lpwan Working Group A. Minaburo
Internet-Draft Acklio
Intended status: Informational L. Toutain
Expires: September 5, 2018 Institut MINES TELECOM; IMT Atlantique
March 04, 2018
LPWAN Static Context Header Compression (SCHC) for CoAP
draft-ietf-lpwan-coap-static-context-hc-03
Abstract
This draft defines the way SCHC header compression can be applied to
CoAP headers. CoAP header structure differs from IPv6 and UDP
protocols since the CoAP Header is flexible header with a variable
number of options themself of a variable length. Another important
difference is the asymmetry in the header information used for
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
or both roles.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 5, 2018.
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to this document. Code Components extracted from this document must
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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
CoAP [rfc7252] is an implementation of the REST architecture for
constrained devices. A 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.
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[I-D.toutain-lpwan-ipv6-static-context-hc] defines a header
compression mechanism for LPWAN network based on a static context.
The context is said static since the field description composing the
Rules and the context are not learned during the packet exchanges but
are previously defined. The context(s) is(are) known by both ends
before transmission.
A context is composed of a set of rules that are referenced by Rule
IDs (identifiers). A rule contains an ordered list of the fields
descriptions containing a field ID (FID) and its position when
repeated, a direction indicator (DI) (upstream, 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
Action (CDA) associated to each field defines the link between the
compressed and decompressed value for each of the header fields.
This document describes how the rules can be applied to CoAP flows.
Compression of the CoAP header may be done in conjunction with the
above layers or independantly.
2. CoAP Compressing
CoAP differs from IPv6 and UDP protocols on the following aspects:
o IPv6 and UDP are symmetrical protocols. The same fields are found
in the request and in the response, only the location in the
header may vary (e.g. source and destination fields). A CoAP
request is different from a response. For example, the URI-path
option is mandatory in the request and is not found in the
response, a 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
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
LPWAN constraints can generate a 1 byte token, but a regular CoAP
client will certainly send a larger token to the Thing. SCHC
compression will not modify the values to offer a better
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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
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
the Type-Length-Value. When applying SCHC header compression.
By sending compressed field information following the rule order,
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
recognize an option. The length will be sent using the same CoAP
encoding (size less than 12 are directly sent, higher values use
the escape mechanisms defined by [rfc7252]). Delta Type is
omitted, the value will be recovered by the decompressor. This
reduces the option length of 4, 12 or 20 bits regarding the
original size of the delta type encoding in the option.
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.
3. Compression of CoAP header fields
This section discusses of the compression of the different CoAP
header fields. These are just examples. The compression should take
into account the nature of the traffic and not only the field values.
Next chapter will define some compression rules for some common
exchanges.
3.1. CoAP version field (2 bits)
This field is bidirectional and can be elided during the SCHC
compression, since it always contains the same value. It appears
only in first position.
FID FL FP DI Value MO CDA Sent
ver 2 1 bi 1 equal not-sent
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3.2. CoAP type field
This field can be managed bidirectionally or unidirectionally.Several
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
used, the transmission of the Type field can be avoided:
* Pos is always 1,
* DI can either be "uplink" if the ES is a CoAP client or
"downlink" if the ES is a CoAP server, or "bidirectional"
* TV is set to the value,
* MO is set to "equal"
* CDA is set to "not-sent".
FID FL FP DI Target Value MO CDA Sent
type 2 1 bi NON equal not-sent
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
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.
FID FL FP DI TV MO CDA Sent
type 2 1 up CON equal not-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
server and the rule handle these two traffics, Type field must be
sent uncompressed.
FID FL FP DI TV MO CDA Sent
type 2 1 bi ignore send-value [2]
3.3. CoAP token length field
This field is bi-directional.
Several strategies can be applied to this field regarding the values:
o no token or a wellknown length, the transmission can be avoided.
A special care must be taken, if CON messages are acknowledged
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with an empty ACK message. In that case the token is not always
present.
FID FL FP DI TV MO CDA Sent
TKL 4 1 bi value ignore send-value [4]
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.
FID FL FP DI TV MO CDA Sent
TKL 4 1 bi 0x0 MSB(2) LSB(2) [2]
o otherwise the field value has to be sent.
FID FL FP DI TV MO CDA Sent
TKL 4 1 bi ignore value-sent [4]
3.4. CoAP code field
This field is bidirectional, but compression can be enhanced using
DI.
The CoAP Code field defines a tricky way to ensure compatibility with
HTTP values. Nevertheless only 21 values are defined by [rfc7252]
compared to the 255 possible values.
