RFC6777: Label Switched Path (LSP) Data Path Delay Metrics in Generalized MPLS and MPLS Traffic Engineering (MPLS-TE) Networks
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Related keywords:
(Bandwidth on Demand)
(Measurement methodologies)
(performance evaluation)
(Performance measurement)
(Provisioning performance)
(uni)
Internet Engineering Task Force (IETF) W. Sun, Ed.
Request for Comments: 6777 SJTU
Category: Standards Track G. Zhang, Ed.
ISSN: 2070-1721 CATR
J. Gao
Huawei
G. Xie
UC Riverside
R. Papneja
Huawei
November 2012
Label Switched Path (LSP) Data Path Delay Metrics in Generalized MPLS
and MPLS Traffic Engineering (MPLS-TE) Networks
Abstract
When setting up a Label Switched Path (LSP) in Generalized MPLS
(GMPLS) and MPLS Traffic Engineering (MPLS-TE) networks, the
completion of the signaling process does not necessarily mean that
the cross-connection along the LSP has been programmed accordingly
and in a timely manner. Meanwhile, the completion of the signaling
process may be used by LSP users or applications that control their
use as an indication that the data path has become usable. The
existence of the inconsistency between the signaling messages and
cross-connection programming, and the possible failure of cross-
connection programming, if not properly treated, will result in data
loss or even application failure. Characterization of this
performance can thus help designers to improve the way in which LSPs
are used and to make applications or tools that depend on and use
LSPs more robust. This document defines a series of performance
metrics to evaluate the connectivity of the data path in the
signaling process.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6777.
Sun, et al. Standards Track [Page 1]
RFC 6777 LSP Data Path Delay Metrics November 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................4
2. Conventions Used in This Document ...............................5
3. Overview of Performance Metrics .................................5
4. Terms Used in This Document .....................................6
5. A Singleton Definition for RRFD .................................7
5.1. Motivation .................................................7
5.2. Metric Name ................................................7
5.3. Metric Parameters ..........................................7
5.4. Metric Units ...............................................7
5.5. Definition .................................................8
5.6. Discussion .................................................8
5.7. Methodologies ..............................................9
6. A Singleton Definition for RSRD ................................10
6.1. Motivation ................................................10
6.2. Metric Name ...............................................10
6.3. Metric Parameters .........................................10
6.4. Metric Units ..............................................11
6.5. Definition ................................................11
6.6. Discussion ................................................11
6.7. Methodologies .............................................12
7. A Singleton Definition for PRFD ................................13
7.1. Motivation ................................................13
7.2. Metric Name ...............................................13
7.3. Metric Parameters .........................................13
7.4. Metric Units ..............................................13
7.5. Definition ................................................14
7.6. Discussion ................................................14
7.7. Methodologies .............................................15
Sun, et al. Standards Track [Page 2]
RFC 6777 LSP Data Path Delay Metrics November 2012
8. A Singleton Definition for PSFD ................................16
8.1. Motivation ................................................16
8.2. Metric Name ...............................................16
8.3. Metric Parameters .........................................16
8.4. Metric Units ..............................................16
8.5. Definition ................................................17
8.6. Discussion ................................................17
8.7. Methodologies .............................................18
9. A Singleton Definition for PSRD ................................19
9.1. Motivation ................................................19
9.2. Metric Name ...............................................19
9.3. Metric Parameters .........................................19
9.4. Metric Units ..............................................19
9.5. Definition ................................................20
9.6. Discussion ................................................20
9.7. Methodologies .............................................21
10. A Definition for Samples of Data Path Delay ...................22
10.1. Metric Name ..............................................22
10.2. Metric Parameters ........................................22
10.3. Metric Units .............................................22
10.4. Definition ...............................................22
10.5. Discussion ...............................................23
10.6. Methodologies ............................................23
10.7. Typical Testing Cases ....................................23
10.7.1. With No LSP in the Network ........................23
10.7.2. With a Number of LSPs in the Network ..............24
11. Some Statistics Definitions for Metrics to Report .............24
11.1. The Minimum of the Metric ................................24
11.2. The Median of the Metric .................................24
11.3. The Percentile of the Metric .............................24
11.4. Failure Probability ......................................25
11.4.1. Failure Count .....................................25
11.4.2. Failure Ratio .....................................25
12. Security Considerations .......................................25
13. References ....................................................26
13.1. Normative References .....................................26
13.2. Informative References ...................................26
Appendix A. Acknowledgements ......................................27
Appendix B. Contributors ..........................................28
Sun, et al. Standards Track [Page 3]
RFC 6777 LSP Data Path Delay Metrics November 2012
1. Introduction
Label Switched Paths (LSPs) are established, controlled, and
allocated for use by management tools or directly by the components
that use them. In this document, we call such management tools and
the components that use LSPs "applications". Such applications may
be Network Management Systems (NMSs); hardware or software components
that forward data onto virtual links; programs or tools that use
dedicated links; or any other user of an LSP.
