< draft-ietf-lpwan-coap-static-context-hc-04.txt		draft-ietf-lpwan-coap-static-context-hc-05.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: January 3, 2019 Institut MINES TELECOM; IMT Atlantique		Expires: April 25, 2019 Institut MINES TELECOM; IMT Atlantique
	R. Andreasen		R. Andreasen
	Universidad de Buenos Aires		Universidad de Buenos Aires
	July 02, 2018		October 22, 2018
	LPWAN Static Context Header Compression (SCHC) for CoAP		LPWAN Static Context Header Compression (SCHC) for CoAP
	draft-ietf-lpwan-coap-static-context-hc-04		draft-ietf-lpwan-coap-static-context-hc-05
	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. CoAP header structure differs from IPv6 and UDP		CoAP headers. CoAP header structure differs from IPv6 and UDP
	protocols since the CoAP		protocols since the CoAP
	use a flexible header with a variable number of options themself of a		use a flexible header with a variable number of options themselves of
	variable length. Another important difference is the asymmetry in		a variable length. Another important difference is the asymmetry in
	the header format used in request and response messages. Most of the		the header format used in request and response messages. 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 January 3, 2019.		This Internet-Draft will expire on April 25, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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
	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		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	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 . . . . . . . . . . . . . . 5
	4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 6		4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 5
	4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 6		4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 5
	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 . . . . . . . . . . . . . . . . . . . . 6
	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 field, CoAP option Uri-Host and Uri-
	Port fields . . . . . . . . . . . . . . . . . . . . . . . 7		Port fields . . . . . . . . . . . . . . . . . . . . . . . 7
	5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 8		5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 7
	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 . . . . . . 8
	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 . . . . . . . . . . . . . . . . . . . . . . . . . 9		6. Other RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 9
	6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 9		6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 10		6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 9
	6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 10		6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 9
	6.4. Time Scale . . . . . . . . . . . . . . . . . . . . . . . 10		6.4. Time Scale . . . . . . . . . . . . . . . . . . . . . . . 10
	6.5. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 10		6.5. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 10
	7. Examples of CoAP header compression . . . . . . . . . . . . . 12		7. Examples of CoAP header compression . . . . . . . . . . . . . 11
	7.1. Mandatory header with CON message . . . . . . . . . . . . 12		7.1. Mandatory header with CON message . . . . . . . . . . . . 11
	7.2. Complete exchange . . . . . . . . . . . . . . . . . . . . 13		7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 13
	7.3. OSCORE Compression . . . . . . . . . . . . . . . . . . . 14		7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 17
	7.4. Example OSCORE Compression . . . . . . . . . . . . . . . 17		8. Normative References . . . . . . . . . . . . . . . . . . . . 27
	8. Normative References . . . . . . . . . . . . . . . . . . . . 22		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
	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. Nevertheless, if limited, the size of a CoAP		constrained devices. Nevertheless, if limited, the size of a CoAP
	header may be too large for LPWAN constraints and some compression		header may be too large for LPWAN constraints and some compression
	may be needed to reduce the header size.		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
	skipping to change at page 5, line 34 ¶		skipping to change at page 5, line 19 ¶
	o In CoAP headers, a field can be duplicated several times, for		o In CoAP headers, a field can be duplicated several times, for
	instances, elements of an URI (path or queries). The position		instances, elements of an URI (path or queries). The position
	defined in a rule, associated to a Field ID, can be used to		defined in a rule, associated to a Field ID, can be used to
	identify the proper element.		identify the proper element.
	[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) removes
	ambiguities for the matching operation.		ambiguities for the matching operation.
	o Field size defined in the CoAP protocol can be to large regarding		o Field size defined in the CoAP protocol can be too large regarding
	LPWAN traffic constraints. This is particularly true for the		LPWAN traffic constraints. This is particularly true for the
	message ID field or Token field. The use of MSB MO can be used to		message ID field or Token field. The use of MSB MO can be used to
	reduce the information carried on LPWANs.		reduce the information carried on LPWANs.
