< draft-ietf-payload-flexible-fec-scheme-16.txt		draft-ietf-payload-flexible-fec-scheme-17.txt >
	PAYLOAD M. Zanaty		PAYLOAD M. Zanaty
	Internet-Draft Cisco		Internet-Draft Cisco
	Intended status: Standards Track V. Singh		Intended status: Standards Track V. Singh
	Expires: July 21, 2019 callstats.io		Expires: August 16, 2019 callstats.io
	A. Begen		A. Begen
	Networked Media		Networked Media
	G. Mandyam		G. Mandyam
	Qualcomm Inc.		Qualcomm Inc.
	January 17, 2019		February 12, 2019
	RTP Payload Format for Flexible Forward Error Correction (FEC)		RTP Payload Format for Flexible Forward Error Correction (FEC)
	draft-ietf-payload-flexible-fec-scheme-16		draft-ietf-payload-flexible-fec-scheme-17
	Abstract		Abstract
	This document defines new RTP payload formats for the Forward Error		This document defines new RTP payload formats for the Forward Error
	Correction (FEC) packets that are generated by the non-interleaved		Correction (FEC) packets that are generated by the non-interleaved
	and interleaved parity codes from source media encapsulated in RTP.		and interleaved parity codes from source media encapsulated in RTP.
	These parity codes are systematic codes, where a number of FEC repair		These parity codes are systematic codes, where a number of FEC repair
	packets are generated from a set of source packets from one or more		packets are generated from a set of source packets from one or more
	source RTP streams. These FEC repair packets are sent in a		source RTP streams. These FEC repair packets are sent in a
	redundancy RTP stream separate from the source RTP stream(s) that		redundancy RTP stream separate from the source RTP stream(s) that
	skipping to change at page 2, line 7 ¶		skipping to change at page 2, line 7 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on July 21, 2019.		This Internet-Draft will expire on August 16, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Parity Codes . . . . . . . . . . . . . . . . . . . . . . 4		1.1. Parity Codes . . . . . . . . . . . . . . . . . . . . . . 4
	1.1.1. One-Dimensionsal (1-D) Non-interleaved (Row) FEC		1.1.1. One-Dimensional (1-D) Non-interleaved (Row) FEC
	Protection . . . . . . . . . . . . . . . . . . . . . 6		Protection . . . . . . . . . . . . . . . . . . . . . 6
	1.1.2. 1-D Interleaved (Column) FEC Protection . . . . . . . 7		1.1.2. 1-D Interleaved (Column) FEC Protection . . . . . . . 7
	1.1.3. Use Cases for 1-D FEC Protection . . . . . . . . . . 8		1.1.3. Use Cases for 1-D FEC Protection . . . . . . . . . . 8
	1.1.4. Two-Dimensional (2-D) (Row and Column) FEC Protection 10		1.1.4. Two-Dimensional (2-D) (Row and Column) FEC Protection 10
	1.1.5. FEC Overhead Considerations . . . . . . . . . . . . . 12		1.1.5. FEC Protection with Flexible Mask . . . . . . . . . . 12
			1.1.6. FEC Overhead Considerations . . . . . . . . . . . . . 13
	2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 13		2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 13
	3. Definitions and Notations . . . . . . . . . . . . . . . . . . 13		3. Definitions and Notations . . . . . . . . . . . . . . . . . . 13
	3.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 13		3.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 13
	3.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 14		3.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 14
	4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 14		4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 14
	4.1. Source Packets . . . . . . . . . . . . . . . . . . . . . 14		4.1. Source Packets . . . . . . . . . . . . . . . . . . . . . 14
	4.2. FEC Repair Packets . . . . . . . . . . . . . . . . . . . 15		4.2. FEC Repair Packets . . . . . . . . . . . . . . . . . . . 15
	4.2.1. RTP Header of FEC Repair Packets . . . . . . . . . . 16		4.2.1. RTP Header of FEC Repair Packets . . . . . . . . . . 16
	4.2.2. FEC Header of FEC Repair Packets . . . . . . . . . . 17		4.2.2. FEC Header of FEC Repair Packets . . . . . . . . . . 17
	5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 25		5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 25
	skipping to change at page 3, line 28 ¶		skipping to change at page 3, line 28 ¶
	7.1.2. Example SDP for Flexible FEC Protection with explicit		7.1.2. Example SDP for Flexible FEC Protection with explicit
	signalling in the SDP . . . . . . . . . . . . . . . . 44		signalling in the SDP . . . . . . . . . . . . . . . . 44
