[Docs] [txt|pdf] [draft-ietf-sieve-...] [Diff1] [Diff2]

PROPOSED STANDARD

Network Working Group                                     P. Saint-Andre
Request for Comments: 5437                                         Cisco
Category: Standards Track                                    A. Melnikov
                                                           Isode Limited
                                                            January 2009


                     Sieve Notification Mechanism:
           Extensible Messaging and Presence Protocol (XMPP)

Status of This Memo

   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 Notice

   Copyright (c) 2009 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.

Abstract

   This document describes a profile of the Sieve extension for
   notifications, to allow notifications to be sent over the Extensible
   Messaging and Presence Protocol (XMPP), also known as Jabber.

















Saint-Andre & Melnikov      Standards Track                     [Page 1]

RFC 5437               Sieve Notify Method: XMPP            January 2009


Table of Contents

   1. Introduction ....................................................3
      1.1. Overview ...................................................3
      1.2. Terminology ................................................3
   2. Definition ......................................................3
      2.1. Notify Parameter "method" ..................................3
      2.2. Test notify_method_capability ..............................3
      2.3. Notify Tag ":from" .........................................4
      2.4. Notify Tag ":importance" ...................................4
      2.5. Notify Tag ":message" ......................................4
      2.6. Notify Tag ":options" ......................................4
      2.7. XMPP Syntax ................................................4
   3. Examples ........................................................6
      3.1. Basic Action ...............................................6
      3.2. Action with "body" .........................................7
      3.3. Action with "body", ":importance", ":message", and
           "subject" ..................................................7
      3.4. Action with ":from", ":message", ":importance",
           "body", and "subject" ......................................8
   4. Requirements Conformance ........................................9
   5. Internationalization Considerations ............................10
   6. Security Considerations ........................................11
   7. IANA Considerations ............................................12
   8. References .....................................................12
      8.1. Normative References ......................................12
      8.2. Informative References ....................................13
























Saint-Andre & Melnikov      Standards Track                     [Page 2]

RFC 5437               Sieve Notify Method: XMPP            January 2009


1.  Introduction

1.1.  Overview

   The [NOTIFY] extension to the [SIEVE] mail filtering language is a
   framework for providing notifications by employing URIs to specify
   the notification mechanism.  This document defines how xmpp URIs (see
   [XMPP-URI]) are used to generate notifications via the Extensible
   Messaging and Presence Protocol [XMPP], which is widely implemented
   in Jabber instant messaging technologies.

1.2.  Terminology

   This document inherits terminology from [NOTIFY], [SIEVE], and
   [XMPP].  In particular, the terms "parameter" and "tag" are used as
   described in [NOTIFY] to refer to aspects of Sieve scripts, and the
   term "key" is used as described in [XMPP-URI] to refer to aspects of
   an XMPP URI.

   The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
   interpreted as described in [TERMS].

2.  Definition

2.1.  Notify Parameter "method"

   The "method" parameter MUST be a URI that conforms to the xmpp URI
   scheme (as specified in [XMPP-URI]) and that identifies an XMPP
   account associated with the email inbox.  The URI MAY include the
   resource identifier of an XMPP address and/or the query component
   portion of an XMPP URI, but SHOULD NOT include an authority component
   or fragment identifier component.  The processing application MUST
   extract an XMPP address from the URI in accordance with the
   processing rules specified in [XMPP-URI].  The resulting XMPP address
   MUST be encapsulated in XMPP syntax as the value of the XMPP 'to'
   attribute.

2.2.  Test notify_method_capability

   In response to a notify_method_capability test for the "online"
   notification-capability, an implementation SHOULD return a value of
   "yes" if it has knowledge of an active presence session (see
   [XMPP-IM]) for the specified XMPP notification-uri; otherwise, it
   SHOULD return a value of "maybe" (since typical XMPP systems may not
   allow a Sieve engine to gain knowledge about the presence of XMPP
   entities).



