draft-ietf-tsvwg-nqb-06.txt   draft-ietf-tsvwg-nqb-07.txt 
Transport Area Working Group G. White Transport Area Working Group G. White
Internet-Draft CableLabs Internet-Draft CableLabs
Intended status: Standards Track T. Fossati Intended status: Standards Track T. Fossati
Expires: 13 January 2022 ARM Expires: 29 January 2022 ARM
12 July 2021 28 July 2021
A Non-Queue-Building Per-Hop Behavior (NQB PHB) for Differentiated A Non-Queue-Building Per-Hop Behavior (NQB PHB) for Differentiated
Services Services
draft-ietf-tsvwg-nqb-06 draft-ietf-tsvwg-nqb-07
Abstract Abstract
This document specifies properties and characteristics of a Non- This document specifies properties and characteristics of a Non-
Queue-Building Per-Hop Behavior (NQB PHB). The purpose of this NQB Queue-Building Per-Hop Behavior (NQB PHB). The purpose of this NQB
PHB is to provide a separate queue that enables smooth, low-data- PHB is to provide a separate queue that enables smooth, low-data-
rate, application-limited traffic flows, which would ordinarily share rate, application-limited traffic flows, which would ordinarily share
a queue with bursty and capacity-seeking traffic, to avoid the a queue with bursty and capacity-seeking traffic, to avoid the
latency, latency variation and loss caused by such traffic. This PHB latency, latency variation and loss caused by such traffic. This PHB
is implemented without prioritization and without rate policing, is implemented without prioritization and without rate policing,
skipping to change at page 1, line 47 skipping to change at page 1, line 47
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This Internet-Draft will expire on 13 January 2022. This Internet-Draft will expire on 29 January 2022.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Non-Queue-Building Behavior . . . . . . . . . . . . . . . . . 4 3. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The NQB PHB and its Relationship to the Diffserv 3.1. Non-Queue-Building Behavior . . . . . . . . . . . . . . . 4
Architecture . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Relationship to the Diffserv Architecture . . . . . . . . 4
5. DSCP Marking of NQB Traffic . . . . . . . . . . . . . . . . . 6 3.3. Relationship to L4S . . . . . . . . . . . . . . . . . . . 6
5.1. End-to-end usage and DSCP Re-marking . . . . . . . . . . 7 4. DSCP Marking of NQB Traffic . . . . . . . . . . . . . . . . . 6
5.2. Aggregation of the NQB PHB with other Diffserv PHBs . . . 8 4.1. Non-Queue-Building Sender Requirements . . . . . . . . . 6
6. Non-Queue-Building PHB Requirements . . . . . . . . . . . . . 8 4.2. Aggregation of the NQB DSCP with other Diffserv PHBs . . 7
7. Impact on Higher Layer Protocols . . . . . . . . . . . . . . 9 4.3. End-to-end usage and DSCP Re-marking . . . . . . . . . . 8
8. The NQB PHB and Tunnels . . . . . . . . . . . . . . . . . . . 10 4.4. The NQB DSCP and Tunnels . . . . . . . . . . . . . . . . 9
9. Relationship to L4S . . . . . . . . . . . . . . . . . . . . . 10 5. Non-Queue-Building PHB Requirements . . . . . . . . . . . . . 9
10. Configuration and Management . . . . . . . . . . . . . . . . 11 5.1. Primary Requirements . . . . . . . . . . . . . . . . . . 10
11. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 11 5.2. Traffic Protection . . . . . . . . . . . . . . . . . . . 11
11.1. DOCSIS Access Networks . . . . . . . . . . . . . . . . . 11 6. Impact on Higher Layer Protocols . . . . . . . . . . . . . . 12
11.2. Mobile Networks . . . . . . . . . . . . . . . . . . . . 11 7. Configuration and Management . . . . . . . . . . . . . . . . 12
11.3. WiFi Networks . . . . . . . . . . . . . . . . . . . . . 12 8. Example Use Cases . . . . . . . . . . . . . . . . . . . . . . 12
11.3.1. Interoperability with Existing WiFi Networks . . . . 12 8.1. DOCSIS Access Networks . . . . . . . . . . . . . . . . . 12
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 8.2. Mobile Networks . . . . . . . . . . . . . . . . . . . . . 13
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8.3. WiFi Networks . . . . . . . . . . . . . . . . . . . . . . 13
14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8.3.1. Interoperability with Existing WiFi Networks . . . . 14
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
15.1. Normative References . . . . . . . . . . . . . . . . . . 14 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
15.2. Informative References . . . . . . . . . . . . . . . . . 15 11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
Appendix A. DSCP Remarking Pathologies . . . . . . . . . . . . . 17 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. DSCP Remarking Pathologies . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
This document defines a Differentiated Services per-hop behavior This document defines a Differentiated Services per-hop behavior
(PHB) called "Non-Queue-Building Per-Hop Behavior" (NQB PHB), which (PHB) called "Non-Queue-Building Per-Hop Behavior" (NQB PHB), which
isolates traffic flows that are relatively low data rate and that do isolates traffic flows that are relatively low data rate and that do
not themselves materially contribute to queueing delay and loss, not themselves materially contribute to queueing delay and loss,
allowing them to avoid the queuing delays and losses caused by other allowing them to avoid the queuing delays and losses caused by other
traffic. Such Non-Queue-Building flows (for example: interactive traffic. Such Non-Queue-Building flows (for example: interactive
voice, gaming, machine-to-machine applications) are application voice, gaming, machine-to-machine applications) are application
limited flows that are distinguished from traffic flows managed by an limited flows that are distinguished from traffic flows managed by an
end-to-end congestion control algorithm. end-to-end congestion control algorithm.
The vast majority of packets that are carried by broadband access The vast majority of packets that are carried by broadband access
networks are managed by an end-to-end congestion control algorithm, networks are managed by an end-to-end congestion control algorithm,
such as Reno, Cubic or BBR. These congestion control algorithms such as Reno, Cubic or BBR. These congestion control algorithms
attempt to seek the available capacity of the end-to-end path (which attempt to seek the available capacity of the end-to-end path (which
can frequently be the access network link capacity), and in doing so can frequently be the access network link capacity), and in doing so
generally overshoot the available capacity, causing a queue to build- generally overshoot the available capacity, causing a queue to build-
up at the bottleneck link. This queue build up results in queuing up at the bottleneck link. This queue build up results in queuing
delay (variable latency) and possibly packet loss that affects all of delay (variable latency) and possibly packet loss that can affect all
the applications that are sharing the bottleneck link. of the applications that are sharing the bottleneck link.
