Internet DRAFT - draft-demjanenko-payload-tsvcis
draft-demjanenko-payload-tsvcis
Payload Working Group Victor Demjanenko
Internet-Draft John Punaro
Intended Status: Standards Track David Satterlee
VOCAL Technologies, Ltd.
Expires: April 16, 2018 October 13, 2017
RTP Payload Format for TSVCIS Codec
draft-demjanenko-payload-tsvcis-00
Status of This Memo
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Abstract
This document describes the RTP payload format for the Tactical
Secure Voice Cryptographic Interoperability Specification (TSVCIS)
speech coder. TSVCIS is a scalable narrowband voice coder supporting
varying encoder data rates and fallbacks. It is implemented as an
augmentation to the Mixed Excitation Linear Prediction Enhanced
(MELPe) speech coder by conveying additional speech coder parameters
for enhancing voice quality. TSVCIS augmented speech data is
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 1]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
processed in conjunction with its temporal matched MELP 2400 speech
data. The RTP packetization of TSVCIS and MELPe speech coder data is
described in detail.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. MELPe Bitstream Definitions . . . . . . . . . . . . . . . 5
3.1.1. 2400 bps Bitstream Structure . . . . . . . . . . . . . 6
3.1.2. 1200 bps Bitstream Structure . . . . . . . . . . . . . 6
3.1.3. 600 bps Bitstream Structure . . . . . . . . . . . . . 7
3.1.4. Comfort Noise Bitstream Definition . . . . . . . . . . 8
3.2. TSVCIS Bitstream Definition . . . . . . . . . . . . . . . 8
3.3. Multiple TSVCIS Frames in an RTP Packet . . . . . . . . . 10
3.4. Congestion Control Considerations . . . . . . . . . . . . 11
4. Payload Format Parameters . . . . . . . . . . . . . . . . . . 11
4.1. Media Type Definitions . . . . . . . . . . . . . . . . . . 11
4.2. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Declarative SDP Considerations . . . . . . . . . . . . . . 14
4.4. Offer/Answer SDP Considerations . . . . . . . . . . . . . 15
5. Discontinuous Transmissions . . . . . . . . . . . . . . . . . 15
6. Packet Loss Concealment . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. RFC Editor Considerations . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This document describes how compressed Tactical Secure Voice
Cryptographic Interoperability Specification (TSVCIS) speech as
produced by the TSVCIS codec may be formatted for use as an RTP
payload. The TSVCIS speech coder (or TSVCIS speech aware
communications equipment on any intervening transport link) may
adjust to restricted bandwidth conditions by reducing the amount of
augmented speech data and relying on the underlying MELPe speech
coder for the most constrained bandwidth links.
Details are provided for packetizing the TSVCIS augmented speech data
along with MELPe 2400 bps speech parameters in a RTP packet. The
sender may send one or more codec data frames per packet, depending
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 2]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
on the application scenario or based on transport network conditions,
bandwidth restrictions, delay requirements, and packet loss
tolerance.
1.1. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Best current practices for writing an RTP payload format
specification were followed [RFC2736].
2. Background
The MELP speech coder was developed by the US military as an upgrade
from the LPC-based CELP standard vocoder for low-bitrate
communications [MELP]. ("LPC" stands for "Linear-Predictive Coding",
and "CELP" stands for "Code-Excited Linear Prediction".) MELP was
further enhanced and subsequently adopted by NATO as MELPe for use by
its members and Partnership for Peace countries for military and
other governmental communications as international NATO Standard
STANAG 4591 [MELPE].
The Tactical Secure Voice Cryptographic Interoperability
Specification (TSVCIS) is a specification written by the Tactical
Secure Voice Working Group (TSVWG) for enabling all modern tactical
secure voice devices to be interoperable across the Department of
Defense [TSVCIS]. One of the most important aspects is that the
voice modes defined in TSVCIS are based on a fixed rate variant of
Naval Research Lab's (NRL's) Variable Date Rate (VDR) Vocoder which
uses the MELPe standard as its base [NRLVDR]. A complete TSVCIS
speech frame consists of MELPe speech parameters and corresponding
TSVCIS augmented speech data.
