< draft-ietf-avt-rtp-clearmode-04.txt   draft-ietf-avt-rtp-clearmode-05.txt >
Audio/Video Transport Audio/Video Transport
Internet Draft R. Kreuter Internet Draft R. Kreuter
Document: draft-ietf-avt-rtp-clearmode-04.txt Siemens AG Document: draft-ietf-avt-rtp-clearmode-05.txt Siemens AG
Expires: June 2004 December 2003 Expires: October 2004 April 2004
RTP payload format for a 64 kbit/s transparent call RTP payload format for a 64 kbit/s transparent call
Status of this Memo Status of this Memo
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Abstract Abstract
This document describes how to carry 64 kbit/s data streams This document describes how to carry 64 kbit/s channel data
transparently in RTP packets, using a pseudo-codec called transparently in RTP packets, using a pseudo-codec called
"Clearmode". It also serves as registration for a related MIME type "Clearmode". It also serves as registration for a related MIME type
called "audio/clearmode". called "audio/clearmode".
"Clearmode" is a basic feature of VoIP media gateways. "Clearmode" is a basic feature of VoIP media gateways.
Table of Contents Table of Contents
1. Introduction..................................................2 1. Introduction..................................................1
2. Conventions used in this document.............................3 2. Conventions used in this document.............................2
3. 64 kbit/s data stream handling and RTP header parameters......3 3. 64 kbit/s data stream handling and RTP header parameters......2
4. IANA Considerations...........................................3 4. IANA Considerations...........................................3
5. Mapping to Session Description Protocol (SDP) parameters......4 5. Mapping to Session Description Protocol (SDP) parameters......3
6. Security Considerations.......................................5 6. Security Considerations.......................................4
7. References....................................................6 7. References....................................................4
8. Author's Address..............................................6 8. Acknowledgements..............................................5
9. IPR Notice....................................................6 9. Author's Address..............................................5
10. Full Copyright Statement.....................................7 10. Full Copyright Statement.....................................5
11. Disclaimer...................................................5
1. Introduction 1. Introduction
[Note to the RFC Editor: This paragraph is to be deleted when this [Note to the RFC Editor: This paragraph is to be deleted when this
draft is published as an RFC. All references to RFC yyyy in section draft is published as an RFC. All references to RFC yyyy in section
4 should be replaced by the RFC number of this draft, when published. 4 should be replaced by the RFC number of this draft, when published.
All references to RFC XXXX in sections 4 and 5 should be replaced by All references to RFC XXXX in sections 4 and 5 should be replaced by
the RFC number of the revision of RFC 2327, when published.] the RFC number of the revision of RFC 2327, when published.]
Voice over IP (VoIP) media gateways need to carry all data streams Voice over IP (VoIP) media gateways need to carry all possible data
generated by analog or integrated services digital network (ISDN) streams generated by analog terminals or integrated services digital
terminals via an IP network. network (ISDN) terminals via an IP network. Within this document a
VoIP media gateway is a device that converts a (digital or analog)
linear data stream to a digital packetized data stream or vice versa.
Refer to RFC 2719 [12] for an introduction into the basic
architecture of a media gateway based network.
ISDN wideband speech terminals do not rely on a voice data Usually a VoIP media gateway does some processing on the data it
processing, like echo cancellation or dual tone multifrequency (DTMF) converts besides packetization or depacketization; e.g. echo
detection, within a VoIP media gateway. Moreover, ISDN data cancellation or dual tone multifrequency (DTMF) detection, and
terminals e.g. will produce data streams that are not compatible with especially a coding/decoding. But there is a class of data streams
a non-linear encoding as is used for voice. that does not rely or even does not allow any data processing within
the VoIP media gateway except for packetization or depacketization.
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 For such applications, there exists a necessity for a transparent
relay of 64 kbit/s data streams in real-time transport protocol (RTP) 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" [6] packets. This mode is often referred to as "clear-channel data"
or "64 kbit/s unrestricted". No encoder/decoder is needed in that or "64 kbit/s unrestricted". No encoder/decoder is needed in that
case, but a unique RTP payload type is necessary and a related MIME case, but a unique RTP payload type is necessary and a related MIME
type is to be registered for signaling purposes. type is to be registered for signaling purposes.
