Network Working Group G. Fioccola, Ed.
Internet-Draft A. Capello, Ed.
Intended status: Experimental M. Cociglio
Expires: December 28, 2017 L. Castaldelli
Telecom Italia
M. Chen, Ed.
L. Zheng, Ed.
Huawei Technologies
G. Mirsky, Ed.
ZTE
T. Mizrahi, Ed.
Marvell
June 26, 2017
Alternate Marking method for passive and hybrid performance monitoring
draft-ietf-ippm-alt-mark-05
Abstract
This document describes a method to perform packet loss, delay and
jitter measurements on live traffic. This method is based on
Alternate Marking (Coloring) technique. A report on the operational
experiment done at Telecom Italia is explained in order to give an
example and show the method applicability. This technique can be
applied in various situations as detailed in this document and could
be considered passive or hybrid depending on the application.
Status of This Memo
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This Internet-Draft will expire on December 28, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of the method . . . . . . . . . . . . . . . . . . . 4
3. Detailed description of the method . . . . . . . . . . . . . 6
3.1. Packet loss measurement . . . . . . . . . . . . . . . . . 6
3.2. Timing aspects . . . . . . . . . . . . . . . . . . . . . 10
3.3. One-way delay measurement . . . . . . . . . . . . . . . . 11
3.3.1. Single marking methodology . . . . . . . . . . . . . 11
3.3.2. Double marking methodology . . . . . . . . . . . . . 13
3.4. Delay variation measurement . . . . . . . . . . . . . . . 14
4. Considerations . . . . . . . . . . . . . . . . . . . . . . . 15
4.1. Synchronization . . . . . . . . . . . . . . . . . . . . . 15
4.2. Data Correlation . . . . . . . . . . . . . . . . . . . . 15
4.3. Packet Re-ordering . . . . . . . . . . . . . . . . . . . 16
5. Implementation and deployment . . . . . . . . . . . . . . . . 17
5.1. Report on the operational experiment at Telecom Italia . 17
5.1.1. Coloring the packets . . . . . . . . . . . . . . . . 19
5.1.2. Counting the packets . . . . . . . . . . . . . . . . 20
5.1.3. Collecting data and calculating packet loss . . . . . 21
5.1.4. Metric transparency . . . . . . . . . . . . . . . . . 22
5.2. IP flow performance measurement (IPFPM) . . . . . . . . . 22
5.3. OAM Passive Performance Measurement . . . . . . . . . . . 22
5.4. RFC6374 Use Case . . . . . . . . . . . . . . . . . . . . 22
5.5. Application to active performance measurement . . . . . . 23
6. Hybrid measurement . . . . . . . . . . . . . . . . . . . . . 23
7. Compliance with RFC6390 guidelines . . . . . . . . . . . . . 23
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
12.1. Normative References . . . . . . . . . . . . . . . . . . 27
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12.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
Nowadays, most of the traffic in Service Providers' networks carries
contents that are highly sensitive to packet loss [RFC2680], delay
[RFC2679], and jitter [RFC3393].
In view of this scenario, Service Providers need methodologies and
tools to monitor and measure network performances with an adequate
accuracy, in order to constantly control the quality of experience
perceived by their customers. On the other hand, performance
monitoring provides useful information for improving network
management (e.g. isolation of network problems, troubleshooting,
etc.).
A lot of work related to OAM, that includes also performance
monitoring techniques, has been done by Standards Developing
Organizations(SDOs): [RFC7276] provides a good overview of existing
OAM mechanisms defined in IETF, ITU-T and IEEE. Considering IETF, a
lot of work has been done on fault detection and connectivity
verification, while a minor effort has been dedicated so far to
performance monitoring. The IPPM WG has defined standard metrics to
measure network performance; however, the methods developed in this
WG mainly refer to focus on active measurement techniques. More
recently, the MPLS WG has defined mechanisms for measuring packet
loss, one-way and two-way delay, and delay variation in MPLS
networks[RFC6374], but their applicability to passive measurements
has some limitations, especially for pure connection-less networks.
The lack of adequate tools to measure packet loss with the desired
accuracy drove an effort to design a new method for the performance
monitoring of live traffic, possibly easy to implement and deploy.
The effort led to the method described in this document: basically,
it is a passive performance monitoring technique, potentially
applicable to any kind of packet based traffic, including Ethernet,
IP, and MPLS, both unicast and multicast. The method addresses
primarily packet loss measurement, but it can be easily extended to
one-way delay and delay variation measurements as well.
The method has been explicitly designed for passive measurements but
it can also be used with active probes. Passive measurements are
usually more easily understood by customers and provide a much better
accuracy, especially for packet loss measurements.
RFC 7799 [RFC7799] defines passive and hybrid methods of measurement.
In particular, Passive Methods of Measurement are based solely on
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observations of an undisturbed and unmodified packet stream of
interest; Hybrid Methods are Methods of Measurement that use a
combination of Active Methods and Passive Methods.
Taking into consideration these definitions, Alternate Marking Method
could be considered Hybrid or Passive depending on the case. In case
the marking field is obtained by changing existing field values of
the packets (e.g. DSCP field), the technique is Hybrid. In case the
marking field is dedicated, reserved and is included in the protocol
specification Alternate Marking technique can be considered as
Passive (e.g. RFC6374 Synonymous Flow Label or OAM Marking Bits in
BIER Header).
This document is organized as follows:
o Section 2 gives an overview of the method, including a comparison
with different measurement strategies;
o Section 3 describes the method in detail;
o Section 4 reports considerations about synchronization, data
correlation and packet re-ordering;
o Section 5 reports examples of implementation and deployment of the
method. Furthermore the operational experiment done at Telecom
Italia is described;
o Section 6 introduces Hybrid measurement aspects;
o Section 7 is about the Compliance with RFC6390 guidelines;
o Section 8 includes some security aspects;
o Section 9 finally summarizes some concluding remarks.
2. Overview of the method
In order to perform packet loss measurements on a live traffic flow,
different approaches exist. The most intuitive one consists in
numbering the packets, so that each router that receives the flow can
immediately detect a packet missing. This approach, though very
simple in theory, is not simple to achieve: it requires the insertion
of a sequence number into each packet and the devices must be able to
extract the number and check it in real time. Such a task can be
difficult to implement on live traffic: if UDP is used as the
transport protocol, the sequence number is not available; on the
other hand, if a higher layer sequence number (e.g. in the RTP
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header) is used, extracting that information from each packet and
process it in real time could overload the device.
