< draft-mizrahi-ippm-compact-alternate-marking-04.txt   draft-mizrahi-ippm-compact-alternate-marking-05.txt >
Network Working Group T. Mizrahi Network Working Group T. Mizrahi
Internet-Draft Huawei Network.IO Innovation Lab Internet-Draft Huawei Network.IO Innovation Lab
Intended status: Informational C. Arad Intended status: Informational C. Arad
Expires: October 16, 2019 Expires: January 7, 2020
G. Fioccola G. Fioccola
Huawei Technologies Huawei Technologies
M. Cociglio M. Cociglio
Telecom Italia Telecom Italia
M. Chen M. Chen
L. Zheng L. Zheng
Huawei Technologies Huawei Technologies
G. Mirsky G. Mirsky
ZTE Corp. ZTE Corp.
April 14, 2019 July 6, 2019
Compact Alternate Marking Methods for Passive and Hybrid Performance Compact Alternate Marking Methods for Passive and Hybrid Performance
Monitoring Monitoring
draft-mizrahi-ippm-compact-alternate-marking-04 draft-mizrahi-ippm-compact-alternate-marking-05
Abstract Abstract
This memo introduces new alternate marking methods that require a This memo introduces new alternate marking methods that require a
compact overhead of either a single bit per packet, or zero bits per compact overhead of either a single bit per packet, or zero bits per
packet. This memo also presents a summary of alternate marking packet. This memo also presents a summary of alternate marking
methods, and discusses the tradeoffs among them. The target audience methods, and discusses the tradeoffs among them. The target audience
of this document is network protocol designers; this document is of this document is network protocol designers; this document is
intended to help protocol designers choose the best alternate marking intended to help protocol designers choose the best alternate marking
method(s) based on the protocol's constraints and requirements. method(s) based on the protocol's constraints and requirements.
skipping to change at page 1, line 47 skipping to change at page 1, line 47
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 October 16, 2019. This Internet-Draft will expire on January 7, 2020.
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
skipping to change at page 2, line 35 skipping to change at page 2, line 35
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5
3. Marking Abstractions . . . . . . . . . . . . . . . . . . . . 5 3. Marking Abstractions . . . . . . . . . . . . . . . . . . . . 5
4. Double Marking . . . . . . . . . . . . . . . . . . . . . . . 7 4. Double Marking . . . . . . . . . . . . . . . . . . . . . . . 7
5. Single-bit Marking . . . . . . . . . . . . . . . . . . . . . 8 5. Single-bit Marking . . . . . . . . . . . . . . . . . . . . . 8
5.1. Single Marking Using the First Packet . . . . . . . . . . 8 5.1. Single Marking Using the First Packet . . . . . . . . . . 8
5.2. Single Marking using the Mean Delay . . . . . . . . . . . 8 5.2. Single Marking using the Mean Delay . . . . . . . . . . . 8
5.3. Single Marking using a Multiplexed Marking Bit . . . . . 8 5.3. Single Marking using a Multiplexed Marking Bit . . . . . 8
5.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . 8 5.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . 8
5.3.2. Timing and Synchronization Aspects . . . . . . . . . 9 5.4. Pulse Marking . . . . . . . . . . . . . . . . . . . . . . 9
5.4. Pulse Marking . . . . . . . . . . . . . . . . . . . . . . 11 6. Zero Marking Hashed . . . . . . . . . . . . . . . . . . . . . 10
6. Zero Marking Hashed . . . . . . . . . . . . . . . . . . . . . 12 6.1. Hash-based Sampling . . . . . . . . . . . . . . . . . . . 10
6.1. Hash-based Sampling . . . . . . . . . . . . . . . . . . . 12 6.1.1. Hashed Pulse Marking . . . . . . . . . . . . . . . . 11
6.1.1. Hashed Pulse Marking . . . . . . . . . . . . . . . . 13 6.1.2. Hashed Step Marking . . . . . . . . . . . . . . . . . 11
6.1.2. Hashed Step Marking . . . . . . . . . . . . . . . . . 13 7. Single Marking Hashed . . . . . . . . . . . . . . . . . . . . 11
7. Single Marking Hashed . . . . . . . . . . . . . . . . . . . . 13 8. Timing and Synchronization Aspects . . . . . . . . . . . . . 12
8. Summary of Marking Methods . . . . . . . . . . . . . . . . . 14 8.1. Synchronization Aspects in Multiplexed Marking . . . . . 13
9. Alternate Marking using Reserved Values . . . . . . . . . . . 19 9. Multipoint Marking Methods . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 10. Summary of Marking Methods . . . . . . . . . . . . . . . . . 15
11. Security Considerations . . . . . . . . . . . . . . . . . . . 20 11. Alternate Marking using Reserved Values . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . 20 13. Security Considerations . . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . 20 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
14.1. Normative References . . . . . . . . . . . . . . . . . . 20
14.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
1.1. Background 1.1. Background
Alternate marking, defined in [RFC8321], is a method for measuring Alternate marking, defined in [RFC8321], is a method for measuring
packet loss, packet delay, and packet delay variation. Typical delay packet loss, packet delay, and packet delay variation. Typical delay
measurement protocols require the two measurement points (MPs) to measurement protocols require the two measurement points (MPs) to
exchange timestamped test packets. In contrast, the alternate exchange timestamped test packets. In contrast, the alternate
marking method does not require control packets to be exchanged. marking method does not require control packets to be exchanged.
