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CoAP option for no server-response
draft-tcs-coap-no-response-option-10

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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
Last updated 2015-04-15
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draft-tcs-coap-no-response-option-10
CoRE                                                   A. Bhattacharyya
Internet Draft                                         S. Bandyopadhyay
Intended status: Standards track                                 A. Pal
Expires: October 2015                    Tata Consultancy Services Ltd.
                                                         April 15, 2015

                    CoAP option for no server-response
                   draft-tcs-coap-no-response-option-10

   Abstract

   There can be M2M scenarios where responses from server against
   requests from client might be considered redundant. This kind of
   open-loop exchange (with no response path from the server to the
   client) may be desired to minimize resource consumption in
   constrained systems while simultaneously updating a bulk of
   resources or updating a resource with a very high frequency. CoAP
   already provides a non-confirmable (NON) mode of message exchange
   where the server end-point does not respond with ACK. However,
   obeying the request/response semantics, the server end-point
   responds back with a status code indicating "the result of the
   attempt to understand and satisfy the request".

   This draft introduces a header option for CoAP called 'No-Response'.
   Using this option the client explicitly tells the server to suppress
   responses against the particular request. This option also provides
   granular control to enable suppression of a particular class or a
   combination of response-classes. This option may be effective for
   both unicast and multicast requests. Present draft also discusses
   few exemplary applications which benefit from this option.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   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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   This Internet-Draft will expire on October 15, 2015.

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   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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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...............................................3
   2. Option Definition..............................................4
      2.1. Granular control over response suppression................5
   3. Exemplary application scenarios................................7
      3.1. Frequent update of geo-location from vehicles to backend..7
      3.2. Multicasting actuation command from a handheld device to a
      group of appliances............................................8
         3.2.1. Using granular response suppression..................8
   4. Miscellaneous aspects..........................................8
      4.1. Re-using Tokens...........................................9
      4.2. Taking care of congestion................................10
   5. Example.......................................................10
      5.1. Using No-Response with PUT...............................10
      5.2. Using No-Response with POST..............................11
         5.2.1. POST updating a fixed target resource...............11
         5.2.2. POST updating through query-string..................12
   6. IANA Considerations...........................................13
   7. Security Considerations.......................................14
   8. Acknowledgments...............................................14

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   9. References....................................................14
      9.1. Normative References.....................................14
      9.2. Informative References...................................14

1. Introduction

   This draft proposes a new header option for Constrained Application
   Protocol (CoAP) [RFC7252] called 'No-Response'. This option enables
   the client end-point to explicitly express its disinterest in
   receiving responses back from the server end-point. This option
   enables to express disinterest in all kinds of response by default.
   However, fine grain control to suppress responses of a particular
   class or a combination of response classes is also possible.

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

1.1. Potential benefits

   Use of No-Response option should be driven by typical application
   requirement and, particularly, characteristics of the information to
   be updated. If this option is opportunistically used in a fitting
   M2M application then the concerned systems may benefit in the
   following aspects:

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

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

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

       * Reduction in overall communication cost.

1.2. Terminology

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

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119.

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2. Option Definition

   The properties of this option are given 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 a request option. It is Elective and Non-Repeatable.

   Note: Since CoAP maintains a clear separation between the
      request/response and the messaging layer, this option does not
      have any dependency on the type of message (confirmable/ non-
      confirmable). However, NON type of messages are best fitting with
      this option considering the expected benefits out of it. Using
      No-Response with NON messages gets rid of any kind of reverse
      traffic and the interaction becomes completely open-loop.

       Using this option with CON type of requests may not have any
      significance if piggybacked responses are triggered. Even if the
      response is suppressed it does not reduce any traffic in that
      case. But, in case the server responds with a separate response
      (which, may be, the client does not care about) then this option
      can be useful. Suppressing the separate response reduces one
      additional traffic in this case.

   This option 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 disinterest in all or
   a particular class or combination of classes of responses as
   described in the next sub-section. The following table provides a
   'ready-reference' on possible applicability of this option for all
   the four REST methods. This table is prepared in view of the type of
   possible interactions foreseen so far.