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+------+------------------------------+-----------+
| Code | Description | Mapping |
+------+------------------------------+-----------+
| 0.00 | | 0x00 |
| 0.01 | GET | 0x01 |
| 0.02 | POST | 0x02 |
| 0.03 | PUT | 0x03 |
| 0.04 | DELETE | 0x04 |
| 0.05 | FETCH | 0x05 |
| 0.06 | PATCH | 0x06 |
| 0.07 | iPATCH | 0x07 |
| 2.01 | Created | 0x08 |
| 2.02 | Deleted | 0x09 |
| 2.03 | Valid | 0x0A |
| 2.04 | Changed | 0x0B |
| 2.05 | Content | 0x0C |
| 4.00 | Bad Request | 0x0D |
| 4.01 | Unauthorized | 0x0E |
| 4.02 | Bad Option | 0x0F |
| 4.03 | Forbidden | 0x10 |
| 4.04 | Not Found | 0x11 |
| 4.05 | Method Not Allowed | 0x12 |
| 4.06 | Not Acceptable | 0x13 |
| 4.12 | Precondition Failed | 0x14 |
| 4.13 | Request Entity Too Large | 0x15 |
| 4.15 | Unsupported Content-Format | 0x16 |
| 5.00 | Internal Server Error | 0x17 |
| 5.01 | Not Implemented | 0x18 |
| 5.02 | Bad Gateway | 0x19 |
| 5.03 | Service Unavailable | 0x1A |
| 5.04 | Gateway Timeout | 0x1B |
| 5.05 | Proxying Not Supported | 0x1C |
+------+------------------------------+-----------+
Figure 1: Example of CoAP code mapping
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
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.
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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.
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
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
Code field can be elided. The entry below shows a rule for a client
sending only GET request.
FID FL FP DI TV MO CDA Sent
code 8 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 FL FP DI Target Value MO CDA Sent
code 8 1 dw [0.01, 0.02] match-mapping mapping-sent [1]
The same approach can be applied to responses.
3.5. CoAP Message ID field
This field is bidirectional.
Message ID is used for two purposes:
o To acknowledge a CON message with an ACK.
o To avoid duplicate messages.
In LPWAN, since a message can be received by several radio gateway,
some LPWAN technologies include a sequence number in L2 to avoid
duplicate frames. Therefore if the message does not need to be
acknowledged (NON or RST message), the Message ID field can be
avoided.
FID FL FP DI TV MO CDA Sent
Mid 8 1 bi ignore not-sent
The decompressor must generate a value.
[[Note; check id this field is not used by OSCOAP .]]
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To optimize information sent on the LPWAN, shorter values may be used
during the exchange, but Message ID values generated a common CoAP
implementation will not take into account this limitation. Before
the compression, a proxy may be needed to reduce the size.
FID FL FP DI TV MO CDA Sent
Mid 8 1 bi 0x0000 MSB(12) LSB(4) [4]
Otherwise if no compression is possible, the field has to be sent
FID FL FP DI TV MO CDA Sent
Mid 8 1 bi ignore value-sent [8]
3.6. CoAP Token field
This field is bi-directional.
Token is used to identify transactions and varies from one
transaction to another. Therefore, it is usually necessary to send
the value of the token field on the LPWAN network. The optimization
will occur by using small values.
Common CoAP implementations may generate large tokens, even if
shorter tokens could be used regarding the LPWAN characteristics. A
proxy may be needed to reduce the size of the token before
compression.
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
below:
FID FL FP DI TV MO CDA Sent
tkl 4 1 bi 2 equal not-sent
token 8 1 bi 0x00 MSB(12) LSB(4) [4]
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
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.
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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
examples below describe the rules for an ES acting as a server.
FID FL FP DI TV MO CDA Sent
content 16 1 up value equal not-sent
If several possible value are expected by the client, a matching-list
can be used.
FID FL FP DI TV MO CDA 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
do not send the option type and the decompressor reconstruct it
regarding the position in the rule.
FID FL FP DI TV MO CDA Sent
content 16 1 up ignore value-sent [0-16]
4.2. CoAP option Accept field
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
possible payload type and is never found in server response.
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
accept options with their positions. Since the order in which the
Accept value are sent, the position order can be modified. The rule
below
FID FL FP DI TV MO CDA Sent
accept 16 1 up 41 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
this order.
The rule below:
FID FL FP DI TV MO CDA Sent
accept 16 0 up 41 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 not influence the rule selection. The decompression will
reconstruct the header regarding the rule order.
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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 FL FP DI TV MO CDA Sent
accept 16 1 up [50,41] match-mapping mapping-sent [1]
accept 16 2 up [50,61] match-mapping mapping-sent [1]
accept 16 3 up [61,71] match-mapping mapping-sent [1]
Finally, the option can be explicitly sent.