An alternate approach is to count the number of packets sent on one
end, the number of packets received on the other end, and to compare
the two values. This operation is much simpler to implement, but
requires that the devices performing the measurement are in sync: in
order to compare two counters it is required that they refer exactly
to the same set of packets. Since a flow is continuous and cannot be
stopped when a counter has to be read, it could be difficult to
determine exactly when to read the counter. A possible solution to
overcome this problem is to virtually split the flow in consecutive
blocks by inserting periodically a delimiter so that each counter
refers exactly to the same block of packets. The delimiter could be
for example a special packet inserted artificially into the flow.
However, delimiting the flow using specific packets has some
limitations. First, it requires generating additional packets within
the flow and requires the equipment to be able to process those
packets. In addition, the method is vulnerable to out of order
reception of delimiting packets and, to a lesser extent, to their
loss.
The method proposed in this document follows the second approach, but
it doesn't use additional packets to virtually split the flow in
blocks. Instead, it "colors" the packets so that the packets
belonging to the same block will have the same color, whilst
consecutive blocks will have different colors. Each change of color
represents a sort of auto-synchronization signal that guarantees the
consistency of measurements taken by different devices along the
path.
Figure 1 represents a very simple network and shows how the method
can be used to measure packet loss on different network segments: by
enabling the measurement on several interfaces along the path, it is
possible to perform link monitoring, node monitoring or end-to-end
monitoring. The method is flexible enough to measure packet loss on
any segment of the network and can be used to isolate the faulty
element.
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Traffic flow
========================================================>
+------+ +------+ +------+ +------+
---<> R1 <>-----<> R2 <>-----<> R3 <>-----<> R4 <>---
+------+ +------+ +------+ +------+
. . . . . .
. . . . . .
. <------> <-------> .
. Node Packet Loss Link Packet Loss .
. .
<--------------------------------------------------->
End-to-End Packet loss
Figure 1: Available measurements
3. Detailed description of the method
This section describes in detail how the method operate. A special
emphasis is given to the measurement of packet loss, that represents
the core application of the method, but applicability to delay and
jitter measurements is also considered.
3.1. Packet loss measurement
The basic idea is to virtually split traffic flows into consecutive
blocks: each block represents a measurable entity unambiguously
recognizable by all network devices along the path. By counting the
number of packets in each block and comparing the values measured by
different network devices along the path, it is possible to measure
packet loss occurred in any single block between any two points.
As discussed in the previous section, a simple way to create the
blocks is to "color" the traffic (two colors are sufficient) so that
packets belonging to different consecutive blocks will have different
colors. Whenever the color changes, the previous block terminates
and the new one begins. Hence, all the packets belonging to the same
block will have the same color and packets of different consecutive
blocks will have different colors. The number of packets in each
block depends on the criterion used to create the blocks: if the
color is switched after a fixed number of packets, then each block
will contain the same number of packets (except for any losses); but
if the color is switched according to a fixed timer, then the number
of packets may be different in each block depending on the packet
rate.
The following figure shows how a flow looks like when it is split in
traffic blocks with colored packets.
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A: packet with A coloring
B: packet with B coloring
| | | | |
| | Traffic flow | |
------------------------------------------------------------------->
BBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA
------------------------------------------------------------------->
... | Block 5 | Block 4 | Block 3 | Block 2 | Block 1
| | | | |
Figure 2: Traffic coloring
Figure 3 shows how the method can be used to measure link packet loss
between two adjacent nodes.
Referring to the figure, let's assume we want to monitor the packet
loss on the link between two routers: router R1 and router R2.
According to the method, the traffic is colored alternatively with
two different colors, A and B. Whenever the color changes, the
transition generates a sort of square-wave signal, as depicted in the
following figure.
Color A ----------+ +-----------+ +----------
| | | |
Color B +-----------+ +-----------+
Block n ... Block 3 Block 2 Block 1
<---------> <---------> <---------> <---------> <--------->
Traffic flow
===========================================================>
Color ...AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA...
===========================================================>
Figure 3: Computation of link packet loss
Traffic coloring could be done by R1 itself or by an upward router.
R1 needs two counters, C(A)R1 and C(B)R1, on its egress interface:
C(A)R1 counts the packets with color A and C(B)R1 counts those with
color B. As long as traffic is colored A, only counter C(A)R1 will
be incremented, while C(B)R1 is not incremented; vice versa, when the
traffic is colored as B, only C(B)R1 is incremented. C(A)R1 and
C(B)R1 can be used as reference values to determine the packet loss
from R1 to any other measurement point down the path. Router R2,
similarly, will need two counters on its ingress interface, C(A)R2
and C(B)R2, to count the packets received on that interface and
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colored with color A and B respectively. When an A block ends, it is
possible to compare C(A)R1 and C(A)R2 and calculate the packet loss
within the block; similarly, when the successive B block terminates,
it is possible to compare C(B)R1 with C(B)R2, and so on for every
successive block.
Likewise, by using two counters on R2 egress interface it is possible
to count the packets sent out of R2 interface and use them as
reference values to calculate the packet loss from R2 to any
measurement point down R2.
Using a fixed timer for color switching offers a better control over
the method: the (time) length of the blocks can be chosen large
enough to simplify the collection and the comparison of measures
taken by different network devices. It's preferable to read the
value of the counters not immediately after the color switch: some
packets could arrive out of order and increment the counter
associated to the previous block (color), so it is worth waiting for
some time. A safe choice is to wait L/2 time units (where L is the
duration for each block) after the color switch, to read the still
counter of the previous color, so the possibility to read a running
counter instead of a still one is minimized. The drawback is that
the longer the duration of the block, the less frequent the
measurement can be taken.
The following table shows how the counters can be used to calculate
the packet loss between R1 and R2. The first column lists the
sequence of traffic blocks while the other columns contain the
counters of A-colored packets and B-colored packets for R1 and R2.
In this example, we assume that the values of the counters are reset
to zero whenever a block ends and its associated counter has been
read: with this assumption, the table shows only relative values,
that is the exact number of packets of each color within each block.
If the values of the counters were not reset, the table would contain
cumulative values, but the relative values could be determined simply
by difference from the value of the previous block of the same color.
The color is switched on the basis of a fixed timer (not shown in the
table), so the number of packets in each block is different.
