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.
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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
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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
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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.
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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.
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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
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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. 
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