FID FL FP DI TV MO CDA Sent
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
a rule entry. It is used only by the server to inform of the caching
duration and is never found in client requests.
If the duration is known by both ends, value can be elided on the
LPWAN.
A matching list can be used if some wellknown values are defined.
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,
second is small for LPWAN ]]
5. CoAP option Uri-Path and Uri-Query fields
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
specific resource and are never found in server response.
The Matching Operator behavior has not changed, but the value must
take a position value, if the entry is repeated :
FID FL FP DI TV MO CDA Sent
URI-Path 1 up foo equal not-sent
URI-Path 2 up bar equal not-sent
Figure 2: Position entry.
For instance, the rule Figure 2 matches with /foo/bar, but not /bar/
foo.
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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
directly the CoAP option with length and value.
For instance for a CoMi path /c/X6?k="eth0" the rule can be set to:
FID FL FP DI TV MO CDA Sent
URI-Path 1 up c equal not-sent
URI-Path 2 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB
Figure 3: CoMi URI compression
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)
followed by the query option (i.e. 0x05 "eth0").
A Mapping list can be used to reduce size of variable Paths or
Queries. In that case, to optimize the compression, several elements
can be regrouped into a single entry. Numbering of elements do not
change, MO comparison is set with the first element of the matching.
FID FL FP DI TV MO CDA Sent
URI-Path 1 up {0:"/c/c", equal not-sent
1:"/c/d"
URI-Path 3 up ignore value-sent
URI-Query 1 up k= MSB (16) LSB
Figure 4: complex path example
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
in a rule entry. They are used only by the client to access to a
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"
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
set to "not-sent"
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5.2. CoAP option ETag, If-Match, If-None-Match, Location-Path and
Location-Query fields
These fields are unidirectional.
These fields values cannot be stored in a rule entry. They must
always be sent with the request.
[[Can include OSCOAP Object security in that category ]]
6. Other RFCs
6.1. Block
Block option should be avoided in LPWAN. The minimum size of 16
bytes can be incompatible with some LPWAN technologies.
[[Note: do we recommand LPWAN fragmentation since the smallest value
of 16 is too big?]]
6.2. Observe
[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
the maximum size for this option (3 bytes). To reduce the
transmission size either the Thing implementation should limit the
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
not require Observe response, a rule must allow the transmission of
this message.
6.3. No-Response
[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
is set to this value, MO is set to "equal" and CDF is set to "not-
sent".
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
used to reduce the size.
7. Protocol analysis
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8. Examples of CoAP header compression
8.1. Mandatory header with CON message
In this first scenario, the LPWAN compressor receives from outside
client a POST message, which is immediately acknowledged by the
Thing. For this simple scenario, the rules are described Figure 5.
Rule ID 1
+-------------+--+--+--+------+---------+-------------++------------+
| Field |FL|FP|DI|Target| Match | CDA || Sent |
| | | | |Value | Opera. | || [bits] |
+-------------+--+--+--+------+---------+-------------++------------+
|CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | | |bi| |ignore |value-sent ||TT |
|CoAP TKL | | |bi| 0 |equal |not-sent || |
|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
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
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
be set to 0 through a CoAP proxy. Uri-Path contains a single element
indicated in the matching operator.
Figure 6 shows the time diagram of the exchange. A LPWAN Application
Server sends a CON message. Compression reduces the header sending
only the Type, a mapped code and the least 9 significant bits of
Message ID. The receiver decompresses the header. .
The CON message is a request, therefore the LC process to a dynamic
mapping. When the ES receives the ACK message, this will not
initiate locally a message ID mapping since it is a response. The LC
receives the ACK and uncompressed it to restore the original value.
Dynamic Mapping context lifetime follows the same rules as message ID
duration.
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End System LPWA LC
| |
| rule id=1 |<--------------------
|<-------------------| +-+-+--+----+------+
<------------------- | TTCC CCCM MMMM MMMM| |1|0| 4|0.01|0x0034|
+-+-+--+----+-------+ | 0000 0010 0011 0100| | 0xb4 p a t|
|1|0| 1|0.01|0x0034 | | | | h |
| 0xb4 p a t | | | +------+
| h | | |
+------+ | |
| |
| |
---------------------->| rule id=1 |
+-+-+--+----+--------+ |------------------->|
|1|2| 0|2.05| 0x0034 | | TTCC CCCM MMMM MMMM|--------------------->
+-+-+--+----+--------+ | 1001 1000 0011 0100| +-+-+--+----+------+
| | |1|2| 0|2.05|0x0034|
v v +-+-+--+----+------+
Figure 6: Compression with global addresses
The message can be further optimized by setting some fields
unidirectional, as described in Figure 7. Note that Type is no more
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
code all the responses in the matching list Figure 1)
Rule ID 2
+-------------+--+--+--+------+---------+------------++------------+
| Field |FL|FP|DI|Target| MO | CDA || Sent |
| | | | |Value | | || [bits] |
+-------------+--+--+--+------+---------+------------++------------+
|CoAP version | | |bi|01 |equal |not-sent || |
|CoAP Type | | |dw|CON |equal |not-sent || |
|CoAP Type | | |up| ACK |equal |not-sent || |
|CoAP TKL | | |bi|0 |equal |not-sent || |
|CoAP Code | | |dw|ML2 |match-map|mapping-sent||CCCC C |
|CoAP Code | | |up|ML3 |match-map|mapping-sent||CCCC C |
|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}
Figure 7: CoAP Context to compress header without token
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8.2. Complete exchange
In that example, the Thing is using CoMi and sends queries for 2 SID.
