mirror of
https://github.com/moparisthebest/xeps
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1050 lines
97 KiB
XML
1050 lines
97 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM 'xep.ent'>
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>In-Band Real Time Text</title>
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<abstract>This is a specification for real-time text transmitted in-band over an XMPP session.</abstract>
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&LEGALNOTICE;
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<number>0301</number>
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<status>Experimental</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<approver>Council</approver>
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<dependencies>
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<spec>XMPP Core</spec>
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<spec>XEP-0020</spec>
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</dependencies>
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<supersedes/>
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||
<supersededby/>
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||
<shortname>NOT_YET_ASSIGNED</shortname>
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||
<author>
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||
<firstname>Mark</firstname>
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<surname>Rejhon</surname>
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<email>mark@realjabber.org</email>
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<jid>markybox@gmail.com</jid>
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<uri>http://www.realjabber.org</uri>
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||
</author>
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||
<revision>
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||
<version>0.7</version>
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||
<date>2012-08-08</date>
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||
<initials>MDR</initials>
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||
<remark><p>Simplifications and grammatical corrections. Some sections (1, 6.2, 6.4) shortened with simpler language.</p></remark>
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||
</revision>
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||
<revision>
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||
<version>0.6</version>
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||
<date>2012-07-28</date>
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||
<initials>MDR</initials>
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||
<remark><p>Changes and improvements in preparation for advance to Draft. Unified
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<e/> element (Erase Text) to handle all possible text deletions.
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Clarify the Unicode terminology used in this specification, and move
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section 4.5.4 downwards to section 4.7 to improve reading
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order.</p></remark>
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</revision>
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||
<revision>
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||
<version>0.5</version>
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||
<date>2012-07-22</date>
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||
<initials>MDR</initials>
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||
<remark><p>Minor corrections and clarifications.</p></remark>
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||
</revision>
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||
<revision>
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||
<version>0.4</version>
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||
<date>2012-07-20</date>
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||
<initials>MDR</initials>
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||
<remark><p>Spelling, grammar, and clarification edits, including section clarifications recommended from public discussion. Interop with XEP-0308 message correction.</p></remark>
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</revision>
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||
<revision>
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||
<version>0.3</version>
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||
<date>2012-06-07</date>
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||
<initials>MDR</initials>
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||
<remark><p>Edits recommended from public discussion.</p></remark>
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||
</revision>
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||
<revision>
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||
<version>0.2</version>
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||
<date>2012-03-18</date>
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||
<initials>MDR</initials>
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||
<remark><p>Lots of edits. Simplifications, improvements and corrections. Forward and backward compatible with version 0.1.</p></remark>
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||
</revision>
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<revision>
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||
<version>0.1</version>
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||
<date>2011-06-29</date>
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<initials>psa</initials>
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||
<remark><p>Initial published version.</p></remark>
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||
</revision>
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||
<revision>
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||
<version>0.0.3</version>
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||
<date>2011-06-25</date>
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||
<initials>MDR</initials>
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||
<remark><p>Third draft, recommended edits.</p></remark>
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</revision>
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||
<revision>
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<version>0.0.2</version>
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||
<date>2011-06-15</date>
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<initials>MDR</initials>
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<remark><p>Second draft.</p></remark>
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</revision>
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<revision>
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||
<version>0.0.1</version>
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||
<date>2011-02-21</date>
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||
<initials>MDR</initials>
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||
<remark><p>First draft.</p></remark>
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||
</revision>
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</header>
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||
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||
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<section1 topic="Introduction" anchor="introduction">
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<p>This document defines a specification for real-time text transmitted in-band over an XMPP network.</p>
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<p><strong>Real-time text is text transmitted instantly while it is being typed or created.</strong> The recipient can immediately read the sender's text as it is written, without waiting. Text can be used conversationally, similar to a telephone conversation, where one listens while the other is speaking. It eliminates waiting times found in messaging. Real-time text has been around for decades in various implementations:</p>
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<ul>
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<li>The 'talk' command on UNIX systems since the 1970's.</li>
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<li>TTY and text telephones.</li>
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<li>For SIP, real-time text is sent using <span class="ref"><strong><link url="http://tools.ietf.org/html/rfc4103">IETF RFC 4103</link></strong></span> <note>RFC 4103: RTP Payload for Text Conversation. <<link url="http://tools.ietf.org/html/rfc4103">http://tools.ietf.org/html/rfc4103</link>>.</note> with <span class="ref"><strong><link url="http://www.itu.int/rec/T-REC-T.140">ITU-T T.140</link></strong></span> <note>ITU-T T.140: Protocol for multimedia application text conversation. <<link url="http://www.itu.int/rec/T-REC-T.140">http://www.itu.int/rec/T-REC-T.140</link>>.</note> presentation coding.</li>
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<li>The <span class="ref"><strong><link url="http://help.aol.com/help/microsites/microsite.do?cmd=displayKC&externalId=223568">Real-Time IM</link></strong></span> <note>AOL AIM Real Time Text: <<link url="http://help.aol.com/help/microsites/microsite.do?cmd=displayKC&externalId=223568">http://help.aol.com/help/microsites/microsite.do?cmd=displayKC&externalId=223568</link>>.</note> feature found in AOL Instant Messenger.</li>
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<li>A component within Total Conversation, used by <span class="ref"><strong><link url="http://www.reach112.eu">Reach112</link></strong></span> <note>Reach112: European emergency service with real-time text. <<link url="http://www.reach112.eu">http://www.reach112.eu</link>>.</note> in Europe, an accessible emergency service with real-time text.</li>
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</ul>
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<p>Real-time text allows continuous and rapid communication in text, to complement general-purpose instant messaging. It can also allow immediate conversation in situations where speech cannot be used (e.g. quiet environments, privacy, deaf and hard of hearing). Real-time text is also beneficial in emergency situations, due to its immediacy. For a visual animation of real-time text, see <span class="ref"><strong><link url="http://www.realtimetext.org">Real-Time Text Taskforce</link></strong></span>
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<note>Real-Time Text Taskforce, a foundation for real-time text standardization <<link url="http://www.realtimetext.org">http://www.realtimetext.org</link>>.</note>.</p>
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</section1>
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<section1 topic="Requirements" anchor="requirements">
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<section2 topic="Fluid Real-Time Text" anchor="fluid_realtime_text">
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<ol>
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<li>Allow transmission of real-time text with a low latency.</li>
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<li>Balance low latencies versus system, network and server limitations.</li>
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<li>Support message editing in real-time, including text insertions and deletions.</li>
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<li>Support transmission and reproduction of the original intervals between key presses, to preserve look-and-feel of typing independently of transmission intervals.</li>
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</ol>
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</section2>
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<section2 topic="In-Band Transmission" anchor="inband_transmission">
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<ol>
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<li>Reliable real-time text delivery.</li>
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<li>Be backwards compatible with XMPP clients that do not support real-time text.</li>
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<li>Minimize reliance on network traversal mechanisms and/or out-of-band transmission protocols.</li>
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<li>Compatible with multi-user chat (MUC) and simultaneous logins.</li>
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</ol>
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</section2>
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<section2 topic="Flexible and Interoperable" anchor="flexible_and_interoperable">
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<ol>
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<li>Allow use within existing instant-messaging user interfaces, with minimal UI modifications.</li>