Ideally, the completion of the signaling process means that the
signaled LSP is ready to carry traffic. However, in actual
implementations, vendors may choose to program the cross-connection
in a pipelined manner, so that the overall LSP provisioning delay can
be reduced. In such situations, the data path may not be ready for
use instantly after the signaling process completes. Implementation
deficiency may also cause inconsistency between the signaling process
and data path provisioning. For example, if the data plane fails to
program the cross-connection accordingly but does not manage to
report this to the control plane, the signaling process may complete
successfully while the corresponding data path will never become
functional at all.
On the other hand, the completion of the signaling process may be
used in many cases as an indication of data path connectivity. For
example, when invoking through the User-Network Interface (UNI)
[RFC4208], a client device or an application may use the reception of
the correct Resv message as an indication that the data path is fully
functional and start to transmit traffic. This will result in data
loss or even application failure.
Although RSVP(-TE) specifications have suggested that the cross-
connections are programmed before signaling messages are propagated
upstream, it is still worthwhile to verify the conformance of an
implementation and measure the delay, when necessary.
This document defines a series of performance metrics to evaluate the
connectivity of the data path during the signaling process. The
metrics defined in this document complement the control plane metrics
defined in [RFC5814]. These metrics can be used to verify the
conformance of implementations against related specifications, as
elaborated in [RFC6383]. They also can be used to build more robust
applications.
Sun, et al. Standards Track [Page 4]
RFC 6777 LSP Data Path Delay Metrics November 2012
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Overview of Performance Metrics
In this memo, we define five performance metrics to characterize the
performance of data path provisioning with GMPLS/MPLS-TE signaling.
These metrics complement the metrics defined in [RFC5814], in the
sense that the completion of the signaling process for an LSP and the
programming of cross-connections along the LSP may not be consistent.
The performance metrics in [RFC5814] characterize the performance of
LSP provisioning from the pure signaling point of view, while the
metric in this document takes into account the validity of the data
path.
The five metrics are:
o Resv Received, Forward Data (RRFD) - the delay between the point
when the Resv message is received by the ingress node and the
forward data path becomes ready for use.
o Resv Sent, Reverse Data (RSRD) - the delay between the point when
the Resv message is sent by the egress node and the reverse data
path becomes ready for use.
o PATH Received, Forward Data (PRFD) - the delay between the point
when the PATH message is received by the egress node and the
forward data path becomes ready for use.
o PATH Sent, Forward Data (PSFD) - the delay between the point when
the PATH message is sent by the ingress node and the forward data
path becomes ready for use.
o PATH Sent, Reverse Data (PSRD) - the delay between the point when
the PATH message is sent by the ingress node and the reverse data
path becomes ready for use.
As in [RFC5814], we continue to use the structures and notions
introduced and discussed in the IP Performance Metrics (IPPM)
Framework documents [RFC2330] [RFC2679] [RFC2681]. The reader is
assumed to be familiar with the notions in those documents. The
reader is also assumed to be familiar with the definitions in
[RFC5814].
Sun, et al. Standards Track [Page 5]
RFC 6777 LSP Data Path Delay Metrics November 2012
4. Terms Used in This Document
o Forward data path - the data path from the ingress node to the
egress node. Instances of a forward data path include the data
path of a unidirectional LSP and a data path from the ingress node
to the egress node in a bidirectional LSP.
o Reverse data path - the data path from the egress node to the
ingress node in a bidirectional LSP.
o Data path delay - the time needed to complete the data path
configuration, in relation to the signaling process. Five types
of data path delay are defined in this document, namely RRFD,
RSRD, PRFD, PSFD, and PSRD. Data path delay as used in this
document must be distinguished from the transmission delay along
the data path, i.e., the time needed to transmit traffic from one
side of the data path to the other.
o Error-free signal - data-plane-specific indication of connectivity
of the data path. For example, for interfaces capable of packet
switching, the reception of the first error-free packet from one
side of the LSP to the other may be used as the error-free signal.
For Synchronous Digital Hierarchy/Synchronous Optical Network
(SDH/SONET) cross-connects, the disappearance of alarm can be used
as the error-free signal. Throughout this document, we will use
"error-free signal" as a general term. An implementation must
choose a proper data path signal that is specific to the data path
technology being tested.
o Ingress/egress node - in this memo, an ingress/egress node means a
measurement endpoint with both control plane and data plane
features. Typically, the control plane part on an ingress/egress
node interacts with the control plane of the network under test.
The data plane part of an ingress/egress node will generate data
path signals and send the signal to the data plane of the network
under test, or receive data path signals from the network under
test.
Sun, et al. Standards Track [Page 6]
RFC 6777 LSP Data Path Delay Metrics November 2012
5. A Singleton Definition for RRFD
This part defines a metric for forward data path delay when an LSP is
set up.
As described in [RFC6383], the completion of the RSVP-TE signaling
process does not necessarily mean that the cross-connections along
the LSP being set up are in place and ready to carry traffic. This
metric defines the time difference between the reception of a Resv
message by the ingress node and the completion of the cross-
connection programming along the forward data path.