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+-------+--------+--------+--------+--------+------+
| Block | C(A)R1 | C(B)R1 | C(A)R2 | C(B)R2 | Loss |
+-------+--------+--------+--------+--------+------+
| 1 | 375 | 0 | 375 | 0 | 0 |
| | | | | | |
| 2 | 0 | 388 | 0 | 388 | 0 |
| | | | | | |
| 3 | 382 | 0 | 381 | 0 | 1 |
| | | | | | |
| 4 | 0 | 377 | 0 | 374 | 3 |
| | | | | | |
| ... | ... | ... | ... | ... | ... |
| | | | | | |
| 2n | 0 | 387 | 0 | 387 | 0 |
| | | | | | |
| 2n+1 | 379 | 0 | 377 | 0 | 2 |
+-------+--------+--------+--------+--------+------+
Table 1: Evaluation of counters for packet loss measurements
During an A block (blocks 1, 3 and 2n+1), all the packets are
A-colored, therefore the C(A) counters are incremented to the number
seen on the interface, while C(B) counters are zero. Vice versa,
during a B block (blocks 2, 4 and 2n), all the packets are B-colored:
C(A) counters are zero, while C(B) counters are incremented.
When a block ends (because of color switching) the relative counters
stop incrementing and it is possible to read them, compare the values
measured on router R1 and R2 and calculate the packet loss within
that block.
For example, looking at the table above, during the first block
(A-colored), C(A)R1 and C(A)R2 have the same value (375), which
corresponds to the exact number of packets of the first block (no
loss). Also during the second block (B-colored) R1 and R2 counters
have the same value (388), which corresponds to the number of packets
of the second block (no loss). During blocks three and four, R1 and
R2 counters are different, meaning that some packets have been lost:
in the example, one single packet (382-381) was lost during block
three and three packets (377-374) were lost during block four.
The method applied to R1 and R2 can be extended to any other router
and applied to more complex networks, as far as the measurement is
enabled on the path followed by the traffic flow(s) being observed.
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3.2. Timing aspects
This document introduces two color switching method: one is based on
fixed number of packet, the other is based on fixed timer. But the
method based on fixed timer is preferable because is more
deterministic, and will be considered in the rest of the dcoument.
By considering the clock error between network devices R1 and R2,
they must be synchronized to the same clock reference with an
accuracy of +/- L/2 time units, where L is the time duration of the
block. So each colored packet can be assigned to the right batch by
each router. This is because the minimum time distance between two
packets of the same color but belonging to different batches is L
time units.
In practice, there are also out of order at batch boundaries,
strictly related to the delay between measurement points. This means
that, without considering clock error, we wait L/2 after color
switching to be sure to take a still counter.
In summary we need to take into account two contributions: clock
error between network devices and the interval we need to wait to
avoid out of order because of network delay.
The following figure explains both issues.
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
...=========>|<==================><==================>|<==========...
| L/2 L/2 |
|<===>| |<===>|
d | | d
|<==========================>|
available counting interval
Figure 4: Timing aspects
It is assumed that all network devices are synchronized to a common
reference time with an accuracy of +/- A/2. Thus, the difference
between the clock values of any two network devices is bounded by A.
The guardband d is given by:
d = A + D_max - D_min,
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where A is the clock accuracy, D_max is an upper bound on the network
delay between the network devices, and D_min is a lower bound on the
delay.
The available counting interval is L - 2d that must be > 0.
The condition that must be satisfied and is a requirement on the
synchronization accuracy is:
d < L/2.
3.3. One-way delay measurement
The same principle used to measure packet loss can be applied also to
one-way delay measurement. There are three alternatives, as
described hereinafter.
3.3.1. Single marking methodology
The alternation of colors can be used as a time reference to
calculate the delay. Whenever the color changes (that means that a
new block has started) a network device can store the timestamp of
the first packet of the new block; that timestamp can be compared
with the timestamp of the same packet on a second router to compute
packet delay. Considering Figure 2, R1 stores a timestamp TS(A1)R1
when it sends the first packet of block 1 (A-colored), a timestamp
TS(B2)R1 when it sends the first packet of block 2 (B-colored) and so
on for every other block. R2 performs the same operation on the
receiving side, recording TS(A1)R2, TS(B2)R2 and so on. Since the
timestamps refer to specific packets (the first packet of each block)
we are sure that timestamps compared to compute delay refer to the
same packets. By comparing TS(A1)R1 with TS(A1)R2 (and similarly
TS(B2)R1 with TS(B2)R2 and so on) it is possible to measure the delay
between R1 and R2. In order to have more measurements, it is
possible to take and store more timestamps, referring to other
packets within each block.
In order to coherently compare timestamps collected on different
routers, the network nodes must be in sync. Furthermore, a
measurement is valid only if no packet loss occurs and if packet
misordering can be avoided, otherwise the first packet of a block on
R1 could be different from the first packet of the same block on R2
(f.i. if that packet is lost between R1 and R2 or it arrives after
the next one).
The following table shows how timestamps can be used to calculate the
delay between R1 and R2. The first column lists the sequence of
blocks while other columns contain the timestamp referring to the
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first packet of each block on R1 and R2. The delay is computed as a
difference between timestamps. For the sake of simplicity, all the
values are expressed in milliseconds.
+-------+---------+---------+---------+---------+-------------+
| Block | TS(A)R1 | TS(B)R1 | TS(A)R2 | TS(B)R2 | Delay R1-R2 |
+-------+---------+---------+---------+---------+-------------+
| 1 | 12.483 | - | 15.591 | - | 3.108 |
| | | | | | |
| 2 | - | 6.263 | - | 9.288 | 3.025 |
| | | | | | |
| 3 | 27.556 | - | 30.512 | - | 2.956 |
| | | | | | |
| | - | 18.113 | - | 21.269 | 3.156 |
| | | | | | |
| ... | ... | ... | ... | ... | ... |
| | | | | | |
| 2n | 77.463 | - | 80.501 | - | 3.038 |
| | | | | | |
| 2n+1 | - | 24.333 | - | 27.433 | 3.100 |
+-------+---------+---------+---------+---------+-------------+
Table 2: Evaluation of timestamps for delay measurements
The first row shows timestamps taken on R1 and R2 respectively and
referring to the first packet of block 1 (which is A-colored). Delay
can be computed as a difference between the timestamp on R2 and the
timestamp on R1. Similarly, the second row shows timestamps (in
milliseconds) taken on R1 and R2 and referring to the first packet of
block 2 (which is B-colored). Comparing timestamps taken on
different nodes in the network and referring to the same packets
(identified using the alternation of colors) it is possible to
measure delay on different network segments.
