Internet DRAFT - draft-fossati-core-publish-monitor-options
draft-fossati-core-publish-monitor-options
Internet Engineering Task Force T. Fossati
Internet-Draft KoanLogic
Intended status: Standards Track P. Giacomin
Expires: September 11, 2012 Freelance
S. Loreto
Ericsson
March 10, 2012
Publish and Monitor Options for CoAP
draft-fossati-core-publish-monitor-options-01
Abstract
This memo defines two additional Options for the Constrained
Application Protocol (CoAP) especially targeted at sleepy sensors:
Publish and Monitor.
The Publish Option enables opportunistic updates of a given resource
state, by temporarily delegating the authority of the Publish'ed
resource to a Proxy node. The whole process is driven by the
(sleepy) origin -- which may actually never need to listen.
The Monitor Option complements the typical Observe pattern, enabling
the tracking of a resource hosted by a node sleeping most of the
time, by taking care of establishing and maintaining an Observe
relationship with the (sleepy) origin on behalf of the (sleepy)
client.
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). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on September 11, 2012.
Copyright Notice
Fossati, et al. Expires September 11, 2012 [Page 1]
Internet-Draft Publish and Monitor Options for CoAP March 2012
Copyright (c) 2012 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. Requirements Language and Motivation . . . . . . . . . . . 3
2. Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Publish Option . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. Publishing a Resource . . . . . . . . . . . . . . . . 4
2.1.2. Updating a Resource . . . . . . . . . . . . . . . . . 5
2.1.3. Unpublishing a Resource . . . . . . . . . . . . . . . 6
2.1.4. Value Format . . . . . . . . . . . . . . . . . . . . . 6
2.1.5. Discovery . . . . . . . . . . . . . . . . . . . . . . 6
2.1.5.1. Publishing the /.well-known/core Resource . . . . 6
2.1.5.2. Resource Directory . . . . . . . . . . . . . . . . 7
2.2. Monitor Option . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Public Monitor Registration . . . . . . . . . . . . . 8
2.2.2. Monitor De-registration . . . . . . . . . . . . . . . 9
2.2.2.1. Explicit De-registration . . . . . . . . . . . . . 10
2.2.2.2. Implicit De-registration . . . . . . . . . . . . . 10
2.2.3. Resource Refresh . . . . . . . . . . . . . . . . . . . 10
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Fossati, et al. Expires September 11, 2012 [Page 2]
Internet-Draft Publish and Monitor Options for CoAP March 2012
1. Introduction
The proposal described in this memo covers the following use case:
a node N, which is sleeping most of the time, depends one or more
resources hosted at another sleepy node M. In cases as such, the
probability of an empty intersection between their respective wake
periods is very high, making it hard for the two to synchronize.
In this scenario, using the basic observe [I-D.ietf-core-observe]
functionality is not enough, as it could lead to lost state updates
in case N is offline while M pushes its notifications; further, the
observation may never bootstrap since its initialization needs both
client and origin awake at the same time.
This memo introduces two extensions to the Proxy caching
functionality that give the Proxy an explicit mediation role in the
sleepy-to-sleepy CoAP [I-D.ietf-core-coap] communication.
1.1. Requirements Language and Motivation
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 [RFC2119].
This specification makes use of the following terminology:
Sleepy Device: a sensor/actuator (usually battery operated) that
powers down its radio beyond the normal radio duty cycle in order
to save energy.
and tries to provide an in-protocol solution for the requirement REQ3
stated in [I-D.shelby-core-coap-req]:
The ability to deal with sleeping nodes. Devices may be
powered down at any point in time but periodically "wake up"
for brief periods of time.
2. Options
+-----+----------+---------+--------+--------+---------+
| No. | C/E | Name | Format | Length | Default |
+-----+----------+---------+--------+--------+---------+
| YY | Critical | Publish | uint | 1 B | 0x2 |
| XX | Critical | Monitor | (none) | 0 B | (none) |
+-----+----------+---------+--------+--------+---------+
Fossati, et al. Expires September 11, 2012 [Page 3]
Internet-Draft Publish and Monitor Options for CoAP March 2012
2.1. Publish Option
The Publish Option enables the sleepy origin to temporarily (i.e. for
a specified "lease" time) delegate the authority of one of its hosted
resources to a Proxy node that will start to behave as the origin for
the Publish'ed resource. This allows a sleepy sensor to use the
Proxy as the rendezvous point for one-way sleepy to sleepy signaling.
