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CoRE                                                   A. Bhattacharyya
Internet Draft                                         S. Bandyopadhyay
Intended status: Standards track                                 A. Pal
Expires: February 2015                   Tata Consultancy Services Ltd.
                                                         August 5, 2014



                    CoAP option for no server-response
                   draft-tcs-coap-no-response-option-07


   Abstract

   There can be typical M2M scenarios where responses from the data
   sink to the data source against request from the source might be
   considered redundant. This kind of open-loop exchange (with no
   reverse path from the sink to the source) may be desired while
   updating resources in constrained systems looking for maximized
   throughput with minimized resource consumption. CoAP already
   provides a non-confirmable (NON) mode of exchange where the
   receiving end-point does not respond with ACK. However, the
   receiving end-point responds the sender with a status code
   indicating "the result of the attempt to understand and satisfy the
   request".

   This draft introduces a header option: 'No-Response' to suppress
   responses from the receiver and discusses exemplary use cases which
   motivated this proposition based on real experience. This option
   also provides granularity by allowing suppression of a typical class
   or a combination of classes of responses. This option may be
   effective for both unicast and multicast scenarios.

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




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   The list of current Internet-Drafts can be accessed at
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Table of Contents


   1. Introduction...................................................3
      1.1. Granular suppression of responses.........................3
      1.2. Terminology...............................................3
   2. Potential benefits.............................................4
   3. Exemplary application scenarios................................4
      3.1. Frequent update of geo-location from vehicles to backend..4
      3.2. Multicasting actuation command from a handheld device to a
      group of appliances............................................5
         3.2.1. Using granular response suppression..................5
   4. Option Definition..............................................6
      4.1. Granularity in response suppression.......................7
   5. Miscellaneous aspects..........................................9
      5.1. Re-use interval for message IDs...........................9
      5.2. Re-using Tokens...........................................9
      5.3. Taking care of congestion................................10
      5.4. Duality with the 'Observe' option........................10
   6. Example.......................................................11
      6.1. Request/response Scenario................................11
         6.1.1. Using No-Response with PUT..........................11
         6.1.2. Using No-Response with POST.........................12
            6.1.2.1. POST updating a target resource................12


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            6.1.2.2. POST performing updates through resource creation
            ........................................................13
      6.2. An end-to-end system combining No-Response and Observe...14
   7. IANA Considerations...........................................16
   8. Security Considerations.......................................16
   9. Acknowledgments...............................................16
   10. References...................................................16
      10.1. Normative References....................................16
      10.2. Informative References..................................17

1. Introduction

   This draft proposes a new header option 'No-Response' for
   Constrained Application Protocol (CoAP) [RFC7252]. This option
   enables the sender end-point to explicitly express its disinterest
   in getting responses back from the receiving end-point. By default
   this option expresses disinterest in any kind of response. This
   option should be applicable along with non-confirmable (NON)
   updates. At present this option will have no effect if used with
   confirmable (CON) mode.

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

1.1. Granular suppression of responses

   This option enables granularity by allowing the sender to choose the
   typical class or combination of classes of responses which it is
   disinterested in. For example, a sender 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
   sender. No response is required in case of 2.xx classes. A similar
   scheme is described in Section 3.7 of [I-D.ietf-core-groupcomm] on
   the server side. Here the server may perform granular suppression
   for group communication. But in that case the server itself decides
   whether to suppress responses or not. This option enables the
   clients to explicitly inform the server about the disinterest in
   responses.

1.2. Terminology

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





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   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. Potential benefits

   If this option is opportunistically used with fitting M2M
   applications then the concerned systems may benefit in the following
   aspects:

       * Reduction in network clogging by effectively reducing 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 communication cost.

       * Help satisfy hard real-time requirements since waiting due to
   closed loop latency MAY be completely avoided.

3. Exemplary application scenarios

   Next sub-sections describe some exemplary user stories which may
   potentially benefit by using 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 each of which is equipped with a sensor-gateway comprising
   sensors like GPS and Accelerometer. The sensor-gateway connects to
   the Internet using a low-bandwidth cellular (e.g. GPRS) connection.
   The GPS co-ordinates are periodically updated to the backend server
   by the gateway. The update rate in case of ITS 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 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.