For the sake of simplicity, in the above example a single measurement
is provided within a block, taking into account only the first packet
of each block. The number of measurements can be easily increased by
considering multiple packets in the block: for instance, a timestamp
could be taken every N packets, thus generating multiple delay
measurements. Taking this to the limit, in principle the delay could
be measured for each packet, by taking and comparing the
corresponding timestamps (possible but impractical from an
implementation point of view).
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3.3.1.1. Mean delay
As mentioned before, the method previously exposed for measuring the
delay is sensitive to out of order reception of packets. In order to
overcome this problem, a different approach has been considered: it
is based on the concept of mean delay. The mean delay is calculated
by considering the average arrival time of the packets within a
single block. The network device locally stores a timestamp for each
packet received within a single block: summing all the timestamps and
dividing by the total number of packets received, the average arrival
time for that block of packets can be calculated. By subtracting the
average arrival times of two adjacent devices it is possible to
calculate the mean delay between those nodes. When computing the
mean delay, measurement error could be augmented by accumulating
measurement error of a lot of packets. This method is robust to out
of order packets and also to packet loss (only a small error is
introduced). Moreover, it greatly reduces the number of timestamps
(only one per block for each network device) that have to be
collected by the management system. On the other hand, it only gives
one measure for the duration of the block (f.i. 5 minutes), and it
doesn't give the minimum, maximum and median delay values (RFC 6703
[RFC6703]). This limitation could be overcome by reducing the
duration of the block (f.i. from 5 minutes to a few seconds), that
implicates an highly optimized implementation of the method.
By summing the mean delays of the two directions of a path, it is
also possible to measure the two-way mean delay (round-trip delay).
3.3.2. Double marking methodology
The Single marking methodology for one-way delay measurement is
sensitive to out of order reception of packets. The first approach
to overcome this problem is described before and is based on the
concept of mean delay. But the limitation of mean delay is that it
doesn't give information about the delay values distribution for the
duration of the block. Additionally it may be useful to have not
only the mean delay but also the minimum, maximum and median delay
values and, in wider terms, to know more about the statistic
distribution of delay values. So in order to have more information
about the delay and to overcome out of order issues, a different
approach can be introduced: it is based on double marking
methodology.
Basically, the idea is to use the first marking to create the
alternate flow and, within this colored flow, a second marking to
select the packets for measuring delay/jitter. The first marking is
needed for packet loss and mean delay measurement. The second
marking creates a new set of marked packets that are fully identified
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over the network, so that a network device can store the timestamps
of these packets; these timestamps can be compared with the
timestamps of the same packets on a second router to compute packet
delay values for each packet. The number of measurements can be
easily increased by changing the frequency of the second marking.
But the frequency of the second marking must be not too high in order
to avoid out of order issues. Between packets with the second
marking there should be a security time gap (e.g. this gap could be,
at the minimum, the mean network delay calculated with the previous
methodology) to avoid out of order issues and also to have a number
of measurement packets that is rate independent. If a second marking
packet is lost, the delay measurement for the considered block is
corrupted and should be discarded.
Mean delay is calculated on all the packets of a sample and is a
simple computation to be performed for single marking method. In
some cases the mean delay measure is not sufficient to characterize
the sample, and more statistics of delay extent data are needed, e.g.
percentiles, variance and median delay values. The conventional
range (maximum-minimum) should be avoided for several reasons,
including stability of the maximum delay due to the influence by
outliers. RFC 5481 [RFC5481] section 6.5 highlights how the 99.9th
percentile of delay and delay variation is more helpful to
performance planners. To overcome this drawback the idea is to
couple the mean delay measure for the entire batch with double
marking method, where a subset of batch packets are selected for
extensive delay calculation by using a second marking. In this way
it is possible to perform a detailed analysis on these double marked
packets. Please note that there are classic algorithms for median
and variance calculation, but are out of the scope of this document.
The comparison between the mean delay for the entire batch and the
mean delay on these double marked packets gives an useful information
since it is possible to understand if the double marking measurements
are actually representative of the delay trends.
3.4. Delay variation measurement
Similarly to one-way delay measurement (both for single marking and
double marking), the method can also be used to measure the inter-
arrival jitter. We refer to the definition in RFC 3393 [RFC3393].
The alternation of colors, for single marking method, can be used as
a time reference to measure delay variations. In case of double
marking, the time reference is given by the second marked packets.
Considering the example depicted in Figure 2, R1 stores a timestamp
TS(A)R1 whenever it sends the first packet of a block and R2 stores a
timestamp TS(B)R2 whenever it receives the first packet of a block.
The inter-arrival jitter can be easily derived from one-way delay
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measurement, by evaluating the delay variation of consecutive
samples.
The concept of mean delay can also be applied to delay variation, by
evaluating the average variation of the interval between consecutive
packets of the flow from R1 to R2.
4. Considerations
This section highlights some considerations about the methodology.
4.1. Synchronization
The Alternate Marking technique does not require a strong
synchronization, especially for packet loss and two-way delay
measurement. Only one-way delay measurement requires network devices
to have synchronized clocks.
The color switching is the reference for all the network devices, and
the only requirement to be achieved is that all network devices have
to recognize the right batch along the path.
If the length of the measurement period is L time units, then all
network devices must be synchronized to the same clock reference with
an accuracy of +/- L/2 time units (without considering network
delay). This level of accuracy guarantees that all network devices
consistently match the color bit to the correct block. For example,
if the color is toggeled every second (L = 1 second), then clocks
must be synchronized with an accuracy of +/- 0.5 second to a common
time reference.
This synchronization requirement can be satisfied even with a
relatively inaccurate synchronization method. This is true for
packet loss and two-way delay measurement, instead, for one-way delay
measurement clock synchronization must be accurate.
Therefore, a system that uses only packet loss and two-way delay
measurement does not require synchronization. This is because the
value of the clocks of network devices does not affect the
computation of the two-way delay measurement.
4.2. Data Correlation
Data Correlation is the mechanism to compare counters and timestamps
for packet loss, delay and delay variation calculation. It could be
performed in several ways depending on the alternate marking
application and use case.
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o A possibility is to use a centralized solution using Network
Management System (NMS) to correlate data;
o Another possibility is to define a protocol based distributed
solution, by defining a new protocol or by extending the existing
protocols (e.g. RFC6374, TWAMP, OWAMP) in order to communicate
the counters and timestamps between nodes.
In the following paragraphs an example data correlation mechanism is
explained and could be use independently of the adopted solutions.
