CoAP option for no server-response
draft-tcs-coap-no-response-option-08

CoRE                                                   A. Bhattacharyya
Internet Draft                                         S. Bandyopadhyay
Intended status: Standards track                                 A. Pal
Expires: July 2015                       Tata Consultancy Services Ltd.
                                                       January 21, 2015

                    CoAP option for no server-response
                   draft-tcs-coap-no-response-option-08

   Abstract

   There can be typical M2M scenarios where responses from server
   against request from client might be considered redundant. This kind
   of open-loop exchange (with no reverse path from the server to the
   client) may be typically 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 exchange where the
   server end-point does not respond with ACK. However, 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'.
   The option explicitly tells the server to suppress responses about
   the state of the resource against the request from the client. This
   option also provides granular control by allowing suppression of a
   typical class or a combination of classes of responses. This option
   may be effective for both unicast and multicast requests. This draft
   discusses few exemplary applications which might benefit from this
   option.

Status of this Memo

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Table of Contents

   1. Introduction...................................................3
      1.1. Granular suppression of responses.........................3
      1.2. Potential benefits........................................3
      1.3. Terminology...............................................4
   2. Option Definition..............................................4
      2.1. Granularity in 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............................................7
         3.2.1. Using granular response suppression..................8
   4. Miscellaneous aspects..........................................8
      4.1. Re-use interval for message IDs...........................8
      4.2. Re-using Tokens...........................................8
      4.3. Taking care of congestion.................................9
      4.4. Duality with the 'Observe' option.........................9
   5. Example.......................................................10
      5.1. Request/response Scenario................................10
         5.1.1. Using No-Response with PUT..........................10
         5.1.2. Using No-Response with POST.........................11
            5.1.2.1. POST updating a target resource................11

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            5.1.2.2. POST updating through resource creation........12
      5.2. An end-to-end system combining No-Response and Observe...13
   6. IANA Considerations...........................................15
   7. Security Considerations.......................................15
   8. Acknowledgments...............................................15
   9. References....................................................15
      9.1. Normative References.....................................15
      9.2. Informative References...................................16

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
   getting responses back from the server end-point. By default this
   option expresses disinterest in all kinds of response. But fine
   grain control over responses of a particular class is also possible.
   This option should be applicable along with non-confirmable (NON)
   requests. 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 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 is required in case of 2.xx responses. A similar scheme is
   described in Section 3.7 of [RFC7390] on the server side where the
   server may decide to suppress responses for group communication at a
   granular level. But in that case the server itself decides about
   response suppression and client does not have any knowledge about
   that. On the other hand, the 'No-Response' option enables the
   clients to explicitly inform the server about its disinterest in
   responses.

1.2. Potential benefits

   Use of No-Response option is driven by typical application scenario
   and the 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:

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       * 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.

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

1.3. Terminology

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

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

2. Option Definition

   The properties of this option are given in Table 1.

   +--------+---+---+---+---+-------------+--------+--------+---------+
   | Number | C | U | N | R |   Name      | Format | Length | Default |
   +--------+---+---+---+---+-------------+--------+--------+---------+
   |   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 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

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   the four REST methods. This table is prepared in view of the type of
   application scenarios foreseen so far.

   +-------------+----------------------------------------------------+
   | 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 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       |
   |    POST     | creates 'transient' resources as part of name/value|
   |             | pair in a query string for frequent updates (may be|
   |             | to update some database; see Section 5.1.2.2).     |
   +-------------+----------------------------------------------------+
   |             | Deletion is usually a permanent action and the     |
   |    DELETE   | client SHOULD make sure that the deletion actually |
   |             | happened. SHOULD NOT be applicable.                |
   +-------------+----------------------------------------------------+
              Table 2: Suggested applicability of No-Response

2.1. 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.      |
   +-------+-----------------------+---------------------------------+
   |   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 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: When No-Response is used with empty or 0 value
      in a request, the client end-point SHOULD cease listening to
      response against the particular request. On the other hand,
      opening up at least one class of response means that the client
      end-point can no longer completely cease listening activity and
      must be configured to listen up to some application specific
      time-out period for the particular request. The client end-point
      never knows whether the present update will be a success or a
      failure. Thus, for example, if the client decides to open up the
      response for errors (4.xx & 5.xx) then it has to wait for the
      entire time-out period even for the instances where the request
      is successful (and the server is not supposed to send back a
      response). A point to be noted in this context is that there may
      be situations when the response on errors might get lost. In such
      a situation the client would wait up to the time-out period but
      will not receive any response. But this should not lead to the
      impression to the client that the request was successful. The
      application designer needs to tackle such situation. For example,
      while performing frequent updates, the client may strategically
      interweave requests without No-Response into a series of requests
      with No-Response to check time to time if things are fine at the
      server end the server is actively responding.

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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 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.

   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
   thousands 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 sensor-gateways 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 and thereby not
   affecting the end applications.

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.

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   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.

4. Miscellaneous aspects

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

4.1. Re-use interval for message IDs

   Since No-Response is used along with NON requests, '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.

4.2. 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, 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 after 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 [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
   MAX_SERVER_RESPONSE_DELAY is simply the expected maximum response
   delay from the particular 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]with group size (G) = 1 for unicast request.

   Note that 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.

4.3. 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 the interval
   between updates time-to-time.

4.4. Duality with the 'Observe' option

   Unlike the multicast actuation scenarios (example in Section 3.2),
   scenarios like frequent update using No-Response (example in Section
   3.1) leads to an interesting observation. The 'No-Response' option
   can be seen to complement the 'Observe' option with NON-
   notifications ([I-D.ietf-core-observe]). In case of the later the

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   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. 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 publish/subscribe kind of application. A typical example is
   illustrated in Section 5.2.

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. Request/response Scenario

5.1.1. 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.

5.1.2. 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.

5.1.2.1. 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.

5.1.2.2. POST updating 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 comprising of query strings.
   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.

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

   This example illustrates the publish/subscribe scenario pointed out
   in Section 4.4 above. The 'No-Response' option can be combined with
   the 'Observe' option with NON-notifications to create a lightweight
   end-to-end publish/subscribe system. For example, the updates from a
   remote vehicle may be observed by a remote observer in a handheld as
   shown in figure 4.

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   Pub      Server                                            Sub
   (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.]                                     |
   |        |                                                   |
   +----->  |                                                   |
   | POST   |                                                   |
   |      Header: POST (T=NON, Code=0.02, MID=0x7d39)           |
   |        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 'publisher' and 'Observe' with
                  NON-notifications by the 'subscriber'.

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6. IANA Considerations

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

   +--------+--------------+----------------------------+
   | Number |     Name     |          Reference         |
   +--------+--------------+----------------------------+
   |   92   | No-Response  | Section 4 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, 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

   [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

9.2. 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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