Network Working Group A. Minaburo
Internet-Draft Acklio
Intended status: Informational L. Toutain
Expires: July 16, 2017 Institut Mines Telecom Atlantique
January 12, 2017
CoAP Traffic
draft-toutain-lpwan-coap-traffic-00
Abstract
This document describes different CoAP scenarios for the SCHC
compression. It goes from the simplest exchange without
acknowledgments to a basic study of the CoMI traffic.
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1. Introduction
This document describes different CoAP scenarios for the SCHC
compression. It goes from the simplest exchange without
acknowledgments to a basic study of the CoMI traffic. These
scenarios currently do not cover cases where encryption is used
(COSE, OSCOAP,...).
2. scenario 1 - Unidirectional traffic
2.1. CoAP POST without Acknowledgement from thing
The thing sends a CoAP POST/PUT request without acknowledgment using
CoAP NON message and no response option [RFC7967]. This is a common
traffic in a LPWAN network to minimize the downlink.
thing LPWAN SCHC CoAP Server
| | |
| | NON POST MID=0x00AB |
| | Token = 0x11 |
| | Path = /elm1/elm2 |
| | Content-format = val |
| | NoResponse = 0|2|8|16 |
| rule-id value | Value |
|------------------------------->| |
| | ------------------------------>|
Figure 1: POST with no ACK
Compression Objectives:
o do not send version, type, token length, code because they are
defined in the rule.
o compress Message ID and Token.
o do not sent options because they are defined in the rule.
o send value
*** NOTE: The Mid may not be sent, since no acknowledgement is
expected. Nevertheless several copies of the same message will not
be detected by the receiver which will view them as several requests.
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This can be solved at L2 if the technology sends the frame with
unique value.
2.2. Scenario 2 - CoAP POST without Acknowledgement to thing
Same as Section 2.1 but request comes from network to thing.
Selected values for Mid, token need to be control to allow a better
compression rate. A CoAP proxy is need to normalize these values.
thing LPWAN SCHC CoAP Server
| | |
| | NON POST MID=0xCDAB |
| | Token = 0x11223344 |
| | Path = /elm1/elm2 |
| | Content-format = val |
| | NoResponse = 0|2|8|16 |
| | Value |
| rule-id Value |<-------------------------------|
|<-------------------------------| |
| | |
Figure 2: POST with no ACK
Compression Objectives:
o do not send version, type, token length, code because they are
defined in the rule.
o reduce value size and compress Message ID and Token.
o do not sent options because they are defined in the rule
o send value
3. bi-directional traffic
3.1. Scenario 3 - CoAP ack
Same as Section 2.1 but the network acknowledge the CoAP message.
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thing LPWAN SCHC CoAP Server
| | |
| | CON POST MID=0x00AB |
| | Token = 0x11 |
| | Path = /elm1/elm2 |
| | Content-format = val |
| TDB | NoResponse = 0|2|8|16 |
|------------------------------->| Value |
| |------------------------------->|
| | |
| | ACK 0.00 MID=0x00AB |
| TBD |<-------------------------------|
|<-------------------------------|
Figure 3: POST with no ACK
Objectives:
o Thing
* do not send version, token length.
* compress type, Message ID, Token and code.
* do not sent options.
* send value
o Network
* compress type and code.
3.2. Scenario 4 - REST ack
Same as Section 2.1 but the thing wait for an acknowledgement at REST
level. Response code can be 2.04, 2.01, 2.02, 4.0Y, 5.0Y.
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thing LPWAN SCHC CoAP Server
| | |
| | NON POST MID=0x00AB |
| | Token = 0x11 |
| | Path = /elm1/elm2 |
|------------------------------->| Value |
| TBD |------------------------------->|
| | |
| | NON X.YY MID=0x1234 |
| | Token = 0x11 |
| TBD |<-------------------------------|
|<-------------------------------| |
Figure 4: POST with no ACK
Objectives:
o Thing
* do not send version, token length.
* compress type, Message ID and Token.
* compress code.
* do not sent options
* send value
o Network
* do not send version, token length.