	7.2. On the Use of the RTP Stream Identifier Source		7.2. On the Use of the RTP Stream Identifier Source
	Description . . . . . . . . . . . . . . . . . . . . . . . 44		Description . . . . . . . . . . . . . . . . . . . . . . . 44
	8. Congestion Control Considerations . . . . . . . . . . . . . . 45		8. Congestion Control Considerations . . . . . . . . . . . . . . 45
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 45		9. Security Considerations . . . . . . . . . . . . . . . . . . . 45
	10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46		10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
	11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46		11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 46		12. References . . . . . . . . . . . . . . . . . . . . . . . . . 46
	12.1. Normative References . . . . . . . . . . . . . . . . . . 46		12.1. Normative References . . . . . . . . . . . . . . . . . . 46
	12.2. Informative References . . . . . . . . . . . . . . . . . 47		12.2. Informative References . . . . . . . . . . . . . . . . . 48
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
	1. Introduction		1. Introduction
	This document defines new RTP payload formats for the Forward Error		This document defines new RTP payload formats for the Forward Error
	Correction (FEC) that is generated by the non-interleaved and		Correction (FEC) that is generated by the non-interleaved and
	interleaved parity codes from a source media encapsulated in RTP		interleaved parity codes from a source media encapsulated in RTP
	[RFC3550]. The type of the source media protected by these parity		[RFC3550]. The type of the source media protected by these parity
	codes can be audio, video, text or application. The FEC data are		codes can be audio, video, text or application. The FEC data are
	generated according to the media type parameters, which are		generated according to the media type parameters, which are
	skipping to change at page 6, line 13 ¶		skipping to change at page 6, line 13 ¶
	recovery process to be useful. The repair window is defined as the		recovery process to be useful. The repair window is defined as the
	time that spans a FEC block, which consists of the source packets and		time that spans a FEC block, which consists of the source packets and
	the corresponding repair packets. At the receiver side, the FEC		the corresponding repair packets. At the receiver side, the FEC
	decoder SHOULD buffer source and repair packets at least for the		decoder SHOULD buffer source and repair packets at least for the
	duration of the repair window, to allow all the repair packets to		duration of the repair window, to allow all the repair packets to
	arrive. The FEC decoder can start decoding the already received		arrive. The FEC decoder can start decoding the already received
	packets sooner; however, it should not register a FEC decoding		packets sooner; however, it should not register a FEC decoding
	failure until it waits at least for the duration of the repair		failure until it waits at least for the duration of the repair
	window.		window.
	1.1.1. One-Dimensionsal (1-D) Non-interleaved (Row) FEC Protection		1.1.1. One-Dimensional (1-D) Non-interleaved (Row) FEC Protection
	Consider a group of D x L source packets that have sequence numbers		Consider a group of D x L source packets that have sequence numbers
	starting from 1 running to D x L, and a repair packet is generated by		starting from 1 running to D x L, and a repair packet is generated by
	applying the XOR operation to every L consecutive packets as sketched		applying the XOR operation to every L consecutive packets as sketched
	in Figure 3. This process is referred to as 1-D non-interleaved FEC		in Figure 3. This process is referred to as 1-D non-interleaved FEC
	protection. As a result of this process, D repair packets are		protection. As a result of this process, D repair packets are
	generated, which are referred to as non-interleaved (or row) FEC		generated, which are referred to as non-interleaved (or row) FEC
	repair packets. In general D and L represent values that describe		repair packets. In general D and L represent values that describe
	how packets are grouped together from a depth and length perspective		how packets are grouped together from a depth and length perspective
	(respectively) when interleaving all D x L source packets.		(respectively) when interleaving all D x L source packets.
