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RTP Payload Format for the Secure Communication Interoperability Protocol (SCIP) Codec
draft-ietf-avtcore-rtp-scip-09

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9607.
Authors Dan Hanson , MikeFaller , Keith Maver
Last updated 2024-07-24 (Latest revision 2024-02-14)
Replaces draft-hanson-avtcore-rtp-scip
RFC stream Internet Engineering Task Force (IETF)
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Stream WG state Submitted to IESG for Publication
Document shepherd Dr. Bernard D. Aboba
Shepherd write-up Show Last changed 2022-11-17
IESG IESG state Became RFC 9607 (Proposed Standard)
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Responsible AD Murray Kucherawy
Send notices to jonathan.lennox@8x8.com, bernard.aboba@gmail.com
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
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Details
draft-ietf-avtcore-rtp-scip-09
Payload Working Group                                          D. Hanson
Internet-Draft                                                 M. Faller
Intended status: Standards Track                                K. Maver
Expires: 16 August 2024           General Dynamics Mission Systems, Inc.
                                                        13 February 2024

    RTP Payload Format for the Secure Communication Interoperability
                         Protocol (SCIP) Codec
                     draft-ietf-avtcore-rtp-scip-09

Abstract

   This document describes the RTP payload format of the Secure
   Communication Interoperability Protocol (SCIP).  SCIP is an
   application layer protocol that provides end-to-end capability
   exchange, packetization/de-packetization of media, reliable
   transport, and payload encryption.

   SCIP handles packetization/de-packetization of the encrypted media
   and acts as a tunneling protocol, treating SCIP payloads as opaque
   octets to be encapsulated within RTP payloads prior to transmission
   or decapsulated on reception.  SCIP payloads are sized to fit within
   the maximum transmission unit (MTU) when transported over RTP thereby
   avoiding fragmentation.

   SCIP transmits encrypted traffic and does not require the use of
   Secure RTP (SRTP) for payload protection.  SCIP also provides for
   reliable transport at the application layer, so it is not necessary
   to negotiate RTCP retransmission capabilities.

   To establish reliable communications using SCIP over RTP, it is
   important that middle boxes avoid parsing or modifying SCIP payloads.
   Because SCIP payloads are confidentiality and integrity protected and
   are only decipherable by the originating and receiving SCIP devices,
   modification of the payload by middle boxes would be detected as an
   integrity failure in SCIP devices, resulting in retransmission and/or
   communication failure.  Middle boxes do not need to parse the SCIP
   payloads to correctly transport them.  Not only is parsing
   unnecessary to tunnel/detunnel SCIP within RTP, but the parsing and
   filtering of SCIP payloads by middle boxes would likely lead to
   ossification of the evolving SCIP protocol.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 16 August 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Key Points  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  RTP Header Fields . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Congestion Control Considerations . . . . . . . . . . . .   9
     4.3.  Use of Augmented RTP Transport Protocols with SCIP  . . .   9
   5.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  10
     5.1.  Media Subtype "audio/scip"  . . . . . . . . . . . . . . .  10
     5.2.  Media Subtype "video/scip"  . . . . . . . . . . . . . . .  11
     5.3.  Mapping to SDP  . . . . . . . . . . . . . . . . . . . . .  12
     5.4.  SDP Offer/Answer Considerations . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  SCIP Contact Information  . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16

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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Key Points

   *  SCIP is an application layer protocol that uses RTP as a
      transport.  This document defines the SCIP media subtypes to be
      listed in the Session Description Protocol (SDP) and only requires
      a basic RTP transport channel for SCIP payloads.  This basic
      transport channel is comparable to [RFC4040] Clearmode.

   *  SCIP is designed to be network agnostic.  It can operate over any
      digital link, including non-IP modem-based PSTN and ISDN.  The
      SCIP media subtypes listed in this document were developed for
      SCIP to operate over RTP.

   *  SCIP handles packetization/de-packetization of payloads by
      producing encrypted media packets that are not greater than the
      MTU size.  The SCIP payload is opaque to the network, therefore,
      SCIP functions as a tunneling protocol for the encrypted media,
      without the need for middle boxes to parse SCIP payloads.  Since
      SCIP payloads are integrity protected, modification of the SCIP
      payload is detected as an integrity violation by SCIP endpoints
      leading to communication failure.

