draft-ietf-lpwan-coap-static-context-hc-02.txt   draft-ietf-lpwan-coap-static-context-hc-03.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: March 10, 2018 Institut MINES TELECOM ; IMT Atlantique Expires: September 5, 2018 Institut MINES TELECOM; IMT Atlantique
September 06, 2017 March 04, 2018
LPWAN Static Context Header Compression (SCHC) for CoAP LPWAN Static Context Header Compression (SCHC) for CoAP
draft-ietf-lpwan-coap-static-context-hc-02 draft-ietf-lpwan-coap-static-context-hc-03
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 Header is flexible header with a variable protocols since the CoAP Header is flexible header with a variable
number of options themself of a variable length. Another important number of options themself of a variable length. Another important
difference is the asymmetry in the header information used for difference is the asymmetry in the header information used for
request and response messages. This draft takes into account the request and response messages. This draft takes into account the
fact that a thing can play the role of a CoAP client, a CoAP client fact that a thing can play the role of a CoAP client, a CoAP client
skipping to change at page 1, line 38 skipping to change at page 1, line 38
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 March 10, 2018. This Internet-Draft will expire on September 5, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 43 skipping to change at page 2, line 43
7. Protocol analysis . . . . . . . . . . . . . . . . . . . . . . 13 7. Protocol analysis . . . . . . . . . . . . . . . . . . . . . . 13
8. Examples of CoAP header compression . . . . . . . . . . . . . 14 8. Examples of CoAP header compression . . . . . . . . . . . . . 14
8.1. Mandatory header with CON message . . . . . . . . . . . . 14 8.1. Mandatory header with CON message . . . . . . . . . . . . 14
8.2. Complete exchange . . . . . . . . . . . . . . . . . . . . 16 8.2. Complete exchange . . . . . . . . . . . . . . . . . . . . 16
9. Normative References . . . . . . . . . . . . . . . . . . . . 17 9. Normative References . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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. Gateway between CoAP and HTTP can be easily constrained devices. A Gateway between CoAP and HTTP can be easily
built since both protocols uses the same address space (URL), caching built since both protocols uses the same address space (URL), caching
mechanisms and methods. mechanisms and methods.
Nevertheless, if limited, the size of a CoAP header may be too large Nevertheless, if limited, the size of a CoAP header may be too large
for LPWAN constraints and some compression may be needed to reduce for LPWAN constraints and some compression may be needed to reduce
the header size. the header size.
[I-D.toutain-lpwan-ipv6-static-context-hc] defines a header [I-D.toutain-lpwan-ipv6-static-context-hc] defines a header
compression mechanism for LPWAN network based on a static context. compression mechanism for LPWAN network based on a static context.
The context is said static since the element values composing the The context is said static since the field description composing the
context are not learned during the packet exchanges but are Rules and the context are not learned during the packet exchanges but
previously defined. The context(s) is(are) known by both ends before are previously defined. The context(s) is(are) known by both ends
transmission. before transmission.
A context is composed of a set of rules (contexts) that are A context is composed of a set of rules that are referenced by Rule
referenced by Rule IDs (identifiers). A rule contains an ordered IDs (identifiers). A rule contains an ordered list of the fields
list of the header fields containing a field ID (FID) and its descriptions containing a field ID (FID) and its position when
position when repeated, a direction indicator (DI) (upstream, repeated, a direction indicator (DI) (upstream, downstream and
downstream and bidirectional) and some associated Target Values (TV) bidirectional) and some associated Target Values (TV) which are
which are expected in the message header. A Matching Operator (MO) expected in the message header. A Matching Operator (MO) is
is associated to each header field description. The rule is selected associated to each header field description. The rule is selected if
if all the MOs fit the TVs. In that case, a Compression all the MOs fit the TVs. In that case, a Compression/Decompression
Decompression Function (CDF) associated to each field defines the Action (CDA) associated to each field defines the link between the
link between the compressed and decompressed value for each of the compressed and decompressed value for each of the header fields.
header fields.
This document describes how the rules can be applied to CoAP flows. Compression of the This document describes how the rules can be applied to CoAP flows.
CoAP header may be done in conjunction with the above layers or independantly. Compression of the CoAP header may be done in conjunction with the
above layers or independantly.
2. CoAP Compressing 2. CoAP Compressing
CoAP differs from IPv6 and UDP protocols on the following CoAP differs from IPv6 and UDP protocols on the following aspects:
aspects:
o IPv6 and UDP are symmetrical protocols. The same fields are found o IPv6 and UDP are symmetrical protocols. The same fields are found
in the request and in the response, only location in the header in the request and in the response, only the location in the
may vary (e.g. source and destination fields). A CoAP request is header may vary (e.g. source and destination fields). A CoAP
different from an response. For example, the URI-path option is request is different from a response. For example, the URI-path
mandatory in the request and is not found in the response, request option is mandatory in the request and is not found in the
may contain an Accept option and the response a Content-format response, a request may contain an Accept option and the response
option. a Content-format option.
