Payload Working Group D. Hanson
Internet Draft M. Faller
Intended status: Standards Track K. Maver
Expires: February 26, 2022 General Dynamics Mission Systems
August 25, 2021
RTP Payload Format for the SCIP Codec
draft-hanson-avtcore-rtp-scip-00.txt
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Abstract
This document describes the RTP payload format of the Secure
Communication Interoperability Protocol (SCIP) as audio and
video media subtypes. It provides RFC 6838 compliant media
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subtype definitions. SCIP-214.2 and SCIP-210 describe the
protocols that comprise the SCIP RTP packet payload. This
document follows the registration for related media types
called "audio/scip" and "video/scip" with IANA and formatted
according to RFC 4855.
Table of Contents
1. Introduction..............................................2
1.1. Conventions..........................................2
1.2. Abbreviations........................................3
2. Background................................................3
3. Media Format Description..................................4
4. Payload Format............................................5
4.1. RTP Header Fields....................................5
5. Payload Format Parameters.................................5
5.1. Media Subtype "audio/scip"...........................6
5.2. Media Subtype "video/scip"...........................7
5.3. Mapping to SDP.......................................8
5.4. SDP Offer/Answer Considerations......................9
6. Security Considerations...................................9
7. IANA Considerations.......................................9
8. References................................................9
8.1. Normative References.................................9
8.2. Informative References..............................11
9. Authors' Addresses.......................................12
1. Introduction
The IANA registration of media subtype types in the IETF tree
created two similar media subtypes "scip" under the audio and
video media types [AUDIOSCIP], [VIDEOSCIP]. This document, as
the common top-level reference, provides information on their
similarities and differences and the usage of those media
subtypes.
This document details usage of the scip pseudo-codec as a
secure session establishment protocol and transport protocol
over RTP. It provides a reference for network security
policymakers, network equipment OEMs, procurement personnel,
and government agency and commercial industry representatives.
1.1. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described
in [RFC2119].
Best current practices for writing an RTP payload format
specification were followed [RFC2736] [RFC8088].
1.2. Abbreviations
The following abbreviations are used in this document.
AVP: Audio/Video Profile
DTX: Discontinuous Transmission
FNBDT: Future Narrowband Digital Terminal
ICWG: Interoperability Control Working Group
IICWG: International Interoperability Control Working
Group
NATO: North Atlantic Treaty Organization
SCIP: Secure Communication Interoperability Protocol
SDP: Session Description Protocol
2. Background
The Secure Communication Interoperability Protocol (SCIP)
allows the negotiation of several voice, data, and video
applications using various encryption suites. SCIP also
provides several important characteristics that have led to its
broad acceptance in the international user community. These
features include end-to-end security at the application layer,
authentication of user identity, the ability to apply different
security levels for each secure session, and secure
communication over any end-to-end data connection.
SCIP began in the U.S. as the FNBDT (Future Narrowband Digital
Terminal) Protocol. A combined Department of Defense and
vendor consortium formed a governing organization named the
ICWG (Interoperability Control Working Group). In time, the
group expanded to include NATO, NATO partners and European
vendors under the name IICWG (International Interoperability
Control Working Group), which was later renamed the SCIP
Working Group.
SCIP is presently implemented in U.S. and NATO secure voice,
video, and data products operating on commercial, private, and
tactical IP networks worldwide using the scip media subtype.
First generation SCIP devices operated on circuit-switched
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networks. SCIP was then expanded to radio and IP networks.
The scip media subtype transports SCIP secure session
establishment signaling and secure application traffic. The
built-in negotiation and flexibility provided by the SCIP
standards make it a natural choice for many scenarios that
require various secure applications and associated encryption
suites. SCIP has been endorsed by many nations as the secure
end-to-end solution for secure voice, video, and data devices.
SCIP standards are currently available to participating
government/military communities and select OEMs of equipment
that support SCIP.
However, SCIP must operate over global networks (including
private and commercial networks). Without access to necessary
information to support SCIP, some networks may not support the
SCIP media subtypes. Issues may occur simply because
information is not as readily available to OEMs, network
administrators, and network architects.