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<li>Allow alternate optional presentations of real-time text, including split screen and/or other layouts.</li>
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<li>Protocol design ensures integrity of real-time text, and allows extensions for new features.</li>
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<li>Allow use within gateways to interoperate with other real-time text protocols, including RFC 4103 and ITU-T T.140.</li>
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</ol>
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</section2>
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<section2 topic="Accessible" anchor="accessible">
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<ol>
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<li>Allow XMPP to follow the <span class="ref"><strong><link url="http://www.itu.int/rec/T-REC-F.703">ITU-T Rec. F.703</link></strong></span> <note>ITU-T Rec. F.703: Multimedia conversational services. <<link url="http://www.itu.int/rec/T-REC-F.703">http://www.itu.int/rec/T-REC-F.703</link>>.</note> Total Conversation standard for simultaneous voice, video, and real-time text.</li>
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<li>Be a candidate technology for use with next generation emergency services (e.g. 9-1-1 and 1-1-2).</li>
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<li>Be suitable for transcription services and (when coupled with voice at user's choice) for TTY/text telephone alternatives, relay services, and captioned telephone systems.</li>
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<li>Allow immediate conversational text through mobile phone text messaging and mainstream instant messaging.</li>
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</ol>
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</section2>
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</section1>
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<section1 topic="Glossary" anchor="glossary">
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<p><strong>action element</strong> – An XML element that represents a single real-time message edit, such as text insertion or deletion.</p>
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<p><strong>character</strong> - A single Unicode code point. See <link url="#unicode_character_counting">Unicode Character Counting</link>.</p>
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<p><strong>real-time</strong> – A conversational latency of less than 1 second, as defined by <span class="ref"><strong><link url="http://www.itu.int/rec/T-REC-F.700">ITU-T Rec. F.700</link></strong></span> <note>ITU-T Rec. F.700: Framework Recommendation for multimedia services <<link url="http://www.itu.int/rec/T-REC-F.700">http://www.itu.int/rec/T-REC-F.700</link>>.</note>, section 2.1.2.1.</p>
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<p><strong>real-time text</strong> – Text transmitted instantly while it is being typed or created.</p>
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<p><strong>real-time message</strong> – Recipient's real-time view of the sender's message still being typed or created.</p>
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<p><strong>RTT</strong> – Acronym for real-time text.</p>
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</section1>
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<section1 topic="Protocol" anchor="protocol">
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<section2 topic="RTT Element" anchor="rtt_element">
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<p>Real-time text is transmitted via an <rtt/> child element of a <message/> stanza. The <rtt/> element is transmitted at regular intervals by the sender client while a message is being composed, to allow the recipient to see the latest message text from the sender, without waiting for the full message sent in a <body/> element.</p>
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<p>This is a basic example of a <em><strong>real-time message</strong></em> "Hello, my Juliet!” transmitted in real-time while it is being typed, before a final message delivery in a <body/> element (to remain <link url="#backwards_compatible">Backwards Compatible</link>):</p>
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<p><strong>Example 1: Introductory Example</strong></p>
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<p><code><![CDATA[<message to='juliet@capulet.lit' from='romeo@montague.lit/orchard' type='chat' id='a01'>
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<rtt xmlns='urn:xmpp:rtt:0' seq='0' event='new'>
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<t>Hello, </t>
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</rtt>
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</message>
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<message to='juliet@capulet.lit' from='romeo@montague.lit/orchard' type='chat' id='a02'>
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<rtt xmlns='urn:xmpp:rtt:0' seq='1'>
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<t>my </t>
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</rtt>
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</message>
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<message to='juliet@capulet.lit' from='romeo@montague.lit/orchard' type='chat' id='a03'>
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<rtt xmlns='urn:xmpp:rtt:0' seq='2'>
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<t>Juliet!</t>
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</rtt>
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</message>
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<message to='juliet@capulet.lit' from='romeo@montague.lit/orchard' type='chat' id='a04'>
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<body>Hello, my Juliet!</body>
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</message>]]></code></p>
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<p>The <rtt/> element contains a series of one or more child elements called <em><strong>action elements</strong></em> that represent <link url="#realtime_text_actions">Real-Time Text Actions</link> such as text being appended, inserted, or deleted. Example 1 illustrates only the <t/> action element, which appends text to the end of a message.</p>
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<p>Transmission of the <rtt/> element occurs at a regular <link url="#transmission_interval">Transmission Interval</link> whenever the sender is actively composing a message. If there are no changes to the message since the last transmission, no transmission occurs.</p>
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<p>There MUST NOT be more than one <rtt/> element per <message/> stanza.</p>
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<p>The namespace of the <rtt/> element is “urn:xmpp:rtt:0”.</p>
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</section2>
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<section2 topic="RTT Attributes" anchor="rtt_attributes">
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<section3 topic="seq" anchor="seq">
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<p>This REQUIRED attribute is a counter to maintain the integrity of real-time text. (The bounds of <strong>seq</strong> is 31-bits, the range of positive values of a signed integer.)</p>
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<p>Senders MUST increment the <strong>seq</strong> attribute by 1 in each subsequent <rtt/> transmitted without an <link url="#event">event</link> attribute. When an <rtt/> element has an <link url="#event">event</link> attribute, senders MAY instead use any value as the new starting value for <strong>seq</strong>. A random starting <strong>seq</strong> value is RECOMMENDED for best integrity during <link url="#usage_with_multiuser_chat_and_simultaneous_logins">Usage with Multi-User Chat and Simultaneous Logins</link>. Senders SHOULD limit the size of the new starting <strong>seq</strong> value, to keep <rtt/> compact while allowing plenty of incrementing room, and prevent wraparound from ever happening.</p>
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<p>Recipients MUST monitor the <strong>seq</strong> value to verify the integrity of real-time text. See <link url="#keeping_realtime_text_synchronized">Keeping Real-Time Text Synchronized</link>.</p>
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</section3>
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<section3 topic="event" anchor="event">
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<p>This attribute signals events for real-time text, such as the start of a new real-time message. Recipient clients MUST ignore <rtt/> containing unsupported <strong>event</strong> values. The use of <rtt/> elements without an <strong>event</strong> attribute is for transmitting changes to an existing real-time message. The <strong>event</strong> attribute is used in the situations specified below:</p>
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<table>
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<tr>
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<th>event</th>
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<th>Description</th>
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<th>Sender Support</th>
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<th>Recipient Support</th>
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</tr>
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<tr>
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<td>new</td>
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<td>Begin a new real-time message.</td>
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<td><strong>REQUIRED</strong></td>
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<td><strong>REQUIRED</strong></td>
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</tr>
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<tr>
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<td>reset</td>
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<td>Reset the current real-time message.</td>
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<td>RECOMMENDED</td>
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<td><strong>REQUIRED</strong></td>
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</tr>
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<tr>
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<td>init</td>
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<td>Signals the start of real-time text.</td>
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<td>OPTIONAL</td>
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<td>RECOMMENDED</td>
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</tr>
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<tr>
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<td>cancel</td>
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<td>Signals the end of real-time text.</td>
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<td>OPTIONAL</td>
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<td>RECOMMENDED</td>
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</tr>
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</table>
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<p><strong>event='new'</strong><br />
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Senders MUST use this value when transmitting the first <rtt/> element containing <link url="#action_elements">Action Elements</link> (i.e. when sending the first character(s) of a new message). Recipient clients MUST initialize a new real-time message for display, and then process action elements within the <rtt/> element. If a real-time message already exists, from the same sender in the same chat session, its content MUST be replaced (i.e. cleared prior to processing action elements). Senders MAY send subsequent <rtt/> elements that do not contain an <strong>event</strong> attribute.</p>
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<p><strong>event='reset'</strong><br />
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For recipients, both <strong>'new'</strong> and <strong>'reset'</strong> are logically identical, and differ only for implementation purposes (e.g. highlighting newly-started messages). Recipient clients MUST initialize a new real-time message for display, and then process action elements within the <rtt/> element. If a real-time message already exists, from the same sender in the same chat session, its content MUST be replaced (i.e. cleared prior to processing action elements). Senders MAY send subsequent <rtt/> elements that do not contain an <strong>event</strong> attribute. Recipients MUST be able to process <strong>'reset'</strong> without first receiving <strong>'new'</strong>. See <link url="#message_reset">Message Reset</link>, used for <link url="#keeping_realtime_text_synchronized">Keeping Real-Time Text Synchronized</link> and <link url="#basic_realtime_text">Basic Real-Time Text</link>.</p>