Even when a field is "symmetric" (i.e. found in both directions) Even when a field is "symmetric" (i.e. found in both directions)
the values carried are different. For instance the Type field the values carried are different. For instance the Type field
will contain a CON value in the request and a ACK or RST value in will contain a CON value in the request and a ACK or RST value in
the response. Exploiting the asymmetry in compression will allow the response. Exploiting the asymmetry in compression will allow
to send no bit in the compressed request and a single bit in the to send no bit in the compressed request and a single bit in the
answer. Same behavior can be applied to the CoAP Code field (O.OX answer. Same behavior can be applied to the CoAP Code field (O.OX
code are present in the request and Y.ZZ in the answer). code are present in the request and Y.ZZ in the answer).
o CoAP also obeys to the client/server paradigm and the compression o CoAP also obeys to the client/server paradigm and the compression
rate can be different if the request is issued from a LPWAN node rate can be different if the request is issued from an LPWAN node
or from an non LPWAN device. For instance a Thing (ES) aware of or from an non LPWAN device. For instance a Thing (ES) aware of
LPWAN constraints can generate a 1 byte token, but a regular CoAP LPWAN constraints can generate a 1 byte token, but a regular CoAP
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
compression rate. Nevertheless a proxy placed before the compression rate. Nevertheless a proxy placed before the
compressor may change some field values to offer a better compressor may change some field values to offer a better
compression rate and maintain the necessary context for compression rate and maintain the necessary context for
interoperability with existing CoAP implementations. interoperability with existing CoAP implementations.
o In IPv6 and UDP header fields have a fixed size. In CoAP, Token o In IPv6 and UDP header fields have a fixed size. In CoAP, Token
size may vary from 0 to 8 bytes, length is given by a field in the size may vary from 0 to 8 bytes, length is given by a field in the
header. More systematically, the CoAP options are described using header. More systematically, the CoAP options are described using
the Type-Length-Value. When applying SCHC header compression. the Type-Length-Value. When applying SCHC header compression.
By sending compressed field information following the rule order, By sending compressed field information following the rule order,
SCHC offers a serialization/deserialization mechanism. Since a SCHC offers a serialization/deserialization mechanism. Since a
field exists to indicate the token length there is no ambiguity. field exists to indicate the token length there is no ambiguity.
For options, the rule indicates also the expected options found For options, the rule indicates also the expected options found
the int CoAP header. Therefore only the length is needed to the int CoAP header. Therefore only the length is needed to
recognise an option. The length will be send using the same CoAP recognize an option. The length will be sent using the same CoAP
encoding (size less than 12 are directly sent, higher values uses encoding (size less than 12 are directly sent, higher values use
the escape mechanisms defined by [rfc7252]). Delta Type is the escape mechanisms defined by [rfc7252]). Delta Type is
omitted, the value will be recovered by the decompressor. This omitted, the value will be recovered by the decompressor. This
reduce the option length of 4, 12 or 20 bits regarding the reduces the option length of 4, 12 or 20 bits regarding the
orignial size of the delta type encoding in the option. original size of the delta type encoding in the option.
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) or accepted instances, elements of an URI (path or queries) or accepted
formats. The position defined in a rule, associated to a Field formats. The position defined in a rule, associated to a Field
ID, can be used to identify the proper element. ID, can be used to identify the proper element.
3. Compression of CoAP header fields 3. Compression of CoAP header fields
This section discusses of the compression of the different CoAP This section discusses of the compression of the different CoAP
header fields. These are just examples. The compression should take header fields. These are just examples. The compression should take
into account the nature of the traffic and not only the field values. into account the nature of the traffic and not only the field values.
Next chapter will define some compression rules for some common Next chapter will define some compression rules for some common
exchanges. exchanges.
3.1. CoAP version field (2 bits) 3.1. CoAP version field (2 bits)
This field is bidirectional and can be elided during the SCHC This field is bidirectional and can be elided during the SCHC
compression, since it always contains the same value. It appears compression, since it always contains the same value. It appears
only in first position. only in first position.
FID Pos DI TV MO CDF FID FL FP DI Value MO CDA Sent
ver 1 bi 1 equal not-sent ver 2 1 bi 1 equal not-sent
3.2. CoAP type field 3.2. CoAP type field
This field can be managed bidirectionally or unidirectionally.Several This field can be managed bidirectionally or unidirectionally.Several
strategies can be applied to this field regarding the values used: strategies can be applied to this field regarding the values used:
o If the ES is a client or a Server and non confirmable message are o If the ES is a client or a Server and non confirmable message are
used, the transmission of the Type field can be avoided: used, the transmission of the Type field can be avoided:
* Pos is always 1, * Pos is always 1,
* DI can either be "uplink" if the ES is a CoAP client or * DI can either be "uplink" if the ES is a CoAP client or
"downlink" if the ES is a CoAP server, or "bidirectional" "downlink" if the ES is a CoAP server, or "bidirectional"
* TV is set to the value, * TV is set to the value,
* MO is set to "equal" * MO is set to "equal"
* CDF is set to "not-sent". * CDA is set to "not-sent".
FID Pos DI TV MO CDF FID FL FP DI Target Value MO CDA Sent
type 1 bi NON equal not-sent type 2 1 bi NON equal not-sent
o If the ES is either a client or a Server and confirmable message o If the ES is either a client or a Server and confirmable message
are used, the DI can be used to elide the type on the request and are used, the DI can be used to elide the type on the request and
compress it to 1 bit on the response. The example above shows the compress it to 1 bit on the response. The example above shows the
rule for a ES acting as a client, directions need to be reversed rule for a ES acting as a client, directions need to be reversed
for a ES acting as a server. for a ES acting as a server.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
type 1 up CON equal not-sent type 2 1 up CON equal not-sent
type 1 dw {0:ACK, 1:RST} match-mapping mapping-sent type 2 1 dw [ACK,RST] match-mapping mapping-sent [1]
o Otherwise if the ES is acting simultaneously as a client and a o Otherwise if the ES is acting simultaneously as a client and a
server and the rule handle these two traffics, Type field must be server and the rule handle these two traffics, Type field must be
sent uncompressed. sent uncompressed.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
type 1 bi ignore send-value type 2 1 bi ignore send-value [2]
3.3. CoAP token length field 3.3. CoAP token length field
This field is bi-directional. This field is bi-directional.
