One document matched: draft-ietf-core-dynlink-01.xml
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<rfc ipr="trust200902" docName="draft-ietf-core-dynlink-01" category="info">
<front>
<title abbrev="Dynamic Resource Linking for CoRE">Dynamic Resource Linking for Constrained RESTful Environments</title>
<author initials="Z." surname="Shelby" fullname="Zach Shelby">
<organization>ARM</organization>
<address>
<postal>
<street>150 Rose Orchard</street>
<city>San Jose</city>
<code>95134</code>
<country>FINLAND</country>
</postal>
<phone>+1-408-203-9434</phone>
<email>zach.shelby@arm.com</email>
</address>
</author>
<author initials="Z.V." surname="Vial" fullname="Matthieu Vial">
<organization>Schneider-Electric</organization>
<address>
<postal>
<street></street>
<city>Grenoble</city>
<code></code>
<country>FRANCE</country>
</postal>
<phone>+33 (0)47657 6522</phone>
<email>matthieu.vial@schneider-electric.com</email>
</address>
</author>
<author initials="M." surname="Koster" fullname="Michael Koster">
<organization>SmartThings</organization>
<address>
<postal>
<street>665 Clyde Avenue</street>
<city>Mountain View</city>
<code>94043</code>
<country>USA</country>
</postal>
<email>michael.koster@smartthings.com</email>
</address>
</author>
<author initials="C." surname="Groves" fullname="Christian Groves">
<organization>Huawei</organization>
<address>
<postal>
<street></street>
<city></city>
<code></code>
<country>Australia</country>
</postal>
<email>Christian.Groves@nteczone.com</email>
</address>
</author>
<date year="2016" month="October" day="28"/>
<area>art</area>
<workgroup>CoRE Working Group</workgroup>
<keyword>Internet-Draft</keyword> <keyword>CoRE</keyword> <keyword>CoAP</keyword> <keyword>Link Binding</keyword> <keyword>Observe</keyword>
<abstract>
<t>For CoAP <xref target="RFC7252"/> Dynamic linking of state updates between resources, either on an endpoint or between endpoints, is defined with the concept of Link Bindings. This specification defines conditional observation attributes that work with Link Bindings or with CoAP Observe <xref target="RFC7641"/>.</t>
<t>Editor’s note:</t>
<t>o The git repository for the draft is found at https://github.com/core-wg/dynlink</t>
<t>o Examples need to be added.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>IETF Standards for machine to machine communication in constrained environments describe a REST protocol and a set of related information standards that may be used to represent machine data and machine metadata in REST interfaces. CoRE Link-format is a standard for doing Web Linking <xref target="RFC5988"/> in constrained environments.</t>
<t>This specification introduces the concept of a Link Binding, which defines a new link relation type to create a dynamic link between resources over which to exchange state updates. Specifically, a Link Binding is a link for binding the state of 2 resources together such that updates to one are sent over the link to the other. CoRE Link Format representations are used to configure, inspect, and maintain Link Bindings. This specification additionally defines a set of conditional Observe Attributes for use with Link Bindings and with the standalone CoRE Observe <xref target="RFC7641"/> method.</t>
</section>
<section anchor="terminology" title="Terminology">
<t>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this specification are to be interpreted as described in <xref target="RFC2119"/>.</t>
<t>This specification requires readers to be familiar with all the terms and concepts that are discussed in <xref target="RFC5988"/> and <xref target="RFC6690"/>. This specification makes use of the following additional terminology:</t>
<t><list style="hanging">
<t hangText='Link Binding:'>
A unidirectional logical link between a source resource and a destination resource, over which state information is synchronized.</t>
<t hangText='State Synchronization:'>
Depending on the binding method (Polling, Observe, Push) different REST methods may be used to synchronize the resource values between a source and a destination. The process of using a REST method to achieve this is defined as “State Synchronization”. The endpoint triggering the state synchronization is the synchronization initiator.</t>
</list></t>
</section>
<section anchor="bindings" title="Link Bindings">