In contrast to traditional congestion-controlled applications, there In contrast to traditional congestion-controlled applications, there
are a variety of relatively low data rate applications that do not are a variety of relatively low data rate applications that do not
materially contribute to queueing delay and loss, but are nonetheless materially contribute to queueing delay and loss, but are nonetheless
subjected to it by sharing the same bottleneck link in the access subjected to it by sharing the same bottleneck link in the access
network. Many of these applications may be sensitive to latency or network. Many of these applications may be sensitive to latency or
latency variation, as well as packet loss, and thus produce a poor latency variation, as well as packet loss, and thus produce a poor
quality of experience in such conditions. quality of experience in such conditions.
Active Queue Management (AQM) mechanisms (such as PIE [RFC8033], Active Queue Management (AQM) mechanisms (such as PIE [RFC8033],
DOCSIS-PIE [RFC8034], or CoDel [RFC8289]) can improve the quality of DOCSIS-PIE [RFC8034], or CoDel [RFC8289]) can improve the quality of
experience for latency sensitive applications, but there are experience for latency sensitive applications, but there are
practical limits to the amount of improvement that can be achieved practical limits to the amount of improvement that can be achieved
without impacting the throughput of capacity-seeking applications, without impacting the throughput of capacity-seeking applications.
particularly when only a few of such flows are present. For example, AQMs generally allow a significant amount of queue depth
variation in order to accommodate the behaviors of congestion control
algorithms such as Reno and Cubic. If the AQM attempted to control
the queue much more tightly, applications using those algorithms
would not perform well. Alternatively, flow queueuing systems, such
as fq_codel [RFC8290] can be employed to isolate flows from one
another, but these are not appropriate for all bottleneck links, due
to complexity or other reasons.
The NQB PHB supports differentiating between these two classes of The NQB PHB supports differentiating between these two classes of
traffic in bottleneck links and queuing them separately in order that traffic in bottleneck links and queuing them separately in order that
both classes can deliver satisfactory quality of experience for their both classes can deliver satisfactory quality of experience for their
applications. applications.
To be clear, a network implementing the NQB PHB solely provides To be clear, a network implementing the NQB PHB solely provides
isolation for traffic classified as behaving in conformance with the isolation for traffic classified as behaving in conformance with the
NQB DSCP (and optionally enforces that behavior). It is the NQB NQB DSCP (and optionally enforces that behavior). It is the NQB
senders' behavior itself which results in low latency and low loss. senders' behavior itself which results in low latency and low loss.
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. Non-Queue-Building Behavior 3. Context
3.1. Non-Queue-Building Behavior
There are many applications that send traffic at relatively low data There are many applications that send traffic at relatively low data
rates and/or in a fairly smooth and consistent manner such that they rates and/or in a fairly smooth and consistent manner such that they
are highly unlikely to exceed the available capacity of the network are highly unlikely to exceed the available capacity of the network
path between source and sink. These applications do not on their own path between source and sink. These applications may themselves only
cause queues to form in network buffers, but nonetheless can be cause very small, transient queues to form in network buffers, but
subjected to packet delay and delay variation as a result of sharing nonetheless they can be subjected to packet delay and delay variation
a network buffer with applications that do cause queues to form. as a result of sharing a network buffer with applications that tend
Many of these applications are negatively affected by excessive to cause large and/or standing queues to form. Many of these
packet delay and delay variation. Such applications are ideal applications are negatively affected by excessive packet delay and
candidates to be queued separately from the applications that are the delay variation. Such applications are ideal candidates to be queued
cause of queue buildup, latency and loss. separately from the applications that are the cause of queue buildup,
latency and loss.
These Non-queue-building (NQB) flows are typically UDP flows that
don't seek the maximum capacity of the link (examples: online games,
voice chat, DNS lookups, real-time IoT analytics data). Here the
data rate is limited by the application itself rather than by network
capacity - these applications send, at most, the equivalent of a few
well-spaced packets per RTT, even if the packets are not actually
RTT-clocked. In today's network this corresponds to an instantaneous
data rate (packet size divided by packet inter-arrival time) of no
more than about 1 Mbps (e.g. no more than one 1250 B packet every 10
ms), but there is no precise bound since it depends on the conditions
in which the application is operating.
Note that, while such flows ordinarily don't implement a traditional
congestion control mechanism, they nonetheless are expected to comply
with existing guidance for safe deployment on the Internet, for
example the requirements in [RFC8085] and Section 2 of [RFC3551]
(also see the circuit breaker limits in Section 4.3 of [RFC8083] and
the description of inelastic pseudowires in Section 4 of [RFC7893]).
To be clear, the description of NQB flows in this document should not
be interpreted as suggesting that such flows are in any way exempt
from this responsibility.
In contrast, Queue-building (QB) flows include traffic which uses TCP In contrast, Queue-building (QB) flows include those that use TCP or
or QUIC, with Cubic, Reno or other TCP congestion control algorithms QUIC, with Cubic, Reno or other TCP congestion control algorithms
that probe for the link capacity and induce latency and loss as a that probe for the link capacity and induce latency and loss as a
result. Other types of QB flows include those that frequently send result. Other types of QB flows include those that frequently send
at a high burst rate (e.g. several consecutive packets sent well in at a high burst rate (e.g. several consecutive packets sent well in
excess of 1 Mbps) even if the long-term average data rate is much excess of 1 Mbps) even if the long-term average data rate is much
lower. lower.