In addition to the augmented speech data, the TSVCIS specification
identifies which speech coder and framing bits are to be encrypted,
and how they are protected by forward error correction (FEC)
techniques (using block codes). At the RTP transport layer, only the
speech coder related bits need to be considered and are conveyed in
unencrypted form. In most IP-based network deployments, standard
link encryption methods (SRTP, VPNs, FIPS 140 link encryptors or Type
1 Ethernet encryptors) would be used to secure the RTP speech
contents. Further, it is desirable to support the highest voice
quality between endpoint which is only possible without the overhead
of FEC.
TSVCIS augmented speech data is derived from the signal processing
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 3]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
and data already performed by the MELPe speech coder. For the
purposes of this specification, only the general parameter nature of
TSVCIS will be characterized. Depending on the bandwidth available
(and FEC requirements), a varying number of TSVCIS specific speech
coder parameters need to be transported. These are first byte-packed
and then conveyed from encoder to decoder.
Byte packing of TSVCIS speech data into packed parameters is
processed as per the following example:
Two-bit field: bits A and B (A is MSB, B is LSB)
Six-bit field: bits C, D, E, F, G, and H (C is MSB, H is LSB)
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
| H | G | F | E | D | C | B | A |
+------+------+------+------+------+------+------+------+
This packing method places the two-bit field "first" in the lowest
bits followed by the next six-bit field. Parameters may be split
between octets with the most significant bits in the earlier octet.
Any unfilled bits in the last octet SHOULD be filled with zero.
In order to accommodate a varying amount of TSVCIS augmented speech
data, it is only necessary to specify the number of octets containing
the packed TSVCIS parameters. The encoding to do so is presented in
Section 3.2. The preferred sets of TSVCIS parameters is specified in
the speech coder specification [TSVCIS] and is beyond the scope of
this RFC to describe or limit.
3. Payload Format
The TSVCIS codec augments the standard MELP 2400, 1200 and 600
bitrates and hence uses 22.5, 67.5, or 90 ms frames with a sampling
rate clock of 8 kHz, so the RTP timestamp MUST be in units of 1/8000
of a second.
The RTP payload for TSVCIS has the format shown in Figure 1. No
additional header specific to this payload format is needed. This
format is intended for situations where the sender and the receiver
send one or more codec data frames per packet.
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 |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 4]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
| |
+ one or more frames of TSVCIS |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Packet Format Diagram
The RTP header of the packetized encoded TSVCIS speech has the
expected values as described in [RFC3550]. The usage of the M bit
SHOULD be as specified in the applicable RTP profile -- for example,
[RFC3551], where [RFC3551] specifies that if the sender does not
suppress silence (i.e., sends a frame on every frame interval), the
M bit will always be zero. When more than one codec data frame is
present in a single RTP packet, the timestamp is, as always, that of
the oldest data frame represented in the RTP packet.
The assignment of an RTP payload type for this new packet format is
outside the scope of this document and will not be specified here. It
is expected that the RTP profile for a particular class of
applications will assign a payload type for this encoding, or if that
is not done, then a payload type in the dynamic range shall be chosen
by the sender.
3.1. MELPe Bitstream Definitions
The TCVCIS speech coder includes all three MELPe coder rates used as
base speech parameters or as speech coders for bandwidth restricted
links. RTP packetization of MELPe follows RFC 8130 and is repeated
here for all three MELPe rates [RFC8130] which with promoted
suggestions or recommendations now regarded as requirements. The
bits previously labeled as RSVA, RSVB, and RSVC in RFC 8130 SHOULD be
filled with rate coding, CODA, CODB, and CODC, as shown in Table 1
(compatible with Table 7 in Section 3.3 of [RFC8130]).
+-------------------+------+------+------+------+
| Coder Bitrate | CODA | CODB | CODC |Length|
+-------------------+------+------+------+------+
| 2400 bps | 0 | 0 | N/A | 7 |
+-------------------+------+------+------+------+
| 1200 bps | 1 | 0 | 0 | 11 |
+-------------------+------+------+------+------+
| 600 bps | 0 | 1 | N/A | 7 |
+-------------------+------+------+------+------+
| Comfort Noise | 1 | 0 | 1 | 2 |
+-------------------+------+------+------+------+
| TSVCIS data | 1 | 1 | N/A | var. |
+-------------------+------+------+------+------+
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 5]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
Table 1: TSVCIS/MELPe Frame Bitrate Indicators and Frame Length
The total number of bits used to describe one MELPe frame of 2400 bps
speech is 54, which fits in 7 octets (with two rate code bits). For
MELPe 1200 bps speech, the total number of bits used is 81, which
fits in 11 octets (with three rate code bits and four unused bits).
