Internet DRAFT - draft-ietf-mpls-tp-temporal-hitless-psm
draft-ietf-mpls-tp-temporal-hitless-psm
Network Working Group A. D'Alessandro
Internet-Draft Telecom Italia
Intended status: Informational L. Andersson
Expires: March 5, 2018 Huawei Technologies
S. Ueno
NTT Communications
K. Arai
Y. Koike
NTT
September 1, 2017
Requirements for hitless MPLS path segment monitoring
draft-ietf-mpls-tp-temporal-hitless-psm-14.txt
Abstract
One of the most important OAM capabilities for transport network
operation is fault localisation. An in-service, on-demand segment
monitoring function of a transport path is indispensable,
particularly when the service monitoring function is activated only
between end points. However, the current segment monitoring approach
defined for MPLS (including the transport profile (MPLS-TP)) in RFC
6371 "Operations, Administration, and Maintenance Framework for MPLS-
Based Transport Networks" has drawbacks. This document provides an
analysis of the existing MPLS-TP OAM mechanisms for the path segment
monitoring and provides requirements to guide the development of new
OAM tools to support a Hitless Path Segment Monitoring (HPSM).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 5, 2018.
D'Alessandro, et al. Expires March 5, 2018 [Page 1]
Internet-Draft Hitless path segment monitoring September 2017
Copyright Notice
Copyright (c) 2017 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
to this document. Code Components extracted from this document must
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
4. Requirements for Hitless Path Segment Monitoring . . . . . . 7
4.1. Backward compatibility . . . . . . . . . . . . . . . . . 7
4.2. Non-intrusive segment monitoring . . . . . . . . . . . . 8
4.3. Multiple segments monitoring . . . . . . . . . . . . . . 8
4.4. Single and multiple level monitoring . . . . . . . . . . 8
4.5. HPSM and end-to-end proactive monitoring independence . . 9
4.6. Arbitrary segment monitoring . . . . . . . . . . . . . . 10
4.7. Fault while HPSM is operational . . . . . . . . . . . . . 11
4.8. HPSM Manageability . . . . . . . . . . . . . . . . . . . 12
4.9. Supported OAM functions . . . . . . . . . . . . . . . . . 13
5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
According to the MPLS-TP OAM requirements RFC 5860 [RFC5860],
mechanisms MUST be available for alerting service providers of faults
or defects that affects their services. In addition, to ensure that
faults or service degradation can be localized, operators need a
function to diagnose the detected problem. Using end-to-end
D'Alessandro, et al. Expires March 5, 2018 [Page 2]
Internet-Draft Hitless path segment monitoring September 2017
monitoring for this purpose is insufficient in that an operator will
not be able to localize a fault or service degradation accurately.
A segment monitoring function that can focus on a specific segment of
a transport path and that can provide a detailed analysis is
indispensable to promptly and accurately localize the fault. A path
segment monitoring function has been defined to perform this task for
MPLS-TP. However, as noted in the MPLS-TP OAM Framework RFC 6371
[RFC6371], the current method for segment monitoring of a transport
path has implications that hinder the usage in an operator network.
This document, after elaborating on the problem statement for the
path segment monitoring function as it is currently defined, provides
requirements for an on-demand segment monitoring function without
traffic distruption. Further works are required to evaluate how
proposed requirements match with current MPLS architecture and to
identify possibile solutions.
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 RFC 2119 [RFC2119].
2.1. Terminology
HPSM - Hitless Path Segment Monitoring
LSP - Label Switched Path
LSR - Label Switching Router
ME - Maintenance Entity
MEG - Maintenance Entity Group
MEP - Maintenance Entity Group End Point
MIP - Maintenance Entity Group Intermediate Point
OTN - Optical Transport Network
TCM - Tandem connection monitoring
SPME - Sub-path Maintenance Element
D'Alessandro, et al. Expires March 5, 2018 [Page 3]
Internet-Draft Hitless path segment monitoring September 2017
3. Problem Statement
To monitor (and to protect and/or manage) MPLS-TP network segments a
Sub-Path Maintenance Element (SPME) function has been defined in RFC
5921 [RFC5921]. The SPME is defined between the edges of the segment
of a transport path that needs to be monitored, protected, or
managed. SPME is created by stacking the shim header (MPLS header)
according to RFC 3031 [RFC3031] and it is defined as the segment
where the header is stacked. OAM messages can be initiated at the
edge of the SPME and sent to the peer edge of the SPME or to a MIP
along the SPME by setting the TTL value of the label stack entry
(LSE) and interface identifier value at the corresponding
hierarchical LSP level in case of a per-node model.
