draft-ietf-lpwan-coap-static-context-hc-01.txt   draft-ietf-lpwan-coap-static-context-hc-02.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: September 11, 2017 Institut MINES TELECOM ; IMT Atlantique Expires: March 10, 2018 Institut MINES TELECOM ; IMT Atlantique
March 10, 2017 September 06, 2017
LPWAN Static Context Header Compression (SCHC) for CoAP LPWAN Static Context Header Compression (SCHC) for CoAP
draft-ietf-lpwan-coap-static-context-hc-01 draft-ietf-lpwan-coap-static-context-hc-02
Abstract Abstract
This draft discusses the way SCHC header compression can be applied This draft defines the way SCHC header compression can be applied to
to CoAP headers in an LPWAN flow regarding the generated traffic. CoAP headers. CoAP header structure differs from IPv6 and UDP
CoAP protocol differs from IPv6 and UDP protocols because the CoAP protocols since the CoAP Header is flexible header with a variable
Header has a flexible header due to variable options. Another number of options themself of a variable length. Another important
important difference is the asymmetric format in the header difference is the asymmetry in the header information used for
information used in the request and the response packets. This draft request and response messages. This draft takes into account the
shows that the Client and the Server do not uses the same fields and fact that a thing can play the role of a CoAP client, a CoAP client
how the SCHC header compression can be used. or both roles.
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-
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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
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This Internet-Draft will expire on September 11, 2017. This Internet-Draft will expire on March 10, 2018.
Copyright Notice Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. CoAP Compressing . . . . . . . . . . . . . . . . . . . . . . 3
3. Compression of CoAP header fields . . . . . . . . . . . . . . 4
3.1. CoAP version field (2 bits) . . . . . . . . . . . . . . . 4
3.2. CoAP type field . . . . . . . . . . . . . . . . . . . . . 5
3.3. CoAP token length field . . . . . . . . . . . . . . . . . 5
3.4. CoAP code field . . . . . . . . . . . . . . . . . . . . . 6
3.5. CoAP Message ID field . . . . . . . . . . . . . . . . . . 8
3.6. CoAP Token field . . . . . . . . . . . . . . . . . . . . 9
4. CoAP options . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. CoAP option Content-format field. . . . . . . . . . . . . 9
4.2. CoAP option Accept field . . . . . . . . . . . . . . . . 10
4.3. CoAP option Max-Age field, CoAP option Uri-Host and Uri-
Port fields . . . . . . . . . . . . . . . . . . . . . . . 11
5. CoAP option Uri-Path and Uri-Query fields . . . . . . . . . . 11
5.1. CoAP option Proxy-URI and Proxy-Scheme fields . . . . . . 12
5.2. CoAP option ETag, If-Match, If-None-Match, Location-Path
and Location-Query fields . . . . . . . . . . . . . . . . 13
6. Other RFCs . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Block . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Observe . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.3. No-Response . . . . . . . . . . . . . . . . . . . . . . . 13
7. Protocol analysis . . . . . . . . . . . . . . . . . . . . . . 13
8. Examples of CoAP header compression . . . . . . . . . . . . . 14
8.1. Mandatory header with CON message . . . . . . . . . . . . 14
8.2. Complete exchange . . . . . . . . . . . . . . . . . . . . 16
9. Normative References . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
CoAP [rfc7252] is an implementation of the REST architecture for
constrained devices. Gateway between CoAP and HTTP can be easily
built since both protocols uses the same address space (URL), caching
mechanisms and methods.
Nevertheless, if limited, the size of a CoAP header may be too large
for LPWAN constraints and some compression may be needed to reduce
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.
Where the context is said static since the element values composing The context is said static since the element values composing the
the context are not learned during the packet exchanges but are context are not learned during the packet exchanges but are
previously defined. The context(s) is(are) known by both ends before previously defined. The context(s) is(are) known by both ends before
transmission. transmission.
A context is composed of a set of rules (contexts) that are A context is composed of a set of rules (contexts) that are
referenced by Rule IDs (identifiers). A rule describes the header referenced by Rule IDs (identifiers). A rule contains an ordered
fields with some associated Target Values (TV). A Matching Operator list of the header fields containing a field ID (FID) and its
(MO) is associated to each header field description. The rule is position when repeated, a direction indicator (DI) (upstream,
selected if all the MOs fit the TVs. In that case, a Compression downstream and bidirectional) and some associated Target Values (TV)
which are expected in the message header. A Matching Operator (MO)
is associated to each header field description. The rule is selected
if all the MOs fit the TVs. In that case, a Compression
Decompression Function (CDF) associated to each field defines the Decompression Function (CDF) associated to each field defines the
link between the compressed and decompressed value for each of the link between the compressed and decompressed value for each of the
header fields. header fields.
