CoRE A. Bhattacharyya
Internet Draft S. Bandyopadhyay
Intended status: Standards track A. Pal
Expires: April 2016 T. Bose
Tata Consultancy Services Ltd.
October 15, 2015
CoAP option for no server-response
draft-tcs-coap-no-response-option-12
Abstract
There can be M2M scenarios where responses from server against
requests from client might be considered redundant. This kind of
open-loop exchange (with no response path from the server to the
client) may be desired to minimize resource consumption in
constrained systems while simultaneously updating a bulk of
resources or updating a resource with a very high frequency. CoAP
already provides a non-confirmable (NON) mode of message exchange
where the server end-point does not respond with ACK. However,
obeying the request/response semantics, the server end-point
responds back with a status code indicating "the result of the
attempt to understand and satisfy the request".
This draft introduces a header option for CoAP called 'No-Response'.
Using this option the client explicitly tells the server to suppress
responses against the particular request. This option also provides
granular control to enable suppression of a particular class or a
combination of response-classes. This option may be effective for
both unicast and multicast requests. Present draft also discusses
few exemplary applications which benefit from this option.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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months and may be updated, replaced, or obsoleted by other documents
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This Internet-Draft will expire on April 15, 2016.
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Table of Contents
1. Introduction...................................................3
1.1. Potential benefits........................................3
1.2. Terminology...............................................4
2. Option Definition..............................................4
2.1. Granular control over response suppression................5
3. Exemplary application scenarios................................7
3.1. Frequent update of geo-location from vehicles to backend..7
3.2. Multicasting actuation command from a handheld device to a
group of appliances............................................8
3.2.1. Using granular response suppression..................9
4. Miscellaneous aspects..........................................9
4.1. Re-using Tokens...........................................9
4.2. Taking care of congestion................................10
4.3. Handling No-Response option for a reverse proxy..........11
5. Example.......................................................11
5.1. Using No-Response with PUT...............................11
5.2. Using No-Response with POST..............................12
5.2.1. POST updating a fixed target resource...............12
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5.2.2. POST updating through query-string..................13
6. IANA Considerations...........................................14
7. Security Considerations.......................................15
8. Acknowledgments...............................................15
9. References....................................................15
9.1. Normative References.....................................15
9.2. Informative References...................................15
1. Introduction
This draft proposes a new header option for Constrained Application
Protocol (CoAP) [RFC7252] called 'No-Response'. This option enables
the client end-point to explicitly express its disinterest in
receiving responses back from the server end-point. This option
allows all classes of response by default. Fine grain control to
suppress responses of a particular class or a combination of
response classes is also possible.
Along with the technical details this draft presents some practical
application scenarios which should bring out the usefulness of this
option.
Wherever, in this draft, it is mentioned that a request from client
is with No-Response the intended meaning is that the client
expressed its disinterest for all or some selected classes of
responses.
1.1. Potential benefits
Use of No-Response option should be driven by typical application
requirement and, particularly, characteristics of the information to
be updated. If this option is opportunistically used in a fitting
M2M application then the concerned systems may benefit in the
following aspects:
* Reduction in network clogging due to effective reduction of
the overall traffic.
* Reduction in server-side loading by relieving the server from
responding to each request when not necessary.
* Reduction in battery consumption at the constrained end-point.
* Reduction in overall communication cost.
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1.2. Terminology
The terms used in this draft are in conformance with those defined
in [RFC7252].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
2. Option Definition
The properties of this option are given in Table 1.
+--------+---+---+---+---+-------------+--------+--------+---------+
| Number | C | U | N | R | Name | Format | Length | Default |
+--------+---+---+---+---+-------------+--------+--------+---------+
| 284 | | | X | | No-Response | uint | 0-1 | 0 |
+--------+---+---+---+---+-------------+--------+--------+---------+
Table 1: Option Properties
This option is a request option. It is Elective and Non-Repeatable.
Note: Since CoAP maintains a clear separation between the
request/response and the messaging layer, this option does not
have any dependency on the type of message (confirmable/ non-
confirmable). However, NON type of messages are best fitting with
this option considering the expected benefits out of it. Using
No-Response with NON messages gets rid of any kind of reverse
traffic and the interaction becomes completely open-loop.
Using this option with CON type of requests may not have any
significance if piggybacked responses are triggered. But, in case
the server responds with a separate response (which, may be, the
client does not care about) then this option can be useful.
Suppressing the separate response reduces one additional traffic
in this case.
This option contains values to indicate disinterest in all or a
particular class or combination of classes of responses as described
in the next sub-section. The following table provides a 'ready-
reference' on possible applicability of this option for all the four
REST methods. This table is prepared in view of the type of possible
interactions foreseen so far.