	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 an LPWAN node		rate can be different if the request is issued from an LPWAN node
	or from an non LPWAN device. For instance a Device (Dev) aware of		or from an non LPWAN device. For instance a Device (Dev) 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
	client will certainly send a larger token to the Thing. SCHC		client will certainly send a larger token to the Thing. SCHC
	compression will not modify the values to offer a better		compression will not modify the values to offer a better
	skipping to change at page 6, line 48 ¶		skipping to change at page 6, line 30 ¶
	reduced to the set of request the client is able to process.		reduced to the set of request the client is able to process.
	All the response codes should be compressed with a SCHC rule.		All the response codes should 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.
	Server memorizes the value for a EXCHANGE_LIFETIME period (by default		Server memorizes the value for a EXCHANGE_LIFETIME period (by default
	247 seconds) for CON messages and a NON_LIFETIME period (by default		247 seconds) for CON messages and a NON_LIFETIME period (by default
	145 seconds) for NON messages. During that period, a server		145 seconds) for NON messages. During that period, a server
	receiving the same Message ID value will process the message has a		receiving the same Message ID value will process the message as a
	retransmission. After this period, it will be processed as a new		retransmission. After this period, it will be processed as a new
	messages.		messages.
	In case the Device is a client, the size of the message ID field may		In case the Device is a client, the size of the message ID field may
	the too large regarding the number of messages sent. Client may use		the too large regarding the number of messages sent. Client may use
	only small message ID values, for instance 4 bit long. Therefore a		only small message ID values, for instance 4 bit long. Therefore a
	MSB can be used to limit the size of the compression residue.		MSB can be used to limit the size of the compression residue.
	In case the Device is a server, client may be located outside of the		In case the Device is a server, client may be located outside of the
	LPWAN area and view the device as a regular device connected to the		LPWAN area and view the device as a regular device connected to the
	skipping to change at page 7, line 23 ¶		skipping to change at page 7, line 5 ¶
	space offered by this field. A CoAP proxy can be set before the SCHC		space offered by this field. A CoAP proxy can be set before the SCHC
	C/D to reduce the value of the Message ID, to allow its compression		C/D to reduce the value of the Message ID, to allow its compression
	with the MSB matching operator and LSB CDA.		with the MSB matching operator and LSB CDA.
	4.5. CoAP Token fields		4.5. CoAP Token fields
	Token is defined through two CoAP fields, Token Length in the		Token is defined through two CoAP fields, Token Length in the
	mandatory header and Token Value directly following the mandatory		mandatory header and Token Value directly following the mandatory
	CoAP header.		CoAP header.
	Token Length is processed as a tradition protocol field. If the		Token Length is processed as any protocol field. If the value
	value remains the same during all the transaction, the size can be		remains the same during all the transaction, the size can be stored
	stored in the context and elided during the transmission. Otherwise		in the context and elided during the transmission. Otherwise it will
	it will have to the send as a compression residue.		have to the send as a compression residue.
	Token Value size should not be defined directly in the rule in the		Token Value size should not be defined directly in the rule in the
	Field Length (FL). Instead a specific function designed as "TKL"		Field Length (FL). Instead a specific function designed as "TKL"
	must be used. This function informs the SCHC C/D that the length of		must be used and length do not have to the sent with the residue.
	this field has to be read from the Token Length field.		During the decompression, this function returns the value contained
			in the Token Length field.
	5. CoAP options		5. CoAP options
	5.1. CoAP Content and Accept options.		5.1. CoAP Content and Accept options.
	These field are both unidirectional and must not be set to		These field are both unidirectional and must not be set to
	bidirectional in a rule entry.		bidirectional in a rule entry.
	If single value is expected by the client, it can be stored in the TV		If single value is expected by the client, it can be stored in the TV
	and elided during the transmission. Otherwise, if several possible		and elided during the transmission. Otherwise, if several possible
	values are expected by the client, a matching-list should be used to		values are expected by the client, a matching-list should be used to
	limit the size of the residue. If not the possible, the value as to		limit the size of the residue. If is not possible, the value has to
	be sent as a residue (fixed or variable length).		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 field, CoAP option Uri-Host and Uri-Port
	fields		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, value can be elided on the		If the duration is known by both ends, value can be elided on the
	skipping to change at page 8, line 35 ¶		skipping to change at page 8, line 18 ¶
	change, MO comparison is set with the first element of the matching.		change, MO comparison is set with the first element of the matching.
