		within the OSCORE option: the flag bits, the piv, the kid context,
	and the kid. It is thus recommended that the parser split the OSCORE		and the kid. It is thus recommended that the parser split the OSCORE
	option into the 4 subsequent fields:		option into the 4 subsequent fields:
	o CoAP OSCORE_flags,		o CoAP OSCORE_flags,
	o CoAP OSCORE_piv,		o CoAP OSCORE_piv,
	o CoAP OSCORE_kidctxt,		o CoAP OSCORE_kidctxt,
	o CoAP OSCORE_kid.		o CoAP OSCORE_kid.
	These fields are shown superimposed on the OSCORE Option format in		These fields are shown superimposed on the OSCORE Option format in
	Figure 4, the CoAP OSCORE_kidctxt field including the size bits s.		Figure 4, the CoAP OSCORE_kidctxt field including the size bits s.
	Their size SHOULD be reduced using the MSB matching operator.		Their size SHOULD be reduced using SCHC compression.
	7. Examples of CoAP header compression		7. Examples of CoAP header compression
	7.1. Mandatory header with CON message		7.1. Mandatory header with CON message
	In this first scenario, the LPWAN compressor at the Network Gateway		In this first scenario, the LPWAN compressor at the Network Gateway
	side receives from a client on the Internet a POST message, which is		side receives from a client on the Internet a POST message, which is
	immediately acknowledged by the Device. For this simple scenario,		immediately acknowledged by the Device. For this simple scenario,
	the rules are described Figure 5.		the rules are described Figure 5.
	Rule ID 1		Rule ID 1
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	| Field |FL|FP|DI|Target| Match | CDA || Sent |		| Field |FL|FP|DI|Target| Match | CDA || Sent |
	| | | | |Value | Opera. | || [bits] |		| | | | |Value | Opera. | || [bits] |
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	|CoAP version | | |bi| 01 |equal |not-sent || |		|CoAP version | | |bi| 01 |equal |not-sent || |
	|CoAP version | | |bi| 01 |equal |not-sent || |
	|CoAP Type | | |dw| CON |equal |not-sent || |		|CoAP Type | | |dw| CON |equal |not-sent || |
	|CoAP Type | | |up|[ACK, | | || |		|CoAP Type | | |up|[ACK, | | || |
	| | | | | RST] |match-map|matching-sent|| T |		| | | | | RST] |match-map|matching-sent|| T |
	|CoAP TKL | | |bi| 0 |equal |not-sent || |		|CoAP TKL | | |bi| 0 |equal |not-sent || |
	|CoAP Code | | |bi| ML1 |match-map|matching-sent|| CC CCC |		|CoAP Code | | |bi|[0.00,| | || |
	|CoAP MID | | |bi| 0000 |MSB(7 ) |LSB(9) || M-ID|		| | | | | ... | | || |
			| | | | | 5.05]|match-map|matching-sent|| CC CCC |
			|CoAP MID | | |bi| 0000 |MSB(7 ) |LSB || M-ID|
	|CoAP Uri-Path| | |dw| path |equal 1 |not-sent || |		|CoAP Uri-Path| | |dw| path |equal 1 |not-sent || |
	+-------------+--+--+--+------+---------+-------------++------------+		+-------------+--+--+--+------+---------+-------------++------------+
	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. The 26 method and
	bits using a matching list. Uri-Path contains a single element		response codes defined in [rfc7252] has been shrunk to 5 bits using a
	indicated in the matching operator.		matching list. Uri-Path contains a single element indicated in the
			matching operator.
	Figure 6 shows the time diagram of the exchange. A client in the
	Application Server sends a CON request. It can go through a proxy
	which reduces the message ID to a smallest value, with at least the 9
	most significant bits equal to 0. SCHC Compression reduces the
	header sending only the Type, a mapped code and the least 9
	significant bits of Message ID.
