CoRE A. Bhattacharyya
Internet Draft S. Bandyopadhyay
Intended status: Standards track A. Pal
Expires: February 2015 Tata Consultancy Services Ltd.
August 5, 2014
CoAP option for no server-response
draft-tcs-coap-no-response-option-07
Abstract
There can be typical M2M scenarios where responses from the data
sink to the data source against request 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 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-Response' 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 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.
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Table of Contents
1. Introduction...................................................3
1.1. Granular suppression of responses.........................3
1.2. Terminology...............................................3
2. Potential benefits.............................................4
3. Exemplary application scenarios................................4
3.1. Frequent update of geo-location from vehicles to backend..4
3.2. Multicasting actuation command from a handheld device to a
group of appliances............................................5
3.2.1. Using granular response suppression..................5
4. Option Definition..............................................6
4.1. Granularity in response suppression.......................7
5. Miscellaneous aspects..........................................9
5.1. Re-use interval for message IDs...........................9
5.2. Re-using Tokens...........................................9
5.3. Taking care of congestion................................10
5.4. Duality with the 'Observe' option........................10
6. Example.......................................................11
6.1. Request/response Scenario................................11
6.1.1. Using No-Response with PUT..........................11
6.1.2. Using No-Response with POST.........................12
6.1.2.1. POST updating a target resource................12
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6.1.2.2. POST performing updates through resource creation
........................................................13
6.2. An end-to-end system combining No-Response and Observe...14
7. IANA Considerations...........................................16
8. Security Considerations.......................................16
9. Acknowledgments...............................................16
10. References...................................................16
10.1. Normative References....................................16
10.2. Informative References..................................17
1. Introduction
This draft proposes a new header option 'No-Response' for
Constrained Application Protocol (CoAP) [RFC7252]. 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. 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 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
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 that 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 [RFC7252].
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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 in network clogging by effectively reducing 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 communication cost.
* Help satisfy hard real-time requirements since waiting due to
closed loop latency MAY be completely avoided.
3. Exemplary application scenarios
Next sub-sections describe some exemplary user stories which may
potentially benefit by using 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 each of which 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. 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.
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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 4 bytes of application layer plus several
bytes originating from the lower layers. Thus the cumulative load on
the network will be quite significant.
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. 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.
Mapping the above scenario to the benefits mentioned in Section 2
reveals that use of 'No-Response' will help in:
* Reduction in 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. 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 uses No-
Response option along with NON 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.
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4. Option Definition
The properties of this option are as 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 interest/ 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 application scenarios
foreseen so far.
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+-------------+----------------------------------------------------+
| Method Name | Remarks on applicability |
+-------------+----------------------------------------------------+
| | This option does not apply to GET under usual |
| | circumstances when the client requests the contents|
| | of a resource. However, this option MAY be useful |
| | for special GET requests. At present only one such|
| | application is identified which is the |
| | 'cancellation' procedure for 'Observe'. Observe- |
| GET | cancellation requires a client to issue a GET |
| | request which has the same token as the token of |
| | the original observe request and includes an |
| | Observe Option with the value set to 'deregister' |
| | (1). In this case the server response does not |
| | contain any payload. Under such situation the |
| | client MAY express its disinterest in the response |
| | from the server. |
+-------------+----------------------------------------------------+
| | Mostly 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 |
| | performs resource creation and the client does not |
| | refer to the resource in future. For example, |
| | than updating a fixed resource, POST API may |
| POST | contain a query-string with name/value pairs for a |
| | defined action (ex. 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 |
| | 6.1.2.2). |
+-------------+----------------------------------------------------+
| | Deletion is usually a permanent action and the |
| DELETE | client SHOULD make sure that the deletion actually |
| | happened. SHOULD NOT be applicable. |
+-------------+----------------------------------------------------+
Table 2: Applicability of No-Response for different methods
4.1. 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 (same as |
| | | empty value). |
+-------+-----------------------+---------------------------------+
| 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
XOR of 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: The use of No-Response 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-Response 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 some application specific 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). This kind of situation may arise for
the scenario in Section 3.2.1. Under such circumstances the use
of No-Response 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.
A point to be noted in view of the above example is that there
may be situations when the response on errors might get lost. In
such a situation the sender would wait up to the time-out period
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but will not receive any response. But this should not lead to
the impression to the sender that the request was successful. The
situation will worsen if the receiver is no longer active. The
application designer needs to tackle such situation. For example,
the sender may strategically insert requests without No-Response
after N numbers of requests with No-Response.
5. Miscellaneous aspects
This section further describes few important implementation aspects
worth considering while using No-Response. The following discussion
does not mandate anything, rather provides suggestive guidelines for
the application developer.
5.1. Re-use interval for message IDs
Since No-Response is primarily based on CoAP-NON, '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.
5.2. 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 when 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 till 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 [I-D.ietf-core-
groupcomm]:
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 [I-D.ietf-core-groupcomm] for multicast request. But for unicast
request MAX_SERVER_RESPONSE_DELAY is simply the expected maximum
response delay from the 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]where group size (G) = 1 for unicast request.
If it is not possible for the client to get a reasonable estimate of
the MAX_SERVER_RESPONSE_DELAY then the client SHOULD use a unique
token for the request with No-Response to be safe.
5.3. 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 time-to-time
the interval between updates.
5.4. Duality with the 'Observe' option
Unlike the multicast actuation scenarios (Section 3.2), scenarios
like frequent update using No-Response leads to an interesting
observation. The 'No-Response' option in a sense complements the
'Observe' option with NON-notifications ([I-D.ietf-core-observe]).
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In case of the later the 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. For example, the scenario of location update described in
Section 3.1 above might also be deployed using observe with NON-
notifications. In that case the backend infrastructure would have to
subscribe to each individual sensor gateway at the vehicles. But,
the 'book-keeping' exercise required at the backend for such an
implementation may not be very trivial and deployment with No-
Response may be far more straight-forward. 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 producer-consumer application. A typical example is illustrated
in Section 6.2.
6. 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.
6.1. Request/response Scenario
6.1.1. 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.
6.1.2. 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.
6.1.2.1. 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.
6.1.2.2. POST performing updates 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 which the client would not
refer to in future. 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.
6.2. An end-to-end system combining No-Response and Observe
This example illustrates the scenario pointed out in Section 5.3
above. The 'No-Response' option can be combined with the 'Observe'
option with NON-notifications to create a lightweight end-to-end
producer-consumer system. For example, the vehicular updates from a
remote vehicle may be observed by a remote observer in a PDA as
shown in figure 4.
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Producer Server Consumer
(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.] |
| | |
+-----> | 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 |
| | |
| +-----> |
| | 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 'producer' and observe with NON-
notifications by the 'consumer'.
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7. IANA Considerations
The IANA is requested to add the following option number entries:
+--------+--------------+----------------------------+
| Number | Name | Reference |
+--------+--------------+----------------------------+
| 92 | No-Response | Section 4 of this document |
+--------+--------------+----------------------------+
8. 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].
9. Acknowledgments
Thanks to Carsten Bormann, Esko Dijk, Bert Greevenbosch, Akbar
Rahman and Claus Hartke for their valuable inputs.
10. References
10.1. 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-
14, June 30, 2014
[I-D.ietf-core-groupcomm]
Rahman, A. and Dijk, E.,"Group Communication for CoAP", draft-ietf
core-groupcomm-21, July 31, 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
10.2. 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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