[xiph-commits] r8559 - trunk/speex/doc

philkerr at motherfish-iii.xiph.org philkerr at motherfish-iii.xiph.org
Thu Dec 30 13:29:26 PST 2004


Author: philkerr
Date: 2004-12-30 13:29:26 -0800 (Thu, 30 Dec 2004)
New Revision: 8559

Added:
   trunk/speex/doc/draft-herlein-speex-rtp-profile-03.xml
Log:


Added: trunk/speex/doc/draft-herlein-speex-rtp-profile-03.xml
===================================================================
--- trunk/speex/doc/draft-herlein-speex-rtp-profile-03.xml	2004-12-30 18:41:59 UTC (rev 8558)
+++ trunk/speex/doc/draft-herlein-speex-rtp-profile-03.xml	2004-12-30 21:29:26 UTC (rev 8559)
@@ -0,0 +1,815 @@
+<?xml version='1.0'?>
+<!DOCTYPE rfc SYSTEM 'rfc2629.dtd'>
+<?rfc toc="yes" ?>
+
+<rfc ipr="full3667" docName="RTP Payload Format for the Speex Codec">
+
+<front>
+<title>draft-herlein-speex-rtp-profile-03</title>
+
+<author initials="G" surname="Herlein" fullname="Greg Herlein">
+<organization></organization>
+<address>
+<email>gherlein at herlein.com</email>
+<postal>
+<street>2034 Filbert Street</street>
+<city>San Francisco</city> 
+<region>California</region>
+<code>94123</code>
+<country>United States</country> 
+</postal>
+</address>
+</author>
+
+<author initials="S" surname="Morlat" fullname="Simon Morlat">
+<address>
+<email>simon.morlat at linphone.org</email>
+<postal>
+<street>35, av de Vizille App 42</street>
+<city>Grenoble</city>
+<code>38000</code>
+<country>France</country>
+</postal>
+</address>
+</author>
+
+<author initials="J" surname="Jean-Marc" fullname="Jean-Marc Valin">
+<address>
+<email>jean-marc.valin at hermes.usherb.ca</email>
+<postal>
+<street>Department of Electrical and Computer Engineering</street>
+<street>University of Sherbrooke</street>
+<street>2500 blvd Universite</street>
+<city>Sherbrooke</city>
+<region>Quebec</region>
+<code>J1K 2R1</code>
+<country>Canada</country>
+</postal>
+</address>
+</author>
+
+<author initials="R" surname="Hardiman" fullname="Roger Hardiman">
+<address>
+<email>roger at freebsd.org</email>
+<postal>
+<street>49 Nettleton Road</street>
+<city>Cheltenham</city>
+<region>Gloucestershire</region>
+<code>GL51 6NR</code>
+<country>England</country>
+</postal>
+</address>
+</author>
+
+
+<author initials="P" surname="Kerr" fullname="Phil Kerr">
+<address>
+<email>phil at plus24.com</email>
+<postal>
+<country>England</country>
+</postal>
+</address>
+</author>
+
+<date day="01" month="January" year="2005" />
+
+<area>General</area>
+<workgroup>AVT Working Group</workgroup>
+<keyword>I-D</keyword>
+
+<keyword>Internet-Draft</keyword>
+<keyword>Speex</keyword>
+<keyword>RTP</keyword>
+<abstract>
+<t>
+Speex is an open-source voice codec suitable for use in Voice over
+IP (VoIP) type applications.  This document describes the payload
+format for Speex generated bit streams within an RTP packet.  Also
+included here are the necessary details for the use of Speex with
+the Session Description Protocol (SDP) and a preliminary method of
+using Speex within H.323 applications.
+</t>
+</abstract>
+</front>
+
+<middle>
+
+<section anchor="Conventions used in this document" title="Conventions used in this document">
+<t>
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+document are to be interpreted as described in RFC 2119 <xref target="rfc2119"></xref>.