	skipping to change at page 12, line 32 ¶		skipping to change at page 12, line 32 ¶
	+===+ +===+ +===+ +===+		+===+ +===+ +===+ +===+
	|C_1| |C_2| |C_3| |C_4|		|C_1| |C_2| |C_3| |C_4|
	+===+ +===+ +===+ +===+		+===+ +===+ +===+ +===+
	Figure 8: Example scenario #2 where 2-D parity FEC protection fails		Figure 8: Example scenario #2 where 2-D parity FEC protection fails
	error recovery		error recovery
	1.1.5. FEC Overhead Considerations		1.1.5. FEC Protection with Flexible Mask
			It is possible to define FEC protection for selected packets in the
			source stream. This would enable differential protection, i.e.
			application of FEC selectively to packets that require a higher level
			of reliability then the other packets in the source stream. The
			sender will be required to send a bitmap indicating the packets to be
			protected, i.e. a "mask", to the receiver. Since the mask can be
			modified during an RTP session ("flexible mask"), this kind of FEC
			protection can also be used to implement FEC dynamically (e.g. for
			adaptation to different types of traffic during the RTP session).
			1.1.6. FEC Overhead Considerations
	The overhead is defined as the ratio of the number of bytes belonging		The overhead is defined as the ratio of the number of bytes belonging
	to the repair packets to the number of bytes belonging to the		to the repair packets to the number of bytes belonging to the
	protected source packets.		protected source packets.
	Generally, repair packets are larger in size compared to the source		Generally, repair packets are larger in size compared to the source
	packets. Also, not all the source packets are necessarily equal in		packets. Also, not all the source packets are necessarily equal in
	size. However, assuming that each repair packet carries an equal		size. However, assuming that each repair packet carries an equal
	number of bytes as carried by a source packet, the overhead for		number of bytes as carried by a source packet, the overhead for
	different FEC protection methods can be computed as follows:		different FEC protection methods can be computed as follows:
	skipping to change at page 14, line 16 ¶		skipping to change at page 14, line 26 ¶
	L: Number of columns of the source block (length of each row).		L: Number of columns of the source block (length of each row).
	D: Number of rows of the source block (depth of each column).		D: Number of rows of the source block (depth of each column).
	bitmask: A 15-bit, 46-bit, or 110-bit mask indicating which source		bitmask: A 15-bit, 46-bit, or 110-bit mask indicating which source
	packets are protected by a FEC repair packet. If the bit i in the		packets are protected by a FEC repair packet. If the bit i in the
	mask is set to 1, the source packet number N + i is protected by		mask is set to 1, the source packet number N + i is protected by
	this FEC repair packet, where N is the sequence number base		this FEC repair packet, where N is the sequence number base
	indicated in the FEC repair packet. The most significant bit of		indicated in the FEC repair packet. The most significant bit of
	the mask corresponds to i=0. The least signficant bit of the mask		the mask corresponds to i=0. The least significant bit of the
	corresponds to i=14 in the 15-bit mask, i=45 in the 46-bit mask,		mask corresponds to i=14 in the 15-bit mask, i=45 in the 46-bit
	or i=109 in the 110-bit mask.		mask, or i=109 in the 110-bit mask.
	4. Packet Formats		4. Packet Formats
	This section describes the formats of the source packets and defines		This section describes the formats of the source packets and defines
	the formats of the FEC repair packets.		the formats of the FEC repair packets.
	4.1. Source Packets		4.1. Source Packets
	The source packets contain the information that identifies the source		The source packets contain the information that identifies the source
	block and the position within the source block occupied by the		block and the position within the source block occupied by the
	skipping to change at page 16, line 19 ¶		skipping to change at page 16, line 21 ¶
	Version (V) 2 bits: This MUST be set to 2 (binary 10), as this		Version (V) 2 bits: This MUST be set to 2 (binary 10), as this
	specification requires all source RTP packets and all FEC repair		specification requires all source RTP packets and all FEC repair
	packets to use RTP version 2. The reason for this restriction is		packets to use RTP version 2. The reason for this restriction is
	the first 2 bits of the FEC header contain other information (R		the first 2 bits of the FEC header contain other information (R
	and F bits) rather than recovering the RTP version field.		and F bits) rather than recovering the RTP version field.