Several strategies can be applied to this field regarding the values: Several strategies can be applied to this field regarding the values:
o no token or a wellknown length, the transmission can be avoided. o no token or a wellknown length, the transmission can be avoided.
A special care must be taken, if CON messages are acknowledged A special care must be taken, if CON messages are acknowledged
with an empty ACK message. In that case the token is not always with an empty ACK message. In that case the token is not always
present. present.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
TKL 1 bi value ignore send-value TKL 4 1 bi value ignore send-value [4]
o If the length is changing from one message to an other, the Token o If the length is changing from one message to an other, the Token
Length field must be sent. If the Token length can be limited, Length field must be sent. If the Token length can be limited,
then only the least significant bits have to be sent. The example then only the least significant bits have to be sent. The example
below allows values between 0 and 3. below allows values between 0 and 3.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
TKL 1 bi 0x0 MSB(2) LSB(2) TKL 4 1 bi 0x0 MSB(2) LSB(2) [2]
o otherwise the field value has to be sent. o otherwise the field value has to be sent.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
TKL 1 bi ignore value-sent TKL 4 1 bi ignore value-sent [4]
3.4. CoAP code field 3.4. CoAP code field
This field is bidirectional, but compression can be enhanced using This field is bidirectional, but compression can be enhanced using
DI. DI.
The CoAP Code field defines a tricky way to ensure compatibility with The CoAP Code field defines a tricky way to ensure compatibility with
HTTP values. Nevertheless only 21 values are defined by [rfc7252] HTTP values. Nevertheless only 21 values are defined by [rfc7252]
compared to the 255 possible values. compared to the 255 possible values.
+------+------------------------------+-----------+ +------+------------------------------+-----------+
| Code | Description | Mapping | | Code | Description | Mapping |
+------+------------------------------+-----------+ +------+------------------------------+-----------+
| 0.00 | | 0x00 | | 0.00 | | 0x00 |
| 0.01 | GET | 0x01 | | 0.01 | GET | 0x01 |
| 0.02 | POST | 0x02 | | 0.02 | POST | 0x02 |
| 0.03 | PUT | 0x03 | | 0.03 | PUT | 0x03 |
| 0.04 | DELETE | 0x04 | | 0.04 | DELETE | 0x04 |
| 0.05 | FETCH | 0x05 | | 0.05 | FETCH | 0x05 |
| 0.06 | PATCH | 0x06 | | 0.06 | PATCH | 0x06 |
| 0.07 | iPATCH | 0x07 | | 0.07 | iPATCH | 0x07 |
| 2.01 | Created | 0x08 | | 2.01 | Created | 0x08 |
| 2.02 | Deleted | 0x09 | | 2.02 | Deleted | 0x09 |
| 2.03 | Valid | 0x0A | | 2.03 | Valid | 0x0A |
| 2.04 | Changed | 0x0B | | 2.04 | Changed | 0x0B |
| 2.05 | Content | 0x0C | | 2.05 | Content | 0x0C |
| 4.00 | Bad Request | 0x0D | | 4.00 | Bad Request | 0x0D |
| 4.01 | Unauthorized | 0x0E | | 4.01 | Unauthorized | 0x0E |
| 4.02 | Bad Option | 0x0F | | 4.02 | Bad Option | 0x0F |
| 4.03 | Forbidden | 0x10 | | 4.03 | Forbidden | 0x10 |
| 4.04 | Not Found | 0x11 | | 4.04 | Not Found | 0x11 |
| 4.05 | Method Not Allowed | 0x12 | | 4.05 | Method Not Allowed | 0x12 |
| 4.06 | Not Acceptable | 0x13 | | 4.06 | Not Acceptable | 0x13 |
| 4.12 | Precondition Failed | 0x14 | | 4.12 | Precondition Failed | 0x14 |
| 4.13 | Request Entity Too Large | 0x15 | | 4.13 | Request Entity Too Large | 0x15 |
| 4.15 | Unsupported Content-Format | 0x16 | | 4.15 | Unsupported Content-Format | 0x16 |
| 5.00 | Internal Server Error | 0x17 | | 5.00 | Internal Server Error | 0x17 |
| 5.01 | Not Implemented | 0x18 | | 5.01 | Not Implemented | 0x18 |
| 5.02 | Bad Gateway | 0x19 | | 5.02 | Bad Gateway | 0x19 |
| 5.03 | Service Unavailable | 0x1A | | 5.03 | Service Unavailable | 0x1A |
| 5.04 | Gateway Timeout | 0x1B | | 5.04 | Gateway Timeout | 0x1B |
| 5.05 | Proxying Not Supported | 0x1C | | 5.05 | Proxying Not Supported | 0x1C |
+------+------------------------------+-----------+ +------+------------------------------+-----------+
Figure 1: Example of CoAP code mapping Figure 1: Example of CoAP code mapping
Figure 1 gives a possible mapping, it can be changed to add new codes Figure 1 gives a possible mapping, it can be changed to add new codes
or reduced if some values are never used by both ends. It could or reduced if some values are never used by both ends. It could
efficiently be coded on 5 bits. efficiently be coded on 5 bits.