2.1.1. Publishing a Resource
P S
| PUT | Proxy-URI: coap://sleepy.example.org/res
|<--------+ Publish: 0110
| r | Content-Type: text/plain
| | ETag: 0xabcd
| | Max-Age: 1200
| |
| 2.01 |
+-------->|
| |
Figure 1
The origin server publishes one of its hosted resources, specified by
the enclosed Proxy-URI, by PUT'ing it to the Proxy with a Publish
Option attached. The Publish Option value specifies the CoAP methods
that clients are allowed to use on the resource (see Section 2.1.4).
The example in Figure 1 shows a delegation where the GET and PUT
methods are allowed while POST and DELETE are explicitly prohibited,
meaning that the resource can be read and updated by clients, but it
can't be deleted nor created.
The Proxy, which is voluntarily charged by the resource owner to act
as the delegated origin for the "lease" time specified by Max-Age,
replies with a 2.01 if the authority transfer has succeeded. An
exact duplicate of the submitted representation is created, and from
now on it can be accessed using the original URI provided that
clients go through the delegated Proxy. If the Publish operation
does not succeed, the origin transfer fails, and an appropriate
response code is returned.
An ETag MAY be supplied as a metadata to be included in responses
involving the Publish'ed representation. If no Max-Age is given, a
default of 3600 seconds MUST be assumed. The Max-Age value, either
implicit or explicit, determines the lifetime of the origin
delegation. When the Max-Age value is elapsed, the Proxy MUST delete
the Publish'ed resource value and fall back to its usual proxying
Fossati, et al. Expires September 11, 2012 [Page 4]
Internet-Draft Publish and Monitor Options for CoAP March 2012
function.
The Publish Option is critical and MUST be present in the request
only. If the Proxy does not recognize it, a 4.02 (Bad Option) MUST
be returned to the client. If the option value is not correctly
formatted (see Section 2.1.4), a 4.00 (Bad Request) MUST be returned
to the client.
It is sufficient for any client wishing to access the resource to do
so using the Proxy node that, following the Publish operation, will
start behaving a the origin, satisfying requests on behalf of the
sleeping node.
The Proxy MUST save the identity of the resource Publish'er in order
to distinguish "maintainance" operations such as update and explicit
deletion, from "regular" access to the published resource by clients.
An interesting outcome of this communication strategy is that the
sleepy origin may really never need to listen on its radio interface.
2.1.2. Updating a Resource
P S
| PUT | Proxy-URI: coap://sleepy.example.org/res
|<--------+ Publish: 0110
| r | Content-Type: text/plain
| | ETag: 0xdcba
| | Max-Age: 1200
| |
| 2.04 |
+-------->|
| |
Figure 2
In order to update the delegated resource state, the sleepy node
shall send the very same request to the Proxy, which in turn replies
with a 2.04 (Changed) status code in case the update operation has
succeeded, or an appropriate error code in case it fails.
Fossati, et al. Expires September 11, 2012 [Page 5]
Internet-Draft Publish and Monitor Options for CoAP March 2012
2.1.3. Unpublishing a Resource
P S
| DELETE | Proxy-URI: coap://sleepy.example.org/res
|<---------+ Publish: 0x0
| |
| |
| 2.02 |
+--------->|
| |
The delegation of a given resource can be explicitly revoked by the
real origin at any time before the lease time expires, by issuing a
DELETE request to the Proxy hosting the resource duplicate with a
Publish Option with value 0x0.
On successful deletion of the delegation a 2.02 (Deleted) response
code is returned by the Proxy.
2.1.4. Value Format
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|C R U D 0 0 0 0|
+-+-+-+-+-+-+-+-+
Each of the first 4 bits is a flag field indicating whether the
associated CoAP method (respectively: POST, GET, PUT and DELETE) is
allowed on the Publish'ed resource. The remaining 4 bits are unused
and MUST be set to 0.
In case the value is missing, the default is assumed to be 0x2, i.e.
the resource is read-only.
An all-0 value is used to explicitly revoke the delegation (see
Section 2.1.3.)
If the delegated Proxy receives a request with a method that is not
compatible with the supplied mask, it MUST respond with a 4.05
(Method Not Allowed) response code.
2.1.5. Discovery
2.1.5.1. Publishing the /.well-known/core Resource
The [I-D.ietf-core-link-format] has no explicit text about "well-
known" discovery of devices through a Proxy, nor about the
cacheability rules for such resource. Even if it seems reasonable to
Fossati, et al. Expires September 11, 2012 [Page 6]
Internet-Draft Publish and Monitor Options for CoAP March 2012
assume that the /.well-known/core URI is both query-able and
cacheable through a Proxy, on the contrary the situation is not very
much so.