When data is collected on the upstream and downstream node, e.g.,
packet counts for packet loss measurement or timestamps for packet
delay measurement, and periodically reported to or pulled by other
nodes or NMS, a certain data correlation mechanism SHOULD be in use
to help the nodes or NMS to tell whether any two or more packet
counts are related to the same block of markers, or any two
timestamps are related to the same marked packet.
The alternate marking method described in this document literally
split the packets of the measured flow into different measurement
blocks, in addition a Block Number could be assigned to each of such
measurement block. The BN is generated each time a node reads the
data (packet counts or timestamps), and is associated with each
packet count and timestamp reported to or pulled by other nodes or
NMS. The value of BN could be calculated as the modulo of the local
time (when the data are read) and the interval of the marking time
period.
When the nodes or NMS see, for example, same BNs associated with two
packet counts from an upstream and a downstream node respectively, it
considers that these two packet counts corresponding to the same
block, i.e. that these two packet counts belong to the same block of
markers from the upstream and downstream node. The assumption of
this BN mechanism is that the measurement nodes are time
synchronized. This requires the measurement nodes to have a certain
time synchronization capability (e.g., the Network Time Protocol
(NTP) [RFC5905], or the IEEE 1588 Precision Time Protocol (PTP)
[IEEE1588]). Synchronization aspects are further discussed in
Section 4.
4.3. Packet Re-ordering
Due to ECMP, packet re-ordering is very common in IP network. The
accuracy of marking based PM, especially packet loss measurement, may
be affected by packet re-ordering. Take a look at the following
example:
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Block : 1 | 2 | 3 | 4 | 5 |...
--------|---------|---------|---------|---------|---------|---
Node R1 : AAAAAAA | BBBBBBB | AAAAAAA | BBBBBBB | AAAAAAA |...
Node R2 : AAAAABB | AABBBBA | AAABAAA | BBBBBBA | ABAAABA |...
Figure 5: Packet Reordering
In the following paragraphs an example of data correlation mechanism
is explained and could be use independently of the adopted solutions.
Most of the packet re-ordering occur at the edge of adjacent blocks,
and they are easy to handle if the interval of each block is
sufficient large. Then, it can assume that the packets with
different marker belong to the block that they are more close to. If
the interval is small, it is difficult and sometime impossible to
determine to which block a packet belongs. See above example, the
packet with the marker of "B" in block 3, there is no safe way to
tell whether the packet belongs to block 2 or block 4.
To choose a proper interval is important and how to choose a proper
interval is out of the scope of this document. But an implementation
SHOULD provide a way to configure the interval and allow a certain
degree of packet re-ordering.
5. Implementation and deployment
The methodology described in the previous sections can be applied in
various situations. Basically Alternate Marking technique could be
used in many cases for performance measurement. The only requirement
is to select and mark the flow to be monitored; in this way packets
are batched by the sender and each batch is alternately marked such
that can be easily recognized by the receiver.
An example of implementation and deployment is explained in the next
section, just to clarify how the method can work.
5.1. Report on the operational experiment at Telecom Italia
The method described in this document, also called PNPM (Packet
Network Performance Monitoring), has been invented and engineered in
Telecom Italia and it's currently being used in Telecom Italia's
network. The methodology has been applied by leveraging functions
and tools available on IP routers and it's currently being used to
monitor packet loss in some portions of Telecom Italia's network.
The application of the method to delay measurement is currently being
evaluated in Telecom Italia's labs. This section describes how the
features currently available on existing routing platforms can be
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used to apply the method, in order to give an example of
implementation and deployment.
The fundamental steps for this implementation of the method can be
summarized in the following items:
o coloring the packets;
o counting the packets;
o collecting data and calculating the packet loss.
o metric transparency.
Before going deeper into the implementation details, it's worth
mentioning two different strategies that can be used when
implementing the method:
o flow-based: the flow-based strategy is used when only a limited
number of traffic flows need to be monitored. This could be the
case, for example, of IPTV channels or other specific applications
traffic with high QoS requirements (i.e. Mobile Backhauling
traffic). According to this strategy, only a subset of the flows
is colored. Counters for packet loss measurements can be
instantiated for each single flow, or for the set as a whole,
depending on the desired granularity. A relevant problem with
this approach is the necessity to know in advance the path
followed by flows that are subject to measurement. Path rerouting
and traffic load-balancing increase the issue complexity,
especially for unicast traffic. The problem is easier to solve
for multicast traffic where load balancing is seldom used,
especially for IPTV traffic where static joins are frequently used
to force traffic forwarding and replication. Another application
is on Mobile Backhauling, implemented with a VPN MPLS in Telecom
Italia's network; where the monitoring is between the Provider
Edge nodes of the VPN MPLS.
o link-based: measurements are performed on all the traffic on a
link by link basis. The link could be a physical link or a
logical link (for instance an Ethernet VLAN or a MPLS PW).
Counters could be instantiated for the traffic as a whole or for
each traffic class (in case it is desired to monitor each class
separately), but in the second case a couple of counters is needed
for each class.
The current implementation in Telecom Italia uses the first strategy.
As mentioned, the flow-based measurement requires the identification
of the flow to be monitored and the discovery of the path followed by
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the selected flow. It is possible to monitor a single flow or
multiple flows grouped together, but in this case measurement is
consistent only if all the flows in the group follow the same path.
Moreover, a Service Provider should be aware that, if a measurement
is performed by grouping many flows, it is not possible to determine
exactly which flow was affected by packets loss. In order to have
measures per single flow it is necessary to configure counters for
each specific flow. Once the flow(s) to be monitored have been
identified, it is necessary to configure the monitoring on the proper
nodes. Configuring the monitoring means configuring the policy to
intercept the traffic and configuring the counters to count the
packets. To have just an end-to-end monitoring, it is sufficient to
enable the monitoring on the first and the last hop routers of the
path: the mechanism is completely transparent to intermediate nodes
and independent from the path followed by traffic flows. On the
contrary, to monitor the flow on a hop-by-hop basis along its whole
path it is necessary to enable the monitoring on every node from the
source to the destination. In case the exact path followed by the
flow is not known a priori (i.e. the flow has multiple paths to reach
the destination) it is necessary to enable the monitoring system on
every path: counters on interfaces traversed by the flow will report
packet count, counters on other interfaces will be null.
5.1.1. Coloring the packets
The coloring operation is fundamental in order to create packet
blocks. This implies choosing where to activate the coloring and how
to color the packets.
