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Network Working Group Request for Comments: 3342 Category: Standards Track |
G. Klyne Clearswift Corporation M. Rose Dover Beach Consulting, Inc. M. Schwartz Code On The Road, LLC E. Dixon H. Franklin J. Kint D. New S. Pead July 2002 |
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The Internet Society (2002). All Rights Reserved.
Application Exchange (APEX), at its core, provides a best-effort application-layer datagram service. Options are used to alter the semantics of the core service. This memo defines various options to change the default behavior of APEX's "relaying mesh".
1. The attachOverride Option
2. The dataTiming Option
2.1 Upper-Bounds on Delivery
2.1.1 Final Hop Report
2.1.2 Timing Error Report
2.2 Reporting on Delayed Delivery
2.2.1 Transient Timing Report
3. The hold4Endpoint Option
4. The dataHopping Option
5. Initial Registrations
5.1 Registration: The attachOverride Option
5.2 Registration: The dataTiming Option
5.3 Registration: The hold4Endpoint Option
5.4 Registration: The dataHopping Option
6. The APEX Party Pack DTD
7. Security Considerations
References
A. Acknowledgements
B. IANA Considerations
Authors' Addresses
Full Copyright Statement
Section 5.1 contains the APEX option registration for the "attachOverride" option.
The default behavior of the APEX relaying mesh, in the absence of processing options, is to allow at most one application to attach as a particular endpoint, on a "first come, first served" basis. The "attachOverride" option provides gives preference to the current application trying to attach.
If this option is present in the "attach" operation (c.f., Section 4.4.1 of [1]) and if any application is already attached as the specified endpoint, that endpoint has its attachment terminated (c.f., Section 4.4.3 of [1]) concurrently with processing of that "attach" operation. The "code" attribute of the resulting "terminate" operation is set to 556.
Note that any data being expected by the previously-attached application may instead be delivered to the last application to successfully attach. Accordingly, applications should take care to properly deal with incoming data having unrecognized transaction- identifiers (c.f., Section 6.1.1 of [1]).
This option provides for a new attachment to automatically terminate any existing attachment for the same endpoint. For example, this might be helpful when a new attachment is required from a different device while a previously-used device is still attached e.g.,
+-------+ +-------+
| | -- attach -----> | |
| appl. | | relay |
| #1 | <--------- ok -- | |
+-------+ +-------+
C: <attach endpoint='fred@example.com' transID='1' />
S: <ok />
... some time later appl #2 starts on a different computer ...
+-------+ +-------+
| | <----- attach -- | |
+-------+ | | | appl. |
| | <-- terminate -- | relay | -- ok ---------> | #2 |
| appl. | | | +-------+
| #1 | -- ok ---------> | |
+-------+ +-------+
C: <attach endpoint='fred@example.com' transID='2'>
<option internal='attachOverride' transID='3' />
</attach>
S: <ok />
C: <terminate transID='1' code='556'>overriden</terminate>
S: <ok />
Section 5.2 contains the APEX option registration for the "dataTiming" option. This option contains a "dataTiming" element (c.f., Section 6).
The default behavior of the APEX relaying mesh is "immediate, best effort", and expects that all relays and endpoints are able to process and transfer data without delay -- in the absence of processing options, if a relay is unavailable, then data is silently dropped. The "dataTiming" option provides for controlled queuing delays in processing, whilst providing reasonable deterministic behavior for the originator.
There are two types of delays addressed by the "dataTiming" option:
Accordingly, the "dataTiming" option allows for:
This option does not provide any functionality with respect to the priority of the data. Nor does this option have any effect on other parts of the relaying process.
Further, note that because this option is processed on a per-hop basis, the originator must set the "targetHop" attribute to the value "all" and the "mustUnderstand" attribute to the value "true".
The "noLaterThan" attribute of the "dataTiming" option provides for control over delays that may occur in transit through the relaying mesh or to the recipient endpoint.
