RFC3343
Network Working Group M. Rose Request for Comments: 3343 Dover Beach Consulting, Inc. Category: Experimental G. Klyne
Nine by Nine
D. Crocker
Brandenburg InternetWorking
April 2003
The Application Exchange (APEX) Presence Service
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo describes the Application Exchange (APEX) presence service, addressed as the well-known endpoint "apex=presence". The presence service is used to manage presence information for APEX endpoints.
Contents
Introduction
This memo describes a presence service that is built upon the APEX [1] "relaying mesh". The APEX presence service is used to manage presence information for APEX endpoints.
APEX, at its core, provides a best-effort datagram service. Within an administrative domain, all relays must be able to handle messages for any endpoint within that domain. APEX services are logically defined as endpoints, but given their ubiquitous semantics they do not necessarily need to be associated with a single physical endpoint. As such, they may be provisioned co-resident with each relay within an administrative domain, even though they are logically provided on top of the relaying mesh, i.e.,
+----------+ +----------+ +----------+ +---------+
| APEX | | APEX | | APEX | | |
| access | | presence | | report | | ... |
| service | | service | | service | | |
+----------+ +----------+ +----------+ +---------+
| | | |
| | | |
+----------------------------------------------------------------+ | | | APEX core | | | +----------------------------------------------------------------+
That is, applications communicate with an APEX service by exchanging data with a "well-known endpoint" (WKE).
APEX applications communicate with the presence service by exchanging data with the well-known endpoint "apex=presence" in the corresponding administrative domain, e.g., "[email protected]" is the endpoint associated with the presence service in the "example.com" administrative domain.
Note that within a single administrative domain, the presence service makes use of the APEX access [3] service in order to determine if an originator is allowed to view or manage presence information.
Use and Management of Presence Information
Management of presence information falls into three categories:
o applications may update the presence information associated with
an endpoint;
o applications may subscribe to receive presence information
associated with an endpoint; and,
o applications may find out who is subscribed to receive presence
information.
Each is now described in turn.
Update of Presence Information
When an application wants to modify the presence information associated with an endpoint, it sends a publish operation to the service, e.g.,
+-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<publish publisher='[email protected]' transID='1'
timeStamp='2000-05-14T13:30:00-08:00'>
<presence publisher='[email protected]'
lastUpdate='2000-05-14T13:02:00-08:00'
publisherInfo='http://www.example.com/fred/'>
<tuple
destination='apex:fred/[email protected]'
availableUntil='2000-05-14T14:02:00-08:00' />
<tuple destination='mailto:[email protected]'
availableUntil='2525-12-31T23:59:59-08:00' />
</presence>
</publish>
</data-content>
S: <ok />
Note that this example uses the "subaddress" convention specified in Section 2.2 of [1] (e.g., "fred/appl=im") to denote multiplexing of traffic for a particular endpoint. Of course, popular applications may have their own URI method assigned to them (e.g., "im:[email protected]").
The service immediately responds with a reply operation containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<reply code='250' transID='1' />
</data-content>
S: <ok />
Distribution of Presence Information
When an application wants to (periodically) receive the presence information associated with an endpoint, it sends a subscribe operation to the service, e.g.,
+-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<subscribe publisher='[email protected]' duration='86400'
transID='100' />
</data-content>
S: <ok />
The service immediately responds with a publish operation containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<publish publisher='[email protected]' transID='100'
timeStamp='2000-05-14T13:30:00-08:00'>
<presence publisher='[email protected]'
lastUpdate='2000-05-14T13:02:00-08:00'
publisherInfo='http://www.example.com/fred/'>
<tuple
destination='apex:fred/[email protected]'
availableUntil='2000-05-14T14:02:00-08:00' />
</presence>
</publish>
</data-content>
S: <ok />
Subsequently, for up to the specified "duration", the service sends new publish operations whenever there are any changes to the endpoint's presence information. If the "duration" is zero-valued, a one time poll of the presence information is achieved; otherwise, at the end of the "duration", a terminate operation is sent.
