wdiff rfc7005.original rfc7005.txt

Audio/Video Transport Working Group
Internet Engineering Task Force (IETF) A. Clark
Internet-Draft
Request for Comments: 7005 Telchemy
Intended status:
Category: Standards Track V. Singh
Expires: December 30, 2013
ISSN: 2070-1721 Aalto University
Q. Wu
Huawei
June 28,
September 2013

RTP Control Protocol (RTCP) Extended Report (XR) Block
for De-Jitter Buffer Metric Reporting
draft-ietf-xrblock-rtcp-xr-jb-14.txt

Abstract

This document defines an RTP Control Protocol (RTCP) Extended Report
(XR) Block block that allows the reporting of De-Jitter Buffer de-jitter buffer metrics for
a range of RTP applications.

Status of this This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on December 30, 2013.
http://www.rfc-editor.org/info/rfc7005.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. De-Jitter Buffer Metrics Block . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Extended Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . . . 4
3. De-Jitter Buffer Operation . . . . . . . . . . . . . . . . . . 5 4
3.1. Idealized De-Jitter Buffer . . . . . . . . . . . . . . . . 5 4
3.2. Fixed De-Jitter Buffer . . . . . . . . . . . . . . . . . . 6 5
3.3. Adaptive De-Jitter Buffer . . . . . . . . . . . . . . . . 6 5
4. De-Jitter Buffer Metrics Block . . . . . . . . . . . . . . . . 7 6
4.1. Report Block Structure . . . . . . . . . . . . . . . . . . 7 6
4.2. Definition of Fields in De-Jitter Buffer Metrics Block . . 7 6
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11 9
5.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 11 9
5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 11 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9
6.1. New RTCP XR Block Type value Value . . . . . . . . . . . . . . . 12 9
6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 12 10
6.3. Contact information Information for registrations Registrations . . . . . . . . . . 12 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 10
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 16 11
Appendix A. Metrics represented using RFC6390 Represented Using the Template from
RFC 6390 . . . . . 17
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 20
B.1. draft-ietf-xrblock-rtcp-xr-jb-12 . . . . . . . . . . . . . 20
B.2. draft-ietf-xrblock-rtcp-xr-jb-11 . . . . . . . . . . . . . 20
B.3. draft-ietf-xrblock-rtcp-xr-jb-10 . . . . . . . . . . . . . 20
B.4. draft-ietf-xrblock-rtcp-xr-jb-09 . . . . . . . . . . . . . 20
B.5. draft-ietf-xrblock-rtcp-xr-jb-08 . . . . . . . . . . . . . 20
B.6. draft-ietf-xrblock-rtcp-xr-jb-07 . . . . . . . . . . . . . 20
B.7. draft-ietf-xrblock-rtcp-xr-jb-05 . . . . . . . . . . . . . 21
B.8. draft-ietf-xrblock-rtcp-xr-jb-03 . . . . . . . . . . . . . 21
B.9. draft-ietf-xrblock-rtcp-xr-jb-02 . . . . . . . . . . . . . 21
B.10. draft-ietf-xrblock-rtcp-xr-jb-01 . . . . . . . . . . . . . 21
B.11. draft-ietf-xrblock-rtcp-xr-jb-00 . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 12

1. Introduction

1.1. De-Jitter Buffer Metrics Block

This document defines a new block type to augment those defined in
[RFC3611],
[RFC3611] for use in a range of RTP applications.

The new block type provides information on jitter de-jitter buffer
configuration and performance.

The metric belongs to the class of transport-related end system end-system
metrics defined in [RFC6792].

Instances of this metrics block refer by Synchronization synchronization source
(SSRC) to the separate auxiliary Measurement Information block
[RFC6776] Block
[RFC6776], which contains information such as the SSRC of the
measured stream, and RTP sequence numbers and time intervals
indicating the span of the report.

1.2. RTCP and RTCP XR Extended Reports

The use of RTCP for reporting is defined in [RFC3550]. [RFC3611]
defines an extensible structure for reporting using an RTCP Extended
Report (XR). This document defines a new Extended Report block for
use with [RFC3550] and [RFC3611].