+</t>
+</section>
+
+<section anchor="Overview of the Speex Codec" title="Overview of the Speex Codec">
+
+<t>
+Speex is based on the CELP <xref target="CELP"></xref> encoding technique with support for 
+either narrowband (nominal 8kHz), wideband (nominal 16kHz) or 
+ultra-wideband (nominal 32kHz), and (non-optimal) rates up to 48 kHz 
+sampling also available.  The main characteristics can be summarized 
+as follows:
+</t>
+
+<t>
+<list style="symbols">
+<t>Free software/open-source</t>
+<t>Integration of wideband and narrowband in the same bit-stream</t>
+<t>Wide range of bit-rates available</t>
+<t>Dynamic bit-rate switching and variable bit-rate (VBR)</t>
+<t>Voice Activity Detection (VAD, integrated with VBR)</t>
+<t>Variable complexity</t>
+</list>
+</t>
+
+</section>
+
+<section anchor="RTP payload format for Speex" title="RTP payload format for Speex">
+
+<t>
+For RTP based transportation of Speex encoded audio the standard 
+RTP header [2] is followed by one or more payload data blocks. 
+An optional padding terminator may also be used. 
+</t>
+<artwork><![CDATA[
+      0                   1                   2                   3
+      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                         RTP Header                            |
+     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+     |                 one or more frames of Speex ....              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |        one or more frames of Speex ....       |    padding    |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+]]></artwork>
+
+</section>
+
+<section anchor="RTP Header" title="RTP Header">
+
+<artwork><![CDATA[
+      0                   1                   2                   3
+      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |                           timestamp                           |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |           synchronization source (SSRC) identifier            |
+     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+     |            contributing source (CSRC) identifiers             |
+     |                              ...                              |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+]]></artwork>
+
+<t>
+The RTP header begins with an octet of fields (V, P, X, and CC) to   
+support specialized RTP uses (see <xref target="rfc3550"></xref> and <xref target="rfc3551"></xref> for details). For 
+Speex the following values are used.
+</t>
+
+<t>Version (V): 2 bits</t><t>
+   This field identifies the version of RTP. The version
+   used by this specification is two <xref target="rfc3550"></xref>.
+</t>
+
+<t>Padding (P): 1 bit</t><t>
+      If the padding bit is set, the packet contains one or more
+      additional padding octets at the end which are not part of
+      the payload.  P is set if the total packet size is less than 
+      the MTU.  
+</t>
+
+<t>Extension (X): 1 bit</t><t>
+      If the extension, X, bit is set, the fixed header MUST be 
+      followed by exactly one header extension, with a format defined 
+      in Section 5.3.1. of <xref target="rfc3550"></xref>. 
+</t>
+
+<t>CSRC count (CC): 4 bits</t><t>
+      The CSRC count contains the number of CSRC identifiers.
+</t>
+
+<t>Marker (M): 1 bit</t><t>
+      The M bit indicates if the packet contains comfort noise.  This 
+      field is used in conjunction with the cng SDP attribute and is 
+      detailed further in section 5 below.  In normal usage this bit 
+      is set if the packet contains comfort noise.
+</t>
+
+<t>Payload Type (PT): 7 bits</t><t>
+      An RTP profile for a class of applications is expected to assign 
+      a payload type for this format, or a dynamically allocated 
+      payload type SHOULD be chosen which designates the payload as 
+      Speex.
+</t>
+
+<t>Sequence number: 16 bits</t><t>
+      The sequence number increments by one for each RTP data packet
+      sent, and may be used by the receiver to detect packet loss and
+      to restore packet sequence.  This field is detailed further in
+      <xref target="rfc3550"></xref>.
+</t>
+
+<t>Timestamp: 32 bits</t><t>
+      A timestamp representing the sampling time of the first sample of
+      the first Speex packet in the RTP packet.  The clock frequency 
+      MUST be set to the sample rate of the encoded audio data.