Even if the number of code can be increase with other RFC, Even if the number of code can be increase with other RFC,
implementations may use a limited number of values, which can help to implementations may use a limited number of values, which can help to
reduce the number of bits sent on the LPWAN. reduce the number of bits sent on the LPWAN.
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The field can be treated differently in upstream than in downstream. The field can be treated differently in upstream than in downstream.
If the Thing is a client an entry can be set on the uplink message If the Thing is a client an entry can be set on the uplink message
with a code matching for 0.0X values and another for downlink values with a code matching for 0.0X values and another for downlink values
for Y.ZZ codes. It is the opposite if the thing is a server. for Y.ZZ codes. It is the opposite if the thing is a server.
If the ES always sends or receives requests with the same method, the If the ES always sends or receives requests with the same method, the
Code field can be elided. The entry below shows a rule for a client Code field can be elided. The entry below shows a rule for a client
sending only GET request. sending only GET request.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
code 1 up GET equal not-sent code 8 1 up GET equal not-sent
If the client may send different methods, a matching-list can be If the client may send different methods, a matching-list can be
applied. For table Figure 1, 3 bits are necessary, but it could be applied. For table Figure 1, 3 bits are necessary, but it could be
less if fewer methods are used. Example below gives an example where less if fewer methods are used. Example below gives an example where
the ES is a server and receives only GET and POST requests. the ES is a server and receives only GET and POST requests.
FID Pos DI TV MO CDF FID FL FP DI Target Value MO CDA Sent
code 1 dw {0:0.01, 1:0.02}match-mapping mapping-sent code 8 1 dw [0.01, 0.02] match-mapping mapping-sent [1]
The same approach can be applied to responses. The same approach can be applied to responses.
3.5. CoAP Message ID field 3.5. CoAP Message ID field
This field is bidirectional. This field is bidirectional.
Message ID is used for two purposes: Message ID is used for two purposes:
o To acknowledge a CON message with an ACK. o To acknowledge a CON message with an ACK.
o To avoid duplicate messages. o To avoid duplicate messages.
In LPWAN, since a message can be received by several radio gateway, In LPWAN, since a message can be received by several radio gateway,
some LPWAN technologies include a sequence number in L2 to avoid some LPWAN technologies include a sequence number in L2 to avoid
duplicate frames. Therefore if the message does not need to be duplicate frames. Therefore if the message does not need to be
acknowledged (NON or RST message), the Message ID field can be acknowledged (NON or RST message), the Message ID field can be
avoided. avoided.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
Mid 1 bi ignore not-sent Mid 8 1 bi ignore not-sent
The decompressor must generate a value. The decompressor must generate a value.
[[Note; check id this field is not used by OSCOAP .]] [[Note; check id this field is not used by OSCOAP .]]
To optimize information sent on the LPWAN, shorter values may be used To optimize information sent on the LPWAN, shorter values may be used
during the exchange, but Message ID values generated a common CoAP during the exchange, but Message ID values generated a common CoAP
implementation will not take into account this limitation. Before implementation will not take into account this limitation. Before
the compression, a proxy may be needed to reduce the size. the compression, a proxy may be needed to reduce the size.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
Mid 1 bi 0x0000 MSB(12) LSB(4) Mid 8 1 bi 0x0000 MSB(12) LSB(4) [4]
Otherwise if no compression is possible, the field has to be sent Otherwise if no compression is possible, the field has to be sent
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
Mid 1 bi ignore value-sent Mid 8 1 bi ignore value-sent [8]
3.6. CoAP Token field 3.6. CoAP Token field
This field is bi-directional. This field is bi-directional.
Token is used to identify transactions and varies from one Token is used to identify transactions and varies from one
transaction to another. Therefore, it is usually necessary to send transaction to another. Therefore, it is usually necessary to send
the value of the token field on the LPWAN network. The optimization the value of the token field on the LPWAN network. The optimization
will occur by using small values. will occur by using small values.
Common CoAP implementations may generate large tokens, even if Common CoAP implementations may generate large tokens, even if
shorter tokens could be used regarding the LPWAN characteristics. A shorter tokens could be used regarding the LPWAN characteristics. A
proxy may be needed to reduce the size of the token before proxy may be needed to reduce the size of the token before
compression. compression.
The size of the compress token sent is known by a combination of the The size of the compress token sent is known by a combination of the
Token Length field and the rule entry. For instance, with the entry Token Length field and the rule entry. For instance, with the entry
below: below:
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
tkl 1 bi 2 equal not-sent tkl 4 1 bi 2 equal not-sent
token 1 bi 0x00 MSB(12) LSB(4) token 8 1 bi 0x00 MSB(12) LSB(4) [4]
The uncompressed token is 2 bytes long, but the compressed size will The uncompressed token is 2 bytes long, but the compressed size will
be 4 bits. be 4 bits.
4. CoAP options 4. CoAP options
4.1. CoAP option Content-format field. 4.1. CoAP option Content-format field.
This field is unidirectional and must not be set to bidirectional in This field is unidirectional and must not be set to bidirectional in
a rule entry. It is used only by the server to inform the client a rule entry. It is used only by the server to inform the client
about of the payload type and is never found in client requests. about of the payload type and is never found in client requests.