	Device LPWAN SCHC C/D		SCHC Compression reduces the header sending only the Type, a mapped
	| |		code and the least significant bits of Message ID (9 bits in the
	| rule id=1 |<--------------------		example above).
	|<-------------------| +-+-+--+----+------+
	<------------------- | CCCCCMMMMMMMMM | |1|0| 4|0.01|0x0034|
	+-+-+--+----+-------+ | 00001000110100 | | 0xb4 p a t|
	|1|0| 1|0.01|0x0034 | | | | h |
	| 0xb4 p a t | | | +------+
	| h | | |
	+------+ | |
	| |
	| |
	---------------------->| rule id=1 |
	+-+-+--+----+--------+ |------------------->|
	|1|2| 0|2.05| 0x0034 | | TCCCCCMMMMMMMMM |--------------------->
	+-+-+--+----+--------+ | 001100000110100 | +-+-+--+----+------+
	| | |1|2| 0|2.05|0x0034|
	v v +-+-+--+----+------+
	Figure 6: Compression with global addresses		Note that a request sent by a client located an Application Server to
			a server in the device, may not be compressed through this rule since
			the MID will not start with 7 bits equal to 0. A CoAP proxy, before
			the core SCHC C/D can rewrite the message ID to a value matched by
			the rule.
	7.2. OSCORE Compression		7.2. OSCORE Compression
	OSCORE aims to solve the problem of end-to-end encryption for CoAP		OSCORE aims to solve the problem of end-to-end encryption for CoAP
	messages. The goal, therefore, is to hide as much of the message as		messages. The goal, therefore, is to hide as much of the message as
	possible while still enabling proxy operation.		possible while still enabling proxy operation.
	Conceptually this is achieved by splitting the CoAP message into an		Conceptually this is achieved by splitting the CoAP message into an
	Inner Plaintext and Outer OSCORE Message. The Inner Plaintext		Inner Plaintext and Outer OSCORE Message. The Inner Plaintext
	contains sensible information which is not necessary for proxy		contains sensible information which is not necessary for proxy
	operation. This, in turn, is the part of the message which can be		operation. This, in turn, is the part of the message which can be
	encrypted until it reaches its end destination. The Outer Message		encrypted until it reaches its end destination. The Outer Message
	acts as a shell matching the format of a regular CoAP message, and		acts as a shell matching the format of a regular CoAP message, and
	includes all Options and information needed for proxy operation and		includes all Options and information needed for proxy operation and
	caching. This decomposition is illustrated in Figure 7.		caching. This decomposition is illustrated in Figure 6.
	CoAP options are sorted into one of 3 classes, each granted a		CoAP options are sorted into one of 3 classes, each granted a
	specific type of protection by the protocol:		specific type of protection by the protocol:
	o Class E: Encrypted options moved to the Inner Plaintext,		o Class E: Encrypted options moved to the Inner Plaintext,
	o Class I: Integrity-protected options included in the AAD for the		o Class I: Integrity-protected options included in the AAD for the
	encryption of the Plaintext but otherwise left untouched in the		encryption of the Plaintext but otherwise left untouched in the
	Outer Message,		Outer Message,
	skipping to change at page 14, line 44 ¶		skipping to change at page 14, line 38 ¶
	+-+-+---+--------+---------------+....+ +-------+-----......+		+-+-+---+--------+---------------+....+ +-------+-----......+
	| Token | | Options (E) |		| Token | | Options (E) |
	+--------------------------------.....+ +-------+------.....+		+--------------------------------.....+ +-------+------.....+
	| Options (IU) | | OxFF |		| Options (IU) | | OxFF |
	. . +-------+-----------+		. . +-------+-----------+
	. OSCORE Option . | |		. OSCORE Option . | |
	+------+-------------------+ | Payload |		+------+-------------------+ | Payload |
	| 0xFF | | |		| 0xFF | | |
	+------+ +-------------------+		+------+ +-------------------+
	Figure 7: OSCORE inner and outer header form a CoAP message		Figure 6: A CoAP message is split into an OSCORE outer and plaintext
	Figure 7 shows the message format for the OSCORE Message and		Figure 6 shows the message format for the OSCORE Message and
	Plaintext.		Plaintext.
	In the Outer Header, the original message code is hidden and replaced		In the Outer Header, the original message code is hidden and replaced
	by a default dummy value. As seen in sections 4.1.3.5 and 4.2 of		by a default dummy value. As seen in sections 4.1.3.5 and 4.2 of
	[I-D.ietf-core-object-security], the message code is replaced by POST		[I-D.ietf-core-object-security], the message code is replaced by POST
	for requests and Changed for responses when Observe is not used. If		for requests and Changed for responses when Observe is not used. If
	Observe is used, the message code is replaced by FETCH for requests		Observe is used, the message code is replaced by FETCH for requests
	and Content for responses.		and Content for responses.