In fact, since the "well-known" interface relies on the resource
origin being implicitly defined by the source address of the UDP
packet carrying the response, quering the "well-known" interface
(either unicast or multicast) through a Proxy-URI has little hope to
be fully functional. The (ab)use of a an implicit L3 locator as the
identifier of the resource authority makes "well-known" discovery
generally incompatible with Proxy mediated communication, unless each
target URI in a link is given as a URI and not as a relative-ref
(section 4.1 of [RFC3986]).
Consequently, in this proposal we assume that the /.well-known/core
of a sleepy node can be Publish'ed if and only if the target URI in
the each link is not a relative-ref.
Its registration is the same as in Figure 1, but the Proxy MAY need
to treat it in a way that is slightly different from other "normal"
delegated resources. In fact, while delegation is in place (i.e. the
lease period is not elapsed, and neither explicit revocation has
happened) the Proxy MAY be able to respond to filtered queries
(section 4.1 of [I-D.ietf-core-link-format]) regarding the Publish'ed
/.well-known/core.
2.1.5.2. Resource Directory
Given the strong requirement on the link formatting given in
Section 2.1.5.1, it could be preferable (or even necessary) to use
the Resource Directory [I-D.shelby-core-resource-directory] as a
means of delegating the discovery of the resources hosted at a sleepy
node.
This can be done either by the sleepy node, or automatically by the
delegated Proxy when a Publish request is received.
[[Automatic push to RD: check it out]]
2.2. Monitor Option
The Monitor Option is a variant of the Observe Option that is aimed
at solving some issues that may occur when sleepy sensors are
involved.
Suppose that the resource of interest is not in cache, and a sleepy
endpoint wants to Observe it through the Proxy. If the origin of the
requested resource is sleeping at the time the observation is
Fossati, et al. Expires September 11, 2012 [Page 7]
Internet-Draft Publish and Monitor Options for CoAP March 2012
requested, the requesting node gets an error, and may need to stay
awake and retry until the target node gets ready -- which is clearly
not an option in case the sensor has a very small duty cycle.
The Monitor Option is used to ask a Proxy to keep a given resource
fresh by observing it, while the requesting node is sleeping. Thus
the sleepy sensor can possibly get the latest representation
published by the monitored resource when it wakes up, even if the
origin is sleeping -- and was sleeping at the time the Monitor has
been requested.
The Monitor Option is critical and MUST be present in the request
only. If the Proxy does not recognize it, a 4.02 (Bad Option) MUST
be returned to the client.
2.2.1. Public Monitor Registration
P C
| POST | Proxy-URI: coap://sleepy.example.org/res
|<-------+ Monitor: <empty>
| | Max-Age: 86400
| | Content-Type: application/json
| 2.01 |
+------->| Location-Path: temp
| | Location-Path: res
| |
Figure 3
The client POST's the resource to be monitored, identified by the
Proxy-URI. The request message contains an empty Monitor Option, and
possibly specifies a TTL (i.e. an implicit de-registration
indication) for the monitor through Max-Age. One or more content
types for the acceptable representations of the resource are
optionally specified via the Accept option. In case no TTL is
supplied, a default value of 3600 seconds is assumed.
The operation creates a "monitor" resource at the Proxy, that MUST
maintain a fresh carbon copy of one or more representations of the
requested resource depending on the supplied Content-Type's. For
convenience, multiple "monitor" resources corresponding to the same
target resource, can be coalesced into the same monitor object at the
Proxy -- possibly with the same URI. In such case, a set containing
one entry for each registered client is kept, which holds the client
identities, their expiry and one or more preferred media types for
their representation(s). When all entries are deleted (either
because clients have explicitly deregistered the monitor, or the
monitor period has expired), the corresponding "monitor" object is
Fossati, et al. Expires September 11, 2012 [Page 8]
Internet-Draft Publish and Monitor Options for CoAP March 2012
deleted. Note that an underlying cache entry MAY still be kept in
case the cached representation(s) are still fresh (i.e. the Max-Age
of the "monitor" resource and Max-Age of the target resource have
completely different semantics.)
If the monitor resource is successfully created, the server MUST
return a 2.01 response containing one or more Location-Path and/or
Location-Query Options to identify the monitored resource instance,
which can be used from now on by the requester as an alias to the
target resource.
