Internet DRAFT - draft-ietf-lpwan-coap-static-context-hc
draft-ietf-lpwan-coap-static-context-hc
lpwan Working Group A. Minaburo
Internet-Draft Acklio
Intended status: Standards Track L. Toutain
Expires: September 9, 2021 Institut MINES TELECOM; IMT Atlantique
R. Andreasen
Universidad de Buenos Aires
March 08, 2021
LPWAN Static Context Header Compression (SCHC) for CoAP
draft-ietf-lpwan-coap-static-context-hc-19
Abstract
This draft defines how to compress the Constrained Application
Protocol (CoAP) using the Static Context Header Compression (SCHC).
SCHC is a header compression mechanism adapted for Constrained
Devices. SCHC uses a static description of the header to reduce the
header's redundancy and size. While RFC 8724 describes the SCHC
compression and fragmentation framework, and its application for
IPv6/UDP headers, this document applies SCHC for CoAP headers. The
CoAP header structure differs from IPv6 and UDP since CoAP uses a
flexible header with a variable number of options, themselves of
variable length. The CoAP protocol messages format is asymmetric:
the request messages have a header format different from the one in
the response messages. This specification gives guidance on applying
SCHC to flexible headers and how to leverage the asymmetry for more
efficient compression Rules.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 9, 2021.
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. SCHC Applicability to CoAP . . . . . . . . . . . . . . . . . 4
3. CoAP Headers compressed with SCHC . . . . . . . . . . . . . . 7
3.1. Differences between CoAP and UDP/IP Compression . . . . . 8
4. Compression of CoAP header fields . . . . . . . . . . . . . . 9
4.1. CoAP version field . . . . . . . . . . . . . . . . . . . 9
4.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 9
4.3. CoAP code field . . . . . . . . . . . . . . . . . . . . . 9
4.4. CoAP Message ID field . . . . . . . . . . . . . . . . . . 10
4.5. CoAP Token fields . . . . . . . . . . . . . . . . . . . . 10
5. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. CoAP Content and Accept options. . . . . . . . . . . . . 11
5.2. CoAP option Max-Age, Uri-Host, and Uri-Port fields . . . 11
5.3. CoAP option Uri-Path and Uri-Query fields . . . . . . . . 11
5.3.1. Variable number of Path or Query elements . . . . . . 13
5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme
fields . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path,
and Location-Query fields . . . . . . . . . . . . . . . . 13
6. SCHC compression of CoAP extension RFCs . . . . . . . . . . . 13
6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 14
6.4. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Examples of CoAP header compression . . . . . . . . . . . . . 15
7.1. Mandatory header with CON message . . . . . . . . . . . . 15
7.2. OSCORE Compression . . . . . . . . . . . . . . . . . . . 16
7.3. Example OSCORE Compression . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
9. Security considerations . . . . . . . . . . . . . . . . . . . 31
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10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
11. Normative References . . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
CoAP [RFC7252] is a command/response protocol designed for micro-
controllers with a small RAM and ROM and optimized for REST-based
(Representative state transfer) services. Although the Constrained
Devices leads the CoAP design, a CoAP header's size is still too
large for LPWAN (Low Power Wide Area Networks). SCHC header
compression over CoAP header is required to increase performance or
use CoAP over LPWAN technologies.
The [RFC8724] defines SCHC, a header compression mechanism for the
LPWAN network based on a static context. Section 5 of the [RFC8724]
explains where compression and decompression occur in the
architecture. The SCHC compression scheme assumes as a prerequisite
that both end-points know the static context before transmission.
The way the context is configured, provisioned, or exchanged is out
of this document's scope.
CoAP is an application protocol, so CoAP compression requires
installing common Rules between the two SCHC instances. SCHC
compression may apply at two different levels: at IP and UDP in the
LPWAN network and another at the application level for CoAP. These
two compressions may be independent. Both follow the same principle
described in [RFC8724]. As different entities manage the CoAP
compression at different levels, the SCHC Rules driving the
compression/decompression are also different. The [RFC8724]
describes how to use SCHC for IP and UDP headers. This document
specifies how to apply SCHC compression to CoAP headers.
SCHC compresses and decompresses headers based on common contexts
between Devices. SCHC context includes multiple Rules. Each Rule
can match the header fields to specific values or ranges of values.
If a Rule matches, the matched header fields are replaced by the
RuleID and the Compression Residue that contains the residual bits of
the compression. Thus, different Rules may correspond to different
protocol headers in the packet that a Device expects to send or
receive.
A Rule describes the packets' entire header with an ordered list of
fields descriptions; see section 7 of [RFC8724]. Thereby
each description contains the field ID (FID), its length (FL), and
its position (FP), a direction indicator (DI) (upstream, downstream,
and bidirectional), and some associated Target Values (TV). The
direction indicator is used for compression to give the best TV to
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the FID when these values differ in the transmission direction. So a
field may be described several times.
A Matching Operator (MO) is associated with each header field
description. The Rule is selected if all the MOs fit the TVs for all
fields of the incoming header. A Rule cannot be selected if the
message contains an unknown field to the SCHC compressor.
In that case, a Compression/Decompression Action (CDA) associated
with each field gives the method to compress and decompress each
field. Compression mainly results in one of 4 actions:
o send the field value (value-sent),
o send nothing (not-sent),
o send some least significant bits of the field (LSB) or,
o send an index (mapping-sent).
After applying the compression, there may be some bits to be sent.
These values are called Compression Residue.
SCHC is a general mechanism applied to different protocols, the exact
Rules to be used depending on the protocol and the Application.