* compress type, Message ID and token.
* reduce MID size in response and compress it.
3.3. Scenario 5 - GET
Same as Section 3.2 but GET request and value in response..
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thing LPWAN SCHC CoAP Server
| | |
| | NON GET MID=0x00AB |
| | Token = 0x11 |
| TBD | Accept = val |
|------------------------------->| Path = /elm1/elm2 |
| |------------------------------->|
| | |
| | NON 2.05 MID=0x1234 |
| | Token = 0x11 |
| | Content-format = val |
| | Value |
| TDB |<-------------------------------|
|<-------------------------------| |
Figure 5: POST with no ACK
Objectives:
o Thing
* do not send version, type, token length.
* compress Message ID and Token.
* compress code.
* do not sent options
o Network
* reduce MID size in response and compress it.
* compress code.
* send token.
* send value
4. CoMI
[I-D.vanderstok-core-comi] defines the different exchanges using
CoMI. The path /c gives access to the CoMI module.
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4.1. GET
With the GET method, /c is followed by the SID integer value coded in
base64. A query parameter allows to specify a particular instance by
sending the YANG keys. If no value is given then the full structure
is returned. For instance (taken from the draft):
o GET /c/a3
o GET /c/Bf4?k="eth0"
o GET /c
Objective:
o allow to compress partially the path and send only the SID value
on the radio link.
4.2. FETCH
The FETCH method uses a CBOR structure sent in the payload instead of
the URI.
FETCH /c/ Content-Format (application/YANG-fetch+cbor)
<CBOR array of instance identifiers>
Figure 6: FETCH Structure
The CBOR structure is an array containing either CBOR Integer for SID
or array with a SID and a list of filtering parameters.
FETCH /c Content-Format (application/YANG-fetch+cbor)
[ 1719, # ID 1719
[-186, "eth0"] # ID 1533 with name = "eth0"
]
Figure 7: FETCH with CBOR parameters
For the compression point of view, Fetch is a new code value 0.05.
But to send dynamically SIDs and keys, the CBOR structure must be
understood by SCHC.
4.3. PUT/POST
PUT allows to remplace or create a data resource instance, POST
always add a data resource instance. Draft imposes to use a
confirmable CoAP message (which may not needed since there is REST
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confirmation). POST URI contains only the SID value and PUT can add
a query parameter with keys.
4.4. iPATCH
As for FETCH, the URI is static and the parameters are sent in a CBOR
array containing the SID and then values.
iPATCH /c Content-Format(application/YANG-patch+cbor)
[
[1533, "eth0"] , # interface (ID = 1533)
{
+4 : "eth0", # name (ID 1537)
+1 : "Ethernet adaptor", # description (ID 1534)
+5 : 1179, # type (ID 1538),
# identity ethernetCsmacd
+2 : true # enabled (ID 1535)
}
+203 , 60 # timezone-utc-offset (delta = 1736 - 1533)
]
2.04 Changed
Figure 8: iPATCH with CBOR parameters
4.5. DELETE
If GET and PUT/POST can be replaced by FETCH and iPATCH to have a
more compact representation of SID and keys, DELETE imposes to put
these values in the URI.
4.6. Examples
Figure 9 gives the YANG module tree for SCHC. Two keys are defined:
one for the rule-id and the other for the position (field-id).
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module: ietf-lpwan-compression
+--rw compression-context
+--rw context-rules* [rule-id]
+--rw rule-id uint8
+--rw rule-fields* [position]
+--rw name? string
+--rw position uint8
+--rw target-value? lpwan-types
+--rw matching-operator? matching-operator-type
+--rw matching-operator-value? lpwan-types
+--rw compression-decompression-function? compression-decompression-function-type
+--rw compression-decompression-function-value? lpwan-types
Figure 9: Generic module tree
Figure 10 gives some SID value that may be applied to this YANG
module. Note that Matching Operators and Compression/Decompression
Functions are identified by a SID value.