If this option is present in the "data" operation (c.f., Section 4.4.4 of [1]) and the value of the "noLaterThan" attribute is non- zero, then:
Immediately prior to sending the data to the next relay, the value of the "noLaterThan" attribute is adjusted to reflect the processing time of the data at the local relay (e.g., the time required to determine the next relay, to successfully issue a "bind" operation, and then be ready to immediately issue a "data" operation).
If the value of the "noLaterThan" attribute becomes less than or equal to zero, an error in processing has occurred, the data element is not sent to the next relay, and if the "reportErrors" attribute is true, the APEX report service is invoked to send a timing error report.
If the relay does not receive an "ok" element from the recipient endpoint within the number of milli-seconds indicated by the value of the "noLaterThan" attribute, an error in processing has occurred, and if the "reportErrors" attribute is true, the APEX report service is invoked to send a timing error report.
Otherwise, if the data is successfully transmitted to the recipient, and the "returnTrip" attribute is non-zero, the APEX report service is invoked to send a final hop report.
Note that in some cases, a relay may be able to predict this outcome without actually connecting to the next relay; if so, a timing error report may be sent without connecting to the next relay.
If the APEX report service (c.f., Section 6.2 of [1]) is invoked to send a final hop report, it issues a data operation with:
For example:
+-------+ +-------+
| | -- data -------> | |
| relay | | appl. |
| | <--------- ok -- | #2 |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='86'>
<dataTiming noLaterThan='10000' returnTrip='20000' />
</option>
</data>
S: <ok />
+-------+ +-------+
| | <------- data -- | |
| appl. | | relay |
| #1 | -- ok ---------> | |
+-------+ +-------+
C: <data content='#Content'>
<originator identity='apex=report@example.com' />
<recipient identity='fred@example.com' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='99'>
<dataTiming noLaterThan='20000' />
</option>
<data-content Name='Content'>
<statusResponse transID='86'>
<destination identity='barney@example.com'>
<reply code='250' />
</destination>
</statusResponse>
</data-content>
</data>
S: <ok />
If the APEX report service (c.f., Section 6.2 of [1]) is invoked to send a timing error report, it issues a data operation with:
For example:
+-------+ +-------+
| | -- data -------> | |
| appl. | | relay |
| | <--------- ok -- | |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='86'>
<dataTiming noLaterThan='6000' reportErrors='true' />
</option>
</data>
S: <ok />
... some time later ...
+-------+ +-------+
| | <------- data -- | |
| appl. | | relay |
| | -- ok ---------> | |
+-------+ +-------+
C: <data content='#Content'>
<originator identity='apex=report@example.com' />
<recipient identity='fred@example.com' />
<data-content Name='Content'>
<statusResponse transID='86'>
<destination identity='barney@example.com'>
<reply code='550' />
</destination>
</statusResponse>
</data-content>
</data>
S: <ok />
The "reportAfter" attribute of the "dataTiming" option provides for the originator to be notified if delivery is delayed beyond a specified time. Delivery of the data is not affected. Note that if the value of the "noLaterThan" attribute is non-zero, then it provides the operational upper-bounds for the "reportAfter" attribute.
If this option is present in the "data" operation (c.f., Section 4.4.4 of [1]) and the value of the "reportAfter" attribute is non- zero, then:
Immediately prior to sending the data to the next relay, the value of the "reportAfter" attribute is adjusted to reflect the processing time of the data at the local relay (e.g., the time required to determine the next relay, to successfully issue a "bind" operation, and then be ready to immediately issue a "data" operation).
If the value of the "reportAfter" attribute becomes less than or equal to zero, then its value is set to zero and the APEX report service is invoked to send a transient timing report; regardless, the data element is sent to the next relay.
If the relay does not receive an "ok" element from the recipient endpoint within the number of milli-seconds indicated by the value of the "reportAfter" attribute, then its value is set to zero and the APEX report service is invoked to send a transient timing report.
If the APEX report service (c.f., Section 6.2 of [1]) is invoked to send a transient timing report, it issues a data operation with:
For example:
+-------+ +-------+
| | -- data -------> | |
| appl. | | relay |
| #1 | <--------- ok -- | |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='86'>
<dataTiming reportAfter='60000' />
</option>
</data>
S: <ok />
... some time later ...