Instead, every data packet carries a color indicator, which divides Instead, every data packet carries a marking bit, which is used for
the traffic into consecutive blocks of packets. triggering measurement events. Note that the frequency of these
measurement events is dependent on the users' application(s) and the
node characteristics.
The color value is toggled periodically, as illustrated in Figure 1. The marking bit can be used as a color indication, as defined in
[RFC8321], which is toggled periodically. This approach is
illustrated in Figure 1.
A: packet with color 0 A: packet with color 0
B: packet with color 1 B: packet with color 1
Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
Time ----------------------------------------------------------> Time ---------------------------------------------------------->
| | | | | | | | | |
| Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ...
| | | | | | | | | |
Color 0000000000 1111111111 0000000000 1111111111 0000000000 Color 0000000000 1111111111 0000000000 1111111111 0000000000
skipping to change at page 9, line 31 skipping to change at page 9, line 31
Color 0000000000 1111111111 0000000000 1111111111 0000000000 Color 0000000000 1111111111 0000000000 1111111111 0000000000
^ ^ ^ ^ ^ ^ ^ ^ ^ ^
Packets | | | | | Packets | | | | |
marked for | | | | | marked for | | | | |
timestamping | | | | | timestamping | | | | |
v v v v v v v v v v
Muxed bit 0000100000 1111011111 0000100000 1111101111 0001000000 Muxed bit 0000100000 1111011111 0000100000 1111101111 0001000000
Figure 6: Alternate marking with multiplexed bit. Figure 6: Alternate marking with multiplexed bit.
5.3.2. Timing and Synchronization Aspects
It is assumed that all MPs are synchronized to a common reference
time with an accuracy of +/- A/2. Thus, the difference between the
clock values of any two MPs is bounded by A. Clocks can be
synchronized for example using NTP [RFC5905], PTP [IEEE1588], or by
other means. The common reference time is used for dividing the time
domain into equal-sized measurement periods, such that all packets
forwarded during a measurement period have the same color, and
consecutive periods have alternating colors.
The single marking bit incorporates two multiplexed values. From the
monitoring MP's perspective, the two values are Time-Division
Multiplexed (TDM), as depicted in Figure 7. It is assumed that the
start time of every measurement period is known to both the
initiating MP and the monitoring MP. If the measurement period is L,
then during the first and the last L/4 time units of each block the
marking bit is interpreted by the monitoring MP as a color indicator.
During the middle part of the block, the marking bit is interpreted
as a timestamp indicator; if the value of this bit is different than
the color value, the corresponding packet is used as a reference for
delay measurement.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========><==================><========>|<========>
L/4 L/4 L/2 L/4 L/4
<===================><==================><===================>
Detect color Detect timestamping Detect color
change indication change
Figure 7: Multiplexed marking field interpretation at the receiving
measurement point.
In order to prevent ambiguity in the receiver's interpretation of the
marking field, the initiating MP is permitted to set the timestamp
indication only during a specific interval, as depicted in Figure 8.