Saint-Andre & Melnikov      Standards Track                     [Page 3]

RFC 5437               Sieve Notify Method: XMPP            January 2009


2.3.  Notify Tag ":from"

   If included, the ":from" tag MUST be an electronic address that
   conforms to the "Mailbox" rule defined in [RFC5321].  The value of
   the ":from" tag MAY be included in the human-readable XML character
   data of the XMPP notification; alternatively or in addition, it MAY
   be transformed into formal XMPP syntax, in which case it MUST be
   encapsulated as the value of an XMPP SHIM (Stanza Headers and
   Internet Metadata) [SHIM] header named "Resent-From".

2.4.  Notify Tag ":importance"

   The ":importance" tag has no special meaning for this notification
   mechanism, and this specification puts no restriction on its use.
   The value of the ":importance" tag MAY be transformed into XMPP
   syntax (in addition to or instead of including appropriate text in
   the XML character data of the XMPP <body/> element); if so, it SHOULD
   be encapsulated as the value of an XMPP SHIM (Stanza Headers and
   Internet Metadata) [SHIM] header named "Urgency", where the XML
   character of that header is "high" if the value of the ":importance"
   tag is "1", "medium" if the value of the ":importance" tag is "2",
   and "low" if the value of the ":importance" tag is "3".

2.5.  Notify Tag ":message"

   If the ":message" tag is included, that string MUST be transformed
   into the XML character data of an XMPP <body/> element (where the
   string is generated according to the guidelines specified in Section
   3.6 of [NOTIFY]).

2.6.  Notify Tag ":options"

   The ":options" tag has no special meaning for this notification
   mechanism.  Any handling of this tag is the responsibility of an
   implementation.

2.7.  XMPP Syntax

   The xmpp mechanism results in the sending of an XMPP message to
   notify a recipient about an email message.  The general XMPP syntax
   is as follows:

   o  The notification MUST be an XMPP <message/> stanza.








Saint-Andre & Melnikov      Standards Track                     [Page 4]

RFC 5437               Sieve Notify Method: XMPP            January 2009


   o  The value of the XMPP 'from' attribute SHOULD be the XMPP address
      of the notification service associated with the Sieve engine or
      the XMPP address of the entity to be notified.  The value of the
      XMPP 'from' attribute MUST NOT be generated from the Sieve ":from"
      tag.

   o  The value of the XMPP 'to' attribute MUST be the XMPP address
      specified in the XMPP URI contained in the "method" notify
      parameter.

   o  The value of the XMPP 'type' attribute MUST be 'headline' or
      'normal'.

   o  The XMPP <message/> stanza MUST include a <body/> child element.
      If the ":message" tag is included in the Sieve script, that string
      MUST be used as the XML character data of the <body/> element.  If
      not and if the XMPP URI contained in the "method" notify parameter
      specified a "body" key in the query component, that value SHOULD
      be used.  Otherwise, the XML character data SHOULD be some
      configurable text indicating that the message is a Sieve
      notification.

   o  The XMPP <message/> stanza MAY include a <subject/> child element.
      If the XMPP URI contained in the "method" notify parameter
      specified a "subject" key in the query component, that value
      SHOULD be used as the XML character data of the <subject/>
      element.  Otherwise, the XML character data SHOULD be some
      configurable text indicating that the message is a Sieve
      notification.

   o  The XMPP <message/> stanza SHOULD include a URI, for the recipient
      to use as a hint in locating the message, encapsulated as the XML
      character data of a <url/> child element of an <x/> element
      qualified by the 'jabber:x:oob' namespace, as specified in [OOB].
      If included, the URI SHOULD be an Internet Message Access Protocol
      [IMAP] URL that specifies the location of the message, as defined
      in [IMAP-URL], but MAY be another URI type that can specify or
      hint at the location of an email message, such as a URI for an
      HTTP resource [HTTP] or a Post Office Protocol Version 3 (POP3)
      mailbox [POP-URL] at which the message can be accessed.  It is not
      expected that an XMPP user agent shall directly handle such a URI,
      but instead that it shall invoke an appropriate helper application
      to handle the URI.

   o  The XMPP <message/> stanza MAY include an XMPP SHIM (Stanza
      Headers and Internet Metadata) [SHIM] header named "Resent-From".
      If the Sieve script included a ":from" tag, the "Resent-From"




Saint-Andre & Melnikov      Standards Track                     [Page 5]

RFC 5437               Sieve Notify Method: XMPP            January 2009


      value MUST be the value of the ":from" tag; otherwise, the
      "Resent-From" value SHOULD be the envelope recipient address of
      the original email message that triggered the notification.