For MELPe 600 bps speech, the total number of bits used is 54, which
fits in 7 octets (with two rate code bits). The comfort nosie frame
consists of 13 bits, which fits in 2 octets (with three rate code
bits). TSVCIS packed parameters will use the last code combination
in a trailing byte as discussed in Section 3.2.
It should be noted that CODB for both the 2400 and 600 bps modes MAY
deviate from the values in Table 1 when bit 55 is used as an end-to-
end framing bit. Frame decoding would remain distinct as CODA being
zero on its own would indicate a 7-byte frame for either rate and the
use of 600 bps speech coding could be deduced from the RTP timestamp
(and anticipated by the SDP negotiations).
3.1.1. 2400 bps Bitstream Structure
The 2400 bps MELPe RTP payload is constructed as per Figure 2. Note
that CODA must be filled with 0 and CODB SHOULD be filled with 0 as
per Section 3.1. CODB MAY contain an end-to-end framing bit if
required by the endpoints.
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
| B_08 | B_07 | B_06 | B_05 | B_04 | B_03 | B_02 | B_01 |
+------+------+------+------+------+------+------+------+
| B_16 | B_15 | B_14 | B_13 | B_12 | B_11 | B_10 | B_09 |
+------+------+------+------+------+------+------+------+
| B_24 | B_23 | B_22 | B_21 | B_20 | B_19 | B_18 | B_17 |
+------+------+------+------+------+------+------+------+
| B_32 | B_31 | B_30 | B_29 | B_28 | B_27 | B_26 | B_25 |
+------+------+------+------+------+------+------+------+
| B_40 | B_39 | B_38 | B_37 | B_36 | B_35 | B_34 | B_33 |
+------+------+------+------+------+------+------+------+
| B_48 | B_47 | B_46 | B_45 | B_44 | B_43 | B_42 | B_41 |
+------+------+------+------+------+------+------+------+
| CODA | CODB | B_54 | B_53 | B_52 | B_51 | B_50 | B_49 |
+------+------+------+------+------+------+------+------+
Figure 2: Packed MELPe 2400 bps Payload Octets
3.1.2. 1200 bps Bitstream Structure
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 6]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
The 1200 bps MELPe RTP payload is constructed as per Figure 3. Note
that CODA, CODB, and CODC MUST be filled with 1, 0, and 0
respectively as per Section 3.1. RSV0 SHOULD be coded as 0.
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
| B_08 | B_07 | B_06 | B_05 | B_04 | B_03 | B_02 | B_01 |
+------+------+------+------+------+------+------+------+
| B_16 | B_15 | B_14 | B_13 | B_12 | B_11 | B_10 | B_09 |
+------+------+------+------+------+------+------+------+
| B_24 | B_23 | B_22 | B_21 | B_20 | B_19 | B_18 | B_17 |
+------+------+------+------+------+------+------+------+
| B_32 | B_31 | B_30 | B_29 | B_28 | B_27 | B_26 | B_25 |
+------+------+------+------+------+------+------+------+
| B_40 | B_39 | B_38 | B_37 | B_36 | B_35 | B_34 | B_33 |
+------+------+------+------+------+------+------+------+
| B_48 | B_47 | B_46 | B_45 | B_44 | B_43 | B_42 | B_41 |
+------+------+------+------+------+------+------+------+
| B_56 | B_55 | B_54 | B_53 | B_52 | B_51 | B_50 | B_49 |
+------+------+------+------+------+------+------+------+
| B_64 | B_63 | B_62 | B_61 | B_60 | B_59 | B_58 | B_57 |
+------+------+------+------+------+------+------+------+
| B_72 | B_71 | B_70 | B_69 | B_68 | B_67 | B_66 | B_65 |
+------+------+------+------+------+------+------+------+
| B_80 | B_79 | B_78 | B_77 | B_76 | B_75 | B_74 | B_73 |
+------+------+------+------+------+------+------+------+
| CODA | CODB | CODC | RSV0 | RSV0 | RSV0 | RSV0 | B_81 |
+------+------+------+------+------+------+------+------+
Figure 3: Packed MELPe 1200 bps Payload Octets
3.1.3. 600 bps Bitstream Structure
The 600 bps MELPe RTP payload is constructed as per Figure 4. Note
CODA must be filled with 0 and CODB SHOULD be filled with 1 as per
Section 3.1. CODB MAY contain an end-to-end framing bit if required
by the endpoints.