	Padding (P) bit: Source packets can have optional RTP padding,		Padding (P) bit: Source packets can have optional RTP padding,
	which can be recovered. FEC repair packets can have optional RTP		which can be recovered. FEC repair packets can have optional RTP
	padding, which is independent of the RTP padding of the source		padding, which is independent of the RTP padding of the source
	pakcets.		packets.
	Extension (X) bit: Source packets can have optional RTP header		Extension (X) bit: Source packets can have optional RTP header
	extensions, which can be recovered. FEC repair packets can have		extensions, which can be recovered. FEC repair packets can have
	optional RTP header extensions, which are independent of the RTP		optional RTP header extensions, which are independent of the RTP
	header extensions of the source packets.		header extensions of the source packets.
	CSRC Count (CC) 4 bits, and CSRC List (CSRC_i) 32 bits each:		CSRC Count (CC) 4 bits, and CSRC List (CSRC_i) 32 bits each:
	Source packets can have an optional CSRC list and count, which can		Source packets can have an optional CSRC list and count, which can
	be recovered. FEC repair packets MUST use the CSRC list and count		be recovered. FEC repair packets MUST use the CSRC list and count
	to specify the SSRC(s) of the source RTP stream(s) protected by		to specify the SSRC(s) of the source RTP stream(s) protected by
	skipping to change at page 26, line 6 ¶		skipping to change at page 26, line 6 ¶
	o D: indicates the number of rows of the source block that are		o D: indicates the number of rows of the source block that are
	protected by this FEC block and it applies to all the source		protected by this FEC block and it applies to all the source
	SSRCs. D is a positive integer.		SSRCs. D is a positive integer.
	o ToP: indicates the type of protection applied by the sender: 0 for		o ToP: indicates the type of protection applied by the sender: 0 for
	1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC		1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC
	protection, 2 for 2-D parity FEC protection, and 3 for		protection, 2 for 2-D parity FEC protection, and 3 for
	retransmission. There can only be one value listed for ToP. The		retransmission. There can only be one value listed for ToP. The
	absence of the ToP field means that all protection types are		absence of the ToP field means that all protection types are
	allowed.		allowed. An offer that lists more than one ToP value MUST be
			rejected.
	Note that both L and D in the optional parameters should follow the		Note that both L and D in the optional parameters should follow the
	value pairings stated in Section 4.2.2.2 if included.		value pairings stated in Section 4.2.2.2 if included.
	Encoding considerations: This media type is framed (See Section 4.8		Encoding considerations: This media type is framed (See Section 4.8
	in the template document [RFC6838]) and contains binary data.		in the template document [RFC6838]) and contains binary data.
	Security considerations: See Section 9 of [RFCXXXX].		Security considerations: See Section 9 of [RFCXXXX].
	Interoperability considerations: None.		Interoperability considerations: None.
	skipping to change at page 27, line 27 ¶		skipping to change at page 27, line 29 ¶
	o D: indicates the number of rows of the source block that are		o D: indicates the number of rows of the source block that are
	protected by this FEC block and it applies to all the source		protected by this FEC block and it applies to all the source
	SSRCs. D is a positive integer.		SSRCs. D is a positive integer.
	o ToP: indicates the type of protection applied by the sender: 0 for		o ToP: indicates the type of protection applied by the sender: 0 for
	1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC		1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC
	protection, 2 for 2-D parity FEC protection, and 3 for		protection, 2 for 2-D parity FEC protection, and 3 for
	retransmission. There can only be one value listed for ToP. The		retransmission. There can only be one value listed for ToP. The
	absence of the ToP field means that all protection types are		absence of the ToP field means that all protection types are
	allowed.		allowed. An offer that lists more than one ToP value MUST be
			rejected.
	Note that both L and D in the optional parameters should follow the		Note that both L and D in the optional parameters should follow the
	value pairings stated in Section 4.2.2.2 if included.		value pairings stated in Section 4.2.2.2 if included.
	Encoding considerations: This media type is framed (See Section 4.8		Encoding considerations: This media type is framed (See Section 4.8
	in the template document [RFC6838]) and contains binary data.		in the template document [RFC6838]) and contains binary data.
