CoRE A. Bhattacharyya Internet Draft S. Bandyopadhyay Intended status: Standards track A. Pal Expires: April 2014 Tata Consultancy Services Ltd. October 8, 2013 CoAP option for no server-response draft-tcs-coap-no-response-option-03 Abstract There can be typical M2M scenarios where responses from the data sink to the data source against request/ notification from the source might be considered redundant. This kind of open-loop exchange (with no reverse path from the sink to the source) may be desired while updating resources or notifying about the updated status of a resource in constrained systems looking for maximized throughput with minimized resource consumption. CoAP already provides a non-confirmable (NON) mode of exchange where The receiving end-point does not respond with ACK. However, the receiving end-point responds the sender with a status code indicating "the result of the attempt to understand and satisfy the request". This draft introduces a header option: 'No-Resp' to suppress responses from the receiver and discusses exemplary use cases which motivated this proposition based on real experience. This option also provides granularity by allowing suppression of a typical class or a combination of classes of responses. This option is applicable for both request/ response as well as resource-observe mode and may be effective for both unicast and multicast scenarios. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents Bhattacharyya, et al. Expires April 8, 2014 [Page 1] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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." 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 8, 2014. Copyright Notice Copyright (c) 2013 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. Terminology...............................................4 2. Potential benefits.............................................4 3. Exemplary application scenarios................................4 3.1. Frequent update of geo-location from vehicles to backend (Category 1)...................................................5 3.1.1. Benefits using No-Resp...............................6 Bhattacharyya, et al. Expires April 8, 2014 [Page 2] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 3.2. A fleet-tracking application running on a PDA or smart-phone (Category 2)...................................................6 3.2.1. Benefits using No-Resp...............................6 3.3. Multicasting traffic congestion information to PDAs/ smart- phones using resource-observe (Category 2 with pseudo multicast) ...............................................................7 3.3.1. Using granular response suppression..................7 3.3.2. Benefits using No-Resp...............................7 4. Option Definition..............................................7 4.1. Achieving granular suppression............................9 5. Example.......................................................10 5.1. Request/response Scenario................................11 5.1.1. Using No-Resp with PUT..............................11 5.1.2. Using No-Resp with POST.............................11 5.1.2.1. POST updating a target resource................11 5.1.2.2. POST performing updates through resource creation ........................................................12 5.2. Resource-observe Scenario................................13 6. IANA Considerations...........................................14 7. Security Considerations.......................................14 8. Acknowledgments...............................................15 9. References....................................................15 9.1. Normative References.....................................15 1. Introduction This draft proposes a new header option 'No-Resp' for Constrained Application Protocol (CoAP). This option enables the sender end- point to explicitly express its disinterest in getting responses back from the receiving end-point. By default this option expresses disinterest in any kind of response. This option should be applicable along with non-confirmable (NON) updates/ notifications. 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 utility of this option. 1.1. Granular suppression of responses This option enables granularity by allowing the sender to choose the typical class or combination of classes of responses which it is disinterested in. For example, a sender may explicitly tell the receiver that no response is required unless something 'bad' happens and a response of class 4.xx or 5.xx is to be fed back to the sender. No response is required in case of 2.xx classes. A similar Bhattacharyya, et al. Expires April 8, 2014 [Page 3] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 scheme is described in Section 3.7 of [I-D.ietf-core-groupcomm] on the server side. Here the server may perform granular suppression for group communication. But in this case the server itself decides whether to suppress responses or not. This option enables the clients to explicitly inform the server about the disinterest in responses. 1.2. Terminology The terms used in this draft are in conformance with those defined in [I-D.ietf-core-coap]. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119. 