<t>In a M2M RESTful environment, endpoints may directly exchange the content of their resources to operate the distributed system. For example, a light switch may supply on-off control information that may be sent directly to a light resource for on-off control. Beforehand, a configuration phase is necessary to determine how the resources of the different endpoints are related to each other. This can be done either automatically using discovery mechanisms or by means of human intervention and a so-called commissioning tool. In this specification the abstract relationship between two resources is called a link Binding. The configuration phase necessitates the exchange of binding information so a format recognized by all CoRE endpoints is essential. This specification defines a format based on the CoRE Link-Format to represent binding information along with the rules to define a binding method which is a specialized relationship between two resources. The purpose of a binding is to synchronize the content between a source resource and a destination resource. The destination resource MAY be a group resource if the authority component of the destination URI contains a group address (either a multicast address or a name that resolves to a multicast address). Since a binding is unidirectional, the binding entry defining a relationship is present only on one endpoint. The binding entry may be located either on the source or the destination endpoint depending on the binding method.</t>
<section anchor="binding_methods" title="Binding Methods">
<t>A binding method defines the rules to generate the web-transfer exchanges that synchronize state between source and destination resources. By using REST methods content is sent from the source resource to the destination resource.</t>
<t>The following table gives a summary of the binding methods defined in this specification.</t>
<texttable title="Binding Method Summary" anchor="bindsummary">
<ttcol align='left'>Name</ttcol>
<ttcol align='left'>Identifier</ttcol>
<ttcol align='left'>Location</ttcol>
<ttcol align='left'>Method</ttcol>
<c>Polling</c>
<c>poll</c>
<c>Destination</c>
<c>GET</c>
<c>Observe</c>
<c>obs</c>
<c>Destination</c>
<c>GET + Observe</c>
<c>Push</c>
<c>push</c>
<c>Source</c>
<c>PUT</c>
</texttable>
<t>The description of a binding method must define the following aspects:</t>
<t><list style="hanging">
<t hangText='Identifier:'>
This is the value of the "bind" attribute used to identify the method.</t>
<t hangText='Location:'>
This information indicates whether the binding entry is stored on the source or on the destination endpoint.</t>
<t hangText='REST Method:'>
This is the REST method used in the Request/Response exchanges.</t>
<t hangText='Conditions:'>
A binding method definition must state how the condition attributes of the abstract binding definition are actually used in this specialized binding.</t>
</list></t>
<t>The binding methods are described in more detail below.</t>
<section anchor="polling" title="Polling">
<t>The Polling method consists of sending periodic GET requests from the destination endpoint to the source resource and copying the content to the destination resource. The binding entry for this method MUST be stored on the destination endpoint. The destination endpoint MUST ensure that the polling frequency does not exceed the limits defined by the pmin and pmax attributes of the binding entry. The copying process MAY filter out content from the GET requests using value-based conditions (e.g based on the Change Step, Less Than, Greater Than attributes).</t>
</section>
<section anchor="observe" title="Observe">
<t>The Observe method creates an observation relationship between the destination endpoint and the source resource. On each notification the content from the source resource is copied to the destination resource. The creation of the observation relationship requires the CoAP Observation mechanism <xref target="RFC7641"/> hence this method is only permitted when the resources are made available over CoAP. The binding entry for this method MUST be stored on the destination endpoint. The binding conditions are mapped as query string parameters (see <xref target="observation"/>).</t>
</section>
<section anchor="push" title="Push">
<t>When the Push method is assigned to a binding, the source endpoint sends PUT requests to the destination resource when the binding condition attributes are satisfied for the source resource. The source endpoint MUST only send a notification request if the binding conditions are met. The binding entry for this method MUST be stored on the source endpoint.</t>