	Security considerations: See Section 9 of [RFCXXXX].		Security considerations: See Section 9 of [RFCXXXX].
	Interoperability considerations: None.		Interoperability considerations: None.
	skipping to change at page 28, line 47 ¶		skipping to change at page 28, line 51 ¶
	o D: indicates the number of rows of the source block that are		o D: indicates the number of rows of the source block that are
	protected by this FEC block and it applies to all the source		protected by this FEC block and it applies to all the source
	SSRCs. D is a positive integer.		SSRCs. D is a positive integer.
	o ToP: indicates the type of protection applied by the sender: 0 for		o ToP: indicates the type of protection applied by the sender: 0 for
	1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC		1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC
	protection, 2 for 2-D parity FEC protection, and 3 for		protection, 2 for 2-D parity FEC protection, and 3 for
	retransmission. There can only be one value listed for ToP. The		retransmission. There can only be one value listed for ToP. The
	absence of the ToP field means that all protection types are		absence of the ToP field means that all protection types are
	allowed.		allowed. An offer that lists more than one ToP value MUST be
			rejected.
	Note that both L and D in the optional parameters should follow the		Note that both L and D in the optional parameters should follow the
	value pairings stated in Section 4.2.2.2 if included.		value pairings stated in Section 4.2.2.2 if included.
	Encoding considerations: This media type is framed (See Section 4.8		Encoding considerations: This media type is framed (See Section 4.8
	in the template document [RFC6838]) and contains binary data.		in the template document [RFC6838]) and contains binary data.
	Security considerations: See Section 9 of [RFCXXXX].		Security considerations: See Section 9 of [RFCXXXX].
	Interoperability considerations: None.		Interoperability considerations: None.
	skipping to change at page 30, line 20 ¶		skipping to change at page 30, line 24 ¶
	o D: indicates the number of rows of the source block that are		o D: indicates the number of rows of the source block that are
	protected by this FEC block and it applies to all the source		protected by this FEC block and it applies to all the source
	SSRCs. D is a positive integer.		SSRCs. D is a positive integer.
	o ToP: indicates the type of protection applied by the sender: 0 for		o ToP: indicates the type of protection applied by the sender: 0 for
	1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC		1-D interleaved FEC protection, 1 for 1-D non-interleaved FEC
	protection, 2 for 2-D parity FEC protection, and 3 for		protection, 2 for 2-D parity FEC protection, and 3 for
	retransmission. There can only be one value listed for ToP. The		retransmission. There can only be one value listed for ToP. The
	absence of the ToP field means that all protection types are		absence of the ToP field means that all protection types are
	allowed.		allowed. An offer that lists more than one ToP value MUST be
			rejected.
	Note that both L and D in the optional parameters should follow the		Note that both L and D in the optional parameters should follow the
	value pairings stated in Section 4.2.2.2 if included.		value pairings stated in Section 4.2.2.2 if included.
	Encoding considerations: This media type is framed (See Section 4.8		Encoding considerations: This media type is framed (See Section 4.8
	in the template document [RFC6838]) and contains binary data.		in the template document [RFC6838]) and contains binary data.
	Security considerations: See Section 9 of [RFCXXXX].		Security considerations: See Section 9 of [RFCXXXX].
	Interoperability considerations: None.		Interoperability considerations: None.
	skipping to change at page 35, line 15 ¶		skipping to change at page 35, line 15 ¶
	Note that the same algorithms are used by the 1-D parity codes,		Note that the same algorithms are used by the 1-D parity codes,
	regardless of whether the FEC protection is applied over a column or		regardless of whether the FEC protection is applied over a column or
	a row. The 2-D parity codes, on the other hand, usually require		a row. The 2-D parity codes, on the other hand, usually require
	multiple iterations of the procedures described here. This iterative		multiple iterations of the procedures described here. This iterative
	decoding algorithm is further explained in Section 6.3.4.		decoding algorithm is further explained in Section 6.3.4.