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   +-------------+----------------------------------------------------+
   | Method Name |              Remarks on applicability              |
   +-------------+----------------------------------------------------+
   |             | This 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 with Observe option set to 'deregister'    |
   |             | (1). Since, in this case, the server response does |
   |             | not contain any payload the client MAY express its |
   |             | disinterest in server responses.                   |
   +-------------+----------------------------------------------------+
   |             | Suitable for frequent updates (particularly in NON |
   |     PUT     | mode) on existing resources. Might not be useful   |
   |             | when PUT creates a new resource.                   |
   +-------------+----------------------------------------------------+
   |             | If POST is used to update a target resource        |
   |             | then No-Response can be used in the same manner as |
   |             | in PUT. This option may also be useful while       |
   |     POST    | updating through query strings rather than updating|
   |             | a fixed target resource (see Section 5.2.2 for an  |
   |             | example).                                          |
   +-------------+----------------------------------------------------+
   |             | Deletion is usually a permanent action and the     |
   |    DELETE   | client SHOULD make sure that the deletion actually |
   |             | happened. SHOULD NOT be applicable.                |
   +-------------+----------------------------------------------------+
    Table 2: Suggested applicability of No-Response for different REST
                                  methods

2.1. Granular control over response suppression

   This option enables granular control over response suppression by
   allowing the client to express its disinterest in a typical class or
   combination of classes of responses. For example, a client may
   explicitly tell the receiver that no response is required unless
   something 'bad' happens and a response of class 4.xx or 5.xx is to
   be fed back to the client. No response of the class 2.xx is
   required.

   Note: Section 3.7 of [RFC7390] describes a scheme where a server in
      the multicast group may decide on its own to suppress responses
      for group communication with granular control. Client does not
      have any knowledge about that. On the other hand, the 'No-

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      Response' option enables the clients to explicitly inform the
      servers about its disinterest in responses. Such explicit control
      on the client side may be helpful for debugging network
      resources. An example scenario is described in Section 3.2.

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

   +-------+-----------------------+---------------------------------+
   | Value | Binary Representation |          Description            |
   +-------+-----------------------+---------------------------------+
   |   0   |      00000000         |    Suppress all responses.      |
   +-------+-----------------------+---------------------------------+
   |   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

   XORing 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 allow 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: When No-Response is used with empty or 0 value
      in a request the client end-point SHOULD cease listening to
      response against the particular request. On the other hand,
      opening up at least one class of response means that the client
      end-point can no longer completely cease listening activity and
      must be configured to listen up to some application specific
      time-out period for the particular request. The client end-point
      never knows whether the present update will be a success or a
      failure. Thus, for example, if the client decides to open up the
      response for errors (4.xx & 5.xx) then it has to wait for the
      entire time-out period even for the instances where the request
      is successful (and the server is not supposed to send back a
      response). A point to be noted in this context is that there may
      be situations when the response on errors might get lost. In such
      a situation the client would wait up to the time-out period but
      will not receive any response. But this should not lead to the
      impression to the client that the request was successful. The
      application designer needs to tackle such situation. For example,

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      while performing frequent updates, the client may strategically
      interweave requests without No-Response into a series of requests
      with No-Response to check time to time if things are fine at the
      server end and the server is actively responding.

3. Exemplary application scenarios

   This section describes some exemplary user stories which may
   potentially get benefitted through the use of No-Response option.

3.1. Frequent update of geo-location from vehicles to backend

   Let us consider an intelligent traffic system (ITS) consisting of
   vehicles equipped with a sensor-gateway comprising sensors like GPS
   and Accelerometer. The sensor-gateway acts as a CoAP client end-
   point. It connects to the Internet using a low-bandwidth cellular
   (e.g. GPRS) connection. The GPS co-ordinates of the vehicle are
   periodically updated to the backend server. The update rate is
   adaptive to the motional-state of the vehicle. If the vehicle moves
   fast the update rate is high as the position of the vehicle changes
   rapidly. If the vehicle is static or moves slowly then the update
   rate is low. This ensures that bandwidth and energy is not consumed
   unnecessarily. The motional-state of the vehicle is inferred by a
   local analytics running on the sensor-gateway which uses the
   accelerometer data and the rate of change in GPS co-ordinates. The
   back-end server hosts applications which use the updates for each
   vehicle and produce necessary information for remote users.

   Retransmitting a location co-ordinate which the vehicle has already
   crossed is not efficient as it adds redundant traffic to the
   network. So, the updates are done in NON mode. However, given the
   huge number of vehicles updating frequently, the NON exchange will
   also trigger huge number of status responses from the backend. Thus
   the cumulative load on the network will be quite significant.

