Internet Engineering Task Force (IETF) D. Hanson

Internet Engineering Task Force (IETF) D. Hanson
Request for Comments: 9607 M. Faller
Category: Standards Track K. Maver
ISSN: 2070-1721 General Dynamics Mission Systems, Inc.
July 2024

RTP Payload Format for the Secure Communication Interoperability
Protocol (SCIP) Codec

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 session
establishment, payload encryption, packetization and de-packetization
of media, and reliable transport. This document provides a globally
available reference that can be used for the development of network
equipment and procurement of services that support SCIP traffic. The
intended audience is network security policymakers; network
administrators, architects, and original equipment manufacturers
(OEMs); procurement personnel; and government agency and commercial
industry representatives.

IESG Note

This IETF specification depends upon a second technical specification
that is not available publicly, namely [SCIP210]. The IETF was
therefore unable to conduct a security review of that specification,
independently or when carried inside Audio/Video Transport (AVT).
Implementers need to be aware that the IETF hence cannot verify any
of the security claims contained in this document.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9607.

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 and restrictions with respect
to this document. Code Components 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
2. Introduction
2.1. Conventions
2.2. Abbreviations
3. Background
4. Payload Format
4.1. RTP Header Fields
4.2. Congestion Control Considerations
4.3. Use of Augmented RTPs with SCIP
5. Payload Format Parameters
5.1. Media Subtype "audio/scip"
5.2. Media Subtype "video/scip"
5.3. Mapping to SDP
5.4. SDP Offer/Answer Considerations
6. Security Considerations
7. IANA Considerations
8. SCIP Contact Information
9. References
9.1. Normative References
9.2. Informative References
Authors' Addresses

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 Clearmode as defined by
[RFC4040].

* 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.

* 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 middleboxes to
not attempt parsing of the SCIP payload. As described in this
document, such parsing serves no useful purpose.

* 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 and 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 middleboxes 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.

2. Introduction

This document details usage of the "audio/scip" and "video/scip"
pseudo-codecs [MediaTypes] as a secure session establishment protocol
and media transport protocol over RTP.

It discusses how:

1. encrypted audio and video codec payloads are transported over
RTP;

2. the IP network layer does not implement SCIP as a protocol since
SCIP operates at the application layer in endpoints;

3. the IP network layer enables SCIP traffic to transparently pass
through the network;

4. some network devices do not recognize SCIP and may remove the
SCIP codecs from the SDP media payload declaration before
forwarding to the next network node; and finally,

5. SCIP endpoint devices do not operate on networks if the SCIP
media subtype is removed 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 and de-packetization, retransmission,
capability exchange, version negotiation, and payload encryption.
Since the traffic is encrypted, neither the RTP transport nor
middleboxes 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 middleboxes, 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.

The best current practices for writing an RTP payload format
specification, as per [RFC2736] and [RFC8088], were followed.

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-Visual Profile

AVPF: Audio-Visual Profile with Feedback

FNBDT: Future Narrowband Digital Terminal

ICWG: Interoperability Control Working Group

IICWG: International Interoperability Control Working Group

MELPe: Mixed Excitation Linear Prediction Enhanced

MTU: Maximum Transmission Unit

NATO: North Atlantic Treaty Organization

OEM: Original Equipment Manufacturer

SAVP: Secure Audio-Visual Profile

SAVPF: Secure Audio-Visual Profile with 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.

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
and 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 the "audio/scip"
and "video/scip" media subtypes that enable 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
that 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 identifies and indicates support for 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].

[RFC4040] 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.

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 and 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.

+-----------+ +-----------------------+
| 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 [RFC3550].

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., Mixed Excitation Linear Prediction Enhanced
(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 [RFC4585], Section 6.3
are OPTIONAL when transporting video data.

4.3. Use of Augmented RTPs with SCIP

The SCIP application-layer protocol uses RTP as a basic transport for
the "audio/scip" and "video/scip" payloads. Additional RTPs 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]

* "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 (SDP)" a.k.a. 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 from [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"

Type name: audio

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 transcoding of the audio
stream as it traverses the network.

Security considerations: See Section 6.

Interoperability considerations: N/A

Published specification: [SCIP210]

Applications that use this media type: N/A

Fragment identifier considerations: none

Additional information:

Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A

Person & email address to contact for further information: Michael
Faller ([email protected] or [email protected]) and
Daniel Hanson ([email protected])

Intended usage: COMMON

Restrictions on usage: N/A

Authors: Michael Faller ([email protected] or
[email protected]) and Daniel Hanson ([email protected])

Change controller: SCIP Working Group ([email protected])

5.2. Media Subtype "video/scip"

Type name: video

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 transcoding of the video
stream as it traverses the network.

Security considerations: See Section 6.

Interoperability considerations: N/A

Published specification: [SCIP210]

Applications that use this media type: N/A

Fragment identifier considerations: none

Additional information:

Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A

Person & email address to contact for further information: Michael
Faller ([email protected] or [email protected]) and
Daniel Hanson ([email protected])

Intended usage: COMMON

Restrictions on usage: N/A

Authors: Michael Faller ([email protected] or
[email protected]) and Daniel Hanson ([email protected])

Change controller: SCIP Working Group ([email protected])

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:

* 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

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 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 headers 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 in the "Media Types" registry [MediaTypes]. IANA has
updated these registrations to reference this document.

8. SCIP Contact Information

The SCIP protocol is maintained by the SCIP Working Group. The
current SCIP-210 specification [SCIP210] may be requested from the
email address below.

SCIP Working Group, CIS3 Partnership
NATO Communications and Information Agency
Oude Waalsdorperweg 61
2597 AK The Hague, Netherlands
Email: [email protected]

An older public version of the SCIP-210 specification can be
downloaded from https://www.iad.gov/SecurePhone/index.cfm. A U.S.
Department of Defense Root Certificate should be installed to access
this website.

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>.

[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

[MediaTypes]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.

[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>.

[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)",
<https://datatracker.ietf.org/wg/rmcat/about>.

[SCIP210] SCIP Working Group, "SCIP Signaling Plan, SCIP-210".
Available by request via email to
<[email protected]>.

Authors' Addresses

Daniel Hanson
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026
United States of America
Email: [email protected]

Michael Faller
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026
United States of America
Email: [email protected], [email protected]

Keith Maver
General Dynamics Mission Systems, Inc.
150 Rustcraft Road
Dedham, MA 02026
United States of America
Email: [email protected]