+-------+ +-------+
| | <------- data -- | |
| relay | | relay |
| #n-1 | -- ok ---------> | #n |
+-------+ +-------+
C: <data content='#Content'>
<originator identity='apex=report@example.com' />
<recipient identity='fred@example.com' />
<data-content Name='Content'>
<statusResponse transID='86'>
<destination identity='barney@example.com'>
<reply code='350' />
</destination>
</statusResponse>
</data-content>
</data>
S: <ok />
Section 5.3 contains the APEX option registration for the "hold4Endpoint" option.
The default behavior of the APEX relaying mesh, in the absence of processing options, is to silently drop data for a recipient if its endpoint isn't attached. The "hold4Endpoint" option provides for data to be queued if the recipient endpoint is not attached.
If this option is present in the "data" operation (c.f., Section 4.4.4 of [1]), and the value of the "hold4Endpoint" attribute is true then:
If the recipient's endpoint is not currently attached, the relay will queue the data waiting for an application to attach as that endpoint.
Note that in the absence of an upper-bounds on delivery, such as limits provided by the dataTiming option (Section 2), the data will be queued indefinitely for the endpoint.
For example:
+-------+ +-------+
| | -- data -------> | |
| appl. | | relay |
| #1 | <--------- ok -- | |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='hold4Endpoint' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='86'>
<dataTiming noLaterThan='60000' />
</option>
</data>
S: <ok />
... some time later the recipient's endpoint attaches ...
+-------+ +-------+
| | <----- attach -- | |
| | | |
| | -- ok ---------> | |
| relay | | appl. |
| | -- data -------> | #2 |
| | | |
| | <--------- ok -- | |
+-------+ +-------+
C: <attach endpoint='barney@example.com' transID='2'>
<option internal='attachOverride' transID='3' />
</attach>
S: <ok />
C: <data content='cid:1@example.com'>
<originator identity='fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='hold4Endpoint' />
<option internal='dataTiming' targetHop='all'
mustUnderstand='true' transID='86'>
<dataTiming noLaterThan='18000' />
</option>
</data>
S: <ok />
To detect misconfigurations that cause forwarding loops in the APEX relaying mesh, the APEX pubsub service re-introduces a mechanism similar to the IP TTL [2] mechanism, in the form of an APEX option. Section 5.4 contains the APEX option registration for the "dataHopping" option.
If this option is present in the "data" operation (c.f., Section 4.4.4 of [1]) and the value of the "noMoreThan" attribute is non- zero, then:
Immediately prior to sending the data to the next relay, the value of the "noMoreThan" attribute is reduced by 1.
If the value of the "noMoreThan" attribute becomes less than or equal to zero, an error in processing has occurred, the data element is not sent to the next relay, and if the "reportErrors" attribute is true, the APEX report service is invoked to send an error report.
Further, note that because this option is processed on a per-hop basis, the originator must set the "targetHop" attribute to the value "all" and the "mustUnderstand" attribute to the value "true".
If the APEX report service (c.f., Section 6.2 of [1]) is invoked to send an error report, it issues a data operation with:
For example:
+-------+ +-------+
| | -- data -------> | |
| appl. | | relay |
| | <--------- ok -- | #1 |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='appl=pubsub/topic=fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='dataHopping' targetHop='all'
mustUnderstand='true' transID='86'>
<dataHopping noMoreThan='2' reportErrors='true' />
</option>
</data>
S: <ok />
+-------+ +-------+
| | -- data -------> | |
| relay | | relay |
| #1 | <--------- ok -- | #2 |
+-------+ +-------+
C: <data content='cid:1@example.com'>
<originator identity='appl=pubsub/topic=fred@example.com' />
<recipient identity='barney@example.com' />
<option internal='dataHopping' targetHop='all'
mustUnderstand='true' transID='86'>
<dataHopping noMoreThan='1' reportErrors='true' />
</option>
</data>
S: <ok />
relay #2 determines that further relaying is necessary:
+-------+ +-------+
| | <------- data -- | |
| relay | | relay |
| #1 | -- ok ---------> | #2 |
+-------+ +-------+
C: <data content='#Content'>
<originator identity='apex=report@example.com' />
<recipient identity='appl=pubsub/topic=fred@example.com' />
<data-content Name='Content'>
<statusResponse transID='86'>
<destination identity='barney@example.com'>
<reply code='550' />
</destination>
</statusResponse>
</data-content>
</data>
S: <ok />
The APEX option registration template is defined in Section 7.1 of [1].
