Payload Working Group Victor Demjanenko Internet-Draft David Satterlee Intended Status: Standards Track VOCAL Technologies, Ltd. Expires: August 11, 2017 February 7, 2017 RTP Payload Format for MELPe Codec draft-ietf-payload-melpe-06 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 Mixed Excitation Linear Prediction Enhanced (MELPe) speech coder. MELPe's three different speech encoding rates and sample frames sizes are supported. Comfort noise procedures and packet loss concealment are detailed. Demjanenko, Satterlee Expires August 11, 2017 [Page 1] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Conventions, Definitions and Acronyms . . . . . . . . . . . 3 2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1 MELPe Bitstream Definition . . . . . . . . . . . . . . . . 5 3.1.1 2400 bps Bitstream Structure . . . . . . . . . . . . . . 6 3.1.2 1200 bps Bitstream Structure . . . . . . . . . . . . . . 8 3.1.3 600 bps Bitstream Structure . . . . . . . . . . . . . . 11 3.2 MELPe Comfort Noise Bitstream Definition . . . . . . . . . 15 3.3 Multiple MELPe frames in a RTP packet . . . . . . . . . . . 17 3.4 Congestion Control Considerations . . . . . . . . . . . . . 19 4 Payload Format Parameters . . . . . . . . . . . . . . . . . . . 19 4.1 Media Type Definition . . . . . . . . . . . . . . . . . . . 20 4.2 Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . 23 4.3 Declarative SDP Considerations . . . . . . . . . . . . . . 24 4.4 Offer/Answer SDP Considerations . . . . . . . . . . . . . . 24 5 Discontinious Transmission . . . . . . . . . . . . . . . . . . 25 6 Packet Loss Concealment . . . . . . . . . . . . . . . . . . . . 25 7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 27 8 Security Considerations . . . . . . . . . . . . . . . . . . . . 27 9 RFC Editor Considerations . . . . . . . . . . . . . . . . . . . 27 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 10.1 Normative References . . . . . . . . . . . . . . . . . . . 27 10.2 Informative References . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Demjanenko, Satterlee Expires August 11, 2017 [Page 2] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 1 Introduction This document describes how compressed MELPe speech as produced by the MELPe codec may be formatted for use as an RTP payload. Details are provided to packetize the three different codec bit-rate data frames (2400, 1200, and 600) into RTP packets. The sender may send one or more codec data frames per packet, depending on the application scenario or based on the transport network condition, bandwidth restriction, delay requirements and packet-loss tolerance. 1.1 Conventions, Definitions and Acronyms 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 RTP payload format [RFC2736] were followed. 2 Background The MELP speech coder was developed by the US military as an upgrade from LPC-based CELP standard vocoder for low bit-rate communications [MELP]. 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 [MELPE]. The MELP speech coder algorithm developed by Atlanta Signal Processing (ASPI), Texas Instruments (TI), SignalCom (now Microsoft) and Thales Communications with noise preprocessor contributions from AT&T under contract with NSA/DOD as international NATO Standard STANAG 4591. Commercial/civilian applications have arisen because of the low bit- rate property of MELPe with its (relatively) high intelligibility. As such MELPe is being used in a variety of wired and radio communications systems. VoIP/SIP systems need to transport MELPe without decoding and re-encoding in order to preserve its intelligibility. Hence it is desirable and necessary to define the proper payload formatting and use conventions of MELPe in RTP payloads. The MELPe codec [MELPE] supports three different vocoder bit rates; 2400, 1200, and 600 bps. The basic 2400 bps bit-rate vocoder uses a 22.5 ms frame of speech consisting of 180 8000 Hz, 16-bit speech samples. The 1200 and 600 bps bit-rate vocoders uses respectively three and four 22.5 ms frames of speech each. These reduced bit-rate vocoders internally use multiple 2400 bps parameter sets with further Demjanenko, Satterlee Expires August 11, 2017 [Page 3] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 processing to strategically remove redundancy. The payload sizes for each of the bitrates are 54, 81, and 54 bits respectively for the 2400, 1200, and 600 bps frames. Dynamic bit-rate switching is permitted but only if supported by both endpoints. The MELPe algorithm distinguishes between voiced and un-voiced speech and encodes each differently. Unvoiced speech can be coded with fewer information bits for the same quality. Forward error correction (FEC) is applied to the 2400 bps codec unvoiced speech for better protection of the subtle differences in signal reconstruction. The lower bit-rate coders do not allocate any bits for FEC and