Section 10 of the [RFC8724] describes the compression scheme for IPv6
and UDP headers. This document targets the CoAP header compression
using SCHC.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. SCHC Applicability to CoAP
SCHC Compression for CoAP header MAY be done in conjunction with the
lower layers (IPv6/UDP) or independently. The SCHC adaptation
layers, described in Section 5 of [RFC8724], may be used as shown in
Figure 1, Figure 2, and Figure 3.
In the first example, Figure 1, a Rule compresses the complete header
stack from IPv6 to CoAP. In this case, the Device and the NGW
perform SCHC C/D (Static Context Header Compression Compressor/
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Decompressor). The Application communicating with the Device does
not implement SCHC C/D.
(Device) (NGW) (App)
+--------+ +--------+
| CoAP | | CoAP |
+--------+ +--------+
| UDP | | UDP |
+--------+ +----------------+ +--------+
| IPv6 | | IPv6 | | IPv6 |
+--------+ +--------+-------+ +--------+
| SCHC | | SCHC | | | |
+--------+ +--------+ + + +
| LPWAN | | LPWAN | | | |
+--------+ +--------+-------+ +--------+
((((LPWAN)))) ------ Internet ------
Figure 1: Compression/Decompression at the LPWAN boundary.
Figure 1 shows the use of SCHC header compression above layer 2 in
the Device and the NGW. The SCHC layer receives non-encrypted
packets and can apply compression Rules to all the headers in the
stack. On the other end, the NGW receives the SCHC packet and
reconstructs the headers using the Rule and the Compression Residue.
After the decompression, the NGW forwards the IPv6 packet toward the
destination. The same process applies in the other direction when a
non-encrypted packet arrives at the NGW. Thanks to the IP forwarding
based on the IPv6 prefix, the NGW identifies the Device and
compresses headers using the Device's Rules.
In the second example, Figure 2, the SCHC compression is applied in
the CoAP layer, compressing the CoAP header independently of the
other layers. The RuleID, the Compression Residue, and CoAP payload
are encrypted using a mechanism such as DTLS. Only the other end
(App) can decipher the information. If needed, layers below use SCHC
to compress the header as defined in [RFC8724] (represented in dotted
lines).
This use case needs an end-to-end context initialization between the
Device and the Application. The context initialization is out of the
scope of this document.
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(Device) (NGW) (App)
+--------+ +--------+
| CoAP | | CoAP |
+--------+ +--------+
| SCHC | | SCHC |
+--------+ +--------+
| DTLS | | DTLS |
+--------+ +--------+
. udp . . udp .
.......... .................. ..........
. ipv6 . . ipv6 . . ipv6 .
.......... .................. ..........
. schc . . schc . . . .
.......... .......... . . .
. lpwan . . lpwan . . . .
.......... .................. ..........
((((LPWAN)))) ------ Internet ------
Figure 2: Standalone CoAP end-to-end Compression/Decompression
The third example, Figure 3, shows the use of Object Security for
Constrained RESTful Environments (OSCORE) [RFC8613]. In this case,
SCHC needs two Rules to compress the CoAP header. A first Rule
focused on the inner header. The result of this first compression is
encrypted using the OSCORE mechanism. Then a second Rule compresses
the outer header, including the OSCORE Options.
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(Device) (NGW) (App)
+--------+ +--------+
| CoAP | | CoAP |
| inner | | inner |
+--------+ +--------+
| SCHC | | SCHC |
| inner | | inner |
+--------+ +--------+
| CoAP | | CoAP |
| outer | | outer |
+--------+ +--------+
| SCHC | | SCHC |
| outer | | outer |
+--------+ +--------+
. udp . . udp .
.......... .................. ..........
. ipv6 . . ipv6 . . ipv6 .
.......... .................. ..........
. schc . . schc . . . .
.......... .......... . . .
. lpwan . . lpwan . . . .
.......... .................. ..........
((((LPWAN)))) ------ Internet ------
Figure 3: OSCORE compression/decompression.
In the case of several SCHC instances, as shown in Figure 2 and
Figure 3, the Rules may come from different provisioning domains.
This document focuses on CoAP compression represented in the dashed
boxes in the previous figures.
3. CoAP Headers compressed with SCHC
The use of SCHC over the CoAP header uses the same description, and
compression/decompression techniques like the one for IP and UDP
explained in the [RFC8724]. For CoAP, the SCHC Rules description
uses the direction information to optimize the compression by
reducing the number of Rules needed to compress headers. The field
description MAY define both request/response headers and target
values in the same Rule, using the DI (direction indicator) to make
the difference.
As for other header compression protocols, when the compressor does
not find a correct Rule to compress the header, the packet MUST be
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sent uncompressed using the RuleID dedicated to this purpose. Where
the Compression Residue is the complete header of the packet. See
section 6 of [RFC8724].
3.1. Differences between CoAP and UDP/IP Compression
CoAP compression differs from IPv6 and UDP compression in the
following aspects:
o The CoAP protocol is asymmetric; the headers are different for a
request or a response. For example, the URI-Path option is
mandatory in the request, and it might not be present in the
response. A request might contain an Accept option, and the
response might include a Content-Format option. In comparison,
IPv6 and UDP returning path swap the value of some fields in the
header. However, all the directions have the same fields (e.g.,
source and destination address fields).