In case of flow-based measurements, it is desirable, in general, to
have a single coloring node because it is easier to manage and
doesn't rise any risk of conflict (consider the case where two nodes
color the same flow). Thus it is advantageous to color the flow as
close as possible to the source. In addition, coloring a flow close
to the source allows an end-to-end measure if a measurement point is
enabled on the last-hop router as well. The only requirement is that
the coloring must change periodically and every node along the path
must be able to identify unambiguously the colored packets. For
link-based measurements, all traffic needs to be colored when
transmitted on the link. If the traffic had already been colored,
then it has to be re-colored because the color must be consistent on
the link. This means that each hop along the path must (re-)color
the traffic; the color is not required to be consistent along
different links.
Traffic coloring can be implemented by setting a specific bit in the
packet header and changing the value of that bit periodically. With
current router implementations, only QoS related fields and features
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offer the required flexibility to set bits in the packet header. In
case a Service Provider only uses the three most significant bits of
the DSCP field (corresponding to IP Precedence) for QoS
classification and queuing, it is possible to use the two less
significant bits of the DSCP field (bit 0 and bit 1) to implement the
method without affecting QoS policies. One of the two bits (bit 0)
could be used to identify flows subject to traffic monitoring (set to
1 if the flow is under monitoring, otherwise it is set to 0), while
the second (bit 1) can be used for coloring the traffic (switching
between values 0 and 1, corresponding to color A and B) and creating
the blocks.
In practice, coloring the traffic using the DSCP field can be
implemented by configuring on the router output interface an access
list that intercepts the flow(s) to be monitored and applies to them
a policy that sets the DSCP field accordingly. Since traffic
coloring has to be switched between the two values over time, the
policy needs to be modified periodically: an automatic script can be
used perform this task on the basis of a fixed timer. In Telecom
Italia's implementation this timer is set to 5 minutes: this value
showed to be a good compromise between measurement frequency and
stability of the measurement (i.e. possibility to collect all the
measures referring to the same block).
5.1.2. Counting the packets
Assuming that the coloring of the packets is performed only by the
source node, the nodes between source and destination (included) have
to count the colored packets that they receive and forward: this
operation can be enabled on every router along the path or only on a
subset, depending on which network segment is being monitored (a
single link, a particular metro area, the backbone, the whole path).
Since the color switches periodically between two values, two
counters (one for each value) are needed: one counter for packets
with color A and one counter for packets with color B. For each flow
(or group of flows) being monitored and for every interface where the
monitoring is active, a couple of counters is needed. For example,
in order to monitor separately 3 flows on a router with 4 interfaces
involved, 24 counters are needed (2 counters for each of the 3 flows
on each of the 4 interfaces). If traffic is colored using the DSCP
field, as in Telecom Italia's implementation, an access-list that
matches specific DSCP values can be used to count the packets of the
flow(s) being monitored.
In case of link-based measurements the behaviour is similar except
that coloring and counting operations are performed on a link by link
basis at each endpoint of the link.
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Another important aspect to take into consideration is when to read
the counters: in order to count the exact number of packets of a
block the routers must perform this operation when that block has
ended: in other words, the counter for color A must be read when the
current block has color B, in order to be sure that the value of the
counter is stable. This task can be accomplished in two ways. The
general approach suggests to read the counters periodically, many
times during a block duration, and to compare these successive
readings: when the counter stops incrementing means that the current
block has ended and its value can be elaborated safely.
Alternatively, if the coloring operation is performed on the basis of
a fixed timer, it is possible to configure the reading of the
counters according to that timer: for example, if each block is 5
minutes long, reading the counter for color A every 5 minute in the
middle of the subsequent block (with color B) is a safe choice. A
sufficient margin should be considered between the end of a block and
the reading of the counter, in order to take into account any out-of-
order packets. The choice of a 5 minutes timer for colore switching
was also inspired by these considerations.
5.1.3. Collecting data and calculating packet loss
The nodes enabled to perform performance monitoring collect the value
of the counters, but they are not able to directly use this
information to measure packet loss, because they only have their own
samples. For this reason, an external Network Management System
(NMS) is required to collect and elaborate data and to perform packet
loss calculation. The NMS compares the values of counters from
different nodes and can calculate if some packets were lost (even a
single packet) and also where packets were lost.
The value of the counters needs to be transmitted to the NMS as soon
as it has been read. This can be accomplished by using SNMP or FTP
and can be done in Push Mode or Polling Mode. In the first case,
each router periodically sends the information to the NMS, in the
latter case it is the NMS that periodically polls routers to collect
information. In any case, the NMS has to collect all the relevant
values from all the routers within one cycle of the timer (5
minutes).
If link-based measurement is used, it would be possible to use a
protocol to exchange values of counters between the two endpoints in
order to let them perform the packet loss calculation for each
traffic direction. A similar approach could be complicated if
applied to a flow-based measurement.
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5.1.4. Metric transparency
In Telecom Italia's implementation the source node colors the packets
with a policy that is modified periodically via an automatic script
in order to alternate the DSCP field of the packets. The nodes
between source and destination (included) have to count with an
access-list the colored packets that they receive and forward.
Moreover the destination node has an important role: the colored
packets are intercepted and a policy restores and sets the DSCP field
of all the packets to the initial value. In this way the metric is
transparent because outside the section of the network under
monitoring the traffic flow is unchanged.
In such a case, thanks to this restoring technique, network elements
outside the Alternate Marking monitoring domain (e.g. the two
Provider Edge nodes of the Mobile Backhauling VPN MPLS) are totally
anaware that packets were marked. So this restoring technique makes
Alternate Marking completely transparent outside its monitoring
domain.
5.2. IP flow performance measurement (IPFPM)
This application of marking method is described in
[I-D.chen-ippm-coloring-based-ipfpm-framework].
5.3. OAM Passive Performance Measurement
In [I-D.ietf-bier-mpls-encapsulation] two OAM bits from Bit Index
Explicit Replication (BIER) Header are reserved for the passive
performance measurement marking method. [I-D.ietf-bier-pmmm-oam]
details the measurement for multicast service over BIER domain.
[I-D.mirsky-sfc-pmamm] describes how the alternate marking method can
be used as the passive performance measurement method in a Service
Function Chaining (SFC) domain.
The application of the marking method to Network Virtualization
Overlays (NVO3) protocols is a work in progress.