Note that Step 5 of Section 4.4 requires that the "lastUpdate" attribute of a presence entry be supplied in order to update that entry; accordingly, applications must successfully retrieve a presence entry prior to trying to update that entry. This is usually accomplished by subscribing with a zero-valued duration. (Regardless, administrators should ensure that applications authorized to update a presence entry are also authorized to retrieve that entry.)
Either the subscriber or the service may cancel a subscription by sending a terminate operation, e.g.,
+-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<terminate transID='100' />
</data-content>
S: <ok />
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<reply code='250' transID='100' />
</data-content>
S: <ok />
or
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<terminate transID='100' />
</data-content>
S: <ok />
Distribution of Watcher Information
When an application wants to (periodically) receive notices about endpoints that are subscribed to receive presence information, it sends a watch operation to the service, e.g.,
+-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<watch publisher='[email protected]' duration='86400'
transID='2' />
</data-content>
S: <ok />
The service immediately responds with a reply operation containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'
<reply code='250' transID='2' />
</data-content>
S: <ok />
For each current subscriber, the service immediately sends a notify operation containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<notify subscriber='[email protected]' transID='2'
duration='86000' action='subscribe' />
</data-content>
S: <ok />
Subsequently, for up to the specified "duration", the service sends new notify operations whenever an application subscribes successfully or a subscription is terminated. If the "duration" is zero-valued, a one time poll of the watcher information is achieved; otherwise, at the end of the "duration", a terminate operation is sent.
Either the watcher or the service may cancel the request by sending a terminate operation, e.g.,
+-------+ +-------+ | | -- data -------> | | | appl. | | relay | | | <--------- ok -- | | +-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<terminate transID='2' />
</data-content>
S: <ok />
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<reply code='250' transID='2' />
</data-content>
S: <ok />
or
+-------+ +-------+
| | <------- data -- | |
| relay | | pres. |
| | -- ok ---------> | svc. |
+-------+ +-------+
C:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
<data-content Name='Content'>
<terminate transID='2' />
</data-content>
S: <ok />
Format of Presence Entries
Each administrative domain is responsible for maintaining a "presence entry" for each of its endpoints (regardless of whether those endpoints are currently attached to the relaying mesh).
Section 6 defines the syntax for presence entries. Each presence entry has a "publisher" attribute, a "lastUpdate" attribute, a "publisherInfo" attribute, and contains one or more "tuple" elements:
o the "publisher" attribute specifies the endpoint associated with
the presence entry;
o the "lastUpdate" attribute specifies the date and time that the
service last updated the presence entry;
o the "publisherInfo" attribute specifies arbitrary information
about the publisher (using a URI); and,
o each "tuple" element specifies information about an entity
associated with the endpoint.
Each "tuple" element has a "destination" attribute, an "availableUntil" attribute, a "tupleInfo" attribute, and contains zero or more "capability" elements:
o the "destination" attribute identifies the entity as a URI (e.g.,
"apex:fred/[email protected]" or "mailto:[email protected]");
o the "availableUntil" attribute specifies the latest date and time
that the entity is capable of receiving messages;
o the "tupleInfo" attribute specifies arbitrary information about
the entity (using a URI); and,
o each "capability" element contains a specification as to the kinds
of content the entity is capable of receiving.
Each "capability" element contains arbitrary character data formatted according to the standard indicated in the element's "baseline" attribute.
The Presence Service
Section 5 contains the APEX service registration for the presence service:
o Within an administrative domain, the service is addressed using
the well-known endpoint of "apex=presence".
o Section 6 defines the syntax of the operations exchanged with the
service.
o A consumer of the service initiates communications by sending data
containing the subscribe, watch, or publish operation.
o In addition to replying to these operations, the service may also
initiate communications by sending data containing the terminate, publish, or notify operations.
An implementation of the service must maintain information about both presence entries and in-progress operations in persistent storage.
Consult Section 6.1.1 of [1] for a discussion on the properties of long-lived transaction-identifiers.