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
| B_08 | B_07 | B_06 | B_05 | B_04 | B_03 | B_02 | B_01 |
+------+------+------+------+------+------+------+------+
| B_16 | B_15 | B_14 | B_13 | B_12 | B_11 | B_10 | B_09 |
+------+------+------+------+------+------+------+------+
| B_24 | B_23 | B_22 | B_21 | B_20 | B_19 | B_18 | B_17 |
+------+------+------+------+------+------+------+------+
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 7]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
| B_32 | B_31 | B_30 | B_29 | B_28 | B_27 | B_26 | B_25 |
+------+------+------+------+------+------+------+------+
| B_40 | B_39 | B_38 | B_37 | B_36 | B_35 | B_34 | B_33 |
+------+------+------+------+------+------+------+------+
| B_48 | B_47 | B_46 | B_45 | B_44 | B_43 | B_42 | B_41 |
+------+------+------+------+------+------+------+------+
| CODA | CODB | B_54 | B_53 | B_52 | B_51 | B_50 | B_49 |
+------+------+------+------+------+------+------+------+
Figure 4: Packed MELPe 600 bps Payload Octets
3.1.4. Comfort Noise Bitstream Definition
The comfort noise MELPe RTP payload is constructed as per Figure 5.
Note that CODA, CODB, and CODC MUST be filled with 1, 0, and 1
respectively as per Section 3.1.
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
| B_08 | B_07 | B_06 | B_05 | B_04 | B_03 | B_02 | B_01 |
+------+------+------+------+------+------+------+------+
| CODA | CODB | CODC | B_13 | B_12 | B_11 | B_10 | B_09 |
+------+------+------+------+------+------+------+------+
Figure 5: Packed MELPe Comfort Noise Payload Octets
3.2. TSVCIS Bitstream Definition
The TSVCIS augmented speech data as packed parameters MUST be placed
immediately after a corresponding MELPe 2400 bps payload. The packed
parameters are counted in octets (TC). In the preferred placement,
shown in Figure 6, a single trailing octet SHALL be appended to
include a two-bit rate code, CODA and CODB, (both bits set to one)
and a six-bit modified count (MTC). The special modified count value
of all ones (representing a MTC value of 63) SHALL NOT be used for
this format as it is used as the indicator for the alternate packing
format shown next. In a standard implementation, the TSVCIS speech
coder uses a minimum of 15 octets for parameters in octet packed
form. The modified count (MTC) MUST be reduced by 15 from the full
octet count (TC). Computed MTC = TC-15. This accommodates a maximum
of 77 parameter octets (maximum value of MTC is 62, 77 is the sum of
62+15).
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
1 | T008 | T007 | T006 | T005 | T004 | T003 | T002 | T001 |
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 8]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
+------+------+------+------+------+------+------+------+
2 | T016 | T015 | T014 | T013 | T012 | T011 | T010 | T009 |
+------+------+------+------+------+------+------+------+
3 | T024 | T023 | T022 | T021 | T020 | T019 | T018 | T017 |
+------+------+------+------+------+------+------+------+
4 | T032 | T031 | T030 | T029 | T028 | T027 | T026 | T025 |
+------+------+------+------+------+------+------+------+
5 | T040 | T039 | T038 | T037 | T036 | T035 | T034 | T033 |
+------+------+------+------+------+------+------+------+
6 | T048 | T047 | T046 | T045 | T044 | T043 | T042 | T041 |
+------+------+------+------+------+------+------+------+
7 | TO56 | TO55 | T054 | T053 | T052 | T051 | T050 | T049 |
+------+------+------+------+------+------+------+------+
8 | T064 | T063 | T062 | T061 | T060 | T059 | T058 | T057 |
+------+------+------+------+------+------+------+------+
9 | T072 | T071 | T070 | T069 | T068 | T067 | T066 | T065 |
+------+------+------+------+------+------+------+------+
10 | T080 | T079 | T078 | T077 | T076 | T075 | T074 | T073 |
+------+------+------+------+------+------+------+------+
11 | T088 | T087 | T086 | T085 | T084 | T083 | T082 | T081 |
+------+------+------+------+------+------+------+------+
12 | TO96 | TO95 | T094 | T093 | T092 | T091 | T090 | T089 |
+------+------+------+------+------+------+------+------+
13 | T104 | T103 | T102 | T101 | T100 | T099 | T098 | T097 |
+------+------+------+------+------+------+------+------+
14 | T112 | T111 | T110 | T109 | T108 | T107 | T106 | T105 |
+------+------+------+------+------+------+------+------+
15 | T120 | T119 | T118 | T117 | T116 | T115 | T114 | T113 |
+------+------+------+------+------+------+------+------+
| . . . . |
+------+------+------+------+------+------+------+------+
TC+1 | CODA | CODB | modified octet count |
+------+------+------+------+------+------+------+------+
Figure 6: Preferred Packed TSVCIS Payload Octets
In order to accommodate all other NRL VDR configurations for TSVCIS,
an alternate parameter placement MUST use two trailing bytes as shown
in Figure 7. The last trailing byte MUST be filled with a two-bit
rate code, CODA and CODB, (both bits set to one) and its six-bit
count field MUST be filled with ones. The second to last trailing
byte MUST contain the parameter count (TC) in octets and MAY
represent any value from one to 255. The value of zero SHALL be
considered as reserved.