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<p><strong>event='init'</strong><br />
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Clients MAY use this value to signal the other end that real-time text is being activated. It can be used to signal activation of real-time text before starting a new real-time message (since it may take a while before the sender starts composing). If used, this <rtt/> element MUST be empty with no action elements. See <link url="#activating_and_deactivating_realtime_text">Activating and Deactivating Real-Time Text</link>.</p>
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<p><strong>event='cancel'</strong><br />
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Clients MAY use this value to signal the other end to stop transmitting real-time text. If used, this <rtt/> element MUST be empty with no action elements. Recipients SHOULD discontinue sending back <rtt/> elements for the remainder of the same chat session (or unless <strong>'init'</strong> is used again). See <link url="#activating_and_deactivating_realtime_text">Activating and Deactivating Real-Time Text</link>.</p>
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||
</section3>
|
||
<section3 topic="id" anchor="id">
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||
<p>This attribute is used only if &xep0308; (XEP-0308) is implemented at the same time as this specification. If a client supports both XEP-0301 and XEP-0308, clients MUST use this attribute if real-time text is used during editing of the previously delivered message.</p>
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||
<p>This <strong>id</strong> attribute refers to the <message/> stanza containing the <body/> that is being edited (See 'Business Rules' in XEP-0308). When used, <strong>id</strong> MUST be included in all <rtt/> elements transmitted during message correction of the previous message. The whole message MUST be retransmitted via <rtt event='reset'/> (<link url="#message_reset">Message Reset</link>) when beginning to edit the previous message, or when switching between messages (e.g. editing the new partially-composed message versus editing of the previously delivered message).</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Body Element" anchor="body_element">
|
||
<p>The real-time message is considered complete upon receipt of a <body/> element in a <message/> stanza. The delivered text in the <body/> element is considered the final message text, and supersedes the real-time message. In the ideal case, the text from the <body/> element is redundant since this delivered text is identical to the final contents of the real-time message.</p>
|
||
<p>Senders MAY transmit the <body/> element in the same or separate message stanza as the one containing the <rtt/> element. Senders MUST include an <link url="#event">event</link> attribute in the next <rtt/> element that is transmitted after a message stanza containing a <body/> element.</p>
|
||
<section3 topic="Backwards Compatible" anchor="backwards_compatible">
|
||
<p>The real-time text standard simply provides early delivery of text before the <body/> element. The <body/> element continues to follow the &xmppcore; specification. In particular, XMPP implementations need to ignore XML elements they do not understand. Clients, that do not support real-time text, will continue to behave normally, displaying complete lines of messages as they are delivered.</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Transmission Interval" anchor="transmission_interval">
|
||
<p>For the best balance between interoperability and usability, the default transmission interval of <rtt/> elements for a continuously-changing message SHOULD be approximately <strong>0.7 seconds</strong>. This interval meets ITU-T Rec. F.700 Section A.3.2.1 for good quality real-time conversation. If a different transmission interval needs to be used, the interval SHOULD be <strong>between 0.3 seconds and 1 second</strong>.</p>
|
||
<p>A longer interval will lead to a less optimal user experience in most network conditions. Conversely, a much shorter interval can lead to <link url="#congestion_considerations">Congestion Considerations</link>. To provide fluid real-time text, one or more of the following methods can be used:</p>
|
||
<ul>
|
||
<li><link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> for natural typing display, independently of the transmission interval.</li>
|
||
<li>Use of <link url="#time_critical_and_low_latency_methods">Time Critical and Low Latency Methods</link>, for real-time captioning/transcription.</li>
|
||
<li>For other options or reduced-precision options, see <link url="#lowbandwidth_and_lowprecision_text_smoothing">Low-Bandwidth and Low-Precision Text Smoothing</link>.</li>
|
||
</ul>
|
||
</section2>
|
||
<section2 topic="Real-Time Text Actions" anchor="realtime_text_actions">
|
||
<p>The <rtt/> element MAY contain one or more <em><strong>action elements</strong></em> representing real-time text operations, including text being appended, inserted, or deleted.</p>
|
||
<p>Many chat clients allow a sender to edit their message before sending (via a Send button, or pressing Enter). The inclusion of real-time text functionality, in existing client software, needs to preserve the sender's existing expectation of being able to edit their messages. In a chat session with real-time text, the recipient can see the sender compose and edit their message before it is completed.</p>
|
||
<section3 topic="Action Elements" anchor="action_elements">
|
||
<p>This is a short summary of action elements that operate on a real-time message. These elements are kept compact in order to save bandwidth, since a single <rtt/> element can contain a huge number of action elements (e.g. during <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>). For detailed information, see <link url="#list_of_action_elements">List of Action Elements</link>.</p>
|
||
<table>
|
||
<tr>
|
||
<th>Action</th>
|
||
<th>Element</th>
|
||
<th>Description</th>
|
||
<th>Sender Support</th>
|
||
<th>Recipient Support</th>
|
||
</tr>
|
||
<tr>
|
||
<td>Insert Text</td>
|
||
<td><t p='#'>text</t></td>
|
||
<td>Insert specified <em><strong>text</strong></em> at position <em><strong>p</strong></em> in message.</td>
|
||
<td><strong>REQUIRED</strong></td>
|
||
<td><strong>REQUIRED</strong></td>
|
||
</tr>
|
||
<tr>
|
||
<td>Erase Text</td>
|
||
<td><e p='#' n='#'/></td>
|
||
<td>Remove <em><strong>n</strong></em> characters before position <em><strong>p</strong></em> in message<em>.</em></td>
|
||
<td>RECOMMENDED</td>
|
||
<td><strong>REQUIRED</strong></td>
|
||
</tr>
|
||
<tr>
|
||
<td>Wait Interval</td>
|
||
<td><w n='#'/></td>
|
||
<td>Wait <em><strong>n</strong></em> milliseconds.</td>
|
||
<td>RECOMMENDED</td>
|
||
<td>RECOMMENDED</td>
|
||
</tr>
|
||
</table>
|
||
</section3>
|
||
<section3 topic="Attribute Values" anchor="attribute_values">
|
||
<ul>
|
||
<li><p>For <link url="#element_e_erase_text">Element <e/> – Erase Text</link>:<br />
|
||
The <em><strong>n</strong></em> attribute is a length value, in number of characters. If <em><strong>n</strong></em> is omitted, the default value of <em><strong>n</strong></em> MUST be 1.</p></li>
|
||
<li><p>For <link url="#element_t_insert_text">Element <t/> – Insert Text</link> and <link url="#element_e_erase_text">Element <e/> – Erase Text</link>:<br />
|
||
The <em><strong>p</strong></em> attribute is an absolute position value, as a character position index into the real-time message, where 0 represents the beginning of the message. If <em><strong>p</strong></em> is omitted, the default value of <em><strong>p</strong></em> MUST point to the end of the message (i.e. <em><strong>p</strong></em> is set to the current length of the real-time message).</p></li>
|
||
<li><p>For the purpose of this specification, the word "character" represents a single Unicode code point. See <link url="#unicode_character_counting">Unicode Character Counting</link>.</p></li>
|
||
<li><p>Senders MUST NOT use negative values for any attribute, nor use <em><strong>p</strong></em> values beyond the current message length. However, recipients receiving such values MUST clip negative values to 0, and clip excessively high <em><strong>p</strong></em> values to the current length of the real-time message. Modifications only occur within the boundaries of the current real-time message.</p></li>
|
||
</ul>
|
||
</section3>
|
||
<section3 topic="List of Action Elements" anchor="list_of_action_elements">
|
||
<p>Recipients MUST be able to process all <t/> and <e/> action elements for incoming <rtt/> transmissions, even if senders do not use all of these for outgoing <rtt/> transmissions (e.g. <link url="#basic_realtime_text">Basic Real-Time Text</link>). Support for <w/> is RECOMMENDED for both senders and recipients, in order to accommodate <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>. Recipients MUST ignore unexpected or unsupported elements within <rtt/>, while continuing to process subsequent action elements (Compatibility is ensured via <link url="#namespace_versioning">Namespace Versioning</link>). Action elements are immediate child elements of the <rtt/> element, and are never nested. See examples in <link url="#use_cases">Use Cases</link>.</p>
|
||
<section4 topic="Element <t/> – Insert Text" anchor="element_t_insert_text">
|
||
<p>Supports the transmission of text, including key presses, and text block inserts.<br />
|
||
<em>Note: Text can be any</em> <em>subset of text allowed in the <body/> element of a <message/>. If <t/> is empty, no text modification takes place.</em></p>
|
||
<p><code><![CDATA[<t>text</t>]]></code></p>
|
||
<p>Append specified <em><strong>text</strong></em> at the end of message. (<em><strong>p</strong></em> defaults to message length).<br />
|
||
<em>Note: This action element is the minimum sender support REQUIRED for <link url="#basic_realtime_text">Basic Real-Time Text</link>.</em></p>
|
||
<p><code><![CDATA[<t p='#'>text</t>]]></code></p>
|
||
<p>Inserts specified <em><strong>text</strong></em> at position <em><strong>p</strong></em> in the message text.</p>
|
||
|
||
|
||
|
||
</section4>
|
||
<section4 topic="Element <e/> – Erase Text" anchor="element_e_erase_text">
|
||
<p>Supports the behavior of backspace key presses. Text is removed towards beginning of the message. This element is also used for all delete operations, including the delete key, and text block deletes.<br />
|
||
<em>Note: Excess backspaces MUST be ignored. Thus, text is backspaced only to the beginning of the message, in situations where the value of p is excessively large.</em></p>
|
||
<p><code><![CDATA[<e/>]]></code></p>
|
||
<p>Remove 1 character from end of message. (<em><strong>n</strong></em> defaults to 1, and <em><strong>p</strong></em> defaults to message length)</p>
|
||
<p><code><![CDATA[<e p='#'/>]]></code></p>
|
||
<p>Remove 1 character before character position <em><strong>p</strong></em> in message. (<em><strong>n</strong></em> defaults to 1)</p>
|
||
<p><code><![CDATA[<e n='#'/>]]></code></p>
|
||
<p>Remove <em><strong>n</strong></em> characters from end of message. (<em><strong>p</strong></em> defaults to message length)</p>
|
||
<p><code><![CDATA[<e n='#' p='#'/>]]></code></p>
|
||
<p>Remove <em><strong>n</strong></em> characters before character position <em><strong>p</strong></em> in message.</p>
|
||
</section4>
|
||
<section4 topic="Element <w/> – Wait Interval" anchor="element_w_wait_interval">
|
||
<p>Allow for the transmission of intervals, between real-time text actions, to recreate the pauses between key presses. See <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>.</p>
|
||
<p><code><![CDATA[<w n='#'/>]]></code></p>
|
||
<p>Wait <em><strong>n</strong></em> milliseconds before processing the next action element. This pause MAY be approximate, and not necessarily be of millisecond precision. The <em><strong>n</strong></em> value SHOULD NOT exceed the <link url="#transmission_interval">Transmission Interval</link>. Also, if a <link url="#body_element">Body Element</link> arrives, pauses SHOULD be interrupted to prevent a delay in message delivery.</p>
|
||
</section4>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Keeping Real-Time Text Synchronized" anchor="keeping_realtime_text_synchronized">
|
||
<p>In a chat session, it is important that real-time text stays identical on both the sender and recipient ends. The loss of a single <rtt/> transmission could represent missing text or missing edits. Also, recipients can connect after the sender has already started composing a message. Recovery of in-progress real-time message via <link url="#message_reset">Message Reset</link> is useful in several situations:</p>
|
||
<ul>
|
||
<li>Resuming after connecting (e.g. wireless reception, recipient started or restarted software).</li>
|
||
<li>Resuming after recipient discarded <link url="#stale_messages">Stale Messages</link> (e.g. sender resumes composing hours later).</li>