	FID FL FP DI TV MO CDA		FID FL FP DI TV MO CDA
	URI-Path 1 up ["/a/b", equal not-sent		URI-Path 1 up ["/a/b", equal not-sent
	"/c/d"]		"/c/d"]
	URI-Path 3 up ignore value-sent		URI-Path 3 up ignore value-sent
	Figure 2: complex path example		Figure 2: complex path example
	In Figure 2 a single bit residue can be used to code one of the 2		In Figure 2 a single bit residue can be used to code one of the 2
	paths. If regrouping was not allowed, a 2 bits residue whould have		paths. If regrouping was not allowed, a 2 bits residue is needed.
	been needed.
	5.3.1. Variable length Uri-Path and Uri-Query		5.3.1. Variable length Uri-Path and Uri-Query
	When the length is known at the rule creation, the Field Length must		When the length is known at the rule creation, the Field Length must
	be set to variable, and the unit is set to bytes.		be set to variable, and the unit is set to bytes.
	The MSB MO can be apply to a Uri-Path or Uri-Query element. Since		The MSB MO can be apply to a Uri-Path or Uri-Query element. Since
	MSB value is given in bit, the size must always be a multiple of 8		MSB value is given in bit, the size must always be a multiple of 8
	bits and the LSB CDA must not carry any value.		bits and the LSB CDA must not carry any value.
	skipping to change at page 9, line 32 ¶		skipping to change at page 9, line 12 ¶
	residue with a length of 0 to indicate that this Uri-Path is empty.		residue with a length of 0 to indicate that this Uri-Path is empty.
	This add 4 bits to the compression residue.		This add 4 bits to the compression residue.
	5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme fields		5.4. CoAP option Size1, Size2, 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 CDA 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 CDA is
	set to "not-sent"		set to "not-sent"
	5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path and		5.5. 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 compression residues.		always be sent with the compression residues.
	skipping to change at page 10, line 8 ¶		skipping to change at page 9, line 37 ¶
	6.1. Block		6.1. Block
	Block [rfc7959] allows a fragmentation at the CoAP level. SCHC		Block [rfc7959] allows a fragmentation at the CoAP level. SCHC
	includes also a fragmentation protocol. They are compatible. If a		includes also a fragmentation protocol. They are compatible. If a
	block option is used, its content must be sent as a compression		block option is used, its content must be sent as a compression
	residue.		residue.
	6.2. 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 CDA 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 device implementation should limit the		transmission size either the device implementation should limit the
	value increase or a proxy can modify the incrementation.		delta between two consecutive value or a proxy can modify the
			incrementation.
	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 does
	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.
	6.3. 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 known by both ends,		by a server to a request. If the value is not known by both ends,
	then TV is set to this value, MO is set to "equal" and CDF is set to		then TV is set to this value, MO is set to "equal" and CDA is set to
	"not-sent".		"not-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. Time Scale
	Time scale [I-D.toutain-core-time-scale] option allows a client to		Time scale [I-D.toutain-core-time-scale] option allows a client to
	inform the server that it is in a slow network and that message ID		inform the server that it is in a slow network and that message ID
	skipping to change at page 11, line 9 ¶		skipping to change at page 10, line 32 ¶
	6.5. OSCORE		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) ...
	+-+-+-+-+-+-+-+-+---------------------------------		+-+-+-+-+-+-+-+-+---------------------------------
	| |		| | |
	| <--------- CoAP OSCORE_piv ------------------> |		|<-- CoAP -->|<------ CoAP OSCORE_piv ------> |
			OSCORE_flags
	<- 1 byte -> <------ s bytes ----->		<- 1 byte -> <------ s bytes ----->
	+------------+----------------------+-----------------------+		+------------+----------------------+-----------------------+
	| s (if any) | kid context (if any) | kid (if any) ... |		| s (if any) | kid context (if any) | kid (if any) ... |
	+------------+----------------------+-----------------------+		+------------+----------------------+-----------------------+
	| | |		| | |
	| <------ CoAP OSCORE_kidctxt ----->|<-- CoAP OSCORE_kid -->|		| <------ CoAP OSCORE_kidctxt ----->|<-- CoAP OSCORE_kid -->|
	Figure 4: OSCORE Option		Figure 4: OSCORE Option
	The encoding of the OSCORE Option Value defined in Section 6.1 of		The encoding of the OSCORE Option Value defined in Section 6.1 of
	[I-D.ietf-core-object-security] is repeated in Figure 4.		[I-D.ietf-core-object-security] is repeated in Figure 4.