This RFC provides essential information about audio/scip and
video/scip media subtypes that enables network equipment
manufacturers to include scip as a known audio and video media
subtype in their equipment and enables network administrators
to define and implement a compatible security policy.
All current IP-based SCIP devices support "scip" as a media
subtype. Registration of scip as a media subtype provides a
common reference for network equipment manufacturers to
recognize SCIP in a payload declaration.
3. Media Format Description
The "scip" media subtype indicates support for and identifies
SCIP traffic that is being transferred using RTP. SCIP traffic
requires end-to-end bit integrity, therefore transcoding SHALL
NOT be performed over the end-to-end IP connection. The
audio/scip and video/scip media subtype data streams within the
network, including the VoIP network, MUST be a transparent
relay and be treated as "clear-channel data", similar to the
Clearmode media subtype defined by RFC 4040. However,
Clearmode is defined as a gateway protocol and limited to a
sample rate of 8000 Hz and 64kbps bandwidth only [RFC4040].
Clearmode is not defined for the higher sample and data rates
required for some SCIP traffic.
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4. Payload Format
The RTP Packet content of SCIP traffic is dependent upon the
SCIP session state. SCIP secure session establishment uses
protocols defined in SCIP-210 [SCIP210] to negotiate an
application. SCIP secure traffic may consist of the encrypted
output of codecs such as MELPe [RFC8130], G.729D [RFC3551],
H.264 [RFC6184], or other media encodings, based on the
application negotiated during SCIP secure session
establishment. SCIP traffic is highly variable and may include
other SCIP signaling information in the media stream. SCIP
traffic may not always be a continuous stream at the bit rate
specified in the SDP [RFC8866] since discontinuous transmission
(DTX) or other mechanisms may be used. The SCIP payload size
will vary, especially during SCIP secure session establishment.
4.1. RTP Header Fields
The RTP header fields SHOULD conform to RFC 3550. This is a
SHOULD rather than a SHALL in recognition that legacy SCIP-
enabled products may not strictly adhere to RFC 3550.
SCIP traffic may be continuous or discontinuous. The Timestamp
field increments based on the sampling clock for discontinuous
transmission as described in [RFC3550], Section 5.1. The
Timestamp field for continuous transmission applications is
dependent on the sampling rate of the media as specified in the
media subtype's specification (e.g., MELPe [RFC8130]). Note
that during a call, both discontinuous and continuous traffic
is highly probable. Therefore, a jitter buffer MAY be
implemented in endpoint devices only but SHOULD NOT be
implemented in network devices.
The Marker bit SHOULD be set to zero for discontinuous traffic.
The Marker bit for continuous traffic is based on the
underlying media subtype specification. This specification is
a SHOULD rather than a SHALL in recognition that legacy SCIP-
enabled products may not strictly adhere to the media subtype
specification.
5. Payload Format Parameters
The SCIP RTP payload format is identified using the scip media
subtype, which is registered in accordance with [RFC4855] and
per the media type registration template form [RFC6838]. A
clock rate of 8000 Hz SHALL be used for "audio/scip". A clock
rate of 90000 Hz SHALL be used for "video/scip".
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5.1. Media Subtype "audio/scip"
Media type name: audio
Media subtype name: scip
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: Binary. This media subtype is only
defined for transfer via RTP. There SHALL be no
encoding/decoding (transcoding) of the audio stream as it
traverses the network.
Security considerations: See Section 6.
