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Constrained Application Protocol (CoAP) Option for No Server Response

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7967.
Authors Abhijan Bhattacharyya , Soma Bandyopadhyay , Arpan Pal , Tulika Bose
Last updated 2018-12-20 (Latest revision 2016-05-12)
RFC stream Independent Submission
Intended RFC status Informational
IETF conflict review conflict-review-tcs-coap-no-response-option
Stream ISE state Published RFC
Consensus boilerplate Unknown
Document shepherd Eliot Lear
Shepherd write-up Show Last changed 2016-06-07
IESG IESG state Became RFC 7967 (Informational)
Telechat date (None)
Responsible AD (None)
Send notices to "Nevil Brownlee" <>
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
CoRE                                                   A. Bhattacharyya
Internet Draft                                         S. Bandyopadhyay
Intended status: Informational                                   A. Pal
Expires: November 2016                                          T. Bose
                                         Tata Consultancy Services Ltd.
                                                           May 12, 2016

                    CoAP option for no server-response


   There can be M2M scenarios where responses from a server against
   requests from client are 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
   updating a bulk of resources simultaneously, or updating a resource
   with a very high frequency. CoAP already provides Non-confirmable
   (NON) messages that are not acknowledged by the recipient. However,
   the request/response semantics still require the server to respond
   with a status code indicating "the result of the attempt to
   understand and satisfy the request".

   This specification introduces a CoAP option called 'No-Response'.
   Using this option the client can explicitly express to the server
   its disinterest in all responses against the particular request.
   This option also provides granular control to enable expression of
   disinterest to a particular class of response or a combination of
   response-classes. The server MAY decide to suppress the response by
   not transmitting it back to the client according to the value of No-
   Response option in the request. This option may be effective for
   both unicast and multicast requests. This document also discusses a
   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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

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   Internet-Drafts are draft documents valid for a maximum of six
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   This Internet-Draft will expire on November 12, 2016.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
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   warranty as described in the Simplified BSD License.

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
      2.2. Method-specific Applicability Consideration...............7
   3. Miscellaneous Aspects..........................................8
      3.1. Re-using Tokens...........................................9
      3.2. Taking Care of Congestion Control and Server-side Flow
      3.3. Considerations Regarding Caching of Responses............11
      3.4. Handling No-Response Option for a HTTP-to-CoAP Reverse Proxy
   4. Exemplary Application Scenarios...............................11
      4.1. Frequent Update of Geo-location from Vehicles to Backend

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         4.1.1. Using No-Response with PUT..........................13
         4.1.2. Using No-Response with POST.........................13
   POST updating a fixed target resource..........13
   POST updating through query-string.............14
      4.2. Multicasting Actuation Command from a Handheld Device to a
      Group of Appliances...........................................15
         4.2.1. Using Granular Response Suppression.................16
   5. IANA Considerations...........................................16
   6. Security Considerations.......................................16
   7. Acknowledgments...............................................16
   8. References....................................................16
      8.1. Normative References.....................................16
      8.2. Informative References...................................17

1. Introduction

   This specification defines a new option for Constrained Application
   Protocol (CoAP) [RFC7252] called 'No-Response'. This option enables
   clients to explicitly express their disinterests in receiving
   responses back from the server. The disinterest can be expressed at
   the granularity of response classes (e.g., 2.xx or the combination
   of 2.xx and 5.xx). By default this option indicates interest in all
   response classes. The server MAY decide to suppress the response by
   not transmitting it back to the client according to the value of the
   No-Response option in the request.

   Along with the technical details this document presents some
   practical application scenarios which bring out the usefulness of
   this option.

   Wherever, in this document, it is mentioned that a request from a
   client is with No-Response the intended meaning is that the client
   expresses its disinterest for all or some selected classes of

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 system may benefit in the
   following aspects (however, it is to be noted, this option is
   elective and servers can simply ignore the preference expressed by
   the client):

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       * Reduction in network congestion due to effective reduction of
   the overall traffic.

       * Reduction in server-side load by relieving the server from
   responding to each request when not necessary.

       * Reduction in battery consumption at the constrained end-

       * Reduction in overall communication cost.

1.2. Terminology

   The terms used in this document are in conformance with those
   defined in [RFC7252].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119.

2. Option Definition

   The properties of No-Response option are given in Table 1.

   | Number | C | U | N | R |   Name      | Format | Length | Default |
   |   258  |   | X | - |   | No-Response |  uint  |  0-1   |    0    |
                           Table 1: Option Properties

   This option is a request option. It is Elective and Non-Repeatable.
   This option is Unsafe-to-forward as the intermediary MUST know how
   to interpret this option. Otherwise the intermediary, without
   knowledge about the special unidirectional nature of the request,
   would wait for responses.