	The first byte is used for flags that specify the contents of the		The first byte is used for flags that specify the contents of the
	OSCORE option. The 3 most significant bits are reserved and always		OSCORE option. The 3 most significant bits are reserved and always
	set to 0. Bit h, when set, indicates the presence of the kid context		set to 0. Bit h, when set, indicates the presence of the kid context
	field in the option. Bit k, when set, indicates the presence of a		field in the option. Bit k, when set, indicates the presence of a
	kid field. The 3 least significant bits n indicate to length of the		kid field. The 3 least significant bits n indicate the length of the
	piv field in bytes, n = 0 taken to mean that no piv is present.		piv field in bytes. When n = 0, no piv is present.
	After the flag byte follow the piv field, kid context field and kid		After the flag byte follow the piv field, kid context field and kid
	field in order and if present; the length of the kid context field is		field in order and if present; the length of the kid context field is
	encoded in the first byte denoting by s the length of the kid context		encoded in the first byte denoting by s the length of the kid context
	in bytes.		in bytes.
	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 - this makes it possible		the OSCORE Option and the fields it contains.
	to do a preliminary processing of the message in preparation for
	regular SCHC compression.
	Conceptually, the OSCORE option can transmit up to 3 distinct pieces		Conceptually, it discerns up to 4 distinct pieces of information
	of information at a time: the piv, the kid context, and the kid.		within the OSCORE option: the flag bits, the piv, the kid context,
	This draft proposes that the SCHC Parser split the contents of this		and the kid. It is thus recommended that the parser split the OSCORE
	option into 3 SCHC fields:		option into the 4 subsequent fields:
			o CoAP OSCORE_flags,
	o CoAP OSCORE_piv,		o CoAP OSCORE_piv,
	o CoAP OSCORE_ctxt,		o CoAP OSCORE_kidctxt,
	o CoAP OSCORE_kid.		o CoAP OSCORE_kid.
	These fields are superposed on the OSCORE Option format in Figure 4,		These fields are superposed on the OSCORE Option format in Figure 4,
	and include the corresponding flag and size bits for each part of the		the CoAP OSCORE_kidctxt field including the size bits s. Their size
	option. Both the flag and size bits can be omitted by use of the MSB		may be reduced using the MSB matching operator.
	matching operator on each field.
	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 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
	Device. For this simple scenario, the rules are described Figure 5.		Device. For this simple scenario, the rules are described Figure 5.
	Rule ID 1		Rule ID 1
	skipping to change at page 13, line 26 ¶		skipping to change at page 13, line 26 ¶
	| |		| |
	---------------------->| rule id=1 |		---------------------->| rule id=1 |
	+-+-+--+----+--------+ |------------------->|		+-+-+--+----+--------+ |------------------->|
	|1|2| 0|2.05| 0x0034 | | TCCCCCMMMMMMMMM |--------------------->		|1|2| 0|2.05| 0x0034 | | TCCCCCMMMMMMMMM |--------------------->
	+-+-+--+----+--------+ | 001100000110100 | +-+-+--+----+------+		+-+-+--+----+--------+ | 001100000110100 | +-+-+--+----+------+
	| | |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
	7.2. Complete exchange		7.2. OSCORE Compression
	In that example, the Thing is using CoMi and sends queries for 2 SID.
	CON
	MID=0x0012 | |
	POST | |
	Accept X | |
	/c/k=AS |------------------------>|
	| |
	| |
	|<------------------------| ACK MID=0x0012
	| | 0.00
	| |
	| |
	|<------------------------| CON
	| | MID=0X0034
	| | Content-Format X
	ACK MID=0x0034 |------------------------>|
	0.00
	7.3. 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, which are otherwise required to terminate their TLS or DTLS		messages. The goal, therefore, is to hide as much of the message as
	protection at the proxy, as discussed in Section 11.2 of [rfc7252].		possible while still enabling proxy operation.