Since the receiver is willing to receive the timestamp indication
during the middle L/2 time units of the block, the sender refrains
from sending the timestamp indication during a guardband interval of
d time units at the beginning and end of the L/2-period.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========>|<================>|<========>|
L/4 L/4 | L/2 | L/4
<=>|<=> <=>|<=>
d d d d
<==========>
permissible
timestamping
indication
interval
Figure 8: A time domain view.
The guardband d is given by d = A + D_max - D_min, where A is the
clock accuracy, D_max is an upper bound on the network delay between
the MPs, and D_min is a lower bound on the delay. It is
straightforward from Figure 8 that d < L/4 must be satisfied. The
latter implies a minimal requirement on the synchronization accuracy.
All MPs must be synchronized to the same reference time with an
accuracy of +/- L/8. Depending on the system topology, in some
systems the accuracy requirement will be even more stringent, subject
to d < L/4. Note that the accuracy requirement of the conventional
alternate marking method [RFC8321] is +/- L/2, while the multiplexed
marking method requires an accuracy of +/- L/8.
Note that we assume that the middle L/2-period is designated as the
timestamp indication period, allowing a sufficiently long guardband
between the transitions. However, a system may be configured to use
a longer timestamp indication period or a shorter one, if it is
guaranteed that the synchronization accuracy meets the guardband
requirements (i.e., the constraints on d).
5.4. Pulse Marking 5.4. Pulse Marking
Pulse marking uses a single marking bit that is used as a trigger for Pulse marking uses a single marking bit that is used as a trigger for
both LM and DM. In this method the two MPs maintain a single per- both LM and DM. In this method the two MPs maintain a single per-
flow counter for LM, in contrast to the color-based methods which flow counter for LM, in contrast to the color-based methods which
require two counters per flow. In each block one of the packets is require two counters per flow. In each block one of the packets is
marked. The marked packet triggers two actions in each of MPs: marked. The marked packet triggers two actions in each of MPs:
o The timestamp is captured for DM. o The timestamp is captured for DM.
o The value of the counter is captured for LM. o The value of the counter is captured for LM.
In each period, each of the MPs exports the timestamp and counter- In each period, each of the MPs exports the timestamp and counter-
stamp to the management system, which can then compute the loss and stamp to the management system, which can then compute the loss and
delay in that period. It should be noted that as in [RFC8321], if delay in that period. It should be noted that as in [RFC8321], if
the length of the measurement period is L time units, then all the length of the measurement period is L time units, then all
network devices must be synchronized to the same clock reference with network devices must be synchronized to the same clock reference with
an accuracy of +/- L/2 time units. an accuracy of +/- L/2 time units.
The pulse marking approach is illustrated in Figure 9. Since both LM The pulse marking approach is illustrated in Figure 7. Since both LM
and DM use a pulse-based trigger, if the marked packet is lost then and DM use a pulse-based trigger, if the marked packet is lost then
no measurement is available in this period. Moreover, the LM no measurement is available in this period. Moreover, the LM
accuracy may be affected by out-of-order delivery. accuracy may be affected by out-of-order delivery.
P: packet - all packets have the same color P: packet - all packets have the same color
Packets PPPPPPPPPP PPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP Packets PPPPPPPPPP PPPPPPPPP PPPPPPPPPP PPPPPPPPPP PPPPPPPPPP
Time ----------------------------------------------------------> Time ---------------------------------------------------------->
| | | | | | | | | |
| Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ... | Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ...
| | | | | | | | | |
^ ^ ^ ^ ^ ^ ^ ^ ^ ^
Packets | | | | | Packets | | | | |
marked for | | | | | marked for | | | | |
DM and LM | | | | | DM and LM | | | | |
v v v v v v v v v v
Marking bit 0000100000 0000100000 0000100000 0000010000 0001000000 Marking bit 0000100000 0000100000 0000100000 0000010000 0001000000
Figure 9: Pulse marking method. Figure 7: Pulse marking method.