   *  SCIP includes built-in mechanisms that negotiate protocol message
      versions and capabilities.  To avoid SCIP protocol ossification
      (as described in [RFC9170]), it is important for middle boxes to
      not attempt parsing of the SCIP payload.  As described in this
      document, such parsing serves no useful purpose.

2.  Introduction

   The purpose of this document is to provide enough information to
   enable SCIP payloads to be transported through the network without
   modification or filtering.  The document provides a reference for
   network security policymakers; network equipment OEMs,
   administrators, and architects; procurement personnel; and government
   agency and commercial industry representatives.

   The document details usage of the "audio/scip" and "video/scip"
   pseudo-codecs [AUDIOSCIP], [VIDEOSCIP] as a secure session
   establishment protocol and media transport protocol over RTP.  It
   discusses (1) how encrypted audio and video codec payloads are
   transported over RTP; (2) the IP network layer not implementing SCIP
   as a protocol since SCIP operates at the application layer in
   endpoints; (3) the IP network layer enabling SCIP traffic to
   transparently pass through the network; (4) network devices not
   recognizing SCIP, and thus removing the scip codecs from the SDP

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   media payload declaration before forwarding to the next network node;
   and finally, (5) SCIP endpoint devices not operating on networks due
   to the scip media subtype removal from the SDP media payload
   declaration.

   The United States, along with its NATO Partners, have implemented
   SCIP in secure voice, video, and data products operating on
   commercial, private, and tactical IP networks worldwide using the
   scip media subtype.  The SCIP data traversing the network is
   encrypted, and network equipment in-line with the session cannot
   interpret the traffic stream in any way.  SCIP-based RTP traffic is
   opaque and can vary significantly in structure and frequency making
   traffic profiling not possible.  Also, as the SCIP protocol continues
   to evolve independently of this document, any network device that
   attempts to filter traffic (e.g., deep packet inspection) may cause
   unintended consequences in the future when changes to the SCIP
   traffic may not be recognized by the network device.

   The SCIP protocol defined in SCIP-210 [SCIP210] includes built-in
   support for packetization/de-packetization, retransmission,
   capability exchange, version negotiation, and payload encryption.
   Since the traffic is encrypted, neither the RTP transport nor middle
   boxes can usefully parse or modify SCIP payloads; modifications are
   detected as integrity violations resulting in retransmission, and
   eventually, communication failure.

   Because knowledge of the SCIP payload format is not needed to
   transport SCIP signaling or media through middle boxes, SCIP-210
   represents an informative reference.  While older versions of the
   SCIP-210 specification are publicly available, the authors strongly
   encourage network implementers to treat SCIP payloads as opaque
   octets.  When handled correctly, such treatment does not require
   referring to SCIP-210, and any assumptions about the format of SCIP
   messages defined in SCIP-210 are likely to lead to protocol
   ossification and communication failures as the protocol evolves.

      |  Note: The IETF has not conducted a security review of SCIP and
      |  therefore has not verified the claims contained in this
      |  document.

2.1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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   Best current practices for writing an RTP payload format
   specification were followed [RFC2736] [RFC8088].

   When referring to the Secure Communication Interoperability Protocol,
   the uppercase acronym "SCIP" is used.  When referring to the media
   subtype scip, lowercase "scip" is used.

2.2.  Abbreviations

   The following abbreviations are used in this document.

   AVP:      Audio/Video Profile
   AVPF:     Audio/Video Profile Feedback
   ICWG:     Interoperability Control Working Group
   IICWG:    International Interoperability Control Working Group
   NATO:     North Atlantic Treaty Organization
   OEM:      Original Equipment Manufacturer
   SAVP:     Secure Audio/Video Profile
   SAVPF:    Secure Audio/Video Profile Feedback
   SCIP:     Secure Communication Interoperability Protocol
   SDP:      Session Description Protocol
   SRTP:     Secure Real-Time Transport Protocol
   STANAG:   Standardization Agreement

3.  Background

   The Secure Communication Interoperability Protocol (SCIP) allows the
   negotiation of several voice, data, and video applications using
   various cryptographic suites.  SCIP also provides several important
   characteristics that have led to its broad acceptance as a secure
   communications protocol.

   SCIP began in the United States as the Future Narrowband Digital
   Terminal (FNBDT) Protocol in the late 1990s.  A combined U.S.
   Department of Defense and vendor consortium formed a governing
   organization named the Interoperability Control Working Group (ICWG)
   to manage the protocol.  In time, the group expanded to include NATO,
   NATO partners and European vendors under the name International
   Interoperability Control Working Group (IICWG), which was later
   renamed the SCIP Working Group.