The [RFC8724] defines the use of a direction indicator (DI) in the
Field Descriptor, which allows a single Rule to process a message
header differently depending on the direction.
o Even when a field is "symmetric" (i.e., found in both directions),
the values carried in each direction are different. The
compression may use a "match-mapping" MO to limit the range of
expected values in a particular direction and reduce the
Compression Residue's size. Through the direction indicator (DI),
a field description in the Rules splits the possible field value
into two parts, one for each direction. For instance, if a client
sends only CON requests, the Type can be elided by compression,
and the answer may use one single bit to carry either the ACK or
RST type. The field Code has the same behavior, the 0.0X code
format value in the request, and the Y.ZZ code format in the
response.
o In SCHC, the Rule defines the different header fields' length, so
SCHC does not need to send it. In IPv6 and UDP headers, the
fields have a fixed size, known by definition. On the other hand,
some CoAP header fields have variable lengths, and the Rule
description specifies it. For example, in a URI-path or URI-
query, the Token size may vary from 0 to 8 bytes, and the CoAP
options use the Type-Length-Value encoding format.
When doing SCHC compression of a variable-length field,
Section 7.5.2 from [RFC8724] offers the possibility to define a
function for the Field length in the Field Description to know the
length before compression. If the field length is unknown, the
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Rule will set it as a variable, and SCHC will send the compressed
field's length in the Compression Residue.
o A field can appear several times in the CoAP headers. It is found
typically for elements of a URI (path or queries). The SCHC
specification [RFC8724] allows a Field ID to appear several times
in the Rule and uses the Field Position (FP) to identify the
correct instance, thereby removing the matching operation's
ambiguity.
o Field lengths defined in the CoAP protocol can be too
large regarding LPWAN traffic constraints. For instance, this is
particularly true for the Message-ID field and the Token field.
SCHC uses different Matching operators (MO) to perform the
compression. See section 7.4 of [RFC8724]. In this case, SCHC
can apply the Most Significant Bits (MSB) MO to reduce the
information carried on LPWANs.
4. Compression of CoAP header fields
This section discusses the compression of the different CoAP header
fields. The CoAP compression with SCHC follows Section 7.1 of
[RFC8724].
4.1. CoAP version field
CoAP version is bidirectional and MUST be elided during the SCHC
compression since it always contains the same value. In the future,
or if a new version of CoAP is defined, new Rules will be needed to
avoid ambiguities between versions.
4.2. CoAP type field
The CoAP protocol [RFC7252] has four types of messages: two requests
(CON, NON), one response (ACK), and one empty message (RST).
The SCHC compression SHOULD elide this field if, for instance, a
client is sending only NON or only CON messages. For the RST
message, SCHC may use a dedicated Rule. For other usages, SCHC can
use a "match-mapping" MO.
4.3. CoAP code field
The code field is an IANA registry [RFC7252], and it indicates the
Request Method used in CoAP. The compression of the CoAP code field
follows the same principle as that of the CoAP type field. If the
Device plays a specific role, SCHC may split the code values into two
fields description, the request codes with the 0 class and the
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response values. SCHC will use the direction indicator to identify
the correct value in the packet.
If the Device only implements a CoAP client, SCHC compression may
reduce the request code to the set of requests the client can
process.
For known values, SCHC can use a "match-mapping" MO. If SCHC cannot
compress the code field, it will send the values in the Compression
Residue.
4.4. CoAP Message ID field
SCHC can compress the Message ID field with the "MSB" MO and the
"LSB" CDA. See section 7.4 of [RFC8724].
4.5. CoAP Token fields
CoAP defines the Token using two CoAP fields, Token Length in the
mandatory header and Token Value directly following the mandatory
CoAP header.
SCHC processes the Token length as any header field. If the value
does not change, the size can be stored in the TV and elided during
the transmission. Otherwise, SCHC will send the token length in the
Compression Residue.
For the Token Value, SCHC MUST NOT send it as a variable-length in
the Compression Residue to avoid ambiguity with Token Length.
Therefore, SCHC MUST use the Token length value to define the size of
the Compression Residue. SCHC designates a specific function "tkl"
that the Rule MUST use to complete the field description. During the
decompression, this function returns the value contained in the Token
Length field.
5. CoAP options
CoAP defines options placed after the basic header in Option Numbers
order; see [RFC7252]. Each Option instance in a message uses the
format Delta-Type (D-T), Length (L), Value (V). The SCHC Rule builds
the description of the option by using in the Field ID the Option
Number built from D-T; in TV, the Option Value; and the Option Length
uses section 7.4 of [RFC8724]. When the Option Length has a well-
known size, the Rule may keep the length value. Therefore, SCHC
compression does not send it. Otherwise, SCHC Compression carries
the length of the Compression Residue, in addition to the Compression
Residue value.
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CoAP requests and responses do not include the same options. So
Compression Rules may reflect this asymmetry by tagging the direction
indicator.
Note that length coding differs between CoAP options and SCHC
variable size Compression Residue.
The following sections present how SCHC compresses some specific CoAP
options.
If CoAP introduces a new option, the SCHC Rules MAY be updated, and
the new Field ID description MUST be assigned to allow its
compression. Otherwise, if no Rule describes this new option, the
SCHC compression is not achieved, and SCHC sends the CoAP header
without compression.
5.1. CoAP Content and Accept options.
If the client expects a single value, it can be stored in the TV and
elided during the transmission. Otherwise, if the client expects
several possible values, a "match-mapping" SHOULD be used to limit
the Compression Residue's size. If not, SCHC has to send the option
value in the Compression Residue (fixed or variable length).
5.2. CoAP option Max-Age, Uri-Host, and Uri-Port fields
SCHC compresses these three fields in the same way. When the value
of these options is known, SCHC can elide these fields. If the
option uses well-known values, SCHC can use a "match-mapping" MO.
Otherwise, SCHC will use "value-sent" MO, and the Compression Residue
will send these options' values.