rely on strong error protection and correction in the communications channel. Comfort noise handling for MELPe follows the procedures in SCIP-210 Appendix B [SCIP210]. After VAD no longer indicates the presence of speech/voice, a grace period of a minimum of two comfort noise vocoder fames are to be transmitted. The contents of the comfort noise frames is described in the next section. Packet loss concealment (PLC) exploits the FEC (and more precisely, any combination of two set bits in the pitch/voicing parameter) of the 2400 bps speech coder. The pitch/voicing parameter has a sparse set of permitted values. A value of zero indicates a non-voiced frame. At least three bits are set for all valid pitch parameters. The PLC erasure indication utilizes any of the two bit set errored/erasure encodings of a non-voiced frame as will be described infra. 3 Payload Format The MELPe codec 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 MELPe has the format shown in Figure 1. No additional header specific to this payload format is needed. This format is intended for the situations where the sender and the receiver send one or more codec data frames per packet. Demjanenko, Satterlee Expires August 11, 2017 [Page 4] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 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 | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | + one or more frames of MELPe | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 - Packet format diagram The RTP header of the packetized encoded MELPe speech has the expected values as described in [RFC3550]. The usage of M bit SHOULD be as specified in the applicable RTP profile, for example, RFC 3551 [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 then 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 Definition The total number of bits used to describe one frame of 2400 bps speech is 54, which fits in 7 octets (with two unused bits). For the 1200 bps speech the total number of bits used is 81, which fits in 11 octets (with seven unused bits). For the 600 bps speech the total number of bits used is 54, which fits in 7 octets (with two unused bits). Unused bits, shown below as RSVA, RSVB, etc., are coded as described in 3.3 in support of dynamic bit-rate switching. In the MELPe bitstream definition, the most significant bits are considered priority bits. The intention was that these bits receive greater protection in the underlying communications channel. For IP networks, such additional protection is irrelevant. However, for convenience of interoperable gateway devices, the bitstreams will be presented identically in IP networks. Demjanenko, Satterlee Expires August 11, 2017 [Page 5] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 3.1.1 2400 bps Bitstream Structure According to Table 3 of [MELPE], the 2400 bit/s MELPe bit transmission order (bit priority is not shown for clarity) is the following: +--------+-------------+-------------+ | Bit | Voiced | Unvoiced | +--------+-------------+-------------+ | B_01 | g20 | g20 | | B_02 | BP0 | FEC10 | | B_03 | P0 | P0 | | B_04 | LSF20 | LSF20 | | B_05 | LSF30 | LSF30 | | B_06 | g23 | g23 | | B_07 | g24 | g24 | | B_08 | LSF35 | LSF35 | +--------+-------------+-------------+ | B_09 | g21 | g21 | | B_10 | g22 | g22 | | B_11 | P4 | P4 | | B_12 | LSF34 | LSF34 | | B_13 | P5 | P5 | | B_14 | P1 | P1 | | B_15 | P2 | P2 | | B_16 | LSF40 | LSF40 | +--------+-------------+-------------+ | B_17 | P6 | P6 | | B_18 | LSF10 | LSF10 | | B_19 | LSF16 | LSF16 | | B_20 | LSF45 | LSF45 | | B_21 | P3 | P3 | | B_22 | LSF15 | LSF15 | | B_23 | LSF14 | LSF14 | | B_24 | LSF25 | LSF25 | +--------+-------------+-------------+ | B_25 | BP3 | FEC13 | | B_26 | LSF13 | LSF13 | | B_27 | LSF12 | LSF12 | | B_28 | LSF24 | LSF24 | | B_29 | LSF44 | LSF44 | | B_30 | FM0 | FEC40 | | B_31 | LSF11 | LSF11 | | B_32 | LSF23 | LSF23 | +--------+-------------+-------------+ | B_33 | FM7 | FEC22 | | B_34 | FM6 | FEC21 | Demjanenko, Satterlee Expires August 11, 2017 [Page 6] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 | B_35 | FM5 | FEC20 | | B_36 | g11 | g11 | | B_37 | g10 | g10 | | B_38 | BP2 | FEC12 | | B_39 | BP1 | FEC11 | | B_40 | LSF21 | LSF21 | +--------+-------------+-------------+ | B_41 | LSF33 | LSF33 | | B_42 | LSF22 | LSF22 | | B_43 | LSF32 | LSF32 | | B_44 | LSF31 | LSF31 | | B_45 | LSF43 | LSF43 | | B_46 | LSF42 | LSF42 | | B_47 | AF | FEC42 | | B_48 | LSF41 | LSF41 | +--------+-------------+-------------+ | B_49 | FM4 | FEC32 | | B_50 | FM3 | FEC31 | | B_51 | FM2 | FEC30 | | B_52 | FM1 | FEC41 | | B_53 | g12 | g12 | | B_54 | SYNC | SYNC | +--------+-------------+-------------+ NOTES: g = Gain BP = Bandpass Voicing P = Pitch/Voicing LSF = Line Spectral Frequencies FEC = Forward Error Correction Parity Bits FM = Fourier Magnitudes AF = Aperiodic Flag B_01 = least significant bit of data set Table 