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   First generation SCIP devices operated on circuit-switched 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 protocols make it a natural choice for many
   scenarios that require various secure applications and associated
   encryption suites.  SCIP has been adopted by NATO in STANAG 5068.
   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 document provides essential information about audio/scip and
   video/scip media subtypes that enables network equipment
   manufacturers to include settings for "scip" as a known audio and
   video media subtype in their equipment.  This enables network
   administrators to define and implement a compatible security policy
   which includes audio and video media subtypes "audio/scip" and
   "video/scip", respectively, as permitted codecs on the network.

   All current IP-based SCIP endpoints implement "scip" as a media
   subtype.  Registration of scip as a media subtype provides a common
   reference for network equipment manufacturers to recognize SCIP in an
   SDP payload declaration.

4.  Payload Format

   The "scip" media subtype indicates support for and identifies SCIP
   traffic that is being transported over RTP.  Transcoding, lossy
   compression, or other data modifications MUST NOT be performed by the
   network on the SCIP RTP payload.  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 [RFC4040].

   RFC 4040 is referenced because Clearmode does not define specific RTP
   payload content, packet size, or packet intervals, but rather enables
   Clearmode devices to signal that they support a compatible mode of
   operation and defines a transparent channel on which devices may
   communicate.  This document takes a similar approach.  Network
   devices that implement support for SCIP need to enable SCIP endpoints
   to signal that they support SCIP and provide a transparent channel on
   which SCIP endpoints may communicate.

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   SCIP is an application layer protocol that is defined in SCIP-210.
   The SCIP traffic consists of encrypted SCIP control messages and
   codec data.  The payload size and interval will vary considerably
   depending on the state of the SCIP protocol within the SCIP device.

   Figure 1 below illustrates the RTP payload format for SCIP.

    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                          |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |
   |                          SCIP payload                         |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: SCIP RTP Payload Format

   The SCIP codec produces an encrypted bitstream that is transported
   over RTP.  Unlike other codecs, SCIP does not have its own upper
   layer syntax (e.g., no Network Adaptation Layer (NAL) units), but
   rather encrypts the output of the audio/video codecs that it uses
   (e.g., G.729D, H.264 [RFC6184], etc.).  SCIP achieves this by
   encapsulating the encrypted codec output that has been previously
   formatted according to the relevant RTP payload specification for
   that codec.  SCIP endpoints MAY employ mechanisms, such as Inter-
   media RTP Synchronization as described in [RFC8088] Section 3.3.4, to
   synchronize audio/scip and video/scip streams.

   Figure 2 below illustrates notionally how codec packets and SCIP
   control messages are packetized for transmission over RTP.

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   +-----------+              +-----------------------+
   |   Codec   |              | SCIP control messages |
   +-----------+              +-----------------------+
         |                                |
         |                                |
         V                                V
   +--------------------------------------------------+
   |             Packetizer* (<= MTU size)            |
   +--------------------------------------------------+
             |                        |
             |                        |
             V                        |
     +--------------+                 |
     |  Encryption  |                 |
     +--------------+                 |
             |                        |
             |                        |
             V                        V
   +--------------------------------------------------+
   |                      RTP                         |
   +--------------------------------------------------+

                      Figure 2: SCIP RTP Architecture

      |  * Packetizer: The SCIP application layer will ensure that all
      |  traffic sent to the RTP layer will not exceed the MTU size.
      |  The receiving SCIP RTP layer will handle packet identification,
      |  ordering, and reassembly.  When required, the SCIP application
      |  layer handles error detection and retransmission.

   As described above, the SCIP RTP payload format is variable and
   cannot be described in specificity in this document.  Details can be
   found in SCIP-210.  SCIP will continue to evolve and as such the SCIP
   RTP traffic MUST NOT be filtered by network devices based upon what
   currently is observed or documented.  The focus of this document is
   for network devices to consider the SCIP RTP payload as opaque and
   allow it to traverse the network.  Network devices MUST NOT modify
   SCIP RTP packets.

4.1.  RTP Header Fields

   The SCIP RTP header fields SHALL conform to RFC 3550.

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   SCIP traffic may be continuous or discontinuous.  The Timestamp field
   MUST increment 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).  Note that during a SCIP session, both
   discontinuous and continuous traffic are highly probable.