|
||
<li>Resuming after lost message stanzas (e.g. <link url="#congestion_considerations">Congestion Considerations</link>).</li>
|
||
<li>During <link url="#simultaneous_logins">Simultaneous Logins</link> (e.g. switching systems, switching windows, simultaneous typing).</li>
|
||
<li>During <link url="#multiuser_chat">Multi-User Chat</link> (e.g. participants joining/leaving while other participants are composing).</li>
|
||
</ul>
|
||
<p>Recipient clients MUST keep track of separate real-time message per sender, including maintaining independent <link url="#seq">seq</link> values. For implementation simplicity, recipient clients MAY track incoming <rtt/> elements per bare JID. Conflicting <rtt/> elements, from separate <link url="#simultaneous_logins">Simultaneous Logins</link>, is handled via the remainder of this section. Alternatively, recipient clients MAY keep track of separate real-time messages per full JID and/or per <thread/>.</p>
|
||
<section3 topic="Staying In Sync" anchor="staying_in_sync">
|
||
<p>For <rtt/> elements that do not contain an <link url="#event">event</link> attribute:</p>
|
||
<ol>
|
||
<li>Senders MUST increment the <link url="#seq">seq</link> attribute in steps of 1, for consecutively transmitted <rtt/> elements.</li>
|
||
<li>Recipients MUST monitor the <link url="#seq">seq</link> attribute value of received <rtt/> elements, to verify that it is incrementing by 1.</li>
|
||
</ol>
|
||
</section3>
|
||
<section3 topic="Recovery From Loss of Sync" anchor="recovery_from_loss_of_sync">
|
||
<p>Loss of sync occurs if the <link url="#seq">seq</link> attribute do not increment by 1 as expected when <link url="#staying_in_sync">Staying In Sync</link>. In this case:</p>
|
||
<ul>
|
||
<li>Recipients MUST keep the pre-existing real-time message unchanged; and</li>
|
||
<li>Recipients MUST ignore action elements within the current and subsequent <rtt/> elements; and</li>
|
||
<li>An indication can be used to show the loss of sync (e.g. color coding, modified chat state message).</li>
|
||
</ul>
|
||
<p>Recovery occurs when the recipient receives the following:</p>
|
||
<ul>
|
||
<li>A <body/> element. The <link url="#body_element">Body Element</link> supersedes the real-time message.</li>
|
||
<li>An <rtt/> element containing an <link url="#event">event</link> attribute (e.g. new message, or <link url="#message_reset">Message Reset</link>).</li>
|
||
</ul>
|
||
</section3>
|
||
<section3 topic="Message Reset" anchor="message_reset">
|
||
<p>A message reset is a retransmission of the sender's partially composed text. The recipient can redisplay the real-time message as a result. It allows real-time text conversation to resume quickly, without waiting for senders to start a new message.</p>
|
||
<p>Retransmission SHOULD be done at an average interval of 10 seconds during active typing or composing. This interval is frequent enough to minimize user waiting time, while being infrequent enough to reduce bandwidth overhead. This interval MAY vary to a longer interval, in order to reduce average bandwidth (e.g. long messages, infrequent or minor message changes). For quicker recipient recovery, senders MAY adjust the timing of the message retransmissions to occur right after any of the following additional events: </p>
|
||
<ul>
|
||
<li>When the recipient starts sending messages from a different full JID (e.g. switched systems);</li>
|
||
<li>When the recipient sends a presence update (e.g. from offline to online);</li>
|
||
<li>When the sender resumes composing after an extended pause (e.g. recipient may have cleared <link url="#stale_messages">Stale Messages</link>);</li>
|
||
<li>When the conversation is unlocked (e.g. section 5.1 of &xmppim;);</li>
|
||
</ul>
|
||
<p>A message reset is done using the <rtt/> attribute <link url="#event">event</link> value of <strong>'reset'</strong> (see <link url="#rtt_attributes">RTT Attributes</link>).</p>
|
||
<p><code><![CDATA[<rtt event='reset' seq='#' xmlns='urn:xmpp:rtt:0'>
|
||
<t>This is a retransmission of the entire real-time message.</t>
|
||
</rtt>]]></code></p>
|
||
<p>Note: There are no restrictions on using multiple <link url="#action_elements">Action Elements</link> during a message reset (e.g. typing or backspacing occurring at the end of a retransmitted message).</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Accurate Processing of Action Elements" anchor="accurate_processing_of_action_elements">
|
||
<p>Real-time text is generated based on text normally allowed to be transmitted within the <body/> element.</p>
|
||
<p>Incorrectly generated <link url="#action_elements">Action Elements</link> and <link url="#attribute_values">Attribute Values</link> can lead to inconsistencies between the sender and recipient during real-time editing. The Unicode characters of the real-time text needs to make it transparently from the sender to the recipient, without unexpected modifications after sender pre-processing. This is the chain between the sender's creation of real-time text, to the recipient's processing of real-time text. Transparent transmission of Unicode characters is possible with sender pre-processing, as long as the transmission from the sender to the recipient remains standards-compliant, including compliant XML processors and compliant XMPP servers.</p>
|
||
<p>Any inconsistencies that occur during real-time message editing (e.g. non-compliant servers that modify messages, incorrect <link url="#unicode_character_counting">Unicode Character Counting</link>) will recover upon delivery of the <link url="#body_element">Body Element</link>, upon the next <link url="#message_reset">Message Reset</link>, and/or during <link url="#basic_realtime_text">Basic Real-Time Text</link>.</p>
|
||
<section3 topic="Unicode Character Counting" anchor="unicode_character_counting">
|
||
<p>For this specification, a "character" represents a single Unicode code point. This is the same definition used in section 1.1 of <span class="ref"><strong><link url="http://tools.ietf.org/html/rfc5198">IETF RFC 5198</link></strong></span> <note>RFC 5198: Unicode Format for Network Interchange. <<link url="http://tools.ietf.org/html/rfc5198">http://tools.ietf.org/html/rfc5198</link>>.</note>. For platform-independent interoperability of <link url="#action_elements">Action Elements</link>, calculations on <link url="#attribute_values">Attribute Values</link> (<em><strong>p</strong></em> and <em><strong>n</strong></em>) MUST be based on counts of Unicode code points.</p>
|
||
<p>Many platforms use different internal encodings (i.e. string formats) that are different from the transmission encoding (UTF-8). These factors need to be considered:</p>
|
||
<ul>
|
||
<li><p>Multiple Unicode code points (e.g. combining marks, accents) can form a combining character sequence.<br />
|
||
<em>Action elements operate on Unicode code points individually.</em></p></li>
|
||
<li><p>Unicode code points U+10000 through U+10FFFF are represented as a surrogate pair in some Unicode encodings (e.g. UTF-16).<br />
|
||
<em>Action elements operate on Unicode code points as a whole, not on separate components of a surrogate pair.</em></p></li>
|
||
<li><p>XMPP transmission uses UTF-8, which use a variable number of bytes per Unicode code point.<br /><em>Action elements operate on Unicode code points as a whole, not on separate bytes.</em></p></li>
|
||
</ul>
|
||
<p>Lengths and positions in <link url="#attribute_values">Attribute Values</link> are relative to the internal Unicode text of the real-time message, independently of the directionality of actual displayed text. As a result, any valid Unicode text direction can be used with real-time text (right-to-left, left-to-right, and bidirectional). One way for implementers to visualize this, is to simply visualize Unicode text as an array of individual code points, and treat <link url="#attribute_values">Attribute Values</link> as array indexes.</p>
|
||
</section3>
|
||
<section3 topic="Guidelines for Senders" anchor="guidelines_for_senders">
|
||
<p>Sender clients MUST generate real-time text (<link url="#action_elements">Action Elements</link> and <link url="#attribute_values">Attribute Values</link>) based on the plain text version of the sender's message with pre-processing completed. This is separate and concurrent to any displayed presentation of the same message (e.g. formatting, emoticon graphics, &xep0071;).</p>
|
||
<p>Pre-processing before generating real-time text, include Unicode normalization, conversion of emoticons graphics to text, removal of illegal characters, line-break conversion, and any other necessary text modifications. For Unicode normalization, sender clients SHOULD ensure the message is in Unicode Normalization Form C ("NFC"), specified by section 3 of RFC 5198, and within many other standards such as Canonical XML 1.0.</p>
|
||
<p>If Unicode combining character sequences (e.g. letter with multiple accents) are used for <link url="#element_t_insert_text">Element <t/> – Insert Text</link>, then complete combining character sequences SHOULD be sent. In situations where modifications are required to an existing combining character sequence (e.g. adding an additional accent), an <link url="#element_e_erase_text">Element <e/> – Erase Text</link> SHOULD be used to delete the existing combining character sequence, before transmitting a complete replacement sequence via the <t/> element. (However, recipients SHOULD NOT assume this behavior from sending clients. See <link url="#guidelines_for_recipients">Guidelines for Recipients</link>).</p>
|
||
<p>For the purpose of calculating <link url="#attribute_values">Attribute Values</link>, any line breaks MUST be treated as a single character. Conversion of line breaks into a single LINE FEED U+000A is REQUIRED for XML processors, according to section 2.11 of <span class="ref"><strong><link url="http://www.w3.org/TR/xml/">XML</link></strong></span> <note>XML: Extensible Markup Language 1.0 (Fifth Edition). <<link url="http://www.w3.org/TR/xml/">http://www.w3.org/TR/xml/</link>>.</note>. In addition, XML character entities are counted as a single character.</p>
|
||
</section3>
|
||
<section3 topic="Guidelines for Recipients" anchor="guidelines_for_recipients">
|
||
<p>For <link url="#element_t_insert_text">Element <t/> – Insert Text</link>, text MUST be obtained using compliant XML processing (including entities converted to characters). Recipient clients SHOULD ensure that the received text is in Unicode Normalization Form C ("NFC"). After this, recipient clients MUST NOT do any other modifications to resulting real-time messages. This is to allow accurate processing of subsequent <link url="#action_elements">Action Elements</link> and <link url="#attribute_values">Attribute Values</link> (The recipient client can separately process/modify a copy of the same real-time message text, if necessary for the purpose of display presentation).</p>
|
||
<p>It is possible for <link url="#element_t_insert_text">Element <t/> – Insert Text</link> to contain any subset sequence of Unicode code points from the sender’s message. This can result in situations where text transmitted in <t/> elements is an incomplete combining character sequence (e.g. Unicode combining mark(s) without a base character) which becomes a complete sequence when inserted within the recipient's real-time message (e.g. additional accent for an existing combining character sequence). These are still complete individual code points, even if the sequence is incomplete.</p>
|
||
</section3>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="Determining Support" anchor="determining_support">
|
||
<p>If a client supports this real-time text protocol, it MUST advertise that fact in its responses to &xep0030; information requests ("disco#info") by returning a feature of <strong>urn:xmpp:rtt:0</strong></p>
|
||
<p><strong>Example 1. A disco#info query</strong></p>
|
||
<p><code><![CDATA[<iq from='romeo@montague.lit/orchard'
|
||
id='disco1'
|
||
to='juliet@capulet.lit/balcony'
|
||
type='get'>
|
||
<query xmlns='http://jabber.org/protocol/disco#info'/>
|
||
</iq>
|
||
|
||
]]></code></p>
|
||
<p><strong>Example 2. A disco#info response</strong></p>
|
||
<p><code><![CDATA[<iq from='juliet@capulet.lit/balcony'
|
||
id='disco1'
|
||
to='romeo@montague.lit/orchard'
|
||
type='result'>
|
||
<query xmlns='http://jabber.org/protocol/disco#info'>
|
||
<feature var='urn:xmpp:rtt:0'/>
|
||
</query>
|
||
</iq>
|
||
|
||
]]></code></p>
|
||
<p>In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in &xep0115;. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.</p>
|
||
<p>See <link url="#activating_and_deactivating_realtime_text">Activating and Deactivating Real-Time Text</link> for more information, including implicit discovery.</p>
|
||
</section1>
|
||
<section1 topic="Implementation Notes" anchor="implementation_notes">
|
||
<section2 topic="Text Presentation" anchor="text_presentation">
|
||
<section3 topic="Avoid Bursty Text Presentation" anchor="avoid_bursty_text_presentation">