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+-------------+----------------------------------------------------+
| Method Name | Remarks on applicability |
+-------------+----------------------------------------------------+
| | This SHOULD NOT be used with GET under usual |
| | circumstances when the client requests the contents|
| | of a resource. However, this option may be useful |
| | for special GET requests. At present only one such|
| | application is identified which is the |
| | 'cancellation' procedure for 'Observe'. Observe- |
| GET | cancellation requires a client to issue a GET |
| | request with Observe option set to 'deregister' |
| | (1). Since, in this case, the server response does |
| | not contain any payload the client MAY express its |
| | disinterest in server responses. |
+-------------+----------------------------------------------------+
| | Suitable for frequent updates (particularly in NON |
| PUT | mode) on existing resources. Might not be useful |
| | when PUT creates a new resource. |
+-------------+----------------------------------------------------+
| | If POST is used to update a target resource |
| | then No-Response can be used in the same manner as |
| | in PUT. This option may also be useful while |
| POST | updating through query strings rather than updating|
| | a fixed target resource (see Section 5.2.2 for an |
| | example). |
+-------------+----------------------------------------------------+
| | Deletion is usually a permanent action and the |
| DELETE | client MAY want to ensure that the deletion |
| | actually happened. MAY NOT be applicable. |
+-------------+----------------------------------------------------+
Table 2: Suggested applicability of No-Response for different REST
methods
2.1. Granular control over response suppression
This option enables granular control over response suppression by
allowing the client to express its disinterest in a typical class or
combination of classes of responses. For example, a client may
explicitly tell the receiver that no response is required unless
something 'bad' happens and a response of class 4.xx or 5.xx is to
be fed back to the client. No response of the class 2.xx is
required.
Note: Section 3.7 of [RFC7390] describes a scheme where a server in
the multicast group may decide on its own to suppress responses
for group communication with granular control. Client does not
have any knowledge about that. On the other hand, the 'No-
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Response' option enables the clients to explicitly inform the
servers about its disinterest in responses. Such explicit control
on the client side may be helpful for debugging network
resources. An example scenario is described in Section 3.2.
This option is defined as a bit-map (Table 3) to achieve granular
suppression.
+-------+-----------------------+---------------------------------+
| Value | Binary Representation | Description |
+-------+-----------------------+---------------------------------+
| 0 | <empty> | Allow all responses. |
+-------+-----------------------+---------------------------------+
| 2 | 00000010 | Suppress 2.xx responses. |
+-------+-----------------------+---------------------------------+
| 8 | 00001000 | Suppress 4.xx responses. |
+-------+-----------------------+---------------------------------+
| 16 | 00010000 | Suppress 5.xx responses. |
+-------+-----------------------+---------------------------------+
| 127 | 01111111 | Suppress all responses. |
+-------+-----------------------+---------------------------------+
Table 3: Option values
The conventions used in deciding the option values are:
1. To suppress an individual class: Set bit number (n-1) starting
from the LSB (bit number 0) to suppress all responses belonging to
class n.xx. So,
option value to suppress n.xx class = 2**(n-1).
2. To suppress combination of classes: Set each corresponding bit
according to point 1 above. Example: The option value will be 18
(binary: 00010010) to suppress both 2.xx and 5.xx responses. This is
essentially bitwise OR of the corresponding individual values for
suppressing 2.xx and 5.xx. At present the "CoAP Response Codes"
registry (Ref. Section 12.1.2 of [RFC7252]) defines only 2.xx, 4.xx
and 5.xx responses.
So, an option value of 22 (binary: 00010110) will effectively
suppress all currently defined response codes.
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3. To suppress all possible responses: The maximum reserved response
code for CoAP is 7.31 (Ref. Section 12.1 of [RFC7252]). So, setting
bit positions 0-6 will suppress all responses according to the
combination operation defined in point 2 above. Hence, the value to
block all present and possible future responses is: 2**7 - 1 = 127.
Implementation Note: When No-Response is used with empty or 0 value
in a request the client end-point SHOULD cease listening to
response against the particular request. On the other hand,
opening up at least one class of response means that the client
end-point can no longer completely cease listening activity and
must be configured to listen up to some application specific
time-out period for the particular request. The client end-point
never knows whether the present update will be a success or a
failure. Thus, for example, if the client decides to open up the
response for errors (4.xx & 5.xx) then it has to wait for the
entire time-out period even for the instances where the request
is successful (and the server is not supposed to send back a
response). A point to be noted in this context is that there may
be situations when the response on errors might get lost. In such
a situation the client would wait up to the time-out period but
will not receive any response. But this should not lead to the
impression to the client that the request was successful. The
application designer needs to tackle such situation. For example,
while performing frequent updates, the client may strategically
interweave requests without No-Response into a series of requests
with No-Response to check time to time if things are fine at the
server end and the server is actively responding.