   The Marker bit SHALL be set to zero for discontinuous traffic.  The
   Marker bit for continuous traffic is based on the underlying media
   subtype specification.  The underlying media is opaque within SCIP
   RTP packets.

4.2.  Congestion Control Considerations

   The bitrate of SCIP may be adjusted depending on the capability of
   the underlying codec (such as MELPe [RFC8130], G.729D [RFC3551],
   etc.).  The number of encoded audio frames per packet may also be
   adjusted to control congestion.  Discontinuous transmission may also
   be used if supported by the underlying codec.

   Since UDP does not provide congestion control, applications that use
   RTP over UDP SHOULD implement their own congestion control above the
   UDP layer [RFC8085] and MAY also implement a transport circuit
   breaker [RFC8083].  Work in the RTP Media Congestion Avoidance
   Techniques (RMCAT) working group [RMCAT] describes the interactions
   and conceptual interfaces necessary between the application
   components that relate to congestion control, including the RTP
   layer, the higher-level media codec control layer, and the lower-
   level transport interface, as well as components dedicated to
   congestion control functions.

   Use of the packet loss feedback mechanisms in AVPF [RFC4585] and
   SAVPF [RFC5124] are OPTIONAL because SCIP itself manages
   retransmissions of some errored or lost packets.  Specifically, the
   Payload-Specific Feedback Messages defined in RFC 4585 section 6.3
   are OPTIONAL when transporting video data.

4.3.  Use of Augmented RTP Transport Protocols with SCIP

   The SCIP application layer protocol uses RTP as a basic transport for
   the audio/scip and video/scip payloads.  Additional RTP transport
   protocols that do not modify the SCIP payload are considered OPTIONAL
   in this document and are discretionary for a SCIP device vendor to
   implement.  Some examples include but are not limited to:

   *  RTP Payload Format for Generic Forward Error Correction [RFC5109]

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   *  Multiplexing RTP Data and Control Packets on a Single Port
      [RFC5761]

   *  Symmetric RTP/RTP Control Protocol (RTCP) [RFC4961]

   *  Negotiating Media Multiplexing Using the Session Description
      Protocol (BUNDLE) [RFC9143]

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".

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 7.

   Interoperability considerations: N/A

   Published specifications: [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

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      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

   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 7.

   Interoperability considerations: N/A

   Published specifications: [SCIP210]

   Applications which use this media: N/A

   Fragment Identifier considerations: none

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   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

   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 implemented according to Section 3 of [RFC4855].

   Since SCIP includes its own facilities for capabilities exchange, it
   is only necessary to negotiate the use of SCIP within SDP Offer/
   Answer; the specific codecs to be encapsulated within SCIP are then
   negotiated via the exchange of SCIP control messages.

   The information carried in the media type specification has a
   specific mapping to fields in the Session Description Protocol (SDP)
   [RFC8866], which is commonly used to describe RTP sessions.  When SDP
   is used to specify sessions employing the SCIP codec, the mapping is
   as follows:

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   *  The media type ("audio") goes in SDP "m=" as the media name for
      audio/scip, and the media type ("video") goes in SDP "m=" as the
      media name for video/scip.

   *  The media subtype ("scip") goes in SDP "a=rtpmap" as the encoding
      name.  The required parameter "rate" also goes in "a=rtpmap" as
      the clock rate.

   *  The optional parameters "ptime" and "maxptime" go in the SDP
      "a=ptime" and "a=maxptime" attributes, respectively.

   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

5.4.  SDP Offer/Answer Considerations

   In accordance with the SDP Offer/Answer model [RFC3264], the SCIP
   device SHALL list the SCIP payload type number in order of preference
   in the "m" media line.

   For example, an SDP Offer with scip as the preferred audio media
   subtype:

     m=audio 50000 RTP/AVP 96 0 8
     a=rtpmap:96 scip/8000
     a=rtpmap:0 PCMU/8000
     a=rtpmap:8 PCMA/8000

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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 lies 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 do not inherently pose a
   denial-of-service threat due to the receipt of pathological data.
   Nor does the RTP payload format contain any active content.

   SCIP only encrypts the contents transported in the RTP payload; it
   does not protect the RTP header or RTCP packets.  Applications
   requiring additional RTP header and/or RTCP security might consider
   mechanisms such as SRTP [RFC3711], however these additional
   mechanisms are considered OPTIONAL in this document.