3.1 - The bitstream definition for MELPe 2400 bps. The 2400 bps MELPe RTP payload is constructed as per Figure 2. Note that bit B_01 is placed in the LSB of the first byte with all other bits in sequence. When filling octets, the least significant bits of the seventh octet are filled with bits B_49 to B_54 respectively. Demjanenko, Satterlee Expires August 11, 2017 [Page 7] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 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 | +------+------+------+------+------+------+------+------+ | RSVA | RSVB | 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 According to Tables D9a and D9b of [MELPE], the 1200 bit/s MELPe bit transmission order is the following: +--------+-------------+-------------+ | Bit | Modes 1-4 | Mode 5 | | | (Voiced) | (Unvoiced) | +--------+-------------+-------------+ | B_01 | Syn | Syn | | B_02 | Pitch&UV0 | Pitch&UV0 | | B_03 | Pitch&UV1 | Pitch&UV1 | | B_04 | Pitch&UV2 | Pitch&UV2 | | B_05 | Pitch&UV3 | Pitch&UV3 | | B_06 | Pitch&UV4 | Pitch&UV4 | | B_07 | Pitch&UV5 | Pitch&UV5 | | B_08 | Pitch&UV6 | Pitch&UV6 | +--------+-------------+-------------+ | B_09 | Pitch&UV7 | Pitch&UV7 | | B_10 | Pitch&UV8 | Pitch&UV8 | | B_11 | Pitch&UV9 | Pitch&UV9 | | B_12 | Pitch&UV10 | Pitch&UV10 | | B_13 | Pitch&UV11 | Pitch&UV11 | | B_14 | LSP0 | LSP0 | | B_15 | LSP1 | LSP1 | | B_16 | LSP2 | LSP2 | Demjanenko, Satterlee Expires August 11, 2017 [Page 8] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 +--------+-------------+-------------+ | B_17 | LSP3 | LSP3 | | B_18 | LSP4 | LSP4 | | B_19 | LSP5 | LSP5 | | B_20 | LSP6 | LSP6 | | B_21 | LSP7 | LSP7 | | B_22 | LSP8 | LSP8 | | B_23 | LSP9 | LSP9 | | B_24 | LSP10 | LSP10 | +--------+-------------+-------------+ | B_25 | LSP11 | LSP11 | | B_26 | LSP12 | LSP12 | | B_27 | LSP13 | LSP13 | | B_28 | LSP14 | LSP14 | | B_29 | LSP15 | LSP15 | | B_30 | LSP16 | LSP16 | | B_31 | LSP17 | LSP17 | | B_32 | LSP18 | LSP18 | +--------+-------------+-------------+ | B_33 | LSP19 | LSP19 | | B_34 | LSP20 | LSP20 | | B_35 | LSP21 | LSP21 | | B_36 | LSP22 | LSP22 | | B_37 | LSP23 | LSP23 | | B_38 | LSP24 | LSP24 | | B_39 | LSP25 | LSP25 | | B_40 | LSP26 | LSP26 | +--------+-------------+-------------+ | B_41 | LSP27 | GAIN0 | | B_42 | LSP28 | GAIN1 | | B_43 | LSP29 | GAIN2 | | B_44 | LSP30 | GAIN3 | | B_45 | LSP31 | GAIN4 | | B_46 | LSP32 | GAIN5 | | B_47 | LSP33 | GAIN6 | | B_48 | LSP34 | GAIN7 | +--------+-------------+-------------+ | B_49 | LSP35 | GAIN8 | | B_50 | LSP36 | GAIN9 | | B_51 | LSP37 | | | B_52 | LSP38 | | | B_53 | LSP39 | | | B_54 | LSP40 | | | B_55 | LSP41 | | | B_56 | LSP42 | | +--------+-------------+-------------+ | B_57 | GAIN0 | | | B_58 | GAIN1 | | Demjanenko, Satterlee Expires August 11, 2017 [Page 9] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 | B_59 | GAIN2 | | | B_60 | GAIN3 | | | B_61 | GAIN4 | | | B_62 | GAIN5 | | | B_63 | GAIN6 | | | B_64 | GAIN7 | | +--------+-------------+-------------+ | B_65 | GAIN8 | | | B_66 | GAIN9 | | | B_67 | BP0 | | | B_68 | BP1 | | | B_69 | BP2 | | | B_70 | BP3 | | | B_71 | BP4 | | | B_72 | BP5 | | +--------+-------------+-------------+ | B_73 | JITTER | | | B_74 | FS0 | | | B_75 | FS1 | | | B_76 | FS2 | | | B_77 | FS3 | | | B_78 | FS4 | | | B_79 | FS5 | | | B_80 | FS6 | | +--------+-------------+-------------+ | B_81 | FS7 | | +--------+-------------+-------------+ NOTES: BP = Band pass voicing FS = Fourier magnitudes Table 3.2 - The bitstream definition for MELPe 1200 bps. The 1200 bps MELPe RTP payload is constructed as per Figure 3. Note that bit B_01 is placed in the LSB of the first byte with all other bits in sequence. When filling octets, the least significant bit of the eleventh octet is filled with bit B_81. Demjanenko, Satterlee Expires August 11, 2017 [Page 10] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 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 | +------+------+------+------+------+------+------+------+ | RSVA | RSVB | RSVC | RSV0 | RSV0 | RSV0 | RSV0 | B_81 | +------+------+------+------+------+------+------+------+ Figure 3 - Packed MELPe 1200 bps payload octets. 3.1.3 600 bps Bitstream Structure According to Tables M-11 to M-16 of [MELPE], the 600 bit/s MELPe bit transmission order (bit priority is not shown for clarity) is the following: +--------+-------------+-------------+-------------+ | Bit | Mode 1 | Mode 2 | Mode 3 | | | (Voiced) | (voiced) | (voiced) | +--------+-------------+-------------+-------------+ | B_01 | Voicing (4) | Voicing (4) | Voicing (4) | | B_02 | Voicing (3) | Voicing (3) | Voicing (3) | | B_03 | Voicing (2) | Voicing (2) | Voicing (2) | | B_04 | Voicing (1) | Voicing (1) | Voicing (1) | | B_05 | Voicing (0) | Voicing (0) | Voicing (0) | | B_06 | LSF1,4 (3) | Pitch (5) | Pitch (7) | | B_07 | LSF1,4 (2) | Pitch (4) | Pitch (6) | | B_08 | LSF1,4 (1) | Pitch (3) | Pitch (5) | Demjanenko, Satterlee Expires August 11, 2017 [Page 11] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 +--------+-------------+-------------+-------------+ | B_09 | LSF1,4 (0) | Pitch (2) | Pitch (4) | | B_10 | LSF1,3 (3) | Pitch (1) | Pitch (3) | | B_11 | LSF1,3 (2) | Pitch (0) | Pitch (2) | | B_12 | LSF1,3 (1) | LSF1,3 (3) | Pitch (1) | | B_13 | LSF1,3 (0) | LSF1,3 (2) | Pitch (0) | | B_14 | LSF1,2 (3) | LSF1,3 (1) | LSF1,3 (3) | | B_15 | LSF1,2 (2) | LSF1,3 (0) | LSF1,3 (2) | | B_16 | LSF1,2 (1) | LSF1,2 (3) | LSF1,3 (1) | +--------+-------------+-------------+-------------+ | B_17 | LSF1,2 (0) | LSF1,2 (2) | LSF1,3 (0) | | B_18 | LSF1,1 (5) | LSF1,2 (1) | LSF1,2 (4) | | B_19 | LSF1,1 (4) | LSF1,2 (0) | LSF1,2 (3) | | B_20 | LSF1,1 (3) | LSF1,1 (5) | LSF1,2 (2) | | B_21 | LSF1,1 (2) | LSF1,1 (4) | LSF1,2 (1) | | B_22 | LSF1,1 (1) | LSF1,1 (3) | LSF1,2 (0) | | B_23 | LSF1,1 (0) | LSF1,1 (2) | LSF1,1 (5) | | B_24 | LSF2,4 (3) | LSF1,1 (1) | LSF1,1 (4) | +--------+-------------+-------------+-------------+ | B_25 | LSF2,4 (2) | LSF1,1 (0) | LSF1,1 (3) | | B_26 | LSF2,4 (1) | LSF2,3 (3) | LSF1,1 (2) | | B_27 | LSF2,4 (0) | LSF2,3 (2) | LSF1,1 (1) | | B_28 | LSF2,3 (3) | LSF2,3 (1) | LSF1,1 (0) | | B_29 | LSF2,3 (2) | LSF2,3 (0) | LSF2,3 (3) | | B_30 | LSF2,3 (1) | LSF2,2 (4) | LSF2,3 (2) | | B_31 | LSF2,3 (0) | LSF2,2 (3) | LSF2,3 (1) | | B_32 | LSF2,2 (3) | LSF2,2 (2) | LSF2,3 (0) | +--------+-------------+-------------+-------------+ | B_33 | LSF2,2 (2) | LSF2,2 (1) | LSF2,2 (4) | | B_34 | LSF2,2 (1) | LSF2,2 (0) | LSF2,2 (3) | | B_35 | LSF2,2 (0) | LSF2,1 (6) | LSF2,2 (2) | | B_36 | LSF2,1 (5) | LSF2,1 (5) | LSF2,2 (1) | | B_37 | LSF2,1 (4) | LSF2,1 (4) | LSF2,2 (0) | | B_38 | LSF2,1 (3) | LSF2,1 (3) | LSF2,1 (5) | | B_39 | LSF2,1 (2) | LSF2,1 (2) | LSF2,1 (4) | | B_40 | LSF2,1 (1) | LSF2,1 (1) | LSF2,1 (3) | +--------+-------------+-------------+-------------+ | B_41 | LSF2,1 (0) | LSF2,1 (0) | LSF2,1 (2) | | B_42 | GAIN2 (5) | GAIN2 (5) | LSF2,1 (1) | | B_43 | GAIN2 (4) | GAIN2 (4) | LSF2,1 (0) | | B_44 | GAIN2 (3) | GAIN2 (3) | GAIN2 (4) | | B_45 | GAIN2 (2) | GAIN2 (2) | GAIN2 (3) | | B_46 | GAIN2 (1) | GAIN2 (1) | GAIN2 (2) | | B_47 | GAIN2 (0) | GAIN2 (0) | GAIN2 (1) | | B_48 | GAIN1 (6) | GAIN1 (6) | GAIN2 (0) | +--------+-------------+-------------+-------------+ | B_49 | GAIN1 (5) | GAIN1 (5) | GAIN1 (5) | | B_50 | GAIN1 (4) | GAIN1 (4) | GAIN1 (4) | Demjanenko, Satterlee Expires August 11, 2017 [Page 12] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 | B_51 | GAIN1 (3) | GAIN1 (3) | GAIN1 (3) | | B_52 | GAIN1 (2) | GAIN1 (2) | GAIN1 (2) | | B_53 | GAIN1 (1) | GAIN1 (1) | GAIN1 (1) | | B_54 | GAIN1 (0) | GAIN1 (0) | GAIN1 (0) | +--------+-------------+-------------+-------------+ Table 3.3a - The bitstream definition for MELPe 600 bps (part 1 of 2). +--------+-------------+-------------+-------------+ | Bit | Mode 4 | Mode 5 | Mode 6 | | | (voiced) | (voiced) | (voiced) | +--------+-------------+-------------+-------------+ | B_01 | Voicing (4) | Voicing (4) | Voicing (4) | | B_02 | Voicing (3) | Voicing (3) | Voicing (3) | | B_03 | Voicing (2) | Voicing (2) | Voicing (2) | | B_04 | Voicing (1) | Voicing (1) | Voicing (1) | | B_05 | Voicing (0) | Voicing (0) | Voicing (0) | | B_06 | Pitch (7) | Pitch (7) | Pitch (7) | | B_07 | Pitch (6) | Pitch (6) | Pitch (6) | | B_08 | Pitch (5) | Pitch (5) | Pitch (5) | +--------+-------------+-------------+-------------+ | B_09 | Pitch (4) | Pitch (4) | Pitch (4) | | B_10 | Pitch (3) | Pitch (3) | Pitch (3) | | B_11 | Pitch (2) | Pitch (2) | Pitch (2) | | B_12 | Pitch (1) | Pitch (1) | Pitch (1) | | B_13 | Pitch (0) | Pitch (0) | Pitch (0) | | B_14 | LSF1,3 (3) | LSF1,3 (3) | LSF1,3 (3) | | B_15 | LSF1,3 (2) | LSF1,3 (2) | LSF1,3 (2) | | B_16 | LSF1,3 (1) | LSF1,3 (1) | LSF1,3 (1) | +--------+-------------+-------------+-------------+ | B_17 | LSF1,3 (0) | LSF1,3 (0) | LSF1,3 (0) | | B_18 | LSF1,2 (3) | LSF1,2 (4) | LSF1,2 (4) | | B_19 | LSF1,2 (2) | LSF1,2 (3) | LSF1,2 (3) | | B_20 | LSF1,2 (1) | LSF1,2 (2) | LSF1,2 (2) | | B_21 | LSF1,2 (0) | LSF1,2 (1) | LSF1,2 (1) | | B_22 | LSF1,1 (5) | LSF1,2 (0) | LSF1,2 (0) | | B_23 | LSF1,1 (4) | LSF1,1 (5) | LSF1,1 (6) | | B_24 | LSF1,1 (3) | LSF1,1 (4) | LSF1,1 (5) | +--------+-------------+-------------+-------------+ | B_25 | LSF1,1 (2) | LSF1,1 (3) | LSF1,1 (4) | | B_26 | LSF1,1 (1) | LSF1,1 (2) | LSF1,1 (3) | | B_27 | LSF1,1 (0) | LSF1,1 (1) | LSF1,1 (2) | | B_28 | LSF2,3 (3) | LSF1,1 (0) | LSF1,1 (1) | | B_29 | LSF2,3 (2) | LSF2,3 (3) | LSF1,1 (0) | | B_30 | LSF2,3 (1) | LSF2,3 (2) | LSF2,3 (3) | | B_31 | LSF2,3 (0) | LSF2,3 (1) | LSF2,3 (2) | | B_32 | LSF2,2 (4) | LSF2,3 (0) | LSF2,3 (1) | Demjanenko, Satterlee Expires August 11, 2017 [Page 13] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 +--------+-------------+-------------+-------------+ | B_33 | LSF2,2 (3) | LSF2,2 (4) | LSF2,3 (0) | | B_34 | LSF2,2 (2) | LSF2,2 (3) | LSF2,2 (4) | | B_35 | LSF2,2 (1) | LSF2,2 (2) | LSF2,2 (3) | | B_36 | LSF2,2 (0) | LSF2,2 (1) | LSF2,2 (2) | | B_37 | LSF2,1 (6) | LSF2,2 (0) | LSF2,2 (1) | | B_38 | LSF2,1 (5) | LSF2,1 (5) | LSF2,2 (0) | | B_39 | LSF2,1 (4) | LSF2,1 (4) | LSF2,1 (6) | | B_40 | LSF2,1 (3) | LSF2,1 (3) | LSF2,1 (5) | +--------+-------------+-------------+-------------+ | B_41 | LSF2,1 (2) | LSF2,1 (2) | LSF2,1 (4) | | B_42 | LSF2,1 (1) | LSF2,1 (1) | LSF2,1 (3) | | B_43 | LSF2,1 (0) | LSF2,1 (0) | LSF2,1 (2) | | B_44 | GAIN2 (4) | GAIN2 (4) | LSF2,1 (1) | | B_45 | GAIN2 (3) | GAIN2 (3) | LSF2,1 (0) | | B_46 | GAIN2 (2) | GAIN2 (2) | GAIN1 (8) | | B_47 | GAIN2 (1) | GAIN2 (1) | GAIN1 (7) | | B_48 | GAIN2 (0) | GAIN2 (0) | GAIN1 (6) | +--------+-------------+-------------+-------------+ | B_49 | GAIN1 (5) | GAIN1 (5) | GAIN1 (5) | | B_50 | GAIN1 (4) | GAIN1 (4) | GAIN1 (4) | | B_51 | GAIN1 (3) | GAIN1 (3) | GAIN1 (3) | | B_52 | GAIN1 (2) | GAIN1 (2) | GAIN1 (2) | | B_53 | GAIN1 (1) | GAIN1 (1) | GAIN1 (1) | | B_54 | GAIN1 (0) | GAIN1 (0) | GAIN1 (0) | +--------+-------------+-------------+-------------+ Notes: xxxx (0) = LSB xxxx (nbits-1) = MSB LSF1,p = MSVQ indice of the pth stage of the two first frames LSF2,p = MSVQ indice of the pth stage of the two last frames GAIN1 = VQ/MSVQ indice of the 1st stage GAIN2 = MSVQ indice of the 2nd stage Table 3.3b - The bitstream definition for MELPe 600 bps (part 2 of 2). The 600 bps MELPe RTP payload is constructed as per Figure 4. Note that bit B_01 is placed in the LSB of the first byte with all other bits in sequence. When filling octets, the least significant bits of the seventh octet are filled with bits B_49 to B_54 respectively. Demjanenko, Satterlee Expires August 11, 2017 [Page 14] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 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 | +------+------+------+------+------+------+------+------+ | RSVA | RSVB | B_54 | B_53 | B_52 | B_51 | B_50 | B_49 | +------+------+------+------+------+------+------+------+ Figure 4 - Packed MELPe 600 bps payload octets. 3.2 MELPe Comfort Noise Bitstream Definition Table B.3-1 of [SCIP210] identifies the usage of MELPe 2400 bps parameters for conveying comfort noise. Demjanenko, Satterlee Expires August 11, 2017 [Page 15] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 +-------------------------------------+----------------+ | MELPe Parameter | Value | +-------------------------------------+----------------+ | msvq[0] (line spectral frequencies) | * See Note | +-------------------------------------+----------------+ | msvq[1] (line spectral frequencies) | Set to 0 | +-------------------------------------+----------------+ | msvq[2] (line spectral frequencies) | Set to 0 | +-------------------------------------+----------------+ | msvq[3] (line spectral frequencies) | Set to 0 | +-------------------------------------+----------------+ | fsvq (Fourier magnitudes) | Set to 0 | +-------------------------------------+----------------+ | gain[0] (gain) | Set to 0 | +-------------------------------------+----------------+ | gain[1] (gain) | * See Note | +-------------------------------------+----------------+ | pitch (pitch - overall voicing) | Set to 0 | +-------------------------------------+----------------+ | bp (bandpass voicing) | Set to 0 | +-------------------------------------+----------------+ | af (aperiodic flag/jitter index) | Set to 0 | +-------------------------------------+----------------+ | sync (sync bit) | Alternations | +-------------------------------------+----------------+ Note: The default values are the respective parameters from the vocoder frame. It is preferred that msvq[0] and gain[1] values be derived by averaging the respective parameter from some number of previous vocoder frames. Table 3.4 - MELPe Comfort Noise Parameters Since only msvq[0] (also known as LSF1x or the first LSP) and gain[1] (also known as g2x or the second gain) are needed, the following bit order is used for comfort noise frames. Demjanenko, Satterlee Expires August 11, 2017 [Page 16] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 +--------+-------------+ | Bit | Comfort | | | Noise | +--------+-------------+ | B_01 | LSF10 | | B_02 | LSF11 | | B_03 | LSF12 | | B_04 | LSF13 | | B_05 | LSF14 | | B_06 | LSF15 | | B_07 | LSF16 | | B_08 | g20 | +--------+-------------+ | B_09 | g21 | | B_10 | g22 | | B_11 | g23 | | B_12 | g24 | | B_13 | SYNC | +--------+-------------+ NOTES: g = Gain LSF = Line Spectral Frequencies Table 3.5 - The bitstream definition for MELPe Comfort Noise. The Comfort Noise MELPe RTP payload is constructed as per Figure 5. Note that bit B_01 is placed in the LSB of the first byte with all other bits in sequence. When When filling octets, the least significant bits of the second octet are filled with bits B_09 to B_13 respectively. 