3.  Examples

   In the following examples, the sender of the email has an address of
   <mailto:juliet@example.org>, the entity to be notified has an email
   address of <mailto:romeo@example.com> and an XMPP address of
   romeo@im.example.com (resulting in an XMPP URI of
   <xmpp:romeo@im.example.com>), and the notification service associated
   with the Sieve engine has an XMPP address of notify.example.com.

   Note: In the following examples, line breaks are included in XMPP
   URIs solely for the purpose of readability.

3.1.  Basic Action

   The following is a basic Sieve notify action with only a method.  The
   XML character data of the XMPP <body/> and <subject/> elements are
   therefore generated by the Sieve engine based on configuration.  In
   addition, the Sieve engine includes a URI pointing to the message.

   Basic action (Sieve syntax)

     notify "xmpp:romeo@im.example.com"

   The resulting XMPP <message/> stanza might be as follows:

   Basic action (XMPP syntax)

     <message from='notify.example.com'
              to='romeo@im.example.com'
              type='headline'
              xml:lang='en'>
       <subject>SIEVE</subject>
       <body>&lt;juliet@example.com&gt; You got mail.</body>
       <x xmlns='jabber:x:oob'>
         <url>
           imap://romeo@example.com/INBOX;UIDVALIDITY=385759043/;UID=18
         </url>
       </x>
     </message>








Saint-Andre & Melnikov      Standards Track                     [Page 6]

RFC 5437               Sieve Notify Method: XMPP            January 2009


3.2.  Action with "body"

   The following action contains a "body" key in the query component of
   the XMPP URI but no ":message" tag in the Sieve script.  As a result,
   the XML character data of the XMPP <body/> element in the XMPP
   notification is taken from the XMPP URI.  In addition, the Sieve
   engine includes a URI pointing to the message.

   Action with "body" (Sieve syntax)

     notify "xmpp:romeo@im.example.com?message
              ;body=Wherefore%20art%20thou%3F"

   The resulting XMPP <message/> stanza might be as follows.

   Action with "body" (XMPP syntax)

     <message from='notify.example.com'
              to='romeo@im.example.com'
              type='headline'
              xml:lang='en'>
       <subject>SIEVE</subject>
       <body>Wherefore art thou?</body>
       <x xmlns='jabber:x:oob'>
         <url>
           imap://romeo@example.com/INBOX;UIDVALIDITY=385759044/;UID=19
         </url>
       </x>
     </message>

3.3.  Action with "body", ":importance", ":message", and "subject"

   The following action specifies an ":importance" tag and a ":message"
   tag in the Sieve script, as well as a "body" key and a "subject" key
   in the query component of the XMPP URI.  As a result, the ":message"
   tag from the Sieve script overrides the "body" key from the XMPP URI
   when generating the XML character data of the XMPP <body/> element.
   In addition, the Sieve engine includes a URI pointing to the message.

   Action with "body", ":importance", ":message", and "subject" (Sieve
   syntax)

     notify :importance "1"
            :message "Contact Juliet immediately!"
            "xmpp:romeo@im.example.com?message
              ;body=You%27re%20in%20trouble
              ;subject=ALERT%21"




Saint-Andre & Melnikov      Standards Track                     [Page 7]

RFC 5437               Sieve Notify Method: XMPP            January 2009


   The resulting XMPP <message/> stanza might be as follows.