	6.3.1. Associating the Source and Repair Packets		6.3.1. Associating the Source and Repair Packets
	Before associating source and repair packets, the receiver must know		Before associating source and repair packets, the receiver must know
	in which RTP sessions the source and repair respectively are being		in which RTP sessions the source and repair respectively are being
	sent. After this is established by the reciever the first step is		sent. After this is established by the receiver the first step is
	associating the source and repair packets. This association can be		associating the source and repair packets. This association can be
	via flexible bitmasks, or fixed L and D offsets which can be in the		via flexible bitmasks, or fixed L and D offsets which can be in the
	FEC header or signaled in SDP in optional payload format parameters		FEC header or signaled in SDP in optional payload format parameters
	when L=D=0 in the FEC header.		when L=D=0 in the FEC header.
	6.3.1.1. Using Bitmasks		6.3.1.1. Using Bitmasks
	To use flexible bitmasks, the first two FEC header bits MUST have R=0		To use flexible bitmasks, the first two FEC header bits MUST have R=0
	and F=0. A 15-bit, 46-bit, or 110-bit mask indicates which source		and F=0. A 15-bit, 46-bit, or 110-bit mask indicates which source
	packets are protected by a FEC repair packet. If the bit i in the		packets are protected by a FEC repair packet. If the bit i in the
	mask is set to 1, the source packet number N + i is protected by this		mask is set to 1, the source packet number N + i is protected by this
	FEC repair packet, where N is the sequence number base indicated in		FEC repair packet, where N is the sequence number base indicated in
	the FEC header. The most significant bit of the mask corresponds to		the FEC header. The most significant bit of the mask corresponds to
	i=0. The least signficant bit of the mask corresponds to i=14 in the		i=0. The least significant bit of the mask corresponds to i=14 in
	15-bit mask, i=45 in the 46-bit mask, or i=109 in the 110-bit mask.		the 15-bit mask, i=45 in the 46-bit mask, or i=109 in the 110-bit
			mask.
	The bitmasks are able to represent arbitrary protection patterns, for		The bitmasks are able to represent arbitrary protection patterns, for
	example, 1-D interleaved, 1-D non-interleaved, 2-D.		example, 1-D interleaved, 1-D non-interleaved, 2-D.
	6.3.1.2. Using L and D Offsets		6.3.1.2. Using L and D Offsets
	Denote the set of the source packets associated with repair packet p*		Denote the set of the source packets associated with repair packet p*
	by set T(p*). Note that in a source block whose size is L columns by		by set T(p*). Note that in a source block whose size is L columns by
	D rows, set T includes D source packets plus one repair packet for		D rows, set T includes D source packets plus one repair packet for
	the FEC protection applied over a column, and L source packets plus		the FEC protection applied over a column, and L source packets plus
	skipping to change at page 43, line 14 ¶		skipping to change at page 43, line 14 ¶
	o Clearly identify which SSRC's are associated with each source		o Clearly identify which SSRC's are associated with each source
	block.		block.
	o Clearly identify which repair packets correspond to which source		o Clearly identify which repair packets correspond to which source
	blocks.		blocks.
	o Make use of repair packets to recover source data associated with		o Make use of repair packets to recover source data associated with
	specific SSRC's.		specific SSRC's.
	This section provides several Sesssion Description Protocol (SDP)		This section provides several Session Description Protocol (SDP)
	examples to demonstrate how these requirements can be met.		examples to demonstrate how these requirements can be met.
	7.1. SDP Examples		7.1. SDP Examples
	This section provides two SDP [RFC4566] examples. The examples use		This section provides two SDP [RFC4566] examples. The examples use
	the FEC grouping semantics defined in [RFC5956].		the FEC grouping semantics defined in [RFC5956].
	7.1.1. Example SDP for Flexible FEC Protection with in-band SSRC		7.1.1. Example SDP for Flexible FEC Protection with in-band SSRC
	mapping		mapping
	skipping to change at page 45, line 22 ¶		skipping to change at page 45, line 22 ¶
	networks, FEC repair streams may consume a significant part of the		networks, FEC repair streams may consume a significant part of the
	available bandwidth and consequently may congest the network. In		available bandwidth and consequently may congest the network. In
	such cases, the applications MUST NOT arbitrarily increase the amount		such cases, the applications MUST NOT arbitrarily increase the amount
	of FEC protection since doing so may lead to a congestion collapse.		of FEC protection since doing so may lead to a congestion collapse.