This draft discusses the way SCHC can be applied to CoAP headers, how This document describes how the rules can be applied to CoAP flows. Compression of the
to extend MOs to match a specific element when several fields of the CoAP header may be done in conjunction with the above layers or independantly.
same type are presented in the header. It also introduces the notion
of bidirectional or unidirectional (upstream and downstream) fields.
2. CoAP Compressing 2. CoAP Compressing
CoAP [RFC7252] is an implementation of the REST architecture for CoAP differs from IPv6 and UDP protocols on the following
constrained devices. Gateway between CoAP and HTTP can be easily
built since both protocols uses the same address space (URL), caching
mechanisms and methods.
Nevertheless, if limited, the size of a CoAP header may be too large
for LPWAN constraints and some compression may be needed to reduce
the header size. CoAP compression is not straightforward. Some
differences between IPv6/UDP and CoAP can be highlighted. CoAP
differs from IPv6 and UDP protocols in 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 position in the header in the request and in the response, only location in the header
may change (e.g. source and destination fields). A CoAP request may vary (e.g. source and destination fields). A CoAP request is
is different from an response. For example, the URI-path option different from an response. For example, the URI-path option is
is mandatory in the request and is not found in the response. mandatory in the request and is not found in the response, request
may contain an Accept option and the response a Content-format
option.
Even when a field is "symmetric" (i.e. found in both directions)
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
the response. Exploiting the asymmetry in compression will allow
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
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 a 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
cleint will certainly send a larger token to the Thing. client will certainly send a larger token to the Thing. SCHC
compression will not modify the values to offer a better
compression rate. Nevertheless a proxy placed before the
compressor may change some field values to offer a better
compression rate and maintain the necessary context for
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 the Type-Length-Value. When applying SCHC header compression.
token size is not known at the rule creation, the sender and the
receiver must agree on its compressed size.
o The options type in CoAP is not defined with the same value. The
Delta TLV coding makes that the type is not independent of
previous option and may vary regarding the options contained in
the header.
2.1. CoAP behavior
A LPWAN node can either be a client or a server and sometimes both.
In the client mode, the LPWAN node sends request to a server and
expects an answer or acknowledgements. Acknowledgements can be at 2
different levels:
o In the transport level, a CON message is acknowledged by an ACK
message. A NON confirmable message is not acknowledged at all.
o In REST level, a REST request is acknowledged by an "error" code.
The [RFC7967] defines an option to limit the number of
acknowledgements.
Note that acknowledgement can be optimized and a REST level
acknowledgement can be used as a transport level acknowledgement.
2.2. CoAP protocol analysis
CoAP header format defines the following fields:
o version (2 bits): this field can be elided during the SCHC
compresssion
o type (2 bits). It defines the type of the transport messages, 4
values are defined, regarding the type of exchange. If only NON
messages are sent or CON/ACK messages, this field can be reduced
to 0 or 1 bit.
o token length (4 bits). The standard allows up to 8 bytes for a
token. If a fixed token size is chosen, then this field can be
elided. If some variation in length are needed then 1 or 2 bits
could be enough for most of LPWAN applications.
o code (8 bits). This field codes the request and the response
values. In CoAP these values are represented in a more compact
way then the coding used in HTTP, but the coding is not optimal.
o message id (16 bits). This value of this header field is used to
acknowledge CON frames. The size of this field is computed to
allow the anticipation (how many frames can be sent without
acknowledgement). When a value is used, the [RFC7252] defines the
time before it can be reused without ambiguities. This size
defined may be too large for a LPWAN node sending or receiving few
messages a day.
o Token (0 to 8 bytes). Token header field is used to identify
active flows. Regarding the usage for LPWAN (stability in time
and limited number), a short token (1 Byte or less) can be enough.
o options are coded using delta-TLV. The delta-T depends on
previous values, length is encoded inside the option. The
[RFC7252] distinguishes repeatable options that can appear several
times in the header. Among them we can distinguish:
* list options which appear several time in the header but are
exclusive such as the Accept option.