Use of XML and MIME
Section 4.1 of [1] describes how arbitrary MIME content is exchanged as a BEEP [2] payload. For example, to transmit:
<originator identity='[email protected]' />
<recipient identity='[email protected]' />
where "..." refers to: <reply code='250' transID='1' />
then the corresponding BEEP message might look like this:
C: MSG 1 1 . 42 1234 C: Content-Type: multipart/related; boundary="boundary"; C: start="<[email protected]>"; C: type="application/beep+xml" C: C: --boundary C: Content-Type: application/beep+xml C: Content-ID: <[email protected]> C: C: C: <originator identity='[email protected]' /> C: <recipient identity='[email protected]' /> C: C: --boundary C: Content-Type: application/beep+xml C: Content-ID: <[email protected]> C: C: <reply code='250' transID='1' /> C: --boundary-- C: END
or this:
C: MSG 1 1 . 42 1234 C: Content-Type: application/beep+xml C: C: C: <originator identity='[email protected]' /> C: <recipient identity='[email protected]' /> C: <data-content Name='Content'> C: <reply code='250' transID='1' /> C: </data-content> C: C: END
The Subscribe Operation
When an application wants to (periodically) receive the presence information associated with an endpoint, it sends a "subscribe" element to the service.
The "subscribe" element has a "publisher" attribute, a "duration" attribute, a "transID" attribute, and no content:
o the "publisher" attribute specifies the endpoint associated with
the presence entry;
o the "transID" attribute specifies the transaction-identifier
associated with this operation; and,
o the "duration" attribute specifies the maximum number of seconds
for which the originator is interested in receiving updated presence information.
When the service receives a "subscribe" element, we refer to the "publisher" attribute of that element as the "subject", and the service performs these steps:
1. If the subject is outside of this administrative domain, a "reply"
element having code 553 is sent to the originator.
2. If the subject does not refer to a valid endpoint, a "reply"
element having code 550 is sent to the originator.
3. If the subject's access entry does not contain a
"presence:subscribe" token for the originator, a "reply" element having code 537 is sent to the originator.
4. If the originator already has an in-progress subscribe operation
for the subject, then the previous subscribe operation is silently terminated, and processing continues.
5. If the "transID" attribute refers to an in-progress subscribe or
watch operation for the originator, a "reply" element having code 555 is sent to the originator.
6. Otherwise:
1. A "publish" element, corresponding to the subject's presence
entry, is immediately sent to the originator.
2. For each endpoint currently watching subscribers to the
subject's presence information, a "notify" element is
immediately as sent (c.f., Step 6.3 of Section 4.6).
3. For up to the amount of time indicated by the "duration"
attribute of the "subscribe" element, if the subject's presence
entry changes, an updated "presence" element is sent to the
originator using the publish operation (Section 4.4). Finally,
when the amount of time indicated by the "duration" attribute
expires, a terminate operation (Section 4.5) is sent to the
originator.
Note that if the duration is zero-valued, then the subscribe operation is making a one-time poll of the presence information. Accordingly, Step 6.3 above does not occur.
Regardless of whether a "publish" or "reply" element is sent to the originator, the "transID" attribute is identical to the value found in the "subscribe" element sent by the originator.
The Watch Operation
When an application wants to (periodically) receive notices about endpoints that are subscribed to receive presence entry, it sends a "watch" element to the service.
The "watch" element has a "publisher" attribute, a "duration" attribute, a "transID" attribute, and no content:
o the "publisher" attribute specifies the endpoint associated with
the presence entry;
o the "transID" attribute specifies the transaction-identifier
associated with this operation; and,
o the "duration" attribute specifies the maximum number of seconds
for which the originator is interested in watching subscribers.
When the service receives a "watch" element, we refer to the "publisher" attribute of that element as the "subject", and the service performs these steps:
1. If the subject is outside of this administrative domain, a "reply"
element having code 553 is sent to the originator.
2. If the subject does not refer to a valid endpoint, a "reply"
element having code 550 is sent to the originator.