|
||
<p>If a long <link url="#transmission_interval">Transmission Interval</link> is used without <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>, then incoming text will appear in intermittent bursts if the display of text is not smoothed. This hurts user experience of real-time text.</p>
|
||
</section3>
|
||
<section3 topic="Preserving Key Press Intervals" anchor="preserving_key_press_intervals">
|
||
<p>For high quality presentation of real-time text, the original look-and-feel of typing can be preserved independently of the transmission interval. This is achieved using <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> between other <link url="#action_elements">Action Elements</link>. Sender clients can transmit the length of pauses between key presses, and send multiple key presses in a single <message/> stanza. Recipient clients that process <w/> elements are able to display the sender's typing smoothly, without sudden bursts of text. See <link url="#examples_of_key_press_intervals">Examples of Key Press Intervals</link>.</p>
|
||
<p>When key press intervals are preserved at high precision, all subtleties of typing are preserved, including the 'mood' (calm typing versus panicked or emphatic typing, etc.). Much as VoIP allows accurate packet transmission of sound, this spec allows accurate packet transmission of original typing look-and-feel. This enables the real-time feel of typing over virtually any network connection, without requiring frequent transmission intervals. Look and feel of typing is also preserved over variable latency connections including &xep0206;, mobile phone, satellite and long international connections with heavy packet-bursting tendencies.</p>
|
||
</section3>
|
||
<section3 topic="Time Critical and Low Latency Methods" anchor="time_critical_and_low_latency_methods">
|
||
<p>There are specialized situations such as live transcriptions and captioning (e.g. transcription service, closed captioning provider, captioned telephone, Communication Access Realtime Translation (CART), relay services) that demands low latency transmission. Such systems typically use voice recognition and/or stenotype machines, which output text in word bursts rather than a character at a time. It is acceptable for senders with bursty output to immediately transmit word bursts of text without buffering. This eliminates any lag caused by the <link url="#transmission_interval">Transmission Interval</link>. It is not necessary to transmit <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> for real-time transcription.</p>
|
||
</section3>
|
||
<section3 topic="Low-Bandwidth and Low-Precision Text Smoothing" anchor="lowbandwidth_and_lowprecision_text_smoothing">
|
||
<p>Some software platforms (e.g. JavaScript, BOSH, mobile devices) may have low-precision timers that impact <link url="#transmission_interval">Transmission Interval</link> and/or <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>. Clients can optimize for bandwidth, performance and/or screen repaints by eliminating, merging, or ignoring <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> selectively, especially those containing shorter intervals. In addition, it is acceptable for the transmission interval of <rtt/> to vary, either intentionally for optimizations, or due to precision limitation, preferably within the range recommended by <link url="#transmission_interval">Transmission Interval</link>. Compression can also be used to reduce bandwidth (e.g. TLS compression or &xep0138;) .</p>
|
||
<p>Clients can choose to implement alternate text-smoothing methods, such as adaptive-rate character-at-a-time output, and/or word buffering for incoming real-time text. Word buffering prevents most typing mistakes from being displayed, which can be a useful mode of operation for certain recipients who may dislike watching the sender's typing mistakes.</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Activating and Deactivating Real-Time Text" anchor="activating_and_deactivating_realtime_text">
|
||
<p>There are many possible ways to implement turning on/off real-time text. Clients can send outgoing real-time text by default. Other clients might choose to do user-initiated activation (e.g. via a button).</p>
|
||
<section3 topic="Activation Guidelines" anchor="activation_guidelines">
|
||
<p>Sender clients can <strong>simply begin transmitting real-time text</strong> (i.e. send <rtt/> elements), either immediately or upon user-initiated activation.</p>
|
||
<p>For one-on-one chats, it can be beneficial for clients to easily synchronize the enabling/disabling of real-time text. Upon receiving incoming real-time text, recipient clients can automatically do an appropriate response, such as:</p>
|
||
<ul>
|
||
<li>Activate immediately (begin transmitting <rtt/> elements too); or</li>
|
||
<li>Activate after user confirmation prompt (for <link url="#privacy">Privacy</link> considerations); or</li>
|
||
<li>Deny (transmit <rtt event='cancel'/>); or</li>
|
||
<li>Ignore (discard incoming <rtt/> elements); or</li>
|
||
<li>Display only incoming real-time text (e.g. <link url="#multiuser_chat">Multi-User Chat</link> participants control their own outgoing real-time text).</li>
|
||
</ul>
|
||
<p>For any client, the preferred first <rtt/> element to send is <rtt <link url="#event">event</link>='init'/> as it can quickly signal activation of real-time text, without waiting for the sender to begin composing a new message, and since it is usable regardless of discovery.</p>
|
||
<p>Before sending real-time text, it is preferable for a sender client to explicitly discover whether the recipient client supports the protocol defined herein (using <link url="#determining_support">Determining Support</link>). In the absence of explicit discovery or negotiation, the sender client can implicitly request and discover the use of real-time text, by sending <rtt event='init'/> upon activation. It is inappropriate to send any further <rtt/> elements, until support is confirmed either by incoming <rtt/> elements or via discovery. Implicit discovery allows usage of real-time text as an enhancement to &xep0085; (XEP-0085 Section 5.1), during all situations where it can be used. See <link url="#usage_with_chat_states">Usage with Chat States</link>.</p>
|
||
</section3>
|
||
<section3 topic="Deactivation Guidelines" anchor="deactivation_guidelines">
|
||
<p>Real-time text can be deactivated by transmitting <rtt <link url="#event">event</link>='cancel'/>, or simply by ending the chat session. Recipient clients can respond to deactivation with appropriate response(s), including:</p>
|
||
<ul>
|
||
<li>Stop transmitting <rtt/> elements as well (not applicable to <link url="#multiuser_chat">Multi-User Chat</link>); and</li>
|
||
<li>Handle the sender's unfinished incoming real-time message (such as clearing it and/or saving it); and</li>
|
||
<li>Inform the recipient user that sender ended real-time text (or denied/cancelled, if no real-time text was received).</li>
|
||
</ul>
|
||
<p>Sending an <rtt event='cancel'/> is also useful in situations where the user closes a chat window, and ends the chat session. It is also useful when the user wants to deactivate or deny real-time text, while still continuing the chat session. After <rtt event='cancel'/>, any client can reactivate real-time text again using <rtt event='init'/>.</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Optional Remote Cursor" anchor="optional_remote_cursor">
|
||
<p>Recipient clients might choose to display a cursor (or caret) within incoming real-time messages. This enhances usability of real-time text further, since it becomes easier for a recipient to observe the sender's real-time message edits.</p>
|
||
<p>If a remote cursor is not used, then clients can simply ignore calculating a cursor position and skip this section. <link url="#action_elements">Action Elements</link> only use absolute positioning (relative positions are not used by this standard), so clients do not need to remember the position value from previous action elements.</p>
|
||
<section3 topic="Calculating Cursor Position" anchor="calculating_cursor_position">
|
||
<p>When <t/> or <e/> action elements are processed in incoming real-time text, the beginning value for the cursor position calculation is the absolute position value of the <em><strong>p</strong></em> attribute, according to <link url="#attribute_values">Attribute Values</link>. The recipient can calculate the cursor position as follows:</p>
|
||
<ul>
|
||
<li><p>After <link url="#element_t_insert_text">Element <t/> – Insert Text</link>, the cursor position is the <em><strong>p</strong></em> attribute plus the length of the text being inserted. The cursor position is put at the end of the inserted text.<br />
|
||
<em>This is the normal forward cursor movement during text insertion.</em></p></li>
|
||
<li><p>After <link url="#element_e_erase_text">Element <e/> – Erase Text</link>, the cursor position is the <em><strong>p</strong></em> attribute minus the <em><strong>n</strong></em> attribute.<br />
|
||
<em>This is the normal backwards cursor movement to a backspace key.</em></p></li>
|
||
<li><p>After an empty <link url="#element_t_insert_text">Element <t/> – Insert Text</link> (in the format of <strong><t p='#'/></strong> with no text to insert), the cursor position is the <strong>p</strong> attribute, and no text modification is done.<br />
|
||
<em>This allows cursor response to arrow keys and/or mouse repositioning the cursor.</em></p></li>
|
||
</ul>
|
||
<p>The remote cursor needs to be clearly distinguishable from the sender's real local cursor. One example is to use a non-blinking cursor, easily emulated with a Unicode character or the vertical bar character '|'.</p>
|
||
<p>It is acceptable for the sender to transmit <link url="#element_t_insert_text">Element <t/> – Insert Text</link> as empty elements (with the cursor position in the <em><strong>p</strong></em> attribute) whenever the cursor position is changing without any text modifications (i.e. via arrow keys or mouse). This allows recipients supporting a remote cursor, to show the cursor movements. These extra elements are ignored by recipients that do not support a remote cursor.</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Sending Real-Time Text" anchor="sending_realtime_text">
|
||
<p>This section lists several possible methods of generating real-time text for transmission. For most situations, the preferred methodology is <link url="#monitoring_message_changes_instead_of_key_presses">Monitoring Message Changes Instead Of Key Presses</link>.</p>
|
||
<section3 topic="Monitoring Message Changes Instead Of Key Presses" anchor="monitoring_message_changes_instead_of_key_presses">
|
||
<p>Experience has found that the most reliable method for generating real-time text, is to monitor for <strong>text changes</strong> to the sender’s message entry field, instead of key press events. Text change events have the following advantages:</p>
|
||
<ul>
|
||
<li>It captures all typing, including edits and deletes.</li>
|
||
<li>It captures copy & paste operations, as well as edits made via a pointing device.</li>
|
||
<li>It captures all automatic text changes (e.g. spell checker, auto-correct, macros, transcription, assistive devices).</li>
|
||
<li>It captures characters requiring multiple key presses to compose (e.g. accents, combining marks).</li>
|
||
<li>It makes no assumptions about different keyboards or input method editors (e.g. Chinese).</li>
|
||
<li>Text change events are more portable across platforms, including on mobile phones.</li>
|
||
</ul>
|
||
<p>During a text change event, the sender’s current message text can be compared to the old message text from the previous text change event. The difference in text, between consecutive text change events, is typically a one character difference (e.g. key press) or one text block difference (e.g. auto-correct, cut, paste). In order to calculate what text changes took place, the first changed character and the last changed character is determined. From this, it is simple to generate <link url="#action_elements">Action Elements</link> for a single text block deletion and/or insertion. In addition, if <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> is supported, then <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> records the time elapsed between text change events.</p>
|
||
<p>Sender software can do the following:</p>
|
||
<ol>
|
||
<li><p>Monitor for text changes in the sender’s message. Whenever a text change event occurs, compute action element(s) and append these action element(s) to a buffer. Repeating this step during every text change event, is equivalent to recording a small sequence of typing.</p></li>
|
||
<li><p>During every <link url="#transmission_interval">Transmission Interval</link>, all buffered action elements are transmitted in <rtt/> element in a <message/> stanza. This is equivalent to transmitting a small sequence of typing at a time.</p></li>
|
||