   Action with "body", ":importance", ":message", and "subject" (XMPP
   syntax)

     <message from='notify.example.com'
              to='romeo@im.example.com'
              type='headline'
              xml:lang='en'>
       <subject>ALERT!</subject>
       <body>Contact Juliet immediately!</body>
       <headers xmlns='http://jabber.org/protocol/shim'>
         <header name='Urgency'>high</header>
       </headers>
       <x xmlns='jabber:x:oob'>
         <url>
           imap://romeo@example.com/INBOX;UIDVALIDITY=385759045/;UID=20
         </url>
       </x>
     </message>

3.4.  Action with ":from", ":message", ":importance", "body", and
      "subject"

   The following action specifies a ":from" tag, an ":importance" tag,
   and a ":message" tag in the Sieve script, as well as a "body" key and
   a "subject" key in the query component of the XMPP URI.  As a result,
   the ":message" tag from the Sieve script overrides the "body" key
   from the XMPP URI when generating the XML character data of the XMPP
   <body/> element.  In addition, the Sieve engine includes a URI
   pointing to the message, as well as an XMPP SHIM (Stanza Headers and
   Internet Metadata) [SHIM] header named "Resent-From" (which
   encapsulates the value of the ":from" tag).

   Action with ":from", ":importance", ":message", "body", and "subject"
   (Sieve syntax)

     notify :from "romeo.my.romeo@example.com"
            :importance "1"
            :message "Contact Juliet immediately!"
            "xmpp:romeo@im.example.com?message
              ;body=You%27re%20in%20trouble
              ;subject=ALERT%21"

   The resulting XMPP <message/> stanza might be as follows.






Saint-Andre & Melnikov      Standards Track                     [Page 8]

RFC 5437               Sieve Notify Method: XMPP            January 2009


   Action with ":from", ":importance", ":message", "body", and "subject"
   (XMPP syntax)

     <message from='notify.example.com'
              to='romeo@im.example.com'
              type='headline'
              xml:lang='en'>
       <subject>ALERT!</subject>
       <body>Contact Juliet immediately!</body>
       <headers xmlns='http://jabber.org/protocol/shim'>
         <header name='Resent-From'>romeo.my.romeo@example.com</header>
         <header name='Urgency'>high</header>
       </headers>
       <x xmlns='jabber:x:oob'>
         <url>
           imap://romeo@example.com/INBOX;UIDVALIDITY=385759045/;UID=21
         </url>
       </x>
     </message>

4.  Requirements Conformance

   Section 3.8 of [NOTIFY] specifies a set of requirements for Sieve
   notification methods.  The conformance of the xmpp notification
   mechanism is provided here.

   1.   An implementation of the xmpp notification method SHOULD NOT
        modify the final notification text (e.g., to limit the length);
        however, a given deployment MAY do so (e.g., if recipients pay
        per character or byte for XMPP messages).  Modification of
        characters themselves should not be necessary, since XMPP
        character data is encoded in [UTF-8].

   2.   An implementation MAY ignore parameters specified in the
        ":from", ":importance", and ":options" tags.

   3.   There is no recommended default message for an implementation to
        include if the ":message" tag is not specified.

   4.   A notification sent via the xmpp notification method MAY include
        a timestamp in the textual message.

   5.   The value of the XMPP 'from' attribute MUST be the XMPP address
        of the notification service associated with the Sieve engine.
        The value of the Sieve ":from" tag MAY be transformed into the
        value of an XMPP SHIM (Stanza Headers and Internet Metadata)
        [SHIM] header named "Resent-From".




Saint-Andre & Melnikov      Standards Track                     [Page 9]

RFC 5437               Sieve Notify Method: XMPP            January 2009


   6.   The value of the XMPP 'to' attribute MUST be the XMPP address
        specified in the XMPP URI contained in the "method" parameter.

   7.   In accordance with [XMPP-URI], an implementation MUST ignore any
        URI action or key it does not understand (i.e., the URI MUST be
        processed as if the action or key were not present).  It is
        RECOMMENDED to support the XMPP "message" query type (see
        [QUERIES]) and the associated "body" and "subject" keys, which
        SHOULD be mapped to the XMPP <body/> and <subject/> child
        elements of the XMPP <message/> stanza, respectively.  However,
        if included, then the Sieve notify ":message" tag MUST be mapped
        to the XMPP <body/> element, overriding the "body" key (if any)
        included in the XMPP URI.