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 | +------+------+------+------+------+------+------+------+ | RSVA | RSVB | RSVC | B_13 | B_12 | B_11 | B_10 | B_09 | +------+------+------+------+------+------+------+------+ Figure 5 - Packed MELPe Comfort Noise payload octets. 3.3 Multiple MELPe frames in a RTP packet A MELPe RTP packet MAY consist of zero or more MELPe coder frames, Demjanenko, Satterlee Expires August 11, 2017 [Page 17] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 followed by zero or one MELPe Comfort Noise frames. The presence of a comfort noise frame can be deduced from the length of the RTP payload. The default packetization interval is one coder frame (22.5, 67.5 or 90 ms) according to the coder bit rate (2400, 1200 or 600 bps). For some applications, a longer packetization interval is used to reduce the packet rate. A MELPe RTP packet comprised of no coder frame and no comfort noise frame MAY be used periodically by an end point to indicate connectivity by an otherwise idle receiver. All MELPe frames in a single RTP packet MUST be of the same coder bit rate. Dynamic switching between frame rates within an RTP stream may be permitted (if supported by both ends) provided that reserved bits, RSVA, RSVB, and RSVC are filled in as per Table 3.6. If bit-rate switching is not used, all reserved bits are encoded as 0 by the sender and ignored by the receiver. (RSV0 is always coded as 0). +-------------------+------+------+------+ | Coder Bit Rate | RSVA | RSVB | RSVC | +-------------------+------+------+------+ | 2400 bps | 0 | 0 | N/A | +-------------------+------+------+------+ | 1200 bps | 1 | 0 | 0 | +-------------------+------+------+------+ | 600 bps | 0 | 1 | N/A | +-------------------+------+------+------+ | Comfort Noise | 1 | 0 | 1 | +-------------------+------+------+------+ | (reserved) | 1 | 1 | N/A | +-------------------+------+------+------+ Table 3.6 - MELPe Frame Bit Rate Indicators. It is important to observe that senders have the following additional restrictions: Senders SHOULD NOT include more 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 is consistent with the application. For example, in a telephony and other real time applications where delay is important, then the fewer frames per packet the lower the delay, whereas for Demjanenko, Satterlee Expires August 11, 2017 [Page 18] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 bandwidth constrained links or delay insensitive streaming messaging application, more than one or many frames per 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 MELPe frames is to count the total number of octets within the RTP packet, and divide the octet count by the number of expected octets per frame (7/11/7 per frame). Keep in mind the last frame can be a 2 octet comfort noise frame. When dynamic bit-rate switching is used and more than one frame is contained in a RTP packet, it is RECOMMENDED to inspect the coder rate bits contained in the last octet. If the coder bit rate indicates a Comfort Noise frame, then inspect the third last octet for the coder bit rate. All MELPe speech frames in the RTP packet will be of this same coder bit rate. 3.4 Congestion Control Considerations The target bitrate of MELPe 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 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 as well implement a transport circuit breaker [RFC8083] (formerly [draft-ietf-avtcore-rtp-circuit- breakers]). 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 MELP, MELP2400, MELP1200, and MELP600 media types which is registered in accordance with RFC 4855 [RFC4855] and using the template of RFC 6838 [RFC6838]. Demjanenko, Satterlee Expires August 11, 2017 [Page 19] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 4.1 Media Type Definition Type names: audio Subtype name: MELP, MELP2400, MELP1200, and MELP600 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 MELPe, this corresponds to the 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 MELPe, this corresponds to the 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 bit rates supported. Possible values are a comma-separated list of rates from the set: 2400, 1200, 600. The modes are listed in order of preference; first is preferred. If "bitrate" is not present, the fixed coder bit rate of 2400 MUST be used. The alternate encoding names, "MELP2400", "MELP1200", and "MELP600" directly specify the MELPe coder bit rate of 2400, 1200, and 600 respectively and MUST NOT specify a "bitrate" parameter. Encoding considerations: This media type is framed and binary, see section 4.8 in RFC6838 [RFC6838]. Security considerations: Please see the security considerations in section 8 of RFCxxxx (this RFC). Demjanenko, Satterlee Expires August 11, 2017 [Page 20] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 Interoperability considerations: Early implementations used MELP2400, MELP1200, and MELP600 to indicate both coder type and bit rate. These media type names should be preserved with this registration. 