1.3. Performance Metrics Framework

The

"Guidelines for Considering New Performance Metrics Framework Metric Development"
[RFC6390] provides guidance on the definition and specification of
performance metrics. The "Guidelines for Use of the RTP Monitoring Architectures
Framework" [RFC6792] provides guideline for guidance on the reporting block format
using RTCP XR. Metrics described in this draft document are in accordance
with the guidelines in [RFC6390]and [RFC6792].

1.4. Applicability

Real-time applications employ a de-jitter buffer [RFC5481] to absorb
jitter introduced on the path from source to destination. These
metrics are used to report how the de-jitter buffer at the receiving
end of the RTP stream behaves as a result of jitter in the network; and
they are applicable to a range of RTP applications.

These metrics are corresponding correspond to terminal related terminal-related factors that affect
real-time application quality and are useful to provide for providing a better
end-user quality of experience (QoE) when these terminal-related
factors are used as inputs to calculate QoE metrics [QMB].

2. Terminology

2.1. Standards Language

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].

3. De-Jitter Buffer Operation

A de-jitter buffer is required to absorb delay variation in the
network delivery of media packets. A de-jitter buffer works by
holding media data for a period of time after it is received and
before it is played out. Packets that arrive early are held in the
de-jitter buffer longer. If packets arrive too early early, they may be
discarded if there is no available de-jitter buffer space. If
packets are delayed excessively by the network network, they may be discarded
if they miss their playout time.

The de-jitter buffer can be considered as a time window with the early
edge aligned with the delay corresponding to the earliest arriving
packet and the late edge representing the maximum permissible delay
before a late arriving packet would be discarded. The delay applied
to packets that arrive on time or at their expected arrival time is
known as the Nominal Delay nominal delay, and this is equivalent to the time
difference/ buffer
difference/buffer size difference between the on-time packets insertion point of the
on-time packets and the point at which the packets are read out.

The reference for the expected arrival time may, may be, for example, be the
first packet in the session or the running average delay. If all
packets arrived at their expected arrival time, then every packet
would be held in the de-jitter buffer exactly the Nominal Delay. nominal delay.

The de-jitter buffer maximum delay is the delay that is applied to an
the earliest arriving packet that is not discarded and corresponds to
the early edge of the de-jitter buffer time window.

3.1. Idealized De-Jitter Buffer

In practice practice, de-jitter buffer implementations vary considerably
however considerably;
however, they should behave in a manner conceptually consistent with
an idealized de-jitter buffer buffer, which is described as follows:

(i).

(i) Receive the first packet and delay playout by D ms. Keep the
RTP timestamp (TS) and receive time as a reference.

RTP Timestamp(TS)[1] TS[1]

receive time[1]

Assume that both are normalized in ticks (there are 10 000 10,000
ticks in a millisecond).

(ii).

(ii) Receive the next packet
(iii). packet.

(iii) Calculate r = RTP TS[n] - RTP TS[1] and t = receive time[n] -
receive time[1]. If r == t t, then the packet arrived on time.
If r < t t, then the packet arrived late late, and if r > t t, then the
packet arrived early.

(iv).

(iv) Delay playout of packet by D + (r-t)

(v). (r-t).

(v) Go back to (ii) (ii).

Note that this idealized implementation assumes that the sender's RTP
clock is synchronized to the clock in the receiver receiver, which is used to
timestamp packet arrivals. If there is no such inherent
synchronization, the system may need to use an adaptive de-jitter
buffer or other techniques to ensure reliable reception.

3.2. Fixed De-Jitter Buffer

A fixed de-jitter buffer lacks provision to track network the condition of
the network and has a fixed size size, and packets leaving the de-jitter
buffer have a constant delay. For fixed de-jitter buffer
implementation, the nominal delay is set to a constant value
corresponding to the packets that arrive at their expected arrival time
time, while the maximum delay is set to a constant value
corresponding to the fixed size of the de-
jitter de-jitter buffer.

3.3. Adaptive De-Jitter Buffer

An adaptive de-jitter buffer can adapt to the change in the network's
delay and has variable size or variable delay. It allows the nominal
delay to be set to a low value initially, initially to minimize user perceived
delay, however
delay; however, it can automatically extend the late edge (and
possibly also retract the early edge) of a buffer window if a
significant proportion of the packets are arriving late (and hence
being discarded).

