As the IETF continues to produce and standardize different
Operations, Administration, and Maintenance (OAM) protocols and
technologies, various qualifiers and modifiers are prepended to the
OAM acronym. While, at first glance, the most used appear to be well
understood, the same qualifier may be interpreted differently in
different contexts. A case in point is the qualifiers "in-band" and
"out-of-band" which have their origins in the radio lexicon and which
have been extrapolated into other communication networks.¶
This document considers some common qualifiers and modifiers that are
prepended to the OAM acronym, and lays out guidelines for their use
in future IETF work.¶
This document updates RFC 6291 by adding to the guidelines for the
use of the term "OAM".¶
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 https://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."¶
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It is not uncommon for historical and popular terms to have fundamental nuances in how they are interpreted or understood. This was, for example, the case with the acronym "OAM", and [RFC6291] provided guidelines for its use as well as definitions of its constituent parts.¶
Characterizations or qualifiers for "OAM" often encounter similar
problems, such as with the adjective phrases "in-band" and "out-of-
band". This document considers some common qualifiers and modifiers
that are prepended to the OAM acronym, and lays out guidelines for
their use in future IETF work to achieve unambiguous
characterization.¶
Additionally, this document recommends avoiding the creation and use of extended acronyms for the qualifiers of "OAM". For example, the first "O" in "OOAM" could mean out-of-band, overlay, or something else.¶
This document updates [RFC6291] by adding to the guidelines for the
use of the term "OAM".¶
Historically, the terms "in-band" and "out-of-band" appear in radio communications, where there actually was a "Band" (i.e., a "Channel" or "Frequency".) It was also used extensively in telephony signaling [RFC4733].¶
While those terms, useful in their simplicity, continued to be broadly used to mean "within something" and "outside said something", a challenge is presented for IP communications which does not have a "band" per se, and, in fact, has multiple "somethings" that OAM can go within or outside. A frequently encountered case is the use of in-band to mean either in-packet or in-path.¶
The guidance in this document is to avoid the terms "*-band" and instead find finer-granularity descriptive terms.
The definitions presented in this document are for use in all future IETF documents that refer
to OAM, and the terms "in-band OAM" and "out-of-band OAM" are not to
be used in future documents.¶
The OAM messages are carried as part of data traffic. This was sometimes referred to as "in-band".¶
Dedicated-Packet OAM:
The OAM messages have their own OAM packets, separate from data traffic. This was sometimes referred to as "out-of-band".¶
The MPLS echo request/reply messages [RFC8029] are an example of "Dedicated-Packet OAM", since they are described as "An MPLS echo request/reply is a (possibly labeled) IPv4 or IPv6 UDP packet".¶
In Situ OAM [RFC9197] is an example of "In-Packet OAM", given that it 'records OAM information
within the packet while the packet traverses a particular network
domain. The term "in situ" refers to the fact that the OAM data is
added to the data packets rather than being sent within packets
specifically dedicated to OAM.'¶
Initially "In Situ OAM" [IETF96-In-Band-OAM] was also referred to as "In-band OAM", but was renamed due to the overloaded meaning of "in-band OAM". Further, [RFC9232] also intertwines the terms "in-band" with "in situ", though [I-D.song-opsawg-ifit-framework] settled on using "In Situ". Other similar uses, including [P4-INT-2.1] and [I-D.kumar-ippm-ifa], still use variations of "in-band", "in band", or "inband".¶
Packet Treatment:
OAM in relation to the treatment of user data packets, as for example QoS treatment.¶
Equal-QoS-Treatment OAM:
The OAM packets receive the same QoS treatment as user data packets. This was sometimes referred to as "in-band".¶
Different-QoS-Treatment OAM:
The OAM packets receive different QoS treatment as user data packets. This was sometimes referred to as "out-of-band".¶
For a case of either "Non-Path-Congruent OAM" or "Different-QoS-Treatment OAM", [I-D.ietf-detnet-oam-framework] says
"Out-of-band OAM is an active OAM whose path through the DetNet domain is not topologically identical to the path of the monitored DetNet flow, or its test packets receive different QoS and/or PREOF treatment, or both." [I-D.ietf-raw-architecture] uses similar text.¶