5.1. Motivation
RRFD is useful for the following reasons:
o For the reasons described in [RFC6383], the data path may not be
ready for use instantly after the completion of the RSVP-TE
signaling process. The delay itself is part of the implementation
performance.
o The completion of the signaling process may be used by application
designers as an indication of data path connectivity. The
existence of this delay and the potential failure of cross-
connection programming, if not properly treated, will result in
data loss or application failure. The typical value of this delay
can thus help designers to improve the application model.
5.2. Metric Name
RRFD = Resv Received, Forward Data path
5.3. Metric Parameters
o ID0, the ingress Label Switching Router (LSR) ID
o ID1, the egress LSR ID
o T, a time when the setup is attempted
5.4. Metric Units
The value of RRFD is either a real number of milliseconds or
undefined.
Sun, et al. Standards Track [Page 7]
RFC 6777 LSP Data Path Delay Metrics November 2012
5.5. Definition
For a real number dT,
RRFD from ingress node ID0 to egress node ID1 at T is dT
means that
o ingress node ID0 sends a PATH message to egress node ID1,
o the last bit of the corresponding Resv message is received by
ingress node ID0 at T, and
o an error-free signal is received by egress node ID1 by using a
data-plane-specific test pattern at T+dT.
5.6. Discussion
The following issues are likely to come up in practice:
o The accuracy of RRFD depends on the clock resolution of both the
ingress node and egress node. Clock synchronization between the
ingress node and egress node is required.
o The accuracy of RRFD is also dependent on how the error-free
signal is received and may differ significantly when the
underlying data plane technology is different. For instance, for
an LSP between a pair of Ethernet interfaces, the ingress node may
use a rate-based method to verify the connectivity of the data
path and use the reception of the first error-free frame as the
error-free signal. In this case, the interval between two
successive frames has a significant impact on accuracy. It is
RECOMMENDED that the ingress node use small intervals, under the
condition that the injected traffic does not exceed the capacity
of the forward data path. The value of such intervals MUST be
reported.
o The accuracy of RRFD is also dependent on the time needed to
propagate the error-free signal from the ingress node to the
egress node. A typical value for propagating the error-free
signal from the ingress node to the egress node under the same
measurement setup MAY be reported. The methodology to obtain such
values is outside the scope of this document.
o The accuracy of this metric is also dependent on the physical-
layer serialization/deserialization of the test signal for certain
data path technologies. For instance, for an LSP between a pair
Sun, et al. Standards Track [Page 8]
RFC 6777 LSP Data Path Delay Metrics November 2012
of low-speed Ethernet interfaces, the time needed to serialize/
deserialize a large frame may not be negligible. In this case, it
is RECOMMENDED that the ingress node use small frames. The
average length of the frame MAY be reported.
o It is possible that under some implementations, a node may program
the cross-connection before it sends a PATH message further
downstream, and the data path may be ready for use before a Resv
message reaches the ingress node. In such cases, RRFD can be a
negative value. It is RECOMMENDED that a PRFD measurement be
carried out to further characterize the forward data path delay
when a negative RRFD value is observed.
o If an error-free signal is received by the egress node before a
PATH message is sent on the ingress node, an error MUST be
reported and the measurement SHOULD terminate.
o If the corresponding Resv message is received but no error-free
signal is received by the egress node within a reasonable period
of time, i.e., a threshold, RRFD MUST be treated as undefined.
The value of the threshold MUST be reported.
o If the LSP setup fails, this metric value MUST NOT be counted.
5.7. Methodologies
Generally, the methodology would proceed as follows:
o Make sure that the network has enough resources to set up the
requested LSP.
o Start the data path measurement and/or monitoring procedures on
the ingress node and egress node. If an error-free signal is
received by the egress node before a PATH message is sent, report
an error and terminate the measurement.
o At the ingress node, form the PATH message according to the LSP
requirements and send the message towards the egress node.
o Upon receiving the last bit of the corresponding Resv message,
take the timestamp (T1) on the ingress node as soon as possible.
o When an error-free signal is observed on the egress node, take the
timestamp (T2) as soon as possible. An estimate of RRFD (T2 - T1)
can be computed.
Sun, et al. Standards Track [Page 9]
RFC 6777 LSP Data Path Delay Metrics November 2012
o If the corresponding Resv message arrives but no error-free signal
is received within a reasonable period of time by the ingress
node, RRFD is deemed to be undefined.
o If the LSP setup fails, RRFD is not counted.
6. A Singleton Definition for RSRD
This part defines a metric for reverse data path delay when an LSP is
set up.
As described in [RFC6383], the completion of the RSVP-TE signaling
process does not necessarily mean that the cross-connections along
the LSP being set up are in place and ready to carry traffic. This
metric defines the time difference between the completion of the
signaling process and the completion of the cross-connection
programming along the reverse data path. This metric MAY be used
together with RRFD to characterize the data path delay of a
bidirectional LSP.
6.1. Motivation
RSRD is useful for the following reasons:
o For the reasons described in [RFC6383], the data path may not be
ready for use instantly after the completion of the RSVP-TE
signaling process. The delay itself is part of the implementation
performance.
o The completion of the signaling process may be used by application
designers as an indication of data path connectivity. The
existence of this delay and the possible failure of cross-
connection programming, if not properly treated, will result in
data loss or application failure. The typical value of this delay
can thus help designers to improve the application model.