MPLS-TP segment monitoring should satisfy two network objectives
according to section 3.8 of RFC 6371 [RFC6371]:
(N1) The monitoring and maintenance of current transport paths has
to be conducted in-service without traffic disruption.
(N2) Segment monitoring must not modify the forwarding of the
segment portion of the transport path.
The SPME function that has been defined in RFC 5921 [RFC5921] has
the following drawbacks:
(P1) It increases network management complexity, because a new
sublayer and new MEPs and MIPs have to be configured for the SPME.
(P2) Original conditions of the path change.
(P3) The client traffic over a transport path is disrupted if the
SPME is configured on-demand.
Problem (P1) is related to the management of each additional sub-
layer required for segment monitoring in a MPLS-TP network. When an
SPME is applied to administer on-demand OAM functions in MPLS-TP
networks, a rule for operationally differentiating those SPME will be
required at least within an administrative domain. This forces
operators to implement at least an additional layer into the
management systems that will only be used for on-demand path segment
monitoring. From the perspective of operation, increasing the number
of managed layers and managed addresses/identifiers is not desirable
in view of keeping the management systems as simple as possible.
Moreover, using the currently defined methods, on-demand setting of
SPMEs causes problems (P2) and (P3) due to additional label stacking.
D'Alessandro, et al. Expires March 5, 2018 [Page 4]
Internet-Draft Hitless path segment monitoring September 2017
Problem (P2) arises from the fact that MPLS exposed label value and
MPLS frames length changes. The monitoring function should monitor
the status without changing any condition of the target, to be
monitored, segment or transport path. Changing the settings of the
original shim header should not be allowed because this change
corresponds to creating a new segment of the original transport path
that differs from the original one. When the conditions of the path
change, the measured values or observed data will also change and
this may make the monitoring meaningless because the result of the
measurement would no longer reflect the performance of the connection
where the original fault or degradation occurred. As an example,
setting up an on-demand SPME will result in the LSRs within the
monitoring segment only looking at the added (stacked) labels and not
at the labels of the original LSP. This means that problems stemming
from incorrect (or unexpected) treatment of labels of the original
LSP by the nodes within the monitored segment cannot be identified
when setting up SPME. This might include hardware problems during
label look-up, mis-configuration, etc. Therefore operators have to
pay extra attention to correctly setting and checking the label
values of the original LSP in the configuration. Of course, the
reverse of this situation is also possible, e.g., an incorrect or
unexpected treatment of SPME labels can result in false detection of
a fault where no problem existed originally.
Figure 1 shows an example of SPME settings. In the figure, "X" is
the label value of the original path expected at the tail-end of node
D. "210" and "220" are label values allocated for SPME. The label
values of the original path are modified as well as the values of the
stacked labels. As shown in Figure 1, SPME changes both the length
of MPLS frames and the label value(s). In particular, performance
monitoring measurements (e.g. Delay Measurement and Packet Loss
Measurement) are sensitive to these changes. As an example,
increasing the packet lenght may impact on packet loss due to MTU
settings, modifying the label stack may introduce packet loss or it
may fix packet loss depending on the configuration status so
modifying network conditions. Such changes influence packets delay
too even if, from a practical point of view, it is likely that only a
few services will experience a practical impact.
