DetNet F. Theoleyre
Internet-Draft CNRS
Intended status: Standards Track G. Papadopoulos
Expires: April 28, 2021 IMT Atlantique
G. Mirsky
ZTE Corp.
CJ. Bernardos
UC3M
October 25, 2020
Operations, Administration and Maintenance (OAM) features for DetNet
draft-theoleyre-detnet-oam-support-00
Abstract
Deterministic Networking (DetNet), as defined in RFC 8655, is aimed
to provide a bounded end-to-end latency on top of the network
infrastructure, comprising both Layer 2 bridged and Layer 3 routed
segments. This document's primary purpose is to detail the specific
requirements of the Operation, Administration, and Maintenance (OAM)
recommended to maintain a deterministic network. With the
implementation of the OAM framework in DetNet, an operator will have
a real-time view of the network infrastructure regarding the
network's ability to respect the Service Level Objective (SLO), such
as packet delay, delay variation, and packet loss ratio, assigned to
each data flow.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 28, 2021.
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Table of Contents
1. TEMPORARY EDITORIAL NOTES . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Role of OAM in DetNet . . . . . . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Information Collection . . . . . . . . . . . . . . . . . 5
4.2. Continuity Check . . . . . . . . . . . . . . . . . . . . 5
4.3. Connectivity Verification . . . . . . . . . . . . . . . . 6
4.4. Route Tracing . . . . . . . . . . . . . . . . . . . . . . 6
4.5. Fault Verification/detection . . . . . . . . . . . . . . 6
4.6. Fault Isolation/identification . . . . . . . . . . . . . 7
5. Administration . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Collection of metrics . . . . . . . . . . . . . . . . . . 7
5.2. Worst-case metrics . . . . . . . . . . . . . . . . . . . 7
6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Replication / Elimination . . . . . . . . . . . . . . . . 8
6.2. Resource Reservation . . . . . . . . . . . . . . . . . . 8
6.3. Soft transition after reconfiguration . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. TEMPORARY EDITORIAL NOTES
This document is an Internet Draft, so it is work-in-progress by
nature. It contains the following work-in-progress elements:
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o "TODO" statements are elements which have not yet been written by
the authors for some reason (lack of time, ongoing discussions
with no clear consensus, etc). The statement does indicate that
the text will be written at some time.
2. Introduction
Deterministic Networking (DetNet) [RFC8655] has proposed to provide a
bounded end-to-end latency on top of the network infrastructure,
comprising both Layer 2 bridged and Layer 3 routed segments. Their
work encompasses the data plane, OAM, time synchronization,
management, control, and security aspects.
Operations, Administration, and Maintenance (OAM) Tools are of
primary importance for IP networks [RFC7276]. DetNet OAM should
provide a toolset for fault detection, localization, and performance
measurement.
This document's primary purpose is to detail the specific
requirements of the OAM features recommended to maintain a
deterministic/reliable network. Specifically, it investigates the
requirements for a deterministic network, supporting critical flows.
In this document, the term OAM will be used according to its
definition specified in [RFC6291]. DetNet expects to implement an
OAM framework to maintain a real-time view of the network
infrastructure, and its ability to respect the Service Level
Objectives (SLO), such as packet delay, delay variation, and packet
loss ratio, assigned to each data flow.
2.1. Terminology
The following terms are used througout this document as defined
below:
o OAM entity: a data flow to be monitored for defects and/or its
performance metrics measured.
o Maintenance End Point (MEP): OAM systems traversed by a data flow
when entering/exiting the network. In DetNet, it corresponds with
the source and destination of a data flow. OAM messages can be
exchanged between two MEPs.
o Maintenance Intermediate endPoint (MIP): an OAM system along the
flow; a MIP MAY respond to an OAM message generated by the MEP.
o Control and management plane: the control and management planes
are used to configure and control the network (long-term).
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Relative to a data flow, the control and/or management plane can
be out-of-band.
o Active measurement methods (as defined in [RFC7799]) modify a
normal data flow by inserting novel fields, injecting specially
constructed test packets [RFC2544]). It is critical for the
quality of information obtained using an active method that
generated test packets are in-band with the monitored data flow.