4. De-Jitter Buffer Metrics Block

This block describes the configuration and operating parameters of
the de-jitter buffer in the receiver of the RTP end system or RTP
mixer which that sends the report. Instances of this metrics block refer
by use the
SSRC to refer to the separate auxiliary Measurement Information Block
[RFC6776]
[RFC6776], which describes the measurement interval periods in use. use (see
[RFC6776], Section 4.2). This metrics block relies on the
measurement interval in the Measurement Information Block indicating
the span of the report and MUST be sent in the same compound RTCP
packet as the Measurement Information Block. If the measurement
interval is not received in the same compound RTCP packet as this
metrics block, this metrics block MUST be discarded.

4.1. Report Block Structure

De-Jitter Buffer (DJB) Metrics Block

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=DJB BT=23 | I |C| Rsvd. resv | block length=3 Block Length=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DJB nominal | DJB maximum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DJB high water high-water mark | DJB low water low-water mark |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Report Block Structure

4.2. Definition of Fields in De-Jitter Buffer Metrics Block

Block type Type (BT): 8 bits

A de-jitter buffer De-Jitter Buffer Metrics Report Block is identified by the
constant DJB.

[Note to RFC Editor: please replace DJB with the IANA provided
RTCP XR block type for this block.] 23.

Interval Metric flag (I): 2 bits

This field is used to indicate whether the de-jitter buffer
metrics are Sampled, Interval Interval, or Cumulative metrics:

I=01: Sampled Value - the reported value is a sampled
instantaneous value.

I=10: Interval Duration - the reported value applies to the
most recent measurement interval duration between successive
metrics reports.

I=11: Cumulative Duration - the reported value applies to the
accumulation period characteristic of cumulative measurements.

In this document, de-jitter buffer Metrics metrics can only be sampled , and
cannot be measured over definite intervals. Also, the value I=00
is reserved for future use. Senders MUST NOT use the values
I=00 or I=10 I=00,
I=10, or I=11. If a block is received with I=00 or I=10 I=00, I=10, or I=11,
the receiver MUST discard the block.

Jitter Buffer Configuration (C): 1 bit

This field is used to identify the de-jitter buffer method in use
at the receiver, according to the following code:

0 = Fixed de-jitter buffer

1 = Adaptive de-jitter buffer

Reserved (Rsvd.): (resv): 5 bits

These bits are reserved. They MUST be set to zero by senders and
ignored by receivers (See [RFC6709] section 4.2). (see [RFC6709], Section 4.2).

Block Length: 16 bits

The length of this report block in 32-bit words, minus one, in
accordance with the definition in [RFC3611]. This field MUST be
set to 3 to match the fixed length of the report block.

de-jitter

SSRC of Source: 32 bits

As defined in Section 4.1 of [RFC3611].

De-jitter buffer nominal delay (DJB nominal): 16 bits

This is the current nominal de-jitter buffer delay in
milliseconds, which (in
milliseconds) that corresponds to the nominal de-jitter buffer
delay for packets that arrive exactly on time. It is calculated
based on the time spent in the de-jitter buffer for the packet
that arrives exactly on time. This parameter MUST be provided for
both fixed and adaptive de-jitter buffer implementations.

The measured value is an unsigned value. If the measured value
exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
over-range measurement. If the measurement is unavailable, the
value 0xFFFF MUST be reported.

de-jitter

De-jitter buffer maximum delay (DJB maximum): 16 bits

This is the current maximum de-jitter buffer delay in milliseconds
which (in
milliseconds) that corresponds to the earliest arriving packet
that would not be discarded. It is calculated based on the time
spent in the de-
jitter de-jitter buffer for the earliest arriving packet packet.
In simple queue
implementations implementations, this may correspond to the size
of the de-jitter buffer. In adaptive de-jitter buffer
implementations, this value may vary dynamically. This parameter
MUST be provided for both fixed and adaptive de-jitter buffer
implementations.

de-jitter

De-jitter buffer high water high-water mark (DJB high water high-water mark): 16 bits

This is the highest value of the de-jitter buffer nominal delay in
milliseconds which
(in milliseconds) that occurred at any time during the reporting
interval. This parameter MUST be provided for adaptive de-jitter
buffer implementations implementations, and its value MUST be set to JB DJB maximum
for fixed de-jitter buffer implementations.

de-jitter

De-jitter buffer low water low-water mark (DJB low water low-water mark): 16 bits

This is the lowest value of the de-jitter buffer nominal delay in
milliseconds which (in
milliseconds) that occurred at any time during the reporting
interval. This parameter MUST be provided for adaptive de-jitter
buffer implementations implementations, and its value MUST be set to JB DJB maximum
for fixed de-jitter buffer implementations.