	CoAP proxies are men-in-the-middle, but not all of the information
	they have access to is necessary for their operation. The goal,
	therefore, is to hide as much of the message as 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 and need not be decrypted until it reaches its end		encrypted until it reaches its end destination. The Outer Message
	destination. The Outer Message acts as a shell matching the format		acts as a shell matching the format of a regular CoAP message, and
	of a regular CoAP message, and includes all Options and information		includes all Options and information needed for proxy operation and
	needed for proxy operation and caching. This decomposition is		caching. This decomposition is illustrated in Figure 7.
	illustrated in Figure 7.
	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: Enrypted options moved to the Inner Plaintext,		o Class E: Encrypted options moved to the Inner Plaintext,
	o Class I: Intergrity-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,
	o Class U: Unprotected options left untouched in the Outer Message.		o Class U: Unprotected options left untouched in the Outer Message.
	Additionally, the OSCORE Option is added as an Outer option,		Additionally, the OSCORE Option is added as an Outer option,
	signaling that the message is OSCORE protected. This option carries		signaling that the message is OSCORE protected. This option carries
	the information necessary to retrieve the Security Context with which		the information necessary to retrieve the Security Context with which
	the message was encrypted so that it may be correctly decrypted at		the message was encrypted so that it may be correctly decrypted at
	the other end-point.		the other end-point.
	Orignal CoAP Message		Original CoAP Message
	+-+-+---+-------+---------------+		+-+-+---+-------+---------------+
	|v|t|tkl| code | Msg Id. |		|v|t|tkl| code | Msg Id. |
	+-+-+---+-------+---------------+....+		+-+-+---+-------+---------------+....+
	| Token |		| Token |
	+-------------------------------.....+		+-------------------------------.....+
	| Options (IEU) |		| Options (IEU) |
	. .		. .
	. .		. .
	+------+-------------------+		+------+-------------------+
	| 0xFF |		| 0xFF |
	skipping to change at page 15, line 41 ¶		skipping to change at page 14, line 47 ¶
	| 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 7: OSCORE inner and outer header form a CoAP message
	Figure 7 shows the message format for the OSCORE Message and		Figure 7 shows the message format for the OSCORE Message and
	Plaintext. In the Outer Header, the original message code is hidden		Plaintext.
	and replaced by a default value (POST or FETCH) depending on whether
	the original message was a Request or a Response. The original		In the Outer Header, the original message code is hidden and replaced
	message code is put into the first byte of the Plaintext. Following		by a default dummy value. As seen in sections 4.1.3.5 and 4.2 of
	the message code come the class E options and if present the original
	message Payload preceded by its payload marker.		[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
			Observe is used, the message code is replaced by FETCH for requests
			and Content for responses.
			The original message code is put into the first byte of the
			Plaintext. Following the message code, the class E options comes and
			if present the original message Payload is preceded by its payload
			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 8.
			This Ciphertext is, as defined in RFC 5116, the concatenation of the
			encrypted Plaintext and its authentication tag. Note that Inner
			Compression only affects the Plaintext before encryption, thus we can
			only aim to reduce this first, variable length component of the
			Ciphertext. The authentication tag is fixed in length and considered
			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 .
	+------+-------------------+		+------+-------------------+
	skipping to change at page 16, line 29 ¶		skipping to change at page 16, line 7 ¶
	| |		| |
	| Encrypted Inner Header and |		| Encrypted Inner Header and |
	| Payload |		| Payload |
	| |		| |
	+--------------------------------+		+--------------------------------+
	Figure 8: OSCORE message		Figure 8: 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. This way compression reaches all fields of		encryption, see Figure 9.
	the original CoAP message.
			This translates into a segmented process where SCHC compression is
			applied independently in 2 stages, each with its corresponding set of
			rules, with the Inner SCHC Rules and the Outer SCHC Rules. This way
			compression is applied to all fields of the original CoAP message.
			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
			implement Inner SCHC Compression/Decompression.