2. Potential benefits If this option is opportunistically used with fitting M2M applications then the concerned systems may benefit in the following aspects: * Reduction of network clogging * Reduction in server-side loading * Reduction in battery consumption at the constrained end-point * Reduction in communication cost at the constrained end-point * May help to satisfy hard real-time requirements (since, waiting due to closed loop latency is completely avoided) 3. Exemplary application scenarios The described scenarios are confined within a communication pattern where there is a direct communication channel between a constrained device (the device may well be a constrained gateway) and an unconstrained backend. Also, we consider only the scenario of data updates which may happen in the following 2 forms: 1) Through a push to the server by the client using PUT or POST (request/ response) 2) Through notifications by the server to client in response to an 'observe' request by the client Bhattacharyya, et al. Expires April 8, 2014 [Page 4] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 The application scenarios are classified into 2 categories as below: Category 1) Data-source=constrained device; Data-sink=backend. Category 2) Data-source=backend; Data-sink=constrained device. Next sub-section describes the user stories and the potential benefits in each of the cases through the use of No-Resp option. An Intelligent Traffic System (ITS) is considered as the base application. The application scenarios are formed out of its different aspects. 3.1. Frequent update of geo-location from vehicles to backend (Category 1) Each vehicle in ITS is equipped with a sensor-gateway comprising sensors like GPS and Accelerometer. The sensor-gateway connects to the Internet using a low-bandwidth cellular (e.g. GPRS) connection. The GPS co-ordinates are periodically updated to the backend server by the gateway. In case of ITS the update rate is adaptive to the motional-state of the vehicle. If the vehicle moves fast the update rate is high as the position of the vehicle changes rapidly. If the vehicle is static or moves slowly then the update rate is low. This ensures that bandwidth and energy is not consumed unnecessarily. The motional-state of the vehicle is inferred by a local analytics, running on the sensor-gateway, using 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. The application may act in request/ response mode where the sensor- gateways push data to the backend. Or it can act in resource-observe mode where the backend initiates the exchange by sending observe requests to the sensor-gateways and receive updates in the form of notifications. Retransmitting a location co-ordinate which is already passed by a vehicle is not efficient as it adds redundant traffic to the network. So, the updates are done in NON mode. However, given the thousands of vehicles updating frequently, the NON exchange will also trigger huge number of status responses from the backend. Each response in the air is of 4bytes of application layer plus several bytes originating from the lower layers. Thus the cumulative load on the network will be quite significant. Bhattacharyya, et al. Expires April 8, 2014 [Page 5] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 On the contrary, if the edge devices explicitly declare that they do not need any status response then significant load will be reduced from the network and the server as well. 3.1.1. Benefits using No-Resp Thus mapping the above scenario to the benefits mentioned in section 2 reveals that use of 'No-Resp' will help in: * Reduction of network clogging * Reduction in server-side loading * Help in achieving real-time requirements as the application is not bound by any delay due to closed loop latency 3.2. A fleet-tracking application running on a PDA or smart-phone (Category 2) Now, let us consider the other side of the ITS backend. Say, the security personnel in a city are on high alert and want to track a high-speed train carrying some important statesmen. The application on the hand-held device subscribes to the ITS backend server and receives continuous real-time updates. If the handheld has to send a status response for each notification it receives then that will cost the device both in terms of communication cost and battery life. This can be avoided if, similar to the above scenario, the backend explicitly specifies that no response from the handheld is required. So, the backend uses 'No- Resp' for each of the notifications. 3.2.1. Benefits using No-Resp Thus mapping the above scenario to the benefits mentioned in section 2 reveals that use of 'No-Resp' will help in: * Reduction in battery consumption at the constrained end-point * Reduction in communication cost at the constrained end-point * Help in achieving real-time requirements as the application is not bound by any delay due to closed loop latency. Bhattacharyya, et al. Expires April 8, 2014 [Page 6] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 3.3. Multicasting traffic congestion information to PDAs/ smart-phones using resource-observe (Category 2 with pseudo multicast) The ITS might have an application which runs some analytics at the backend and determines the instantaneous traffic congestion spots in a city. The analytics is done based on the real-time geo-location updates received from the vehicles within the system. The backend application multicasts the results of the analytics to the constrained handheld devices which subscribed for real-time updates on congestion points. So, in stricter terms, it is a pseudo multicast using resource observe. In this case the backend may use No-Resp option along with NON notifications to reduce the traffic generated due to simultaneous status responses from hundreds of subscribed handheld devices. 