D'Alessandro, et al. Expires March 5, 2018 [Page 5]
Internet-Draft Hitless path segment monitoring September 2017
(Before SPME settings)
--- --- --- --- ---
| | | | | | | | | |
| | | | | | | | | |
--- --- --- --- ---
A--100--B--110--C--120--D--130--E <= transport path
MEP MEP
(After SPME settings)
--- --- --- --- ---
| | | | | | | | | |
| | | | | | | | | |
--- --- --- --- ---
A--100--B-----------X---D--130--E <= transport path
MEP MEP
210--C--220 <= SPME
MEP' MEP'
Figure 1: SPME settings example
Problem (P3) can be avoided if the operator sets SPMEs in advance and
maintains them until the end of life of a transport path. But this
does not support on-demand. Furthermore SMPEs cannot be set
arbitrarily because overlapping of path segments is limited to
nesting relationships. As a result, possible SPME configurations of
segments of an original transport path are limited due to the
characteristic of the SPME shown in Figure 1, even if SPMEs are pre-
configured.
Although the make-before-break procedure in the survivability
document RFC 6372 [RFC6372] supports configuration for monitoring
according to the framework document RFC 5921 [RFC5921], without
traffic distruption, the configuration of an SPME is not possible
without violating network objective (N2). These concerns are
described in section 3.8 of RFC 6371 [RFC6371].
Additionally, the make-before-break approach typically relies on a
control plane and requires additional functionalities for a
management system to properly support SPME creation and traffic
switching from the original transport path to the SPME.
As an example, the old and new transport resources (e.g. LSP
tunnels) might compete with each other for resources which they have
in common. Depending on availability of resources, this competition
can cause admission control to prevent the new LSP tunnel from being
established as this bandwidth accounting deviates from traditional
(non control plane) management system operation. While SPMEs can be
D'Alessandro, et al. Expires March 5, 2018 [Page 6]
Internet-Draft Hitless path segment monitoring September 2017
applied in any network context (single domain, multi domain, single
carrier, multi carrier, etc.), the main applications are in inter-
carrier or inter-domain segment monitoring where they are typically
pre- configured or pre-instantiated. SPME instantiates a
hierarchical path (introducing MPLS label stacking) through which OAM
packets can be sent. The SPME monitoring function is also mainly
important for protecting bundles of transport paths and carriers'
carrier solutions within an administrative domain.
The analogy for SPME in other transport technologies is Tandem
Connection Monitoring (TCM), used in Optical Transport Networks (OTN)
and Ethernet transport networks, which supports on-demand but does
not affect the path. For example in OTN, TCM allows the insertion
and removal of performance monitoring overhead within the frame at
intermediate points in the network. It is done such that their
insertion and removal do not change the conditions of the path.
Though as the OAM overhead is part of the frame (designated overhead
bytes), it is constrained to a pre-defined number of monitoring
segments.
To summarize: the problem statement is that the current sub-path
maintenance based on a hierarchical LSP (SPME) is problematic for
pre-configuration in terms of increasing the number of managed
objects by layer stacking and identifiers/addresses. An on-demand
configuration of SPME is one of the possible approaches for
minimizing the impact of these issues. However, the current
procedure is unfavourable because the on-demand configuration for
monitoring changes the condition of the original monitored path. To
avoid or minimize the impact of the drawbacks discussed above, a more
efficient approach is required for the operation of an MPLS-TP
transport network. A monitoring mechanism, named Hitless Path
Segment Monitoring (HPSM), supporting on-demand path segment
monitoring without traffic disruption is needed.
4. Requirements for Hitless Path Segment Monitoring
In the following sections, mandatory (M) and optional (O)
requirements for the Hitless Path Segment Monitoring function are
listed.
4.1. Backward compatibility
HPSM would be an additional OAM tool that would not replace SPME. As
such:
(M1) HPSM MUST be compatible with the usage of SPME
(O1) HPSM SHOULD be applicable at the SPME layer too
D'Alessandro, et al. Expires March 5, 2018 [Page 7]
Internet-Draft Hitless path segment monitoring September 2017
(M2) HPSM MUST support both the per-node and per-interface model
as specified in RFC 6371 [RFC6371].
4.2. Non-intrusive segment monitoring
One of the major problems of legacy SPME highlighted in section 3 is
that it may not monitor the original path and it could disrupt
service traffic when set-up on demand.
(M3) HPSM MUST NOT change the original conditions of transport
path (e.g. must not change the length of MPLS frames, the exposed
label values, etc.)
(M4) HPSM MUST support on-demand provisioning without traffic
disruption.