In other words, a test packet is required to cross the same
network nodes and links and receive the same Quality of Service
(QoS) treatment as a data packet.
o Passive measurement methods [RFC7799] infer information by
observing unmodified existing flows.
o Hybrid measurement methods [RFC7799] is the combination of
elements of both active and passive measurement methods.
2.2. Acronyms
OAM: Operations, Administration, and Maintenance
DetNet: Deterministic Networking
SLO: Service Level Objective
QoS: Quality of Service
SNMP: Simple Network Management Protocol
SDN: Software Defined Network
<TODO> we need here an exhaustive list, to be completed after the
document has evolved.
2.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Role of OAM in DetNet
DetNet networks expect to provide communications with predictable low
packet delay and packet loss. Most critical applications will define
an SLO to be required for the data flows it generates.
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To respect strict guarantees, DetNet can use an orchestrator able to
monitor and maintain the network. Typically, a Software-Defined
Network (SDN) controller places DetNet flows in the deployed network
based on their the SLO. Thus, resources have to be provisioned a
priori for the regular operation of the network. OAM represents the
essential elements of the network operation and necessary for OAM
resources that need to be accounted for to maintain the network
operational.
Fault-tolerance also assumes that multiple paths could be provisioned
so that an end-to-end circuit is maintained by adapting to the
existing conditions. The central controller/orchestrator typically
controls the Packet Replication, Elimination, and Ordering Functions
(PREOF) on a node. OAM is expected to support monitoring and
troubleshooting PREOF on a particular node and within the domain.
Note that PREOF can also be controlled by a set of distributed
controllers, in those scenarios where DetNet solutions involve more
than one single central controller.
4. Operation
OAM features will enable DetNet with robust operation both for
forwarding and routing purposes.
4.1. Information Collection
Information about the state of the network can be collected using
several mechanisms. Some protocols, e.g., Simple Network Management
Protocol (SNMP), send queries. Others, e.g., YANG-based data models,
generate notifications based on the publish-subscribe method. In
either way, information about the state of the network being
collected and sent to the controller.
Also, we can characterize methods of transporting OAM information
relative to the path of data. For instance, OAM information may be
transported out-of-band or in-band with the data flow.
4.2. Continuity Check
Continuity check is used to monitor the continuity of a path, i.e.,
that there exists a way to deliver the packets between two endpoints
A and B.
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4.3. Connectivity Verification
In addition to the Continuity Check, DetNet solutions have to verify
the connectivity. This verification considers additional
constraints, i.e., the absence of misconnection.
In particular, resources have to be reserved for a given flow, so
they are booked for use without being impacted by other flows.
Similarly, the destination does not receive packets from different
flows through its interface.
It is worth noting that the test and data packets MUST follow the
same path, i.e., the connectivity verification has to be conducted
in-band without impacting the data traffic. Test packets MUST share
fate with the monitored data traffic without introducing congestion
in normal network conditions.
4.4. Route Tracing
Ping and traceroute are two ubiquitous tools that help localize and
characterize a failure in the network. They help to identify a
subset of the list of routers in the route. However, to be
predictable, resources are reserved per flow in DetNet. Thus, DetNet
needs to define route tracing tools able to track the route for a
specific flow.
DetNet with IP data plane is NOT RECOMMENDED to use multiple paths or
links, i.e., Equal-Cost Multipath (ECMP) [I-D.ietf-detnet-ip]. As
the result, OAM in IP ECMP environment is outside the scope of this
document.
4.5. Fault Verification/detection
DetNet expects to operate fault-tolerant networks. Thus, mechanisms
able to detect faults before they impact the network performance are
needed.
The network has to detect when a fault occurred, i.e., the network
has deviated from its expected behavior. While the network must
report an alarm, the cause may not be identified precisely. For
instance, the end-to-end reliability has decreased significantly, or
a buffer overflow occurs.
DetNet OAM mechanisms SHOULD allow a fault detection in real time.
They MAY, when possible, predict faults based on current network
conditions. They MAY also identify and report the cause of the
actual/predicted network failure.
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4.6. Fault Isolation/identification
The network has isolated and identified the cause of the fault. For
instance, the replication process behaves not as expected to a
specific intermediary router.
