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CoRE                                                   A. Bhattacharyya
Internet Draft                                         S. Bandyopadhyay
Intended status: Informational                                   A. Pal
Expires: October 2016                                           T. Bose
                                         Tata Consultancy Services Ltd.
                                                          April 4, 2016



                    CoAP option for no server-response
                   draft-tcs-coap-no-response-option-15


   Abstract

   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 tell the server to
   suppress all responses against the particular request. This option
   also provides granular control to enable suppression of a particular
   class of response or a combination of response-classes. 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-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents




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   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on October 4, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   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................................10
      3.3. Handling No-Response Option for a HTTP-to-CoAP Reverse Proxy
      ..............................................................10
   4. Exemplary Application Scenarios...............................11
      4.1. Frequent Update of Geo-location from Vehicles to Backend
      Server........................................................11
         4.1.1. Using No-Response with PUT..........................12
         4.1.2. Using No-Response with POST.........................13
            4.1.2.1. POST updating a fixed target resource..........13
            4.1.2.2. POST updating through query-string.............14


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      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.

   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
   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 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):

       * 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.




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       * Reduction in battery consumption at the constrained end-
   point(s).

       * 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",
   "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 No-Response 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 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) should have no effect on the interpretation of this
      option. However, considering the CoAP-over-UDP scenario, 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 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.




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   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 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. 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 3.2.

   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
   byte.

   +-------+-----------------------+---------------------------------+
   | Value | Binary Representation |          Description            |
   +-------+-----------------------+---------------------------------+
   |   0   |      <empty>          |    Interested in 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 2: Option values


   The conventions used in deciding the option values are:





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   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 26 (binary: 00011010)
   will effectively suppress all currently defined response codes.



   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 127 (binary:
   01111111).

   Note: When No-Response is used with value 127 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
      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


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      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 section as this is a purely a suggestive table.





































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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 4.1.2.2 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
                                  methods

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
   developer.


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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
   semantics.

   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:

   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. 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
                                 estimate)

   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

   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 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]. More
   precisely, it maps to the scenario where the application cannot
   maintain an RTT estimate. 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 simply CON messages) to get an RTT estimate
   between the endpoints.

3.3. 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



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   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 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.

   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.

   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


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      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. 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.

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

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.

























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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.

4.1.2. Using No-Response with POST

4.1.2.1. 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.



4.1.2.2. 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: 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.

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, send a multicast request to switch
   on/ off all the lights of a building. 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 assigned number 284 to this option in the CoAP Option
   Numbers registry:

          +--------+--------------+----------------------------+
          | Number |     Name     |          Reference         |
          +--------+--------------+----------------------------+
          |   284  | 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
   inputs.

8. References

8.1. Normative References

   [RFC7252]

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

   [RFC7641]




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

   [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

   [I-D.ietf-core-http-mapping]

   Castellani, A., et al., "Guidelines for HTTP-CoAP Mapping
   Implementations", draft-ietf-core-http-mapping-07, July 3, 2015



8.2. Informative References

   [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
   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





















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