[I-D.ietf-detnet-oam-framework] uses Combined OAM when it says "In-band OAM is an active OAM that is in-band within the monitored DetNet OAM domain when it traverses the same set of links and interfaces receiving the same QoS and Packet Replication, Elimination, and Ordering Functions (PREOF) treatment as the monitored DetNet flow". [I-D.ietf-raw-architecture] uses similar text.¶
There are many examples of "in-band OAM" and "out-of-band OAM" in published RFCs. While interpreting those, it is important to understand the semantics of what "band" is a proxy for, and to be more explicit if those documents are updated. This document does not change the meaning of any terms in any prior RFCs.¶
For example, [RFC5085] says "as in-band traffic with the PW's data, or out-of-band", and "in-band (i.e., following the same data-plane faith as PW data)". Hence, the term "band" refers to the "Pseudowire data".¶
[RFC7799] provides clear definitions for active and passive
performance assessment such that the construction of metrics and
methods can be described as either "Active" or "Passive". Even
though [RFC7799] does not include the specific terms "Active",
"Passive", or "Hybrid" as modifiers of "OAM", the following terms
are used in many RFCs and are provided here for use in all future
IETF documents that refer to OAM.¶
Active OAM:
Depends on dedicated instrumentation OAM packets.¶
Passive OAM:
Depends solely on the observation of one
or more existing data packet streams, and does not use dedicated OAM packets.¶
Hybrid OAM:
Uses instrumentation or modification of data packets themselves. [RFC9341] and [RFC9197] are examples labeled "Hybrid OAM" under this definition.¶
Compound OAM:
Uses a combination of at least two of Active OAM, Passive OAM, and Hybrid OAM (i.e., a combination of atomic OAM packets, data packet modification for OAM, and no OAM packet). Note that
[RFC7799] also uses the term "Hybrid" to refer to metric types
in-between active and passive, for OAM there are no in-betweens per se,
only active, passive, hybrid, or a combination.
Compound OAM can further be characterized in a more explicit way, for nuanced use-cases.¶
[RFC7799] adds to the confusion by describing "passive methods" as
"out of band". Following the guidelines of this document, OAM may be
qualified according to the terms described in Sections 2 and 3 of this document, and the term "out of band OAM" is not to be used in future
documents.¶
The creation of this document was triggered when observing one of many on-mailing-list discussions of what these terms mean, and how to abbreviate them. Participants on that mailing thread include, alphabetically: Adrian Farrel, Alexander Vainshtein, Florian Kauer, Frank Brockners, Greg Mirsky, Italo Busi, Loa Andersson, Med Boucadair, Michael Richardson, Quan Xiong, Stewart Bryant, Tom Petch, Eduard Vasilenko, and Xiao Min.¶
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, , <https://www.rfc-editor.org/info/rfc6291>.
[RFC7799]
Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, , <https://www.rfc-editor.org/info/rfc7799>.
Mirsky, G., Theoleyre, F., Papadopoulos, G. Z., Bernardos, C. J., Varga, B., and J. Farkas, "Framework of Operations, Administration and Maintenance (OAM) for Deterministic Networking (DetNet)", Work in Progress, Internet-Draft, draft-ietf-detnet-oam-framework-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-oam-framework-10>.
Schulzrinne, H. and T. Taylor, "RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals", RFC 4733, DOI 10.17487/RFC4733, , <https://www.rfc-editor.org/info/rfc4733>.
[RFC5085]
Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, , <https://www.rfc-editor.org/info/rfc5085>.
[RFC6669]
Sprecher, N. and L. Fang, "An Overview of the Operations, Administration, and Maintenance (OAM) Toolset for MPLS-Based Transport Networks", RFC 6669, DOI 10.17487/RFC6669, , <https://www.rfc-editor.org/info/rfc6669>.
[RFC8029]
Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, , <https://www.rfc-editor.org/info/rfc8029>.
[RFC9197]
Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi, Ed., "Data Fields for In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197, , <https://www.rfc-editor.org/info/rfc9197>.
[RFC9232]
Song, H., Qin, F., Martinez-Julia, P., Ciavaglia, L., and A. Wang, "Network Telemetry Framework", RFC 9232, DOI 10.17487/RFC9232, , <https://www.rfc-editor.org/info/rfc9232>.
[RFC9341]
Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T., and T. Zhou, "Alternate-Marking Method", RFC 9341, DOI 10.17487/RFC9341, , <https://www.rfc-editor.org/info/rfc9341>.