4.3. Multiple segments monitoring
Along a transport path there may be the need to support
simultaneously monitoring multiple segments
(M5) HPSM MUST support configuration of multiple monitoring
segments along a transport path.
--- --- --- --- ---
| | | | | | | | | |
| A | | B | | C | | D | | E |
--- --- --- --- ---
MEP MEP <= ME of a transport path
*------* *----* *--------------* <=three HPSM monit. instances
Figure 2: Multiple HPSM instances example
4.4. Single and multiple level monitoring
HPSM would apply mainly for on-demand diagnostic purposes. With the
currently defined approach, the most serious problem is that there is
no way to locate the degraded segment of a path without changing the
conditions of the original path. Therefore, as a first step, a
single level, single segment monitoring, not affecting the monitored
path, is required for HPSM. A combination of multi-level and
simultaneous segments monitoring is the most powerful tool for
accurately diagnosing the performance of a transport path. However,
in the field, a single level, multiple segments approach would be
less complex for management and operations.
D'Alessandro, et al. Expires March 5, 2018 [Page 8]
Internet-Draft Hitless path segment monitoring September 2017
(M6) HPSM MUST support single-level segment monitoring
(O2) HPSM MAY support multi-level segment monitoring.
Figure 3 shows an example of multi-level HPSM.
--- --- --- --- ---
| | | | | | | | | |
| A | | B | | C | | D | | E |
--- --- --- --- ---
MEP MEP <= ME of a transport path
*-----------------* <=On-demand HPSM level 1
*-------------* <=On-demand HPSM level 2
*-* <=On-demand HPSM level 3
Figure 3: Multi-level HPSM example
4.5. HPSM and end-to-end proactive monitoring independence
There is a need for simultaneously using existing end-to-end
proactive monitoring and on-demand path segment monitoring.
Normally, the on-demand path segment monitoring is configured on a
segment of a maintenance entity of a transport path. In such an
environment, on-demand single-level monitoring should be performed
without disrupting the pro-active monitoring of the targeted end-to-
end transport path to avoid affecting user traffic performance
monitoring.
(M7) HPSM MUST support the capability of being operated
concurrently to, and independently of OAM function operated on the
end-to-end path
--- --- --- --- ---
| | | | | | | | | |
| A | | B | | C | | D | | E |
--- --- --- --- ---
MEP MEP <= ME of a transport path
+-----------------------------+ <= Pro-active end-to-end mon.
*------------------* <= On-demand HPSM
Figure 4: Independence between proactive end-to-end monitoring and
on-demand HPSM
D'Alessandro, et al. Expires March 5, 2018 [Page 9]
Internet-Draft Hitless path segment monitoring September 2017
4.6. Arbitrary segment monitoring
The main objective for on-demand segment monitoring is to diagnose
the fault locations. A possible realistic diagnostic procedure is to
fix one end point of a segment at the MEP of the transport path under
observation and change progressively the length of the segments. It
is therefore possible to monitoring step by step all the path with a
granularity that depends on equipment implementations. For example,
Figure 5 shows the case where the granularity is at interface level
(i.e. monitoring is at each input interface and output interface of
each piece of equipment).
--- --- --- --- ---
| | | | | | | | | |
| A | | B | | C | | D | | E |
--- --- --- --- ---
MEP MEP <= ME of a transport path
+-----------------------------+ <= Pro-active end-to-end mon.
*-----* <= 1st on-demand HPSM
*-------* <= 2nd on-demand HPSM
| |
| |
*-----------------------* <= 4th on-demand HPSM
*-----------------------------* <= 5th on-demand HPSM
Figure 5: Localization of a defect by consecutive on-demand segment
monitoring procedure
Another possible scenario is depicted in Figure 6. In this case, the
operator wants to diagnose a transport path starting at a transit
node, because the end nodes (A and E) are located at customer sites
and consist of small boxes supporting only a subset of OAM functions.
In this case, where the source entities of the diagnostic packets are
limited to the position of MEPs, on-demand segment monitoring will be
ineffective because not all the segments can be diagnosed (e.g.
segment monitoring HPSM 3 in Figure 6 is not available and it is not
possible to determine the fault location exactly).