	If desired, stronger FEC protection MAY be applied only after the		If desired, stronger FEC protection MAY be applied only after the
	source rate has been reduced.		source rate has been reduced.
	In a network-friendly implementation, an application should avoid		In a network-friendly implementation, an application should avoid
	sending/receiving FEC repair streams if it knows that sending/		sending/receiving FEC repair streams if it knows that sending/
	receiving those FEC repair streams would not help at all in		receiving those FEC repair streams would not help at all in
	recovering the missing packets. It is RECOMMENDED that the amount		recovering the missing packets. Examples of where FEC would not be
	and type (row, column, or both) of FEC protection is adjusted		beneficial are: (1) if the successful recovery rate as determined by
			RTCP feedback is low (see [RFC5725] and [RFC7509]), and (2) the
			application has a smaller latency requirement than the repair window
			adopted by the FEC configuration based on the expected burst loss
			duration and the target FEC overhead. It is RECOMMENDED that the
			amount and type (row, column, or both) of FEC protection is adjusted
	dynamically based on the packet loss rate and burst loss length		dynamically based on the packet loss rate and burst loss length
	observed by the applications.		observed by the applications.
	In multicast scenarios, it may be difficult to optimize the FEC		In multicast scenarios, it may be difficult to optimize the FEC
	protection per receiver. If there is a large variation among the		protection per receiver. If there is a large variation among the
	levels of FEC protection needed by different receivers, it is		levels of FEC protection needed by different receivers, it is
	RECOMMENDED that the sender offers multiple repair streams with		RECOMMENDED that the sender offers multiple repair streams with
	different levels of FEC protection and the receivers join the		different levels of FEC protection and the receivers join the
	corresponding multicast sessions to receive the repair stream(s) that		corresponding multicast sessions to receive the repair stream(s) that
	is best for them.		is best for them.
	skipping to change at page 46, line 7 ¶		skipping to change at page 46, line 12 ¶
	of the payload. A suitable security mechanism for this RTP payload		of the payload. A suitable security mechanism for this RTP payload
	format should provide confidentiality, integrity protection, and at		format should provide confidentiality, integrity protection, and at
	least source authentication capable of determining if an RTP packet		least source authentication capable of determining if an RTP packet
	is from a member of the RTP session.		is from a member of the RTP session.
	Note that the appropriate mechanism to provide security to RTP and		Note that the appropriate mechanism to provide security to RTP and
	payloads following this memo may vary. It is dependent on the		payloads following this memo may vary. It is dependent on the
	application, transport and signaling protocol employed. Therefore, a		application, transport and signaling protocol employed. Therefore, a
	single mechanism is not sufficient, although if suitable, using the		single mechanism is not sufficient, although if suitable, using the
	Secure Real-time Transport Protocol (SRTP) [RFC3711] is recommended.		Secure Real-time Transport Protocol (SRTP) [RFC3711] is recommended.
	Other mechanisms that may be used are IPsec [RFC4301] and Transport		Other mechanisms that may be used are IPsec [RFC4301] and Datagram
	Layer Security (TLS, see [RFC8446]) (RTP over TCP); other		Transport Layer Security (DTLS, see [RFC6347]) (RTP over UDP); other
	alternatives may exist.		alternatives may exist.
	Given that FLEX FEC enables the protection of multiple source		Given that FLEX FEC enables the protection of multiple source
	streams, there exists the possibility that multiple source buffers		streams, there exists the possibility that multiple source buffers
	may be created that may not be used. An attacker could leverage		may be created that may not be used. An attacker could leverage
	unused source buffers to as a means of occupying memory in a FLEX FEC		unused source buffers to as a means of occupying memory in a FLEX FEC
	endpoint. Moreover the application source data may not be perfectly		endpoint. Moreover the application source data may not be perfectly
	matched with FLEX FEC source partitioning. If this is the case,		matched with FLEX FEC source partitioning. If this is the case,
	there is a possibility for unprotected source data if, for instance,		there is a possibility for unprotected source data if, for instance,
	the FLEX FEC implementation discards data that does not fit perfectly		the FLEX FEC implementation discards data that does not fit perfectly
	into its source processing requirements.		into its source processing requirements.