	The original message code is put into the first byte of the		The original message code is put into the first byte of the
	Plaintext. Following the message code, the class E options comes and		Plaintext. Following the message code, the class E options comes and
	if present the original message Payload is preceded by its payload		if present the original message Payload is preceded by its payload
	marker.		marker.
	skipping to change at page 15, line 19 ¶		skipping to change at page 15, line 11 ¶
	The original message code is put into the first byte of the		The original message code is put into the first byte of the
	Plaintext. Following the message code, the class E options comes and		Plaintext. Following the message code, the class E options comes and
	if present the original message Payload is preceded by its payload		if present the original message Payload is preceded by its payload
	marker.		marker.
	The Plaintext is now encrypted by an AEAD algorithm which integrity		The Plaintext is now encrypted by an AEAD algorithm which integrity
	protects Security Context parameters and eventually any class I		protects Security Context parameters and eventually any class I
	options from the Outer Header. Currently no CoAP options are marked		options from the Outer Header. Currently no CoAP options are marked
	class I. The resulting Ciphertext becomes the new Payload of the		class I. The resulting Ciphertext becomes the new Payload of the
	OSCORE message, as illustrated in Figure 8.		OSCORE message, as illustrated in Figure 7.
	This Ciphertext is, as defined in RFC 5116, the concatenation of the		This Ciphertext is, as defined in RFC 5116, the concatenation of the
	encrypted Plaintext and its authentication tag. Note that Inner		encrypted Plaintext and its authentication tag. Note that Inner
	Compression only affects the Plaintext before encryption, thus we can		Compression only affects the Plaintext before encryption, thus we can
	only aim to reduce this first, variable length component of the		only aim to reduce this first, variable length component of the
	Ciphertext. The authentication tag is fixed in length and considered		Ciphertext. The authentication tag is fixed in length and considered
	part of the cost of protection.		part of the cost of protection.
	Outer Header		Outer Header
	+-+-+---+--------+---------------+		+-+-+---+--------+---------------+
	|v|t|tkl|new code| Msg Id. |		|v|t|tkl|new code| Msg Id. |
	+-+-+---+--------+---------------+....+		+-+-+---+--------+---------------+....+
	| Token |		| Token |
	+--------------------------------.....+		+--------------------------------.....+
	| Options (IU) |		| Options (IU) |
	. .		. .
	. OSCORE Option .		. OSCORE Option .
	+------+-------------------+		+------+-------------------+
	| 0xFF |		| 0xFF |
	+------+-------------------------+		+------+---------------------------+
	| |		| |
	| Encrypted Inner Header and |		| Ciphertext: Encrypted Inner |
	| Payload |		| Header and Payload |
	| |		| + Authentication Tag |
	+--------------------------------+		| |
			+----------------------------------+
	Figure 8: OSCORE message		Figure 7: OSCORE message
	The SCHC Compression scheme consists of compressing both the		The SCHC Compression scheme consists of compressing both the
	Plaintext before encryption and the resulting OSCORE message after		Plaintext before encryption and the resulting OSCORE message after
	encryption, see Figure 9.		encryption, see Figure 8.
	This translates into a segmented process where SCHC compression is		This translates into a segmented process where SCHC compression is
	applied independently in 2 stages, each with its corresponding set of		applied independently in 2 stages, each with its corresponding set of
	rules, with the Inner SCHC Rules and the Outer SCHC Rules. This way		rules, with the Inner SCHC Rules and the Outer SCHC Rules. This way
	compression is applied to all fields of the original CoAP message.		compression is applied to all fields of the original CoAP message.
	Note that since the Inner part of the message can only be decrypted		Note that since the Inner part of the message can only be decrypted
	by the corresponding end-point, this end-point will also have to		by the corresponding end-point, this end-point will also have to
	implement Inner SCHC Compression/Decompression.		implement Inner SCHC Compression/Decompression.
	skipping to change at page 16, line 50 ¶		skipping to change at page 16, line 41 ¶
	v | +-------+--+		v | +-------+--+
	+--------+ +------------+ | Residue |		+--------+ +------------+ | Residue |
	|Rule ID'| | Encryption | <--- +----------+--------+		|Rule ID'| | Encryption | <--- +----------+--------+
	+--------+--+ +------------+ | |		+--------+--+ +------------+ | |
	| Residue' | | Payload |		| Residue' | | Payload |
	+-----------+-------+ | |		+-----------+-------+ | |
	| Ciphertext | +-------------------+		| Ciphertext | +-------------------+
	| |		| |
	+-------------------+		+-------------------+
	Figure 9: OSCORE Compression Diagram		Figure 8: OSCORE Compression Diagram
	7.3. Example OSCORE Compression		7.3. Example OSCORE Compression
	An example is given with a GET Request and its consequent CONTENT		An example is given with a GET Request and its consequent CONTENT
	Response. A possible set of rules for the Inner and Outer SCHC		Response from a device-based CoAP client to a cloud-based CoAP
			server. A possible set of rules for the Inner and Outer SCHC
	Compression is shown. A dump of the results and a contrast between		Compression is shown. A dump of the results and a contrast between
	SCHC + OSCORE performance with SCHC + COAP performance is also		SCHC + OSCORE performance with SCHC + COAP performance is also
	listed. This gives an approximation to the cost of security with		listed. This gives an approximation to the cost of security with
	SCHC-OSCORE.		SCHC-OSCORE.