5.4. RFC6374 Use Case
RFC6374 [RFC6374] uses the LM packet as the packet accounting
demarcation point. Unfortunately this gives rise to a number of
problems that may lead to significant packet accounting errors in
certain situations. [I-D.ietf-mpls-flow-ident] discusses the desired
capabilities for MPLS flow identification in order to perform a
better in-band performance monitoring of user data packets. A method
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of accomplishing identification is Synonymous Flow Labels (SFL)
introduced in [I-D.bryant-mpls-sfl-framework], while
[I-D.ietf-mpls-rfc6374-sfl] describes RFC6374 performance
measurements with SFL.
5.5. Application to active performance measurement
[I-D.fioccola-ippm-alt-mark-active] describes how to extend the
existing Active Measurement Protocol, in order to implement alternate
marking methodology. [I-D.fioccola-ippm-rfc6812-alt-mark-ext]
describes an extension to the Cisco SLA Protocol Measurement-Type
UDP-Measurement.
6. Hybrid measurement
The method has been explicitly designed for passive measurements but
it can also be used with active measurements. In order to have both
end to end measurements and intermediate measurements (hybrid
measurements) two end points can exchanges artificial traffic flows
and apply alternate marking over these flows. In the intermediate
points artificial traffic is managed in the same way as real traffic
and measured as specified before. So the application of marking
method can simplify also the active measurement, as explained in
[I-D.fioccola-ippm-alt-mark-active].
7. Compliance with RFC6390 guidelines
RFC6390 [RFC6390] defines a framework and a process for developing
Performance Metrics for protocols above and below the IP layer (such
as IP-based applications that operate over reliable or datagram
transport protocols).
This document doesn't aim to propose a new Performance Metric but a
new method of measurement for a few Performance Metrics that have
already been standardized. Nevertheless, it's worth applying
[RFC6390] guidelines to the present document, in order to provide a
more complete and coherent description of the proposed method. We
used a subset of the Performance Metric Definition template defined
by [RFC6390].
o Metric name and description: as already stated, this document
doesn't propose any new Performance Metric. On the contrary, it
describes a novel method for measuring packet loss [RFC2680]. The
same concept, with small differences, can also be used to measure
delay [RFC2679], and jitter [RFC3393]. The document mainly
describes the applicability to packet loss measurement.
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o Method of Measurement or Calculation: according to the method
described in the previous sections, the number of packets lost is
calculated by subtracting the value of the counter on the source
node from the value of the counter on the destination node. Both
counters must refer to the same color. The calculation is
performed when the value of the counters is in a steady state.
o Units of Measurement: the method calculates and reports the exact
number of packets sent by the source node and not received by the
destination node.
o Measurement Points: the measurement can be performed between
adjacent nodes, on a per-link basis, or along a multi-hop path,
provided that the traffic under measurement follows that path. In
case of a multi-hop path, the measurements can be performed both
end-to-end and hop-by-hop.
o Measurement Timing: the method have a constraint on the frequency
of measurements. In order to perform a measure, the counter must
be in a steady state: this happens when the traffic is being
colored with the alternate color; for example in the Telecom
Italia application of the method the time interval is set to 5
minutes.
o Implementation: the Telecom Italia application of the method uses
two encodings of the DSCP field to color the packets; this enables
the use of policy configurations on the router to color the
packets and accordingly configure the counter for each color. The
path followed by traffic being measured should be known in advance
in order to configure the counters along the path and be able to
compare the correct values.
o Use and Applications: the method can be used to measure packet
loss with high precision on live traffic; moreover, by combining
end-to-end and per-link measurements, the method is useful to
pinpoint the single link that is experiencing loss events.
o Reporting Model: the value of the counters has to be sent to a
centralized management system that perform the calculations; such
samples must contain a reference to the time interval they refer
to, so that the management system can perform the correct
correlation; the samples have to be sent while the corresponding
counter is in a steady state (within a time interval), otherwise
the value of the sample should be stored locally.
o Dependencies: the values of the counters have to be correlated to
the time interval they refer to; moreover, as far the Telecom
Italia application of the method is based on DSCP values, there
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are significant dependencies on the usage of the DSCP field: it
must be possible to rely on unused DSCP values without affecting
QoS-related configuration and behavior; moreover, the intermediate
nodes must not change the value of the DSCP field not to alter the
measurement.
o Organization of Results: the method of measurement produces
singletons.
o Parameters: currently, the main parameter of the method is the
time interval used to alternate the colors and read the counters.
8. Security Considerations
This document specifies a method to perform measurements in the
context of a Service Provider's network and has not been developed to
conduct Internet measurements, so it does not directly affect
Internet security nor applications which run on the Internet.
However, implementation of this method must be mindful of security
and privacy concerns.
There are two types of security concerns: potential harm caused by
the measurements and potential harm to the measurements. For what
concerns the first point, the measurements described in this document
are passive, so there are no packets injected into the network
causing potential harm to the network itself and to data traffic.
Nevertheless, the method implies modifications on the fly to the IP
header of data packets: this must be performed in a way that doesn't
alter the quality of service experienced by packets subject to
measurements and that preserve stability and performance of routers
doing the measurements. The measurements themselves could be harmed
by routers altering the marking of the packets, or by an attacker
injecting artificial traffic. Authentication techniques, such as
digital signatures, may be used where appropriate to guard against
injected traffic attacks.
The privacy concerns of network measurement are limited because the
method only relies on information contained in the IP header without
any release of user data.
The measurement itself may be affected by routers (or other network
devices) along the path of IP packets intentionally altering the
value of marking bits of packets. As mentioned above, the mechanism
specified in this document is just in the context of one Service
Provider's network, and thus the routers (or other network devices)
are locally administered and this type of attack can be avoided.
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One of the main security threats in OAM protocols is network
reconnaissance; an attacker can gather information about the network
performance by passively eavesdropping to OAM messages. The
advantage of the methods described in this document is that the
marking bits are the only information that is exchanged between the
network devices. Therefore, passive eavesdropping to data plane
traffic does not allow attackers to gain information about the
network performance.
Delay attacks are another potential threat in the context of this
document. Delay measurement is performed using a specific packet in
each block, marked by a dedicated color bit. Therefore, a man-in-
the-middle attacker can selectively induce synthetic delay only to
delay-colored packets, causing systematic error in the delay
measurements. As discussed in previous sections, the methods
described in this document rely on an underlying time synchronization
protocol. Thus, by attacking the time protocol an attacker can
potentially compromise the integrity of the measurement. A detailed
discussion about the threats against time protocols and how to
mitigate them is presented in RFC 7384 [RFC7384].