	10. IANA Considerations		10. IANA Considerations
	New media subtypes are subject to IANA registration. For the		New media subtypes are subject to IANA registration. For the
	registration of the payload formats and their parameters introduced		registration of the payload formats and their parameters introduced
	in this document, refer to Section 5.		in this document, refer to Section 5.1.
	11. Acknowledgments		11. Acknowledgments
	Some parts of this document are borrowed from [RFC5109]. Thus, the		Some parts of this document are borrowed from [RFC5109]. Thus, the
	author would like to thank the editor of [RFC5109] and those who		author would like to thank the editor of [RFC5109] and those who
	contributed to [RFC5109].		contributed to [RFC5109].
	Thanks to Stephen Botzko , Bernard Aboba , Rasmus Brandt , Brian		Thanks to Stephen Botzko , Bernard Aboba , Rasmus Brandt , Brian
	Baldino , Roni Even , Stefan Holmer , Jonathan Lennox , and Magnus		Baldino , Roni Even , Stefan Holmer , Jonathan Lennox , and Magnus
	Westerlund for providing valuable feedback on earlier versions of		Westerlund for providing valuable feedback on earlier versions of
	skipping to change at page 48, line 38 ¶		skipping to change at page 48, line 45 ¶
	[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,		[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
	"Extended RTP Profile for Real-time Transport Control		"Extended RTP Profile for Real-time Transport Control
	Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,		Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
	DOI 10.17487/RFC4585, July 2006,		DOI 10.17487/RFC4585, July 2006,
	<https://www.rfc-editor.org/info/rfc4585>.		<https://www.rfc-editor.org/info/rfc4585>.
	[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error		[RFC5109] Li, A., Ed., "RTP Payload Format for Generic Forward Error
	Correction", RFC 5109, DOI 10.17487/RFC5109, December		Correction", RFC 5109, DOI 10.17487/RFC5109, December
	2007, <https://www.rfc-editor.org/info/rfc5109>.		2007, <https://www.rfc-editor.org/info/rfc5109>.
			[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
			Report Block Type for RTP Control Protocol (RTCP) Extended
			Reports (XRs)", RFC 5725, DOI 10.17487/RFC5725, February
			2010, <https://www.rfc-editor.org/info/rfc5725>.
			[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
			Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
			January 2012, <https://www.rfc-editor.org/info/rfc6347>.
			[RFC7509] Huang, R. and V. Singh, "RTP Control Protocol (RTCP)
			Extended Report (XR) for Post-Repair Loss Count Metrics",
			RFC 7509, DOI 10.17487/RFC7509, May 2015,
			<https://www.rfc-editor.org/info/rfc7509>.
	[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and		[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
	B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms		B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
	for Real-Time Transport Protocol (RTP) Sources", RFC 7656,		for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
	DOI 10.17487/RFC7656, November 2015,		DOI 10.17487/RFC7656, November 2015,
	<https://www.rfc-editor.org/info/rfc7656>.		<https://www.rfc-editor.org/info/rfc7656>.
	[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,		[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
	and M. Stiemerling, Ed., "Real-Time Streaming Protocol		and M. Stiemerling, Ed., "Real-Time Streaming Protocol
	Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December		Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
	2016, <https://www.rfc-editor.org/info/rfc7826>.		2016, <https://www.rfc-editor.org/info/rfc7826>.
	[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
	Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
	<https://www.rfc-editor.org/info/rfc8446>.
	[SMPTE2022-1]		[SMPTE2022-1]
	SMPTE 2022-1-2007, "Forward Error Correction for Real-Time		SMPTE 2022-1-2007, "Forward Error Correction for Real-Time
	Video/Audio Transport over IP Networks", 2007.		Video/Audio Transport over IP Networks", 2007.
	Authors' Addresses		Authors' Addresses
	Mo Zanaty		Mo Zanaty
	Cisco		Cisco
	Raleigh, NC		Raleigh, NC
	USA		USA
End of changes. 23 change blocks.
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