	Our first example CoAP message is the GET Request in Figure 10		Our first example CoAP message is the GET Request in Figure 9
	Original message:		Original message:
	=================		=================
	0x4101000182bb74656d7065726174757265		0x4101000182bb74656d7065726174757265
	Header:		Header:
	0x4101		0x4101
	01 Ver		01 Ver
	00 CON		00 CON
	0001 tkl		0001 tkl
	skipping to change at page 17, line 37 ¶		skipping to change at page 17, line 28 ¶
	0x0001 = mid		0x0001 = mid
	0x82 = token		0x82 = token
	Options:		Options:
	0xbb74656d7065726174757265		0xbb74656d7065726174757265
	Option 11: URI_PATH		Option 11: URI_PATH
	Value = temperature		Value = temperature
	Original msg length: 17 bytes.		Original msg length: 17 bytes.
	Figure 10: CoAP GET Request		Figure 9: CoAP GET Request
	Its corresponding response is the CONTENT Response in Figure 11.		Its corresponding response is the CONTENT Response in Figure 10.
	Original message:		Original message:
	=================		=================
	0x6145000182ff32332043		0x6145000182ff32332043
	Header:		Header:
	0x6145		0x6145
	01 Ver		01 Ver
	10 ACK		10 ACK
	0001 tkl		0001 tkl
	skipping to change at page 18, line 25 ¶		skipping to change at page 17, line 52 ¶
	0x0001 = mid		0x0001 = mid
	0x82 = token		0x82 = token
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0x32332043		0x32332043
	Original msg length: 10		Original msg length: 10
	Figure 11: CoAP CONTENT Response		Figure 10: CoAP CONTENT Response
	The SCHC Rules for the Inner Compression include all fields that are		The SCHC Rules for the Inner Compression include all fields that are
	already present in a regular CoAP message, what is important is the		already present in a regular CoAP message, what is important is the
	order of appearance and inclusion of only those CoAP fields that go		order of appearance and inclusion of only those CoAP fields that go
	into the Plaintext, Figure 12.		into the Plaintext, Figure 11.
	Rule ID 0		Rule ID 0
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | ||[bits]|		| | | | Value | | ||[bits]|
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	|CoAP Code | |up| 1 | equal |not-sent || |		|CoAP Code | |up| 1 | equal |not-sent || |
	|CoAP Code | |dw|[69,132] | match-map |match-sent || c |		|CoAP Code | |dw|[69,132] | match-map |match-sent || c |
	|CoAP Uri-Path | |up|temperature| equal |not-sent || |		|CoAP Uri-Path | |up|temperature| equal |not-sent || |
	|COAP Option-End| |dw| 0xFF | equal |not-sent || |		|COAP Option-End| |dw| 0xFF | equal |not-sent || |
	+---------------+--+--+-----------+-----------+-----------++------+		+---------------+--+--+-----------+-----------+-----------++------+
	Figure 12: Inner SCHC Rules		Figure 11: Inner SCHC Rules
	Figure 13 shows the Plaintext obtained for our example GET Request		Figure 12 shows the Plaintext obtained for our example GET Request
	and follows the process of Inner Compression and Encryption until we		and follows the process of Inner Compression and Encryption until we
	end up with the Payload to be added in the outer OSCORE Message.		end up with the Payload to be added in the outer OSCORE Message.
	In this case the original message has no payload and its resulting		In this case the original message has no payload and its resulting
	Plaintext can be compressed up to only 1 byte (size of the Rule ID).		Plaintext can be compressed up to only 1 byte (size of the Rule ID).
