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 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." Bhattacharyya, et al. Expires July 21, 2015 [Page 1] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on July 21, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................3 1.1. 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 Bhattacharyya, et al. Expires July 21, 2015 [Page 2] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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: Bhattacharyya, et al. Expires July 21, 2015 [Page 3] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 * 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 Bhattacharyya, et al. Expires July 21, 2015 [Page 4] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 5] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 +-------+-----------------------+---------------------------------+ | 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 6] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 7] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 8] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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 Bhattacharyya, et al. Expires July 21, 2015 [Page 9] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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- , where 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 10] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 11] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 12] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 13] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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'. Bhattacharyya, et al. Expires July 21, 2015 [Page 14] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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] Bhattacharyya, et al. Expires July 21, 2015 [Page 15] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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. Bhattacharyya, et al. Expires July 21, 2015 [Page 16] Internet-Draft draft-tcs-coap-no-response-option-08 January 2015 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 Bhattacharyya, et al. Expires July 21, 2015 [Page 17]