MSB LSB
0 1 2 3 4 5 6 7
+------+------+------+------+------+------+------+------+
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 9]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
1 | T008 | T007 | T006 | T005 | T004 | T003 | T002 | T001 |
+------+------+------+------+------+------+------+------+
2 | T016 | T015 | T014 | T013 | T012 | T011 | T010 | T009 |
+------+------+------+------+------+------+------+------+
| . . . . |
+------+------+------+------+------+------+------+------+
TC+1 | octet count |
+------+------+------+------+------+------+------+------+
TC+2 | CODA | CODB | 1 | 1 | 1 | 1 | 1 | 1 |
+------+------+------+------+------+------+------+------+
Figure 7: Length Unrestricted Packed TSVCIS Payload Octets
3.3. Multiple TSVCIS Frames in an RTP Packet
A TSVCIS RTP packet MAY consist of zero or more TSVCIS coder frames
(each consisting of MELPe and TSVCIS coder data) followed by zero or
one MELPe comfort noise frame. The presence of a comfort noise frame
can be determined by its rate code bits in its last octet.
The default packetization interval is one coder frame (22.5, 67.5, or
90 ms) according to the coder bitrate (2400, 1200, or 600 bps). For
some applications, a longer packetization interval is used to reduce
the packet rate.
A TSVCIS RTP packet comprised of no coder frame and no comfort noise
frame MAY be used periodically by an endpoint to indicate
connectivity by an otherwise idle receiver.
TSVCIS coder frames in a single RTP packet MAY be of different coder
bitrates. With the exception for the variable length TSVCIS
parameter frames, the coder rate bits in the trailing byte identify
the contents and length as per Table 1.
It is important to observe that senders have the following additional
restrictions:
Senders SHOULD NOT include more TSVCIS or MELPe frames in a single
RTP packet than will fit in the MTU of the RTP transport protocol.
Frames MUST NOT be split between RTP packets.
It is RECOMMENDED that the number of frames contained within an RTP
packet be consistent with the application. For example, in telephony
and other real-time applications where delay is important, then the
fewer frames per packet the lower the delay, whereas for bandwidth-
constrained links or delay-insensitive streaming messaging
applications, more than one frame per packet or many frames per
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 10]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
packet would be acceptable.
Information describing the number of frames contained in an RTP
packet is not transmitted as part of the RTP payload. The way to
determine the number of TSVCIS/MELPe frames is to identify each frame
type and length thereby counting the total number of octets within
the RTP packet.
3.4. Congestion Control Considerations
The target bitrate of TSVCIS can be adjusted at any point in time,
thus allowing congestion management. Furthermore, the amount of
encoded speech or audio data encoded in a single packet can be used
for congestion control, since the packet rate is inversely
proportional to the packet duration. A lower packet transmission
rate reduces the amount of header overhead but at the same time
increases latency and loss sensitivity, so it ought to be used
with care.
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 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.
4. Payload Format Parameters
This RTP payload format is identified using the TSVCIS media subtype,
which is registered in accordance with RFC 4855 [RFC4855] and per the
media type registration template from RFC 6838 [RFC6838].