5. SDP Signaling

[RFC3611] defines the use of SDP (Session the Session Description Protocol) Protocol (SDP)
[RFC4566] for signaling the use of XR blocks. However However, XR blocks MAY
be used without prior signaling (see section Section 5 of RFC3611). RFC 3611).

5.1. SDP rtcp-xr-attrib Attribute Extension

This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
in [RFC3611] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document.

xr-format =/ xr-djb-block

xr-djb-block = "de-jitter-buffer"

5.2. Offer/Answer Usage

When SDP is used in offer-answer Offer/Answer context [RFC3264], the SDP Offer/
Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute
parameters applies. For detailed usage of Offer/Answer for
unilateral parameter, parameters, refer to section Section 5.2 of [RFC3611].

6. IANA Considerations

New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
[RFC3611].

6.1. New RTCP XR Block Type value Value

This document assigns the block type value DJB 23 in the IANA "RTP
Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
the "De-Jitter Buffer Metrics Block".

[Note to RFC Editor: please replace DJB with the IANA provided RTCP
XR block type for this block.]

6.2. New RTCP XR SDP Parameter

This document also registers a new parameter "de-jitter-buffer" in
the "RTP Control Protocol Extended Reports (RTCP XR) Session
Description Protocol (SDP) Parameters Registry".

6.3. Contact information Information for registrations Registrations

The contact information for the registrations is:

Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China

7. Security Considerations

It is believed that this proposed RTCP XR report block introduces no new security
considerations beyond those described in [RFC3611]. This block does
not provide per-packet statistics statistics, so the risk to confidentiality
documented in Section 7, paragraph 3 of [RFC3611] does not apply.

8. Contributors

Geoff Hunt wrote the initial draft of this document.

9. Acknowledgments

The authors gratefully acknowledge reviews and feedback provided by
Bruce Adams, Philip Arden, Amit Arora, Claire Bi, Bob Biskner, Benoit
Claise, Kevin Connor, Claus Dahm, Spencer Dawkins, Randy Ethier, Roni
Even, Jim Frauenthal, Kevin Gross, Albert Higashi, Tom Hock, Shane
Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Mohamed Mostafa, Amy
Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Dan Romascanu,
Albrecht Schwarz, Tom Taylor, Hideaki Yamada,Claire Bi,Colin
Perkin, Dan Romascanu, Kevin Gross ,Glen Zorn, Spencer Dawkins Yamada, and
Benoit Claise. Glen Zorn.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with the Session Description Protocol (SDP)", RFC 3264,
June 2002.

[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.

[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003.

[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.

[RFC6776] Clark, A. and Q. Wu, Q., "Measurement Identity and information Information
Reporting
using SDES item Using a Source Description (SDES) Item and XR an
RTCP Extended Report (XR) Block", RFC 6776, August October 2012.

10.2. Informative References

[QMB] Clark, A., "RTP Control Protocol (RTCP) Extended Report
(XR) Blocks for QoE Metric Reporting",
ID draft-ietf-xrblock-rtcp-xr-qoe-08, Work in Progress,
May 2013.

[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, March 2009.

[RFC6390] Clark, A. and B. Claise, "Framework "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.

[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
September 2012.

[RFC6792] Hunt, G., Wu, Q., Hunt, G., and P. Arden, "Monitoring Architectures "Guidelines for RTP", Use of the
RTP Monitoring Framework", RFC 6792, November 2012.

Appendix A. Metrics represented using RFC6390 Template

RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by Represented Using the new Template from RFC
number, when assigned. 6390

a. de-jitter buffer nominal delay De-Jitter Buffer Nominal Delay Metric

* Metric Name: de-jitter De-jitter buffer nominal delay in RTP

* Metric Description: The "expected arrival time" is the time
that a an RTP packet would arrive if there was no delay
variation. The delay applied to packets that arrive at their
expected time is known as the Nominal Delay.