3. If the subject's access entry does not contain a "presence:watch"
token for the originator, a "reply" element having code 537 is sent to the originator.
4. If the originator already has an in-progress watch operation for
the subject, then the previous watch operation is silently terminated, and processing continues.
5. If the "transID" attribute refers to an in-progress subscribe or
watch operation for the originator, a "reply" element having code 555 is sent to the originator.
6. Otherwise:
1. A "reply" element having code 250 is sent to the originator.
2. For each endpoint currently subscribing to the subject's
presence information, a "notify" element is immediately sent to
the originator (c.f., Section 4.6).
3. For up to the amount of time indicated by the "duration"
attribute of the "watch" element, whenever a subscribe
operation succeeds or a subscription is terminated, a "notify"
element is sent to the originator. Finally, when the amount of
time indicated by the "duration" attribute expires, a terminate
operation (Section 4.5) is sent to the originator.
Note that if the duration is zero-valued, then the watch operation is making a one-time poll of the presence information. Accordingly, Step 6.3 above does not occur.
Regardless of whether a "notify" or "reply" element is sent to the originator, the "transID" attribute is identical to the value found in the "presence" element sent by the originator.
The Publish Operation
When an application wants to modify the presence entry associated with an endpoint, it sends a "publish" element to the service. In addition, the service sends a "publish" element to endpoints that have subscribed to see presence information (c.f., Section 4.2).
The "publish" element has a "publisher" attribute, a "transID" attribute, a "timeStamp" attribute, and contains a "presence" element:
o the "publisher" attribute specifies the endpoint to be associated
with the presence entry;
o the "transID" attribute specifies the transaction-identifier
associated with this operation;
o the "timeStamp" attribute specifies the application's notion of
the current date and time; and,
o the "presence" element contains the desired presence entry for the
endpoint.
When the service sends a "publish" element, the "transID" attribute specifies the transaction-identifier associated with the subscribe operation that caused this "publish" element to be sent, and the "timeStamp" attribute specifies the service's notion of the current date and time. No reply is sent by the receiving endpoint.
When the service receives a "publish" element, we refer to the "publisher" attribute of that element as the "subject", and the service performs these steps:
1. If the "publisher" attribute of the "publish" element doesn't
match the "publisher" attribute of the "presence" element contained in the "publish" element, a "reply" element having code 503 is sent to the originator.
2. If the subject is outside of this administrative domain, a "reply"
element having code 553 is sent to the originator.
3. If the subject does not refer to a valid endpoint, a "reply"
element having code 550 is sent to the originator.
4. If the subject's access entry does not contain a
"presence:publish" token for the originator, a "reply" element having code 537 is sent to the originator.
5. If the "lastUpdate" attribute of the "publish" element is not
semantically identical to the "lastUpdate" attribute of the subject's presence entry, a "reply" element having code 555 is sent to the originator. (This allows a simple mechanism for atomic updates.)
6. Otherwise:
1. The subject's presence entry is updated from the "publish"
element.
2. The "lastUpdate" attribute of the presence entry is set to the
service's notion of the current date and time.
3. A "reply" element having code 250 is sent to the originator.
When sending the "reply" element, the "transID" attribute is identical to the value found in the "publish" element sent by the originator.
The Terminate Operation
When an application no longer wishes to subscribe to presence information or to watch endpoints that are subscribed to receive presence information, it sends a "terminate" element to the service; similarly, when the service no longer considers an application to be subscribing or watching, a "terminate" element is sent to the application.
The "terminate" element contains only a "transID" attribute that specifies the transaction-identifier associated an in-progress subscribe or watch operation. Section 9.1 of [1] defines the syntax for the "terminate" element.
When the service receives a "terminate" element, it performs these steps:
1. If the transaction-identifier does not refer to a previous
subscribe or watch operation for the originator, an "error" element having code 550 is returned.
2. Otherwise, the previous subscribe or watch operation for the
originator is terminated, and a "reply" element having code 250 is sent to the originator.
Note that following a terminate operation, the originator may receive further presence or watcher updates. Although the service will send no further updates after processing a terminate operation and sending the reply operation, earlier updates may be in transit.