+
+      Speex uses 20 msec frames and a variable sampling rate clock.  
+      The RTP timestamp MUST be in units of 1/X of a second where X 
+      is the sample rate used.  Speex uses a nominal 8kHz sampling rate
+      for narrowband use, a nominal 16kHz sampling rate for wideband use, 
+      and a nominal 32kHz sampling rate for ultra-wideband use.
+</t>
+
+<t>SSRC/CSRC identifiers:</t><t>
+      These two fields, 32 bits each with one SSRC field and a maximum 
+      of 16 CSRC fields, are as defined in <xref target="rfc3550"></xref>.  
+</t>
+
+</section>
+
+<section anchor="Speex payload" title="Speex payload">
+
+<t>
+For the purposes of packetizing the bit stream in RTP, it is only
+necessary to consider the sequence of bits as output by the Speex
+encoder <xref target="speexenc"></xref>, and present the same sequence to the decoder.  The 
+payload format described here maintains this sequence.  
+</t>
+
+<t>
+A typical Speex frame, encoded at the maximum bitrate, is approx.
+110 octets and the total number of Speex frames SHOULD be kept 
+less than the path MTU to prevent fragmentation.  Speex frames MUST
+NOT be fragmented across multiple RTP packets,
+</t>
+
+<t>
+An RTP packet MAY contain Speex frames of the same bit rate or of
+varying bit rates, since the bit-rate for a frame is conveyed in
+band with the signal.
+</t>
+
+<t>
+The encoding and decoding algorithm can change the bit rate at any
+20 msec frame boundary, with the bit rate change notification provided
+in-band with the bit stream.  Each frame contains both "mode" 
+(narrowband, wideband or ultra-wideband) and "sub-mode" (bit-rate) 
+information in the bit stream.  No out-of-band notification is 
+required for the decoder to process changes in the bit rate sent 
+by the encoder.
+</t>
+
+<t>
+It is RECOMMENDED that values of 8000, 16000 and 32000 be used 
+for normal internet telephony applications, though the sample 
+rate is supported at rates as low as 6000 Hz and as high as 
+48 kHz.
+</t>
+
+<t>
+The RTP payload MUST be padded to provide an integer number of
+octets as the payload length.  These padding bits are LSB aligned
+in network octet order and consist of a 0 followed by all ones
+(until the end of the octet).  This padding is only required for
+the last frame in the packet, and only to ensure the packet
+contents ends on an octet boundary.
+</t>
+
+</section>
+
+<section anchor="Example Speex packet" title="Example Speex packet">
+
+<t>
+In the example below we have a single Speex frame with 5 bits
+of padding to ensure the packet size falls on an octet boundary.
+</t>
+
+<artwork><![CDATA[
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                           timestamp                           |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |         synchronization source (SSRC) identifier              |
+   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+   |         contributing source (CSRC) identifiers                |
+   |                              ...                              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                        ..speex data..                         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                        ..speex data..               |0 1 1 1 1|
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+]]></artwork>
+
+</section>
+
+<section anchor="Multiple Speex frames in a RTP packet" title="Multiple Speex frames in a RTP packet">
+
+<t>
+Below is an example of two Speex frames contained within one RTP 
+packet.  The Speex frame length in this example fall on an octet
+boundary so there is no padding.
+</t>
+
+<t>
+Speex codecs <xref target="speexenc"></xref> are able to detect the the bitrate from the
+payload and are responsible for detecting the 20 msec boundaries
+between each frame.
+</t>
+
+<artwork><![CDATA[
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                           timestamp                           |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |         synchronization source (SSRC) identifier              |
+   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+   |         contributing source (CSRC) identifiers                |
+   |                              ...                              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                        ..speex data..                         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |        ..speex data..         |        ..speex data..         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                        ..speex data..                         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+]]></artwork>
+
+</section>
+
+<section anchor="MIME registration of Speex" title="MIME registration of Speex">
+
+<t>
+Full definition of the MIME <xref target="rfc2045"></xref> type for Speex will be part of the Ogg
+Vorbis MIME type definition application <xref target="rfc3534"></xref>.  