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   Retransmitting a location co-ordinate which is already passed by a
   vehicle is not efficient as it adds redundant traffic to the
   network. So, the updates are done in NON mode. However, given the
   thousands of vehicles updating frequently, the NON exchange will
   also trigger huge number of status responses from the backend. Each
   response in the air is of 4 bytes of application layer plus several
   bytes originating from the lower layers. Thus the cumulative load on
   the network will be quite significant.

   On the contrary, if the edge devices explicitly declare that they do
   not need any status response then significant load will be reduced
   from the network and the server as well. The assumption is that
   since the update rate is high stray losses in geo-locations will be
   compensated with the large update rate and thereby not affecting the
   end applications.

   Mapping the above scenario to the benefits mentioned in Section 2
   reveals that use of 'No-Response' will help in:

       * Reduction in network clogging

       * Reduction in server-side loading

       * Help in achieving real-time requirements as the application is
         not bound by any delay due to closed loop latency

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 uses No-
   Response option along with NON 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.



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4. Option Definition

   The properties of this option are as in Table 1.

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



   This option is Elective and Non-Repeatable. This is a request option
   and primarily intended to be used with non-confirmable update
   requests (e.g., PUT) and should have no effect if used with a CON
   request. This option is not applicable and should have no effect for
   usual GET requests asking for resource representation. However, this
   option MAY be used with special GET request for 'cancellation' of an
   observe session (Section 3.6 of [I-D.ietf-core-observe]). This
   option contains values to optionally indicate interest/ 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 application scenarios
   foreseen so far.





















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   +-------------+----------------------------------------------------+
   | Method Name |              Remarks on applicability              |
   +-------------+----------------------------------------------------+
   |             | This option does not apply to 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 which has the same token as the token of   |
   |             | the original observe request and includes an       |
   |             | Observe Option with the value set to 'deregister'  |
   |             | (1). In this case the server response does not     |
   |             | contain any payload. Under such situation the      |
   |             | client MAY express its disinterest in the response |
   |             | from the server.                                   |
   +-------------+----------------------------------------------------+
   |             | Mostly suitable for frequent updates in NON mode on|
   |     PUT     | existing resources. Might not be useful when       |
   |             | PUT creates a new resource.                        |
   +-------------+----------------------------------------------------+
   |             | If POST is used just to update a target resource   |
   |             | then No-Response can be used in the same manner as |
   |             | in NON-PUT. May also be applicable when POST       |
   |             | performs resource creation and the client does not |
   |             | refer to the resource in future. For example,      |
   |             | than updating a fixed resource, POST API may       |
   |    POST     | contain a query-string with name/value pairs for a |
   |             | defined action (ex. insertion into a database as   |
   |             | part of frequent updates). The resources created   |
   |             | this way may be 'short-lived' resources which the  |
   |             | client will not refer to in future (see Section    |
   |             | 6.1.2.2).                                          |
   +-------------+----------------------------------------------------+
   |             | Deletion is usually a permanent action and the     |
   |    DELETE   | client SHOULD make sure that the deletion actually |
   |             | happened. SHOULD NOT be applicable.                |
   +-------------+----------------------------------------------------+
         Table 2: Applicability of No-Response for different methods



4.1. Granularity in response suppression

   This option is defined as a bit-map (Table 3) to achieve granular
   suppression.


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   +-------+-----------------------+---------------------------------+
   | Value | Binary Representation |          Description            |
   +-------+-----------------------+---------------------------------+
   |   0   |      00000000         | Suppress all responses (same as |
   |       |                       | empty value).                   |
   +-------+-----------------------+---------------------------------+
   |   2   |      00000010         |   Allow 2.xx success responses. |
   +-------+-----------------------+---------------------------------+
   |   8   |      00001000         |     Allow 4.xx client errors.   |
   +-------+-----------------------+---------------------------------+
   |  16   |      00010000         |     Allow 5.xx server errors.   |
   +-------+-----------------------+---------------------------------+
                          Table 3: Option values


   XOR of the values defined for allowing particular classes will
   result in allowing a combination of classes of responses. So, a
   value of 18 (binary: 00010010) will result in allowing all 2.xx and
   5.xx classes of responses. It is to be noted that a value of 26 will
   indicate that all types of responses are to be allowed (which is as
   good as not using No-Response at all).

   Implementation Note: The use of No-Response option is very much
      driven by the application scenario and the characteristics of the
      information to be updated. Judicious use of this option benefits
      the overall system as explained in Sections 2 and 3.