5.3. CoAP option Uri-Path and Uri-Query fields
The Uri-Path and Uri-Query fields are repeatable options; this means
that in the CoAP header, they may appear several times with different
values. SCHC Rule description uses the Field Position (FP) to
distinguish the different instances in the path.
To compress repeatable field values, SCHC may use a "match-mapping"
MO to reduce the size of variable Paths or Queries. In these cases,
to optimize the compression, several elements can be regrouped into a
single entry. The Numbering of elements does not change, and the
first matching element sets the MO comparison.
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+--------+---+--+--+--------+-------------+------------+
| Field |FL |FP|DI| Target | Matching | CDA |
| | | | | Value | Operator | |
+--------+---+--+--+--------+-------------+------------+
|Uri-Path| | 1|up|["/a/b",|match-mapping|mapping-sent|
| | | | |"/c/d"] | | |
|Uri-Path|var| 3|up| |ignore |value-sent |
+--------+---+--+--+--------+-------------+------------+
Figure 4: complex path example
In Figure 4, SCHC can use a single bit in the Compression Residue to
code one of the two paths. If regrouping were not allowed, 2 bits in
the Compression Residue would be needed. SCHC sends the third path
element as a variable size in the Compression Residue.
The length of URI-Path and URI-Query may be known when the rule is
defined. In any case, SCHC MUST set the field length to variable.
The unit to indicate the Compression Residue size is in Byte.
SCHC compression can use the MSB MO to a Uri-Path or Uri-Query
element. However, attention to the length is important because the
MSB value is in bits, and the size MUST always be a multiple of 8
bits.
The length sent at the beginning of a variable-length Compression
Residue indicates the LSB's size in bytes.
For instance, for a CORECONF path /c/X6?k="eth0" the Rule description
can be:
+-------------+---+--+--+--------+---------+-------------+
| Field |FL |FP|DI| Target | Match | CDA |
| | | | | Value | Opera. | |
+-------------+---+--+--+--------+---------+-------------+
|Uri-Path | | 1|up|"c" |equal |not-sent |
|Uri-Path |var| 2|up| |ignore |value-sent |
|Uri-Query |var| 1|up|"k=\"" |MSB(24) |LSB |
+-------------+---+--+--+--------+---------+-------------+
Figure 5: CORECONF URI compression
Figure 5 shows the Rule description for a URI-Path and a URI-Query.
SCHC compresses the first part of the URI-Path with a "not-sent" CDA.
SCHC will send the second element of the URI-Path with the length
(i.e., 0x2 X 6) followed by the query option (i.e., 0x05 eth0").
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5.3.1. Variable number of Path or Query elements
SCHC fixed the number of Uri-Path or Uri-Query elements in a Rule at
the Rule creation time. If the number varies, SCHC SHOULD create
several Rules to cover all the possibilities. Another one is to
define the length of Uri-Path to variable and sends a Compression
Residue with a length of 0 to indicate that this Uri-Path is empty.
However, this adds 4 bits to the variable Compression Residue size.
See section 7.5.2 [RFC8724].
5.4. CoAP option Size1, Size2, Proxy-URI and Proxy-Scheme fields
The SCHC Rule description MAY define sending some field values by
setting the TV to "not-sent," MO to "ignore," and CDA to "value-
sent." A Rule MAY also use a "match-mapping" when there are
different options for the same FID. Otherwise, the Rule sets the TV
to the value, MO to "equal," and CDA to "not-sent."
5.5. CoAP option ETag, If-Match, If-None-Match, Location-Path, and
Location-Query fields
A Rule entry cannot store these fields' values. The Rule description
MUST always send these values in the Compression Residue.
6. SCHC compression of CoAP extension RFCs
6.1. Block
When a packet uses a Block [RFC7959] option, SCHC compression MUST
send its content in the Compression Residue. The SCHC Rule describes
an empty TV with a MO set to "ignore" and a CDA to "value-sent."
Block option allows fragmentation at the CoAP level that is
compatible with SCHC fragmentation. Both fragmentation mechanisms
are complementary, and the node may use them for the same packet as
needed.
6.2. Observe
The [RFC7641] defines the Observe option. The SCHC Rule description
will not define the TV, but MO to "ignore," and the CDA to "value-
sent." SCHC does not limit the maximum size for this option (3
bytes). To reduce the transmission size, either the Device
implementation MAY limit the delta between two consecutive values, or
a proxy can modify the increment.
Since the Observe option MAY use an RST message to inform a server
that the client does not require the Observe response, a specific
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SCHC Rule SHOULD exist to allow the message's compression with the
RST type.
6.3. No-Response
The [RFC7967] defines a No-Response option limiting the responses
made by a server to a request. Different behaviors exist while using
this option to limit the responses made by a server to a request. If
both ends know the value, then the SCHC Rule will describe a TV to
this value, with a MO set to "equal" and CDA set to "not-sent."
Otherwise, if the value is changing over time, the SCHC Rule will set
the MO to "ignore" and CDA to "value-sent." The Rule may also use a
"match-mapping" to compress this option.
6.4. OSCORE
OSCORE [RFC8613] defines end-to-end protection for CoAP messages.
This section describes how SCHC Rules can be applied to compress
OSCORE-protected messages.
0 1 2 3 4 5 6 7 <--------- n bytes ------------->
+-+-+-+-+-+-+-+-+---------------------------------
|0 0 0|h|k| n | Partial IV (if any) ...