+</t>
+
+<t>MIME media type name: audio</t>
+
+<t>MIME subtype: speex</t>
+
+<t>Optional parameters:</t>
+
+<t>Required parameters: to be included in the Ogg MIME specification.</t>
+
+<t>Encoding considerations:</t>
+
+<t>Security Considerations:</t>
+<t>See Section 6 of RFC 3047.</t>
+
+<t>Interoperability considerations: none</t>
+
+<t>Published specification:  </t>
+
+<t>Applications which use this media type:</t>
+
+<t>Additional information: none</t>
+
+<t>Person &amp; email address to contact for further information:<vspace blankLines="1" />
+<list style="empty">
+<t>Greg Herlein &lt;gherlein at herlein.com&gt;</t>
+<t>Jean-Marc Valin &lt;jean-marc.valin at hermes.usherb.ca&gt;</t>
+</list>
+</t>
+
+<t>Intended usage: COMMON</t>
+
+<t>Author/Change controller:</t>
+
+<t>
+<list style="empty">
+<t>Author:  Greg Herlein &lt;gherlein at herlein.com&gt;</t>
+<t>Change controller: Greg Herlein &lt;gherlein at herlein.com&gt;</t>          
+<t>Change controller: IETF AVT Working Group</t>
+</list>
+</t>
+
+<t>
+This transport type signifies that the content is to be interpreted
+according to this document if the contents are transmitted over RTP. 
+Should this transport type appear over a lossless streaming protocol
+such as TCP, the content encapsulation should be interpreted as an 
+Ogg Stream in accordance with <xref target="rfc3534"></xref>, with the exception that the
+content of the Ogg Stream may be assumed to be Speex audio and 
+Speex audio only.
+</t>
+
+</section>
+
+<section anchor="SDP usage of Speex" title="SDP usage of Speex">
+
+<t>
+When conveying information by SDP <xref target="rfc2327"></xref>, the encoding name MUST be
+set to "speex".  An example of the media representation in SDP for
+offering a single channel of Speex at 8000 samples per second might
+be:
+</t>
+
+<vspace blankLines="1" />
+<list style="empty">
+<t>m=audio 8088 RTP/AVP 97</t>
+<t>a=rtpmap:97 speex/8000</t>
+</list>	
+
+<t>
+Note that the RTP payload type code of 97 is defined in this media
+definition to be 'mapped' to the speex codec at an 8kHz sampling
+frequency using the 'a=rtpmap' line.  Any number from 96 to 127
+could have been chosen (the allowed range for dynamic types).  
+</t>
+
+<t>
+The value of the sampling frequency is typically 8000 for narrow band
+operation, 16000 for wide band operation, and 32000 for ultra-wide
+band operation.
+</t>
+
+<t>
+If for some reason the offerer has bandwidth limitations, the client 
+may use the "b=" header, as explained in SDP <xref target="rfc2327"></xref>. The following example
+illustrates the case where the offerer cannot receive more than
+10 kbit/s.
+</t>
+
+<vspace blankLines="1" />
+<list style="empty">
+<t>m=audio 8088 RTP/AVP 97</t>
+<t>b=AS:10</t>
+<t>a=rtmap:97 speex/8000</t>
+</list>	
+
+<t>
+In this case, if the remote part agrees, it should configure its
+Speex encoder so that it does not use modes that produce more than
+10 kbit/s. Note that the "b=" constraint also applies on all
+payload types that may be proposed in the media line ("m=").
