CoRE A. Bhattacharyya Internet Draft S. Bandyopadhyay Intended status: Standards track A. Pal Expires: April 2016 T. Bose Tata Consultancy Services Ltd. October 15, 2015 CoAP option for no server-response draft-tcs-coap-no-response-option-12 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 Bhattacharyya, et al. Expires April 15, 2016 [Page 1] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on April 15, 2016. 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. Potential benefits........................................3 1.2. Terminology...............................................4 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..................9 4. Miscellaneous aspects..........................................9 4.1. Re-using Tokens...........................................9 4.2. Taking care of congestion................................10 4.3. Handling No-Response option for a reverse proxy..........11 5. Example.......................................................11 5.1. Using No-Response with PUT...............................11 5.2. Using No-Response with POST..............................12 5.2.1. POST updating a fixed target resource...............12 Bhattacharyya, et al. Expires April 15, 2016 [Page 2] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 5.2.2. POST updating through query-string..................13 6. IANA Considerations...........................................14 7. Security Considerations.......................................15 8. Acknowledgments...............................................15 9. References....................................................15 9.1. Normative References.....................................15 9.2. Informative References...................................15 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 allows all classes of response by default. 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. Wherever, in this draft, it is mentioned that a request from client is with No-Response the intended meaning is that the client expressed its disinterest for all or some selected classes of responses. 1.1. Potential benefits Use of No-Response option should be driven by typical application requirement and, particularly, characteristics of the information to be updated. If this option is opportunistically used in a fitting M2M application then the concerned 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. Bhattacharyya, et al. Expires April 15, 2016 [Page 3] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 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. 2. Option Definition The properties of this option are given in Table 1. +--------+---+---+---+---+-------------+--------+--------+---------+ | Number | C | U | N | R | Name | Format | Length | Default | +--------+---+---+---+---+-------------+--------+--------+---------+ | 284 | | | X | | No-Response | uint | 0-1 | 0 | +--------+---+---+---+---+-------------+--------+--------+---------+ Table 1: Option Properties This option is a request option. It is Elective and Non-Repeatable. Note: Since CoAP maintains a clear separation between the request/response and the 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. 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 contains values to 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. Bhattacharyya, et al. Expires April 15, 2016 [Page 4] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 +-------------+----------------------------------------------------+ | Method Name | Remarks on applicability | +-------------+----------------------------------------------------+ | | This SHOULD NOT be used with 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 MAY want to ensure that the deletion | | | actually happened. MAY 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- Bhattacharyya, et al. Expires April 15, 2016 [Page 5] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 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 | | Allow all responses. | +-------+-----------------------+---------------------------------+ | 2 | 00000010 | Suppress 2.xx responses. | +-------+-----------------------+---------------------------------+ | 8 | 00001000 | Suppress 4.xx responses. | +-------+-----------------------+---------------------------------+ | 16 | 00010000 | Suppress 5.xx responses. | +-------+-----------------------+---------------------------------+ | 127 | 01111111 | Suppress all responses. | +-------+-----------------------+---------------------------------+ Table 3: Option values The conventions used in deciding the option values are: 1. To suppress an individual class: Set bit number (n-1) starting from the LSB (bit number 0) to suppress all responses belonging to class n.xx. So, option value to suppress n.xx class = 2**(n-1). 2. To suppress combination of classes: Set each corresponding bit according to point 1 above. Example: The option value will be 18 (binary: 00010010) to suppress both 2.xx and 5.xx responses. This is essentially bitwise OR of the corresponding individual values for suppressing 2.xx and 5.xx. At present the "CoAP Response Codes" registry (Ref. Section 12.1.2 of [RFC7252]) defines only 2.xx, 4.xx and 5.xx responses. So, an option value of 22 (binary: 00010110) will effectively suppress all currently defined response codes. Bhattacharyya, et al. Expires April 15, 2016 [Page 6] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 3. To suppress all possible responses: The maximum reserved response code for CoAP is 7.31 (Ref. Section 12.1 of [RFC7252]). So, setting bit positions 0-6 will suppress all responses according to the combination operation defined in point 2 above. Hence, the value to block all present and possible future responses is: 2**7 - 1 = 127. 