If single value is expected by the client, the TV contains that value If single value is expected by the client, the TV contains that value
and MO is set to "equal" and the CDF is set to "not-sent". The and MO is set to "equal" and the CDF is set to "not-sent". The
examples below describe the rules for an ES acting as a server. examples below describe the rules for an ES acting as a server.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
content 1 up value equal not-sent content 16 1 up value equal not-sent
If several possible value are expected by the client, a matching-list If several possible value are expected by the client, a matching-list
can be used. can be used.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
content 1 up {0:50,1:41} match-mapping mapping-sent content 16 1 up [50, 41] match-mapping mapping-sent [1]
Otherwise the value can be sent.The value-sent CDF in the compressor Otherwise the value can be sent.The value-sent CDF in the compressor
do not send the option type and the decompressor reconstruct it do not send the option type and the decompressor reconstruct it
regarding the position in the rule. regarding the position in the rule.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
content 1 up ignore value-sent content 16 1 up ignore value-sent [0-16]
4.2. CoAP option Accept field 4.2. CoAP option Accept field
This field is unidirectional and must not be set to bidirectional in This field is unidirectional and must not be set to bidirectional in
a rule entry. It is used only by the client to inform of the a rule entry. It is used only by the client to inform of the
possible payload type and is never found in server response. possible payload type and is never found in server response.
The number of accept options is not limited and can vary regarding The number of accept options is not limited and can vary regarding
the usage. To be selected a rule must contain the exact number about the usage. To be selected a rule must contain the exact number about
accept options with their positions. Since the order in which the accept options with their positions. Since the order in which the
Accept value are sent, the position order can be modified. The rule Accept value are sent, the position order can be modified. The rule
below below
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
accept 1 up 41 egal not-sent accept 16 1 up 41 egal not-sent
accept 2 up 50 egal not-sent accept 16 2 up 50 egal not-sent
will be selected only if two accept options are in the CoAP header if will be selected only if two accept options are in the CoAP header if
this order. this order.
The rule below: The rule below:
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
accept 0 up 41 egal not-sent accept 16 0 up 41 egal not-sent
accept 0 up 50 egal not-sent accept 16 0 up 50 egal not-sent
will accept a-only CoAP messages with 2 accept options, but the order will accept a-only CoAP messages with 2 accept options, but the order
will not influence the rule selection. The decompression will will not influence the rule selection. The decompression will
reconstruct the header regarding the rule order. reconstruct the header regarding the rule order.
Otherwise a matching-list can be applied to the different values, in Otherwise a matching-list can be applied to the different values, in
that case the order is important to recover the appropriate value and that case the order is important to recover the appropriate value and
the position must be clearly indicate. the position must be clearly indicate.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
accept 1 up {0:50,1:41} match-mapping mapping-sent accept 16 1 up [50,41] match-mapping mapping-sent [1]
accept 2 up {0:50,1:61} match-mapping mapping-sent accept 16 2 up [50,61] match-mapping mapping-sent [1]
accept 3 up {0:61,1:71} match-mapping mapping-sent accept 16 3 up [61,71] match-mapping mapping-sent [1]
Finally, the option can be explicitly sent. Finally, the option can be explicitly sent.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
accept 1 up ignore value-sent accept 1 up ignore value-sent
4.3. CoAP option Max-Age field, CoAP option Uri-Host and Uri-Port 4.3. 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
LPWAN. LPWAN.
skipping to change at page 11, line 45 skipping to change at page 11, line 45
5. CoAP option Uri-Path and Uri-Query fields 5. CoAP option Uri-Path and Uri-Query fields
This fields are unidirectional and must not be set to bidirectional This fields are unidirectional and must not be set to bidirectional
in a rule entry. They are used only by the client to access to a in a rule entry. They are used only by the client to access to a
specific resource and are never found in server response. specific resource and are never found in server response.
The Matching Operator behavior has not changed, but the value must The Matching Operator behavior has not changed, but the value must
take a position value, if the entry is repeated : take a position value, if the entry is repeated :
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
URI-Path 1 up foo equal not-sent URI-Path 1 up foo equal not-sent
URI-Path 2 up bar equal not-sent URI-Path 2 up bar equal not-sent
Figure 2: Position entry. Figure 2: Position entry.
For instance, the rule Figure 2 matches with /foo/bar, but not /bar/ For instance, the rule Figure 2 matches with /foo/bar, but not /bar/
foo. foo.
When the length is not clearly indicated in the rule, the value When the length is not clearly indicated in the rule, the value
length must be sent with the field data, which means for CoAP to send length must be sent with the field data, which means for CoAP to send
directly the CoAP option with length and value. directly the CoAP option with length and value.
For instance for a CoMi path /c/X6?k="eth0" the rule can be set to: For instance for a CoMi path /c/X6?k="eth0" the rule can be set to:
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
URI-Path 1 up c equal not-sent URI-Path 1 up c equal not-sent
URI-Path 2 up ignore value-sent URI-Path 2 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB URI-Query 1 up k= MSB (16) LSB
Figure 3: CoMi URI compression Figure 3: CoMi URI compression
Figure 3 shows the parsing and the compression of the URI. where c is Figure 3 shows the parsing and the compression of the URI. where c is
not sent. The second element is sent with the length (i.e. 0x2 X 6) not sent. The second element is sent with the length (i.e. 0x2 X 6)
followed by the query option (i.e. 0x05 "eth0"). followed by the query option (i.e. 0x05 "eth0").
