[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00 draft-ietf-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]


Html markup produced by rfcmarkup 1.127, available from https://tools.ietf.org/tools/rfcmarkup/