	Outer Message OSCORE Plaintext		Outer Message OSCORE Plaintext
	+-+-+---+--------+---------------+ +-------+		+-+-+---+--------+---------------+ +-------+
	|v|t|tkl|new code| Msg Id. | | code |		|v|t|tkl|new code| Msg Id. | | code |
	+-+-+---+--------+---------------+....+ +-------+-----......+		+-+-+---+--------+---------------+....+ +-------+-----......+
	| Token | | Options (E) |		| Token | | Options (E) |
	+--------------------------------.....+ +-------+------.....+		+--------------------------------.....+ +-------+------.....+
	| Options (IU) | | OxFF |		| Options (IU) | | OxFF |
	. . +-------+-----------+		. . +-------+-----------+
	. OSCORE Option . | |		. OSCORE Option . | |
	skipping to change at page 17, line 39 ¶		skipping to change at page 17, line 5 ¶
	|Rule ID'| | Encryption | <--- +----------+--------+		|Rule ID'| | Encryption | <--- +----------+--------+
	+--------+--+ +------------+ | |		+--------+--+ +------------+ | |
	| Residue' | | Payload |		| Residue' | | Payload |
	+-----------+-------+ | |		+-----------+-------+ | |
	| Ciphertext | +-------------------+		| Ciphertext | +-------------------+
	| |		| |
	+-------------------+		+-------------------+
	Figure 9: OSCORE Compression Diagram		Figure 9: OSCORE Compression Diagram
	7.4. Example OSCORE Compression		7.3. Example OSCORE Compression
	In what follows we present an example GET Request and consequent		An example is given with a GET Request and its consequent CONTENT
	CONTENT Response and show a possible set of rules for the Inner and		Response. A possible set of rules for the Inner and Outer SCHC
	Outer SCHC Compression. We then show a dump of the results and		Compression is shown. A dump of the results and a contrast between
	contrast SCHC + OSCORE performance with SCHC + COAP performance.		SCHC + OSCORE performance with SCHC + COAP performance is also
	This gives an approximation to the cost of security with SCHC-OSCORE.		listed. This gives an approximation to the cost of security with
			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 10
	Original message:		Original message:
	=================		=================
	0x4101000182bb74656d7065726174757265		0x4101000182bb74656d7065726174757265
	Header:		Header:
	0x4101		0x4101
	01 Ver		01 Ver
	00 CON		00 CON
	0001 tkl		0001 tkl
	00000001 Request Code 1 "GET"		00000001 Request Code 1 "GET"
	skipping to change at page 19, line 6 ¶		skipping to change at page 18, line 28 ¶
	0xFF Payload marker		0xFF Payload marker
	Payload:		Payload:
	0x32332043		0x32332043
	Original msg length: 10		Original msg length: 10
	Figure 11: CoAP CONTENT Response		Figure 11: 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 matters is the order		already present in a regular CoAP message, what is important is the
	of appearance and inclusion of only those CoAP fields that go into		order of appearance and inclusion of only those CoAP fields that go
	the Plaintext, Figure 12.		into the Plaintext, Figure 12.
	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 12: Inner SCHC Rules
	The Outer SCHC Rules (Figure 13) must process the OSCORE Options		Figure 13 shows the Plaintext obtained for our example GET Request
	fields. Here we mask off the repeated bits (most importantly the		and follows the process of Inner Compression and Encryption until we
	flag and size bits) with the MSB Mathing Operator.		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
			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
			also yields a fixed-size tag which cannot be compressed and must be
			included in the OSCORE message. This translates into an overhead in
			total message length, which limits the amount of compression that can
			be achieved and plays into the cost of adding security to the
			exchange.
			________________________________________________________
			| |
			| OSCORE Plaintext |
			| |
			| 0x01bb74656d7065726174757265 (13 bytes) |
			| |
			| 0x01 Request Code GET |
			| |
			| bb74656d7065726174757265 Option 11: URI_PATH |
			| Value = temperature |
			|________________________________________________________|
			|
			|
			| Inner SCHC Compression
			|
			v
			_________________________________
			| |
			| Compressed Plaintext |
			| |
			| 0x00 |
			| |
			| Rule ID = 0x00 (1 byte) |
			| (No residue) |
			|_________________________________|
			|
			| AEAD Encryption
			| (piv = 0x04)
			v
			_________________________________________________
			| |
			| encrypted_plaintext = 0xa2 (1 byte) |
			| tag = 0xc54fe1b434297b62 (8 bytes) |
			| |
			| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |
			|_________________________________________________|
			Figure 13: Plaintext compression and encryption for GET Request
			In Figure 14 we repeat the process for the example CONTENT Response.