<li><p>If there are no message changes occurring, no unnecessary transmission takes place.</p></li>
|
||
</ol>
|
||
</section3>
|
||
<section3 topic="Monitoring Key Presses Directly" anchor="monitoring_key_presses_directly">
|
||
<p>Real-time text can be generated via monitoring key presses. However, this does not have the advantages of <link url="#monitoring_message_changes_instead_of_key_presses">Monitoring Message Changes Instead Of Key Presses</link>. Care needs be taken with automatic changes to the message, generated by means other than key presses. This includes spell check auto-correct, copy and pastes, transcription, input method editors, and multiple key presses required to compose a character (i.e. accents). Key press events can miss these text changes, and this can potentially cause incorrect real-time text to be transmitted.</p>
|
||
</section3>
|
||
<section3 topic="Append-Only Real-Time Text" anchor="appendonly_realtime_text">
|
||
<p>The use of <link url="#element_t_insert_text">Element <t/> – Insert Text</link> without any attributes, simply appends text to the end of a message, while the use of <link url="#element_e_erase_text">Element <e/> – Erase Text</link> without any attributes, simply erases text from the end of the message. This sending method can also be useful for special-purpose clients where mid-message editing capabilities are not used (e.g. simple transcription, news tickers, relay services, captioned telephone).</p>
|
||
</section3>
|
||
<section3 topic="Basic Real-Time Text" anchor="basic_realtime_text">
|
||
<p>It is possible for sender clients to use <link url="#message_reset">Message Reset</link> to retransmit the whole real-time message, whenever there are text changes. The advantage is very simple implementation. Disadvantages can include the lack of <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>, and extra bandwidth consumption that can occur with longer messages, unless stream compression is used. The below illustrates transmission of the real-time message “<strong>Hello there!</strong>” at a regular <link url="#transmission_interval">Transmission Interval</link> while the sender is typing.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Hel</t>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='b02'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='456002' event='reset'>
|
||
<t>Hello th</t>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='c03'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='789003' event='reset'>
|
||
<t>Hello there!</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Receiving Real-Time Text" anchor="receiving_realtime_text">
|
||
<p>In order to allow <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> in incoming real-time text, recipient clients can do the following:</p>
|
||
<ol>
|
||
<li><p>Upon receiving <link url="#action_elements">Action Elements</link> in incoming <rtt/> elements, they are added to a queue in the order they are received. This provides immunity to variable network conditions, since the queuing action will smooth out incoming transmission (e.g. receiving new <rtt/> while still processing a delayed <rtt/>).</p></li>
|
||
<li><p>The recipient client processes action elements in the queue in sequential order, including pauses from <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link>. This is equivalent to playing back the sender's original typing.</p></li>
|
||
<li><p>Upon receiving a <link url="#body_element">Body Element</link> indicating a completed message, the full message text from <body/> can be displayed immediately in place of the real-time message, and unprocessed action elements can be cleared from the queue. This ensures final message delivery is not delayed by late processing of action elements.</p></li>
|
||
</ol>
|
||
<p>In processing <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link>, excess lag in incoming real-time text might occur if multiple delayed <rtt/> elements suddenly get delivered (e.g. congestion, intermittent wireless reception). Recipients can avoid excess lag by monitoring the queue for excess <w/> action elements (e.g. unprocessed <w/> elements from two <rtt/> elements ago) and then ignoring or shortening the intervals in <w/> elements. This allows lagged real-time text to "catch up" more quickly.</p>
|
||
</section2>
|
||
<section2 topic="Other Guidelines" anchor="other_guidelines">
|
||
<section3 topic="Message Length" anchor="message_length">
|
||
<p>A large sequence of action elements can result in an <rtt/> larger than the size of a message <body/>. This can occur normally during fast typing when <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> during small messages. However, if the <rtt/> element becomes unusually huge (e.g. macros, multiple copy and pastes, leading to an <rtt/> exceeding one kilobyte) a <link url="#message_reset">Message Reset</link> can instead be used, in order to save bandwidth. (Stream compression is another approach.)</p>
|
||
<p>Clients can limit the length of the text input for the sender's message, in order to keep the size of <message/> stanzas reasonable, including during <link url="#message_reset">Message Reset</link>. Also, large <rtt/> elements may occur in situations such as large copy and pastes. To keep message stanza sizes reasonable, <rtt/> can be transmitted in a separate <message/> than the one containing <body/>.</p>
|
||
<p>For specialized clients that send continuous real-time text (e.g. news ticker, captioning, transcription, TTY gateway), a <link url="#body_element">Body Element</link> can be sent and then a new real-time message started immediately after, every time a message reaches a reasonable size. This allows continuous real-time text without real-time messages becoming excessively large.</p>
|
||
</section3>
|
||
<section3 topic="Usage with Chat States" anchor="usage_with_chat_states">
|
||
<p>Real-time text can be used in conjunction with XEP-0085 Chat States. These are simple guidelines for <message/> stanzas that include an <rtt/> element:</p>
|
||
<ul>
|
||
<li>For <rtt/> transmitted without an accompanying <body/>, include <composing/> chat state.</li>
|
||
<li>For <rtt/> transmitted with an accompanying <body/>, include the <active/> chat state.</li>
|
||
<li>Other chat states are handled as specified by XEP-0085 Chat States.</li>
|
||
</ul>
|
||
</section3>
|
||
<section3 topic="Usage with Multi-User Chat and Simultaneous Logins" anchor="usage_with_multiuser_chat_and_simultaneous_logins">
|
||
<p>The in-band nature of this real-time text standard allows one-to-many situations. Thus, real-time text is appropriate for use with &xep0045; (MUC), as well as concurrent simultaneous logins.</p>
|
||
<section4 topic="Multi-User Chat" anchor="multiuser_chat">
|
||
<p>For simplicity, clients can implement real-time text only for one-on-one chat, and not for MUC. However, it can be appropriate to support <rtt/> elements in MUC, even if not all participants support real-time text. Participants that enable real-time text during group chat need to keep track of multiple concurrent real-time messages on a per-participant basis. Participants, with real-time text, will see real-time text coming from each participant that has real-time text enabled. Participant clients without real-time text (whether unsupported or turned off) will simply see group chat function normally on a line-by-line basis, since it is <link url="#backwards_compatible">Backwards Compatible</link>.</p>
|
||
<p>Participants that turn off real-time text for themselves, can simply ignore incoming <rtt/> and not transmit outgoing <rtt/>. Participant clients in MUC receiving an incoming <rtt <link url="#event">event</link>=’cancel’/> needs to keep outgoing transmission unaffected during <link url="#deactivation_guidelines">Deactivation Guidelines</link> (otherwise, one participant could deny real-time text between other willing participants).</p>
|
||
<p>To minimize on-screen clutter of multiple idle real-time messages, clients can hide idle messages, clear old <link url="#stale_messages">Stale Messages</link>, and/or prioritize the display of the most useful real-time messages. Prominent visibility of real-time text can be assigned to recent typists and/or moderators (e.g. classroom teacher, convention speaker). For the same participant logged in multiple times in the same room, see <link url="#simultaneous_logins">Simultaneous Logins</link>. In situations of simultaneous typing by a large number of participants, see <link url="#congestion_considerations">Congestion Considerations</link>.</p>
|
||
</section4>
|
||
<section4 topic="Simultaneous Logins" anchor="simultaneous_logins">
|
||
<p>In simultaneous login situations, transmitting of <rtt/> works in one-to-many situations without any special software support. For many-to-one situations where there is incoming <rtt/> from more than one simultaneous login, <link url="#keeping_realtime_text_synchronized">Keeping Real-Time Text Synchronized</link> will pause the real-time message upon conflicting <rtt/>, and resume during the next <link url="#message_reset">Message Reset</link>, presumably from the active login. This provides a seamless system-switching experience. A good implementation of <link url="#message_reset">Message Reset</link> will improve user experience, regardless of whether or not the client follows Best Practices For Resource Locking (XEP-0296). Clients can choose to distinguish the <rtt/> streams (via full JID and/or via <thread/>) and keep multiple concurrent real-time messages similar in manner to <link url="#multiuser_chat">Multi-User Chat</link>, with the <link url="#stale_messages">Stale Messages</link> being timed-out.</p>
|
||
</section4>
|
||
</section3>
|
||
<section3 topic="Stale Messages" anchor="stale_messages">
|
||
<p>There are situations where senders pause typing indefinitely. This can result in recipients displaying a real-time message for an extended time period. It may also be a screen clutter concern during <link url="#multiuser_chat">Multi-User Chat</link>. In addition, it may be a resource-consumption concern, as part of <link url="#congestion_considerations">Congestion Considerations</link>.</p>
|
||
<p>It is acceptable for recipients to clear (and/or save) incoming real-time messages that have been idle for an extended time period. There is no specific time-out period defined by this specification. For <link url="#multiuser_chat">Multi-User Chat</link>, the time-out period might be shorter because of the need to reduce screen clutter. For normal chat sessions, the time-out period might need to be longer to allow reasonable interruptions (i.e. sender pausing during a long phone call).</p>
|
||
<p>Senders that resume composing a message (i.e. continues a partially-composed message hours later) can transmit a <link url="#message_reset">Message Reset</link>, which allows recipients to redisplay the real-time message.</p>
|
||
</section3>
|
||
<section3 topic="Performance & Efficiency" anchor="performance_efficiency">
|
||
<p>With real-time text, frequent screen updates can occur. Screen updates are a potential performance bottleneck, since fast typists type many key presses per second. Optimizing screen updates becomes especially important for slower platforms. The real-time message might be implemented as a separate window or separate display element.</p>
|
||
<p>Battery life considerations are closely related to performance, as the addition of real-time text may impact battery life. If <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> are supported, then the implementation of <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> needs to be implemented in a battery-efficient manner. The <link url="#transmission_interval">Transmission Interval</link> may vary dynamically to optimize for battery life and wireless reception. For devices where screen updates are an unavoidable inefficient bottleneck, see <link url="#lowbandwidth_and_lowprecision_text_smoothing">Low-Bandwidth and Low-Precision Text Smoothing</link> to reduce the number of screen updates per second.</p>
|
||
</section3>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="Use Cases" anchor="use_cases">
|
||
<p>Most of these examples are deliberately kept simple. In complete software implementations supporting key press intervals, transmissions will most resemble the last example, <link url="#full_message_including_key_press_intervals">Full Message Including Key Press Intervals</link>. For simplicity, these examples use a bare JID, even in situations where a full JID might be more appropriate.</p>
|
||
<section2 topic="Example of Simple Real-Time Text" anchor="example_of_simple_realtime_text">
|
||
<p>All three examples shown below result in the same real-time message "<strong>HELLO</strong>" created by writing "<strong>HLL</strong>", backspacing two times, and then "<strong>ELLO</strong>". The action elements are <link url="#element_t_insert_text">Element <t/> – Insert Text</link> and <link url="#element_e_erase_text">Element <e/> – Erase Text</link>.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>HLL</t>
|
||
<e/><e/>
|
||