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SID Assigned to
--------- --------------------------------------------------
1000 Module ietf-lpwan-compression
1001 identity /compression-decompression-function
1002 identity /compression-decompression-function/cdf-compute-ipv6-length
1003 identity /compression-decompression-function/cdf-compute-udp-checksum
1004 identity /compression-decompression-function/cdf-compute-udp-length
1005 identity /compression-decompression-function/cdf-esiid-did
1006 identity /compression-decompression-function/cdf-laiid-did
1007 identity /compression-decompression-function/cdf-lsb
1008 identity /compression-decompression-function/cdf-not-sent
1009 identity /compression-decompression-function/cdf-value-sent
1010 identity /matching-operator
1011 identity /matching-operator/mo-equal
1012 identity /matching-operator/mo-ignore
1013 identity /matching-operator/mo-msb
1014 node /compression-context
1015 node /compression-context/context-rules
1016 node /compression-context/context-rules/rule-fields
1017 node /compression-context/context-rules/rule-fields/compression-decompression-function
1018 node /compression-context/context-rules/rule-fields/compression-decompression-function-value
1019 node /compression-context/context-rules/rule-fields/matching-operator
1020 node /compression-context/context-rules/rule-fields/matching-operator-value
1021 node /compression-context/context-rules/rule-fields/name
1022 node /compression-context/context-rules/rule-fields/position
1023 node /compression-context/context-rules/rule-fields/target-value
1024 node /compression-context/context-rules/rule-id
File ietf-lpwan-compression@2016-11-01.sid created
Number of SIDs available : 200
Number of SIDs assigned : 25
Figure 10: Example of SID allocation
Some simple scenarii where SCHC rules can be modified:
o a thing selects a dynamic port number for a flow and informs the
other end of this value.
o a thing informs the other end of the destination IPv6 address.
o Network informs the thing of the IPv6 prefix
Figure 11 gives an example of a simple request where:
o field-SID contains the SID value identifying the Target Value
(1023 in Figure 10),
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o rule-id is the rule to be modified
o field-pos is the value indicating that it is respectively a
ESport, or a prefix
iPATCH /c Content-Format(application/YANG-patch+cbor)
[
[field-SID, rule-id, field-pos], value
]
Figure 11: YANG definition of the IPv6 UDP compression
To set a port number for Rule 10 a CoMI iPTACH is sent. The rule 1
is used for that CoMI request and contains the Path, the content-
format values and also the field-SID for Target Value (1023).
+----------------+------------------------+----------------+-----------------+
| Field | Function | Target Value | Sent compressed |
+----------------+------------------------+----------------+-----------------+
|CoAP version | not-sent | 1 | |
|CoAP Type | not-sent | CON* | t |
|CoAP TKL | compute-token-length | | |
|CoAP Code | map-code | mapping table | CC |
|CoAP MID | remapping | 7 bits | MM |
|CoAP Token | remapping | 8 bits | TTT |
|CoAP Path | not-sent | /c | |
|CoAP content-F | not-sent | YANG-patch+cbor| |
+----------------+------------------------+----------------+-----------------+
* draft mandate a Confirmable message
Figure 12: CoAP Context to compress header with token
Where t defines the request type (0: CON, 1: ACK), CC defines the
code (00: iPTACH, 01: 2.04, 10: ????, 11: ????). Message id is
remapped in 2 bits which allows 4 messages simultaneously in the air
and Token to 3 bits which allows 8 simultaneous pending requests.
The objective will be to sent on the radio link a message containing:
o rule-id for CoMI message : 0x01
o CoAP header : 0xXX (1 byte)
o CBOR Rule-id : 0x0A (10 in the example) (1 byte)
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o CBOR position to identify ESport : 0xPPPPPPPP (4 bytes)
o CBOR port number value : 0xPPPP (2 bytes)
Therefore 9 bytes are sent on the LPWAN radio link.
5. Normative References
[I-D.vanderstok-core-comi]
Stok, P., Bierman, A., Veillette, M., and A. Pelov, "CoAP
Management Interface", draft-vanderstok-core-comi-10 (work
in progress), October 2016.
[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, <http://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 Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Laurent.Toutain@imt-atlantique.fr
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