The Notify Operation
The service sends a "notify" element to endpoints that are watching other endpoints subscribed to presence information (c.f., Section 4.3).
The "notify" element has a "subscriber" attribute, a "transID" attribute, a "duration" attribute, an "action" attribute, and no content:
o the "subscriber" attribute specifies the endpoint that is
subscribed to presence information; and,
o the "transID" attribute specifies the transaction-identifier
associated with the watch operation that caused this "notify" element to be sent;
o the "action" attribute specifies whether a subscription or its
termination has occurred; and,
o if a subscription is being reported, the "duration" attribute
specifies the requested duration of the subscription.
No reply is sent by the receiving endpoint.
The Reply Operation
While processing operations, the service may respond with a "reply" element. Consult Sections 10.2 and 6.1.2 of [1], respectively, for the definition and an exposition of the syntax of the reply element.
Registration: The Presence Service
Well-Known Endpoint: apex=presence
Syntax of Messages Exchanged: c.f., Section 6
Sequence of Messages Exchanged: c.f., Section 4
Access Control Tokens: presence:subscribe, presence:watch,
presence:publish
Contact Information: c.f., the "Authors' Addresses" section of this
memo
The Presence Service DTD
<!ENTITY % APEXCORE PUBLIC "-//IETF//DTD APEX CORE//EN" ""> %APEXCORE;
<!ELEMENT subscribe EMPTY>
<!ATTLIST subscribe
publisher %ENDPOINT; #REQUIRED
transID %UNIQID; #REQUIRED
duration %SECONDS; #REQUIRED>
<!ELEMENT watch EMPTY> <!ATTLIST watch
publisher %ENDPOINT; #REQUIRED
transID %UNIQID; #REQUIRED
duration %SECONDS; #REQUIRED>
<!ELEMENT publish (presence)> <!ATTLIST publish
publisher %ENDPOINT; #REQUIRED
transID %UNIQID; #REQUIRED
timeStamp %TIMESTAMP; #REQUIRED>
<!ELEMENT notify EMPTY> <!ATTLIST notify
subscriber %ENDPOINT; #REQUIRED
transID %UNIQID; #REQUIRED
duration %SECONDS; "0"
action (subscribe|terminate)
"subscribe">
<!ELEMENT presence (tuple+)> <!ATTLIST presence
publisher %ENDPOINT; #REQUIRED
lastUpdate %TIMESTAMP; #REQUIRED
publisherInfo
%URI; "">
<!ELEMENT tuple (capability*)> <!ATTLIST tuple
destination %URI; #REQUIRED
availableUntil
%TIMESTAMP; #REQUIRED
tupleInfo %URI; "">
<!ELEMENT capability (#PCDATA)> <!ATTLIST capability
baseline %URI #REQUIRED>
Security Considerations
Consult [1]'s Section 11 for a discussion of security issues.
In addition, timestamps issued by the the presence service may disclose location information. If this information is considered sensitive, the special timezone value "-00:00" may be used (after converting the local time accordingly).
References
[1] Rose, M., Klyne, G. and D. Crocker, "The Application Exchange
Core", RFC 3340, July 2002.
[2] Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC
3080, March 2001.
[3] Rose, M., Klyne, G. and D. Crocker, "The Application Exchange
(APEX) Access Service", RFC 3341, July 2002.
Acknowledgements
The authors gratefully acknowledge the contributions of: Neil Cook, Eric Dixon, Darren New, Scott Pead, and Bob Wyman.
Authors' Addresses
Marshall T. Rose Dover Beach Consulting, Inc. POB 255268 Sacramento, CA 95865-5268 US
Phone: +1 916 483 8878 EMail: [email protected]
Graham Klyne Nine by Nine
EMail: [email protected]
David H. Crocker Brandenburg InternetWorking 675 Spruce Drive Sunnyvale, CA 94086 US
Phone: +1 408 246 8253 EMail: [email protected] URI: http://www.brandenburg.com/
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