+-+-+-+-+-+-+-+-+---------------------------------
| | |
|<-- CoAP -->|<------ CoAP OSCORE_piv ------> |
OSCORE_flags
<- 1 byte -> <------ s bytes ----->
+------------+----------------------+-----------------------+
| s (if any) | kid context (if any) | kid (if any) ... |
+------------+----------------------+-----------------------+
| | |
| <------ CoAP OSCORE_kidctx ------>|<-- CoAP OSCORE_kid -->|
Figure 6: OSCORE Option
The Figure 6 shows the OSCORE Option Value encoding defined in
Section 6.1 of [RFC8613], where the first byte specifies the Content
of the OSCORE options using flags. The three most significant bits
of this byte are reserved and always 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 kid field. The three least
significant bits n indicate the length of the piv (Partial
Initialization Vector) field in bytes. When n = 0, no piv is
present.
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The flag byte is followed by the piv field, kid context field, and
kid field in this order, and if present, the kid context field's
length is encoded in the first byte denoting by 's' the length of the
kid context in bytes.
To better perform OSCORE SCHC compression, the Rule description needs
to identify the OSCORE Option and the fields it contains.
Conceptually, it discerns up to 4 distinct pieces of information
within the OSCORE option: the flag bits, the piv, the kid context,
and the kid. The SCHC Rule splits into four field descriptions the
OSCORE option to compress them:
o CoAP OSCORE_flags,
o CoAP OSCORE_piv,
o CoAP OSCORE_kidctx,
o CoAP OSCORE_kid.
Figure 6 shows the OSCORE Option format with those four fields
superimposed on it. Note that the CoAP OSCORE_kidctx field directly
includes the size octet s.
7. Examples of CoAP header compression
7.1. Mandatory header with CON message
In this first scenario, the SCHC Compressor at the Network Gateway
side receives a POST message from an Internet client, which is
immediately acknowledged by the Device. Figure 7 describes the SCHC
Rule descriptions for this scenario.
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RuleID 1
+-------------+--+--+--+------+---------+-------------++------------+
| Field |FL|FP|DI|Target| Match | CDA || Sent |
| | | | |Value | Opera. | || [bits] |
+-------------+--+--+--+------+---------+-------------++------------+
|CoAP version | 2| 1|bi| 01 |equal |not-sent || |
|CoAP Type | 2| 1|dw| CON |equal |not-sent || |
|CoAP Type | 2| 1|up|[ACK, |match- |matching- || |
| | | | | RST] |mapping |sent || T |
|CoAP TKL | 4| 1|bi| 0 |equal |not-sent || |
|CoAP Code | 8| 1|bi|[0.00,| | || |
| | | | | ... |match- |matching- || |
| | | | | 5.05]|mapping |sent || CC CCC |
|CoAP MID |16| 1|bi| 0000 |MSB(7 ) |LSB || M-ID|
|CoAP Uri-Path|var 1|dw| path |equal 1 |not-sent || |
+-------------+--+--+--+------+---------+-------------++------------+
Figure 7: CoAP Context to compress header without Token
In this example, SCHC compression elides the version and the Token
Length fields. The 26 method and response codes defined in [RFC7252]
has been shrunk to 5 bits using a "match-mapping" MO. The Uri-Path
contains a single element indicated in the TV and elided with the CDA
"not-sent."
SCHC Compression reduces the header sending only the Type, a mapped
code, and the least significant bits of Message ID (9 bits in the
example above).
Note that a client located in an Application Server sending a request
to a server located in the Device may not be compressed through this
Rule since the MID might not start with 7 bits equal to 0. A CoAP
proxy placed before the SCHC C/D can rewrite the message ID to fit
the value and match the Rule.
7.2. OSCORE Compression
OSCORE aims to solve the problem of end-to-end encryption for CoAP
messages. Therefore, the goal is to hide as much as possible the
message while still enabling proxy operation.
Conceptually this is achieved by splitting the CoAP message into an
Inner Plaintext and Outer OSCORE Message. The Inner Plaintext
contains sensitive information that is not necessary for proxy
operation. However, it is part of the message that can be encrypted
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until it reaches its end destination. The Outer Message acts as a
shell matching the regular CoAP message format and includes all
Options and information needed for proxy operation and caching.
Figure 8 illustrates this analysis.
The CoAP protocol arranges the options into one of 3 classes; each
granted a specific type of protection by the protocol:
o Class E: Encrypted options moved to the Inner Plaintext,
o Class I: Integrity-protected options included in the AAD for the
encryption of the Plaintext but otherwise left untouched in the
Outer Message,
o Class U: Unprotected options left untouched in the Outer Message.
These classes point out that the Outer option contains the OSCORE
Option and that the message is OSCORE protected; this option carries
the information necessary to retrieve the Security Context. The end-
point will use this Security Context to decrypt the message
correctly.
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Original CoAP Packet
+-+-+---+-------+---------------+
|v|t|TKL| code | Msg Id. |
+-+-+---+-------+---------------+....+
| Token |
+-------------------------------.....+
| Options (IEU) |
. .
. .
+------+-------------------+
| 0xFF |
+------+------------------------+
| |
| Payload |
| |
+-------------------------------+
/ \
/ \
/ \
/ \
Outer Header v v Plaintext
+-+-+---+--------+---------------+ +-------+
|v|t|TKL|new code| Msg Id. | | code |
+-+-+---+--------+---------------+....+ +-------+-----......+
| Token | | Options (E) |
+--------------------------------.....+ +-------+------.....+
| Options (IU) | | OxFF |
. . +-------+-----------+
. OSCORE Option . | |
+------+-------------------+ | Payload |
| 0xFF | | |
+------+ +-------------------+
Figure 8: A CoAP packet is split into an OSCORE outer and plaintext
Figure 8 shows the packet format for the OSCORE Outer header and
Plaintext.