* cumulative options which appear several times in the header but
are part of a more generic value such as Uri-Path and Uri-
Query. In that case, some elements may not change during the
Thing lifetime and other may change at each request. For
instance CoMi [I-D.ietf-core-comi] defines the following path
/c/X6?k="eth0", where the first path element "c" does not
change, the second element can vary over time with a different
length (it represents the base64 enconding of a SID) and the
query string can also vary over time.
For a given flow some value options are stable through time.
Observe, ETag, If-Match, If-None-Match and Size varies in each
message.
The CoAP protocol must not be altered by the compression/
decompression phase, but if no semantic is attributed to a value, it
may be changed during this phase. For instance, the compression
phase may reduce the size of a token but must maintain its unicity.
The decompressor will not be able to restore the original value but
the behavior will remain the same. If no special semantic is
assigned to the token, this will be transparent. If a special
semantic is assigned to the token, its compression may not be
possible.
3. SCHC rules for CoAP header compression
This draft refines the rules definition by adding the direction of
the message, from the Thing point of view (uplink, downlink or
bidirectional). It does not introduce new Machting Operator or new
Compression Decompression Function, but add some possibility to check
one particular element when several of them are present at the same
time.
A rule can contain CoAP and IPv6/UDP entries. In that case, IPv6/UDP
entries are tagged bidirectional.
3.1. Directional Rules
By default, an entry in a rule is bidirectional which means that it
can be applied either on the uplink or downlink headers. By
specifying the direction, the LC will take into account the specific
field only if the direction match.
If the Thing is a client, the URI-Path option is only present on
request and not on the response. Therefore, the exact matching
principle to select a rule cannot apply.
Some options are marked unidirectional, the value (uplink or
downlink) depends of the scenario. A Uri-Path option will be marked
uplink if the Thing acts as a client and downlink if the Thing acts
as a server. If the Thing acts both as client and server, two
different rules will be defined.
3.2. Matching Operator
The Matching Operator behavior has not changed, but the value must
take a position value, if the entry is repeated :
FID TV MO CDF
URI-Path foo equal 1 not-sent By sending compressed field information following the rule order,
URI-Path bar equal 2 not-sent SCHC offers a serialization/deserialization mechanism. Since a
field exists to indicate the token length there is no ambiguity.
For options, the rule indicates also the expected options found
the int CoAP header. Therefore only the length is needed to
recognise an option. The length will be send using the same CoAP
encoding (size less than 12 are directly sent, higher values uses
the escape mechanisms defined by [rfc7252]). Delta Type is
omitted, the value will be recovered by the decompressor. This
reduce the option length of 4, 12 or 20 bits regarding the
orignial size of the delta type encoding in the option.
Figure 1: Position entry. o In CoAP headers a field can be duplicated several times, for
instances, elements of an URI (path or queries) or accepted
formats. The position defined in a rule, associated to a Field
ID, can be used to identify the proper element.
For instance, the rule Figure 1 matches with /foo/bar, but not /bar/ 3. Compression of CoAP header fields
foo.
The position is added after the natural argument of the MO, for This section discusses of the compression of the different CoAP
example MSB (4,3) indicates a most significant bit matching of 4 bits header fields. These are just examples. The compression should take
in a field located in position 3. into account the nature of the traffic and not only the field values.
Next chapter will define some compression rules for some common
exchanges.
3.3. Compressed field length 3.1. CoAP version field (2 bits)
When the length is not clearly indicated in the rule, the value This field is bidirectional and can be elided during the SCHC
length must be sent with the field data, which means for CoAP to send compression, since it always contains the same value. It appears
directly the CoAP option where the delta-T is set to 0. only in first position.
For the CoMi path /c/X6?k="eth0" the rule can be set to: FID Pos DI TV MO CDF
ver 1 bi 1 equal not-sent
FID TV MO CDF 3.2. CoAP type field
URI-Path c equal 1 not-sent This field can be managed bidirectionally or unidirectionally.Several
URI-Path ignore 2 value-sent strategies can be applied to this field regarding the values used:
URI-Query k= MSB (16, 1) value-sent
Figure 2: CoMi URI compression 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:
Figure 2 shows the parsing and the compression of the URI. where c is * Pos is always 1,
not sent. The second element is sent with the length (i.e. 0x02 X 6)
followed by the query option (i.e. 0x08 k="eth0").
[[NOTE we don't process URI with a multiple number of path element * DI can either be "uplink" if the ES is a CoAP client or
??]]. "downlink" if the ES is a CoAP server, or "bidirectional"
4. Application to CoAP header fields * TV is set to the value,
This section lists the different CoAP header fields and how they can * MO is set to "equal"
be compressed.