   Note: Since CoAP maintains a clear separation between the
      request/response and the message sub-layer, this option does not
      have any dependency on the type of message (Confirmable/Non-
      confirmable). So, even the absence of message sub-layer (ex.
      CoAP-over-TCP [I-D.ietf-core-coap-tcp-tls-01]) should have no
      effect on the interpretation of this option. However, considering
      the CoAP-over-UDP scenario [RFC7252], 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

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      kind of reverse traffic and the interaction becomes completely

       Using this option with CON type of requests may not serve the
      desired purpose if piggybacked responses are triggered. But, in
      case the server responds with a separate response (which,
      perhaps, the client does not care about) then this option can be
      useful. Suppressing the separate response reduces traffic by one
      additional CoAP message 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.

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
   in such case.

   Note: Section 2.7 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. The client does
      not have any knowledge about that. However, on the other hand,
      the 'No-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 4.2.1.

   The server MUST send back responses of the classes for which the
   client has not expressed any dis-interest. There may be instances
   where a server, on its own, decides to suppress responses. An
   example is suppression of responses by multicast servers as
   described in Section 2.7 of [RFC7390]. If such a server receives a
   request with a No-Response option showing 'interest' in specific
   response classes (i.e., not expressing disinterest for these
   options), then any default behaviour of suppressing response, if
   present, MUST be overridden to deliver those responses which are of
   interest to the client.

   So, for example, suppose a multicast server suppresses all responses
   by default and receives a request with a No-Response option
   expressing disinterest in 2.xx (success) responses only. Note that

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   the option value naturally expresses interest in error responses
   4.xx/5.xx in this case. Then the server must send back a response if
   the concerned request caused an error.

   The option value is defined as a bit-map (Table 2) to achieve
   granular suppression. Its length can be 0 byte (empty value) or 1

   | Value | Binary Representation |          Description            |
   |   0   |      <empty>          |    Interested in all responses. |
   |   2   |      00000010         |    Not interested in 2.xx       |
   |       |                       |    responses.                   |
   |   8   |      00001000         |    Not interested in 4.xx       |
   |       |                       |    responses.                   |
   |   16  |      00010000         |    Not interested in 5.xx       |
   |       |                       |    responses.                   |
                          Table 2: 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. The "CoAP Response Codes" registry (Ref.
   Section 12.1.2 of [RFC7252]) defines 2.xx, 4.xx and 5.xx responses.
   So, an option value of 26 (binary: 00011010) will request to
   suppress all response codes defined in [RFC7252].

   Note: When No-Response is used with value 26 in a request the client
      end-point SHOULD cease listening to response(s) against the
      particular request. On the other hand, showing interest in at

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      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 request will be a success or a failure.
      Thus, for example, if the client decides to open up the response
      for errors (4.xx and 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 necessarily
      successful. In other words, in this case the client cannot
      distinguish between response suppression and message loss. The
      application designer needs to tackle such situation. For example,
      while performing frequent updates, the client may strategically
      interweave requests without No-Response option 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.

2.2. Method-specific Applicability Consideration

   The following table provides a ready-reference on the possible
   applicability of this option for all the four REST methods. This
   table is prepared in view of the type of possible interactions
   foreseen at time of preparing this specification. Capitalization of
   key words like "SHOULD NOT", etc. have not been deliberately used in
   this table as this table is only suggestive.

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   | Method Name |              Remarks on applicability              |
   |             | This should not be used with conventional GET      |
   |             | request when the client requests the contents      |
   |             | of a resource. However, this option may be useful  |
   |             | for exceptional cases where  GET requests has side |
   |     GET     | effects. For instance, the proactive 'cancellation'|
   |             | procedure for observing request [RFC7641] requires |
   |             | a client to issue a GET request with Observe option|
   |             | set to 1 ('deregister'). In case it is more        |
   |             | efficient to use this deregistration instead of    |
   |             | reactive cancellation (rejecting the next          |
   |             | notification with RST), the client MAY express its |
   |             | disinterest in the response to such a GET request. |
   |             | Suitable for frequent updates (particularly in NON |
   |             | messages) on existing resources. Might not be      |
   |             | useful when PUT is used to create a new resource as|
   |             | it may be important for the client to know that    |
   |     PUT     | the resource creation was actually successful in   |
   |             | order to carry out future actions. Also, it may be |
   |             | important to ensure that a resource was actually   |
   |             | created rather than updating an existing 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 for an|
   |             | example).                                          |
   |             | Deletion is usually a permanent action and if the  |
   |    DELETE   | client likes to ensure that the deletion request   |
   |             | was properly executed then this option should not  |
   |             | be used with the request.                          |
    Table 3: Suggested applicability of No-Response for different REST