6. Zero Marking Hashed 6. Zero Marking Hashed
6.1. Hash-based Sampling 6.1. Hash-based Sampling
Hash based selection [RFC5475] is a well-known method for sampling a Hash based selection [RFC5475] is a well-known method for sampling a
subset of packets. As defined in [RFC5475]: subset of packets. As defined in [RFC5475]:
A Hash Function h maps the Packet Content c, or some portion of A Hash Function h maps the Packet Content c, or some portion of
it, onto a Hash Range R. The packet is selected if h(c) is an it, onto a Hash Range R. The packet is selected if h(c) is an
skipping to change at page 14, line 33 skipping to change at page 12, line 39
is assumed that each sample includes the timestamp (used for DM) and is assumed that each sample includes the timestamp (used for DM) and
the hash value, allowing the management system to match the samples the hash value, allowing the management system to match the samples
received from the two MPs. received from the two MPs.
The dynamic process statistically converges at the end of a marking The dynamic process statistically converges at the end of a marking
period and the number of selected samples beyond the initial NMAX period and the number of selected samples beyond the initial NMAX
samples mentioned above is between NMAX/2 and NMAX. Therefore, the samples mentioned above is between NMAX/2 and NMAX. Therefore, the
dynamic approach paces the sampling rate, allowing to bound the dynamic approach paces the sampling rate, allowing to bound the
number of sampled packets per sampling period. number of sampled packets per sampling period.
8. Summary of Marking Methods 8. Timing and Synchronization Aspects
As pointed out in [RFC8321], it is assumed that all MPs are
synchronized to a common reference time with an accuracy of +/- L/2,
where L is the periodic measurement interval. Thus, the difference
between the clock values of any two MPs is bounded by L. Note that
this is a relatively relaxed synchronization requirement that does
not require complex means of synchronization. Clocks can be
synchronized for example using NTP [RFC5905], PTP [IEEE1588], or by
other means.
In the step-based approaches the common reference time is used for
dividing the time domain into equal-sized measurement periods, such
that all packets forwarded during a measurement period have the same
color, and consecutive periods have alternating colors. In the
pulse-based approaches the synchronization helps the management
system to correlate measurements from multiple measurement points
without ambiguity.
8.1. Synchronization Aspects in Multiplexed Marking
The single marking bit incorporates two multiplexed values. From the
monitoring MP's perspective, the two values are Time-Division
Multiplexed (TDM), as depicted in Figure 8. It is assumed that the
start time of every measurement period is known to both the
initiating MP and the monitoring MP. If the measurement period is L,
then during the first and the last L/4 time units of each block the
marking bit is interpreted by the monitoring MP as a color indicator.
During the middle part of the block, the marking bit is interpreted
as a timestamp indicator; if the value of this bit is different than
the color value, the corresponding packet is used as a reference for
delay measurement.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========><==================><========>|<========>
L/4 L/4 L/2 L/4 L/4
<===================><==================><===================>
Detect color Detect timestamping Detect color
change indication change
Figure 8: Multiplexed marking field interpretation at the receiving
measurement point.
In order to prevent ambiguity in the receiver's interpretation of the
marking field, the initiating MP is permitted to set the timestamp
indication only during a specific interval, as depicted in Figure 9.
Since the receiver is willing to receive the timestamp indication
during the middle L/2 time units of the block, the sender refrains
from sending the timestamp indication during a guardband interval of
d time units at the beginning and end of the L/2-period.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========>|<================>|<========>|
L/4 L/4 | L/2 | L/4
<=>|<=> <=>|<=>
d d d d
<==========>
permissible
timestamping
indication
interval
Figure 9: A time domain view.
The guardband d is given by d = A + D_max - D_min, where A is the
clock accuracy, D_max is an upper bound on the network delay between
the MPs, and D_min is a lower bound on the delay. It is
straightforward from Figure 9 that d < L/4 must be satisfied. The
latter implies a minimal requirement on the synchronization accuracy.
All MPs must be synchronized to the same reference time with an
accuracy of +/- L/8. Depending on the system topology, in some
systems the accuracy requirement will be even more stringent, subject
to d < L/4. Note that the accuracy requirement of the conventional
alternate marking method [RFC8321] is +/- L/2, while the multiplexed
marking method requires an accuracy of +/- L/8.
Note that we assume that the middle L/2-period is designated as the
timestamp indication period, allowing a sufficiently long guardband
between the transitions. However, a system may be configured to use
a longer timestamp indication period or a shorter one, if it is
guaranteed that the synchronization accuracy meets the guardband
requirements (i.e., the constraints on d).