4.1. CoAP version field * CDF is set to "not-sent".
This field is bidirectional. FID Pos DI TV MO CDF
type 1 bi NON equal not-sent
This field contains always the same value, therefore the TV may be 1, o If the ES is either a client or a Server and confirmable message
the MO is set to "equal" and the CDF is set to "not-sent" 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
rule for a ES acting as a client, directions need to be reversed
for a ES acting as a server.
4.2. CoAP type field FID Pos DI TV MO CDF
type 1 up CON equal not-sent
type 1 dw {0:ACK, 1:RST} match-mapping mapping-sent
This field is bidirectional or undirectional. 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
sent uncompressed.
Several strategies can be applied to this field regarding the values FID Pos DI TV MO CDF
used: type 1 bi ignore send-value
o if only one type is sent, for example NON message, its 3.3. CoAP token length field
transmission can be avoided. TV is set to the value, MO is set to
"equal" and CDF is set to "not-sent".
o if two values are sent, for example CON and ACK and RST is not This field is bi-directional.
used, this field can be reduced to one bit. TV is set to a
matching value {CON: 0, ACK: 1}, MO is set to match-mapping and
CDF is set to mapping-sent.
o It is also possible avoid transmission of this field by marking it Several strategies can be applied to this field regarding the values:
unidirectional. In one direction, the TV is set to CON, MO is set
to "equal" and CDF is set to "not-sent". On the other direction,
the TV is set to ACK, the MO is set to "equal" and the CDF is set
to "not-sent".
o Otherwise TV is not set, MO is set to "ignore" and CDF is set to o no token or a wellknown length, the transmission can be avoided.
"value-sent". A special care must be taken, if CON messages are acknowledged
with an empty ACK message. In that case the token is not always
present.
4.3. CoAP token length field FID Pos DI TV MO CDF
TKL 1 bi value ignore send-value
This field is bi-directional. 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,
then only the least significant bits have to be sent. The example
below allows values between 0 and 3.
Several strategies can be applied to this field regarding the values: FID Pos DI TV MO CDF
TKL 1 bi 0x0 MSB(2) LSB(2)
o no token or a wellknown length, the transmission can be avoided. o otherwise the field value has to be sent.
TV is set to the length, the MO is set to "equal" and CDF is set
to "not-sent"
o The length is variable from one message to another. TV is not FID Pos DI TV MO CDF
set, MO is set to "ignore" and CDF is set to "value-sent". The TKL 1 bi ignore value-sent
size of the sent value must be known by ends. The size may be 4
bits. The receiver must take into account this value to retrieve
the token. A CoAP proxy may be used before the compression to
reduce the field size.
4.4. CoAP code field 3.4. CoAP code field
This field is unidirectional. The client and the server do not use This field is bidirectional, but compression can be enhanced using
the same values. 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. So, it could efficiently be compared to the 255 possible values.
coded on 5 bits. The number of code may vary over time, some new
codes may be introduced or some applications use a limited number of
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 |
skipping to change at page 8, line 39 skipping to change at page 7, line 39
| 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 3: Example of CoAP code mapping Figure 1: Example of CoAP code mapping
Figure 3 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. or reduced if some values are never used by both ends. It could
efficiently be coded on 5 bits.
Even if the number of code can be increase with other RFC,
implementations may use a limited number of values, which can help to
reduce the number of bits sent on the LPWAN.
The number of code may vary over time, some new codes may be
introduced or some applications use a limited number of values.
The client and the server do not use the same values. This asymmetry
can be exploited to reduce the size sent on the LPWAN.
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.
4.5. CoAP Message ID field 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
sending only GET request.
FID Pos DI TV MO CDF
code 1 up GET equal not-sent
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
less if fewer methods are used. Example below gives an example where
the ES is a server and receives only GET and POST requests.
FID Pos DI TV MO CDF
code 1 dw {0:0.01, 1:0.02}match-mapping mapping-sent
The same approach can be applied to responses.
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. In that case TV is not set, MO is set to ignore and CDF is avoided.
set to "not-sent". The decompressor can generate a number.
[[Note; check id this field is not used by OSCOAP .]] FID Pos DI TV MO CDF
Mid 1 bi ignore not-sent
The decompressor must generate a value.