	The AEAD algorithm preserves this length in its first output, but		The AEAD algorithm preserves this length in its first output, but
	also yields a fixed-size tag which cannot be compressed and has to be		also yields a fixed-size tag which cannot be compressed and has to be
	included in the OSCORE message. This translates into an overhead in		included in the OSCORE message. This translates into an overhead in
	total message length, which limits the amount of compression that can		total message length, which limits the amount of compression that can
	be achieved and plays into the cost of adding security to the		be achieved and plays into the cost of adding security to the
	skipping to change at page 19, line 48 ¶		skipping to change at page 19, line 44 ¶
	| (piv = 0x04)		| (piv = 0x04)
	v		v
	_________________________________________________		_________________________________________________
	| |		| |
	| encrypted_plaintext = 0xa2 (1 byte) |		| encrypted_plaintext = 0xa2 (1 byte) |
	| tag = 0xc54fe1b434297b62 (8 bytes) |		| tag = 0xc54fe1b434297b62 (8 bytes) |
	| |		| |
	| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |		| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |
	|_________________________________________________|		|_________________________________________________|
	Figure 13: Plaintext compression and encryption for GET Request		Figure 12: Plaintext compression and encryption for GET Request
	In Figure 14 we repeat the process for the example CONTENT Response.		In Figure 13 we repeat the process for the example CONTENT Response.
	In this case the misalignment produced by the compression residue (1		In this case the misalignment produced by the compression residue (1
	bit) makes it so that 7 bits of padding have to be applied after the		bit) makes it so that 7 bits of padding have to be applied after the
	payload, resulting in a compressed Plaintext that is the same size as		payload, resulting in a compressed Plaintext that is the same size as
	before compression. This misalignment also causes the hexcode from		before compression. This misalignment also causes the hexcode from
	the payload to differ from the original, even though it has not been		the payload to differ from the original, even though it has not been
	compressed. On top of this, the overhead from the tag bytes is		compressed. On top of this, the overhead from the tag bytes is
	incurred as before.		incurred as before.
	________________________________________________________		________________________________________________________
	| |		| |
	skipping to change at page 21, line 48 ¶		skipping to change at page 20, line 50 ¶
	| (piv = 0x04)		| (piv = 0x04)
	v		v
	_________________________________________________________		_________________________________________________________
	| |		| |
	| encrypted_plaintext = 0x10c6d7c26cc1 (6 bytes) |		| encrypted_plaintext = 0x10c6d7c26cc1 (6 bytes) |
	| tag = 0xe9aef3f2461e0c29 (8 bytes) |		| tag = 0xe9aef3f2461e0c29 (8 bytes) |
	| |		| |
	| ciphertext = 0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes) |		| ciphertext = 0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes) |
	|_________________________________________________________|		|_________________________________________________________|
	Figure 14: Plaintext compression and encryption for CONTENT Response		Figure 13: Plaintext compression and encryption for CONTENT Response
			The Outer SCHC Rules (Figure 16) MUST process the OSCORE Options
	The Outer SCHC Rules (Figure 17) MUST process the OSCORE Options		fields. In Figure 14 and Figure 15 we show a dump of the OSCORE
	fields. In Figure 15 and Figure 16 we show a dump of the OSCORE
	Messages generated from our example messages once they have been		Messages generated from our example messages once they have been
	provided with the Inner Compressed Ciphertext in the payload. These		provided with the Inner Compressed Ciphertext in the payload. These
	are the messages that are to go through Outer SCHC Compression.		are the messages that are to go through Outer SCHC Compression.