In the Outer Header, the original header code is hidden and replaced
by a default dummy value. As seen in Sections 4.1.3.5 and 4.2 of
[RFC8613], the message code is replaced by POST for requests and
Changed for responses when CoAP is not using the Observe option. If
CoAP uses Observe, the OSCORE message code is replaced by FETCH for
requests and Content for responses.
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The first byte of the Plaintext contains the original packet code,
followed by the message code, the class E options, and, if present,
the original message Payload preceded by its payload marker.
An AEAD algorithm now encrypts the Plaintext. This integrity
protects the Security Context parameters and, eventually, any class I
options from the Outer Header. The resulting Ciphertext becomes the
new payload of the OSCORE message, as illustrated in Figure 9.
As defined in [RFC5116], this Ciphertext is the encrypted Plaintext's
concatenation of the authentication tag. Note that Inner Compression
only affects the Plaintext before encryption. Thus only the first
variable-length of the Ciphertext can be reduced. The authentication
tag is fixed in length and is considered part of the cost of
protection.
Outer Header
+-+-+---+--------+---------------+
|v|t|TKL|new code| Msg Id. |
+-+-+---+--------+---------------+....+
| Token |
+--------------------------------.....+
| Options (IU) |
. .
. OSCORE Option .
+------+-------------------+
| 0xFF |
+------+---------------------------+
| |
| Ciphertext: Encrypted Inner |
| Header and Payload |
| + Authentication Tag |
| |
+----------------------------------+
Figure 9: OSCORE message
The SCHC Compression scheme consists of compressing both the
Plaintext before encryption and the resulting OSCORE message after
encryption, see Figure 10.
The OSCORE message 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
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SCHC Rules. This way, compression is applied to all fields of the
original CoAP message.
Note that since the corresponding end-point can only decrypt the
Inner part of the message, this end-point will also have to implement
Inner SCHC Compression/Decompression.
Outer Message OSCORE Plaintext
+-+-+---+--------+---------------+ +-------+
|v|t|TKL|new code| Msg Id. | | code |
+-+-+---+--------+---------------+....+ +-------+-----......+
| Token | | Options (E) |
+--------------------------------.....+ +-------+------.....+
| Options (IU) | | OxFF |
. . +-------+-----------+
. OSCORE Option . | |
+------+-------------------+ | Payload |
| 0xFF | | |
+------+------------+ +-------------------+
| Ciphertext |<---------\ |
| | | v
+-------------------+ | +-----------------+
| | | Inner SCHC |
v | | Compression |
+-----------------+ | +-----------------+
| Outer SCHC | | |
| Compression | | v
+-----------------+ | +-------+
| | |RuleID |
v | +-------+-----------+
+--------+ +------------+ |Compression Residue|
|RuleID' | | Encryption | <-- +----------+--------+
+--------+-----------+ +------------+ | |
|Compression Residue'| | Payload |
+-----------+--------+ | |
| Ciphertext | +-------------------+
| |
+--------------------+
Figure 10: OSCORE Compression Diagram
7.3. Example OSCORE Compression
This section gives an example with a GET Request and its consequent
Content Response from a Device-based CoAP client to a cloud-based
CoAP server. The example also describes a possible set of Rules for
the Inner and Outer SCHC Compression. A dump of the results and a
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contrast between SCHC + OSCORE performance with SCHC + COAP
performance is also listed. This example gives an approximation of
the cost of security with SCHC-OSCORE.
Our first CoAP message is the GET request in Figure 11.
Original message:
=================
0x4101000182bb74656d7065726174757265
Header:
0x4101
01 Ver
00 CON
0001 TKL
00000001 Request Code 1 "GET"
0x0001 = mid
0x82 = token
Options:
0xbb74656d7065726174757265
Option 11: URI_PATH
Value = temperature
Original msg length: 17 bytes.
Figure 11: CoAP GET Request
Its corresponding response is the CONTENT Response in Figure 12.
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Original message:
=================
0x6145000182ff32332043
Header:
0x6145
01 Ver
10 ACK
0001 TKL
01000101 Successful Response Code 69 "2.05 Content"
0x0001 = mid
0x82 = token
0xFF Payload marker
Payload:
0x32332043
Original msg length: 10
Figure 12: CoAP CONTENT Response
The SCHC Rules for the Inner Compression include all fields already
present in a regular CoAP message. The methods described in
Section 4 apply to these fields. As an example, see Figure 13.
RuleID 0
+--------------+--+--+--+-----------+---------+---------++------+
| Field |FL|FP|DI| Target | MO | CDA || Sent |
| | | | | Value | | ||[bits]|
+--------------+--+--+--+-----------+---------+---------++------+
|CoAP Code | 8| 1|up| 1 | equal |not-sent || |
|CoAP Code | 8| 1|dw|[69, | | || |
| | | | |132] |match- |mapping- || |
| | | | | |mapping |sent || c |
|CoAP Uri-Path | | 1|up|temperature| equal |not-sent || |
+--------------+--+--+--+-----------+---------+---------++------+
Figure 13: Inner SCHC Rules
Figure 14 shows the Plaintext obtained for the example GET request.
The packet follows the process of Inner Compression and Encryption
until the payload. The outer OSCORE Message adds the result of the
Inner process.