9. Multipoint Marking Methods
It should be noted that most of the marking methods that were
presented in this memo are intended for point-to-point measurements,
e.g., from MP1 to MP2 in Figure 10. In point-to-multipoint
measurements, the mean delay method can be used to measure the loss
and delay of the entire point-to-multipoint flow (which includes all
the traffic from MP3 to either MP4 or MP5), while other methods such
as double marking can be used to measure the point-to-point
performance, for example from MP3 to MP5. Alternate marking in
multipoint scenarios is discussed in detail in
[I-D.ietf-ippm-multipoint-alt-mark].
MP1 MP2 MP3 MP4
+--+ +--+ +--+ +--+ +--+
| |---------->| | | |----->| |----->| |
+--+ +--+ +--+ +--+ +--+
|
| MP5
| +--+
+------>| |
+--+
Point-to-point measurement Point-to-multipoint measurement
Figure 10: Point-to-point and point-to-multipoint measurements.
10. Summary of Marking Methods
This section summarizes the marking methods described in this memo. This section summarizes the marking methods described in this memo.
Each row in the table of Figure 10 represents a marking method. For Each row in the table of Figure 11 represents a marking method. For
each method the table specifies the number of bits required in the each method the table specifies the number of bits required in the
header, the number of counters per flow for LM, the methods used for header, the number of counters per flow for LM, the methods used for
LM and DM (pulse or step), and also the resilience to disturbances. LM and DM (pulse or step), and also the resilience to disturbances.
+--------------+----+----+------+------+-------------+-------------+ +--------------+----+----+------+------+-------------+-------------+
| Method |# of|# of|LM |DM |Resilience to|Resilience to| | Method |# of|# of|LM |DM |Resilience to|Resilience to|
| |bits|coun|Method|Method|Reordering |Packet drops | | |bits|coun|Method|Method|Reordering |Packet drops |
| | |ters| | +------+------+------+------+ | | |ters| | +------+------+------+------+
| | | | | | LM | DM | LM | DM | | | | | | | LM | DM | LM | DM |
+--------------+----+----+------+------+------+------+------+------+ +--------------+----+----+------+------+------+------+------+------+
skipping to change at page 15, line 37 skipping to change at page 16, line 37
+--------------+----+----+------+------+------+------+------+------+ +--------------+----+----+------+------+------+------+------+------+
|Single marking| 1 | 2 |Step |Hashed| + | + | + | + | |Single marking| 1 | 2 |Step |Hashed| + | + | + | + |
|hashed | | | |pulse | | | | | |hashed | | | |pulse | | | | |
+--------------+----+----+------+------+------+------+------+------+ +--------------+----+----+------+------+------+------+------+------+
+ Accurate measurement. + Accurate measurement.
= Invalidate only if a measured packet is lost (detectable) = Invalidate only if a measured packet is lost (detectable)
- No measurement in case of disturbance (detectable). - No measurement in case of disturbance (detectable).
-- False measurement in case of disturbance (not detectable). -- False measurement in case of disturbance (not detectable).
Figure 10: Detailed Summary of Marking Methods Figure 11: Detailed Summary of Marking Methods
In the context of this comparison two possible disturbances are In the context of this comparison two possible disturbances are
considered: out-of-order delivery, and packet drops. Generally considered: out-of-order delivery, and packet drops. Generally
speaking, pulse based methods are sensitive to packet drops, since if speaking, pulse based methods are sensitive to packet drops, since if
the marked packet is dropped no measurement is recorded in the the marked packet is dropped no measurement is recorded in the
current period. Notably, a missing measurement is detectable by the current period. Notably, a missing measurement is detectable by the
management system, and is not as severe as a false measurement. management system, and is not as severe as a false measurement.
Step-based triggers are generally resilient to out-of-order delivery Step-based triggers are generally resilient to out-of-order delivery
for LM, but are not resilient to out-of-order delivery for DM. for LM, but are not resilient to out-of-order delivery for DM.
Notably, a step-based trigger may yield a false delay measurement Notably, a step-based trigger may yield a false delay measurement
skipping to change at page 16, line 28 skipping to change at page 17, line 28
other methods require two counters per flow. other methods require two counters per flow.