       When No-Response is used with empty or 0 value, the updating
      end-point should cease the listening activity for response
      against the particular request. On the contrary, opening up at
      least one class of responses means that the updating end-point
      can no longer stop listening and must be configured to listen up
      to some application specific time-out period for the particular
      request. The updating end-point never knows whether the present
      update will be a success or a failure. Thus, if the client
      decides to open up the responses 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). This kind of situation may arise for
      the scenario in Section 3.2.1. Under such circumstances the use
      of No-Response may not help improving the performance in terms of
      overall latency. However, the advantages in terms of saving
      network and energy resources will still hold.

      A point to be noted in view of the above example is that there
      may be situations when the response on errors might get lost. In
      such a situation the sender would wait up to the time-out period


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      but will not receive any response. But this should not lead to
      the impression to the sender that the request was successful. The
      situation will worsen if the receiver is no longer active. The
      application designer needs to tackle such situation. For example,
      the sender may strategically insert requests without No-Response
      after N numbers of requests with No-Response.

5. Miscellaneous aspects

   This section further describes few important implementation aspects
   worth considering while using No-Response. The following discussion
   does not mandate anything, rather provides suggestive guidelines for
   the application developer.

5.1. Re-use interval for message IDs

   Since No-Response is primarily based on CoAP-NON, 'NON-LIFETIME' (as
   defined in Section 4.8.2 of [RFC7252]) is suggested as the time
   interval over which a message ID can be safely re-used.

5.2. 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 NON
   request with No-Response does not have any 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 MAY
   emanate a response. This leads to the following two scenarios:

   The first scenario is when 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 'patience' time till which it can
   re-use the token. Appendix-B.4.1 of [I-D.draft-bormann-coap-misc]
   refers to the 'patience' option defined in [I-D.draft-li-coap-
   patience]. 'Patience' option effectively puts a deadline to the
   server to respond back. However, 'patience' is not exposed to the
   protocol level at present. This draft suggests a reuse time for
   tokens with similar expression as in Section 2.5 of [I-D.ietf-core-
   groupcomm]:

   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 [I-D.ietf-core-groupcomm] for multicast request. But for unicast
   request MAX_SERVER_RESPONSE_DELAY is simply the expected maximum
   response delay from the server to which client sent the request.
   This delay includes the maximum Leisure time period as defined in
   Section 8.2 of [RFC7252] and Appendix-B.4.2 of [I-D.draft-bormann-
   coap-misc]where group size (G) = 1 for unicast request.

   If it is not possible for the client to get a reasonable estimate of
   the MAX_SERVER_RESPONSE_DELAY then the client SHOULD use a unique
   token for the request with No-Response to be safe.

5.3. Taking care of congestion

   The possible communication scenarios leveraging the benefits of 'No-
   Response' should primarily fall into the class of low-data volume
   applications as described in Section 3.1.2 of [RFC5405]. Precisely,
   they should map 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, an application developer MAY interweave occasional closed-
   loop exchanges (e.g. CoAP-NON without No-Response or CoAP-CON) to
   get an RTT estimate between the end-points and adjust time-to-time
   the interval between updates.

5.4. Duality with the 'Observe' option

   Unlike the multicast actuation scenarios (Section 3.2), scenarios
   like frequent update using No-Response leads to an interesting
   observation. The 'No-Response' option in a sense complements the
   'Observe' option with NON-notifications ([I-D.ietf-core-observe]).


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   In case of the later the update notifications from the server reach
   the observer client without triggering any response from the
   observer. However, there is a difference in the point of interest.
   In the 'Observe' scenario the interest is expressed by the
   'consumer' to get the data. On the contrary, the updates using 'No-
   Response' applies to the scenario when it is the interest of the
   'producer' to update the data. It is up to the application designer
   to choose between No-Response and 'observe' with notifications in
   NON mode. For example, the scenario of location update described in
   Section 3.1 above might also be deployed using observe with NON-
   notifications. In that case the backend infrastructure would have to
   subscribe to each individual sensor gateway at the vehicles. But,
   the 'book-keeping' exercise required at the backend for such an
   implementation may not be very trivial and deployment with No-
   Response may be far more straight-forward. However, 'No-Response'
   and 'Observe' using NON-notification may be combined together, under
   permitting condition, to achieve high performance gain in an end-to-
   end producer-consumer application. A typical example is illustrated
   in Section 6.2.