3. Exemplary application scenarios
This section describes some exemplary user stories which may
potentially get benefitted through the use of No-Response option.
3.1. Frequent update of geo-location from vehicles to backend
Let us consider an intelligent traffic system (ITS) consisting of
vehicles equipped with a sensor-gateway comprising sensors like GPS
and Accelerometer. The sensor-gateway acts as a CoAP client end-
point. It connects to the Internet using a low-bandwidth cellular
(e.g. GPRS) connection. The GPS co-ordinates of the vehicle are
periodically updated to the backend server. The update rate is
adaptive to the motional-state of the vehicle. If the vehicle moves
fast the update rate is high as the position of the vehicle changes
rapidly. If the vehicle is static or moves slowly then the update
rate is low. This ensures that bandwidth and energy is not consumed
unnecessarily. The motional-state of the vehicle is inferred by a
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local analytics running on the sensor-gateway which uses the
accelerometer data and the rate of change in GPS co-ordinates. The
back-end server hosts applications which use the updates for each
vehicle and produce necessary information for remote users.
Retransmitting a location co-ordinate which the vehicle has already
crossed is not efficient as it adds redundant traffic to the
network. So, the updates are done in NON mode. However, given the
huge number of vehicles updating frequently, the NON exchange will
also trigger huge number of status responses from the backend. Thus
the cumulative load on the network will be quite significant.
On the contrary, if the client end-points on the vehicles explicitly
declare that they do not need any status response back from the
server then significant load will be reduced. The assumption is
that, since the update rate is high, stray losses in geo-locations
will be compensated with the large update rate.
Note: It may be argued that the above example application can also
be implemented using "Observe" option ([I-D.ietf-core-observe])
with NON notifications. But, in practice, implementing with
"Observe" would require lot of book-keeping exercise at the data-
collection end-point at the backend (observer). The observer
needs to maintain all the observe relationships with each
vehicle. The data collection end-point may be unable to know all
its data sources beforehand. The client end-points at vehicles
may go offline or come back online randomly. In case of 'Observe'
the onus is always on the data collection end-point to establish
observe relationship with each data-source. On the other hand,
implementation will be much simpler if the initiative is left on
the data-source to carry out updates using No-Response option.
Putting it another way: the implementation choice depends on the
perspective of interest to initiate the update. In an 'Observe'
scenario the interest is expressed by the data-consumer. On the
contrary, the classic update case applies when it is the interest
of the data-producer. The 'No-Response' option enables to make
classic updates further less resource consuming.
3.2. Multicasting actuation command from a handheld device to a group
of appliances
A handheld device (e.g. a smart phone) may be programmed to act as
an IP enabled switch to remotely operate on a single or group of IP
enabled appliances. For example the smart phone can be programmed to
send a multicast request to switch on/ off all the lights of a
building. In this case the IP switch application can use No-Response
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option along with NON request to reduce the traffic generated due to
simultaneous status responses from hundreds of lights.
Thus No-Response helps in reducing overall communication cost and
the probability of network clogging in this case.
3.2.1. Using granular response suppression
The IP switch application may optionally use granular response
suppression such that the error responses are not suppressed. In
that case the lights which could not execute the request would
respond back and be readily identified. Thus, explicit suppression
of option classes by the multicast client may be useful to debug the
network and the application.
4. Miscellaneous aspects
This section further describes few important implementation aspects
worth considering while using No-Response. The following discussion
does not mandate anything, rather suggests some guidelines for the
application developer.
4.1. Re-using Tokens
Tokens provide a matching criteria between a request and the
corresponding response. The life of a token starts when it is
assigned to a request and ends when the final matching response is
received. Then the token can again be re-used. However, a request
with No-Response typically does not have any guaranteed response
path. So, the client has to decide on its own about when it can
retire a token which has been used in an earlier request so that the
token can be reused in a future request. Since the No-Response
option is 'elective', a server which has not implemented this option
will respond back. This leads to the following two scenarios:
The first scenario is, the client is never going to care about any
response coming back or about relating the response to the original
request. In that case it MAY reuse the token value at liberty.
However, as a second scenario, let us consider that the client sends
two requests where the first request is with No-Response and the
second request, with same token, is without No-Response. In this
case a delayed response to the first one can be interpreted as a
response to the second request (client needs a response in the
second case) if the gap between using the same tokens is not enough.
This creates a problem in the request-response semantics.