Option Identification: attachOverride
Present in: APEX's "attach" element
Contains: nothing
Processing Rules: c.f., Section 1
Contact Information: c.f., the "Authors' Addresses" section of this memo
Option Identification: dataTiming
Present in: APEX's "data" element
Contains: dataTiming (c.f., Section 6)
Processing Rules: c.f., Section 2
Contact Information: c.f., the "Authors' Addresses" section of this memo
Option Identification: hold4Endpoint
Present in: APEX's "data" element
Contains: nothing
Processing Rules: c.f., Section 3
Contact Information: c.f., the "Authors' Addresses" section of this memo
Option Identification: dataHopping
Present in: APEX's "data" element
Contains: dataHopping (c.f., Section 6)
Processing Rules: c.f., Section 4
Contact Information: c.f., the "Authors' Addresses" section of this memo
<!--
DTD for the APEX option party pack, as of 2001-05-14
Refer to this DTD as:
<!ENTITY % APEXPARTY PUBLIC "-//IETF//DTD APEX PARTY//EN" "">
%APEXPARTY;
-->
<!ENTITY % APEXCORE PUBLIC "-//IETF//DTD APEX CORE//EN"
%APEXCORE;
<!--
DTD data types:
entity syntax/reference example
====== ================ =======
hopcount
HOPS 0..255 17
milli-seconds
MILLISECS 0..2147483647 60000
-->
<!ENTITY % HOPS "CDATA">
<!ENTITY % MILLISECS
"CDATA">
<!ELEMENT dataHopping EMPTY>
<!ATTLIST dataHopping
noMoreThan %HOPS; "0"
reportErrors
(true|false) "false">
<!ELEMENT dataTiming EMPTY>
<!ATTLIST dataTiming
noLaterThan %MILLISECS; "0"
returnTrip %MILLISECS; "0"
reportAfter %MILLISECS; "0"
reportErrors
(true|false) "false">
Consult [1]'s Section 11 for a discussion of security issues.
In addition:
[1] Rose, M., Klyne, G. and D. Crocker, "The Application Exchange
Core", RFC 3340, July 2002.
[2] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[3] Newman, D., "Deliver By SMTP Service Extension", RFC 2852, June
2000.
The authors gratefully acknowledge the contributions of Chris Newman and Bob Wyman. Further, the dataTiming option is similar in function to "Deliver By" SMTP service extension defined by Dan Newman in [3].
The IANA completed the registrations specified in Section 5.
Graham Klyne
Clearswift Corporation
1310 Waterside
Arlington Business Park
Theale, Reading RG7 4SA
UK
Phone: +44 11 8903 8903
EMail: Graham.Klyne@MIMEsweeper.com
Marshall T. Rose
Dover Beach Consulting, Inc.
POB 255268
Sacramento, CA 95865-5268
US
Phone: +1 916 483 8878
EMail: mrose@dbc.mtview.ca.us
Michael F. Schwartz
Code On The Road, LLC
EMail: schwartz@CodeOnTheRoad.com
URI: http://www.CodeOnTheRoad.com
Eric Dixon
EMail: edixon@myrealbox.com
Huston Franklin
EMail: huston@franklin.ro
Jay Kint
EMail: d20@icosahedron.org
Darren New
5390 Caminito Exquisito
San Diego, CA 92130
US
Phone: +1 858 350 9733
EMail: dnew@san.rr.com
Scott Pead
EMail: spead@fiber.net
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