6.2. Metric Name
RSRD = Resv Sent, Reverse Data path
6.3. Metric Parameters
o ID0, the ingress LSR ID
o ID1, the egress LSR ID
o T, a time when the setup is attempted
Sun, et al. Standards Track [Page 10]
RFC 6777 LSP Data Path Delay Metrics November 2012
6.4. Metric Units
The value of RSRD is either a real number of milliseconds or
undefined.
6.5. Definition
For a real number dT,
RSRD from ingress node ID0 to egress node ID1 at T is dT
means that
o ingress node ID0 sends a PATH message to egress node ID1,
o the last bit of the corresponding Resv message is sent by egress
node ID1 at T, and
o an error-free signal is received by the ingress node ID0 using a
data-plane-specific test pattern at T+dT.
6.6. Discussion
The following issues are likely to come up in practice:
o The accuracy of RSRD depends on the clock resolution of both the
ingress node and egress node. Clock synchronization between the
ingress node and egress node is required.
o The accuracy of RSRD is also dependent on how the error-free
signal is received and may differ significantly when the
underlying data plane technology is different. For instance, for
an LSP between a pair of Ethernet interfaces, the egress node
(sometimes the tester) may use a rate-based method to verify the
connectivity of the data path and use the reception of the first
error-free frame as the error-free signal. In this case, the
interval between two successive frames has a significant impact on
accuracy. It is RECOMMENDED in this case that the egress node use
small intervals, under the condition that the injected traffic
does not exceed the capacity of the reverse data path. The value
of the interval MUST be reported.
o The accuracy of RSRD is also dependent on the time needed to
propagate the error-free signal from the egress node to the
ingress node. A typical value for propagating the error-free
signal from the egress node to the ingress node under the same
measurement setup MAY be reported. The methodology to obtain such
values is outside the scope of this document.
Sun, et al. Standards Track [Page 11]
RFC 6777 LSP Data Path Delay Metrics November 2012
o The accuracy of this metric is also dependent on the physical-
layer serialization/deserialization of the test signal for certain
data path technologies. For instance, for an LSP between a pair
of low-speed Ethernet interfaces, the time needed to serialize/
deserialize a large frame may not be negligible. In this case, it
is RECOMMENDED that the egress node use small frames. The average
length of the frame MAY be reported.
o If the corresponding Resv message is sent but no error-free signal
is received by the ingress node within a reasonable period of
time, i.e., a threshold, RSRD MUST be treated as undefined. The
value of the threshold MUST be reported.
o If an error-free signal is received before a PATH message is sent
on the ingress node, an error MUST be reported and the measurement
SHOULD terminate.
o If the LSP setup fails, this metric value MUST NOT be counted.
6.7. Methodologies
Generally, the methodology would proceed as follows:
o Make sure that the network has enough resources to set up the
requested LSP.
o Start the data path measurement and/or monitoring procedures on
the ingress node and egress node. If an error-free signal is
received by the ingress node before a PATH message is sent, report
an error and terminate the measurement.
o At the ingress node, form the PATH message according to the LSP
requirements and send the message towards the egress node.
o Upon sending the last bit of the corresponding Resv message, take
the timestamp (T1) on the egress node as soon as possible.
o When an error-free signal is observed on the ingress node, take
the timestamp (T2) as soon as possible. An estimate of RSRD
(T2 - T1) can be computed.
o If the LSP setup fails, RSRD is not counted.
o If no error-free signal is received within a reasonable period of
time by the ingress node, RSRD is deemed to be undefined.
Sun, et al. Standards Track [Page 12]
RFC 6777 LSP Data Path Delay Metrics November 2012
7. A Singleton Definition for PRFD
This part defines a metric for forward data path delay when an LSP is
set up.
In an RSVP-TE implementation, when setting up an LSP, each node may
choose to program the cross-connection before it sends a PATH message
further downstream. In this case, the forward data path may become
ready for use before the signaling process completes, i.e., before
the Resv message reaches the ingress node. This metric can be used
to identify such an implementation practice and give useful
information to application designers.
7.1. Motivation
PRFD is useful for the following reasons:
o PRFD can be used to identify an RSVP-TE implementation practice in
which cross-connections are programmed before a PATH message is
sent downstream.
o The value of PRFD may also help application designers to fine-tune
their application model.
7.2. Metric Name
PRFD = PATH Received, Forward Data path
7.3. Metric Parameters
o ID0, the ingress LSR ID
o ID1, the egress LSR ID
o T, a time when the setup is attempted
7.4. Metric Units
The value of PRFD is either a real number of milliseconds or
undefined.
Sun, et al. Standards Track [Page 13]
RFC 6777 LSP Data Path Delay Metrics November 2012
7.5. Definition
For a real number dT,
PRFD from ingress node ID0 to egress node ID1 at T is dT
means that
o ingress node ID0 sends a PATH message to egress node ID1,
o the last bit of the PATH message is received by egress node ID1 at
T, and
o an error-free signal is received by the egress node ID1 using a
data-plane-specific test pattern at T+dT.