</section>
</section>
<section anchor="relation_type" title="Link Relation">
<t>Since Binding involves the creation of a link between two resources, Web Linking and the CoRE Link-Format are a natural way to represent binding information. This involves the creation of a new relation type, named “boundto”. In a Web link with this relation type, the target URI contains the location of the source resource and the context URI points to the destination resource.</t>
</section>
<section anchor="binding_attributes" title="Binding Attributes">
<t>Web link attributes allow a fine-grained control of the type of state synchronization along with the conditions that trigger an update. This specification defines the attributes below:</t>
<texttable title="Binding Attributes Summary" anchor="weblinkattributes">
<ttcol align='left'>Attribute</ttcol>
<ttcol align='left'>Parameter</ttcol>
<ttcol align='left'>Value</ttcol>
<c>Binding method</c>
<c>bind</c>
<c>xsd:string</c>
<c>Minimum Period (s)</c>
<c>pmin</c>
<c>xsd:integer (>0)</c>
<c>Maximum Period (s)</c>
<c>pmax</c>
<c>xsd:integer (>0)</c>
<c>Change Step</c>
<c>st</c>
<c>xsd:decimal (>0)</c>
<c>Greater Than</c>
<c>gt</c>
<c>xsd:decimal</c>
<c>Less Than</c>
<c>lt</c>
<c>xsd:decimal</c>
</texttable>
<section anchor="bind-method-bind" title="Bind Method (bind)">
<t>This is the identifier of a binding method which defines the rules to synchronize the destination resource. This attribute is mandatory.</t>
</section>
<section anchor="pmin" title="Minimum Period (pmin)">
<t>When present, the minimum period indicates the minimum time to wait (in seconds) before triggering a new state synchronization (even if it has changed). In the absence of this parameter, the minimum period is up to the synchronization initiator. The minimum period MUST be greater than zero otherwise the receiver MUST return a CoAP error code 4.00 “Bad Request” (or equivalent).</t>
</section>
<section anchor="pmax" title="Maximum Period (pmax)">
<t>When present, the maximum period indicates the maximum time in seconds between two consecutive state synchronizations (regardless if it has changed). In the absence of this parameter, the maximum period is up to the synchronization initiator. The maximum period MUST be greater than zero and MUST be greater than the minimum period parameter (if present) otherwise the receiver MUST return a CoAP error code 4.00 “Bad Request” (or equivalent).</t>
</section>
<section anchor="st" title="Change Step (st)">
<t>When present, the change step indicates how much the value of a resource SHOULD change before triggering a new state synchronization (compared to the value of the previous synchronization). Upon reception of a query including the st attribute the current value (CurrVal) of the resource is set as the initial value (STinit). Once the resource value differs from the STinit value (i.e. CurrVal >= STinit + ST or CurrVal <= STint - ST) then a new state synchronization occurs. STinit is then set to the state synchronization value and new state synchronizations are based on a change step against this value. The change step MUST be greater than zero otherwise the receiver MUST return a CoAP error code 4.00 “Bad Request” (or equivalent).</t>
<t>Note: Due to the state synchronization based update of STint it may result in that resource value received in two sequential state synchronizations differs by more than st.</t>
</section>
<section anchor="gt" title="Greater Than (gt)">
<t>When present, Greater Than indicates the upper limit value the resource value SHOULD cross before triggering a new state synchronization. State synchronization only occurs when the resource value exceeds the specified upper limit value. The actual resource value is used for the synchronization rather than the gt value. If the value continues to rise, no new state synchronizations are generated as a result of gt. If the value drops below the upper limit value and then exceeds the upper limit then a new state synchronization is generated.</t>
</section>
<section anchor="lt" title="Less Than (lt)">
<t>When present, Less Than indicates the lower limit value the resource value SHOULD cross before triggering a new state synchronization. State synchronization only occurs when the resource value is less than the specified lower limit value. The actual resource value is used for the synchronization rather than the lt value. If the value continues to fall no new state synchronizations are generated as a result of lt. If the value rises above the lower limit value and then drops below the lower limit then a new state synchronization is generated.</t>