   8.   An implementation MUST NOT include any other extraneous
        information not specified in parameters to the notify action.

   9.   In response to a notify_method_capability test for the "online"
        notification-capability, an implementation SHOULD return a value
        of "yes" if it has knowledge of an active presence session (see
        [XMPP-IM]) for the specified XMPP notification-uri, but only if
        the entity that requested the test is authorized to know the
        presence of the associated XMPP entity (e.g., via explicit
        presence subscription as specified in [XMPP-IM]); otherwise, it
        SHOULD return a value of "maybe" (since typical XMPP systems may
        not allow a Sieve engine to gain knowledge about the presence of
        XMPP entities).

   10.  An implementation SHOULD NOT attempt to retry delivery of a
        notification if it receives an XMPP error of type "auth" or
        "cancel", MAY attempt to retry delivery if it receives an XMPP
        error of type "wait", and MAY attempt to retry delivery if it
        receives an XMPP error of "modify", but only if it makes
        appropriate modifications to the notification (see [XMPP]); in
        any case, the number of retries SHOULD be limited to a
        configurable number no less than 3 and no more than 10.  An
        implementation MAY throttle notifications if the number of
        notifications within a given time period becomes excessive
        according to local service policy.  Duplicate suppression (if
        any) is a matter of implementation and is not specified herein.

5.  Internationalization Considerations

   Although an XMPP address may contain nearly any [UNICODE] character,
   the value of the "method" parameter MUST be a Uniform Resource
   Identifier (see [URI]) rather than an Internationalized Resource
   Identifier (see [IRI]).  The rules specified in [XMPP-URI] MUST be
   followed when generating XMPP URIs.



Saint-Andre & Melnikov      Standards Track                    [Page 10]

RFC 5437               Sieve Notify Method: XMPP            January 2009


   In accordance with Section 13 of RFC 3920, all data sent over XMPP
   MUST be encoded in [UTF-8].

6.  Security Considerations

   Depending on the information included, sending a notification can be
   comparable to forwarding mail to the notification recipient.  Care
   must be taken when forwarding mail automatically, to ensure that
   confidential information is not sent into an insecure environment.
   In particular, implementations MUST conform to the security
   considerations given in [NOTIFY], [SIEVE], and [XMPP].

   [NOTIFY] specifies that a notification method MUST provide mechanisms
   for avoiding notification loops.  One type of notification loop can
   be caused by message forwarding; however, such loops are prevented
   because XMPP does not support the forwarding of messages from one
   XMPP address to another.  Another type of notification loop can be
   caused by auto-replies to XMPP messages received by the XMPP
   notification service associated with the Sieve engine; therefore,
   such a service MUST NOT auto-reply to XMPP messages it receives.

   A common use case might be for a user to create a script that enables
   the Sieve engine to act differently if the user is currently
   available at a particular type of service (e.g., send notifications
   to the user's XMPP address if the user has an active session at an
   XMPP service).  Whether the user is currently available can be
   determined by means of a notify_method_capability test for the
   "online" notification-capability.  In XMPP, information about current
   network availability is called "presence" (see also [MODEL]).  Since
   [XMPP-IM] requires that a user must approve a presence subscription
   before an entity can gain access to the user's presence information,
   a limited but reasonably safe implementation might be for the Sieve
   engine to request a subscription to the user's presence.  The user
   would then need to approve that subscription request so that the
   Sieve engine can act appropriately depending on whether the user is
   online or offline.  However, the Sieve engine MUST NOT use the user's
   presence information when processing scripts on behalf of a script
   owner other than the user, unless the Sieve engine has explicit
   knowledge (e.g., via integration with an XMPP server's presence
   authorization rules) that the script owner is authorized to know the
   user's presence.  While it would be possible to design a more
   advanced approach to the delegation of presence authorization, any
   such approach is left to future standards work.