3. Miscellaneous Aspects

   This section further describes important implementation aspects
   worth considering while using the No-Response option. The following
   discussion contains guidelines and requirements (derived by
   combining [RFC7252], [RFC7390] and [RFC5405]) for the application

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3.1. 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 time interval between using the same Token is
   not long enough. This creates a problem in the request-response

   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. A minimum reuse time for Tokens with a similar
   expression as in Section 2.5 of [RFC7390] SHOULD be used:


   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. For a 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 requests,
   MAX_SERVER_RESPONSE_DELAY has the same interpretation as in Section
   2.5 of [RFC7390]. So, for multicast it is the expected maximum
   server response delay "over all servers that the client can send a
   multicast request to". This response delay for a given server
   includes its specific Leisure period; where Leisure is defined in

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   Section 8.2 of [RFC7252]. In general, the Leisure for a server may
   not be known to the client. A lower bound for Leisure, lb_Leisure,
   is defined in [RFC7252], but not an upper bound as is needed in this
   case. Therefore the upper bound can be estimated by taking N (N>>1)
   times the lower bound lb_Leisure:

                          lb_Leisure = S * G / R

   (S = estimated response size; R = data transfer rate; G = group size

   Any estimate of MAX_SERVER_RESPONSE_DELAY MUST be larger than
   DEFAULT_LEISURE as defined in [RFC7252].

   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 each stream of message.

3.2. Taking Care of Congestion Control and Server-side Flow Control

   This section provides guidelines for basic congestion control.
   Better congestion control mechanisms can be designed as future work.

   If this option is used with NON messages then the interaction
   becomes completely open-loop. Absence of any feedback from the
   server-end affects congestion-control mechanism. In this case the
   communication pattern maps to the scenario where the application
   cannot maintain an RTT estimate as described in Section 3.1.2 of
   [RFC5405].Hence, following [RFC5405], a 3 seconds interval is
   suggested as the minimum interval between successive updates and use
   even less aggressive rate when possible. However, in case of more
   frequent update rates the application MUST have some knowledge about
   the channel and an application developer MUST interweave occasional
   closed-loop exchanges (e.g. NON messages without No-Response or CON
   messages) to get an RTT estimate between the endpoints.

   Interweaving requests without No-Response is a MUST in case of
   aggressive request rate for applications where server-side flow
   control is necessary. For example, as proposed in [I-D.koster-core-
   coap-pubsub], a broker MAY return "4.29 Too Many Requests" in order
   to request a client to slow down the request rate. Interweaving
   requests without No-Response allows the client to listen to such

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3.3. Considerations Regarding Caching of Responses

   The cacheability of CoAP responses does not depend on the request
   method, but it depends on the Response Code. The No-Response option
   does not lead to any impact on cacheability of responses. If a
   request containing No-Response triggers a cacheable response then
   the response MUST be cached. However, the response MAY not be
   transmitted considering the value of the No-Response option in the

   For example, if a request with No-Response triggers a cacheable
   response of 4.xx class with Max-Age !=0 then the response must be
   cached. The cache will return the response to subsequent similar
   requests without No-Response as long as the Max-Age is not elapsed.

3.4. Handling No-Response Option for a HTTP-to-CoAP Reverse Proxy

   A HTTP-to-CoAP reverse proxy MAY translate an incoming HTTP request
   to a corresponding CoAP request indicating that no response is
   required (showing disinterest in all classes of responses) based on
   some application specific requirement.  In this case it is
   RECOMMENDED that the reverse proxy generates an HTTP response with
   status code 204 (No Content) when such response is allowed. The
   generated response is sent after the proxy has successfully sent out
   the CoAP request.

   In case the reverse proxy applies No-Response for particular
   class(es) of response(s) it will wait for responses up to an
   application specific maximum time (T_max) before responding back to
   the HTTP-side. If a response of a desired class is received within
   T_max then the response gets translated to HTTP as defined in [I-
   D.ietf-core-http-mapping]. However if the proxy does not receive any
   response within T_max, it is RECOMMENDED that the reverse Proxy
   sends an HTTP response with status code 204 (No Content) when
   allowed for the specific HTTP request method.

4. Exemplary Application Scenarios

   This section describes some exemplary application scenarios which
   may potentially benefit from the use of No-Response option.