</section>
<section anchor="attribute-interactions" title="Attribute Interactions">
<t>Pmin, pmax, st, gt and lt may be present in the same query.</t>
<t>If pmin and pmax are present in a query then they take precedence over the other parameters. Thus even if st, gt or lt are met, if pmin has not been exceeded then no state synchronization occurs. Likewise if st, gt or lt have not been met and pmax time has expired then state synchronization occurs. The current value of the resource is used for the synchronization. If pmin time is exceeded and st, gt or lt are met then the current value of the resource is synchronized. If st is also included, a state synchronization resulting from pmin or pmax updates STinit with the synchronized value.</t>
<t>If gt and lt are included gt MUST be greater than lt otherwise an error CoAP error code 4.00 “Bad Request” (or equivalent) MUST be returned.</t>
<t>If st is included in a query with a gt or lt attribute then state synchronizations occur only when the conditions described by st AND gt or st AND gl are met.</t>
</section>
</section>
</section>
<section anchor="binding_table" title="Binding Table">
<t>The binding table is a special resource that gives access to the bindings on a endpoint. A binding table resource MUST support the Binding interface defined below. A profile SHOULD allow only one resource table per endpoint.</t>
<section anchor="interfaces" title="Binding Interface Description">
<t>This section defines a REST interface for Binding table resources. The interface supports the link-format type.</t>
<t>The if= column defines the Interface Description (if=) attribute value to be used in the CoRE Link Format for a resource conforming to that interface. When this value appears in the if= attribute of a link, the resource MUST support the corresponding REST interface described in this section. The resource MAY support additional functionality, which is out of scope for this specification. Although this interface description is intended to be used with the CoRE Link Format, it is applicable for use in any REST interface definition.</t>
<t>The Methods column defines the REST methods supported by the interface, which are described in more detail below.</t>
<texttable title="Binding Interface Description" anchor="intdesc">
<ttcol align='left'>Interface</ttcol>
<ttcol align='left'>if=</ttcol>
<ttcol align='left'>Methods</ttcol>
<ttcol align='left'>Content-Formats</ttcol>
<c>Binding</c>
<c>core.bnd</c>
<c>GET, POST, DELETE</c>
<c>link-format</c>
</texttable>
<t>The Binding interface is used to manipulate a binding table. A request with a POST method and a content format of application/link-format simply appends new bindings to the table. All links in the payload MUST have a relation type "boundTo". A GET request simply returns the current state of a binding table whereas a DELETE request empties the table. Individual entries may be dreeleted from the table by specifying the resource path in a DELETE request.</t>
<t>The following example shows requests for adding, retrieving and deleting bindings in a binding table.</t>
<figure title="Binding Interface Example" anchor="figbindexp"><artwork><![CDATA[
Req: POST /bnd/ (Content-Format: application/link-format)
<coap://sensor.example.com/s/light>;
rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
Res: 2.04 Changed
Req: GET /bnd/
Res: 2.05 Content (application/link-format)
<coap://sensor.example.com/s/light>;
rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
Req: DELETE /bnd/a/light
Res: 2.04 Changed
Req: DELETE /bnd/
Res: 2.04 Changed
]]></artwork></figure>
</section>
<section anchor="observation" title="Resource Observation Attributes">
<t>When resource interfaces following this specification are made available over CoAP, the CoAP Observation mechanism <xref target="RFC7641"/> MAY be used to observe any changes in a resource, and receive asynchronous notifications as a result. In addition, a set of query string parameters are defined here to allow a client to control how often a client is interested in receiving notifications and how much a resource value should change for the new representation to be interesting. These query parameters are described in the following table. A resource using an interface description defined in this specification and marked as Observable in its link description SHOULD support these observation parameters. The Change Step parameter can only be supported on resources with an atomic numeric value.</t>