7.6. Discussion
The following issues are likely to come up in practice:
o The accuracy of PRFD depends on the clock resolution of the egress
node. Clock synchronization between the ingress node and egress
node is not required.
o The accuracy of PRFD is also dependent on how the error-free
signal is received and may differ significantly when the
underlying data plane technology is different. For instance, for
an LSP between a pair of Ethernet interfaces, the egress node
(sometimes the tester) may use a rate-based method to verify the
connectivity of the data path and use the reception of the first
error-free frame as the error-free signal. In this case, the
interval between two successive frames has a significant impact on
accuracy. It is RECOMMENDED in this case that the ingress node
use small intervals, under the condition that the injected traffic
does not exceed the capacity of the forward data path. The value
of the interval MUST be reported.
o The accuracy of PRFD is also dependent on the time needed to
propagate the error-free signal from the ingress node to the
egress node. A typical value for propagating the error-free
signal from the ingress node to the egress node under the same
measurement setup MAY be reported. The methodology to obtain such
values is outside the scope of this document.
o The accuracy of this metric is also dependent on the physical-
layer serialization/deserialization of the test signal for certain
data path technologies. For instance, for an LSP between a pair
Sun, et al. Standards Track [Page 14]
RFC 6777 LSP Data Path Delay Metrics November 2012
of low-speed Ethernet interfaces, the time needed to serialize/
deserialize a large frame may not be negligible. In this case, it
is RECOMMENDED that the ingress node use small frames. The
average length of the frame MAY be reported.
o If an error-free signal is received before a PATH message is sent,
an error MUST be reported and the measurement SHOULD terminate.
o If the LSP setup fails, this metric value MUST NOT be counted.
o This metric SHOULD be used together with RRFD. It is RECOMMENDED
that a PRFD measurement be carried out after a negative RRFD value
has already been observed.
7.7. Methodologies
Generally, the methodology would proceed as follows:
o Make sure that the network has enough resources to set up the
requested LSP.
o Start the data path measurement and/or monitoring procedures on
the ingress node and egress node. If an error-free signal is
received by the egress node before a PATH message is sent, report
an error and terminate the measurement.
o At the ingress node, form the PATH message according to the LSP
requirements and send the message towards the egress node.
o Upon receiving the last bit of the PATH message, take the
timestamp (T1) on the egress node as soon as possible.
o When an error-free signal is observed on the egress node, take the
timestamp (T2) as soon as possible. An estimate of PRFD (T2 - T1)
can be computed.
o If the LSP setup fails, PRFD is not counted.
o If no error-free signal is received within a reasonable period of
time by the egress node, PRFD is deemed to be undefined.
Sun, et al. Standards Track [Page 15]
RFC 6777 LSP Data Path Delay Metrics November 2012
8. A Singleton Definition for PSFD
This part defines a metric for forward data path delay when an LSP is
set up.
As described in [RFC6383], the completion of the RSVP-TE signaling
process does not necessarily mean that the cross-connections along
the LSP being set up are in place and ready to carry traffic. This
metric defines the time difference between the point when the PATH
message is sent by the ingress node and the completion of the cross-
connection programming along the LSP forward data path.
8.1. Motivation
PSFD is useful for the following reasons:
o For the reasons described in [RFC6383], the data path setup delay
may not be consistent with the control plane LSP setup delay. The
data path setup delay metric is more precise for LSP setup
performance measurement.
o The completion of the signaling process may be used by application
designers as an indication of data path connectivity. The
difference between the control plane setup delay and data path
delay, and the potential failure of cross-connection programming,
if not properly treated, will result in data loss or application
failure. This metric can thus help designers to improve the
application model.
8.2. Metric Name
PSFD = PATH Sent, Forward Data path
8.3. Metric Parameters
o ID0, the ingress LSR ID
o ID1, the egress LSR ID
o T, a time when the setup is attempted
8.4. Metric Units
The value of PSFD is either a real number of milliseconds or
undefined.
Sun, et al. Standards Track [Page 16]
RFC 6777 LSP Data Path Delay Metrics November 2012
8.5. Definition
For a real number dT,
PSFD from ingress node ID0 to egress node ID1 at T is dT
means that
o ingress node ID0 sends the first bit of a PATH message to egress
node ID1 at T, and
o an error-free signal is received by the egress node ID1 using a
data-plane-specific test pattern at T+dT.