The hash-based sampling approaches reduce the overhead to zero bits, The hash-based sampling approaches reduce the overhead to zero bits,
which is a significant advantage. However, the sampling period in which is a significant advantage. However, the sampling period in
these approaches is not associated with a fixed time interval. these approaches is not associated with a fixed time interval.
Therefore, in some cases adjacent packets may be selected for the Therefore, in some cases adjacent packets may be selected for the
sampling, potentially causing measurement errors. Furthermore, when sampling, potentially causing measurement errors. Furthermore, when
the traffic rate is low, measurements may become signifcantly the traffic rate is low, measurements may become signifcantly
infrequent. infrequent.
It should be noted that most of the marking methods that were
presented in this memo are intended for point-to-point measurements,
e.g., from MP1 to MP2 in Figure 11. In point-to-multipoint
measurements, the mean delay method can be used to measure the loss
and delay of the entire point-to-multipoint flow (which includes all
the traffic from MP3 to either MP4 or MP5), while other methods such
as double marking can be used to measure the point-to-point
performance, for example from MP3 to MP5. Alternate marking in
multipoint scenarios is discussed in detail in
[I-D.ietf-ippm-multipoint-alt-mark].
MP1 MP2 MP3 MP4
+--+ +--+ +--+ +--+ +--+
| |---------->| | | |----->| |----->| |
+--+ +--+ +--+ +--+ +--+
|
| MP5
| +--+
+------>| |
+--+
Point-to-point measurement Point-to-multipoint measurement
Figure 11: Point-to-point and point-to-multipoint measurements.
It is clear from the previous table that packet loss measurement can It is clear from the previous table that packet loss measurement can
be considered resilient to both reordering and packet drops if at be considered resilient to both reordering and packet drops if at
least one bit is used with a step-based approach. Thus, since the least one bit is used with a step-based approach. Thus, since the
packet loss can be considered obvious, the previous table can be packet loss can be considered obvious, the previous table can be
simplified into Figure 12, where only the characteristics of delay simplified into Figure 12, where only the characteristics of delay
measurements are highlighted, along with multipoint-to-multipoint measurements are highlighted. This more compact table allows room
delay measurement compatibility (refer to for an additional column referring to multipoint-to-multipoint
[I-D.ietf-ippm-multipoint-alt-mark] for more details). (Section 9) delay measurement compatibility.
+--------------+----+--------+------------+------------+-----------+ +--------------+----+--------+------------+------------+-----------+
| Marking |# of|LM |DM |DM |DM | | Marking |# of|LM |DM |DM |DM |
| Method |bits|on |Resilience |Resilience |Multipoint | | Method |bits|on |Resilience |Resilience |Multipoint |
| | |All |to |to |compatible | | | |All |to |to |compatible |
| | |Packets |Reordering |Packet drops| | | | |Packets |Reordering |Packet drops| |
+--------------+----+--------+------------+------------+-----------+ +--------------+----+--------+------------+------------+-----------+
|Single marking| 1 | Yes | -- | - | No | |Single marking| 1 | Yes | -- | - | No |
|- 1st packet | | | | | | |- 1st packet | | | | | |
+--------------+----+--------+------------+------------+-----------+ +--------------+----+--------+------------+------------+-----------+
skipping to change at page 19, line 5 skipping to change at page 19, line 5
In the context of delay measurement, both zero marking hashed and In the context of delay measurement, both zero marking hashed and
single marking hashed are resilient to packet drops. Using double single marking hashed are resilient to packet drops. Using double
marking it could also be possible to perform an accurate measurement marking it could also be possible to perform an accurate measurement
in case of packet drops, as long as the packet that is marked for DM in case of packet drops, as long as the packet that is marked for DM
is not dropped. is not dropped.
The single marking hashed method seems the most complete approach, The single marking hashed method seems the most complete approach,
especially because it is also compatible with multipoint-to- especially because it is also compatible with multipoint-to-
multipoint measurements. multipoint measurements.
9. Alternate Marking using Reserved Values 11. Alternate Marking using Reserved Values
As mentioned in Section 1, a marking bit is not necessarily a single As mentioned in Section 1, a marking bit is not necessarily a single
bit, but may be implemented by using two well-known values in one of bit, but may be implemented by using two well-known values in one of
the header fields. Similarly, two-bit marking can be implemented the header fields. Similarly, two-bit marking can be implemented
using four reserved values. using four reserved values.