3.3.1. Using granular response suppression However, an intelligent application may use the granularity feature of this option such that the responses are fed-back to the backend when notification to particular devices causes errors. So the notifications may contain No-Resp saying that a response is to be suppressed only in success conditions and all responses in case of errors should be fed back. The server might eventually stop sending notification to the subscribed clients which responded with consecutive 'bad' responses. This will indirectly help saving network bandwidth. 3.3.2. Benefits using No-Resp Thus mapping the above scenario to the benefits mentioned in section 2 reveals that use of 'No-Resp' will help in: * Reduction of network clogging * Reduction in battery consumption at the constrained end-point * Reduction in communication cost at the constrained end-point 4. Option Definition The properties of this option are as in Table 1. Bhattacharyya, et al. Expires April 8, 2014 [Page 7] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 +--------+-----+----------------+-------------+--------+---------+ | Number | C/E | Name | Data Format | Length | Default | +--------+-----+----------------+-------------+--------+---------+ | TBD | E | No-Resp | uint | 0-1 | (none) | +--------+-----+----------------+-------------+--------+---------+ Table 1: Option Properties This option has a maximum length of 1 byte. When present with an empty value this option would express the sender's disinterest in all kinds of responses. This option may contain values to indicate interest/ disinterest in a particular class or combination of classes of responses as described in the next sub-section. This option is presently defined for update requests (e.g., PUT) in NON mode or for non-confirmable update notifications against an observe request. At present this option should have no effect if used with a CON request. The following table provides a 'ready-reckoner' on possible applicability of this option for all the four REST methods. This table is prepared in view of the type of application scenarios foreseen so far. Bhattacharyya, et al. Expires April 8, 2014 [Page 8] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 +-------------+----------------------------------------------------+ | Method Name | Remarks on applicability | +-------------+----------------------------------------------------+ | GET | Not applicable | +-------------+----------------------------------------------------+ | | Applicable for frequent updates in NON mode on | | | existing fixed resources. Might not be useful when | | | PUT 'creates' a new resource. Under usual | | PUT | circumstances the client would always like to know | | | if the resource was created before attempting for | | | future updates. | +-------------+----------------------------------------------------+ | | If POST is used just to update a target resource | | | then NO-Resp can be used in the same manner as in | | | NON-PUT. May also be applicable when POST performs | | | resource creation and the client does not refer to | | POST | the resource in future. For example, rather than | | | updating a fixed resource, POST API may contain a | | | query-string with name/value pairs for a defined | | | action (e.x. insertion into a database as part of | | | frequent updates). The resources created this way | | | may be 'short-lived' resources which the client | | | will not refer to in future (see section 5.1.2.2). | +-------------+----------------------------------------------------+ | | Not applicable. Deletion is usually a permanent | | DELETE | action and the client should make sure that the | | | deletion actually happened. | +-------------+----------------------------------------------------+ Table 2: Applicability of No-Resp for different methods 4.1. Achieving granular suppression This option is defined as a bit-map (Table 3) to achieve granular suppression. Bhattacharyya, et al. Expires April 8, 2014 [Page 9] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 +-------+-----------------------+---------------------------------+ | Value | Binary Representation | Description | +-------+-----------------------+---------------------------------+ | 0 | 00000000 | Suppress all responses (same as | | | | empty value). | +-------+-----------------------+---------------------------------+ | 1 | 00000001 | Allow 2.xx success responses. | +-------+-----------------------+---------------------------------+ | 2 | 00000010 | Allow 4.xx client errors. | +-------+-----------------------+---------------------------------+ | 4 | 00000100 | Allow 5.xx server errors. | +-------+-----------------------+---------------------------------+ Table 3: Option values XOR of the values defined for allowing particular classes will result in allowing a combination of classes of responses. So, a value of 5 (binary: 00000101) will result in allowing all 2.xx and 5.xx classes of responses. It is to be noted that a value of 7 will indicate that all types of responses are to be allowed (which is as good as not using No-Resp at all). Implementation Note: The use of No-Resp option is very much driven by the application scenario and the characteristics of the information to be updated. Judicious use of this option benefits the overall system as explained in sections 2 and 3. When No-Resp is used with empty or 0 value, the updating end- point should cease the listening activity for response against the particular request. On the contrary, opening up at least one class of responses means that the updating end-point can no longer stop listening and must be configured to listen up to the defined time-out period for the particular request. The updating end-point never knows whether the present update will be a success or a failure. Thus, if the client decides to open up the responses for errors (4.xx & 5.xx) then it has to wait for the entire time-out period even for the instances where the request is successful (and the server is not supposed to send back a response). Under suach circumstances the use of No-Resp may not help improving the performance in terms of overall latency. However, the advantages in terms of saving network and energy resources will still hold. 