<t>ELLO</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>The example above sends the misspelled "<strong>HLL</strong>", then <strong><e/><e/></strong> backspaces 2 times, then sends "<strong>HELLO</strong>".</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>HLL</t>
|
||
<e n='2'/>
|
||
<t>ELLO</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>The example above shows that <strong><e n='2'/></strong> does the same thing as <strong><e/><e/></strong>.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>HLL</t>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='b02'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123002'>
|
||
<e n='2'/>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='c03'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123003'>
|
||
<t>ELLO</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>The example above splits the same real-time text over multiple <message/> stanzas, which would occur if the typing was occurring more slowly, over several <link url="#transmission_interval">Transmission Interval</link> cycles.</p>
|
||
</section2>
|
||
<section2 topic="Example of Multiple Messages" anchor="example_of_multiple_messages">
|
||
<p>The example below represents a short chat session of three separate messages:<br />
|
||
Bob says: "Hello Alice"<br />
|
||
Bob says: "This is Bob"<br />
|
||
Bob says: "How are you?"</p>
|
||
<p><code><![CDATA[<message to='alice@example.com' from='bob@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Hello</t>
|
||
</rtt>
|
||
<composing xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='b02'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123002'>
|
||
<t> Alice</t>
|
||
</rtt>
|
||
<body>Hello Alice</body>
|
||
<active xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='c03'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='456001' event='new'>
|
||
<t>This i</t>
|
||
</rtt>
|
||
<composing xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='d04'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='456002'>
|
||
<t>s Bob</t>
|
||
</rtt>
|
||
<body>This is Bob</body>
|
||
<active xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='e05'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='789001' event='new'>
|
||
<t>How a</t>
|
||
</rtt>
|
||
<composing xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='f06'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='789002'>
|
||
<t>re yo</t>
|
||
</rtt>
|
||
<composing xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>
|
||
|
||
<message to='alice@example.com' from='bob@example.com/home' type='chat' id='g07'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='789003'>
|
||
<t>u?</t>
|
||
</rtt>
|
||
<body>How are you?</body>
|
||
<active xmlns='http://jabber.org/protocol/chatstates'/>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>The example above represents moderate typing speed during a normal <link url="#transmission_interval">Transmission Interval</link>, such as 0.7 seconds between <message/> stanzas for continuous typing. It illustrates the following:</p>
|
||
<ul>
|
||
<li>The <strong><link url="#event">event</link></strong> attribute equals 'new' for the start of every new message.</li>
|
||
<li>The <strong><link url="#seq">seq</link></strong> attribute increments within the same message.</li>
|
||
<li>The <strong><link url="#seq">seq</link></strong> attribute randomizes when beginning a new message.</li>
|
||
<li>This shows <link url="#usage_with_chat_states">Usage with Chat States</link>.</li>
|
||
</ul>
|
||
</section2>
|
||
<section2 topic="Examples of Message Edits" anchor="examples_of_message_edits">
|
||
<p>These examples illustrate real-time message editing via <link url="#action_elements">Action Elements</link>.<br />
|
||
Note: In most situations, during normal human typing speeds at a normal <link url="#transmission_interval">Transmission Interval</link>, smaller fragments of text will be spread over multiple <rtt/> elements, than these demonstration examples below. See <link url="#sending_realtime_text">Sending Real-Time Text</link>.</p>
|
||
<section3 topic="Deleting Text From Message" anchor="deleting_text_from_message">
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Hello Bob, this is Alice!</t>
|
||
<e n='4' p='9'/>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>Final result of real-time message: "<strong>Hello, this is Alice!</strong>"<br />
|
||
This example outputs "<strong>Hello Bob, this is Alice!</strong>" then <strong><e n='4' p='9'/></strong> erases 4 characters before character position index 9. The <link url="#element_e_erase_text">Element <e/> – Erase Text</link> removes the text " <strong>Bob</strong>" including the preceding space character.</p>
|
||
</section3>
|
||
<section3 topic="Inserting Text Into Message" anchor="inserting_text_into_message">
|
||
|
||
|
||
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Hello, this is Alice!</t>
|
||
<t p='5'> Bob</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>Final result of real-time message: "<strong>Hello Bob, this is Alice!</strong>"<br />
|
||
This is because this example outputs "<strong>Hello, this is Alice!</strong>" then the <strong><t p='5'></strong> inserts the specified text " <strong>Bob</strong>" at position 5, using <link url="#element_t_insert_text">Element <t/> – Insert Text</link>.</p>
|
||
</section3>
|
||
<section3 topic="Deleting and Replacing Text In Message" anchor="deleting_and_replacing_text_in_message">
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Hello Bob, tihsd is Alice!</t>
|
||
<e p='16' n='5'/>
|
||
<t p='11'>this</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>Final result of real-time message: "<strong>Hello Bob, this is Alice!</strong>"<br />
|
||
This example outputs "<strong>Hello Bob, tihsd is Alice!</strong>", then <strong><e p='16' n='5'/></strong> erases 5 characters at position 16 in the string of text (which erases the mistyped word "<strong>tihsd</strong>"). Finally, <strong><t p='11'>this</t></strong> inserts the text "<strong>this</strong>" place of the original misspelled word.</p>
|
||
</section3>
|
||
<section3 topic="Multiple Message Edits" anchor="multiple_message_edits">
|
||
<p>This is an example message containing multiple consecutive real-time message edits. This illustrates valid use of the <rtt/> element.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>Helo</t>
|
||
<e/>
|
||
<t>lo...planet</t>
|
||
<e n='6'/>
|
||
<t> World</t>
|
||
<e n='3' p='8'/>
|
||
<t p='5'> there,</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>Resulting real-time message: "<strong>Hello there, World</strong>", completed in the following series of action elements:</p>
|
||
<table>
|
||
<tr>
|
||
<th>Element</th>
|
||
<th>Action</th>
|
||
<th>Real -Time Message</th>
|
||
<th>Cursor Position*</th>
|
||
</tr>
|
||
<tr>
|
||
<td><t>Helo</t></td>
|
||
<td>Output "Helo"</td>
|
||
<td>Helo</td>
|
||
<td>4</td>
|
||
</tr>
|
||
<tr>
|
||
<td><e/></td>
|
||
<td>Erase 1 character from end of line.</td>
|
||
<td>Hel</td>
|
||
<td>3</td>
|
||
</tr>
|
||
<tr>
|
||
<td><t>lo...planet</t></td>
|
||
<td>Output "lo...planet" at end of line.</td>
|
||
<td>Hello...planet</td>
|
||
<td>14</td>
|
||
</tr>
|
||
<tr>
|
||
<td><e n='6'/></td>
|
||
<td>Erase 6 characters from end of line</td>
|
||
<td>Hello...</td>
|
||
<td>8</td>
|
||
</tr>
|
||
<tr>
|
||
<td><t> World</t></td>
|
||
<td>Output " World" at end of line.</td>
|
||
<td>Hello... World</td>
|
||
<td>14</td>
|
||
</tr>
|
||
<tr>
|
||
<td><e n='3' p='8'/></td>
|
||
<td>Erase 3 characters before position 8</td>
|
||
<td>Hello World</td>
|
||
<td>5</td>
|
||
</tr>
|
||
<tr>
|
||
<td><t p='5'> there,</t></td>
|
||
<td>Output " there," at position 5</td>
|
||
<td>Hello there, World</td>
|
||
<td>12</td>
|
||
</tr>
|
||
</table>
|
||
<p>*The Cursor Position column is only relevant if the <link url="#optional_remote_cursor">Optional Remote Cursor</link> is implemented.</p>
|
||
<p>This example does not illustrate <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>. Also, it is noted that most situations, during normal typing speeds at a normal <link url="#transmission_interval">Transmission Interval</link>, the above series of <link url="#action_elements">Action Elements</link> will normally be spread over multiple separate <rtt/> elements.</p>
|
||
</section3>
|
||
</section2>
|
||
<section2 topic="Examples of Key Press Intervals" anchor="examples_of_key_press_intervals">
|
||
<section3 topic="Comparison With and Without Intervals" anchor="comparison_with_and_without_intervals">
|
||
<p>All examples shown below, result in the same real-time message “<strong>HELLO</strong>”. Only the last example follows <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>HELLO</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
<p>The above example outputs “<strong>HELLO</strong>” in a single action element (<link url="#element_t_insert_text">Element <t/> – Insert Text</link>).</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>H</t>
|
||
<t>E</t>
|
||
<t>L</t>
|
||
<t>L</t>
|
||
<t>O</t>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
<p>The above example outputs “<strong>HELLO</strong>” in separate action elements for each key press.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>H</t><w n='101'/>
|
||
<t>E</t><w n='110'/>
|
||
<t>L</t><w n='125'/>
|
||
<t>L</t><w n='103'/>
|
||
<t>O</t><w n='110'/>
|
||
</rtt>
|
||
</message>]]></code></p>
|
||
<p>The above example outputs “<strong>HELLO</strong>” in separate action elements for each key press, while also <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>. The <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> specifies the number of milliseconds between key presses, to allow smooth presentation in recipient clients that support <w/> action elements.</p>
|
||
</section3>
|
||
<section3 topic="Full Message Including Key Press Intervals" anchor="full_message_including_key_press_intervals">
|
||
<p>This example is a transmission of “Hello there!” while <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>. It illustrates a four-second typing sequence:</p>
|
||
<ul>
|
||
<li>The misspelled phrase “Hello tehre!” is typed;</li>
|
||
<li>Optional transmission of cursor movements towards the typing mistake;</li>
|
||
<li>Two backspaces to delete the typing mistake;</li>
|
||
<li>Two correct key presses to correctly spell the word “there”.</li>
|
||
</ul>
|
||
<p>The use <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link>, between key presses, allows the receiving client execute a small pause between action elements. This allows recipient clients to play back the sender's typing fluidly.</p>
|
||
<p><code><![CDATA[<message to='bob@example.com' from='alice@example.com/home' type='chat' id='a01'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123001' event='new'>
|
||
<t>H</t>
|
||
<w n='115'/><t>e</t>
|
||
<w n='154'/><t>l</t>
|
||
<w n='151'/><t>l</t>
|
||
<w n='115'/><t>o</t>
|
||
<w n='165'/>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='b02'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123002'>
|
||
<w n='40'/><t> </t>
|
||
<w n='161'/><t>t</t>
|
||
<w n='137'/><t>e</t>
|
||
<w n='135'/><t>h</t>
|
||
<w n='134'/><t>r</t>
|
||
<w n='93'/>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='c03'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123003'>
|
||
<w n='109'/><t>e</t>
|
||
<w n='115'/><t>!</t>
|
||
<w n='330'/><t p='11'/>
|
||
<w n='108'/><t p='10'/>
|
||
<w n='38'/>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='d04'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123004'>
|
||
<w n='109'/><t p='9'/>
|
||
<w n='111'/><e p='9'/>
|
||
<w n='106'/><e p='8'/>
|
||
<w n='138'/><t p='7'>h</t>
|
||
<w n='209'/><t p='8'>e</t>
|
||
<w n='27'/>
|
||
</rtt>
|
||
</message>
|
||
|
||
<message to='bob@example.com' from='alice@example.com/home' type='chat' id='d04'>
|
||
<rtt xmlns='urn:xmpp:rtt:0' seq='123005'>
|
||
<w n='445'/><t p='12'/>
|
||
</rtt>
|
||
<body>Hello there!</body>
|
||
</message>]]></code></p>
|
||
|
||
|
||
|
||
<p>This example also illustrates the following:</p>
|
||
<ul>
|
||
<li>Typing is done via <link url="#element_t_insert_text">Element <t/> – Insert Text</link>.</li>
|
||
<li>Backspaces are done via <link url="#element_e_erase_text">Element <e/> – Erase Text</link>.</li>
|
||
<li>There is a final transmission with a <link url="#body_element">Body Element</link>, when the message is finished.</li>
|
||
<li>Intervals between key presses are done via <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link>.</li>
|
||
<li>Each <message/> is delivered at a regular <link url="#transmission_interval">Transmission Interval</link>, typically 0.7 seconds.</li>
|
||
<li>Cursor movements via empty <t/> elements. Sender transmission is not essential, but can be desirable for recipient clients supporting an <link url="#optional_remote_cursor">Optional Remote Cursor</link>.</li>
|
||
<li>Recipient clients that do not support <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link> and/or <link url="#optional_remote_cursor">Optional Remote Cursor</link>, will still display this message normally.</li>