			In this case the misalignment produced by the compression residue (1
			bit) makes it so that 7 bits of padding must be applied after the
			payload, resulting in a compressed Plaintext that is the same size as
			before compression. This misalignment also causes the hexcode from
			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
			incurred as before.
			________________________________________________________
			| |
			| OSCORE Plaintext |
			| |
			| 0x45ff32332043 (6 bytes) |
			| |
			| 0x45 Successful Response Code 69 "2.05 Content" |
			| |
			| ff Payload marker |
			| |
			| 32332043 Payload |
			|________________________________________________________|
			|
			|
			| Inner SCHC Compression
			|
			v
			__________________________________________
			| |
			| Compressed Plaintext |
			| |
			| 0x001919902180 (6 bytes) |
			| |
			| 00 Rule ID |
			| |
			| 0b0 (1 bit match-map residue) |
			| 0x32332043 >> 1 (shifted payload) |
			| 0b0000000 Padding |
			|__________________________________________|
			|
			| AEAD Encryption
			| (piv = 0x04)
			v
			_________________________________________________________
			| |
			| encrypted_plaintext = 0x10c6d7c26cc1 (6 bytes) |
			| tag = 0xe9aef3f2461e0c29 (8 bytes) |
			| |
			| ciphertext = 0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes) |
			|_________________________________________________________|
			Figure 14: Plaintext compression and encryption for CONTENT Response
			The Outer SCHC Rules (Figure 17) must process the OSCORE Options
			fields. In Figure 15 and Figure 16 we show a dump of the OSCORE
			Messages generated from our example messages once they have been
			provided with the Inner Compressed Ciphertext in the payload. These
			are the messages that are to go through Outer SCHC Compression.
			Protected message:
			==================
			0x4102000182d7080904636c69656e74ffa2c54fe1b434297b62
			(25 bytes)
			Header:
			0x4102
			01 Ver
			00 CON
			0001 tkl
			00000010 Request Code 2 "POST"
			0x0001 = mid
			0x82 = token
			Options:
			0xd7080904636c69656e74 (10 bytes)
			Option 21: OBJECT_SECURITY
			Value = 0x0904636c69656e74
			09 = 000 0 1 001 Flag byte
			h k n
			04 piv
			636c69656e74 kid
			0xFF Payload marker
			Payload:
			0xa2c54fe1b434297b62 (9 bytes)
			Figure 15: Protected and Inner SCHC Compressed GET Request
			Protected message:
			==================
			0x6144000182d008ff10c6d7c26cc1e9aef3f2461e0c29
			(22 bytes)
			Header:
			0x6144
			01 Ver
			10 ACK
			0001 tkl
			01000100 Successful Response Code 68 "2.04 Changed"
			0x0001 = mid
			0x82 = token
			Options:
			0xd008 (2 bytes)
			Option 21: OBJECT_SECURITY
			Value = b''
			0xFF Payload marker
			Payload:
			0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
			Figure 16: Protected and Inner SCHC Compressed CONTENT Response
			For the flag bits, a number of compression methods could prove to be
			useful depending on the application. The simplest alternative is to
			provide a fixed value for the flags, combining MO equal and CDA not-
			sent. This saves most bits but could hinder flexibility. Otherwise,
			match-mapping could allow to choose from a number of configurations
			of interest to the exchange. If neither of these alternatives is
			desirable, MSB could be used to mask off the 3 hard-coded most
			significant bits.
			Note that fixing a flag bit will limit the choice of CoAP Options
			that can be used in the exchange, since their values are dependent on
			certain options.
			The piv field lends itself to having a number of bits masked off with
			MO MSB and CDA LSB. This could prove useful in applications where
			the message frequency is low such as that found in LPWAN
			technologies. Note that compressing the sequence numbers effectively
			reduces the maximum amount of sequence numbers that can be used in an
			exchange. Once this amount is exceeded, the SCHC Context would need
			to be re-established.
			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
			off, or have the whole field be fixed with MO equal and CDA not-sent.
			The same holds for the kid field.