A Mapping list can be used to reduce size of variable Paths or A Mapping list can be used to reduce size of variable Paths or
Queries. In that case, to optimize the compression, several elements Queries. In that case, to optimize the compression, several elements
can be regrouped into a single entry. Numbering of elements do not can be regrouped into a single entry. Numbering of elements do not
change, MO comparison is set with the first element of the matching. change, MO comparison is set with the first element of the matching.
FID Pos DI TV MO CDF FID FL FP DI TV MO CDA Sent
URI-Path 1 up {0:"/c/c", equal not-sent URI-Path 1 up {0:"/c/c", equal not-sent
1:"/c/d" 1:"/c/d"
URI-Path 3 up ignore value-sent URI-Path 3 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB URI-Query 1 up k= MSB (16) LSB
Figure 4: complex path example Figure 4: complex path example
For instance, the following Path /foo/bar/variable/stable can leads For instance, the following Path /foo/bar/variable/stable can leads
to the rule defined Figure 4. to the rule defined Figure 4.
5.1. CoAP option Proxy-URI and Proxy-Scheme fields 5.1. CoAP option Proxy-URI and Proxy-Scheme fields
These fields are unidirectional and must not be set to bidirectional These fields are unidirectional and must not be set to bidirectional
in a rule entry. They are used only by the client to access to a in a rule entry. They are used only by the client to access to a
skipping to change at page 14, line 12 skipping to change at page 14, line 12
7. Protocol analysis 7. Protocol analysis
8. Examples of CoAP header compression 8. Examples of CoAP header compression
8.1. Mandatory header with CON message 8.1. Mandatory header with CON message
In this first scenario, the LPWAN compressor receives from outside In this first scenario, the LPWAN compressor receives from outside
client a POST message, which is immediately acknowledged by the client a POST message, which is immediately acknowledged by the
Thing. For this simple scenario, the rules are described Figure 5. Thing. For this simple scenario, the rules are described Figure 5.
rule id 1 Rule ID 1
+-------------+------+---------+-------------+-----+----------------+ +-------------+--+--+--+------+---------+-------------++------------+
| Field |TV |MO |CDF |dir | Sent | | Field |FL|FP|DI|Target| Match | CDA || Sent |
+=============+======+=========+=============+=====+================+ | | | | |Value | Opera. | || [bits] |
|CoAP version | 01 |equal |not-sent |bi | | +-------------+--+--+--+------+---------+-------------++------------+
|CoAP Type | |ignore |value-sent |bi |TT | |CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP TKL | 0 |equal |not-sent |bi | | |CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Code | ML1 |match-map|matching-sent|bi | CC CCC | |CoAP Type | | |bi| |ignore |value-sent ||TT |
|CoAP MID | 0000 |MSB(7 ) |LSB(9) |bi | M-ID | |CoAP TKL | | |bi| 0 |equal |not-sent || |
|CoAP Uri-Path| path |equal 1 |not-sent |down | | |CoAP Code | | |bi| ML1 |match-map|matching-sent|| CC CCC |
+-------------+------+---------+-------------+-----+----------------+ |CoAP MID | | |bi| 0000 |MSB(7 ) |LSB(9) || M-ID|
|CoAP Uri-Path| | |dw| path |equal 1 |not-sent || |
+-------------+--+--+--+------+---------+-------------++------------+
Figure 5: CoAP Context to compress header without token Figure 5: CoAP Context to compress header without token
The version and Token Length fields are elided. Code has shrunk to 5 The version and Token Length fields are elided. Code has shrunk to 5
bits using the matching list (as the one given Figure 1: 0.01 is bits using the matching list (as the one given Figure 1: 0.01 is
value 0x01 and 2.05 is value 0x0c) Message-ID has shrunk to 9 bits to value 0x01 and 2.05 is value 0x0c) Message-ID has shrunk to 9 bits to
preserve alignment on byte boundary. The most significant bit must preserve alignment on byte boundary. The most significant bit must
be set to 0 through a CoAP proxy. Uri-Path contains a single element be set to 0 through a CoAP proxy. Uri-Path contains a single element
indicated in the matching operator. indicated in the matching operator.
skipping to change at page 15, line 5 skipping to change at page 15, line 5
only the Type, a mapped code and the least 9 significant bits of only the Type, a mapped code and the least 9 significant bits of
Message ID. The receiver decompresses the header. . Message ID. The receiver decompresses the header. .
The CON message is a request, therefore the LC process to a dynamic The CON message is a request, therefore the LC process to a dynamic
mapping. When the ES receives the ACK message, this will not mapping. When the ES receives the ACK message, this will not
initiate locally a message ID mapping since it is a response. The LC initiate locally a message ID mapping since it is a response. The LC
receives the ACK and uncompressed it to restore the original value. receives the ACK and uncompressed it to restore the original value.
Dynamic Mapping context lifetime follows the same rules as message ID Dynamic Mapping context lifetime follows the same rules as message ID
duration. duration.