4. The NQB PHB and its Relationship to the Diffserv Architecture 3.2. Relationship to the Diffserv Architecture
The IETF has defined the Differentiated Services architecture The IETF has defined the Differentiated Services architecture
[RFC2475] with the intention that it allows traffic to be marked in a [RFC2475] with the intention that it allows traffic to be marked in a
manner that conveys the performance requirements of that traffic manner that conveys the performance requirements of that traffic
either quantitatively or in a relative sense (i.e. priority). The either quantitatively or in a relative sense (i.e. priority). The
architecture defines the use of the Diffserv field [RFC2474] for this architecture defines the use of the Diffserv field [RFC2474] for this
purpose, and numerous RFCs have been written that describe purpose, and numerous RFCs have been written that describe
recommended interpretations of the values (Diffserv Code Points) of recommended interpretations of the values (Diffserv Code Points) of
the field, and standardized treatments (traffic conditioning and per- the field, and standardized treatments (traffic conditioning and per-
hop-behaviors) that can be implemented to satisfy the performance hop-behaviors) that can be implemented to satisfy the performance
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Finally, some jurisdictions impose regulations that limit the ability Finally, some jurisdictions impose regulations that limit the ability
of networks to provide differentiation of services, in large part of networks to provide differentiation of services, in large part
based on the belief that doing so necessarily involves prioritization based on the belief that doing so necessarily involves prioritization
or privileged access to bandwidth, and thus a benefit to one class of or privileged access to bandwidth, and thus a benefit to one class of
traffic always comes at the expense of another. traffic always comes at the expense of another.
In contrast, the NQB PHB has been designed with the goal that it In contrast, the NQB PHB has been designed with the goal that it
avoids many of these issues, and thus could conceivably be deployed avoids many of these issues, and thus could conceivably be deployed
end-to-end across the Internet. The intent of the NQB DSCP is that end-to-end across the Internet. The intent of the NQB DSCP is that
it signals verifiable behavior as opposed to wants and needs. Also, it signals verifiable behavior rather than simply a desire for
the NQB traffic is to be given a separate queue with priority equal differentiated treatment. Also, the NQB traffic is to be given a
to default traffic, and given no reserved bandwidth other than the separate queue with priority equal to default traffic, and given no
bandwidth that it shares with default traffic. As a result, the NQB reserved bandwidth other than the bandwidth that it shares with
PHB does not aim to meet specific application performance default traffic. As a result, the NQB PHB does not aim to meet
requirements. Instead the goal of the NQB PHB is to provide specific application performance requirements. Instead the goal of
statistically better loss, latency, and jitter performance for the NQB PHB is to provide statistically better loss, latency, and
traffic that is itself only an insignificant contributor to those jitter performance for traffic that is itself only an insignificant
degradations. These attributes eliminate many of the tradeoffs that contributor to those degradations. The PHB is also designed to
underlie the handling of differentiated service classes in the minimize any incentives for a sender to mismark its traffic, since
Diffserv architecture as it has traditionally been defined. They neither higher priority nor reserved bandwith are being offered.
also significantly simplify access control and admission control These attributes eliminate many of the tradeoffs that underlie the
handling of differentiated service classes in the Diffserv
architecture as it has traditionally been defined. They also
significantly simplify access control and admission control
functions, reducing them to simple verification of behavior. functions, reducing them to simple verification of behavior.
5. DSCP Marking of NQB Traffic 3.3. Relationship to L4S
Applications that align with the description of NQB behavior in the
preceding section SHOULD identify themselves to the network using a
Diffserv Code Point (DSCP) of 45 (decimal) so that their packets can
be queued separately from QB flows. If the application's traffic
exceeds more than a few packets per RTT, or exceeds approximately 1
Mbps on an instantaneous (inter-packet) basis, the application SHOULD
NOT mark its traffic with the NQB DSCP. In such a case, the
application SHOULD instead implement a congestion control mechanism,
for example as described in Section 3.1 of [RFC8085] or
[I-D.ietf-tsvwg-ecn-l4s-id].
The choice of the value 45 is motivated in part by the desire to The NQB DSCP and PHB described in this draft have been defined to
achieve separate queuing in existing WiFi networks (see operate independently of the experimental L4S Architecture
Section 11.3). [I-D.ietf-tsvwg-l4s-arch]. Nonetheless, the NQB traffic flows are
intended to be compatible with [I-D.ietf-tsvwg-l4s-arch], with the
result being that NQB traffic and L4S traffic can share the low-
latency queue in an L4S DualQ node
[I-D.ietf-tsvwg-aqm-dualq-coupled]. Compliance with the DualQ
Coupled AQM requirements (Section 2.5 of
[I-D.ietf-tsvwg-aqm-dualq-coupled]) is considered sufficient to
support the NQB PHB requirement of fair allocation of bandwidth
between the QB and NQB queues (Section 5).
It is worthwhile to note again that the NQB designation and marking 4. DSCP Marking of NQB Traffic
is intended to convey verifiable traffic behavior, not needs or
wants. Also, it is important that incentives are aligned correctly,
i.e. that there is a benefit to the application in marking its
packets correctly, and a disadvantage (or at least no benefit) to an
application in intentionally mismarking its traffic. Thus, a useful
property of nodes (i.e. network switches and routers) that support
separate queues for NQB and QB flows would be that for NQB flows, the
NQB queue provides better performance than the QB queue; and for QB
flows, the QB queue provides better performance than the NQB queue
(this is discussed further in Section 6 and Section 14). By adhering
to these principles, there is no incentive for senders to mismark
their traffic as NQB, and further, any mismarking can be identified
by the network.
Along these lines, nodes that do not support the NQB PHB SHOULD treat 4.1. Non-Queue-Building Sender Requirements
NQB marked traffic the same as traffic marked "Default", and SHOULD
preserve the NQB marking. In backbone and core network switches
(particularly if shallow-buffered), and nodes that do not typically
experience congestion, treating NQB marked traffic the same as
"Default" may be sufficient to preserve latency performance for NQB
traffic.
5.1. End-to-end usage and DSCP Re-marking Non-queue-building (NQB) flows are typically UDP flows that don't
seek the maximum capacity of the link (examples: online games, voice
chat, DNS lookups, real-time IoT analytics data). Here the data rate
is limited by the application itself rather than by network capacity
- these applications send, at most, the equivalent of a few well-
spaced packets per RTT, even if the packets are not actually RTT-
clocked. In today's network this corresponds to an instantaneous
data rate (packet size divided by packet inter-arrival time) of no
more than about 1 Mbps (e.g. no more than one 1250 B packet every 10
ms), but there is no precise bound since it depends on the conditions
in which the application is operating.