Interoperability considerations: N/A
Published specifications: [SCIP214], [SCIP210]
Applications which use this media: N/A
Fragment Identifier considerations: none
Restrictions on usage: N/A
Additional information:
1. Deprecated alias names for this type: N/A
2. Magic number(s): N/A
3. File extension(s): N/A
4. Macintosh file type code: N/A
5. Object Identifiers: N/A
Person to contact for further information:
1. Name: Michael Faller and Daniel Hanson
2. Email: michael.faller@gd-ms.com and dan.hanson@gd-ms.com
Intended usage: Common, Government and Military
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Authors:
Michael Faller - michael.faller@gd-ms.com
Daniel Hanson - dan.hanson@gd-ms.com
Change controller:
SCIP Working Group - ncia.cis3@ncia.nato.int
5.2. Media Subtype "video/scip"
Media type name: video
Media subtype name: scip
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: Binary. This media subtype is only
defined for transfer via RTP. There SHALL be no
encoding/decoding (transcoding) of the video stream as it
traverses the network.
Security considerations: See Section 6.
Interoperability considerations: N/A
Published specifications: [SCIP214], [SCIP210]
Applications which use this media: N/A
Fragment Identifier considerations: none
Restrictions on usage: N/A
Additional information:
1. Deprecated alias names for this type: N/A
2. Magic number(s): N/A
3. File extension(s): N/A
4. Macintosh file type code: N/A
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5. Object Identifiers: N/A
Person to contact for further information:
1. Name: Michael Faller and Daniel Hanson
2. Email: michael.faller@gd-ms.com and dan.hanson@gd-ms.com
Intended usage: Common, Government and Military
Authors:
Michael Faller - michael.faller@gd-ms.com
Daniel Hanson - dan.hanson@gd-ms.com
Change controller:
SCIP Working Group - ncia.cis3@ncia.nato.int
5.3. Mapping to SDP
The mapping of the above defined payload format media subtype
and its parameters SHALL be done according to Section 3 of
[RFC4855].
An example mapping for audio/scip is:
m=audio 50000 RTP/AVP 96
a=rtpmap:96 scip/8000
An example mapping for video/scip is:
m=video 50002 RTP/AVP 97
a=rtpmap:97 scip/90000
An example mapping for both audio/scip and video/scip is:
m=audio 50000 RTP/AVP 96
a=rtpmap:96 scip/8000
m=video 50002 RTP/AVP 97
a=rtpmap:97 scip/90000
The application negotiation between endpoints will determine
whether the audio and video streams are transported as separate
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streams over the audio and video payload types or as a single
media stream on the video payload type.
5.4. SDP Offer/Answer Considerations
In accordance with the SDP Offer/Answer model [RFC3264], the
SCIP device SHALL list the SCIP payload type in order of
preference in the "m" media line.
6. Security Considerations
RTP packets using the payload format defined in this
specification are subject to the security considerations
discussed in the RTP specification [RFC3550], and in any
applicable RTP profile such as RTP/AVP [RFC3551], RTP/AVPF
[RFC4585], RTP/SAVP [RFC3711], or RTP/ SAVPF [RFC5124].
However, as "Securing the RTP Protocol Framework: Why RTP Does
Not Mandate a Single Media Security Solution" [RFC7202]
discusses, it is not an RTP payload format's responsibility to
discuss or mandate what solutions are used to meet the basic
security goals like confidentiality, integrity, and source
authenticity for RTP in general. This responsibility lays on
anyone using RTP in an application. They can find guidance on
available security mechanisms and important considerations in
"Options for Securing RTP Sessions" [RFC7201]. Applications
SHOULD use one or more appropriate strong security mechanisms.
The rest of this Security Considerations section discusses the
security impacting properties of the payload format itself.
This RTP payload format and its media decoder do not exhibit
any significant non-uniformity in the receiver-side
computational complexity for packet processing, and thus are
unlikely to pose a denial-of-service threat due to the receipt
of pathological data. Nor does the RTP payload format contain
any active content.
7. IANA Considerations
The audio/scip and video/scip media subtypes have been
registered with IANA [AUDIOSCIP] [VIDEOSCIP].
8. References
8.1. Normative References
[AUDIOSCIP] Faller, M., and D. Hanson, "audio/scip", Internet
Assigned Numbers Authority (IANA), 28 January 2021,
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<https://www.iana.org/assignments/media-
types/audio/scip>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC2736] Handley, M. and C. Perkins, "Guidelines for Writers
of RTP Payload Format Specifications", BCP 36, RFC
2736, DOI 10.17487/RFC2736, December 1999,
<https://www.rfc-editor.org/info/rfc2736>.