<t>These query parameters MUST be treated as resources that are read using GET and updated using PUT, and MUST NOT be included in the Observe request. Multiple parameters MAY be updated at the same time by including the values in the query string of a PUT. Before being updated, these parameters have no default value.</t>
<texttable title="Resource Observation Attribute Summary" anchor="resobsattr">
<ttcol align='left'>Resource</ttcol>
<ttcol align='left'>Parameter</ttcol>
<ttcol align='left'>Data Format</ttcol>
<c>Minimum Period</c>
<c>/{resource}?pmin</c>
<c>xsd:integer (>0)</c>
<c>Maximum Period</c>
<c>/{resource}?pmax</c>
<c>xsd:integer (>0)</c>
<c>Change Step</c>
<c>/{resource}?st</c>
<c>xsd:decimal (>0)</c>
<c>Less Than</c>
<c>/{resource}?lt</c>
<c>xsd:decimal</c>
<c>Greater Than</c>
<c>/{resource}?gt</c>
<c>xsd:decimal</c>
</texttable>
<t><list style="hanging">
<t hangText='Minimum Period:'>
As per <xref target="pmin"/></t>
<t hangText='Maximum Period:'>
As per <xref target="pmax"/></t>
<t hangText='Change Step:'>
As per <xref target="st"/></t>
<t hangText='Greater Than:'>
As per <xref target="gt"/></t>
<t hangText='Less Than:'>
As per <xref target="lt"/></t>
</list></t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>An implementation of a client needs to be prepared to deal with responses to a request that differ from what is specified in this specification. A server implementing what the client thinks is a resource with one of these interface descriptions could return malformed representations and response codes either by accident or maliciously. A server sending maliciously malformed responses could attempt to take advantage of a poorly implemented client for example to crash the node or perform denial of service.</t>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<section anchor="interface-description" title="Interface Description">
<t>The specification registers the “binding” CoRE interface description link target attribute value as per <xref target="RFC6690"/>.</t>
<t><list style="hanging">
<t hangText='Attribute Value:'>
binding</t>
</list></t>
<t>Editor’s note: RFC6690 actually indicates the use of core. for CoRE WG documents. Therefore it probably is more correct to register core.binding . However this may cause a problem for existing implementations. One approach may be to register two attributes “binding” and “core.binding.”</t>
<t>Description: The binding interface is used to manipulate a binding table which describes the link bindings between source and destination resources for the purposes of synchronizing their content.</t>
<t>Reference: This specification. Note to RFC editor: please insert the RFC of this specification.</t>
<t>Notes: None</t>
</section>
<section anchor="link-relations-type" title="Link Relations Type">
<t>This specification registers the new “bounto” link relation type as per <xref target="RFC5988"/>.</t>
<t><list style="hanging">
<t hangText='Relation Name:'>
boundto</t>
<t hangText='Description:'>
The purpose of a boundto relation type is to indicate that there is a binding between a source resource and a destination resource for the purposes of synchronizing their content.</t>
<t hangText='Reference:'>
This specification. Note to RFC editor: please insert the RFC of this specification.</t>
<t hangText='Notes:'>
None</t>
<t hangText='Application Data:'>
None</t>
</list></t>
</section>
</section>
<section anchor="acknowledgements" title="Acknowledgements">
<t>Acknowledgement is given to colleagues from the SENSEI project who were critical in the initial development of the well-known REST interface concept, to members of the IPSO Alliance where further requirements for interface types have been discussed, and to Szymon Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann who have provided useful discussion and input to the concepts in this specification.</t>
</section>
<section anchor="changelog" title="Changelog">
<t>draft-ietf-core-dynlink-01</t>
<t><list style="symbols">
<t>General: The term state synchronization has been introduced to describe the process of synchronization between destination and source resources.</t>
<t>General: The document has been restructured the make the information flow better.</t>