At a later time, the client wakes up and wants to access the
monitored resource. It does so by requesting the Proxy monitor
resource that has been previously created.
P C
| GET | URI-Path: temp
|<-------+ URI-Path: res
| | Accept: application/json
| |
| 2.05 |
+------->| (Content)
| |
| |
Figure 4
In case the observation on the target node has not been started
because the Proxy has not yet been able to contact the origin, the
Proxy will return a [TBD] error code.
In case the requested resource was not present on the origin, the
Proxy will return an empty response (i.e. one with no payload.)
[[XXX: add an explicit response code perhaps like HTTP 204 ?]]
In case the monitor resource is not found in the Proxy, either
because the Proxy has rebooted and lost its state, or the monitor
resource has been de-registered (see Section 2.2.2), a 4.04 response
code is returned to the client -- that can recreate it, if needed.
2.2.2. Monitor De-registration
The monitor object MUST be deleted at the Proxy when all its
associated resources have been de-registered or have expired.
In order to save storage, a Proxy MAY decide to delete a monitor
resource in case it has not been requested for a sufficiently long
Fossati, et al. Expires September 11, 2012 [Page 9]
Internet-Draft Publish and Monitor Options for CoAP March 2012
time, or for any other reason. Note that the Proxy may also reboot
and lose its state, including the state associated to any monitored
resource. The requester can realize that the state at the Proxy has
been lost, and re-instantiate the monitor, when it receives an
unexpected 4.04 from the "monitor" resource.
2.2.2.1. Explicit De-registration
P C
| DELETE | Path: temp
|<-------+ Path: res
| |
| 2.02 |
+------->|
| |
Figure 5
Explicit de-registration is performed by a client, with a DELETE on
the URI returned by the Proxy on the corresponding registration.
2.2.2.2. Implicit De-registration
Implicit de-registration MUST occur when the monitoring period
specified by the client via Max-Age expires. If no Max-Age was
supplied at registration time, a default of 3600 seconds MUST be
assumed.
2.2.3. Resource Refresh
In order to minimize the number of messages used by the monitoring
process, the Proxy MUST try to install an observation on the
requested resource. In case this first attempt fails, the Proxy MAY
fall back to repeated poll whose duration is upper bounded by the
Max-Age value indicated by the client during registration.
Usual cache validation MUST be applied to the cached copy of the
monitored resource.
3. Acknowledgements
Bruce Nordman.
4. IANA Considerations
The following entries are added to the CoAP Option Numbers registry:
Fossati, et al. Expires September 11, 2012 [Page 10]
Internet-Draft Publish and Monitor Options for CoAP March 2012
.------------------------------.
| Number | Name | Reference |
:--------:---------:-----------:
| 2n+1 | Publish | RFC XXXX |
+--------+---------+-----------+
| 2m+1 | Monitor | RFC XXXX |
`------------------------------'
5. Security Considerations
Threat: cache poisoning.
Countermeasure: authenticate sender.
Threat: unauthorized de-registration
Countermeasure: authenticate requester.
Threat: Proxy resources' exhaustion.
Countermeasure: authenticate requester + quota limit.
Threat: global state loss.
Countermeasure: cache redundancy.
6. References
6.1. Normative References
[I-D.ietf-core-coap]
Frank, B., Bormann, C., Hartke, K., and Z. Shelby,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-08 (work in progress), October 2011.
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-11 (work in progress),
January 2012.
[I-D.ietf-core-observe]
Hartke, K., "Observing Resources in CoAP",
draft-ietf-core-observe-04 (work in progress),
February 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
Fossati, et al. Expires September 11, 2012 [Page 11]
Internet-Draft Publish and Monitor Options for CoAP March 2012
RFC 3986, January 2005.
6.2. Informative References
[I-D.shelby-core-coap-req]
Shelby, Z., Stuber, M., Sturek, D., Frank, B., and R.
Kelsey, "CoAP Requirements and Features",
draft-shelby-core-coap-req-02 (work in progress),
October 2010.
[I-D.shelby-core-resource-directory]
Krco, S. and Z. Shelby, "CoRE Resource Directory",
draft-shelby-core-resource-directory-02 (work in
progress), October 2011.
Authors' Addresses
Thomas Fossati
KoanLogic
Via di Sabbiuno, 11/5
Bologna 40100
Italy
Email: tho@koanlogic.com
Pierpaolo Giacomin
Freelance
Email: yrz@anche.no
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: salvatore.loreto@ericsson.com
Fossati, et al. Expires September 11, 2012 [Page 12]