Saint-Andre & Melnikov      Standards Track                    [Page 11]

RFC 5437               Sieve Notify Method: XMPP            January 2009


7.  IANA Considerations

   The following template provides the IANA registration of the Sieve
   notification mechanism specified in this document:

     To: iana@iana.org
     Subject: Registration of new Sieve notification mechanism
     Mechanism name: xmpp
     Mechanism URI: RFC 5122 [XMPP-URI]
     Mechanism-specific options: none
     Permanent and readily available reference: RFC 5437
     Person and email address to contact for further information:
          Peter Saint-Andre <registrar@xmpp.org>

   This information has been added to the list of Sieve notification
   mechanisms maintained at <http://www.iana.org>.

8.  References

8.1.  Normative References

   [NOTIFY]    Melnikov, A., Ed., Leiba, B., Ed., Segmuller, W., and T.
               Martin, "Sieve Email Filtering: Extension for
               Notifications", RFC 5435, January 2009.

   [OOB]       Saint-Andre, P., "Out of Band Data", XSF XEP 0066,
               August 2006.

   [QUERIES]   Saint-Andre, P., "XMPP URI Scheme Query Components", XSF
               XEP 0147, September 2006.

   [RFC5321]   Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
               October 2008.

   [SHIM]      Saint-Andre, P. and J. Hildebrand, "Stanza Headers and
               Internet Metadata", XSF XEP 0131, July 2006.

   [SIEVE]     Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email
               Filtering Language", RFC 5228, January 2008.

   [TERMS]     Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [XMPP-URI]  Saint-Andre, P., "Internationalized Resource Identifiers
               (IRIs) and Uniform Resource Identifiers (URIs) for the
               Extensible Messaging and Presence Protocol (XMPP)",
               RFC 5122, February 2008.




Saint-Andre & Melnikov      Standards Track                    [Page 12]

RFC 5437               Sieve Notify Method: XMPP            January 2009


8.2.  Informative References

   [HTTP]      Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
               Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
               Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [IMAP]      Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
               4rev1", RFC 3501, March 2003.

   [IMAP-URL]  Melnikov, A. and C. Newman, "IMAP URL Scheme", RFC 5092,
               November 2007.

   [IRI]       Duerst, M. and M. Suignard, "Internationalized Resource
               Identifiers (IRIs)", RFC 3987, January 2005.

   [MODEL]     Day, M., Rosenberg, J., and H. Sugano, "A Model for
               Presence and Instant Messaging", RFC 2778, February 2000.

   [POP-URL]   Gellens, R., "POP URL Scheme", RFC 2384, August 1998.

   [UNICODE]   The Unicode Consortium, "The Unicode Standard, Version
               3.2.0", 2000.

               The Unicode Standard, Version 3.2.0 is defined by The
               Unicode Standard, Version 3.0 (Reading, MA, Addison-
               Wesley, 2000.  ISBN 0-201-61633-5), as amended by the
               Unicode Standard Annex #27: Unicode 3.1
               (http://www.unicode.org/reports/tr27/) and by the Unicode
               Standard Annex #28: Unicode 3.2
               (http://www.unicode.org/reports/tr28/).

   [URI]       Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
               Resource Identifier (URI): Generic Syntax", STD 66,
               RFC 3986, January 2005.

   [UTF-8]     Yergeau, F., "UTF-8, a transformation format of ISO
               10646", STD 63, RFC 3629, November 2003.

   [XMPP]      Saint-Andre, P., "Extensible Messaging and Presence
               Protocol (XMPP): Core", RFC 3920, October 2004.

   [XMPP-IM]   Saint-Andre, P., "Extensible Messaging and Presence
               Protocol (XMPP): Instant Messaging and Presence",
               RFC 3921, October 2004.







Saint-Andre & Melnikov      Standards Track                    [Page 13]

RFC 5437               Sieve Notify Method: XMPP            January 2009


Authors' Addresses

   Peter Saint-Andre
   Cisco

   EMail: psaintan@cisco.com


   Alexey Melnikov
   Isode Limited

   EMail: Alexey.Melnikov@isode.com







































Saint-Andre & Melnikov      Standards Track                    [Page 14]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/