Audio/Video Transport
                   Internet Draft                                            R. Kreuter
                   Document: draft-ietf-avt-rtp-clearmode-01.txt             Siemens AG
                   Expires: March 2004                                   September 2003
                
                
                            RTP payload format for a 64 kbit/s transparent call
                
                
                Status of this Memo
                
                   This document is an Internet-Draft and is in full conformance with
                   all provisions of Section 10 of RFC 2026.
                
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                Abstract
                
                   This document describes how to carry 64 kbit/s data streams
                   transparently in RTP packets, using a pseudo-codec called
                   "Clearmode".  It also serves as registration for a related MIME type
                   called "audio/clearmode".
                   "Clearmode" is a basic feature of VoIP media gateways.
                
                
                Conventions used in this document
                
                   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.
                
                
                
                
                
                
                
                
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                Table of Contents
                
                   1. Introduction..................................................2
                   2. 64 kbit/s data stream handling and RTP header parameters......2
                   3. Registration of audio/clearmode...............................3
                   4. Mapping to Session Descrition Protocol (SDP) parameters.......4
                   5. Security Considerations.......................................5
                   6. References....................................................5
                   7. Author's Address..............................................6
                   8. IPR Notice....................................................6
                   9. Full Copyright Statement......................................7
                
                
                1. Introduction
                
                   Voice over IP (VoIP) media gateways need to carry all data streams
                   generated by analog or integrated services digital network (ISDN)
                   terminals via an IP network.
                
                   ISDN wideband speech terminals do not rely on a voice data
                   processing, like echo cancellation or dual tone multifrequency (DTMF)
                   detection, within a VoIP media gateway.  And ISDN data terminals e.g.
                   will produce data streams that are not compatible with a non-linear
                   encoding as is used for voice.
                
                   For such applications, there exists a necessity for a transparent
                   relay of 64 kbit/s data streams in real-time transport protocol (RTP)
                   [6] packets.  This mode is often referred to as "clear-channel data"
                   or "64 kbit/s unrestricted".  No encoder/decoder is needed in that
                   case, but an unique RTP payload type is necessary and a related MIME
                   type is to be registered for signaling purposes.
                
                   This payload format document describes a pseudo-codec called
                   "Clearmode", for sample-oriented 64 kbit/s data streams with 8 bits
                   per sample.  It is in accordance with RFC 2736 [3], which provides a
                   guideline for the specification of new RTP payload formats.
                
                   Examples for the use of Clearmode in current VoIP media gateways are
                   the transfer of "ISDN 7 kHz voice" and "ISDN data".
                
                   This document also serves as the MIME type registration according RFC
                   2048 [5], which defines procedures for registration of new MIME types
                   within the IETF tree.
                
                
                2. 64 kbit/s data stream handling and RTP header parameters
                
                   Clearmode does not use any encoding or decoding. It just provides
                   packetization.
                
                
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                   Clearmode assumes that the data to be handled is sample oriented with
                   one octet (8bits) per sample.  There is no restriction on the number
                   of samples per packet.
                
                   The payload packetization/depacketization for Clearmode is similar to
                   the Pulse Code Modulation (PCMU or PCMA) handling described in RFC
                   3551 [7].  Each Clearmode octet SHALL be octet-aligned in a RTP
                   packet.
                
                   A sample rate of 8000 Hz is used.
                   This calculates to a 64 kbit/s transmission rate per channel.
                
                   The Timestamp SHALL be set as described in the RTP specification [6].
                
                   The marker bit is always zero.  Silence suppression is not applicable
                   for Clearmode data streams.
                
                   The payload type is dynamically assigned by means outside the scope
                   of this document.
                
                   This document specifies the use of RTP over unicast and multicast UDP
                   as well as TCP.  (This does not preclude the use of this definition
                   when RTP is carried by other lower-layer protocols.)
                
                
                3. Registration of audio/clearmode
                
                   To: ietf-types@iana.org
                
                   Subject: Registration of MIME media type audio/clearmode
                
                   MIME media type name: audio
                
                   MIME subtype name: clearmode
                
                   Required parameters: none
                
                   Optional parameters: ptime, maxptime
                
                          "ptime" gives the length of time in milliseconds represented
                          by the media in a packet, as described in RFC 2327 [9].
                
                          "maxptime" represents the maximum amount of media which can be
                          encapsulated in each packet, expressed as time in
                          milliseconds, as described in [10].
                