Clearmode is not restricted to the examples described above. It can Clearmode is not restricted to the examples described above. It can
be used by any application, that does not need a special encoding / be used by any application, that does not need a special encoding /
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kHz voice" and "ISDN data" in VoIP media gateways. kHz voice" and "ISDN data" in VoIP media gateways.
This document also serves as the MIME type registration according to This document also serves as the MIME type registration according to
RFC 2048 [5], which defines procedures for registration of new MIME RFC 2048 [5], which defines procedures for registration of new MIME
types within the IETF tree. types within the IETF tree.
2. Conventions used in this document 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2]. document are to be interpreted as described in RFC 2119 [11].
3. 64 kbit/s data stream handling and RTP header parameters 3. 64 kbit/s data stream handling and RTP header parameters
Clearmode does not use any encoding or decoding. It just provides Clearmode does not use any encoding or decoding. It just provides
packetization. packetization.
Clearmode assumes that the data to be handled is sample oriented with Clearmode assumes that the data to be handled is sample oriented with
one octet (8bits) per sample. There is no restriction on the number one octet (8bits) per sample. There is no restriction on the number
of samples per packet other than the 64 kbyte limit imposed by the IP of samples per packet other than the 64 kbyte limit imposed by the IP
protocol. The number of samples SHOULD be less than the path maximum protocol. The number of samples SHOULD be less than the path maximum
transmission unit (MTU) minus combined packet header length. transmission unit (MTU) minus combined packet header length. If the
environment is expected to have tunnels or security encapsulation as
part of operation, the number of samples SHOULD be reduced to allow
for the extra header space used for those.
The payload packetization/depacketization for Clearmode is similar to The payload packetization/depacketization for Clearmode is similar to
the Pulse Code Modulation (PCMU or PCMA) handling described in RFC the Pulse Code Modulation (PCMU or PCMA) handling described in RFC
3551 [7]. Each Clearmode octet SHALL be octet-aligned in a RTP 3551 [7]. Each Clearmode octet SHALL be octet-aligned in a RTP
packet. The sign bit of each octet SHALL correspond to the most packet. The sign bit of each octet SHALL correspond to the most
significant bit of the octet in the RTP packet. significant bit of the octet in the RTP packet.
A sample rate of 8000 Hz MUST be used. A sample rate of 8000 Hz MUST be used.
This calculates to a 64 kbit/s transmission rate per channel. This calculates to a 64 kbit/s transmission rate per channel.
skipping to change at page 4, line 40 skipping to change at page 3, line 51
See Section 6 of RFC yyyy See Section 6 of RFC yyyy
Interoperability considerations: none Interoperability considerations: none
Published specification: RFC yyyy Published specification: RFC yyyy
Applications, which use this media type: Applications, which use this media type:
Voice over IP Media Gateways, transferring "ISDN 64 kb/s Voice over IP Media Gateways, transferring "ISDN 64 kb/s
data", "ISDN 7 kHz voice", or other 64 kbit/s data streams via data", "ISDN 7 kHz voice", or other 64 kbit/s data streams via
a RTP connection an RTP connection
Note: the choice of the "audio" top-level MIME type was made
because the dominant uses of this pseudo-codec are expected to
telephony and voice-gateway-related. The "audio" type allows
the use of sharing of the port in the SDP "m=" line with
codecs such as audio/g711 [9], [10], for one example. This
sharing is an important application and would not be possible
otherwise.
Additional information: none Additional information: none
Intended usage: COMMON Intended usage: COMMON
Author/Change controller: Author/Change controller:
IETF Audio/Video transport working group IETF Audio/Video transport working group
5. Mapping to Session Description Protocol (SDP) parameters 5. Mapping to Session Description Protocol (SDP) parameters
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6. Security Considerations 6. Security Considerations
Implementations using the payload format defined in this Implementations using the payload format defined in this
specification are subject to the security considerations discussed in specification are subject to the security considerations discussed in
the RFC 3550 [6]. The payload format described in this document does the RFC 3550 [6]. The payload format described in this document does
not specify any different security services. The primary function of not specify any different security services. The primary function of
this payload format is to add a transparent transport for a 64 kbit/s this payload format is to add a transparent transport for a 64 kbit/s
data stream. data stream.
Confidentiality of the media streams is achieved by encryption. Confidentiality of the media streams is achieved by encryption, for
example by application of the Secure RTP profile [13].