A notable example is MPLS Synonymous Flow Labels (SFL), as defined in A notable example is MPLS Synonymous Flow Labels (SFL), as defined in
[I-D.ietf-mpls-rfc6374-sfl]. Two MPLS Label values can be used to [I-D.ietf-mpls-rfc6374-sfl]. Two MPLS Label values can be used to
indicate the two colors of a given LSP: the original Label value, and indicate the two colors of a given LSP: the original Label value, and
an SFL value. A similar approach can be applied to IPv6 using the an SFL value. A similar approach can be applied to IPv6 using the
skipping to change at page 20, line 5 skipping to change at page 20, line 5
marked for | | | | | marked for | | | | |
timestamping | | | | | timestamping | | | | |
v v v v v v v v v v
Muxed UUUUWUUUUU WWWWUWWWWW UUUUWUUUUU WWWWWUWWWW UUUWUUUUUU Muxed UUUUWUUUUU WWWWUWWWWW UUUUWUUUUU WWWWWUWWWW UUUWUUUUUU
marking marking
values values
Figure 13: Alternate marking with two multiplexed marking values, U Figure 13: Alternate marking with two multiplexed marking values, U
and W. and W.
10. IANA Considerations 12. IANA Considerations
This memo includes no requests from IANA. This memo includes no requests from IANA.
11. Security Considerations 13. Security Considerations
The security considerations of the alternate marking method are The security considerations of the alternate marking method are
discussed in [RFC8321]. The analysis of Section 8 emphasizes the discussed in [RFC8321]. The analysis of Section 10 emphasizes the
sensitivity of some of the alternate marking methods to packet drops sensitivity of some of the alternate marking methods to packet drops
and to packet reordering. Thus, a malicious attacker may attempt to and to packet reordering. Thus, a malicious attacker may attempt to
tamper with the measurements by either selectively dropping packets, tamper with the measurements by either selectively dropping packets,
or by selectively reordering specific packets. The multiplexed or by selectively reordering specific packets. The multiplexed
marking method Section 5.3 that is defined in this document requires marking method Section 5.3 that is defined in this document requires
slightly more stringent synchronization than the conventional marking slightly more stringent synchronization than the conventional marking
method, potentially making the method more vulnerable to attacks on method, potentially making the method more vulnerable to attacks on
the time synchronization protocol. A detailed discussion about the the time synchronization protocol. A detailed discussion about the
threats against time protocols and how to mitigate them is presented threats against time protocols and how to mitigate them is presented
in [RFC7384]. in [RFC7384].
12. References 14. References
12.1. Normative References 14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli, [RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi, L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
"Alternate-Marking Method for Passive and Hybrid "Alternate-Marking Method for Passive and Hybrid
Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
January 2018, <https://www.rfc-editor.org/info/rfc8321>. January 2018, <https://www.rfc-editor.org/info/rfc8321>.
12.2. Informative References 14.2. Informative References
[I-D.ietf-ippm-multipoint-alt-mark] [I-D.ietf-ippm-multipoint-alt-mark]
Fioccola, G., Cociglio, M., Sapio, A., and R. Sisto, Fioccola, G., Cociglio, M., Sapio, A., and R. Sisto,
"Multipoint Alternate Marking method for passive and "Multipoint Alternate Marking method for passive and
hybrid performance monitoring", draft-ietf-ippm- hybrid performance monitoring", draft-ietf-ippm-
multipoint-alt-mark-01 (work in progress), March 2019. multipoint-alt-mark-02 (work in progress), July 2019.
[I-D.ietf-mpls-rfc6374-sfl] [I-D.ietf-mpls-rfc6374-sfl]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow
Labels", draft-ietf-mpls-rfc6374-sfl-03 (work in Labels", draft-ietf-mpls-rfc6374-sfl-03 (work in
progress), December 2018. progress), December 2018.
[I-D.ietf-mpls-sfl-framework] [I-D.ietf-mpls-sfl-framework]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
and G. Mirsky, "Synonymous Flow Label Framework", draft- and G. Mirsky, "Synonymous Flow Label Framework", draft-
 End of changes. 23 change blocks. 
149 lines changed or deleted 167 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/