+</t>
+
+<t>
+An other way to make recommendations to the remote Speex encoder
+is to use its specific parameters via the a=fmtp: directive.  The
+following parameters are defined for use in this way:
+</t>
+
+<vspace blankLines="1" />
+<list style="empty">
+<t>ptime: duration of each packet in milliseconds.<vspace blankLines="1" /></t>
+
+<t>sr:    actual sample rate in Hz.<vspace blankLines="1" /></t>
+
+<t>ebw:   encoding bandwidth - either 'narrow' or 'wide' or 
+        'ultra' (corresponds to nominal 8000, 16000, and
+		32000 Hz sampling rates).<vspace blankLines="1" /></t>
+
+<t>vbr:   variable bit rate  - either 'on' 'off' or 'vad'
+		(defaults to off).  If on, variable bit rate is
+		enabled.  If off, disabled.  If set to 'vad' then
+		constant bit rate is used but silence will be encoded
+		with special short frames to indicate a lack of voice
+		for that period.<vspace blankLines="1" /></t>
+
+<t>cng:   comfort noise generation - either 'on' or 'off'. If
+		off then silence frames will be silent; if 'on' then
+		those frames will be filled with comfort noise.<vspace blankLines="1" /></t>
+
+<t>mode:  Speex encoding mode. Can be {1,2,3,4,5,6,any}
+                defaults to 3 in narrowband, 6 in wide and ultra-wide.<vspace blankLines="1" /></t>
+
+<t>penh:	use of perceptual enhancement. 1 indicates 
+	 	to the decoder that perceptual enhancement is recommended,
+		0 indicates that it is not. Defaults to on (1).<vspace blankLines="1" /></t>
+</list>	
+
+<t>Examples:</t>
+
+<vspace blankLines="1" />
+<list style="empty">
+   	<t>m=audio 8008 RTP/AVP 97</t>
+	<t>a=rtpmap:97 speex/8000</t>
+	<t>a=fmtp:97 mode=4</t>
+</list>	
+
+<t>
+This examples illustrate an offerer that wishes to receive
+a Speex stream at 8000Hz, but only using speex mode 3.
+</t>
+ 
+<t>
+The offerer may suggest to the remote decoder to activate
+its perceptual enhancement filter like this:
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+	<t>m=audio 8088 RTP/AVP 97</t>
+	<t>a=rtmap:97 speex/8000</t>
+	<t>a=fmtp:97 penh=1 </t>
+</list>	
+	
+<t>
+Several Speex specific parameters can be given in a single
+a=fmtp line provided that they are separated by a semi-colon:
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+   	<t>a=fmtp:97 mode=any;penh=1</t>
+</list>	
+
+<t>
+The offerer may indicate that it wishes to send variable bit rate
+frames with comfort noise:
+</t>
+
+<vspace blankLines="1" />
+<list style="empty">
+	<t>m=audio 8088 RTP/AVP 97</t>
+	<t>a=rtmap:97 speex/8000</t>
+	<t>a=fmtp:97 vbr=on;cng=on</t>
+</list>	
+
+<t>
+The "ptime" attribute is used to denote the packetization 
+interval (ie, how many milliseconds of audio is encoded in a 
+single RTP packet).  Since Speex uses 20 msec frames, ptime values 
+of multiples of 20 denote multiple Speex frames per packet.  
+Values of ptime which are not multiples of 20 MUST be ignored 
+and clients MUST use the default value of 20 instead.
+</t>
+   
+<t>
+In the example below the ptime value is set to 40, indicating that 
+there are 2 frames in each packet.	
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+   	<t>m=audio 8008 RTP/AVP 97</t>
+	<t>a=rtpmap:97 speex/8000</t>
+	<t>a=ptime:40</t>
+</list>	
+
+<t>
+Note that the ptime parameter applies to all payloads listed
+in the media line and is not used as part of an a=fmtp directive.
+</t>
+
+<t>
+Values of ptime not multiple of 20 msec are meaningless, so the 
+receiver of such ptime values MUST ignore them.  If during the 
+life of an RTP session the ptime value changes, when there are 
+multiple Speex frames for example, the SDP value must also reflect 
+the new value. 