End System LPWA LC End System LPWA LC
| | | |
| rule id=1 |<---------------------- | rule id=1 |<--------------------
|<--------------------| +-+-+--+----+--------+ |<-------------------| +-+-+--+----+------+
<-------------------- | TTCC CCCM MMMM MMMM| |1|0| 4|0.01| 0x0034 | <------------------- | TTCC CCCM MMMM MMMM| |1|0| 4|0.01|0x0034|
+-+-+--+----+--------+ | 0000 0010 0011 0100| | 0xb4 p a t | +-+-+--+----+-------+ | 0000 0010 0011 0100| | 0xb4 p a t|
|1|0| 1|0.01| 0x0034 | | | | h | |1|0| 1|0.01|0x0034 | | | | h |
| 0xb4 p a t | | | +------+ | 0xb4 p a t | | | +------+
| h | | | | h | | |
+------+ | | +------+ | |
| | | |
| | | |
+-+-+--+----+--------+ |-------------------->| ---------------------->| rule id=1 |
|1|2| 0|2.05| 0x0034 | | TTCC CCCM MMMM MMMM|------------------------> +-+-+--+----+--------+ |------------------->|
+-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+--------+ |1|2| 0|2.05| 0x0034 | | TTCC CCCM MMMM MMMM|--------------------->
| | |1|2| 0|2.05| 0x0034 | +-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+------+
v v +-+-+--+----+--------+ | | |1|2| 0|2.05|0x0034|
v v +-+-+--+----+------+
Figure 6: Compression with global addresses Figure 6: Compression with global addresses
The message can be further optimized by setting some fields The message can be further optimized by setting some fields
unidirectional, as described in Figure 7. Note that Type is no more unidirectional, as described in Figure 7. Note that Type is no more
sent in the compressed format, Compressed Code size in not changed in sent in the compressed format, Compressed Code size in not changed in
that example (8 values are needed to code all the requests and 21 to that example (8 values are needed to code all the requests and 21 to
code all the responses in the matching list Figure 1) code all the responses in the matching list Figure 1)
rule id 1 Rule ID 2
+-------------+------+---------+-------------+---+----------------+ +-------------+--+--+--+------+---------+------------++------------+
| Field |TV |MO |CDF |dir| Sent | | Field |FL|FP|DI|Target| MO | CDA || Sent |
+=============+======+=========+=============+===+================+ | | | | |Value | | || [bits] |
|CoAP version | 01 |equal |not-sent |bi | | +-------------+--+--+--+------+---------+------------++------------+
|CoAP Type | CON |equal |not-sent |dw | | |CoAP version | | |bi|01 |equal |not-sent || |
|CoAP Type | ACK |equal |not-sent |up | | |CoAP Type | | |dw|CON |equal |not-sent || |
|CoAP TKL | 0 |equal |not-sent |bi | | |CoAP Type | | |up| ACK |equal |not-sent || |
|CoAP Code | ML2 |match-map|mapping-sent |dw |CCCC C | |CoAP TKL | | |bi|0 |equal |not-sent || |
|CoAP Code | ML3 |match-map|mapping-sent |up |CCCC C | |CoAP Code | | |dw|ML2 |match-map|mapping-sent||CCCC C |
|CoAP MID | 0000 |MSB(5) |LSB(11) |bi | M-ID | |CoAP Code | | |up|ML3 |match-map|mapping-sent||CCCC C |
|CoAP Uri-Path| path |equal 1 |not-sent |dw | | |CoAP MID | | |bi|0000 |MSB(5) |LSB(11) || M-ID |
+-------------+------+---------+-------------+---+----------------+ |CoAP Uri-Path| | |dw|path |equal 1 |not-sent || |
+-------------+--+--+--+------+---------+------------++------------+
ML1 = {CON : 0, ACK:1} ML2 = {POST:0, 2.04:1, 0.00:3} ML1 = {CON : 0, ACK:1} ML2 = {POST:0, 2.04:1, 0.00:3}
Figure 7: CoAP Context to compress header without token Figure 7: CoAP Context to compress header without token
8.2. Complete exchange 8.2. Complete exchange
In that example, the Thing is using CoMi and sends queries for 2 SID. In that example, the Thing is using CoMi and sends queries for 2 SID.