As with any IP-based protocol, in some circumstances a receiver may As with any IP-based protocol, in some circumstances a receiver may
be overloaded simply by the receipt of too many packets, either be overloaded simply by the receipt of too many packets, either
desired or undesired. Network-layer authentication MAY be used to desired or undesired. Network-layer authentication MAY be used to
discard packets from undesired sources, but the processing cost of discard packets from undesired sources, but the processing cost of
the authentication itself may be too high. Overload can also occur, the authentication itself may be too high. Overload can also occur,
if the sender chooses to use a smaller packetization period, than the if the sender chooses to use a smaller packetization period, than the
receiver can process. The ptime parameter can be used to negotiate receiver can process. The ptime parameter can be used to negotiate
an appropriate packetization during session setup. an appropriate packetization during session setup.
In general RTP is not an appropriate transfer protocol for reliable In general RTP is not an appropriate transfer protocol for reliable
octet streams. TCP is better in those cases. Besides that, packet octet streams. TCP is better in those cases. Besides that, packet
loss due to congestion is as much an issue for clearmode, as for loss due to congestion is as much an issue for clearmode, as for
other payload formats. Refer to RFC 3551 [7], section 2, for a other payload formats. Refer to RFC 3551 [7], section 2, for a
discussion of this issue. discussion of this issue.
7. References 7. References
Normative References Normative References
[1] S. Bradner, "The Internet Standards Process -- Revision 3", BCP [1] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3667,
9, RFC 2026, October 1996. February 2004.
[2] S. Bradner, "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., Ed., "Intellectual Property Rights in IETF
Levels", BCP 14, RFC 2119, March 1997 Technology", BCP 79, RFC 3668, February 2004.
[3] M. Handley and C. Perkins, "Guidelines for Writers of RTP [3] M. Handley and C. Perkins, "Guidelines for Writers of RTP
Payload Format Specifications", RFC 2736, December 1999 Payload Format Specifications", RFC 2736, December 1999
[4] N. Freed, N. Borenstein, "Multipurpose Internet Mail Extensions [4] N. Freed, N. Borenstein, "Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies ", RFC 2045, (MIME) Part One: Format of Internet Message Bodies ", RFC 2045,
November 1996. November 1996.
[5] N. Freed, J. Klensin and J. Postel, "Multipurpose Internet Mail [5] N. Freed, J. Klensin and J. Postel, "Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures", BCP 13, Extensions (MIME) Part Four: Registration Procedures", BCP 13,
skipping to change at page 6, line 36 skipping to change at page 4, line 76
[6] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, [6] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", RFC "RTP: A Transport Protocol for Real-Time Applications", RFC
3550, July 2003. 3550, July 2003.
[7] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video [7] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", RFC 3551, July 2003. Conferences with Minimal Control", RFC 3551, July 2003.
[8] Casner, S. and P. Hoschka, "MIME Type Registration of RTP [8] Casner, S. and P. Hoschka, "MIME Type Registration of RTP
Payload Types", RFC 3555, July 2003. Payload Types", RFC 3555, July 2003.
[10] M. Handley, V. Jacobson and C. Perkins, draft-ietf-mmusic-sdp- [9] M. Handley, V. Jacobson and C. Perkins, draft-ietf-mmusic-sdp-
new-xx.txt "SDP: Session Description Protocol", revision of new-xx.txt "SDP: Session Description Protocol", revision of
2327, work in progress. 2327, work in progress.
8. Author's Address [10] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
SDP", RFC 3264, June 2002
[11] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
Informational References
[12] L. Ong, et. al., "Framework Architecture for Signaling
Transport", RFC 2719, October 1999.
[13] Baugher, et al., "The Secure Real-time Transport Protocol
(SRTP)", RFC 3711, March 2004
8. Acknowledgements
The editor would like to acknowledge the help of the IETF AVT Working
Group and, in particular the help of Colin Perkins and Magnus
Westerlund for their intensive reviews and comments.
9. Author's Address
Ruediger Kreuter Ruediger Kreuter
Siemens AG Siemens AG
81359 Munich, Germany 81730 Munich, Germany
Email: ruediger.kreuter@siemens.com Email: ruediger.kreuter@siemens.com
9. IPR Notice
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementers or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights, which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
10. Full Copyright Statement 10. Full Copyright Statement
"Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (year). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and translations of it may be copied and furnished to 11. Disclaimer
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
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The limited permissions granted above are perpetual and will not be This document and the information contained herein are provided on an
revoked by the Internet Society or its successors or assigns. "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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