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The most ideal solution would be to always use a unique token for
requests with No-Response. But if a client wants to reuse a token
then in most practical cases the client implementation SHOULD
implement an application specific reuse time after which it can
reuse the token. This draft suggests a reuse time for tokens with
similar expression as in Section 2.5 of [RFC7390]:
TOKEN_REUSE_TIME = NON_LIFETIME + MAX_SERVER_RESPONSE_DELAY +
MAX_LATENCY.
NON_LIFETIME and MAX_LATENCY are defined in 4.8.2 of [RFC7252].
MAX_SERVER_RESPONSE_DELAY has same interpretation as in Section 2.5
of [RFC7390] for multicast request. But for unicast request, since
the message is sent to only one server, MAX_SERVER_RESPONSE_DELAY
means the expected maximum response delay from the particular server
to which client sent the request. For multicast it is the expected
delay "over all servers that the client can send a multicast request
to". This delay includes the maximum Leisure time period as defined
in Section 8.2 of [RFC7252]. [RFC7252] defines a rough lower bound
of leisure as:
lb_Leisure = S * G / R
(S = estimated response size; R = data transfer rate; G = group size
estimate)
Note: If it is not possible for the client to get a reasonable
estimate of the MAX_SERVER_RESPONSE_DELAY then the client, to be
safe, SHOULD use a unique token for request with No-Response to
the same server endpoint.
4.2. Taking care of congestion
A detail technical discussion on congestion control is out-of-scope
of this draft. However, this section of the draft mention certain
aspects on congestion control which may help a detail work on
congestion control for CoAP as a whole.
If this option is used with NON messages then the interaction
becomes completely open-loop. Absence of any feed-back from the
server end affects congestion-control mechanism. In this case the
communication pattern belongs to the class of low-data volume
applications as described in Section 3.1.2 of [RFC5405]. Precisely,
it maps to the scenario where the application cannot maintain an RTT
estimate. Hence, following [RFC5405], a 3s interval is suggested as
the minimum interval between successive updates. However, in case of
frequent updates, an application developer MUST interweave
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occasional closed-loop exchanges (e.g. NON messages without No-
Response or simply CON messages) to get an RTT estimate between the
end-points.
4.3. Handling No-Response option for a reverse proxy
A reverse proxy (HTTP to CoAP) MAY translate an incoming HTTP
request to a corresponding CoAP request indicating that no response
is required based on some application specific requirement. In this
case, it is recommended that the HC Proxy SHOULD send an HTTP
response with status code 204 (No Content).
5. Example
This section illustrates few examples of exchanges based on the
scenario narrated in Section 3.1. Examples for other scenarios can
be easily conceived based on these illustrations.
5.1. Using No-Response with PUT
Figure 1 shows a typical request with this option. The depicted
scenario occurs when the vehicle#n moves very fast and update rate
is high. The vehicle is assigned a dedicated resource: vehicle-stat-
<n>, where <n> can be any string uniquely identifying the vehicle.
The update requests are sent over NON type of messages. The No-
Response option causes the server not to respond back.
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Client Server
| |
| |
+----->| Header: PUT (T=NON, Code=0.03, MID=0x7d38)
| PUT | Token: 0x53
| | Uri-Path: "vehicle-stat-00"
| | Content Type: text/plain
| | No-Response: 127
| | Payload:
| | "VehID=00&RouteID=DN47&Lat=22.5658745&Long=88.4107966667&
| | Time=2013-01-13T11:24:31"
| |
[No response from the server. Next update in 20 secs.]
| |
+----->| Header: PUT (T=NON, Code=0.03, MID=0x7d39)
| PUT | Token: 0x54
| | Uri-Path: "vehicle-stat-00"
| | Content Type: text/plain
| | No-Response: 127
| | Payload:
| | "VehID=00&RouteID=DN47&Lat=22.5649015&Long=88.4103511667&
| | Time=2013-01-13T11:24:51"
Figure 1: Exemplary unreliable update with No-Response option using
PUT.
5.2. Using No-Response with POST
5.2.1. POST updating a fixed target resource
In this case POST acts the same way as PUT. The exchanges are same
as above. The updated values are carried as payload of POST as shown
in Figure 2.