In contrast to some existing standard PHBs, many of which are Note that, while such flows ordinarily don't implement a traditional
typically only meaningful within a Diffserv Domain (e.g. an AS or an congestion control mechanism, they nonetheless are expected to comply
enterprise network), this PHB is expected to be used end-to-end with existing guidance for safe deployment on the Internet, for
across the Internet, wherever suitable operator agreements apply. example the requirements in [RFC8085] and Section 2 of [RFC3551]
Under the [RFC2474] model, this requires that the corresponding DSCP (also see the circuit breaker limits in Section 4.3 of [RFC8083] and
is recognized by all operators and mapped across their boundaries the description of inelastic pseudowires in Section 4 of [RFC7893]).
accordingly. To be clear, the description of NQB flows in this document should not
be interpreted as suggesting that such flows are in any way exempt
from this responsibility.
Absent an explicit agreement to the contrary, networks that support Applications that align with the description of NQB behavior in the
the NQB PHB SHOULD preserve a DSCP marking distinction between NQB preceding paragraphs SHOULD identify themselves to the network using
traffic and Default traffic when forwarding via an interconnect from a Diffserv Code Point (DSCP) of 45 (decimal) so that their packets
or to another network. To facilitate the default treatment of NQB can be queued separately from QB flows. The choice of the value 45
traffic in backbones and core networks, networks SHOULD remap NQB is motivated in part by the desire to achieve separate queuing in
traffic (DSCP 45) to DSCP 5 prior to interconnection, unless agreed existing WiFi networks (see Section 8.3). In networks where another
otherwise between the interconnecting partners. The fact that this (e.g. a local-use) codepoint is designated for NQB traffic, or where
PHB is intended for end-to-end usage does not preclude networks from specialized PHBs are available that can meet specific application
mapping the NQB DSCP to a value other than 45 or 5 for internal requirements (e.g. a guaranteed-latency path for voice traffic), it
usage, as long as the appropriate NQB DSCP is restored when may be preferred to use another DSCP.
forwarding to another network. Additionally, interconnecting
networks are not precluded from negotiating (via an SLA or some other
agreement) a different DSCP to use to signal NQB across the
interconnect.
In order to enable interoperability with WiFi equipment, networks If the application's traffic exceeds more than a few packets per RTT,
SHOULD remap NQB traffic (e.g. DSCP 5) to DSCP 45 prior to a or exceeds approximately 1 Mbps on an instantaneous (inter-packet)
customer access link, subject to the safeguards described in basis, the application SHOULD NOT mark its traffic with the NQB DSCP.
Section 11.3. In such a case, the application has to instead implement a relevant
congestion control mechanism, for example as described in Section 3.1
of [RFC8085] or [I-D.ietf-tsvwg-ecn-l4s-id].
Thus, this document recommends two DSCPs to designate NQB, the value 4.2. Aggregation of the NQB DSCP with other Diffserv PHBs
45 for use by hosts and in WiFi networks, and the value 5 for use
across network interconnections.
5.2. Aggregation of the NQB PHB with other Diffserv PHBs It is RECOMMENDED that networks and nodes that do not support the NQB
PHB be configured to treat NQB marked traffic the same as traffic
marked "Default". It is additionally RECOMMENDED that such networks
and nodes simply classify the NQB DSCP into the same treatment
aggregate as Default traffic, or encapsulate the NQB marked packet,
rather than re-marking NQB traffic as Default. This preservation of
the NQB marking enables hops further along the path to provide the
NQB PHB successfully.
Networks and nodes that aggregate service classes as discussed in In backbone and core network switches (particularly if shallow-
buffered), and nodes that do not typically experience congestion,
treating NQB marked traffic the same as Default may be sufficient to
preserve loss/latency/jitter performance for NQB traffic. In other
nodes, treating NQB marked traffic as Default could result in
degradation of loss/latency/jitter performance but is recommended
nonetheless in order to preserve the incentives described in
Section 5. An alternative, in controlled environments where there is
no risk of mismarking of traffic, would be to aggregate NQB marked
traffic with real-time, latency sensitive traffic. Similarly,
networks and nodes that aggregate service classes as discussed in
[RFC5127] and [RFC8100] may not be able to provide a PDB/PHB that [RFC5127] and [RFC8100] may not be able to provide a PDB/PHB that
meets the requirements of this document. In these cases it is meets the requirements of this document. In these cases it is
recommended that NQB-marked traffic be aggregated into the Elastic RECOMMENDED that NQB-marked traffic be aggregated into the Elastic
Treatment Aggregate (for [RFC5127] networks) or the Default / Elastic Treatment Aggregate (for [RFC5127] networks) or the Default / Elastic
Treatment Aggregate (for [RFC8100] networks), although in some cases Treatment Aggregate (for [RFC8100] networks), although in some cases
a network operator may instead choose to aggregate NQB traffic into a network operator may instead choose to aggregate NQB traffic into
the (Bulk) Real-Time Treatment Aggregate. Either approach comes with the (Bulk) Real-Time Treatment Aggregate. Either approach comes with
trade-offs: aggregating with Default/Elastic traffic could result in trade-offs: when the aggregated traffic encounters a bottleneck,
a degradation of loss/latency/jitter performance for NQB traffic, aggregating with Default/Elastic traffic could result in a
while aggregating with Real-Time risks creating an incentive for degradation of loss/latency/jitter performance for NQB traffic, while
mismarking of non-compliant traffic as NQB. In either case, the NQB aggregating with Real-Time (assuming such traffic is provided a
DSCP SHOULD be preserved in order to limit the negative impact that prioritized PHB) risks creating an incentive for mismarking of non-
such networks would have on end-to-end performance for NQB traffic. compliant traffic as NQB (except in controlled environments). In
This aligns with recommendations in [RFC5127]. either case, the NQB DSCP SHOULD be preserved (possibly via
encapsulation) in order to limit the negative impact that such
networks would have on end-to-end performance for NQB traffic. This
aligns with recommendations in [RFC5127].