[[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. In that the compression, a proxy may be needed to reduce the size.
case, the TV is set to 0x0000, MO is set to "MSB(l)" and CDF is set
to "LSB(16-l)", where "l" is the size of the compressed header.
Otherwise if no compression is needed the TV is not set, MO is set to FID Pos DI TV MO CDF
ignore and CDF is set to "not-sent". Mid 1 bi 0x0000 MSB(12) LSB(4)
4.6. CoAP Token field Otherwise if no compression is possible, the field has to be sent
FID Pos DI TV MO CDF
Mid 1 bi ignore value-sent
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.
Otherwise the TV is not set, the MO is set to ignore and CDF is set The size of the compress token sent is known by a combination of the
to "value-sent". Token Length field and the rule entry. For instance, with the entry
below:
The decompression may know the length of the token field from the FID Pos DI TV MO CDF
token length field. tkl 1 bi 2 equal not-sent
token 1 bi 0x00 MSB(12) LSB(4)
4.7. CoAP option Content-format field. The uncompressed token is 2 bytes long, but the compressed size will
be 4 bits.
4. CoAP options
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 the value is known by both sides, the TV contains that value and If single value is expected by the client, the TV contains that value
MO is set to "equal" and the CDF is set to "not-sent". 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.
Otherwise the TV is not set, MO is set to "ignore" and CDF is set to FID Pos DI TV MO CDF
"value-sent" content 1 up value equal not-sent
A mapping list can also be used to reduce the size. If several possible value are expected by the client, a matching-list
can be used.
4.8. CoAP option Accept field FID Pos DI TV MO CDF
content 1 up {0:50,1:41} match-mapping mapping-sent
Otherwise the value can be sent.The value-sent CDF in the compressor
do not send the option type and the decompressor reconstruct it
regarding the position in the rule.
FID Pos DI TV MO CDF
content 1 up ignore value-sent
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. accept options with their positions. Since the order in which the
Accept value are sent, the position order can be modified. The rule
below
if the accept value must be sent, the TV contains that value, MO is FID Pos DI TV MO CDF
set to "ignore x" where "x" is the accept option's position and CDF accept 1 up 41 egal not-sent
is set to value-sent. Since the value length is not known, it must accept 2 up 50 egal not-sent
be sent as a CoAP TLV with delta-T set to 0.
Otherwise the TV is not set, MO is set to "equal x" where x is the will be selected only if two accept options are in the CoAP header if
accept option's position and CDF is set to "not-sent" this order.
[[note: it could be more liberal and do not provide the same order The rule below:
after decompression]]
4.9. CoAP option Max-Age field FID Pos DI TV MO CDF
accept 0 up 41 egal not-sent
accept 0 up 50 egal not-sent
will accept a-only CoAP messages with 2 accept options, but the order
will not influence the rule selection. The decompression will
reconstruct the header regarding the rule order.
Otherwise a matching-list can be applied to the different values, in
that case the order is important to recover the appropriate value and
the position must be clearly indicate.
FID Pos DI TV MO CDF
accept 1 up {0:50,1:41} match-mapping mapping-sent
accept 2 up {0:50,1:61} match-mapping mapping-sent
accept 3 up {0:61,1:71} match-mapping mapping-sent
Finally, the option can be explicitly sent.
FID Pos DI TV MO CDF
accept 1 up ignore value-sent
4.3. CoAP option Max-Age field, CoAP option Uri-Host and Uri-Port
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, the TV is set with this If the duration is known by both ends, value can be elided on the
duration, the MO is set to "equal" and the CDF is set to "not-sent". LPWAN.
Otherwise the TV is not set, the MO is set to "ignore" and the CDF is A matching list can be used if some wellknown values are defined.
set to "value-sent". Since the value length is not known, it must be
sent as a CoAP TLV with delta-T set to 0. Otherwise the option length and value can be sent on the LPWAN.
[[note: we can reduce (or create a new option) the unit to minute, [[note: we can reduce (or create a new option) the unit to minute,
second is small for LPWAN ]] second is small for LPWAN ]]
4.10. CoAP option Uri-Host and Uri-Port 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 server and are never found in server response. specific resource and are never found in server response.
For each option, if the value is known by both ends, the TV is set The Matching Operator behavior has not changed, but the value must
with this value, the MO is set to "equal" and the CDF is set to "not- take a position value, if the entry is repeated :
sent".