(M8) It SHALL be possible to provision HPSM on an arbitrary
segment of a transport path.
D'Alessandro, et al. Expires March 5, 2018 [Page 10]
Internet-Draft Hitless path segment monitoring September 2017
--- --- ---
--- | | | | | | ---
| A | | B | | C | | D | | E |
--- --- --- --- ---
MEP MEP <= ME of a transport path
+-----------------------------+ <= Pro-active end-to-end mon.
*-----* <= On-demand HPSM 1
*-----------------------* <= On-demand HPSM 2
*---------* <= On-demand HPSM 3
Figure 6: HPSM configuration at arbitrary segments
4.7. Fault while HPSM is operational
Node or link failures may occur while HPSM is active. In this case,
if no resiliency mechanism is set-up on the subtended transport path,
there is no particular requirement for HPSM. If the transport path
is protected, the HPSM function may bring to monitoring unintended
segments. The following examples are provided for clarification.
Protection scenario A is shown in figure 7. In this scenario a
working LSP and a protection LSP are set-up. HPSM is activated
between nodes A and E. When a fault occurs between nodes B and C,
the operation of HPSM is not affected by the protection switch and
continues on the active LSP path.
A - B - C - D - E - F
\ /
G - H - I - L
Where:
- end-to-end LSP: A-B-C-D-E-F
- working LSP: A-B-C-D-E-F
- protection LSP: A-G-H-I-L-F
- HPSM: A-E
Figure 7: Protection scenario A
Protection scenario B is shown in figure 8. The difference with
scenario A is that only a portion of the transport path is protected.
In this case, when a fault occurs between nodes B and C on the
working sub-path B-C-D, traffic will be switched to protection sub-
path B-G-H-D. Assuming that OAM packet termination depends only on
the TTL value of the MPLS label header, the target node of the HPSM
changes from E to D due to the difference of hop counts between the
D'Alessandro, et al. Expires March 5, 2018 [Page 11]
Internet-Draft Hitless path segment monitoring September 2017
working path route (A-B-C-D-E: 4 hops) and protection path route
(A-B-G-H-D-E: 5 hops). In this case the operation of HPSM is
affected.
A - B - C - D - E - F
\ /
G - H
- end-to-end LSP: A-B-C-D-E-F
- working sub-path: B-C-D
- protection sub-path: B-G-H-D
- HPSM: A-E
Figure 8: Protection scenario B
(M9) The HPSM SHOULD avoid monitoring an unintended segment when
one or more failures occur
There are potentially different solutions to satisfy such a
requirement. A possible solution may be to suspend HPSM monitoring
until network restoration takes place. Another possible approach may
be to compare the node/interface ID in the OAM packet with that at
the node reached at TTL termination and if this does not match
through some means trigger a suspension of HPSM monitoring. The
above approaches are valid in any circumstance, both for protected
and unprotected networks LSPs. These examples should not be taken to
limit the design of a solution.
4.8. HPSM Manageability
From managing perspective, increasing the number of managed layers
and managed addresses/identifiers is not desirable in view of keeping
the management systems as simple as possible.
(M10)HPSM SHOULD NOT be based on additional transport layers (e.g.
hierarchical LSPs)
(M11) The same identifiers used for MIPs and/or MEPs SHOULD be
applied to maintenance points for the HPSM when they are
instantiated in the same place along a transport path.
Anyway maintenance points for the HPSM may be different from MIPs
and MEPs functional components as defined in the OAM framework
document RFC 6371 [RFC6371]. Investigating potential solutions
for satisfying proposed HPSM requirements might lead to propose
new functional components that have to be backward compatible with
D'Alessandro, et al. Expires March 5, 2018 [Page 12]
Internet-Draft Hitless path segment monitoring September 2017
MPLS architecture. Solutions are outside the scope of this
document.
4.9. Supported OAM functions
A maintenance point supporting the HPSM function has to be able to
generate and inject OAM packets. OAM functions that may be
applicable for on-demand HPSM are basically the on-demand performance
monitoring functions which are defined in the OAM framework document
RFC 6371 [RFC6371]. The "on-demand" attribute is typically temporary
for maintenance operation.