[RFC3264] Rosenberg, J., and H. Schulzrinne, "An Offer/Answer
Model with Session Description Protocol (SDP)", RFC
3264, June 2002, <https://www.rfc-
editor.org/info/rfc3264>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003,
<https://www.rfc-editor.org/info/rfc3550>.
[RFC3551] Schulzrinne, H., and S. Casner, "RTP Profile for
Audio and Video Conferences with Minimal Control",
RFC 3551, July 2003, <https://www.rfc-
editor.org/info/rfc3551>.
[RFC3711] Baugher, M., McGrew, D., Naslund M., Carrara, E.,
and K. Norrman, "The Secure Real-time Transport
Protocol (SRTP)", RFC 3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and
J. Rey, "Extended RTP Profile for Real-time
Transport Control Protocol (RTCP)-Based Feedback
(RTP/AVPF)", RFC 4585, DOI 10.17487/RFC4585, July
2006, <https://www.rfc-editor.org/info/rfc4585>.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP
Profile for Real-time Transport Control Protocol
(RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, DOI
10.17487/RFC5124, February 2008, <https://www.rfc-
editor.org/info/rfc5124>.
[RFC8866] Begen, A., Kyzivat P., Perkins C., and M. Handley,
"SDP: Session Description Protocol", RFC 8866,
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January 2021, <https://www.rfc-
editor.org/info/rfc8866>.
[SCIP210] SCIP-210, "SCIP Signaling Plan", Revision 3.10, 26
October 2017, request access via email
<ncia.cis3@ncia.nato.int>.
[SCIP214] SCIP-214.2, "Secure Communication Interoperability
Protocol (SCIP) over Real-time Transport Protocol
(RTP)", Revision 1.1, 18 April 2014, request access
via email <ncia.cis3@ncia.nato.int>.
[VIDEOSCIP] Faller, M., and D. Hanson, "video/scip", Internet
Assigned Numbers Authority (IANA), 28 January 2021,
<https://www.iana.org/assignments/media-
types/video/scip>.
8.2. Informative References
[RFC4040] Kreuter, R., "RTP Payload Format for a 64 kbit/s
Transparent Call", RFC 4040, April 2005,
<https://www.rfc-editor.org/info/rfc4040>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007,
<https://www.rfc-editor.org/info/rfc4855>.
[RFC6184] Wang, Y., Even, R., et al. "RTP Payload Format for
H.264 Video", RFC 6184, May 2011, <https://www.rfc-
editor.org/info/rfc6184>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP
13, RFC 6838, January 2013, <https://www.rfc-
editor.org/info/rfc6838>.
[RFC7201] Westerlund, M. and C. Perkins, "Options for
Securing RTP Sessions", RFC 7201, DOI
10.17487/RFC7201, April 2014, <https://www.rfc-
editor.org/info/rfc7201>.
[RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, DOI 10.17487/RFC7202,
April 2014, <https://www.rfc-
editor.org/info/rfc7202>.
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[RFC8088] Westerlund, M. "How to Write an RTP Payload
Format", RFC 8088, May 2017, <http://www.rfc-
editor.org/info/rfc8088>.
[RFC8130] Demjanenko, V., and D. Satterlee, "RTP Payload
Format for MELPe Codec", RFC 8130, March 2017,
<https://www.rfc-editor.org/info/rfc8130>.
9. Authors' Addresses
Daniel Hanson
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026, USA
E-mail: dan.hanson@gd-ms.com
Michael Faller
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026, USA
E-mail: michael.faller@gd-ms.com
Keith Maver
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026, USA
E-mail: keith.maver@gd-ms.com
SCIP Working Group, CIS3 Partnership
NATO Communications and Information Agency
Oude Waalsdorperweg 61, 2597AK
The Hague, The Netherlands
E-mail: ncia.cis3@ncia.nato.int
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