5. Administration
The network SHOULD expose a collection of metrics to support an
operator making proper decisions, including:
o Queuing Delay: the time elapsed between a packet enqueued and its
transmission to the next hop.
o Buffer occupancy: the number of packets present in the buffer, for
each of the existing flows.
The following metrics SHOULD be collected:
o per virtual circuit to measure the end-to-end performance for a
given flow. Each of the paths has to be isolated in multipath
routing strategies.
o per path to detect misbehaving path when multiple paths are
applied.
o per device to detect misbehaving node, when it relays the packets
of several flows.
5.1. Collection of metrics
DetNet OAM SHOULD optimize the number of statistics / measurements to
collected, frequency of collecting. Distributed and centralized
mechanisms MAY be used in combination. Periodic and event-triggered
collection information characterizing the state of a network MAY be
used.
5.2. Worst-case metrics
DetNet aims to enable real-time communications on top of a
heterogeneous multi-hop architecture. To make correct decisions, the
controller needs to know the distribution of packet losses/delays for
each flow, and each hop of the paths. In other words, the average
end-to-end statistics are not enough. The collected information must
be sufficient to allow the controller to predict the worst-case.
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6. Maintenance
DetNet needs to implement a self-healing and self-optimization
approach. The controller MUST be able to continuously retrieve the
state of the network, to evaluate conditions and trends about the
relevance of a reconfiguration, quantifying:
the cost of the sub-optimality: resources may not be used
optimally (e.g., a better path exists).
the reconfiguration cost: the controller needs to trigger some
reconfigurations. For this transient period, resources may be
twice reserved, and control packets have to be transmitted.
Thus, reconfiguration may only be triggered if the gain is
significant.
6.1. Replication / Elimination
When multiple paths are reserved between two maintenance endpoints,
packet replication may be used to introduce redundancy and alleviate
transmission errors and collisions. For instance, in Figure 1, the
source node S is transmitting the packet to both parents, nodes A and
B. Each maintenance endpoint will decide to trigger the packet
replication, elimination or the ordering process when a set of
metrics passes a threshold value.
===> (A) => (C) => (E) ===
// \\// \\// \\
source (S) //\\ //\\ (R) (root)
\\ // \\ // \\ //
===> (B) => (D) => (F) ===
Figure 1: Packet Replication: S transmits twice the same data packet,
to DP(A) and AP (B).
6.2. Resource Reservation
Because the QoS criteria associated with a path may degrade, the
network has to provision additional resources along the path. We
need to provide mechanisms to patch the network configuration.
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6.3. Soft transition after reconfiguration
Since DetNet expects to support real-time flows, DetNet OAM MUST
support soft-reconfiguration, where the novel resources are reserved
before the ancient ones are released. Some mechanisms have to be
proposed so that packets are forwarded through the novel track only
when the resources are ready to be used, while maintaining the global
state consistent (no packet reordering, duplication, etc.)
7. IANA Considerations
This document has no actionable requirements for IANA. This section
can be removed before the publication.
8. Security Considerations
This section will be expanded in future versions of the draft.
9. Acknowledgments
TBD
10. Informative References
[I-D.ietf-detnet-ip]
Varga, B., Farkas, J., Berger, L., Fedyk, D., and S.
Bryant, "DetNet Data Plane: IP", draft-ietf-detnet-ip-07
(work in progress), July 2020.
[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>.
[RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544,
DOI 10.17487/RFC2544, March 1999,
<https://www.rfc-editor.org/info/rfc2544>.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291,
DOI 10.17487/RFC6291, June 2011,
<https://www.rfc-editor.org/info/rfc6291>.
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[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,
<https://www.rfc-editor.org/info/rfc7276>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
Authors' Addresses
Fabrice Theoleyre
CNRS
300 boulevard Sebastien Brant - CS 10413
Illkirch - Strasbourg 67400
FRANCE
Phone: +33 368 85 45 33
Email: theoleyre@unistra.fr
URI: http://www.theoleyre.eu
Georgios Z. Papadopoulos
IMT Atlantique
Office B00 - 102A
2 Rue de la Chataigneraie
Cesson-Sevigne - Rennes 35510
FRANCE
Phone: +33 299 12 70 04
Email: georgios.papadopoulos@imt-atlantique.fr
Grek Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
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