< draft-ietf-tsvwg-le-phb-07.txt   draft-ietf-tsvwg-le-phb-08.txt >
Internet Engineering Task Force R. Bless Internet Engineering Task Force R. Bless
Internet-Draft Karlsruhe Institute of Technology (KIT) Internet-Draft Karlsruhe Institute of Technology (KIT)
Obsoletes: 3662 (if approved) January 20, 2019 Obsoletes: 3662 (if approved) January 30, 2019
Updates: 4594,8325 (if approved) Updates: 4594,8325 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: July 24, 2019 Expires: August 3, 2019
A Lower Effort Per-Hop Behavior (LE PHB) A Lower Effort Per-Hop Behavior (LE PHB)
draft-ietf-tsvwg-le-phb-07 draft-ietf-tsvwg-le-phb-08
Abstract Abstract
This document specifies properties and characteristics of a Lower This document specifies properties and characteristics of a Lower
Effort (LE) per-hop behavior (PHB). The primary objective of this LE Effort (LE) per-hop behavior (PHB). The primary objective of this LE
PHB is to protect best-effort (BE) traffic (packets forwarded with PHB is to protect best-effort (BE) traffic (packets forwarded with
the default PHB) from LE traffic in congestion situations, i.e., when the default PHB) from LE traffic in congestion situations, i.e., when
resources become scarce, best-effort traffic has precedence over LE resources become scarce, best-effort traffic has precedence over LE
traffic and may preempt it. Alternatively, packets forwarded by the traffic and may preempt it. Alternatively, packets forwarded by the
LE PHB can be associated with a scavenger service class, i.e., they LE PHB can be associated with a scavenger service class, i.e., they
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 24, 2019. This Internet-Draft will expire on August 3, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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of sufficiently low urgency that all other traffic takes precedence of sufficiently low urgency that all other traffic takes precedence
over the LE traffic in consumption of network link bandwidth. Low over the LE traffic in consumption of network link bandwidth. Low
urgency traffic has a low priority for timely forwarding, which does urgency traffic has a low priority for timely forwarding, which does
not necessarily imply that it is generally of minor importance. From not necessarily imply that it is generally of minor importance. From
this viewpoint, it can be considered as a network equivalent to a this viewpoint, it can be considered as a network equivalent to a
background priority for processes in an operating system. There may background priority for processes in an operating system. There may
or may not be memory (buffer) resources allocated for this type of or may not be memory (buffer) resources allocated for this type of
traffic. traffic.
Some networks carry packets that ought to consume network resources Some networks carry packets that ought to consume network resources
only when no other traffic is demanding them otherwise. In this only when no other traffic is demanding them. In this point of view,
point of view, packets forwarded by the LE PHB scavenge otherwise packets forwarded by the LE PHB scavenge otherwise unused resources
unused resources only, which led to the name "scavenger service" in only, which led to the name "scavenger service" in early Internet2
early Internet2 deployments (see Appendix A). Other commonly used deployments (see Appendix A). Other commonly used names for LE PHB
names for LE PHB type services are "Lower-than-best-effort" or "Less- type services are "Lower-than-best-effort" or "Less-than-best-
than-best-effort". Alternatively, the effect of this type of traffic effort". Alternatively, the effect of this type of traffic on all
on all other network traffic is strictly limited ("no harm" other network traffic is strictly limited ("no harm" property). This
property). This is distinct from "best-effort" (BE) traffic since is distinct from "best-effort" (BE) traffic since the network makes
the network makes no commitment to deliver LE packets. In contrast, no commitment to deliver LE packets. In contrast, BE traffic
BE traffic receives an implied "good faith" commitment of at least receives an implied "good faith" commitment of at least some
some available network resources. This document proposes a Lower available network resources. This document proposes a Lower Effort
Effort Differentiated Services per-hop behavior (LE PHB) for handling Differentiated Services per-hop behavior (LE PHB) for handling this
this "optional" traffic in a differentiated services node. "optional" traffic in a differentiated services node.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all 14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Applicability 3. Applicability
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violate the operational objectives of the other PHB. violate the operational objectives of the other PHB.
o For multicast traffic from untrusted (e.g., non-local) sources. o For multicast traffic from untrusted (e.g., non-local) sources.
4. PHB Description 4. PHB Description
The LE PHB is defined in relation to the default PHB (best-effort). The LE PHB is defined in relation to the default PHB (best-effort).
A packet forwarded with the LE PHB SHOULD have lower precedence than A packet forwarded with the LE PHB SHOULD have lower precedence than
packets forwarded with the default PHB, i.e., in the case of packets forwarded with the default PHB, i.e., in the case of
congestion, LE marked traffic SHOULD be dropped prior to dropping any congestion, LE marked traffic SHOULD be dropped prior to dropping any
default PHB traffic. Ideally, LE packets SHOULD be forwarded only if default PHB traffic. Ideally, LE packets would be forwarded only
no packet with any other PHB is awaiting transmission. This means when no packet with any other PHB is awaiting transmission. This
that in case of link resource contention LE traffic can be starved means that in case of link resource contention LE traffic can be
completely, which may not be always desired by the network operator's starved completely, which may not be always desired by the network
policy. The used scheduler to implement the LE PHB may reflect this operator's policy. The used scheduler to implement the LE PHB may
policy accordingly. reflect this policy accordingly.
A straightforward implementation could be a simple priority scheduler A straightforward implementation could be a simple priority scheduler
serving the default PHB queue with higher priority than the lower- serving the default PHB queue with higher priority than the lower-
effort PHB queue. Alternative implementations may use scheduling effort PHB queue. Alternative implementations may use scheduling
algorithms that assign a very small weight to the LE class. This, algorithms that assign a very small weight to the LE class. This,
however, could sometimes cause better service for LE packets compared however, could sometimes cause better service for LE packets compared
to BE packets in cases when the BE share is fully utilized and the LE to BE packets in cases when the BE share is fully utilized and the LE
share not. share not.
If a dedicated LE queue is not available, an active queue management If a dedicated LE queue is not available, an active queue management
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authors of previous specifications are acknowledged here: Kathie authors of previous specifications are acknowledged here: Kathie
Nichols and Klaus Wehrle. David Black, Toerless Eckert, Gorry Nichols and Klaus Wehrle. David Black, Toerless Eckert, Gorry
Fairhurst, Ruediger Geib, and Spencer Dawkins provided helpful Fairhurst, Ruediger Geib, and Spencer Dawkins provided helpful
comments and (also text) suggestions. comments and (also text) suggestions.
Appendix C. Change History Appendix C. Change History
This section briefly lists changes between Internet-Draft versions This section briefly lists changes between Internet-Draft versions
for convenience. for convenience.
Changes in Version 08:
o revised two sentences as suggested by Spencer Dawkins
Changes in Version 07: Changes in Version 07:
o revised some text for clarification according to comments from o revised some text for clarification according to comments from
Spencer Dawkins Spencer Dawkins
Changes in Version 06: Changes in Version 06:
o added Multicast Considerations section with input from Toerless o added Multicast Considerations section with input from Toerless
Eckert Eckert
 End of changes. 7 change blocks. 
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