8.6. Discussion
The following issues are likely to come up in practice:
o The accuracy of PSFD depends on the clock resolution of both the
ingress node and egress node. Clock synchronization between the
ingress node and egress node is required.
o The accuracy of PSFD is also dependent on how the error-free
signal is received and may differ significantly when the
underlying data plane technology is different. For instance, for
an LSP between a pair of Ethernet interfaces, the ingress node may
use a rate-based method to verify the connectivity of the data
path and use the reception of the first error-free frame as the
error-free signal. In this case, the interval between two
successive frames has a significant impact on accuracy. It is
RECOMMENDED that the ingress node use small intervals, under the
condition that the injected traffic does not exceed the capacity
of the forward data path. The value of the interval MUST be
reported.
o The accuracy of PSFD is also dependent on the time needed to
propagate the error-free signal from the ingress node to the
egress node. A typical value for propagating the error-free
signal from the ingress node to the egress node under the same
measurement setup MAY be reported. The methodology to obtain such
values is outside the scope of this document.
o The accuracy of this metric is also dependent on the physical-
layer serialization/deserialization of the test signal for certain
data path technologies. For instance, for an LSP between a pair
Sun, et al. Standards Track [Page 17]
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of low-speed Ethernet interfaces, the time needed to serialize/
deserialize a large frame may not be negligible. In this case, it
is RECOMMENDED that the ingress node use small frames. The
average length of the frame MAY be reported.
o If an error-free signal is received before a PATH message is sent,
an error MUST be reported and the measurement SHOULD terminate.
o If the LSP setup fails, this metric value MUST NOT be counted.
o If the PATH message is sent by the ingress node but no error-free
signal is received by the egress node within a reasonable period
of time, i.e., a threshold, PSFD MUST be treated as undefined.
The value of the threshold MUST be reported.
8.7. Methodologies
Generally, the methodology would proceed as follows:
o Make sure that the network has enough resources to set up the
requested LSP.
o Start the data path measurement and/or monitoring procedures on
the ingress node and egress node. If an error-free signal is
received by the egress node before a PATH message is sent, report
an error and terminate the measurement.
o At the ingress node, form the PATH message according to the LSP
requirements and send the message towards the egress node. A
timestamp (T1) may be stored locally in the ingress node when the
PATH message packet is sent towards the egress node.
o When an error-free signal is observed on the egress node, take the
timestamp (T2) as soon as possible. An estimate of PSFD (T2 - T1)
can be computed.
o If the LSP setup fails, PSFD is not counted.
o If no error-free signal is received within a reasonable period of
time by the egress node, PSFD is deemed to be undefined.
Sun, et al. Standards Track [Page 18]
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9. A Singleton Definition for PSRD
This part defines a metric for reverse data path delay when an LSP is
set up.
This metric defines the time difference between the point when the
ingress node sends the PATH message and the completion of the cross-
connection programming along the LSP reverse data path. This metric
MAY be used together with PSFD to characterize the data path delay of
a bidirectional LSP.
9.1. Motivation
PSRD is useful for the following reasons:
o For the reasons described in [RFC6383], the data path setup delay
may not be consistent with the control plane LSP setup delay. The
data path setup delay metric is more precise for LSP setup
performance measurement.
o The completion of the signaling process may be used by application
designers as an indication of data path connectivity. The
difference between the control plane setup delay and data path
delay, and the potential failure of cross-connection programming,
if not properly treated, will result in data loss or application
failure. This metric can thus help designers to improve the
application model.
9.2. Metric Name
PSRD = PATH Sent, Reverse Data path
9.3. Metric Parameters
o ID0, the ingress LSR ID
o ID1, the egress LSR ID
o T, a time when the setup is attempted
9.4. Metric Units
The value of PSRD is either a real number of milliseconds or
undefined.
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9.5. Definition
For a real number dT,
PSRD from ingress node ID0 to egress node ID1 at T is dT
means that
o ingress node ID0 sends the first bit of a PATH message to egress
node ID1 at T, and
o an error-free signal is received through the reverse data path
by the ingress node ID0 using a data-plane-specific test pattern
at T+dT.
9.6. Discussion
The following issues are likely to come up in practice:
o The accuracy of PSRD depends on the clock resolution of the
ingress node. Clock synchronization between the ingress node and
egress node is not required.
o The accuracy of PSRD is also dependent on how the error-free
signal is received and may differ significantly when the
underlying data plane technology is different. For instance, for
an LSP between a pair of Ethernet interfaces, the egress node may
use a rate-based method to verify the connectivity of the data
path and use the reception of the first error-free frame as the
error-free signal. In this case, the interval between two
successive frames has a significant impact on accuracy. It is
RECOMMENDED that the egress node use small intervals, under the
condition that the injected traffic does not exceed the capacity
of the forward data path. The value of the interval MUST be
reported.
o The accuracy of PSRD is also dependent on the time needed to
propagate the error-free signal from the egress node to the
ingress node. A typical value for propagating the error-free
signal from the egress node to the ingress node under the same
measurement setup MAY be reported. The methodology to obtain such
values is outside the scope of this document.
o The accuracy of this metric is also dependent on the physical-
layer serialization/deserialization of the test signal for certain
data path technologies. For instance, for an LSP between a pair
Sun, et al. Standards Track [Page 20]
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of low-speed Ethernet interfaces, the time needed to serialize/
deserialize a large frame may not be negligible. In this case, it
is RECOMMENDED that the egress node use small frames. The average
length of the frame MAY be reported.
o If an error-free signal is received before a PATH message is sent,
an error MUST be reported and the measurement SHOULD terminate.
o If the LSP setup fails, this metric value MUST NOT be counted.
o If the PATH message is sent by the ingress node but no error-free
signal is received by the ingress node within a reasonable period
of time, i.e., a threshold, PSRD MUST be treated as undefined.