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. VOCAL Technologies, Ltd. 520 Lee Entrance, Suite 202 Buffalo, NY 14228 USA Phone: +1 716 688 4675 Email: victor.demjanenko@vocal.com Intended usage: COMMON Demjanenko, Satterlee Expires August 11, 2017 [Page 21] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 Restrictions on usage: This media type 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 Demjanenko, Satterlee Expires August 11, 2017 [Page 22] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 4.2 Mapping to SDP The mapping of the above defined payload format media type 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 MELPe 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=" string. o The parameters "ptime" and "maxptime" go in the SDP "a=ptime" and "a=maxptime" attributes, respectively. When conveying information by SDP, the encoding name SHALL be "MELP" (the same as the media subtype). Alternative encoding name types, "MELP2400", "MELP1200", and "MELP600", MAY be used in SDP to convey fixed bit-rate configurations. These names have been observed in systems that do not support dynamic frame rate switching as specified by the parameter, "bitrate". An example of the media representation in SDP for describing MELPe might be: m=audio 49120 RTP/AVP 97 a=rtpmap:97 MELP/8000 An alternative example of SDP for fixed bit-rate configurations might be: m=audio 49120 RTP/AVP 97 100 101 102 a=rtpmap:97 MELP/8000 a=rtpmap:100 MELP2400/8000 a=rtpmap:101 MELP1200/8000 a=rtpmap:102 MELP600/8000 If the encoding name "MELP" is received without a "bitrate" parameter, the fixed coder bit rate of 2400 MUST be used. The alternate encoding names, "MELP2400", "MELP1200", and "MELP600" directly specify the MELPe coder bit rate of 2400, 1200, and 600 respectively and MUST NOT specify a "bitrate" parameter. Demjanenko, Satterlee Expires August 11, 2017 [Page 23] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 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 bit-rate value indicates the corresponding MELPe coder). An example of the media representation in SDP for describing MELPe when all three coder bit rates are supported might be: m=audio 49120 RTP/AVP 97 a=rtpmap:97 MELP/8000 a=fmtp:97 bitrate=2400,600,1200 Parameter ptime can not be used for the purpose of specifying MELPe operating mode, due to fact that for the 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 packet is carrying 1 frames of 67.5 ms or 3 frames of 22.5 ms etc.). 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 both in media subtype name and in the default mapping to the SDP a=fmtp attribute 4.3 Declarative SDP Considerations For declarative media, the "bitrate" parameter specifes the possible bit rates used by the sender. Multiple MELPe rtpmap values (such as 97, 98, and 99 as used below) MAY be used to convey MELPe coded voice at different bit rates. The receiver can then select an appropriate MELPe codec by using 97, 98, or 99. m=audio 49120 RTP/AVP 97 98 99 a=rtpmap:97 MELP/8000 a=fmtp:97 bitrate=2400 a=rtpmap:98 MELP/8000 a=fmtp:98 bitrate=1200 a=rtpmap:99 MELP/8000 a=fmtp:99 bitrate=600 4.4 Offer/Answer SDP Considerations In an Offer/Answer mode [RFC3264], "bitrate" is a bi-directional parameter. Both sides MUST use a common "bitrate" value or values. The offer contains the bit rates supported by the offerer listed in Demjanenko, Satterlee Expires August 11, 2017 [Page 24] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 its preferred order. The answerer MAY agree to any bit rate by listing the bit rate first in the answerer response. Additionally the answerer MAY indicate any secondary bit rate or bit rates that it supports. The initial bit rate used by both parties SHALL be the first bit rate specified in the answerer response. For example if offerer bit rates are "2400,600", and answer bit rates are "600,2400", the initial bit rate is 600. If other bit rates are provided by the answerer, any common bit rate between offer and answer MAY be used at any time in the future. Activation of these other common bit rates is beyond the scope of this document. The use of a lower bit rate is often important for a case such as when one end point utilizes a bandwidth constrained link (e.g. 1200 bps radio link or slower), where only the lower coder bit rate will work. 5 Discontinious Transmission A primary application of MELPe is for radio communications of voice conversations and discontinuous transmissions are normal. When MELPe is used in an IP network, MELPe RTP packet transmissions may cease and resume frequently. RTP SSRC sequence number gaps indicate lost packets to be filled by PLC while abrupt loss of RTP packets indicate intended