CON
MID=0x0012 | |
POST | |
Accept X | |
/c/k=AS |------------------------>|
| |
| |
|<------------------------| ACK MID=0x0012
| | 0.00
| |
| |
|<------------------------| CON
| | MID=0X0034
| | Content-Format X
ACK MID=0x0034 |------------------------>|
0.00
Rule ID 3
+--------------+--+--+--+------+--------+-----------++------------+
| Field |FL|FP|DI|Target| MO | CDA || Sent |
| | | | |Value | | || [bits] |
+--------------+--+--+--+------+--------+-----------++------------+
|CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | | |up| CON |equal |not-sent || |
|CoAP Type | | |dw| ACK |equal |not-sent || |
|CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | | |up| POST |equal |not-sent || |
|CoAP Code | | |dw| 0.00 |equal |not-sent || |
|CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|CoAP Token | | |up| |ignore |send-value ||TTTTTTTT |
|CoAP Uri-Path | | |dw| /c |equal 1 |not-sent || |
|CoAP Uri-query| | |dw| ML4 |equal 1 |not-sent ||P |
|CoAP Content | | |up| X |equal |not-sent || |
+--------------+--+--+--+------+--------+-----------++------------+
Rule ID 4
+--------------+--+--+--+------+--------+-----------++------------+
| Field |FL|FP|DI|Target| MO | CDA || Sent |
| | | | |Value | | || [bits] |
+--------------+--+--+--+------+--------+-----------++------------+
|CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | | |dw| CON |equal |not-sent || |
|CoAP Type | | |up| ACK |equal |not-sent || |
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|CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | | |dw| 2.05 |equal |not-sent || |
|CoAP Code | | |up| 0.00 |equal |not-sent || |
|CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|CoAP Token | | |dw| |ignore |send-value||TTTTTTTT |
|COAP Accept | | |dw| X |equal |not-sent || |
+--------------+--+--+--+------+---------+----------++------------+
alternative rule:
Rule ID 4
+--------------+--+--+--+------+---------+-----------++------------+
| Field |FL|FP|DI|Target| MO | CDA || Sent |
| | | | |Value | | || [bits] |
+--------------+--+--+--+------+---------+-----------++------------+
|CoAP version | | |bi| 01 |equal |not-sent || |
|CoAP Type | | |bi| ML1 |match-map|match-sent ||t |
|CoAP TKL | | |bi| 1 |equal |not-sent || |
|CoAP Code | | |up| ML2 |match-map|match-sent || cc |
|CoAP Code | | |dw| ML3 |match-map|match-sent || cc |
|CoAP MID | | |bi| 0000 |MSB(8) |LSB ||MMMMMMMM |
|CoAP Token | | |dw| |ignore |send-value ||TTTTTTTT |
|CoAP Uri-Path | | |dw| /c |equal 1 |not-sent || |
|CoAP Uri-query| | |dw| ML4 |equal 1 |not-sent ||P |
|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}
ML4 {NULL:0, k=AS:1, K=AZE:2}
9. Normative References
[I-D.toutain-lpwan-ipv6-static-context-hc]
Minaburo, A. and L. Toutain, "LPWAN Static Context Header
Compression (SCHC) for IPv6 and UDP", draft-toutain-lpwan-
ipv6-static-context-hc-00 (work in progress), September
2016.
[rfc7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
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[rfc7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[rfc7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.
Bose, "Constrained Application Protocol (CoAP) Option for
No Server Response", RFC 7967, DOI 10.17487/RFC7967,
August 2016, <https://www.rfc-editor.org/info/rfc7967>.
Authors' Addresses
Ana Minaburo
Acklio
2bis rue de la Chataigneraie
35510 Cesson-Sevigne Cedex
France
Email: ana@ackl.io
Laurent Toutain
Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Laurent.Toutain@imt-atlantique.fr
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