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. Bhattacharyya, et al. Expires April 8, 2014 [Page 10] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 5.1. Request/response Scenario 5.1.1. Using No-Resp 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-Resp option causes the server not to reply with any status code. Client Server | | | | +----->| Header: PUT (T=NON, Code=0.03, MID=0x7d38) | PUT | Token: 0x53 | | Uri-Path: "vehicle-stat-00" | | Content Type: text/plain | | No-Resp: (empty) | | 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-Resp: (empty) | | Payload: | | "VehID=00&&RouteID=DN47&Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" Figure 1: Exemplary unreliable update with No-Resp option using PUT. 5.1.2. Using No-Resp with POST POST "usually results in a new resource being created or the target resource being updated". Exemplary uses of 'No-Resp' 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 April 8, 2014 [Page 11] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 Client Server | | | | +----->| Header: POST (T=NON, Code=0.02, MID=0x7d38) | POST | Token: 0x53 | | Uri-Path: "vehicle-stat-00" | | Content Type: text/plain | | No-Resp: (empty) | | 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-Resp: (empty) | | Payload: | | "VehID=00&&RouteID=DN47&Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" Figure 2: Exemplary unreliable update with No-Resp option using POST as the update-method. 5.1.2.2. POST performing updates through resource creation In most practical implementations the backend of section 3.1 will have a dedicated database to store the location updates. In such a case the client would send an update string as the POST URI which contains the name/value pairs for each update. Thus frequent updates may be performed through POST by creating such 'short-lived' resources which the client would not refer to in future. Hence 'No- Resp' can be used in same manner as for updating fixed resources. The scenario is depicted in Figure 3. Bhattacharyya, et al. Expires April 8, 2014 [Page 12] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 Client Server | | | | +----->| Header: POST (T=NON, Code=0.02, MID=0x7d38) | POST | Token: 0x53 | | Uri-Path:"/insertInfo?VehID=00&RouteID=DN47 | | &Lat=22.5658745&Long=88.4107966667& | | Time=2013-01-13T11:24:31" | | | | No-Resp: (empty) | | [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?VehID=00&RouteID=DN47 | | &Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" | | No-Resp: (empty) | | Figure 3: Exemplary unreliable update with No-Resp option using POST with a query-string to insert update information to backend database. 5.2. Resource-observe Scenario The resource-observe variant of the scenario of section 3.1 is depicted in Figure 4. Bhattacharyya, et al. Expires April 8, 2014 [Page 13] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 Server Client | | |<-----+ Header : GET (MID=0x5d28) | GET | Token : 0x53 | | Uri-Path: vehicle-stat | | Observe : (empty) | | | | +----->| Header: 2.05 (T=NON, MID=0x7d38) | 2.05 | Token: 0x53 | | Content Type: text/plain | | No-Resp: (empty) | | 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: 2.05 (T=NON, MID=0x7d39) | 2.05 | Token: 0x53 | | Content Type: text/plain | | No-Resp: (empty) | | Payload: | | "VehID=00&&RouteID=DN47&Lat=22.5649015&Long=88.4103511667& | | Time=2013-01-13T11:24:51" Figure 4: Exemplary unreliable update in resource-observe mode with No-Resp option. 6. IANA Considerations The IANA is requested to add the following option number entries: +--------+-----------+----------------------------+ | Number | Name | Reference | +--------+-----------+----------------------------+ | TBD | No-Resp | Section 4 of this document | +--------+-----------+----------------------------+ 7. Security Considerations The No-Resp option defined in this document presents no security considerations beyond those in Section 11 of the base CoAP specification [I-D.ietf-core-coap]. Bhattacharyya, et al. Expires April 8, 2014 [Page 14] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 8. Acknowledgments Thanks to Carsten Bormann, Esko Dijk, Bert Greevenbosch and Akbar Rahman for their valuable inputs. 9. References 9.1. Normative References [I-D.ietf-core-coap] Shelby, Z., Hartke, K. and Bormann, C.,"Constrained Application Protocol (CoAP)", draft-ietf-core-coap-18, June 28, 2013 [I-D.ietf-core-observe] Hartke, K.,"Observing Resources in CoAP", draft-ietf-core-observe- 09, July 15, 2013 [I-D.ietf-core-groupcomm] Rahman, A. and Dijk, E.,"Group Communication for CoAP", draft-ietf core-groupcomm-12, July 30, 2013 Bhattacharyya, et al. Expires April 8, 2014 [Page 15] Internet-Draft draft-tcs-coap-no-response-option-03 October 2013 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 April 8, 2014 [Page 16]