9. Conclusions
The advantages of the method described in this document are:
o easy implementation: it can be implemented using features already
available on major routing platforms;
o low computational effort: the additional load on processing is
negligible;
o accurate packet loss measurement: single packet loss granularity
is achieved with a passive measurement;
o potential applicability to any kind of packet/frame -based
traffic: Ethernet, IP, MPLS, etc., both unicast and multicast;
o robustness: the method can tolerate out of order packets and it's
not based on "special" packets whose loss could have a negative
impact;
o no interoperability issues: the features required to implement the
method are available on all current routing platforms.
The method doesn't raise any specific need for protocol extension,
but it could be further improved by means of some extension to
existing protocols. Specifically, the use of DiffServ bits for
coloring the packets could not be a viable solution in some cases: a
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standard method to color the packets for this specific application
could be beneficial.
10. IANA Considerations
There are no IANA actions required.
11. Acknowledgements
The previous IETF drafts about this technique were:
[I-D.cociglio-mboned-multicast-pm] and [I-D.tempia-opsawg-p3m].
There are some references to this methodology in other IETF works
(e.g. [I-D.ietf-mpls-flow-ident], [I-D.bryant-mpls-sfl-framework]
[I-D.ietf-mpls-rfc6374-sfl], [I-D.ietf-bier-mpls-encapsulation],
[I-D.ietf-bier-pmmm-oam]
[I-D.chen-ippm-coloring-based-ipfpm-framework]).
In addition the authors would like to thank Alberto Tempia Bonda,
Domenico Laforgia, Daniele Accetta and Mario Bianchetti for their
contribution to the definition and the implementation of the method.
12. References
12.1. Normative References
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, DOI 10.17487/RFC2679,
September 1999, <http://www.rfc-editor.org/info/rfc2679>.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680,
DOI 10.17487/RFC2680, September 1999,
<http://www.rfc-editor.org/info/rfc2680>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
<http://www.rfc-editor.org/info/rfc3393>.
12.2. Informative References
[I-D.bryant-mpls-sfl-framework]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
and G. Mirsky, "Synonymous Flow Label Framework", draft-
bryant-mpls-sfl-framework-04 (work in progress), April
2017.
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[I-D.chen-ippm-coloring-based-ipfpm-framework]
Chen, M., Zheng, L., Mirsky, G., Fioccola, G., and T.
Mizrahi, "IP Flow Performance Measurement Framework",
draft-chen-ippm-coloring-based-ipfpm-framework-06 (work in
progress), March 2016.
[I-D.cociglio-mboned-multicast-pm]
Cociglio, M., Capello, A., Bonda, A., and L. Castaldelli,
"A method for IP multicast performance monitoring", draft-
cociglio-mboned-multicast-pm-01 (work in progress),
October 2010.
[I-D.fioccola-ippm-alt-mark-active]
Fioccola, G., Clemm, A., Bryant, S., Cociglio, M.,
Chandramouli, M., and A. Capello, "Alternate Marking
Extension to Active Measurement Protocol", draft-fioccola-
ippm-alt-mark-active-01 (work in progress), March 2017.
[I-D.fioccola-ippm-rfc6812-alt-mark-ext]
Fioccola, G., Clemm, A., Cociglio, M., Chandramouli, M.,
and A. Capello, "Alternate Marking Extension to Cisco SLA
Protocol RFC6812", draft-fioccola-ippm-rfc6812-alt-mark-
ext-01 (work in progress), March 2016.
[I-D.ietf-bier-mpls-encapsulation]
Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J.,
Aldrin, S., and I. Meilik, "Encapsulation for Bit Index
Explicit Replication in MPLS and non-MPLS Networks",
draft-ietf-bier-mpls-encapsulation-07 (work in progress),
June 2017.
[I-D.ietf-bier-pmmm-oam]
Mirsky, G., Zheng, L., Chen, M., and G. Fioccola,
"Performance Measurement (PM) with Marking Method in Bit
Index Explicit Replication (BIER) Layer", draft-ietf-bier-
pmmm-oam-01 (work in progress), January 2017.
[I-D.ietf-mpls-flow-ident]
Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
Mirsky, "MPLS Flow Identification Considerations", draft-
ietf-mpls-flow-ident-04 (work in progress), February 2017.
[I-D.ietf-mpls-rfc6374-sfl]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow
Labels", draft-ietf-mpls-rfc6374-sfl-00 (work in
progress), June 2017.
Fioccola, et al. Expires December 28, 2017 [Page 28]
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[I-D.mirsky-sfc-pmamm]
Mirsky, G. and G. Fioccola, "Performance Measurement (PM)
with Alternate Marking Method in Service Function Chaining
(SFC) Domain", draft-mirsky-sfc-pmamm-00 (work in
progress), April 2017.
[I-D.tempia-opsawg-p3m]
Capello, A., Cociglio, M., Castaldelli, L., and A. Bonda,
"A packet based method for passive performance
monitoring", draft-tempia-opsawg-p3m-04 (work in
progress), February 2014.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
March 2009, <http://www.rfc-editor.org/info/rfc5481>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<http://www.rfc-editor.org/info/rfc6374>.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
DOI 10.17487/RFC6390, October 2011,
<http://www.rfc-editor.org/info/rfc6390>.
[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View",
RFC 6703, DOI 10.17487/RFC6703, August 2012,
<http://www.rfc-editor.org/info/rfc6703>.
[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<http://www.rfc-editor.org/info/rfc7276>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <http://www.rfc-editor.org/info/rfc7384>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <http://www.rfc-editor.org/info/rfc7799>.
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Authors' Addresses
Giuseppe Fioccola (editor)
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: giuseppe.fioccola@telecomitalia.it
Alessandro Capello (editor)
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: alessandro.capello@telecomitalia.it
Mauro Cociglio
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: mauro.cociglio@telecomitalia.it
Luca Castaldelli
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: luca.castaldelli@telecomitalia.it
Mach(Guoyi) Chen (editor)
Huawei Technologies
Email: mach.chen@huawei.com
Lianshu Zheng (editor)
Huawei Technologies
Email: vero.zheng@huawei.com
Fioccola, et al. Expires December 28, 2017 [Page 30]
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Greg Mirsky (editor)
ZTE
USA
Email: gregimirsky@gmail.com
Tal Mizrahi (editor)
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
Fioccola, et al. Expires December 28, 2017 [Page 31]