Nodes that support the NQB PHB may choose to aggregate other service Nodes that support the NQB PHB may choose to aggregate other service
classes into the NQB queue. Candidate service classes for this classes into the NQB queue. Candidate service classes for this
aggregation would include those that carry inelastic traffic that has aggregation would include those that carry inelastic traffic that has
low to very-low tolerance for loss, latency and/or jitter as low to very-low tolerance for loss, latency and/or jitter as
discussed in [RFC4594]. These could include Telephony (EF/VA), discussed in [RFC4594]. These could include Telephony (EF/VA),
Signaling (CS5), Real-Time Interactive (CS4) and Broadcast Video Signaling (CS5), Real-Time Interactive (CS4) and Broadcast Video
(CS3). (CS3).
6. Non-Queue-Building PHB Requirements 4.3. End-to-end usage and DSCP Re-marking
In contrast to some existing standard PHBs, many of which are
typically only meaningful within a Diffserv Domain (e.g. an AS or an
enterprise network), this PHB is expected to be used end-to-end
across the Internet, wherever suitable operator agreements apply.
Under the [RFC2474] model, this requires that the corresponding DSCP
is recognized by all operators and mapped across their boundaries
accordingly.
To support NQB, networks MUST preserve a DSCP marking distinction
between NQB traffic and Default traffic when forwarding via an
interconnect from or to another network. To facilitate the default
treatment of NQB traffic in backbones and core networks discussed in
the previous section (where IP Precedence may be deployed), networks
that support NQB SHOULD remap NQB traffic (DSCP 45) to DSCP 5 prior
to interconnection, unless agreed otherwise between the
interconnecting partners. The fact that this PHB is intended for
end-to-end usage does not preclude networks from mapping the NQB DSCP
to a value other than 45 or 5 for internal usage, as long as the
appropriate NQB DSCP is restored when forwarding to another network.
Additionally, interconnecting networks are not precluded from
negotiating (via an SLA or some other agreement) a different DSCP to
use to signal NQB across the interconnect.
Furthermore, in other network environments where IP Precedence is
deployed, it is RECOMMENDED that the network operator re-mark NQB
traffic to DSCP 5 in order to ensure that it is aggregated with
Default traffic.
In order to enable interoperability with WiFi equipment as described
in Section 8.3.1, networks SHOULD re-mark NQB traffic (e.g. DSCP 5)
to DSCP 45 prior to a customer access link, subject to the safeguards
described in that section.
Thus, this document recommends two DSCPs to designate NQB, the value
45 for use by hosts and in WiFi networks, and the value 5 for use
across network interconnections.
4.4. The NQB DSCP and Tunnels
[RFC2983] discusses tunnel models that support Diffserv. It
describes a "uniform model" in which the inner DSCP is copied to the
outer header at encapsulation, and the outer DSCP is copied to the
inner header at decapsulation. It also describes a "pipe model" in
which the outer DSCP is not copied to the inner header at
decapsulation. Both models can be used in conjunction with the NQB
PHB. In the case of the pipe model, any DSCP manipulation (re-
marking) of the outer header by intermediate nodes would be discarded
at tunnel egress, potentially improving the possibility of achieving
NQB treatment in subsequent nodes.
As is discussed in [RFC2983], tunnel protocols that are sensitive to
reordering can result in undesirable interactions if multiple DSCP
PHBs are signaled for traffic within a tunnel instance. This is true
for NQB marked traffic as well. If a tunnel contains a mix of QB and
NQB traffic, and this is reflected in the outer DSCP in a network
that supports the NQB PHB, it would be necessary to avoid a
reordering-sensitive tunnel protocol.
5. Non-Queue-Building PHB Requirements
It is worthwhile to note again that the NQB designation and marking
is intended to convey verifiable traffic behavior, as opposed to
simply a desire for differentiated treatment. Also, it is important
that incentives are aligned correctly, i.e. that there is a benefit
to the application in marking its packets correctly, and a
disadvantage (or at least no benefit) to an application in
intentionally mismarking its traffic. Thus, a useful property of
nodes (i.e. network switches and routers) that support separate
queues for NQB and QB flows is that for NQB flows, the NQB queue
provides better performance than the QB queue; and for QB flows, the
QB queue provides better performance than the NQB queue (this is
discussed further in this section and Section 11). By adhering to
these principles, there is no incentive for senders to mismark their
traffic as NQB, and further, any mismarking can be identified by the
network.
5.1. Primary Requirements
A node supporting the NQB PHB makes no guarantees on latency or data A node supporting the NQB PHB makes no guarantees on latency or data
rate for NQB marked flows, but instead aims to provide a bound on rate for NQB marked flows, but instead aims to provide a bound on
queuing delay for as many such marked flows as it can, and shed load queuing delay for as many such marked flows as it can, and shed load
when needed. when needed.
A node supporting the NQB PHB MUST provide a queue for non-queue- A node supporting the NQB PHB MUST provide a queue for non-queue-
building traffic separate from any queue used for queue-building building traffic separate from any queue used for queue-building
traffic. traffic.
NQB traffic, in aggregate, SHOULD NOT be rate limited or rate policed NQB traffic, in aggregate, SHOULD NOT be rate limited or rate policed
separately from queue-building traffic of equivalent importance. separately from queue-building traffic of equivalent importance.
The NQB queue SHOULD be given equivalent forwarding preference The NQB queue SHOULD be given equivalent forwarding preference
compared to queue-building traffic of equivalent importance. The compared to queue-building traffic of equivalent importance. The
node SHOULD provide a scheduler that allows QB and NQB traffic of node SHOULD provide a scheduler that allows QB and NQB traffic of
equivalent importance to share the link in a fair manner, e.g. a equivalent importance to share the link in a fair manner, e.g. a
deficit round-robin scheduler with equal weights. Compliance with deficit round-robin scheduler with equal weights. Compliance with
these recommendations helps to ensure that there are no incentives these recommendations helps to ensure that there are no incentives
for QB traffic to be mismarked as NQB. for QB traffic to be mismarked as NQB. In environments where
mismarking is not a potential issue (e.g. a network where a marking
policy is enforced by other means), these requirements may not be
necessary.