6. 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.

6.1. Request/response Scenario

6.1.1. 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 in NON mode. 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: 0
   |      | 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: 0
   |      | 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.

6.1.2. Using No-Response with POST

   POST "usually results in a new resource being created or the target
   resource being updated". Exemplary uses of 'No-Response' for both
   these usual actions of POST are given below.

6.1.2.1. POST updating a 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: 0
   |      | 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: 0
   |      | 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.

6.1.2.2. POST performing updates through resource creation

   In most practical implementations the backend infrastructure as
   described in Section 3.1 will have a dedicated database to store the
   location updates. In such a case the client would send an update
   string as the POST URI which contains the name/value pairs for each
   update. Thus frequent updates may be performed through POST by
   creating such 'short-lived' resources which the client would not
   refer to in future. Hence '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: "insertInfo"
   |      | 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: 0
   |      |
   [No response from the server. Next update in 20 secs.]
   |      |
   +----->| Header: POST (T=NON, Code=0.02, MID=0x7d39)
   | POST | Token: 0x54
   |      | Uri-Path: "insertInfo"
   |      | 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: 0
   |      |

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

6.2.   An end-to-end system combining No-Response and Observe

   This example illustrates the scenario pointed out in Section 5.3
   above. The 'No-Response' option can be combined with the 'Observe'
   option with NON-notifications to create a lightweight end-to-end
   producer-consumer system. For example, the vehicular updates from a
   remote vehicle may be observed by a remote observer in a PDA as
   shown in figure 4.









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   Producer Server                                         Consumer
   (Client)                                                (Client)
   |        |                                                   |
   |        |                                             <-----+
   |        |                                              GET  |
   +----->  |                        (Observe: empty, Token: 30)|
   | POST   |                                                   |
   |        | Header: POST (T=NON, Code=0.02, MID=0x7d38)       |
   |        | Token: 0x53                                       |
   |        | Uri-Path: "insertInfo"                            |
   |        | 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: 0                                    |
   |        |                                                   |
   |        +----->                                             |
   |        | 2.05 (T=NON, MID=0x5d40, Token: 30)               |
   |        |     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: POST (T=NON, Code=0.02, MID=0x7d39)       |
   | POST   | Token: 0x54                                       |
   |        | Uri-Path: "insertInfo"                            |
   |        | 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: 0                                    |
   |        |                                                   |
   |        +----->                                             |
   |        | 2.05 (T=NON, MID=0x5d41, Token: 30)               |
   |        |     Payload:                                      |
   |        |     "VehID=00&RouteID=DN47&Lat=22.5649015&        |
   |        |      Long=88.4103511667& Time=2013-01-13T11:24:51"|
   |        |                                                   |

     Figure 4: Exemplary end-to-end update and observe scenario using
    'No-Response' for NON-updates from 'producer' and observe with NON-
                     notifications by the 'consumer'.


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7. IANA Considerations

   The IANA is requested to add the following option number entries:

   +--------+--------------+----------------------------+
   | Number |     Name     |          Reference         |
   +--------+--------------+----------------------------+
   |   92   | No-Response  | Section 4 of this document |
   +--------+--------------+----------------------------+


8. 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].

9. Acknowledgments

   Thanks to Carsten Bormann, Esko Dijk, Bert Greevenbosch, Akbar
   Rahman and Claus Hartke for their valuable inputs.

10. References

10.1. 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-
   14, June 30, 2014

   [I-D.ietf-core-groupcomm]

   Rahman, A. and Dijk, E.,"Group Communication for CoAP", draft-ietf
   core-groupcomm-21, July 31, 2014

   [I-D.draft-bormann-coap-misc]

   Bormann, C. and Hartke, K., "Miscelleneous additions to CoAP",
   draft-bormann-coap-misc-26, December 19, 2013

   [I-D.draft-kovatsch-lwig-coap]


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   Kovatsch, M., Bergmann, O., Dijk, E., He, X. and Bormann, C., "CoAP
   Implementation Guidance", draft-kovatsch-lwig-coap-03, February 28,
   2014

   [RFC5405]

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

   [I-D.draft-li-coap-patience]

   Li, K., Greevenbosch, B., Dijk, E. and Loreto, S.," CoAP Option
   Extension: Patience", draft-li-core-coap-patience-option-04, July
   04, 2014



10.2. 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




























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