(M12) HPSM MUST support Packet Loss and Packet Delay measurement.
That because these functions are normally only supported at the end
points of a transport path. If a defect occurs, it might be quite
hard to locate the defect or degradation point without using the
segment monitoring function. If an operator cannot locate or narrow
down the cause of the fault, it is quite difficult to take prompt
actions to solve the problem.
Other on-demand monitoring functions (e.g. Delay Variation
measurement) are desirable but not as necessary as the functions
mentioned above.
(O3) HPSM MAY support Packet Delay variation, Throughput
measurement and other performance monitoring and fault management
functions.
Support of out-of-service on-demand performance management functions
(e.g. Throughput measurement) is not required for HPSM.
5. Summary
A new hitless path segment monitoring (HPSM) mechanism is required to
provide on-demand segment monitoring without traffic disruption. It
shall meet the two network objectives described in section 3.8 of RFC
6371 [RFC6371] and summarized in Section 3 of this document.
The mechanism should minimize the problems described in Section 3,
i.e. (P1), (P2) and (P3).
The solution for the on-demand segment monitoring without traffic
disruption needs to cover both the per-node model and the per-
interface model specified in RFC 6371 [RFC6371].
The on-demand segment monitoring without traffic disruption solution
needs to support on-demand Packet Loss Measurement and Packet Delay
D'Alessandro, et al. Expires March 5, 2018 [Page 13]
Internet-Draft Hitless path segment monitoring September 2017
Measurement functions and optionally other performance monitoring and
fault management functions (e.g. Throughput measurement, Packet
Delay variation measurement, Diagnostic test, etc.).
6. Security Considerations
Security is a significant requirement of MPLS Transport Profile. The
document provides a problem statement and requirements to guide the
development of new OAM tools to support Hitless Path Segment
Monitoring. Such new tools must follow the security considerations
provided in OAM Requirements for MPLS-TP in RFC5860 [RFC5860].
7. IANA Considerations
There are no requests for IANA actions in this document.
Note to the RFC Editor - this section can be removed before
publication.
8. Contributors
Manuel Paul
Deutsche Telekom AG
Email: manuel.paul@telekom.de
9. Acknowledgements
The authors would also like to thank Alexander Vainshtein, Dave
Allan, Fei Zhang, Huub van Helvoort, Malcolm Betts, Italo Busi,
Maarten Vissers, Jia He and Nurit Sprecher for their comments and
enhancements to the text.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001, <https://www.rfc-
editor.org/info/rfc3031>.
D'Alessandro, et al. Expires March 5, 2018 [Page 14]
Internet-Draft Hitless path segment monitoring September 2017
[RFC5860] Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
"Requirements for Operations, Administration, and
Maintenance (OAM) in MPLS Transport Networks", RFC 5860,
DOI 10.17487/RFC5860, May 2010, <https://www.rfc-
editor.org/info/rfc5860>.
10.2. Informative References
[RFC5921] Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
<https://www.rfc-editor.org/info/rfc5921>.
[RFC6371] Busi, I., Ed. and D. Allan, Ed., "Operations,
Administration, and Maintenance Framework for MPLS-Based
Transport Networks", RFC 6371, DOI 10.17487/RFC6371,
September 2011, <https://www.rfc-editor.org/info/rfc6371>.
[RFC6372] Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
Profile (MPLS-TP) Survivability Framework", RFC 6372,
DOI 10.17487/RFC6372, September 2011, <https://www.rfc-
editor.org/info/rfc6372>.
Authors' Addresses
Alessandro D'Alessandro
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: alessandro.dalessandro@telecomitalia.it
Loa Andersson
Huawei Technologies
Email: loa@mail01.huawei.com
Satoshi Ueno
NTT Communications
Email: satoshi.ueno@ntt.com
D'Alessandro, et al. Expires March 5, 2018 [Page 15]
Internet-Draft Hitless path segment monitoring September 2017
Kaoru Arai
NTT
Email: arai.kaoru@lab.ntt.co.jp
Yoshinori Koike
NTT
Email: y.koike@vcd.nttbiz.com
D'Alessandro, et al. Expires March 5, 2018 [Page 16]