<t>Clause 3.1: The descriptions of the binding attributes have been updated to clarify their usage.</t>
<t>Clause 3.1: A new clause has been added to discuss the interactions between the resources.</t>
<t>Clause 3.4: Has been simplified to refer to the descriptions in 3.1. As the text was largely duplicated.</t>
<t>Clause 4.1: Added a clarification that individual resources may be removed from the binding table.</t>
<t>Clause 6: Formailised the IANA considerations.</t>
</list></t>
<t>draft-ietf-core-dynlink Initial Version 00:</t>
<t><list style="symbols">
<t>This is a copy of draft-groves-core-dynlink-00</t>
</list></t>
<t>draft-groves-core-dynlink Draft Initial Version 00:</t>
<t><list style="symbols">
<t>This initial version is based on the text regarding the dynamic linking functionality in I.D.ietf-core-interfaces-05.</t>
<t>The WADL description has been dropped in favour of a thorough textual description of the REST API.</t>
</list></t>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor='RFC2119' target='http://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>
<reference anchor='RFC5988' target='http://www.rfc-editor.org/info/rfc5988'>
<front>
<title>Web Linking</title>
<author initials='M.' surname='Nottingham' fullname='M. Nottingham'><organization /></author>
<date year='2010' month='October' />
<abstract><t>This document specifies relation types for Web links, and defines a registry for them. It also defines the use of such links in HTTP headers with the Link header field. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5988'/>
<seriesInfo name='DOI' value='10.17487/RFC5988'/>
</reference>
<reference anchor='RFC6690' target='http://www.rfc-editor.org/info/rfc6690'>
<front>
<title>Constrained RESTful Environments (CoRE) Link Format</title>
<author initials='Z.' surname='Shelby' fullname='Z. Shelby'><organization /></author>
<date year='2012' month='August' />
<abstract><t>This specification defines Web Linking using a link format for use by constrained web servers to describe hosted resources, their attributes, and other relationships between links. Based on the HTTP Link Header field defined in RFC 5988, the Constrained RESTful Environments (CoRE) Link Format is carried as a payload and is assigned an Internet media type. "RESTful" refers to the Representational State Transfer (REST) architecture. A well-known URI is defined as a default entry point for requesting the links hosted by a server. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6690'/>
<seriesInfo name='DOI' value='10.17487/RFC6690'/>
</reference>
</references>
<references title='Informative References'>
<reference anchor='RFC7252' target='http://www.rfc-editor.org/info/rfc7252'>
<front>
<title>The Constrained Application Protocol (CoAP)</title>
<author initials='Z.' surname='Shelby' fullname='Z. Shelby'><organization /></author>
<author initials='K.' surname='Hartke' fullname='K. Hartke'><organization /></author>
<author initials='C.' surname='Bormann' fullname='C. Bormann'><organization /></author>
<date year='2014' month='June' />
<abstract><t>The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.</t><t>CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.</t></abstract>
</front>
<seriesInfo name='RFC' value='7252'/>
<seriesInfo name='DOI' value='10.17487/RFC7252'/>
</reference>
<reference anchor='RFC7641' target='http://www.rfc-editor.org/info/rfc7641'>
<front>
<title>Observing Resources in the Constrained Application Protocol (CoAP)</title>
<author initials='K.' surname='Hartke' fullname='K. Hartke'><organization /></author>
<date year='2015' month='September' />
<abstract><t>The Constrained Application Protocol (CoAP) is a RESTful application protocol for constrained nodes and networks. The state of a resource on a CoAP server can change over time. This document specifies a simple protocol extension for CoAP that enables CoAP clients to "observe" resources, i.e., to retrieve a representation of a resource and keep this representation updated by the server over a period of time. The protocol follows a best-effort approach for sending new representations to clients and provides eventual consistency between the state observed by each client and the actual resource state at the server.</t></abstract>
</front>
<seriesInfo name='RFC' value='7641'/>
<seriesInfo name='DOI' value='10.17487/RFC7641'/>
</reference>
</references>
</back>
</rfc>
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