+</t>
+
+<t>
+Care must be taken when setting the value of ptime so that the 
+RTP packet size does not exceed the path MTU. 
+</t>
+
+</section>
+<section anchor="ITU H.323/H.245 Use of Speex" title="ITU H.323/H.245 Use of Speex">
+
+<t>
+Application is underway to make Speex a standard ITU codec.
+However, until that is finalized, Speex MAY be used in H.323 <xref target="H323"></xref> by
+using a non-standard codec block definition in the H.245 <xref target="H245"></xref> codec
+capability negotiations.  
+</t>
+
+</section>
+
+<section anchor="NonStandardMessage format" title="NonStandardMessage format">
+
+<t>
+For Speex use in H.245 <xref target="H245"></xref> based systems, the fields in the
+NonStandardMessage should be:
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+<t>t35CountryCode   = Hex: B5</t>
+<t>t35Extension     = Hex: 00</t>
+<t>manufacturerCode = Hex: 0026</t>
+<t>[Length of the Binary Sequence (8 bit number)]</t>
+<t>[Binary Sequence consisting of an ASCII string, no NULL terminator]</t>
+</list>
+
+<t>
+The binary sequence is an ascii string merely for ease of use.
+The string is not null terminated.  The format of this string is
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+<t>speex [optional variables]</t>
+</list>
+   
+<t>
+The optional variables are identical to those used for the SDP
+a=fmtp strings discussed in section 5 above.  The string is built
+to be all on one line, each key-value pair separated by a
+semi-colon.  The optional variables MAY be omitted, which causes
+the default values to be assumed.  They are:
+</t>
+
+<vspace blankLines="1" />   
+<list style="empty">
+<t>ebw=narrow;mode=3;vbr=off;cng=off;ptime=20;sr=8000;penh=no;</t>
+</list>
+
+<t>
+The fifth octet of the block is the length of the binary sequence.
+</t>
+
+<t>
+NOTE:  this method can result in the advertising of a large number
+of Speex 'codecs' based on the number of variables possible.  For
+most VoIP applications, use of the default binary sequence of
+'speex' is RECOMMENDED to be used in addition to all other options.
+This maximizes the chances that two H.323 based applications that
+support Speex can find a mutual codec.   
+</t>
+
+</section>
+
+<section anchor="RTP Payload Types" title="RTP Payload Types">
+
+<t>
+Dynamic payload type codes MUST be negotiated 'out-of-band'
+for the assignment of a dynamic payload type from the
+range of 96-127.  H.323 applications MUST use the H.245
+H2250LogicalChannelParameters encoding to accomplish this.  
+</t>
+
+</section>
+
+<section anchor="Security Considerations" title="Security Considerations">
+
+<t>
+RTP packets using the payload format defined in this specification
+are subject to the security considerations discussed in the RTP
+specification <xref target="rfc3550"></xref>, and any appropriate RTP profile.  This implies
+that confidentiality of the media streams is achieved by encryption.
+Because the data compression used with this payload format is applied
+end-to-end, encryption may be performed after compression so there is
+no conflict between the two operations.
+</t>
+
+<t>
+A potential denial-of-service threat exists for data encodings using
+compression techniques that have non-uniform receiver-end
+computational load.  The attacker can inject pathological datagrams
+into the stream which are complex to decode and cause the receiver to
+be overloaded.  However, this encoding does not exhibit any
+significant non-uniformity.
+</t>
+
+<t>
+As with any IP-based protocol, in some circumstances a receiver may
+be overloaded simply by the receipt of too many packets, either
+desired or undesired.  Network-layer authentication may be used to
+discard packets from undesired sources, but the processing cost of
+the authentication itself may be too high.  