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Client Server
| |
| |
+----->| Header: POST (T=NON, Code=0.02, MID=0x7d38)
| POST | Token: 0x53
| | Uri-Path: "vehicle-stat-00"
| | Content Type: text/plain
| | No-Response: 127
| | Payload:
| | "VehID=00&RouteID=DN47&Lat=22.5658745&Long=88.4107966667&
| | Time=2013-01-13T11:24:31"
| |
[No response from the server. Next update in 20 secs.]
| |
+----->| Header: PUT (T=NON, Code=0.02, MID=0x7d39)
| POST | Token: 0x54
| | Uri-Path: "vehicle-stat-00"
| | Content Type: text/plain
| | No-Response: 127
| | Payload:
| | "VehID=00&RouteID=DN47&Lat=22.5649015&Long=88.4103511667&
| | Time=2013-01-13T11:24:51"
Figure 2: Exemplary unreliable update with No-Response option using
POST as the update-method.
5.2.2. POST updating through query-string
It may be possible that the backend infrastructure (as described in
Section 3.1) deploys a dedicated database to store the location
updates. In such a case the client can update through a POST by
sending a query string in the URI. The query-string contains the
name/value pairs for each update. 'No-Response' can be used in same
manner as for updating fixed resources. The scenario is depicted in
Figure 3.
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Client Server
| |
| |
+----->| Header: POST (T=NON, Code=0.02, MID=0x7d38)
| POST | Token: 0x53
| | Uri-Path: "updateOrInsertInfo"
| | Uri-Query: "VehID=00"
| | Uri-Query: "RouteID=DN47"
| | Uri-Query: "Lat=22.5658745"
| | Uri-Query: "Long=88.4107966667"
| | Uri-Query: "Time=2013-01-13T11:24:31"
| | No-Response: 127
| |
[No response from the server. Next update in 20 secs.]
| |
+----->| Header: POST (T=NON, Code=0.02, MID=0x7d39)
| POST | Token: 0x54
| | Uri-Path: "updateOrInsertInfo"
| | Uri-Query: "VehID=00"
| | Uri-Query: "RouteID=DN47"
| | Uri-Query: "Lat=22.5649015"
| | Uri-Query: "Long=88.4103511667"
| | Uri-Query: "Time=2013-01-13T11:24:51"
| | No-Response: 127
| |
Figure 3: Exemplary unreliable update with No-Response option using
POST with a query-string to insert update information to backend
database.
6. IANA Considerations
The IANA has assigned number 284 to this option in the CoAP Option
Numbers registry:
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+--------+--------------+----------------------------+
| Number | Name | Reference |
+--------+--------------+----------------------------+
| 284 | No-Response | Section 2 of this document |
+--------+--------------+----------------------------+
7. Security Considerations
The No-Response option defined in this document presents no security
considerations beyond those in Section 11 of the base CoAP
specification [RFC7252].
8. Acknowledgments
Thanks to Carsten Bormann, Matthias Kovatsch, Esko Dijk, Bert
Greevenbosch, Akbar Rahman and Klaus Hartke for their valuable
inputs.
9. References
9.1. Normative References
[RFC7252]
Shelby, Z., Hartke, K. and Bormann, C.,"Constrained Application
Protocol (CoAP)", RFC 7252, June, 2014
[I-D.ietf-core-observe]
Hartke, K.,"Observing Resources in CoAP", draft-ietf-core-observe-
16, December 30, 2014
[RFC7390]
Rahman, A. and Dijk, E.,"Group Communication for CoAP", RFC 7390,
October, 2014
[RFC5405]
Eggert, L. and Fairhurst, G.," Unicast UDP Usage Guidelines for
Application Designers", RFC 5405, November, 2008
9.2. Informative References
[MOBIQUITOUS 2013]
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Bhattacharyya, A., Bandyopadhyay, S. and Pal, A., "ITS-light:
Adaptive lightweight scheme to resource optimize intelligent
transportation tracking system (ITS)-Customizing CoAP for
opportunistic optimization", 10th International Conference on Mobile
and Ubiquitous Systems: Computing, Networking and Services
(Mobiquitous 2013), December, 2013.
[Sensys 2013]
Bandyopadhyay, S., Bhattacharyya, A. and Pal, A., "Adapting protocol
characteristics of CoAP using sensed indication for vehicular
analytics", 11th ACM Conference on Embedded Networked Sensor Systems
(Sensys 2013), November, 2013.
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Authors' Addresses
Abhijan Bhattacharyya
Tata Consultancy Services Ltd.
Kolkata, India
Email: abhijan.bhattacharyya@tcs.com
Soma Bandyopadhyay
Tata Consultancy Services Ltd.
Kolkata, India
Email: soma.bandyopadhyay@tcs.com
Arpan Pal
Tata Consultancy Services Ltd.
Kolkata, India
Email: arpan.pal@tcs.com
Tulika Bose
Tata Consultancy Services Ltd.
Kolkata, India
Email: tulika.bose@tcs.com
Bhattacharyya, et al. Expires April 15, 2016 [Page 17]