A node supporting the NQB PHB SHOULD treat traffic marked as Default A node supporting the NQB PHB SHOULD treat traffic marked as Default
(DSCP=0) as QB traffic having equivalent importance to the NQB marked (DSCP=0) as QB traffic having equivalent importance to the NQB marked
traffic. A node supporting the NQB DSCP MUST support the ability to traffic. A node supporting the NQB DSCP MUST support the ability to
configure the classification criteria that are used to identify QB configure the classification criteria that are used to identify QB
and NQB traffic of equivalent importance. and NQB traffic of equivalent importance.
The NQB queue SHOULD have a buffer size that is significantly smaller The NQB queue SHOULD have a buffer size that is significantly smaller
than the buffer provided for QB traffic (e.g. single-digit than the buffer provided for QB traffic (e.g. single-digit
milliseconds). It is expected that most QB traffic is engineered to milliseconds). It is expected that most QB traffic is engineered to
work well when the network provides a relatively deep buffer (e.g. on work well when the network provides a relatively deep buffer (e.g. on
the order of tens or hundreds of ms) in nodes where support for the the order of tens or hundreds of ms) in nodes where support for the
NQB PHB is advantageous (i.e. bottleneck nodes). Providing a NQB PHB is advantageous (i.e. bottleneck nodes). Providing a
similarly deep buffer for the NQB queue would be at cross purposes to similarly deep buffer for the NQB queue would be at cross purposes to
providing very low queueing delay, and would erode the incentives for providing very low queueing delay, and would erode the incentives for
QB traffic to be marked correctly. QB traffic to be marked correctly.
5.2. Traffic Protection
It is possible that due to an implementation error or It is possible that due to an implementation error or
misconfiguration, a QB flow would end up getting mismarked as NQB, or misconfiguration, a QB flow would end up getting mismarked as NQB, or
vice versa. In the case of an NQB flow that isn't marked as NQB and vice versa. In the case of an NQB flow that isn't marked as NQB and
ends up in the QB queue, it would only impact its own quality of ends up in the QB queue, it would only impact its own quality of
service, and so it seems to be of lesser concern. However, a QB flow service, and so it seems to be of lesser concern. However, a QB flow
that is mismarked as NQB would cause queuing delays and/or loss for that is mismarked as NQB would cause queuing delays and/or loss for
all of the other flows that are sharing the NQB queue. all of the other flows that are sharing the NQB queue.
To prevent this situation from harming the performance of the real To prevent this situation from harming the performance of the real
NQB flows, network elements that support differentiating NQB traffic NQB flows, network elements that support differentiating NQB traffic
SHOULD support a "traffic protection" function that can identify QB SHOULD support a "traffic protection" function that can identify QB
flows that are mismarked as NQB, and either reclassify those flows/ flows that are mismarked as NQB, and either reclassify those flows/
packets to the QB queue or discard the offending traffic. Such a packets to the QB queue or discard the offending traffic. Such a
function SHOULD be implemented in an objective and verifiable manner, function SHOULD be implemented in an objective and verifiable manner,
basing its decisions upon the behavior of the flow rather than on basing its decisions upon the behavior of the flow rather than on
application-layer constructs. One example algorithm can be found in application-layer constructs. It may be advantageous for a traffic
[I-D.briscoe-docsis-q-protection]. There are some situations where protection function to employ hysteresis to prevent borderline flows
such function may not be necessary. For example, a network element from being reclassified capriciously.
designed for use in controlled environments (e.g. enterprise LAN) may
not require a traffic protection function. Additionally, some
networks may prefer to police the application of the NQB DSCP at the
ingress edge, so that in-network traffic protection is not needed.
7. Impact on Higher Layer Protocols One example traffic protection algorithm can be found in
[I-D.briscoe-docsis-q-protection].
There are some situations where such function may not be necessary.
For example, a network element designed for use in controlled
environments (e.g. enterprise LAN) may not require a traffic
protection function. Additionally, some networks may prefer to
police the application of the NQB DSCP at the ingress edge, so that
in-network traffic protection is not needed.
6. Impact on Higher Layer Protocols
Network elements that support the NQB PHB and that support traffic Network elements that support the NQB PHB and that support traffic
protection as discussed in the previous section introduce the protection as discussed in the previous section introduce the
possibility that flows classified into the NQB queue could experience possibility that flows classified into the NQB queue could experience
out of order delivery or packet loss if their behavior is not out of order delivery or packet loss if their behavior is not
consistent with NQB. This is particularly true if the traffic consistent with NQB. This is particularly true if the traffic
protection algorithm makes decisions on a packet-by-packet basis. In protection algorithm makes decisions on a packet-by-packet basis. In
this scenario, a flow that is (mis)marked as NQB and that causes a this scenario, a flow that is (mis)marked as NQB and that causes a
queue to form in this bottleneck link could see some of its packets queue to form in this bottleneck link could see some of its packets
forwarded by the NQB queue, and some of them either discarded or forwarded by the NQB queue, and some of them either discarded or
redirected to the QB queue. In the case of redirection, depending on redirected to the QB queue. In the case of redirection, depending on
the queueing latency and scheduling within the network element, this the queueing latency and scheduling within the network element, this
could result in packets being delivered out of order. As a result, could result in packets being delivered out of order. As a result,
the use of the NQB DSCP by a higher layer protocol carries some risk the use of the NQB DSCP by a higher layer protocol carries some risk
that an increased amount of out of order delivery or packet loss will that an increased amount of out of order delivery or packet loss will
be experienced. This characteristic provides one disincentive for be experienced. This characteristic provides one disincentive for
mis-marking of traffic. mis-marking of traffic.
8. The NQB PHB and Tunnels 7. Configuration and Management
[RFC2983] discusses tunnel models that support Diffserv. It
describes a "uniform model" in which the inner DSCP is copied to the
outer header at encapsulation, and the outer DSCP is copied to the
inner header at decapsulation. It also describes a "pipe model" in
which the outer DSCP is not copied to the inner header at
decapsulation. Both models can be used in conjunction with the NQB
PHB. In the case of the pipe model, any DSCP manipulation (re-
marking) of the outer header by intermediate nodes would be discarded
at tunnel egress, potentially improving the possibility of achieving
NQB treatment in subsequent nodes.