Otherwise the TV is not set, the MO is set to "ignore" and the CDF is FID Pos DI TV MO CDF
set to "value-sent". Since the value length is not known, it must be URI-Path 1 up foo equal not-sent
sent as a CoAP TLV with delta-T set to 0. URI-Path 2 up bar equal not-sent
4.11. CoAP option Uri-Path and Uri-Query fields Figure 2: Position entry.
This fields are unidirectional and must not be set to bidirectional For instance, the rule Figure 2 matches with /foo/bar, but not /bar/
in a rule entry. They are used only by the client to access to a foo.
specific resource and are never found in server response.
Path and Query option may have different formats. Section 3.2 gives When the length is not clearly indicated in the rule, the value
some examples. length must be sent with the field data, which means for CoAP to send
directly the CoAP option with length and value.
If the URI path as well as the query is composed of 2 or more For instance for a CoMi path /c/X6?k="eth0" the rule can be set to:
elements, then the position must be set in the MO parameters.
If a Path or Query element is stable over the time, then TV is set FID Pos DI TV MO CDF
with its value, MO is set to "equal x" where x is the position in the URI-Path 1 up c equal not-sent
Path or the Query and CDF is set to "not-sent". URI-Path 2 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB
Otherwise if the value varies over time, TV is not set, MO is set to Figure 3: CoMi URI compression
"ignore x" where x is the position in the Path or in the Query and
CDF is set to "value-sent". Since the value length is not known, it Figure 3 shows the parsing and the compression of the URI. where c is
must be sent as a CoAP TLV with deltaT set to 0. not sent. The second element is sent with the length (i.e. 0x2 X 6)
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.
For instance, the following Path /foo/bar/variable/stable can leads FID Pos DI TV MO CDF
to the rule defined Figure 4. URI-Path 1 up {0:"/c/c", equal not-sent
1:"/c/d"
FID TV MO CDF URI-Path 3 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB
URI-Path {"/foo/bar":1, match-mapping 1 mapping-sent
"/bar/foo":2}
URI-Path ignore 3 value-sent
URI-Path stable equal 4 not-sent
Figure 4: complex path example Figure 4: complex path example
4.12. CoAP option Proxy-URI and Proxy-Scheme fields For instance, the following Path /foo/bar/variable/stable can leads
to the rule defined Figure 4.
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
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 CDF 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 CDF is
set to "not-sent" set to "not-sent"
4.13. CoAP option ETag, If-Match, If-None-Match, Location-Path and 5.2. 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 request. always be sent with the request.
[[Can include OSCOAP Object security in that category ]] [[Can include OSCOAP Object security in that category ]]
5. Other RFCs 6. Other RFCs
5.1. Block 6.1. Block
Block option should be avoided in LPWAN. The minimum size of 16 Block option should be avoided in LPWAN. The minimum size of 16
bytes can be incompatible with some LPWAN technologies. bytes can be incompatible with some LPWAN technologies.
[[Note: do we recommand LPWAN fragmentation since the smallest value [[Note: do we recommand LPWAN fragmentation since the smallest value
of 16 is too big?]] of 16 is too big?]]
5.2. 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 CDF 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 Thing implementation should limit the transmission size either the Thing implementation should limit the
value increase or a proxy can be used limit the increase. value increase or a proxy can be used limit the increase.
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 do
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.
5.3. 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 by both ends, then TV by a server to a request. If the value is not by both ends, then TV
is set to this value, MO is set to "equal" and CDF is set to "not- is set to this value, MO is set to "equal" and CDF is set to "not-
sent". sent".
Otherwise, if the value is changing over time, TV is not set, MO is Otherwise, if the value is changing over time, TV is not set, MO is
set to "ignore" and CDF to "value-sent". A matching list can also be set to "ignore" and CDF to "value-sent". A matching list can also be
used to reduce the size. used to reduce the size.
6. Examples of CoAP header compression 7. Protocol analysis
8. Examples of CoAP header compression
6.1. 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 |TV |MO |CDF |dir | Sent |
+=============+======+=========+=============+=====+================+ +=============+======+=========+=============+=====+================+
|CoAP version | 01 |equal |not-sent |bi | | |CoAP version | 01 |equal |not-sent |bi | |
|CoAP Type | |ignore |value-sent |bi |TT | |CoAP Type | |ignore |value-sent |bi |TT |
|CoAP TKL | 0 |equal |not-sent |bi | | |CoAP TKL | 0 |equal |not-sent |bi | |
|CoAP Code | ML1 |match-map|matching-sent|bi | CC CCC | |CoAP Code | ML1 |match-map|matching-sent|bi | CC CCC |
|CoAP MID | 0000 |MSB(7 ) |LSB(9) |bi | M-ID | |CoAP MID | 0000 |MSB(7 ) |LSB(9) |bi | M-ID |
|CoAP Uri-Path| path |equal 1 |not-sent |down | | |CoAP Uri-Path| path |equal 1 |not-sent |down | |
+-------------+------+---------+-------------+-----+----------------+ +-------------+------+---------+-------------+-----+----------------+
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 3: 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.