CON CON
skipping to change at page 16, line 26 skipping to change at page 16, line 26
|<------------------------| ACK MID=0x0012 |<------------------------| ACK MID=0x0012
| | 0.00 | | 0.00
| | | |
| | | |
|<------------------------| CON |<------------------------| CON
| | MID=0X0034 | | MID=0X0034
| | Content-Format X | | Content-Format X
ACK MID=0x0034 |------------------------>| ACK MID=0x0034 |------------------------>|
0.00 0.00
rule id 3 Rule ID 3
+-------------+------+---------+-------------+---+----------------+ +--------------+--+--+--+------+--------+-----------++------------+
| Field |TV |MO |CDF |dir| Sent | | Field |FL|FP|DI|Target| MO | CDA || Sent |
+=============+======+=========+=============+===+================+ | | | | |Value | | || [bits] |
|CoAP version | 01 |equal |not-sent |bi | | +--------------+--+--+--+------+--------+-----------++------------+
|CoAP Type | CON |equal |not-sent |up | | |CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | ACK |equal |not-sent |dw | | |CoAP Type | | |up| CON |equal |not-sent || |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP Type | | |dw| ACK |equal |not-sent || |
|CoAP Code | POST |equal |not-sent |up | | |CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | 0.00 |equal |not-sent |dw | | |CoAP Code | | |up| POST |equal |not-sent || |
|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM | |CoAP Code | | |dw| 0.00 |equal |not-sent || |
|CoAP Token | |ignore |send-value |up |TTTTTTTT | |CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|CoAP Uri-Path| /c |equal 1 |not-sent |dw | | |CoAP Token | | |up| |ignore |send-value ||TTTTTTTT |
|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P | |CoAP Uri-Path | | |dw| /c |equal 1 |not-sent || |
|CoAP Content | X |equal |not-sent |up | | |CoAP Uri-query| | |dw| ML4 |equal 1 |not-sent ||P |
+-------------+------+---------+-------------+---+----------------+ |CoAP Content | | |up| X |equal |not-sent || |
+--------------+--+--+--+------+--------+-----------++------------+
rule id 4 Rule ID 4
+-------------+------+---------+-------------+---+----------------+ +--------------+--+--+--+------+--------+-----------++------------+
| Field |TV |MO |CDF |dir| Sent | | Field |FL|FP|DI|Target| MO | CDA || Sent |
+=============+======+=========+=============+===+================+ | | | | |Value | | || [bits] |
|CoAP version | 01 |equal |not-sent |bi | | +--------------+--+--+--+------+--------+-----------++------------+
|CoAP Type | CON |equal |not-sent |dw | | |CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | ACK |equal |not-sent |up | | |CoAP Type | | |dw| CON |equal |not-sent || |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP Type | | |up| ACK |equal |not-sent || |
|CoAP Code | 2.05 |equal |not-sent |dw | | |CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | 0.00 |equal |not-sent |up | | |CoAP Code | | |dw| 2.05 |equal |not-sent || |
|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM | |CoAP Code | | |up| 0.00 |equal |not-sent || |
|CoAP Token | |ignore |send-value |dw |TTTTTTTT | |CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|COAP Accept | X |equal |not-sent |dw | | |CoAP Token | | |dw| |ignore |send-value||TTTTTTTT |
+-------------+------+---------+-------------+---+----------------+ |COAP Accept | | |dw| X |equal |not-sent || |
+--------------+--+--+--+------+---------+----------++------------+
alternative rule: alternative rule:
rule id 4 Rule ID 4
+-------------+------+---------+-------------+---+----------------+ +--------------+--+--+--+------+---------+-----------++------------+
| Field |TV |MO |CDF |dir| Sent | | Field |FL|FP|DI|Target| MO | CDA || Sent |
+=============+======+=========+=============+===+================+ | | | | |Value | | || [bits] |
|CoAP version | 01 |equal |not-sent |bi | | +--------------+--+--+--+------+---------+-----------++------------+
|CoAP Type | ML1 |match-map|match-sent |bi |t | |CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP Type | | |bi| ML1 |match-map|match-sent ||t |
|CoAP Code | ML2 |match-map|match-sent |up | cc | |CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | ML3 |match-map|match-sent |dw | cc | |CoAP Code | | |up| ML2 |match-map|match-sent || cc |
|CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM | |CoAP Code | | |dw| ML3 |match-map|match-sent || cc |
|CoAP Token | |ignore |send-value |dw |TTTTTTTT | |CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|CoAP Uri-Path| /c |equal 1 |not-sent |dw | | |CoAP Token | | |dw| |ignore |send-value ||TTTTTTTT |
|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P | |CoAP Uri-Path | | |dw| /c |equal 1 |not-sent || |
|CoAP Content | X |equal |not-sent |up | | |CoAP Uri-query| | |dw| ML4 |equal 1 |not-sent ||P |
|COAP Accept | x |equal |not-sent |dw | | |CoAP Content | | |up| X |equal |not-sent || |
+-------------+------+---------+-------------+---+----------------+ |COAP Accept | | |dw| x |equal |not-sent || |
+--------------+--+--+--+------+---------+-----------++------------+
ML1 {CON:0, ACK:1} ML2 {POST:0, 0.00: 1} ML3 {2.05:0, 0.00:1} ML1 {CON:0, ACK:1} ML2 {POST:0, 0.00: 1} ML3 {2.05:0, 0.00:1}
ML4 {NULL:0, k=AS:1, K=AZE:2} ML4 {NULL:0, k=AS:1, K=AZE:2}
9. Normative References 9. Normative References
[I-D.toutain-lpwan-ipv6-static-context-hc] [I-D.toutain-lpwan-ipv6-static-context-hc]
Minaburo, A. and L. Toutain, "LPWAN Static Context Header Minaburo, A. and L. Toutain, "LPWAN Static Context Header
Compression (SCHC) for IPv6 and UDP", draft-toutain-lpwan- Compression (SCHC) for IPv6 and UDP", draft-toutain-lpwan-
ipv6-static-context-hc-00 (work in progress), September ipv6-static-context-hc-00 (work in progress), September
skipping to change at page 18, line 21 skipping to change at page 18, line 26
Ana Minaburo Ana Minaburo
Acklio Acklio
2bis rue de la Chataigneraie 2bis rue de la Chataigneraie
35510 Cesson-Sevigne Cedex 35510 Cesson-Sevigne Cedex
France France
Email: ana@ackl.io Email: ana@ackl.io
Laurent Toutain Laurent Toutain
Institut MINES TELECOM ; IMT Atlantique Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie 2 rue de la Chataigneraie
CS 17607 CS 17607
35576 Cesson-Sevigne Cedex 35576 Cesson-Sevigne Cedex
France France
Email: Laurent.Toutain@imt-atlantique.fr Email: Laurent.Toutain@imt-atlantique.fr
 End of changes. 45 change blocks. 
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