   On the contrary, if the client end-points on the vehicles explicitly
   declare that they do not need any status response back from the
   server then significant load will be reduced. The assumption is
   that, since the update rate is high, stray losses in geo-locations
   will be compensated with the large update rate.

   Note: It may be argued that the above example application can also
      be implemented using "Observe" option ([I-D.ietf-core-observe])
      with NON notifications. But, in practice, implementing with
      "Observe" would require lot of book-keeping exercise at the data-
      collection end-point at the backend (observer). The observer
      needs to maintain all the observe relationships with each

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      vehicle. The data collection end-point may be unable to know all
      its data sources beforehand. The client end-points at vehicles
      may go offline or come back online randomly. In case of 'Observe'
      the onus is always on the data collection end-point to establish
      observe relationship with each data-source. On the other hand,
      implementation will be much simpler if the initiative is left on
      the data-source to carry out updates using No-Response option.
      Putting it another way: the implementation choice depends on the
      perspective of interest to initiate the update. In an 'Observe'
      scenario the interest is expressed by the data-consumer. On the
      contrary, the classic update case applies when it is the interest
      of the data-producer. The 'No-Response' option enables to make
      classic updates further less resource consuming.

3.2. Multicasting actuation command from a handheld device to a group
   of appliances

   A handheld device (e.g. a smart phone) may be programmed to act as
   an IP enabled switch to remotely operate on a single or group of IP
   enabled appliances. For example the smart phone can be programmed to
   send a multicast request to switch on/ off all the lights of a
   building. In this case the IP switch application can use No-Response
   option along with NON request to reduce the traffic generated due to
   simultaneous status responses from hundreds of lights.

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

3.2.1. Using granular response suppression

   The IP switch application may optionally use granular response
   suppression such that the error responses are not suppressed. In
   that case the lights which could not execute the request would
   respond back and be readily identified. Thus, explicit suppression
   of option classes by the multicast client may be useful to debug the
   network and the application.

4. Miscellaneous aspects

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

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4.1. Re-using Tokens

   Tokens provide a matching criteria between a request and the
   corresponding response. The life of a token starts when it is
   assigned to a request and ends when the final matching response is
   received. Then the token can again be re-used. However, a request
   with No-Response 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 will respond back. This leads
   to the following two scenarios:

   The first scenario is, the client is never going to care about any
   response coming back or about relating the response to the original
   request. In that case it MAY reuse the token value at liberty.

   However, as a second scenario, let us consider that the client sends
   two requests where the first request is with No-Response and the
   second request, with same token, is without No-Response. In this
   case a delayed response to the first one can be interpreted as a
   response to the second request (client needs a response in the
   second case) if the gap between using the same tokens is not enough.
   This creates a problem in the request-response semantics.

   The most ideal solution would be to always use a unique token for
   requests with No-Response. But if a client wants to reuse a token
   then in most practical cases the client implementation SHOULD
   implement an application specific reuse time after which it can
   reuse the token. This draft suggests a reuse time for tokens with
   similar expression as in Section 2.5 of [RFC7390]:

   TOKEN_REUSE_TIME = NON_LIFETIME + MAX_SERVER_RESPONSE_DELAY +
   MAX_LATENCY.

   NON_LIFETIME and MAX_LATENCY are defined in 4.8.2 of [RFC7252].
   MAX_SERVER_RESPONSE_DELAY has same interpretation as in Section 2.5
   of [RFC7390] for multicast request. But for unicast request, since
   the message is sent to only one server, MAX_SERVER_RESPONSE_DELAY
   means the expected maximum response delay from the particular server
   to which client sent the request rather than the expected delay
   "over all servers that the client can send a multicast request to".
   This delay includes the maximum Leisure time period as defined in
   Section 8.2 of [RFC7252]. [RFC7252] defines a rough lower bound of
   leisure as:

                          lb_Leisure = S * G / R

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

   In case of unicast request, G = 1 and the lower bound of leisure
   becomes:

                            lb_Leisure = S / R

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

4.2. Taking care of congestion

   A detail technical discussion on congestion control is out-of-scope
   of this draft. However, this section of the draft mention certain
   aspects on congestion control which may help a detail work on
   congestion control for CoAP as a whole.