The value of the threshold MUST be reported.
9.7. Methodologies
Generally, the methodology would proceed as follows:
o Make sure that the network has enough resources to set up the
requested LSP.
o Start the data path measurement and/or monitoring procedures on
the ingress node and egress node. If an error-free signal is
received by the egress node before a PATH message is sent, report
an error and terminate the measurement.
o At the ingress node, form the PATH message according to the LSP
requirements and send the message towards the egress node. A
timestamp (T1) may be stored locally in the ingress node when the
PATH message packet is sent towards the egress node.
o When an error-free signal is observed on the ingress node, take
the timestamp (T2) as soon as possible. An estimate of PSRD
(T2 - T1) can be computed.
o If the LSP setup fails, PSRD is not counted.
o If no error-free signal is received within a reasonable period of
time by the ingress node, PSRD is deemed to be undefined.
Sun, et al. Standards Track [Page 21]
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10. A Definition for Samples of Data Path Delay
In Sections 5, 6, 7, 8, and 9, we defined the singleton metrics of
data path delay. Now, we define how to get one particular sample of
such a delay. Sampling is done to select a particular portion of
singleton values of the given parameters. As in [RFC2330], we use
Poisson sampling as an example.
10.1. Metric Name
Type <X> data path delay sample, where X is either RRFD, RSRD, PRFD,
PSFD, or PSRD.
10.2. Metric Parameters
o ID0, the ingress LSR ID
o ID1, the egress LSR ID
o T0, a time
o Tf, a time
o Lambda, a rate in reciprocal milliseconds
o Th, the LSP holding time
o Td, the maximum waiting time for successful LSP setup
o Ts, the maximum waiting time for an error-free signal
10.3. Metric Units
A sequence of pairs; the elements of each pair are:
o T, a time when setup is attempted
o dT, either a real number of milliseconds or undefined
10.4. Definition
Given T0, Tf, and Lambda, compute a pseudo-random Poisson process
beginning at or before T0, with average arrival rate Lambda, and
ending at or after Tf. Those time values greater than or equal to T0
and less than or equal to Tf are then selected. At each of the times
in this process, we obtain the value of a data path delay sample of
type <X> at this time. The value of the sample is the sequence made
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up of the resulting <time, type <X> data path delay> pairs. If there
are no such pairs, the sequence is of length zero and the sample is
said to be empty.
10.5. Discussion
The following issues are likely to come up in practice:
o The parameters Lambda, Th, and Td should be carefully chosen, as
explained in the discussions for LSP setup delay (see [RFC5814]).
o The parameter Ts should be carefully chosen and MUST be reported
along with the LSP forward/reverse data path delay sample.
10.6. Methodologies
Generally, the methodology would proceed as follows:
o Select specific times, using the specified Poisson arrival
process.
o Set up the LSP and obtain the value of type <X> data path delay.
o Release the LSP after Th, and wait for the next Poisson arrival
process.
10.7. Typical Testing Cases
10.7.1. With No LSP in the Network
10.7.1.1. Motivation
Data path delay with no LSP in the network is important because this
reflects the inherent delay of a device implementation. The minimum
value provides an indication of the delay that will likely be
experienced when an LSP data path is configured under light traffic
load.
10.7.1.2. Methodologies
Make sure that there is no LSP in the network, and proceed with the
methodologies described in Section 10.6.
Sun, et al. Standards Track [Page 23]
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10.7.2. With a Number of LSPs in the Network
10.7.2.1. Motivation
Data path delay with a number of LSPs in the network is important
because it reflects the performance of an operational network with
considerable load. This delay may vary significantly as the number
of existing LSPs varies. It can be used as a scalability metric of a
device implementation.
10.7.2.2. Methodologies
o Set up the required number of LSPs.
o Wait until the network reaches a stable state.
o Then proceed with the methodologies described in Section 10.6.
11. Some Statistics Definitions for Metrics to Report
Given the samples of the performance metric, we now offer several
statistics of these samples to report. From these statistics, we can
draw some useful conclusions regarding a GMPLS network. The value of
these metrics is either a real number of milliseconds or undefined.
In the following discussion, we only consider the finite values.
11.1. The Minimum of the Metric
The minimum of the metric is the minimum of all the dT values in the
sample. In computing this, undefined values SHOULD be treated as
infinitely large. Note that this means that the minimum could thus
be undefined if all the dT values are undefined. In addition, the
metric minimum SHOULD be set to undefined if the sample is empty.
11.2. The Median of the Metric
The median of the metric is the median of the dT values in the given
sample. In computing the median, the undefined values MUST NOT be
included. The median SHOULD be set to undefined if all the dT values
are undefined, or if the sample is empty. When the number of defined
values in the given sample is small, the metric median may not be
typical and SHOULD be used carefully.
11.3. The Percentile of the Metric
The "empirical distribution function" (EDF) of a set of scalar
measurements is a function F(x), which, for any x, gives the
fractional proportion of the total measurements that were <= x.