7.  IANA Considerations

   The audio/scip and video/scip media subtypes have previously been
   registered with IANA [AUDIOSCIP] [VIDEOSCIP].  IANA should update
   [AUDIOSCIP] and [VIDEOSCIP] to reference this document upon
   publication.

8.  SCIP Contact Information

   The SCIP protocol is maintained by the SCIP Working Group.  The
   current SCIP-210 specification may be requested from the email
   address below.

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   SCIP Working Group, CIS3 Partnership
   NATO Communications and Information Agency
   Oude Waalsdorperweg 61
   2597 AK The Hague, Netherlands
   Email: ncia.cis3@ncia.nato.int

   An older public version of the SCIP-210 specification can be
   downloaded from https://www.iad.gov/SecurePhone/index.cfm.

9.  References

9.1.  Normative References

   [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,
              DOI 10.17487/RFC3264, 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, DOI 10.17487/RFC3550,
              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", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, 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, DOI 10.17487/RFC3711, 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>.

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   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8866]  Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
              Session Description Protocol", RFC 8866,
              DOI 10.17487/RFC8866, January 2021,
              <https://www.rfc-editor.org/info/rfc8866>.

9.2.  Informative References

   [AUDIOSCIP]
              Faller, M. and D. Hanson, "audio/scip: Internet Assigned
              Numbers Authority (IANA)", 28 January 2021,
              <https://www.iana.org/assignments/media-types/audio/scip>.

   [RFC4040]  Kreuter, R., "RTP Payload Format for a 64 kbit/s
              Transparent Call", RFC 4040, DOI 10.17487/RFC4040, April
              2005, <https://www.rfc-editor.org/info/rfc4040>.

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
              <https://www.rfc-editor.org/info/rfc4855>.

   [RFC4961]  Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
              BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007,
              <https://www.rfc-editor.org/info/rfc4961>.

   [RFC5109]  Li, A., Ed., "RTP Payload Format for Generic Forward Error
              Correction", RFC 5109, DOI 10.17487/RFC5109, December
              2007, <https://www.rfc-editor.org/info/rfc5109>.

   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port", RFC 5761,
              DOI 10.17487/RFC5761, April 2010,
              <https://www.rfc-editor.org/info/rfc5761>.

   [RFC6184]  Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184,
              DOI 10.17487/RFC6184, May 2011,
              <https://www.rfc-editor.org/info/rfc6184>.

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   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, 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>.

   [RFC8083]  Perkins, C. and V. Singh, "Multimedia Congestion Control:
              Circuit Breakers for Unicast RTP Sessions", RFC 8083,
              DOI 10.17487/RFC8083, March 2017,
              <https://www.rfc-editor.org/info/rfc8083>.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC8088]  Westerlund, M., "How to Write an RTP Payload Format",
              RFC 8088, DOI 10.17487/RFC8088, May 2017,
              <https://www.rfc-editor.org/info/rfc8088>.

   [RFC8130]  Demjanenko, V. and D. Satterlee, "RTP Payload Format for
              the Mixed Excitation Linear Prediction Enhanced (MELPe)
              Codec", RFC 8130, DOI 10.17487/RFC8130, March 2017,
              <https://www.rfc-editor.org/info/rfc8130>.

   [RFC9143]  Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", RFC 9143,
              DOI 10.17487/RFC9143, February 2022,
              <https://www.rfc-editor.org/info/rfc9143>.

   [RFC9170]  Thomson, M. and T. Pauly, "Long-Term Viability of Protocol
              Extension Mechanisms", RFC 9170, DOI 10.17487/RFC9170,
              December 2021, <https://www.rfc-editor.org/info/rfc9170>.

   [RMCAT]    IETF, "RTP Media Congestion Avoidance Techniques (rmcat)
              Working Group",
              <https://datatracker.ietf.org/wg/rmcat/about/>.

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   [SCIP210]  SCIP Working Group, "SCIP Signaling Plan", SCIP-210,
              r3.11, September 2023,
              <https://www.iad.gov/SecurePhone/index.cfm>.

   [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>.

Authors' Addresses

   Daniel Hanson
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: dan.hanson@gd-ms.com

   Michael Faller
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: michael.faller@gd-ms.com

   Keith Maver
   General Dynamics Mission Systems, Inc.
   150 Rustcraft Road
   Dedham, MA 02026
   United States of America
   Email: keith.maver@gd-ms.com

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