|
||
<li>The total sum of all values in <link url="#element_w_wait_interval">Element <w/> – Wait Interval</link> in one <message/> equal the <link url="#transmission_interval">Transmission Interval</link> during periods of continuous typing. This also results in some <w/> interval elements being split between consecutive messages. Although not critical, it can further improve the fluidity of <link url="#receiving_realtime_text">Receiving Real-Time Text</link>.</li>
|
||
<li>See <link url="#monitoring_message_changes_instead_of_key_presses">Monitoring Message Changes Instead Of Key Presses</link> for the best method of implementation.</li>
|
||
</ul>
|
||
</section3>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="Interoperability Considerations" anchor="interoperability_considerations">
|
||
<p>There are other real-time text formats with interoperability considerations relating to the session setup level, the media transport level, and presentation level. Interoperability specifications between multiple real-time text formats can be found at Real-Time Text Taskforce (R3TF).</p>
|
||
<p>It is appropriate for implementers to choose the most appropriate real-time text standard for the session control standard in use during a particular session. For example, clients that use XMPP can utilize this XEP-0301 specification, and clients that use SIP might utilize IETF RFC 4103, <span class="ref"><strong><link url="http://tools.ietf.org/html/rfc5194">IETF RFC 5194</link></strong></span> <note>RFC 5194: Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP). <<link url="http://tools.ietf.org/html/rfc5194">http://tools.ietf.org/html/rfc5194</link>>.</note> and ITU-T T.140). Clients that run on multiple networks, might need to utilize multiple real-time text standards. To interoperate between incompatible real-time text standards, gateway servers can transcode between different real-time text standards, along with other media such as audio and video. This can include TTY and textphones.</p>
|
||
<section2 topic="RFC 4103 and T.140" anchor="rfc_4103_and_t140">
|
||
<p>In the SIP environment, real-time text is specified in IETF RFC 4103 and ITU-T T.140. SIP is a popular real-time session control protocol, and there are many implementations of real-time text controlled by SIP. This includes emergency services in some regions.</p>
|
||
<p>Interoperability considerations include addressing translation, media negotiation and translation, and media transcoding. Transcoding is straightforward between this specification and T.140/RFC4103, except for editing in the middle of messages. Text insertions or deletions, occurring far back in the message, can cause a large number of erase operations in T.140 that consume time and bandwidth. T.140 specifies the use of ISO 6429 control codes for presentation characteristics, such as text color, that are not supported by this specification. During transcoding, these control codes needs to be filtered off in order to not disturb the presentation of text.</p>
|
||
</section2>
|
||
<section2 topic="Total Conversation – Combination with Audio and Video" anchor="total_conversation_combination_with_audio_and_video">
|
||
<p>According to ITU-T Rec. F.703, the “Total Conversation” accessibility standard defines the simultaneous use of audio, video, and real-time text. This is more widespread in certain regions (e.g. Reach 112 in Europe). For convenience, messaging applications can be designed to have automatic negotiation of as many as possible of the three media preferred by the users.</p>
|
||
<p>In the XMPP session environment, the Jingle protocol (&xep0166;) is available for negotiation and transport of the more time-critical, real-time audio and video media. Any combination of audio, video, and real-time text can be used together simultaneously.</p>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="Internationalization Considerations" anchor="internationalization_considerations">
|
||
<p>The primary internationalization consideration involve real-time message editing using <link url="#action_elements">Action Elements</link>, where text is inserted and deleted using position and length values. For this, <link url="#accurate_processing_of_action_elements">Accurate Processing of Action Elements</link> including correct <link url="#unicode_character_counting">Unicode Character Counting</link> will ensure that all possible valid Unicode text can be used via this protocol. This includes text containing multiple scripts/languages, ideographic symbols (e.g. Chinese), right-to-left text (e.g. Arabic), and bidirectional text.</p>
|
||
<p>For accessibility considerations, there is an <span class="ref"><strong><link url="http://www.fasttext.org">International Symbol of Real-Time Text</link></strong></span>
|
||
<note>The International Symbol of Real-Time Text <<link url="http://www.fasttext.org">http://www.fasttext.org</link>>.</note> to alert users to the existence of this feature.</p>
|
||
</section1>
|
||
<section1 topic="Security Considerations" anchor="security_considerations">
|
||
<section2 topic="Privacy" anchor="privacy">
|
||
<p>It is important for users to be made aware of real-time text (e.g. user consent, software notice, introductory explanation). Users of real-time text needs to be aware that their typing is now visible in real-time to everyone in the current chat conversation. This may have security implications if users copy & paste private information into their chat entry buffer (e.g. a shopping invoice) before editing out the private parts of the pasted text (e.g. a credit card number) before they send the message. With real-time message editing, recipients can watch all text changes that occur in the sender's text, before the sender finishes the message. Implementation behaviors and improved education can be added to reduce privacy issues. Examples include showing an introduction upon first activation of feature, special handling for copy and pastes (i.e. preventing them, or prompting for confirmation), recipient confirmation of real-time text via <link url="#activating_and_deactivating_realtime_text">Activating and Deactivating Real-Time Text</link>, etc.</p>
|
||
</section2>
|
||
<section2 topic="Encryption" anchor="encryption">
|
||
<p>Real-time text (<rtt/> elements) transmit the content contained within messages. Therefore, a client that encrypts <body/> also needs to encrypt <rtt/> as well:</p>
|
||
<ul>
|
||
<li><p>Encryption at the stream level (e.g. TLS) can be used normally with this specification. Stream-level encryption is the most common form of encryption.</p></li>
|
||
<li><p>Encryption at the <message/> stanza level (e.g. XEP-0200) can be used for all stanzas containing either <rtt/> or <body/>. It is noted that real-time text can have a higher rate of message stanzas, contributing to additional overhead. See <link url="#congestion_considerations">Congestion Considerations</link>.</p></li>
|
||
<li><p>Encryption at the <body/> level (e.g. deprecated XEP-0027) do not encrypt <rtt/>. In this case, <rtt/> needs to be encrypted separately. It is preferable to use a broader level of encryption, where possible.</p></li>
|
||
</ul>
|
||
</section2>
|
||
<section2 topic="Congestion Considerations" anchor="congestion_considerations">
|
||
<p>The nature of real-time text can result in more frequent transmission of <message/> stanzas than would otherwise happen in a non-real-time text conversation. This can lead to increased network and server loading of XMPP networks.</p>
|
||
<p>Transmission of real-time text can be throttled temporarily during poor network conditions. It is appropriate to use latency monitoring mechanisms (e.g. &xep0184; or &xep0198;) in order to temporarily adjust the <link url="#transmission_interval">Transmission Interval</link> of real-time text beyond the recommended range. This results in lagged text (less real-time) but is better than failure during poor network conditions. The use of <link url="#message_reset">Message Reset</link> can also retransmit real-time text lost by poor network conditions, including stanzas dropped during a network issue or server error. These techniques are useful for mission-critical applications such as next generation emergency services (e.g. text to 9-1-1).</p>
|
||
<p>Excess numbers of real-time messages (e.g. during DoS scenario in <link url="#multiuser_chat">Multi-User Chat</link>) might cause local resource-consumption issues, which can be mitigated by accelerated time-out of <link url="#stale_messages">Stale Messages</link>.</p>
|
||
<p>According to multiple university studies worldwide, the average length of instant messages is under 40 characters. The additional incremental bandwidth overhead of real-time text can be very low for an existing XMPP client, especially one already using many extensions. Bandwidth can also be further mitigated using stream compression, to benefit bandwidth-constrained networks (e.g. GPRS, 3G, satellite).</p>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="IANA Considerations" anchor="iana_considerations">
|
||
<p>This document requires no interaction with the Internet Assigned Numbers Authority (IANA).</p>
|
||
</section1>
|
||
<section1 topic="XMPP Registrar Considerations" anchor="xmpp_registrar_considerations">
|
||
<section2 topic="Protocol Namespaces" anchor="protocol_namespaces">
|
||
<p>The XMPP Registrar should include "urn:xmpp:rtt:0" in its registry of protocol namespaces (see <<link url="http://xmpp.org/registrar/namespaces.html">http://xmpp.org/registrar/namespaces.html</link>>).</p>
|
||
</section2>
|
||
<section2 topic="Namespace Versioning" anchor="namespace_versioning">
|
||
<p>If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.</p>
|
||
</section2>
|
||
</section1>
|
||
<section1 topic="XML Schema" anchor="xml_schema">
|
||
<p><code><![CDATA[<?xml version='1.0' encoding='UTF-8'?>
|
||
|
||
<xs:schema
|
||
xmlns:xs='http://www.w3.org/2001/XMLSchema'
|
||
targetNamespace='urn:xmpp:rtt:0'
|
||
xmlns='urn:xmpp:rtt:0'
|
||
elementFormDefault='qualified'>
|
||
|
||
<xs:annotation>
|
||
<xs:documentation>
|
||
The protocol documented by this schema is defined in
|
||
XEP-0301: http://www.xmpp.org/extensions/xep-0301.html
|
||
</xs:documentation>
|
||
</xs:annotation>
|
||
|
||
<xs:element name='rtt'>
|
||
<xs:complexType>
|
||
<xs:attribute name='seq' type='xs:unsignedInt' use='required'/>
|
||
<xs:attribute name='event' use='optional'>
|
||
<xs:simpleType>
|
||
<xs:restriction base="xs:string">
|
||
<xs:enumeration value="new"/>
|
||
<xs:enumeration value="reset"/>
|
||
<xs:enumeration value="init"/>
|
||
<xs:enumeration value="cancel"/>
|
||
</xs:restriction>
|
||
</xs:simpleType>
|
||
</xs:attribute>
|
||
<xs:attribute name='id' type='xs:string' use='optional'>
|
||
<xs:sequence>
|
||
<xs:element ref='t' minOccurs='0' maxOccurs='unbounded'/>
|
||
<xs:element ref='e' minOccurs='0' maxOccurs='unbounded'/>
|
||
<xs:element ref='w' minOccurs='0' maxOccurs='unbounded'/>
|
||
</xs:sequence>
|
||
</xs:complexType>
|
||
</xs:element>
|
||
|
||
<xs:element name='t' type='xs:string'>
|
||
<xs:complexType>
|
||
<xs:attribute name='p' type='xs:nonNegativeInteger' use='optional'/>
|
||
</xs:complexType>
|
||
</xs:element>
|
||
|
||
<xs:element name='e' type='empty'>
|
||
<xs:complexType>
|
||
<xs:attribute name='p' type='xs:nonNegativeInteger' use='optional'/>
|
||
<xs:attribute name='n' type='xs:nonNegativeInteger' use='optional' default='1'/>
|
||
</xs:complexType>
|
||
</xs:element>
|
||
|
||
<xs:element name='w' type='empty'>
|
||
<xs:complexType>
|
||
<xs:attribute name='n' type='xs:nonNegativeInteger' use='required'/>
|
||
</xs:complexType>
|
||
</xs:element>
|
||
|
||
<xs:simpleType name='empty'>
|
||
<xs:restriction base='xs:string'>
|
||
<xs:enumeration value=''/>
|
||
</xs:restriction>
|
||
</xs:simpleType>
|
||
|
||
</xs:schema>]]></code></p>
|
||
</section1>
|
||
<section1 topic="Acknowledgments" anchor="acknowledgments">
|
||
<p>The members of the Real-Time Text Taskforce (R3TF), <link class="western" href="http://www.realtimetext.org/">www.realtimetext.org</link>, made significant contributions to this specification. Mark Rejhon leads the Jabber/XMPP Taskgroup at R3TF. Members of R3TF who have contributed to this specification include Gunnar Hellstrom, Paul E. Jones, Gregg Vanderheiden, Barry Dingle, and Arnoud van Wijk. Others contributors include Bernard Aboba, Mark Grady, Darren Sturman, Christian Vogler, Norm Williams, and several members from the XMPP Standards Mailing List, including Kevin Smith, Peter Saint Andre and many others.</p>
|
||
<p>The technique of <link url="#preserving_key_press_intervals">Preserving Key Press Intervals</link>, otherwise called "natural typing", was created by Mark Rejhon, who is deaf. It is incorporated into this specification in compliance of the XSF's Intellectual Property Rights Policy at <link class="western" href="http://xmpp.org/extensions/ipr-policy.shtml">http://xmpp.org/extensions/ipr-policy.shtml</link>.</p>
|
||
|
||
|
||
</section1>
|
||
|
||
</xep>
|