4.1. Media Type Definitions
Type name: audio
Subtype names: TSVCIS
Required parameters: N/A
Optional parameters:
ptime: the recommended length of time (in milliseconds)
represented by the media in a packet. It SHALL use the nearest
rounded-up ms integer packet duration. For TSVCIS, this
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 11]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
corresponds to the following values: 23, 45, 68, 90, 112, 135,
156, and 180. Larger values can be used as long as they are
properly rounded. See Section 6 of RFC 4566 [RFC4566].
maxptime: the maximum length of time (in milliseconds) that can be
encapsulated in a packet. It SHALL use the nearest rounded-up
ms integer packet duration. For TSVCIS, this corresponds to
the following values: 23, 45, 68, 90, 112, 135, 156, and 180.
Larger values can be used as long as they are properly rounded.
See Section 6 of RFC 4566 [RFC4566].
bitrate: specifies the MELPe coder bitrates supported. Possible
values are a comma-separated list of rates from the following
set: 2400, 1200, 600. The modes are listed in order of
preference; first is preferred. If "bitrate" is not present,
the fixed coder bitrate of 2400 MUST be used.
tcmax: specifies the TSVCIS maximum value for TC supported or
desired ranging from 1 to 255. If "tcmax" is not present, a
default value of TBD is used.
[EDITOR NOTE - the value for TBD is to be discussed and stated.
A value of 35 is suggested.]
Encoding considerations: This media subtype is framed and binary; see
Section 4.8 of RFC 6838 [RFC6838].
Security considerations: Please see Section 8 of RFCxxxx (this RFC).
Interoperability considerations: N/A
Published specification: N/A
Applications that use this media type: N/A
Additional information: N/A
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:
Victor Demjanenko, Ph.D.
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 12]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Buffalo, NY 14228
United States of America
Phone: +1 716 688 4675
Email: victor.demjanenko@vocal.com
Intended usage: COMMON
Restrictions on usage: The media subtype depends on RTP framing and
hence is only defined for transfer via RTP [RFC3550]. Transport
within other framing protocols is not defined at this time.
Author: Victor Demjanenko
Change controller: IETF Payload working group delegated from the
IESG.
Provisional registration? (standards tree only): No
4.2. Mapping to SDP
The mapping of the above-defined payload format media subtype and its
parameters SHALL be done according to Section 3 of RFC 4855
[RFC4855].
The information carried in the media type specification has a
specific mapping to fields in the Session Description Protocol (SDP)
[RFC4566], which is commonly used to describe RTP sessions. When SDP
is used to specify sessions employing the TSVCIS codec, the mapping
is as follows:
o The media type ("audio") goes in SDP "m=" as the media name.
o The media subtype (payload format name) goes in SDP "a=rtpmap" as
the encoding name.
o The parameter "bitrate" goes in the SDP "a=fmtp" attribute by
copying it as a "bitrate=<value>" string.
o The parameter "tcmax" goes in the SDP "a=fmtp" attribute by
copying it as a "tcmax=<value>" string.
o The parameters "ptime" and "maxptime" go in the SDP "a=ptime" and
"a=maxptime" attributes, respectively.
When conveying information via SDP, the encoding name SHALL be
"TSVCIS" (the same as the media subtype).
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 13]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
An example of the media representation in SDP for describing TSVCIS
might be:
m=audio 49120 RTP/AVP 96
a=rtpmap:96 TSVCIS/8000
The optional media type parameter "bitrate", when present, MUST be
included in the "a=fmtp" attribute in the SDP, expressed as a media
type string in the form of a semicolon-separated list of
parameter=value pairs. The string "value" can be one or more of
2400, 1200, and 600, separated by commas (where each bitrate value
indicates the corresponding MELPe coder). An example of the media
representation in SDP for describing TSVCIS when all three coder
bitrates are supported might be:
m=audio 49120 RTP/AVP 96
a=rtpmap:96 TSVCIS/8000
a=fmtp:96 bitrate=2400,600,1200
The optional media type parameter "tcmax", when present, MUST be
included in the "a=fmtp" attribute in the SDP, expressed as a media
type string in the form of a semicolon-separated list of
parameter=value pairs. The string "value" is an integer number in
the range of 1 to 255 representing the maximum number of TSVCIS
parameter octets supported. An example of the media representation
in SDP for describing TSVCIS with a maximum of 101 octets supported
is as follows:
m=audio 49120 RTP/AVP 96
a=rtpmap:96 TSVCIS/8000
a=fmtp:96 tcmax=101
Parameter "ptime" cannot be used for the purpose of specifying the
TSVCIS operating mode, due to the fact that for certain values it
will be impossible to distinguish which mode is about to be used
(e.g., when ptime=68, it would be impossible to distinguish if the
packet is carrying one frame of 67.5 ms or three frames of 22.5 ms).