			Figure 17 shows a possible set of Outer Rules to compress the Outer
			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 || |
	|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| 68 |equal |not-sent || |		|CoAP Code | |dw| 68 |equal |not-sent || |
	|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 OSCORE_piv| |up| 0x0900 |MSB(12) |LSB ||PPPP |		|CoAP OSCORE_flags | |up| 0x09 |equal |not-sent || |
	|COAP OSCORE_kid| |up|b'\x06client' |MSB(52) |LSB ||KKKK |		|CoAP OSCORE_piv | |up| 0x00 |MSB(4) |LSB ||PPPP |
	|CoAP OSCORE_piv| |dw| b'' |equal |not-sent || |		|COAP OSCORE_kid | |up|0x636c69656e70|MSB(52) |LSB ||KKKK |
	|COAP Option-End| |dw| 0xFF |equal |not-sent || |		|COAP OSCORE_kidctxt| |bi| b'' |equal |not-sent || |
	+---------------+--+--+--------------+---------+-----------++------------+		|CoAP OSCORE_flags | |dw| b'' |equal |not-sent || |
			|CoAP OSCORE_piv | |dw| b'' |equal |not-sent || |
			|CoAP OSCORE_kid | |dw| b'' |equal |not-sent || |
			|COAP Option-End | |dw| 0xFF |equal |not-sent || |
			+-------------------+--+--+--------------+---------+-----------++--------+
	Figure 13: Outer SCHC Rules		Figure 17: Outer SCHC Rules
	Next we show a dump of the compressed message:		These Outer Rules are applied to the example GET Request and CONTENT
			Response. The resulting messages are shown in Figure 18 and
			Figure 19.
	Compressed message:		Compressed message:
	==================		==================
	0x00291287f0a5c4833760d170		0x001489458a9fc3686852f6c4 (12 bytes)
	0x00 = Rule ID		0x00 Rule ID
			1489 Compression Residue
	piv = 0x04		458a9fc3686852f6c4 Padded payload
	Compression residue:		Compression residue:
	0b0001 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
	0xa1fc297120cdd8345c		0xa2c54fe1b434297b62 (9 bytes)
	Compressed message length: 12 bytes		Compressed message length: 12 bytes
	Figure 14: SCHC-OSCORE Compressed GET Request		Figure 18: SCHC-OSCORE Compressed GET Request
	Compressed message:		Compressed message:
	==================		==================
	0x0015f4de9cb814c96aed9b1d981a3a58		0x0014218daf84d983d35de7e48c3c1852 (16 bytes)
	0x00 = Rule ID		0x00 Rule ID
			14 Compression residue
			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
	0xfa6f4e5c0a64b576cd8ecc0d1d2c		0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
	Compressed msg length: 16 bytes		Compressed msg length: 16 bytes
	Figure 15: SCHC-OSCORE Compressed CONTENT Response		Figure 19: 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 mesages according to		with OSCORE. To do this, we compress the CoAP messages according to
	the SCHC rules in Figure 16.		the SCHC rules in Figure 20.
	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] |equal |not-sent || |
	|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 16: SCHC-CoAP Rules (No OSCORE)		Figure 20: SCHC-CoAP Rules (No OSCORE)
	This yields the results in Figure 17 for the Request, and Figure 18		This yields the results in Figure 21 for the Request, and Figure 22
	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 17: CoAP GET Compressed without OSCORE		Figure 21: 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 18: CoAP CONTENT Compressed without OSCORE		Figure 22: 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. Normative References		8. 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-13 (work in		(OSCORE)", draft-ietf-core-object-security-15 (work in
	progress), June 2018.		progress), August 2018.
	[I-D.ietf-lpwan-ipv6-static-context-hc]		[I-D.ietf-lpwan-ipv6-static-context-hc]
	Minaburo, A., Toutain, L., Gomez, C., and D. Barthel,		Minaburo, A., Toutain, L., Gomez, C., and D. Barthel,
	"LPWAN Static Context Header Compression (SCHC) and		"LPWAN Static Context Header Compression (SCHC) and
	fragmentation for IPv6 and UDP", draft-ietf-lpwan-ipv6-		fragmentation for IPv6 and UDP", draft-ietf-lpwan-ipv6-
	static-context-hc-16 (work in progress), June 2018.		static-context-hc-16 (work in progress), June 2018.
	[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),
End of changes. 62 change blocks.
	152 lines changed or deleted		353 lines changed or added
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