4.1. Frequent Update of Geo-location from Vehicles to Backend Server

   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. It
   connects to the Internet using a low-bandwidth cellular (e.g. GPRS)

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   connection. The GPS co-ordinates of the vehicle are periodically
   updated to the backend server.

   While performing frequent location update, retransmitting (through
   the CoAP CON mechanism) a location co-ordinate which the vehicle has
   already left in the meantime is not efficient as it adds redundant
   traffic to the network. Therefore, the updates are done using NON
   messages. However, given the huge number of vehicles updating
   frequently, the NON exchange will also trigger huge number of
   responses from the backend. Thus the cumulative load on the network
   will be quite significant. Also, the client in this case may not be
   interested in getting responses against location update request for
   the location it has already crossed in the meantime and a next
   location update is imminent.

   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 load will be reduced significantly. The assumption is
   that, since the update rate is high, stray losses in geo-location
   reports 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 ([RFC7641]) with NON
      notifications. But, in practice, implementing with Observe would
      require lot of book-keeping 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 an 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. Another way of looking at it
      is, 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 the interest is from the data-
      producer. The 'No-Response' option enables to make classic
      updates further less resource consuming.

   Following subsections illustrate some exemplary exchanges based on
   the application described above.

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4.1.1. Using No-Response with PUT

   Each 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.

   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: 26
   |      | 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 20s.]
   |      |
   +----->| Header: PUT (T=NON, Code=0.03, MID=0x7d39)
   | PUT  | Token: 0x54
   |      | Uri-Path: "vehicle-stat-00"
   |      | Content Type: text/plain
   |      | No-Response: 26
   |      | 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

4.1.2. Using No-Response with POST 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: 26
   |      | 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 20s.]
   |      |
   +----->| Header: POST (T=NON, Code=0.02, MID=0x7d39)
   | POST | Token: 0x54
   |      | Uri-Path: "vehicle-stat-00"
   |      | Content Type: text/plain
   |      | No-Response: 26
   |      | 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. POST updating through query-string

   It may be possible that the backend infrastructure 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: 26
   |      |
   [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: 26
   |      |

    Figure 3: Exemplary unreliable update with No-Response option using
     POST with a query-string to insert update information to backend

4.2. 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, a multicast request to switch on/
   off all the lights of a building can be sent. In this case the IP
   switch application can use the No-Response option in a NON request
   message to reduce the traffic generated due to simultaneous CoAP
   responses from all the lights.

   Thus No-Response helps in reducing overall communication cost and
   the probability of network congestion in this case.

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4.2.1. 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.

5. IANA Considerations

   The IANA has previously assigned number 284 to this option in the
   CoAP Option Numbers Registry. IANA is requested to change this as

          | Number |     Name     |          Reference         |
          |   258  | No-Response  | Section 2 of this document |

6. 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].

7. Acknowledgments

   Thanks to Carsten Bormann, Matthias Kovatsch, Esko Dijk, Bert
   Greevenbosch, Akbar Rahman and Klaus Hartke for their valuable

8. References

8.1. Normative References


   Shelby, Z., Hartke, K. and Bormann, C.,"Constrained Application
   Protocol (CoAP)", RFC 7252, June, 2014

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8.2. Informative References


   Hartke, K.," Observing Resources in the Constrained Application
   Protocol (CoAP)", RFC 7641, September, 2015


   Rahman, A. and Dijk, E.,"Group Communication for CoAP", RFC 7390,
   October, 2014


   Eggert, L. and Fairhurst, G.," Unicast UDP Usage Guidelines for
   Application Designers", RFC 5405, November, 2008


   Castellani, A., et al., "Guidelines for HTTP-CoAP Mapping
   Implementations", draft-ietf-core-http-mapping-09, April 6, 2016


   Koster, M., et al., "Publish-Subscribe Broker for the Constrained
   Application Protocol (CoAP)", draft-koster-core-coap-pubsub-04,
   November 5, 2015


   Bormann, C., et al., "A TCP and TLS Transport for the Constrained
   Application Protocol (CoAP)", draft-ietf-core-coap-tcp-tls-01,
   November 19, 2015

   [Mobiquitous 2013]

   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

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   analytics", 11th ACM Conference on Embedded Networked Sensor Systems
   (Sensys 2013), November, 2013.

Authors' Addresses

   Abhijan Bhattacharyya
   Tata Consultancy Services Ltd.
   Kolkata, India


   Soma Bandyopadhyay
   Tata Consultancy Services Ltd.
   Kolkata, India


   Arpan Pal
   Tata Consultancy Services Ltd.
   Kolkata, India


   Tulika Bose
   Tata Consultancy Services Ltd.
   Kolkata, India


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