* Method of Measurement or Calculation: See section Section 4.2, de-
jitter
de-jitter buffer nominal delay definition [RFCXXXX]. definition.

* Units of Measurement: See section Section 4.2, de-jitter buffer
nominal delay definition [RFCXXXX]. definition.

* Measurement Point(s) with Potential Measurement Domain: See
section 4, 1st paragraph [RFCXXXX].
Section 4.

* Measurement Timing: See section 4, 1st paragraph [RFCXXXX] Section 4 for measurement timing and section
Section 4.2 paragraph [RFCXXXX] for Interval Metric flag.

* Use and applications: Applications: See section 1.4 [RFCXXXX]. Section 1.4.

* Reporting model: Model: See RFC3611. RFC 3611.

b. de-jitter buffer maximum delay De-Jitter Buffer Maximum Delay Metric

* Metric Name: de-jitter De-jitter buffer maximum delay in RTP RTP.

* Metric Description: It is the current maximum de-jitter buffer
delay for RTP traffic which that corresponds to the earliest
arriving packet that would not be discarded.

* Method of Measurement or Calculation: See section Section 4.2, de-
jitter
de-jitter buffer maximum delay definition and section Section 3, the
last
paragraph [RFCXXXX]. paragraph.

* Units of Measurement: See section Section 4.2, de-jitter buffer
maximum delay definition [RFCXXXX]. definition.

* Measurement Point(s) with Potential Measurement Domain: See
section 4, 1st paragraph [RFCXXXX].
Section 4.

* Measurement Timing: See section 4, 1st paragraph [RFCXXXX] Section 4 for measurement timing and section
Section 4.2 paragraph [RFCXXXX] for Interval Metric flag.

* Use and applications: Applications: See section 1.4 [RFCXXXX]. Section 1.4.

* Reporting model: Model: See RFC3611. RFC 3611.

c. de-jitter buffer high water mark De-Jitter Buffer High-Water Mark Metric

* Metric Name: de-jitter De-jitter buffer high water high-water mark in RTP RTP.

* Metric Description: It is the highest value of the de-jitter
buffer nominal delay for RTP traffic which occurred at any
time during the reporting interval.

* Method of Measurement or Calculation: See section Section 4.2, de-
jitter
de-jitter buffer high water high-water mark definition [RFCXXXX]. definition.

* Units of Measurement: See section Section 4.2, de-jitter buffer
nominal delay definition [RFCXXXX]. definition.

* Measurement Point(s) with Potential Measurement Domain: See
section 4, 1st paragraph [RFCXXXX].
Section 4.

* Measurement Timing: See section 4, 1st paragraph [RFCXXXX] Section 4 for measurement timing and section
Section 4.2 paragraph [RFCXXXX] for Interval Metric flag.

* Use and applications: Applications: See section 1.4 [RFCXXXX]. Section 1.4.

* Reporting model: Model: See RFC3611. RFC 3611.

d. de-jitter buffer low water mark De-Jitter Buffer Low-Water Mark Metric

* Metric Name: de-jitter De-jitter buffer low water low-water mark in RTP RTP.

* Metric Description: It is the lowest value of the de-jitter
buffer nominal delay for (for RTP traffic which traffic) that occurred at any
time during the reporting interval.

* Method of Measurement or Calculation: See section Section 4.2, de-
jitter
de-jitter buffer low water low-water mark definition [RFCXXXX]. definition.

* Units of Measurement: See section Section 4.2, de-jitter buffer low
water mark definition [RFCXXXX]. definition.

* Measurement Point(s) with Potential Measurement Domain: See
section
Section 4, 1st paragraph [RFCXXXX]. paragraph.

* Measurement Timing: See section 4, 1st paragraph [RFCXXXX] Section 4 for measurement timing and section
Section 4.2 paragraph [RFCXXXX] for Interval Metric flag.

* Use and applications: Applications: See section 1.4 [RFCXXXX]. Section 1.4.

* Reporting model: Model: See RFC3611.

Appendix B. Change Log

Note to the RFC-Editor: please remove this section prior to
publication as an RFC.

B.1. draft-ietf-xrblock-rtcp-xr-jb-12