Note that the payload format (encoding) names are commonly shown in
upper case. Media subtypes are commonly shown in lower case. These
names are case insensitive in both places. Similarly, parameter
names are case insensitive in both the media subtype name and the
default mapping to the SDP a=fmtp attribute.
4.3. Declarative SDP Considerations
For declarative media, the "bitrate" parameter specifies the possible
bitrates used by the sender. Multiple TSVCIS rtpmap values (such as
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 14]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
97, 98, and 99, as used below) MAY be used to convey TSVCIS-coded
voice at different bitrates. The receiver can then select an
appropriate TSVCIS codec by using 97, 98, or 99.
m=audio 49120 RTP/AVP 97 98 99
a=rtpmap:97 TSVCIS/8000
a=fmtp:97 bitrate=2400
a=rtpmap:98 TSVCIS/8000
a=fmtp:98 bitrate=1200
a=rtpmap:99 TSVCIS/8000
a=fmtp:99 bitrate=600
For declarative media, the "tcmax" parameter specifies the maximum
number of TSVCIS packed parameter octets used by the sender or the
sender's communications channel.
4.4. Offer/Answer SDP Considerations
In the Offer/Answer model [RFC3264], "bitrate" is a bidirectional
parameter. Both sides MUST use a common "bitrate" value or values.
The offer contains the bitrates supported by the offerer, listed in
its preferred order. The answerer MAY agree to any bitrate by
listing the bitrate first in the answerer response. Additionally,
the answerer MAY indicate any secondary bitrate or bitrates that it
supports. The initial bitrate used by both parties SHALL be the
first bitrate specified in the answerer response.
For example, if offerer bitrates are "2400,600" and answer bitrates
are "600,2400", the initial bitrate is 600. If other bitrates are
provided by the answerer, any common bitrate between the offer and
answer MAY be used at any time in the future. Activation of these
other common bitrates is beyond the scope of this document.
The use of a lower bitrate is often important for a case such as when
one endpoint utilizes a bandwidth-constrained link (e.g., 1200 bps
radio link or slower), where only the lower coder bitrate will work.
In the Offer/Answer model [RFC3264], "tcmax" is a bidirectional
parameter. Both sides SHOULD use a common "tcmax" value. The offer
contains the tcmax supported by the offerer. The answerer MAY agree
to any tcmax equal or less than this value by stating the desired
tcmax in the answerer response. The answerer alternatively MAY
identify its own tcmax and rely on TSVCIS ignoring any augmented data
it cannot use.
5. Discontinuous Transmissions
A primary application of TSVCIS is for radio communications of voice
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 15]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
conversations, and discontinuous transmissions are normal. When
TSVCIS is used in an IP network, TSVCIS RTP packet transmissions may
cease and resume frequently. RTP synchronization source (SSRC)
sequence number gaps indicate lost packets to be filled by PLC, while
abrupt loss of RTP packets indicates intended discontinuous
transmissions.
If a TSVCIS coder so desires, it may send a MELPe comfort noise frame
as per Appendix B of [SCIP210] prior to ceasing transmission. A
receiver may optionally use comfort noise during its silence periods.
No SDP negotiations are required.
6. Packet Loss Concealment
TSVCIS packet loss concealment (PLC) uses the special properties and
coding for the pitch/voicing parameter of the MELPe 2400 bps coder.
The PLC erasure indication utilizes any of the errored encodings of a
non-voiced frame as identified in Table 1 of [MELPE]. For the sake of
simplicity, it is preferred that a code value of 3 for the
pitch/voicing parameter be used. Hence, set bits P0 and P1 to one
and bits P2, P3, P4, P5, and P6 to zero.
When using PLC in 1200 bps or 600 bps mode, the MELPe 2400 bps
decoder is called three or four times, respectively, to cover the
loss of a low bitrate MELPe frame.