                   Encoding considerations:
                
                
                
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                          This type is defined for transfer via RTP [6].
                
                   Security considerations:
                
                          Implementations using the profile defined in this
                          specification are subject to the security considerations
                          discussed in RFC 3550 and RFC 3551.
                
                   Interoperability considerations: none
                
                   Published specification: This document
                
                   Applications which use this media type:
                
                          Voice over IP Media Gateways, transferring "ISDN 64 kb/s data"
                          or "ISDN 7 kHz voice" or other VoIP-related 64 kbit/s data
                          streams via a RTP connection.
                
                   Additional information: none
                
                   Intended usage: COMMON
                
                   Author/Change controller:
                
                          This registration is part of the IETF registration tree.
                
                
                4. Mapping to Session Descrition Protocol (SDP) parameters
                
                   Parameters are mapped to SDP [9] in a standard way.
                
                       o  The MIME type (audio) goes in SDP "m=" as the media name.
                
                       o  The MIME subtype (clearmode) goes in SDP "a=rtpmap" as the
                          encoding name.
                
                       o  The optional parameters "ptime" and "maxptime" go in the SDP
                          "a=ptime" and "a=maxptime" attributes, respectively.
                
                
                   An example mapping is as follows:
                
                           audio/clearmode; ptime=10
                
                           m=audio 12345 RTP/AVP 97
                           a=rtpmap:97 CLEARMODE/8000
                           a=ptime:10
                
                
                
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                   Note that the payload format (encoding) names defined in the RTP
                   Profile are commonly shown in upper case.  MIME subtypes are commonly
                   shown in lower case.  These names are case-insensitive in both
                   places.
                
                   Similarly, parameter names are case-insensitive both in MIME types
                   and in the default mapping to the SDP a=fmtp attribute.
                
                
                5. Security Considerations
                
                   Implementations using the profile defined in this specification are
                   subject to the security considerations discussed in the RTP
                   specification [6].  This profile does not specify any different
                   security services.  The primary function of this profile is to add a
                   transparent transport for a 64 kbit/s data stream.
                
                   Confidentiality of the media streams is achieved by encryption.
                
                   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.  Overload can also occur,
                   if the sender chooses to use a smaller packetization period, than the
                   receiver can process.  The ptime parameter can be used to negotiate
                   an appropriate packetization during session setup.
                
                
                6. References
                
                   Normative References
                
                   [1]  S. Bradner, "The Internet Standards Process -- Revision 3", BCP
                        9, RFC 2026, October 1996.
                
                   [2]  S. Bradner, "Key words for use in RFCs to Indicate Requirement
                        Levels", BCP 14, RFC 2119, March 1997
                
                   [3]  M. Handley and C. Perkins, "Guidelines for Writers of RTP
                        Payload Format Specifications", RFC 2736, December 1999
                
                   [4]  N. Freed, N. Borenstein, "Multipurpose Internet Mail Extensions
                        (MIME) Part One: Format of Internet Message Bodies ", RFC 2045,
                        November 1996.
                
                   [5]  N. Freed, J. Klensin and J. Postel, "Multipurpose Internet Mail
                        Extensions (MIME) Part Four: Registration Procedures", BCP 13,
                        RFC 2048, November 1996.
                
                
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                   [6]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
                        "RTP: A Transport Protocol for Real-Time Applications", RFC
                        3550, July 2003.
                
                   [7]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
                        Conferences with Minimal Control", RFC 3551, July 2003.
                
                   [8]  Casner, S. and P. Hoschka, "MIME Type Registration of RTP
                        Payload Types", RFC 3555, July 2003.
                
                   [9]  M. Handley and V. Jacobson, "SDP: Session Description Protocol",
                        RFC 2327, April 1998.
                
                   [10] M. Handley, V. Jacobson and C. Perkins, "SDP: Session
                        Description Protocol", revision of 2327, work in progress.
                
                
                7. Author's Address
                
                   Ruediger Kreuter
                   Siemens AG
                   81359 Munich, Germany
                   Email: ruediger.kreuter@siemens.com
                
                
                8. IPR Notice
                
                   The IETF takes no position regarding the validity or scope of any
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                   this standard. Please address the information to the IETF Executive
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                9. Full Copyright Statement
                
                   "Copyright (C) The Internet Society (2003).  All Rights Reserved.
                
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                   The limited permissions granted above are perpetual and will not be
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