	Protected message:		Protected message:
	==================		==================
	0x4102000182d7080904636c69656e74ffa2c54fe1b434297b62		0x4102000182d7080904636c69656e74ffa2c54fe1b434297b62
	(25 bytes)		(25 bytes)
	Header:		Header:
	0x4102		0x4102
	01 Ver		01 Ver
	00 CON		00 CON
	0001 tkl		0001 tkl
	00000010 Request Code 2 "POST"		00000010 Request Code 2 "POST"
	0x0001 = mid		0x0001 = mid
	0x82 = token		0x82 = token
	Options:		Options:
	0xd7080904636c69656e74 (10 bytes)		0xd8080904636c69656e74 (10 bytes)
	Option 21: OBJECT_SECURITY		Option 21: OBJECT_SECURITY
	Value = 0x0904636c69656e74		Value = 0x0904636c69656e74
	09 = 000 0 1 001 Flag byte		09 = 000 0 1 001 Flag byte
	h k n		h k n
	04 piv		04 piv
	636c69656e74 kid		636c69656e74 kid
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0xa2c54fe1b434297b62 (9 bytes)		0xa2c54fe1b434297b62 (9 bytes)
	Figure 15: Protected and Inner SCHC Compressed GET Request		Figure 14: Protected and Inner SCHC Compressed GET Request
	Protected message:		Protected message:
	==================		==================
	0x6144000182d008ff10c6d7c26cc1e9aef3f2461e0c29		0x6144000182d008ff10c6d7c26cc1e9aef3f2461e0c29
	(22 bytes)		(22 bytes)
	Header:		Header:
	0x6144		0x6144
	01 Ver		01 Ver
	10 ACK		10 ACK
	skipping to change at page 23, line 29 ¶		skipping to change at page 22, line 29 ¶
	Options:		Options:
	0xd008 (2 bytes)		0xd008 (2 bytes)
	Option 21: OBJECT_SECURITY		Option 21: OBJECT_SECURITY
	Value = b''		Value = b''
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)		0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
	Figure 16: Protected and Inner SCHC Compressed CONTENT Response		Figure 15: Protected and Inner SCHC Compressed CONTENT Response
	For the flag bits, a number of compression methods could prove to be		For the flag bits, a number of compression methods could prove to be
	useful depending on the application. The simplest alternative is to		useful depending on the application. The simplest alternative is to
	provide a fixed value for the flags, combining MO equal and CDA not-		provide a fixed value for the flags, combining MO equal and CDA not-
	sent. This saves most bits but could hinder flexibility. Otherwise,		sent. This saves most bits but could hinder flexibility. Otherwise,
	match-mapping could allow to choose from a number of configurations		match-mapping could allow to choose from a number of configurations
	of interest to the exchange. If neither of these alternatives is		of interest to the exchange. If neither of these alternatives is
	desirable, MSB could be used to mask off the 3 hard-coded most		desirable, MSB could be used to mask off the 3 hard-coded most
	significant bits.		significant bits.
	skipping to change at page 24, line 10 ¶		skipping to change at page 23, line 10 ¶
	technologies. Note that compressing the sequence numbers effectively		technologies. Note that compressing the sequence numbers effectively
	reduces the maximum amount of sequence numbers that can be used in an		reduces the maximum amount of sequence numbers that can be used in an
	exchange. Once this amount is exceeded, the SCHC Context would need		exchange. Once this amount is exceeded, the SCHC Context would need
	to be re-established.		to be re-established.
	The size s included in the kid context field MAY be masked off with		The size s included in the kid context field MAY be masked off with
	CDA MSB. The rest of the field could have additional bits masked		CDA MSB. The rest of the field could have additional bits masked
	off, or have the whole field be fixed with MO equal and CDA not-sent.		off, or have the whole field be fixed with MO equal and CDA not-sent.
	The same holds for the kid field.		The same holds for the kid field.
	Figure 17 shows a possible set of Outer Rules to compress the Outer		Figure 16 shows a possible set of Outer Rules to compress the Outer
	Header.		Header.
	Rule ID 0		Rule ID 0
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | ||[bits]|		| | | | Value | | ||[bits]|
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	|CoAP version | |bi| 01 |equal |not-sent || |		|CoAP version | |bi| 01 |equal |not-sent || |
	|CoAP Type | |up| 0 |equal |not-sent || |		|CoAP Type | |up| 0 |equal |not-sent || |
	|CoAP Type | |dw| 2 |equal |not-sent || |		|CoAP Type | |dw| 2 |equal |not-sent || |
	skipping to change at page 24, line 36 ¶		skipping to change at page 23, line 36 ¶
	|CoAP OSCORE_flags | |up| 0x09 |equal |not-sent || |		|CoAP OSCORE_flags | |up| 0x09 |equal |not-sent || |
	|CoAP OSCORE_piv | |up| 0x00 |MSB(4) |LSB ||PPPP |		|CoAP OSCORE_piv | |up| 0x00 |MSB(4) |LSB ||PPPP |
	|COAP OSCORE_kid | |up|0x636c69656e70|MSB(52) |LSB ||KKKK |		|COAP OSCORE_kid | |up|0x636c69656e70|MSB(52) |LSB ||KKKK |
	|COAP OSCORE_kidctxt| |bi| b'' |equal |not-sent || |		|COAP OSCORE_kidctxt| |bi| b'' |equal |not-sent || |
	|CoAP OSCORE_flags | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_flags | |dw| b'' |equal |not-sent || |
	|CoAP OSCORE_piv | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_piv | |dw| b'' |equal |not-sent || |
	|CoAP OSCORE_kid | |dw| b'' |equal |not-sent || |		|CoAP OSCORE_kid | |dw| b'' |equal |not-sent || |
	|COAP Option-End | |dw| 0xFF |equal |not-sent || |		|COAP Option-End | |dw| 0xFF |equal |not-sent || |
	+-------------------+--+--+--------------+--------+---------++------+		+-------------------+--+--+--------------+--------+---------++------+
	Figure 17: Outer SCHC Rules		Figure 16: Outer SCHC Rules
	These Outer Rules are applied to the example GET Request and CONTENT		These Outer Rules are applied to the example GET Request and CONTENT
	Response. The resulting messages are shown in Figure 18 and		Response. The resulting messages are shown in Figure 17 and
	Figure 19.		Figure 18.