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Given a percentage X, the Xth percentile of the metric means the
smallest value of x for which F(x) >= X. In computing the
percentile, undefined values MUST NOT be included.
See [RFC2330] for further details.
11.4. Failure Probability
Given the samples of the performance metric, we now offer two
statistics of failure events of these samples to report: Failure
Count and Failure Ratio. The two statistics can be applied to both
the forward data path and reverse data path. For example, when a
sample of RRFD has been obtained, the forward data path failure
statistics can be obtained, while a sample of RSRD can be used to
calculate the reverse data path failure statistics. Detailed
definitions of Failure Count and Failure Ratio are given below.
11.4.1. Failure Count
Failure Count is defined as the number of the undefined value of the
corresponding performance metric in a sample. The value of Failure
Count is an integer.
11.4.2. Failure Ratio
Failure Ratio is the percentage of the number of failure events to
the total number of requests in a sample. Here, a failure event
means that the signaling completes with no error, while no error-free
signal is observed. The calculation for Failure Ratio is defined as
follows:
Failure Ratio = Number of undefined value/(Number of valid metric
values + Number of undefined value) * 100%.
12. Security Considerations
In the control plane, since the measurement endpoints must be
conformant to signaling specifications and behave as normal signaling
endpoints, it will not incur security issues other than normal LSP
provisioning. However, the measurement parameters must be carefully
selected so that the measurements inject trivial amounts of
additional traffic into the networks they measure. If they inject
"too much" traffic, they can skew the results of the measurement and
in extreme cases cause congestion and denial of service.
In the data plane, the measurement endpoint MUST use a signal that is
consistent with what is specified in the control plane. For example,
in a packet switched case, the traffic injected into the data plane
Sun, et al. Standards Track [Page 25]
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MUST NOT exceed the specified rate in the corresponding LSP setup
request. In a wavelength switched case, the measurement endpoint
MUST use the specified or negotiated lambda with appropriate power.
The security considerations pertaining to the original RSVP protocol
[RFC2205] and its TE extensions [RFC3209] also remain relevant.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, September 1999.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
13.2. Informative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[RFC5814] Sun, W. and G. Zhang, "Label Switched Path (LSP) Dynamic
Provisioning Performance Metrics in Generalized MPLS
Networks", RFC 5814, March 2010.
[RFC6383] Shiomoto, K. and A. Farrel, "Advice on When It Is Safe to
Start Sending Data on Label Switched Paths Established
Using RSVP-TE", RFC 6383, September 2011.
Sun, et al. Standards Track [Page 26]
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Appendix A. Acknowledgements
We wish to thank Adrian Farrel, Lou Berger, and Al Morton for their
comments and help. We also wish to thank Klaas Wierenga and Alexey
Melnikov for their reviews.
This document contains ideas as well as text that have appeared in
existing IETF documents. The authors wish to thank G. Almes, S.
Kalidindi, and M. Zekauskas.
We also wish to thank Weisheng Hu, Yaohui Jin, and Wei Guo in the
state key laboratory of advanced optical communication systems and
networks for their valuable comments. We also wish to thank the
National Natural Science Foundation of China (NSFC) and the
863 program of China for their support.
Sun, et al. Standards Track [Page 27]
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Appendix B. Contributors
Bin Gu
IXIA
Oriental Kenzo Plaza 8M, 48 Dongzhimen Wai Street
Dongcheng District
Beijing 200240
China
Phone: +86 13611590766
EMail: BGu@ixiacom.com
Xueqin Wei
Fiberhome Telecommunication Technology Co., Ltd.
Wuhan
China
Phone: +86 13871127882
EMail: xqwei@fiberhome.com.cn
Tomohiro Otani
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Kamifukuoka Saitama
356-8502
Japan
Phone: +81-49-278-7357
EMail: tm-otani@kddi.com
Ruiquan Jing
China Telecom Beijing Research Institute
118 Xizhimenwai Avenue
Beijing 100035
China
Phone: +86-10-58552000
EMail: jingrq@ctbri.com.cn
Sun, et al. Standards Track [Page 28]
RFC 6777 LSP Data Path Delay Metrics November 2012
Authors' Addresses
Weiqiang Sun (editor)
Shanghai Jiao Tong University
800 Dongchuan Road
Shanghai 200240
China
Phone: +86 21 3420 5359
EMail: sun.weiqiang@gmail.com
Guoying Zhang (editor)
China Academy of Telecommunication Research, MIIT, China
No. 52 Hua Yuan Bei Lu, Haidian District
Beijing 100191
China
Phone: +86 1062300103
EMail: zhangguoying@catr.cn
Jianhua Gao
Huawei Technologies Co., Ltd.
China
Phone: +86 755 28973237
EMail: gjhhit@huawei.com
Guowu Xie
University of California, Riverside
900 University Ave.
Riverside, CA 92521
USA
Phone: +1 951 237 8825
EMail: xieg@cs.ucr.edu
Rajiv Papneja
Huawei Technologies
Santa Clara, CA 95050
Reston, VA 20190
USA
EMail: rajiv.papneja@huawei.com
Sun, et al. Standards Track [Page 29]