As is discussed in [RFC2983], tunnel protocols that are sensitive to
reordering can result in undesirable interactions if multiple DSCP
PHBs are signaled for traffic within a tunnel instance. This is true
for NQB marked traffic as well. If a tunnel contains a mix of QB and
NQB traffic, and this is reflected in the outer DSCP in a network
that supports the NQB PHB, it would be necessary to avoid a
reordering-sensitive tunnel protocol.
9. Relationship to L4S
Traffic flows marked with the NQB DSCP as described in this draft are
intended to be compatible with [I-D.ietf-tsvwg-l4s-arch], with the
result being that NQB traffic and L4S traffic can share the low-
latency queue in an L4S DualQ node
[I-D.ietf-tsvwg-aqm-dualq-coupled]. Compliance with the DualQ
Coupled AQM requirements (Section 2.5 of
[I-D.ietf-tsvwg-aqm-dualq-coupled]) is considered sufficient to
enable fair allocation of bandwidth between the QB and NQB queues.
10. Configuration and Management
As required above, nodes supporting the NQB PHB provide for the As required above, nodes supporting the NQB PHB provide for the
configuration of classifiers that can be used to differentiate configuration of classifiers that can be used to differentiate
between QB and NQB traffic of equivalent importance. The default for between QB and NQB traffic of equivalent importance. The default for
such classifiers is recommended to be the assigned NQB DSCP (to such classifiers is recommended to be the assigned NQB DSCP (to
identify NQB traffic) and the Default (0) DSCP (to identify QB identify NQB traffic) and the Default (0) DSCP (to identify QB
traffic). traffic).
11. Example Use Cases 8. Example Use Cases
11.1. DOCSIS Access Networks 8.1. DOCSIS Access Networks
Residential cable broadband Internet services are commonly configured Residential cable broadband Internet services are commonly configured
with a single bottleneck link (the access network link) upon which with a single bottleneck link (the access network link) upon which
the service definition is applied. The service definition, typically the service definition is applied. The service definition, typically
an upstream/downstream data rate tuple, is implemented as a an upstream/downstream data rate tuple, is implemented as a
configured pair of rate shapers that are applied to the user's configured pair of rate shapers that are applied to the user's
traffic. In such networks, the quality of service that each traffic. In such networks, the quality of service that each
application receives, and as a result, the quality of experience that application receives, and as a result, the quality of experience that
it generates for the user is influenced by the characteristics of the it generates for the user is influenced by the characteristics of the
access network link. access network link.
To support the NQB PHB, cable broadband services MUST be configured To support the NQB PHB, cable broadband services MUST be configured
to provide a separate queue for NQB marked traffic. The NQB queue to provide a separate queue for NQB marked traffic. The NQB queue
MUST be configured to share the service's rate shaped bandwidth with MUST be configured to share the service's rate shaped bandwidth with
the queue for QB traffic. the queue for QB traffic.
11.2. Mobile Networks 8.2. Mobile Networks
Historically, mobile networks have been configured to bundle all Historically, 3GPP mobile networks have utilised "bearers" to
flows to and from the Internet into a single "default" EPS bearer encapsulate each user's user plane traffic through the radio and core
whose buffering characteristics are not compatible with low-latency networks. A "dedicated bearer" may be allocated a Quality of Service
traffic. The established behaviour is rooted partly in the desire to (QoS) to apply any prioritisation to its flows at queues and radio
prioritise operators' voice services over competing over-the-top schedulers. Typically an LTE operator provides a dedicated bearer
services and partly in the fact that the addition of bearers was for IMS VoLTE (Voice over LTE) traffic, which is prioritised in order
prohibitive due to expense. Of late, said consideration seems to to meet regulatory obligations for call completion rates; and a "best
have lost momentum (e.g., with the rise in Multi-RAB (Radio Access effort" default bearer, for Internet traffic. The "best effort"
Bearer) devices) and the incentives might now be aligned towards bearer provides no guarantees, and hence its buffering
allowing a more suitable treatment of Internet real-time flows. characteristics are not compatible with low-latency traffic. The 5G
radio and core systems offer more flexibility over bearer allocation,
meaning bearers can be allocated per traffic type (e.g. loss-
tolerant, low-latency etc.) and hence support more suitable treatment
of Internet real-time flows.
To support the NQB PHB, the mobile network SHOULD be configured to To support the NQB PHB, the mobile network SHOULD be configured to
give UEs a dedicated, low-latency, non-GBR, EPS bearer, e.g. one with give UEs a dedicated, low-latency, non-GBR, EPS bearer, e.g. one with
QCI 7, in addition to the default EPS bearer; or a Data Radio Bearer QCI 7, in addition to the default EPS bearer; or a Data Radio Bearer
with 5QI 7 in a 5G system (see Table 5.7.4-1: Standardized 5QI to QoS with 5QI 7 in a 5G system (see Table 5.7.4-1: Standardized 5QI to QoS
characteristics mapping in [SA-5G]). characteristics mapping in [SA-5G]).
A packet carrying the NQB DSCP SHOULD be routed through the dedicated A packet carrying the NQB DSCP SHOULD be routed through the dedicated
low-latency EPS bearer. A packet that has no associated NQB marking low-latency EPS bearer. A packet that has no associated NQB marking
SHOULD NOT be routed through the dedicated low-latency EPS bearer. SHOULD NOT be routed through the dedicated low-latency EPS bearer.
11.3. WiFi Networks 8.3. WiFi Networks
WiFi networking equipment compliant with 802.11e/n/ac/ax [IEEE802-11] WiFi networking equipment compliant with 802.11e/n/ac/ax [IEEE802-11]
generally supports either four or eight transmit queues and four sets generally supports either four or eight transmit queues and four sets
of associated Enhanced Multimedia Distributed Control Access (EDCA) of associated Enhanced Multimedia Distributed Control Access (EDCA)
parameters (corresponding to the four WiFi Multimedia (WMM) Access parameters (corresponding to the four WiFi Multimedia (WMM) Access
Categories) that are used to enable differentiated media access Categories) that are used to enable differentiated media access
characteristics. As discussed in [RFC8325], most existing WiFi characteristics. As discussed in [RFC8325], most existing WiFi
implementations use a default DSCP to User Priority mapping that implementations use a default DSCP to User Priority mapping that
utilizes the most significant three bits of the Diffserv Field to utilizes the most significant three bits of the Diffserv Field to
select "User Priority" which is then mapped to the four WMM Access select "User Priority" which is then mapped to the four WMM Access
Categories. [RFC8325] also provides an alternative mapping that more Categories. [RFC8325] also provides an alternative mapping that more
closely aligns with the DSCP recommendations provided by the IETF. closely aligns with the DSCP recommendations provided by the IETF.