	Compressed message:		Compressed message:
	==================		==================
	0x001489458a9fc3686852f6c4 (12 bytes)		0x001489458a9fc3686852f6c4 (12 bytes)
	0x00 Rule ID		0x00 Rule ID
	1489 Compression Residue		1489 Compression Residue
	458a9fc3686852f6c4 Padded payload		458a9fc3686852f6c4 Padded payload
	Compression residue:		Compression residue:
	0b 0001 010 0100 0100 (15 bits -> 2 bytes with padding)		0b 0001 010 0100 0100 (15 bits -> 2 bytes with padding)
	mid tkn piv kid		mid tkn piv kid
	Payload		Payload
	0xa2c54fe1b434297b62 (9 bytes)		0xa2c54fe1b434297b62 (9 bytes)
	Compressed message length: 12 bytes		Compressed message length: 12 bytes
	Figure 18: SCHC-OSCORE Compressed GET Request		Figure 17: SCHC-OSCORE Compressed GET Request
	Compressed message:		Compressed message:
	==================		==================
	0x0014218daf84d983d35de7e48c3c1852 (16 bytes)		0x0014218daf84d983d35de7e48c3c1852 (16 bytes)
	0x00 Rule ID		0x00 Rule ID
	14 Compression residue		14 Compression residue
	218daf84d983d35de7e48c3c1852 Padded payload		218daf84d983d35de7e48c3c1852 Padded payload
	Compression residue:		Compression residue:
	0b0001 010 (7 bits -> 1 byte with padding)		0b0001 010 (7 bits -> 1 byte with padding)
	mid tkn		mid tkn
	Payload		Payload
	0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)		0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
	Compressed msg length: 16 bytes		Compressed msg length: 16 bytes
	Figure 19: SCHC-OSCORE Compressed CONTENT Response		Figure 18: SCHC-OSCORE Compressed CONTENT Response
	For contrast, we compare these results with what would be obtained by		For contrast, we compare these results with what would be obtained by
	SCHC compressing the original CoAP messages without protecting them		SCHC compressing the original CoAP messages without protecting them
	with OSCORE. To do this, we compress the CoAP messages according to		with OSCORE. To do this, we compress the CoAP messages according to
	the SCHC rules in Figure 20.		the SCHC rules in Figure 19.
	Rule ID 1		Rule ID 1
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	| Field |FP|DI| Target | MO | CDA || Sent |		| Field |FP|DI| Target | MO | CDA || Sent |
	| | | | Value | | || [bits] |		| | | | Value | | || [bits] |
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	|CoAP version | |bi| 01 |equal |not-sent || |		|CoAP version | |bi| 01 |equal |not-sent || |
	|CoAP Type | |up| 0 |equal |not-sent || |		|CoAP Type | |up| 0 |equal |not-sent || |
	|CoAP Type | |dw| 2 |equal |not-sent || |		|CoAP Type | |dw| 2 |equal |not-sent || |
	|CoAP TKL | |bi| 1 |equal |not-sent || |		|CoAP TKL | |bi| 1 |equal |not-sent || |
	|CoAP Code | |up| 2 |equal |not-sent || |		|CoAP Code | |up| 2 |equal |not-sent || |
	|CoAP Code | |dw| [69,132] |equal |not-sent || |		|CoAP Code | |dw| [69,132] |match-map|map-sent ||C |
	|CoAP MID | |bi| 0000 |MSB(12) |LSB ||MMMM |		|CoAP MID | |bi| 0000 |MSB(12) |LSB ||MMMM |
	|CoAP Token | |bi| 0x80 |MSB(5) |LSB ||TTT |		|CoAP Token | |bi| 0x80 |MSB(5) |LSB ||TTT |
	|CoAP Uri-Path | |up|temperature|equal |not-sent || |		|CoAP Uri-Path | |up|temperature|equal |not-sent || |
	|COAP Option-End| |dw| 0xFF |equal |not-sent || |		|COAP Option-End| |dw| 0xFF |equal |not-sent || |
	+---------------+--+--+-----------+---------+-----------++--------+		+---------------+--+--+-----------+---------+-----------++--------+
	Figure 20: SCHC-CoAP Rules (No OSCORE)		Figure 19: SCHC-CoAP Rules (No OSCORE)
	This yields the results in Figure 21 for the Request, and Figure 22		This yields the results in Figure 20 for the Request, and Figure 21
	for the Response.		for the Response.