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 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 Bhattacharyya, et al. Expires April 15, 2016 [Page 7] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 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 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 Bhattacharyya, et al. Expires April 15, 2016 [Page 8] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 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. 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 typically does not have any guaranteed response path. So, the client has to decide on its own about when it can retire a token which has been used in an earlier request so that the token can be reused in a future request. Since the No-Response option is 'elective', a server which has not implemented this option will respond back. This leads to the following two scenarios: The first scenario is, the client is never going to care about any response coming back or about relating the response to the original request. In that case it MAY reuse the token value at liberty. However, as a second scenario, let us consider that the client sends two requests where the first request is with No-Response and the second request, with same token, is without No-Response. In this case a delayed response to the first one can be interpreted as a response to the second request (client needs a response in the second case) if the gap between using the same tokens is not enough. This creates a problem in the request-response semantics. Bhattacharyya, et al. Expires April 15, 2016 [Page 9] Internet-Draft draft-tcs-coap-no-response-option-12 October 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 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. For multicast it is 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 (S = estimated response size; R = data transfer rate; G = group size estimate) 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 to the same server endpoint. 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 Bhattacharyya, et al. Expires April 15, 2016 [Page 10] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 occasional closed-loop exchanges (e.g. NON messages without No- Response or simply CON messages) to get an RTT estimate between the end-points. 4.3. Handling No-Response option for a reverse proxy A reverse proxy (HTTP to CoAP) MAY translate an incoming HTTP request to a corresponding CoAP request indicating that no response is required based on some application specific requirement. In this case, it is recommended that the HC Proxy SHOULD send an HTTP response with status code 204 (No Content). 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- , where can be any string uniquely identifying the vehicle. The update requests are sent over NON type of messages. The No- Response option causes the server not to respond back. Bhattacharyya, et al. Expires April 15, 2016 [Page 11] Internet-Draft draft-tcs-coap-no-response-option-12 October 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: 127 | | Payload: | | "VehID=00&RouteID=DN47&Lat=22.5658745&Long=88.4107966667& | | Time=2013-01-13T11:24:31" | | [No response from the server. Next update in 20 secs.] | | +----->| Header: PUT (T=NON, Code=0.03, MID=0x7d39) | PUT | Token: 0x54 | | Uri-Path: "vehicle-stat-00" | | Content Type: text/plain | | No-Response: 127 | | Payload: | | "VehID=00&RouteID=DN47&Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" Figure 1: Exemplary unreliable update with No-Response option using PUT. 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. Bhattacharyya, et al. Expires April 15, 2016 [Page 12] Internet-Draft draft-tcs-coap-no-response-option-12 October 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: 127 | | Payload: | | "VehID=00&RouteID=DN47&Lat=22.5658745&Long=88.4107966667& | | Time=2013-01-13T11:24:31" | | [No response from the server. Next update in 20 secs.] | | +----->| Header: PUT (T=NON, Code=0.02, MID=0x7d39) | POST | Token: 0x54 | | Uri-Path: "vehicle-stat-00" | | Content Type: text/plain | | No-Response: 127 | | Payload: | | "VehID=00&RouteID=DN47&Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" Figure 2: Exemplary unreliable update with No-Response option using POST as the update-method. 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. Bhattacharyya, et al. Expires April 15, 2016 [Page 13] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 Client Server | | | | +----->| Header: POST (T=NON, Code=0.02, MID=0x7d38) | POST | Token: 0x53 | | Uri-Path: "updateOrInsertInfo" | | Uri-Query: "VehID=00" | | Uri-Query: "RouteID=DN47" | | Uri-Query: "Lat=22.5658745" | | Uri-Query: "Long=88.4107966667" | | Uri-Query: "Time=2013-01-13T11:24:31" | | No-Response: 127 | | [No response from the server. Next update in 20 secs.] | | +----->| Header: POST (T=NON, Code=0.02, MID=0x7d39) | POST | Token: 0x54 | | Uri-Path: "updateOrInsertInfo" | | Uri-Query: "VehID=00" | | Uri-Query: "RouteID=DN47" | | Uri-Query: "Lat=22.5649015" | | Uri-Query: "Long=88.4103511667" | | Uri-Query: "Time=2013-01-13T11:24:51" | | No-Response: 127 | | Figure 3: Exemplary unreliable update with No-Response option using POST with a query-string to insert update information to backend database. 6. IANA Considerations The IANA has assigned number 284 to this option in the CoAP Option Numbers registry: Bhattacharyya, et al. Expires April 15, 2016 [Page 14] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 +--------+--------------+----------------------------+ | Number | Name | Reference | +--------+--------------+----------------------------+ | 284 | 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 Klaus 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] Bhattacharyya, et al. Expires April 15, 2016 [Page 15] Internet-Draft draft-tcs-coap-no-response-option-12 October 2015 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 April 15, 2016 [Page 16] Internet-Draft draft-tcs-coap-no-response-option-12 October 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 Tulika Bose Tata Consultancy Services Ltd. Kolkata, India Email: tulika.bose@tcs.com Bhattacharyya, et al. Expires April 15, 2016 [Page 17]