In this case, the original message has no payload, and its resulting
Plaintext compressed up to only 1 byte (size of the RuleID). The
AEAD algorithm preserves this length in its first output and yields a
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fixed-size tag. SCHC cannot compress the tag, and the OSCORE message
must include it without compression. The use of integrity protection
translates into an overhead in total message length, limiting 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 |
| |
| RuleID = 0x00 (1 byte) |
| (No Compression Residue) |
|_________________________________|
|
| AEAD Encryption
| (piv = 0x04)
v
_________________________________________________
| |
| encrypted_plaintext = 0xa2 (1 byte) |
| tag = 0xc54fe1b434297b62 (8 bytes) |
| |
| ciphertext = 0xa2c54fe1b434297b62 (9 bytes) |
|_________________________________________________|
Figure 14: Plaintext compression and encryption for GET Request
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Figure 15 shows the process for the example CONTENT Response. The
Compression Residue is 1 bit long. Note that since SCHC adds padding
after the payload, this misalignment causes the hexadecimal code from
the payload to differ from the original, even if SCHC cannot compress
the tag. The overhead for the tag bytes limits the SCHC's
performance but brings security to the transmission.
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________________________________________________________
| |
| 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 RuleID |
| |
| 0b0 (1 bit match-map Compression 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 15: Plaintext compression and encryption for CONTENT Response
The Outer SCHC Rules (Figure 18) must process the OSCORE Options
fields. Figure 16 and Figure 17 shows a dump of the OSCORE Messages
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generated from the example messages. They include the Inner
Compressed Ciphertext in the payload. These are the messages that
have to be compressed by the Outer SCHC Compression.
Protected message:
==================
0x4102000182d8080904636c69656e74ffa2c54fe1b434297b62
(25 bytes)
Header:
0x4102
01 Ver
00 CON
0001 TKL
00000010 Request Code 2 "POST"
0x0001 = mid
0x82 = token
Options:
0xd8080904636c69656e74 (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 16: Protected and Inner SCHC Compressed GET Request
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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 17: Protected and Inner SCHC Compressed CONTENT Response
For the flag bits, some SCHC compression methods are useful,
depending on the Application. The most straightforward alternative
is to provide a fixed value for the flags, combining MO "equal" and
CDA "not-sent." This SCHC definition saves most bits but could
prevent flexibility. Otherwise, SCHC could use a "match-mapping" MO
to choose from several configurations for the exchange. If not, the
SCHC description may use an "MSB" MO to mask off the three hard-coded
most significant bits.
Note that fixing a flag bit will limit CoAP Options choice that can
be used in the exchange since their values are dependent on specific
options.
The piv field lends itself to having some bits masked off with "MSB"
MO and "LSB" CDA. This SCHC description could be useful in
applications where the message frequency is low such as LPWAN
technologies. Note that compressing the sequence numbers may reduce
the maximum number of sequence numbers that can be used in an
exchange. Once the sequence number exceeds the maximum value, the
OSCORE keys need to be re-established.
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The size s included in the kid context field MAY be masked off with
"LSB" CDA. The rest of the field could have additional bits masked
off or have the whole field fixed with MO "equal" and CDA "not-sent."
The same holds for the kid field.
Figure 18 shows a possible set of Outer Rules to compress the Outer
Header.
RuleID 0
+------------------+--+--+--+--------------+-------+--------++------+
| Field |FL|FP|DI| Target | MO | CDA || Sent |
| | | | | Value | | ||[bits]|
+------------------+--+--+--+--------------+-------+--------++------+
|CoAP version | 2| 1|bi| 01 |equal |not-sent|| |
|CoAP Type | 2| 1|up| 0 |equal |not-sent|| |
|CoAP Type | 2| 1|dw| 2 |equal |not-sent|| |
|CoAP TKL | 4| 1|bi| 1 |equal |not-sent|| |
|CoAP Code | 8| 1|up| 2 |equal |not-sent|| |
|CoAP Code | 8| 1|dw| 68 |equal |not-sent|| |
|CoAP MID |16| 1|bi| 0000 |MSB(12)|LSB ||MMMM |
|CoAP Token |tkl 1|bi| 0x80 |MSB(5) |LSB ||TTT |
|CoAP OSCORE_flags | 8| 1|up| 0x09 |equal |not-sent|| |
|CoAP OSCORE_piv |var 1|up| 0x00 |MSB(4) |LSB ||PPPP |
|COAP OSCORE_kid |var 1|up|0x636c69656e70|MSB(52)|LSB ||KKKK |
|COAP OSCORE_kidctx|var 1|bi| b'' |equal |not-sent|| |
|CoAP OSCORE_flags | 8| 1|dw| b'' |equal |not-sent|| |
|CoAP OSCORE_piv |var 1|dw| b'' |equal |not-sent|| |
|CoAP OSCORE_kid |var 1|dw| b'' |equal |not-sent|| |
+------------------+--+--+--+--------------+-------+--------++------+
Figure 18: Outer SCHC Rules
The Outer Rule of Figure 18 is applied to the example GET Request and
CONTENT Response. Figure 19 and Figure 20 show the resulting
messages.
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Compressed message:
==================
0x001489458a9fc3686852f6c4 (12 bytes)
0x00 RuleID
1489 Compression Residue
458a9fc3686852f6c4 Padded payload
Compression Residue:
0b 0001 010 0100 0100 (15 bits -> 2 bytes with padding)
mid tkn piv kid
Payload
0xa2c54fe1b434297b62 (9 bytes)
Compressed message length: 12 bytes
Figure 19: SCHC-OSCORE Compressed GET Request
Compressed message:
==================
0x0014218daf84d983d35de7e48c3c1852 (16 bytes)
0x00 RuleID
14 Compression Residue
218daf84d983d35de7e48c3c1852 Padded payload
Compression Residue:
0b0001 010 (7 bits -> 1 byte with padding)
mid tkn
Payload
0x10c6d7c26cc1e9aef3f2461e0c29 (14 bytes)
Compressed msg length: 16 bytes
Figure 20: SCHC-OSCORE Compressed CONTENT Response
In contrast, comparing these results with what would be obtained by
SCHC compressing the original CoAP messages without protecting them
with OSCORE is done by compressing the CoAP messages according to the
SCHC Rules in Figure 21.