Figure 6 shows the time diagram of the exchange. A LPWAN Application Figure 6 shows the time diagram of the exchange. A LPWAN Application
Server sends a CON message. Compression reduces the header sending Server sends a CON message. Compression reduces the header sending
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. .
skipping to change at page 14, line 37 skipping to change at page 15, line 30
+-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+--------+ +-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+--------+
| | |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
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 3) code all the responses in the matching list Figure 1)
rule id 1 rule id 1
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
| Field |TV |MO |CDF |dir| Sent | | Field |TV |MO |CDF |dir| Sent |
+=============+======+=========+=============+===+================+ +=============+======+=========+=============+===+================+
|CoAP version | 01 |equal |not-sent |bi | | |CoAP version | 01 |equal |not-sent |bi | |
|CoAP Type | CON |equal |not-sent |dw | | |CoAP Type | CON |equal |not-sent |dw | |
|CoAP Type | ACK |equal |not-sent |up | | |CoAP Type | ACK |equal |not-sent |up | |
|CoAP TKL | 0 |equal |not-sent |bi | | |CoAP TKL | 0 |equal |not-sent |bi | |
|CoAP Code | ML2 |match-map|matching-sent|dw |CCCC C | |CoAP Code | ML2 |match-map|mapping-sent |dw |CCCC C |
|CoAP Code | ML3 |match-map|matching-sent|up |CCCC C | |CoAP Code | ML3 |match-map|mapping-sent |up |CCCC C |
|CoAP MID | 0000 |MSB(5) |LSB(11) |bi | M-ID | |CoAP MID | 0000 |MSB(5) |LSB(11) |bi | M-ID |
|CoAP Uri-Path| path |equal 1 |not-sent |dw | | |CoAP Uri-Path| path |equal 1 |not-sent |dw | |
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
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
6.2. 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
MID=0x0012 | | MID=0x0012 | |
POST | | POST | |
Accept X | | Accept X | |
/c/k=AS |------------------------>| /c/k=AS |------------------------>|
| | | |
| | | |
skipping to change at page 16, line 7 skipping to change at page 16, line 36
rule id 3 rule id 3
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
| Field |TV |MO |CDF |dir| Sent | | Field |TV |MO |CDF |dir| Sent |
+=============+======+=========+=============+===+================+ +=============+======+=========+=============+===+================+
|CoAP version | 01 |equal |not-sent |bi | | |CoAP version | 01 |equal |not-sent |bi | |
|CoAP Type | CON |equal |not-sent |up | | |CoAP Type | CON |equal |not-sent |up | |
|CoAP Type | ACK |equal |not-sent |dw | | |CoAP Type | ACK |equal |not-sent |dw | |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP TKL | 1 |equal |not-sent |bi | |
|CoAP Code | POST |equal |not-sent |up | | |CoAP Code | POST |equal |not-sent |up | |
|CoAP Code | 0.00 |equal |not-sent |dw | | |CoAP Code | 0.00 |equal |not-sent |dw | |
|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM | |CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
|CoAP Token | |ignore |send-value |up |TTTTTTTT | |CoAP Token | |ignore |send-value |up |TTTTTTTT |
|CoAP Uri-Path| /c |equal 1 |not-sent |dw | | |CoAP Uri-Path| /c |equal 1 |not-sent |dw | |
|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P | |CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |
|CoAP Content | X |equal |not-sent |up | | |CoAP Content | X |equal |not-sent |up | |
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
rule id 4 rule id 4
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
| Field |TV |MO |CDF |dir| Sent | | Field |TV |MO |CDF |dir| Sent |
+=============+======+=========+=============+===+================+ +=============+======+=========+=============+===+================+
|CoAP version | 01 |equal |not-sent |bi | | |CoAP version | 01 |equal |not-sent |bi | |
|CoAP Type | CON |equal |not-sent |dw | | |CoAP Type | CON |equal |not-sent |dw | |
|CoAP Type | ACK |equal |not-sent |up | | |CoAP Type | ACK |equal |not-sent |up | |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP TKL | 1 |equal |not-sent |bi | |