   If this option is used with NON messages then the interaction
   becomes completely open-loop. Absence of any feed-back from the
   server end affects congestion-control mechanism. In this case the
   communication pattern belongs to the class of low-data volume
   applications as described in Section 3.1.2 of [RFC5405]. Precisely,
   it maps to the scenario where the application cannot maintain an RTT
   estimate. Hence, following [RFC5405], a 3s interval is suggested as
   the minimum interval between successive updates. However, in case of
   frequent updates, an application developer MUST interweave
   occasional closed-loop exchanges (e.g. NON messages without No-
   Response or simply CON messages) to get an RTT estimate between the
   end-points.

5. Example

   This section illustrates few examples of exchanges based on the
   scenario narrated in Section 3.1. Examples for other scenarios can
   be easily conceived based on these illustrations.

5.1. Using No-Response with PUT

   Figure 1 shows a typical request with this option. The depicted
   scenario occurs when the vehicle#n moves very fast and update rate
   is high. The vehicle is assigned a dedicated resource: vehicle-stat-
   <n>, where <n> can be any string uniquely identifying the vehicle.

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   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: 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.

5.2. Using No-Response with POST

5.2.1. POST updating a fixed target resource

   In this case POST acts the same way as PUT. The exchanges are same
   as above. The updated values are carried as payload of POST as shown
   in Figure 2.

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   Client Server
   |      |
   |      |
   +----->| Header: POST (T=NON, Code=0.02, MID=0x7d38)
   | POST | Token: 0x53
   |      | Uri-Path: "vehicle-stat-00"
   |      | Content Type: text/plain
   |      | No-Response: 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.

5.2.2. POST updating through query-string

   It may be possible that the backend infrastructure (as described in
   Section 3.1) deploys a dedicated database to store the location
   updates. In such a case the client can update through a POST by
   sending a query string in the URI. The query-string contains the
   name/value pairs for each update. 'No-Response' can be used in same
   manner as for updating fixed resources. The scenario is depicted in
   Figure 3.

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   Client Server
   |      |
   |      |
   +----->| Header: POST (T=NON, Code=0.02, MID=0x7d38)
   | POST | Token: 0x53
   |      | Uri-Path: "updateOrInsertInfo"
   |      | Uri-Query: "VehID=00"
   |      | Uri-Query: "RouteID=DN47"
   |      | Uri-Query: "Lat=22.5658745"
   |      | Uri-Query: "Long=88.4107966667"
   |      | Uri-Query: "Time=2013-01-13T11:24:31"
   |      | No-Response: 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: "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: 0
   |      |

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

6. IANA Considerations

   The IANA is requested to add the following option entry to the CoAP
   Option Numbers registry:

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

7. Security Considerations

   The No-Response option defined in this document presents no security
   considerations beyond those in Section 11 of the base CoAP
   specification [RFC7252].

8. Acknowledgments

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

9. References

9.1. Normative References

   [RFC7252]

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

   [I-D.ietf-core-observe]

   Hartke, K.,"Observing Resources in CoAP", draft-ietf-core-observe-
   16, December 30, 2014

   [RFC7390]

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

   [RFC5405]

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

9.2. Informative References

   [MOBIQUITOUS 2013]

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   Bhattacharyya, A., Bandyopadhyay, S. and Pal, A., "ITS-light:
   Adaptive lightweight scheme to resource optimize intelligent
   transportation tracking system (ITS)-Customizing CoAP for
   opportunistic optimization", 10th International Conference on Mobile
   and Ubiquitous Systems: Computing, Networking and Services
   (Mobiquitous 2013), December, 2013.

   [Sensys 2013]

   Bandyopadhyay, S., Bhattacharyya, A. and Pal, A., "Adapting protocol
   characteristics of CoAP using sensed indication for vehicular
   analytics", 11th ACM Conference on Embedded Networked Sensor Systems
   (Sensys 2013), November, 2013.

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Authors' Addresses

   Abhijan Bhattacharyya
   Tata Consultancy Services Ltd.
   Kolkata, India

   Email: abhijan.bhattacharyya@tcs.com

   Soma Bandyopadhyay
   Tata Consultancy Services Ltd.
   Kolkata, India

   Email: soma.bandyopadhyay@tcs.com

   Arpan Pal
   Tata Consultancy Services Ltd.
   Kolkata, India

   Email: arpan.pal@tcs.com

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