	Compressed message:		Compressed message:
	==================		==================
	0x0114		0x0114
	0x01 = Rule ID		0x01 = Rule ID
	Compression residue:		Compression residue:
	0b00010100 (1 byte)		0b00010100 (1 byte)
	Compressed msg length: 2		Compressed msg length: 2
	Figure 21: CoAP GET Compressed without OSCORE		Figure 20: CoAP GET Compressed without OSCORE
	Compressed message:		Compressed message:
	==================		==================
	0x010a32332043		0x010a32332043
	0x01 = Rule ID		0x01 = Rule ID
	Compression residue:		Compression residue:
	0b00001010 (1 byte)		0b00001010 (1 byte)
	Payload		Payload
	0x32332043		0x32332043
	Compressed msg length: 6		Compressed msg length: 6
	Figure 22: CoAP CONTENT Compressed without OSCORE		Figure 21: CoAP CONTENT Compressed without OSCORE
	As can be seen, the difference between applying SCHC + OSCORE as		As can be seen, the difference between applying SCHC + OSCORE as
	compared to regular SCHC + COAP is about 10 bytes of cost.		compared to regular SCHC + COAP is about 10 bytes of cost.
	8. IANA Considerations		8. IANA Considerations
	This document has no request to IANA.		This document has no request to IANA.
	9. Security considerations		9. Security considerations
	This document does not have any more Security consideration than the		This document does not have any more Security consideration than the
	ones already raised on [I-D.ietf-lpwan-ipv6-static-context-hc]		ones already raised on [I-D.ietf-lpwan-ipv6-static-context-hc]
	10. Acknowledgements		10. Acknowledgements
	Thanks to all the persons that have give us feedback		The authors would like to thank Dominique Barthel, Carsten Bormann,
			Thomas Fossati, Klaus Hartke, Francesca Palombini, Alexander Pelov,
			Goran Selander.
	11. Normative References		11. Normative References
	[I-D.ietf-core-object-security]		[I-D.ietf-core-object-security]
	Selander, G., Mattsson, J., Palombini, F., and L. Seitz,		Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
	"Object Security for Constrained RESTful Environments		"Object Security for Constrained RESTful Environments
	(OSCORE)", draft-ietf-core-object-security-16 (work in		(OSCORE)", draft-ietf-core-object-security-16 (work in
	progress), March 2019.		progress), March 2019.
	[I-D.ietf-lpwan-ipv6-static-context-hc]		[I-D.ietf-lpwan-ipv6-static-context-hc]
	Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and J.		Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and J.
	Zuniga, "LPWAN Static Context Header Compression (SCHC)		Zuniga, "Static Context Header Compression (SCHC) and
	and fragmentation for IPv6 and UDP", draft-ietf-lpwan-		fragmentation for LPWAN, application to UDP/IPv6", draft-
	ipv6-static-context-hc-18 (work in progress), December		ietf-lpwan-ipv6-static-context-hc-19 (work in progress),
	2018.		July 2019.
	[I-D.toutain-core-time-scale]		[I-D.toutain-core-time-scale]
	Minaburo, A. and L. Toutain, "CoAP Time Scale Option",		Minaburo, A. and L. Toutain, "CoAP Time Scale Option",
	draft-toutain-core-time-scale-00 (work in progress),		draft-toutain-core-time-scale-00 (work in progress),
	October 2017.		October 2017.
	[rfc7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained		[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,
	<https://www.rfc-editor.org/info/rfc7252>.		<https://www.rfc-editor.org/info/rfc7252>.
End of changes. 68 change blocks.
	175 lines changed or deleted		157 lines changed or added
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