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RuleID 1
+---------------+--+--+--+-----------+---------+-----------++-------+
| Field |FL|FP|DI| Target | MO | CDA || Sent |
| | | | | Value | | || [bits]|
+---------------+--+--+--+-----------+---------+-----------++-------+
|CoAP version | 2| 1|bi| 01 |equal |not-sent || |
|CoAP Type | 2| 1|up| 0 |equal |not-sent || |
|CoAP Type | 2| 1|dw| 2 |equal |not-sent || |
|CoAP TKL | 4| 1|bi| 1 |equal |not-sent || |
|CoAP Code | 8| 1|up| 2 |equal |not-sent || |
|CoAP Code | 8| 1|dw| [69,132] |match- |mapping- || |
| | | | | |mapping |sent ||C |
|CoAP MID |16| 1|bi| 0000 |MSB(12) |LSB ||MMMM |
|CoAP Token |tkl 1|bi| 0x80 |MSB(5) |LSB ||TTT |
|CoAP Uri-Path | | 1|up|temperature|equal |not-sent || |
+---------------+--+--+--+-----------+---------+-----------++-------+
Figure 21: SCHC-CoAP Rules (No OSCORE)
Figure 21 Rule yields the SCHC compression results in Figure 22 for
request, and Figure 23 for the response.
Compressed message:
==================
0x0114
0x01 = RuleID
Compression Residue:
0b00010100 (1 byte)
Compressed msg length: 2
Figure 22: CoAP GET Compressed without OSCORE
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Compressed message:
==================
0x010a32332043
0x01 = RuleID
Compression Residue:
0b00001010 (1 byte)
Payload
0x32332043
Compressed msg length: 6
Figure 23: CoAP CONTENT Compressed without OSCORE
As can be seen, the difference between applying SCHC + OSCORE as
compared to regular SCHC + COAP is about 10 bytes.
8. IANA Considerations
This document has no request to IANA.
9. Security considerations
The use of SCHC header compression for CoAP header fields only
affects the representation of the header information. SCHC header
compression itself does not increase or decrease the overall level of
security of the communication. When the connection does not use a
security protocol (such as OSCORE, DTLS, etc.), it is necessary to
use a layer-two security mechanism to protect the SCHC messages.
If LPWAN is the layer-two technology, the SCHC security
considerations of [RFC8724] continue to apply. When using another
layer-two protocol, use of a cryptographic integrity-protection
mechanisms to protect the SCHC headers is REQUIRED. Such
cryptographic integrity protection is necessary in order to continue
to provide the properties that [RFC8724] relies upon.
When SCHC is used with OSCORE, the security considerations of
[RFC8613] continue to apply.
When SCHC is used with the OSCORE outer headers, the Initialization
Vector (IV) size in the Compression Residue must be carefully
selected. There is a tradeoff between compression efficiency (with a
longer "MSB" MO prefix) and the frequency at which the Device must
renew its key material (in order to prevent the IV from expanding to
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an uncompressable value). The key renewal operation itself requires
several message exchanges and requires energy-intensive computation,
but the optimal tradeoff will depend on the specifics of the device
and expected usage patterns.
If an attacker can introduce a corrupted SCHC-compressed packet onto
a link, DoS attacks are possible by causing excessive resource
consumption at the decompressor. However, an attacker able to inject
packets at the link layer is also capable of other, potentially more
damaging, attacks.
SCHC compression emits variable-length Compression Residues for some
CoAP fields. In the compressed header representation, the length
field that is sent is not the length of the original header field but
rather the length of the Compression Residue that is being
transmitted. If a corrupted packet arrives at the decompressor with
a longer or shorter length than the original compressed
representation possessed, the SCHC decompression procedures will
detect an error and drop the packet.
SCHC header compression rules MUST remain tightly coupled between
compressor and decompressor. If the compression rules get out of
sync, a Compression Residue might be decompressed differently at the
receiver than the initial message submitted to compression
procedures. Accordingly, any time the context Rules are updated on
an OSCORE endpoint, that endpoint MUST trigger OSCORE key re-
establishment. Similar procedures may be appropriate to signal Rule
udpates when other message-protection mechanisms are in use.
10. Acknowledgements
The authors would like to thank (in alphabetic order): Christian
Amsuss, Dominique Barthel, Carsten Bormann, Theresa Enghardt, Thomas
Fossati, Klaus Hartke, Benjamin Kaduk, Francesca Palombini, Alexander
Pelov, Goran Selander and Eric Vyncke.
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[RFC7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.
Bose, "Constrained Application Protocol (CoAP) Option for
No Server Response", RFC 7967, DOI 10.17487/RFC7967,
August 2016, <https://www.rfc-editor.org/info/rfc7967>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.
Authors' Addresses
Ana Minaburo
Acklio
1137A avenue des Champs Blancs
35510 Cesson-Sevigne Cedex
France
Email: ana@ackl.io
Minaburo, et al. Expires September 9, 2021 [Page 33]
Internet-Draft LPWAN CoAP compression March 2021
Laurent Toutain
Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Laurent.Toutain@imt-atlantique.fr
Ricardo Andreasen
Universidad de Buenos Aires
Av. Paseo Colon 850
C1063ACV Ciudad Autonoma de Buenos Aires
Argentina
Email: randreasen@fi.uba.ar
Minaburo, et al. Expires September 9, 2021 [Page 34]