discontinuous transmission. If a MELPe coder so desires, it may send a comfort noise frame as per SCIP-210 Appendix B [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 MELPe 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 to use a code value of 3 for the pitch/voicing parameter (represented by the bits P6 to P0 in Table 3.1). Hence, set bits P0 and P1 to one and bits P2, P3, P4, P5, and P6 to zero. When using PLC in a 1200 bps or 600 bps mode, the MELPe 2400 bps decoder is called three or four times respectively to cover the loss of a MELPe frame. Demjanenko, Satterlee Expires August 11, 2017 [Page 25] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 Demjanenko, Satterlee Expires August 11, 2017 [Page 26] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 7 IANA Considerations This memo requests that IANA registers MELP, MELP2400, MELP1200, and MELP600 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 [RFC4855], RTP/SAVP [RFC3711] or RTP/SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] discusses, it is not an RTP payload format's responsibility to discuss or mandate what solutions are used to meet the basic security goals like confidentiality, integrity and source authenticity for RTP in general. This responsibility lays on anyone using RTP in an application. They can find guidance on available security mechanisms and important considerations in Options for Securing RTP Sessions [RFC7201]. Applications SHOULD use one or more appropriate strong security mechanisms. The rest of this security consideration section discusses the security impacting properties of the payload format itself. This RTP payload format and the MELPe decoder do not exhibit any significant non-uniformity in the receiver-side computational complexity for packet processing, and thus are unlikely to pose a denial-of-service threat due to the receipt of pathological data. Nor does the RTP payload format contain any active content. With respect to VAD and its effect on bit rate, please see security consideration in RFC6562 [RFC6562]. 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 [draft-ietf-avtcore-rtp-circuit-breakers] Perkins, C. and V. Singh, Demjanenko, Satterlee Expires August 11, 2017 [Page 27] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 "Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions", draft-ietf-avtcore-rtp-circuit-breakers-18 (work in progress), August 18, 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2736] Handley, M. and Perkins, C., "Guidelines for Writers of RTP Payload Format Specifications", BCP 36, RFC 2736, December 1999. [RFC3264] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with the Session Description Protocol (SDP)" IETF RFC 3264, June 2002. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and Jacobson, V., "RTP: A Transport Protocol for Real-Time Applications", IETF RFC 3550, July 2003. [RFC3551] Schulzrinne, H., and Casner, S., "RTP Profile for Audio and Video Conferences with Minimal Control" IETF RFC 3551, July 2003. [RFC3711] Baugher, et al., "The Secure Real Time Transport Protocol", IETF RFC 3711, March 2004. [RFC4566] Handley, M., Jacobson, V. and Perkins, C., "SDP: Session Description Protocol", IETF RFC RFC4566, July 2006. [RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, February 2007. [RFC5124] Ott, J. and Carrara, E., "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback(RTP/SAVPF)", RFC 5124, February 2008. [RFC6562] Perkins, C. and Valin, J. M., "Guidelines for the Use of Variable Bit Rate Audio with Secure RTP", RFC 6562, March 2012. [RFC6838] Freed, N., Klensin, J. and Hansen, T., "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, January 2013. [RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions", RFC 8083, January 2017. [RFC8085] Eggert, L., Fairhurst, G. and Shepherd, G., "UDP Usage Guidelines", RFC 8085, February 2017. [MELP] Department of Defense Telecommunications Standard, "Analog-to- Demjanenko, Satterlee Expires August 11, 2017 [Page 28] INTERNET DRAFT RTP Payload Format for the MELPe Codec February 7, 2017 Digital Conversion of Voice by 2,400 Bit/Second Mixed Excitation Linear Prediction (MELP)", MIL-STD-3005, December 1999. [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 [RFC7201] Westerlund, M. and Perkins, C., "Options for Securing RTP Sessions", RFC 7201, April 2014. [RFC7202] Perkins, C. and Westerlund, M., "Securing the RTP Framework: Why RTP Does Not Mandate a Single Media Security Solution", RFC 7202, April 2014. Authors' Addresses Victor Demjanenko, Ph.D. VOCAL Technologies, Ltd. 520 Lee Entrance, Suite 202 Buffalo, NY 14228 USA Phone: +1 716 688 4675 Email: victor.demjanenko@vocal.com David Satterlee VOCAL Technologies, Ltd. 520 Lee Entrance, Suite 202 Buffalo, NY 14228 USA Phone: +1 716 688 4675 Email: david.satterlee@vocal.com Demjanenko, Satterlee Expires August 11, 2017 [Page 29]