7. IANA Considerations
This memo requests that IANA registers TSVCIS as specified in Section
4.1. The media type is also requested to be added to the IANA
registry for "RTP Payload Format MIME types"
(http://www.iana.org/assignments/rtp-parameters).
8. 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 discussed in [RFC7202], it is not
an RTP payload format's responsibility to discuss or mandate what
solutions are used to meet such basic security goals as
confidentiality, integrity, and source authenticity for RTP in
general. This responsibility lies with anyone using RTP in an
application. They can find guidance on available security mechanisms
and important considerations in [RFC7201]. Applications SHOULD use
one or more appropriate strong security mechanisms. The rest of this
section discusses the security-impacting properties of the payload
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 16]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
format itself.
This RTP payload format and the TSVCIS 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.
Additionally, the RTP payload format does not contain any active
content.
Please see the security considerations discussed in [RFC6562]
regarding VAD and its effect on bitrates.
9. RFC Editor Considerations
Note to RFC Editor: This section may be removed after carrying out
all the instructions of this section.
10. References
10.1. 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,
<http://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,
<http://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,
<http://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, <http://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,
<http://www.rfc-editor.org/info/rfc3551>.
[RFC8130] Demjanenko, V., and D. Satterlee, "RTP Payload Format for
the Mixed Excitation Linear Prediction Enhanced (MELPe)
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 17]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
Codec", RFC 8130, DOI 10.tbd/RFC8130, March 2017,
<http://www.rfc-editor.org/info/rfc8130>.
[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,
<http://www.rfc-editor.org/info/rfc3711>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
<http://www.rfc-editor.org/info/rfc4855>.
[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, <http://www.rfc-editor.org/info/rfc5124>.
[RFC6562] Perkins, C. and JM. Valin, "Guidelines for the Use of
Variable Bit Rate Audio with Secure RTP", RFC 6562,
DOI 10.17487/RFC6562, March 2012,
<http://www.rfc-editor.org/info/rfc6562>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control:
Circuit Breakers for Unicast RTP Sessions", RFC 8083,
DOI 10.17487/RFC8083, March 2017,
<http://www.rfc-editor.org/info/rfc8083>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", RFC 8085, DOI 10.17487/RFC8085, March 2017,
<http://www.rfc-editor.org/info/rfc8085>.
[NRLVDR] Heide, D., Cohen, A., Lee, Y., and T. Moran, "Universal
Vocoder Using Variable Data Rate Vocoding", Naval Research
Lab, NRL/FR/5555-13-10,239, June 2013.
[MELP] Department of Defense Telecommunications Standard,
"Analog-to-Digital Conversion of Voice by 2,400 Bit/Second
Mixed Excitation Linear Prediction (MELP)", MIL-STD-3005,
December 1999.
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 18]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
[MELPE] North Atlantic Treaty Organization (NATO), "The 600 Bit/S,
1200 Bit/S and 2400 Bit/S NATO Interoperable Narrow Band
Voice Coder", STANAG No. 4591, January 2006.
[SCIP210] National Security Agency, "SCIP Signaling Plan", SCIP-210,
December 2007.
10.2. Informative References
[TSVCIS] National Security Agency, "Tactical Secure Voice
Cryptographic Interoperability Specification (TSVCIS)
Version 2.1", NSA 09-01A, July 2012.
[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,
<http://www.rfc-editor.org/info/rfc4585>.
[RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP
Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
<http://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, <http://www.rfc-editor.org/info/rfc7202>.
[RMCAT] IETF, RTP Media Congestion Avoidance Techniques (rmcat)
Working Group,
<https://datatracker.ietf.org/wg/rmcat/about/>.
Authors' Addresses
Victor Demjanenko, Ph.D.
VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Buffalo, NY 14228
United States of America
Phone: +1 716 688 4675
Email: victor.demjanenko@vocal.com
John Punaro
VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Buffalo, NY 14228
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 19]
INTERNET DRAFT RTP Payload Format for TSVCIS Codec October 13, 2017
United States of America
Phone: +1 716 688 4675
Email: john.punaro@vocal.com
David Satterlee
VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Buffalo, NY 14228
United States of America
Phone: +1 716 688 4675
Email: david.satterlee@vocal.com
Demjanenko, Punaro & SatterleeExpires April 16, 2018 [Page 20]