|CoAP Code | 2.05 |equal |not-sent |dw | | |CoAP Code | 2.05 |equal |not-sent |dw | |
|CoAP Code | 0.00 |equal |not-sent |up | | |CoAP Code | 0.00 |equal |not-sent |up | |
|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM | |CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
|CoAP Token | |ignore |send-value |dw |TTTTTTTT | |CoAP Token | |ignore |send-value |dw |TTTTTTTT |
|COAP Accept | X |equal |not-sent |dw | | |COAP Accept | X |equal |not-sent |dw | |
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
alternative rule: alternative rule:
rule id 4 rule id 4
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
| Field |TV |MO |CDF |dir| Sent | | Field |TV |MO |CDF |dir| Sent |
+=============+======+=========+=============+===+================+ +=============+======+=========+=============+===+================+
|CoAP version | 01 |equal |not-sent |bi | | |CoAP version | 01 |equal |not-sent |bi | |
|CoAP Type | ML1 |equal |match-sent(1)|bi |t | |CoAP Type | ML1 |match-map|match-sent |bi |t |
|CoAP TKL | 1 |equal |not-sent |bi | | |CoAP TKL | 1 |equal |not-sent |bi | |
|CoAP Code | ML2 |equal |match-sent(1)|up | cc | |CoAP Code | ML2 |match-map|match-sent |up | cc |
|CoAP Code | ML3 |equal |match-sent(2)|dw | cc | |CoAP Code | ML3 |match-map|match-sent |dw | cc |
|CoAP MID | 0000 |MSB(8) |LSB(8) |bi |MMMMMMMM | |CoAP MID | 0000 |MSB(8) |LSB |bi |MMMMMMMM |
|CoAP Token | |ignore |send-value |dw |TTTTTTTT | |CoAP Token | |ignore |send-value |dw |TTTTTTTT |
|CoAP Uri-Path| /c |equal 1 |not-sent |dw | | |CoAP Uri-Path| /c |equal 1 |not-sent |dw | |
|CoAP Uri-query ML4 |equal 1 |not-sent |dw |P | |CoAP Uri-query ML4 |equal 1 |not-sent |dw |P |
|CoAP Content | X |equal |not-sent |up | | |CoAP Content | X |equal |not-sent |up | |
|COAP Accept | x |equal |not-sent |dw | | |COAP Accept | x |equal |not-sent |dw | |
+-------------+------+---------+-------------+---+----------------+ +-------------+------+---------+-------------+---+----------------+
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}
7. Normative References 9. Normative References
[I-D.ietf-core-comi]
Stok, P., Bierman, A., Veillette, M., and A. Pelov, "CoAP
Management Interface", draft-ietf-core-comi-00 (work in
progress), January 2017.
[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
2016. 2016.
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol [rfc7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
(IPCP)", RFC 1332, DOI 10.17487/RFC1332, May 1992,
<http://www.rfc-editor.org/info/rfc1332>.
[RFC3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
Compression (ROHC): Framework and four profiles: RTP, UDP,
ESP, and uncompressed", RFC 3095, DOI 10.17487/RFC3095,
July 2001, <http://www.rfc-editor.org/info/rfc3095>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
[RFC4997] Finking, R. and G. Pelletier, "Formal Notation for RObust
Header Compression (ROHC-FN)", RFC 4997,
DOI 10.17487/RFC4997, July 2007,
<http://www.rfc-editor.org/info/rfc4997>.
[RFC5225] Pelletier, G. and K. Sandlund, "RObust Header Compression
Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and
UDP-Lite", RFC 5225, DOI 10.17487/RFC5225, April 2008,
<http://www.rfc-editor.org/info/rfc5225>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained [rfc7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641, Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015, DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>. <https://www.rfc-editor.org/info/rfc7641>.
[RFC7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T. [rfc7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.
Bose, "Constrained Application Protocol (CoAP) Option for Bose, "Constrained Application Protocol (CoAP) Option for
No Server Response", RFC 7967, DOI 10.17487/RFC7967, No Server Response", RFC 7967, DOI 10.17487/RFC7967,
August 2016, <http://www.rfc-editor.org/info/rfc7967>. August 2016, <https://www.rfc-editor.org/info/rfc7967>.
Authors' Addresses Authors' Addresses
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
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