+</t>
+
+</section> 
+
+<section anchor="Acknowledgments" title="Acknowledgments">
+
+<t>
+The authors would like to thank Equivalence Pty Ltd of Australia
+for their assistance in attempting to standardize the use of Speex
+in H.323 applications, and for implementing Speex in their open
+source OpenH323 stack.  The authors would also like to thank Brian
+C. Wiles &lt;brian at streamcomm.com&gt; of StreamComm for his assistance in
+developing the proposed standard for Speex use in H.323
+applications.
+</t>
+
+<t>
+The authors would also like to thank the following members of the 
+Speex and AVT communities for their input:  Ross Finlayson, 
+Federico Montesino Pouzols, Henning Schulzrinne, Magnus Westerlund.
+</t>
+</section> 
+
+</middle>
+
+<back>
+
+<references title="Normative References">
+
+<reference anchor="rfc2119">
+<front>
+<title>Key words for use in RFCs to Indicate Requirement Levels </title>
+<author initials="S." surname="Bradner" fullname="Scott Bradner"></author>
+</front>
+<seriesInfo name="RFC" value="2119" />
+</reference> 
+
+<reference anchor="rfc3550">
+<front>
+<title>RTP: A Transport Protocol for real-time applications</title>
+<author initials="H." surname="Schulzrinne" fullname=""></author>
+<author initials="S." surname="Casner" fullname=""></author>
+<author initials="R." surname="Frederick" fullname=""></author>
+<author initials="V." surname="Jacobson" fullname=""></author>
+</front>
+<seriesInfo name="RFC" value="3550" />
+</reference> 
+
+<reference anchor="rfc2045">
+<front>
+<title>Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
+<author initials="" surname="" fullname=""></author>
+</front>
+<date month="November" year="1998" />
+<seriesInfo name="RFC" value="2045" />
+</reference> 
+
+<reference anchor="rfc2327">
+<front>
+<title>SDP: Session Description Protocol</title>
+<author initials="V." surname="Jacobson" fullname=""></author>
+<author initials="M." surname="Handley" fullname=""></author>
+</front>
+<date month="April" year="1998" />
+<seriesInfo name="RFC" value="2327" />
+</reference> 
+
+<reference anchor="H323">
+<front>
+<title>Packet-based Multimedia Communications Systems</title>
+<author initials="" surname="" fullname=""></author>
+</front>
+<date month="" year="1998" />
+<seriesInfo name="ITU-T Recommendation" value="H.323" />
+</reference> 
+
+<reference anchor="H245">
+<front>
+<title>Control of communications between Visual Telephone Systems and Terminal Equipment</title>
+<author initials="" surname="" fullname=""></author>
+</front>
+<date month="" year="1998" />
+<seriesInfo name="ITU-T Recommendation" value="H.245" />
+</reference> 
+
+<reference anchor="rfc3551">
+<front>
+<title>RTP Profile for Audio and Video Conferences with Minimal Control.</title>
+<author initials="H." surname="Schulzrinne" fullname=""></author>
+<author initials="S." surname="Casner" fullname=""></author>
+</front>
+<date month="July" year="2003" />
+<seriesInfo name="RFC" value="3551" />
+</reference> 
+
+<reference anchor="rfc3534">
+<front>
+<title>The application/ogg Media Type</title>
+<author initials="L." surname="Walleij" fullname=""></author>
+</front>
+<date month="May" year="2003" />
+<seriesInfo name="RFC" value="3534" />
+</reference> 
+
+</references> 
+
+<references title="Informative References">
+
+<reference anchor="speexenc">
+<front>
+<title>Speexenc/speexdec, reference command-line encoder/decoder</title>
+</front>
+<seriesInfo name="Speex website" value="http://www.speex.org/" />
+</reference> 
+
+<reference anchor="CELP">
+<front>
+<title>CELP, U.S. Federal Standard 1016.</title>
+<author initials="" surname="" fullname=""></author>
+</front>
+<seriesInfo name="National Technical Information Service (NTIS) website" value="http://www.ntis.gov/" />
+</reference> 
+
+</references> 
+
+</back>
+</rfc>



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