In addition to the requirements provided in other sections of this In addition to the requirements provided in other sections of this
document, to support the NQB PHB, WiFi equipment SHOULD map the NQB document, to support the NQB PHB, WiFi equipment SHOULD map the NQB
codepoint 45 into a separate queue that shares an Access Category codepoint 45 into a separate queue in the same Access Category as the
with default traffic (i.e. the Best Effort Access Category). queue that carries default traffic (i.e. the Best Effort Access
Category).
11.3.1. Interoperability with Existing WiFi Networks 8.3.1. Interoperability with Existing WiFi Networks
While some existing WiFi equipment may be capable (in some cases via While some existing WiFi equipment may be capable (in some cases via
firmware update) of supporting the NQB PHB requirements, many firmware update) of supporting the NQB PHB requirements, many
currently deployed devices cannot be configured in this way. As a currently deployed devices cannot be configured in this way. As a
result the remainder of this section discusses interoperability with result the remainder of this section discusses interoperability with
these existing WiFi networks, as opposed to PHB compliance. these existing WiFi networks, as opposed to PHB compliance.
In order to increase the likelihood that NQB traffic is provided a In order to increase the likelihood that NQB traffic is provided a
separate queue from QB traffic in existing WiFi equipment that uses separate queue from QB traffic in existing WiFi equipment that uses
the default mapping, the 45 code point is recommended for NQB. This the default mapping, the 45 code point is recommended for NQB. This
maps NQB to UP_5 which is in the "Video" Access Category. While this maps NQB to UP_5 which is in the "Video" Access Category. While this
DSCP to User Priority mapping enables these WiFi systems to support DSCP to User Priority mapping enables these WiFi systems to support
the NQB PHB requirement for segregated queuing, it does not support the NQB PHB requirement for segregated queuing, it does not support
the remaining NQB PHB requirements in Section 6. The ramifications the remaining NQB PHB requirements in Section 5. The ramifications
of, and remedies for this are discussed further below. of, and remedies for this are discussed further below.
Existing WiFi devices are unlikely to support a traffic protection Existing WiFi devices are unlikely to support a traffic protection
algorithm, so traffic mismarked as NQB is not likely to be detected algorithm, so traffic mismarked as NQB is not likely to be detected
and remedied by such devices. and remedied by such devices.
Furthermore, in their default configuration, existing WiFi devices Furthermore, in their default configuration, existing WiFi devices
utilize EDCA parameters that result in statistical prioritization of utilize EDCA parameters that result in statistical prioritization of
the "Video" Access Category above the "Best Effort" Access Category. the "Video" Access Category above the "Best Effort" Access Category.
If left unchanged, this would violate the NQB PHB requirement for If left unchanged, this would violate the NQB PHB requirement for
skipping to change at page 13, line 39 skipping to change at page 15, line 16
selects the "Best Effort" Access Category. Such equipment MUST selects the "Best Effort" Access Category. Such equipment MUST
support the ability to configure the remapping, so that (when support the ability to configure the remapping, so that (when
appropriate safeguards are in place) traffic can be delivered as NQB- appropriate safeguards are in place) traffic can be delivered as NQB-
marked. marked.
Similarly, systems that utilize [RFC8325] but that are unable to Similarly, systems that utilize [RFC8325] but that are unable to
fully support the PHB requirements, SHOULD map the recommended NQB fully support the PHB requirements, SHOULD map the recommended NQB
code point 45 (or the locally determined alternative) to UP_5 in the code point 45 (or the locally determined alternative) to UP_5 in the
"Video" Access Category. "Video" Access Category.
12. Acknowledgements 9. Acknowledgements
Thanks to Stuart Cheshire, Brian Carpenter, Bob Briscoe, Greg Thanks to Diego Lopez, Stuart Cheshire, Brian Carpenter, Bob Briscoe,
Skinner, Toke Hoeiland-Joergensen, Luca Muscariello, David Black, Greg Skinner, Toke Hoeiland-Joergensen, Luca Muscariello, David
Sebastian Moeller, Ruediger Geib, Jerome Henry, Steven Blake, Black, Sebastian Moeller, Ruediger Geib, Jerome Henry, Steven Blake,
Jonathan Morton, Roland Bless, Kevin Smith, Martin Dolly, and Kyle Jonathan Morton, Roland Bless, Kevin Smith, Martin Dolly, and Kyle
Rose for their review comments. Thanks also to Gorry Fairhurst, Ana Rose for their review comments. Thanks also to Gorry Fairhurst, Ana
Custura, and Ruediger Geib for their input on selection of Custura, and Ruediger Geib for their input on selection of
appropriate DSCPs. appropriate DSCPs.
13. IANA Considerations 10. IANA Considerations
This document requests that IANA assign the Differentiated Services This document requests that IANA assign the Differentiated Services
Field Codepoints (DSCP) 5 ('0b000101', 0x05) and 45 ('0b101101', Field Codepoints (DSCP) 5 ('0b000101', 0x05) and 45 ('0b101101',
0x2D) from the "Differentiated Services Field Codepoints (DSCP)" 0x2D) from the "Differentiated Services Field Codepoints (DSCP)"
registry (https://www.iana.org/assignments/dscp-registry/) ("DSCP registry (https://www.iana.org/assignments/dscp-registry/) ("DSCP
Pool 3 Codepoints", Codepoint Space xxxx01, Standards Action) as the Pool 3 Codepoints", Codepoint Space xxxx01, Standards Action) as the
RECOMMENDED codepoints for Non-Queue-Building behavior. RECOMMENDED codepoints for Non-Queue-Building behavior.
14. Security Considerations 11. Security Considerations
When the NQB PHB is fully supported in bottleneck links, there is no When the NQB PHB is fully supported in bottleneck links, there is no
incentive for an application to mismark its packets as NQB (or vice incentive for an application to mismark its packets as NQB (or vice
versa). If a queue-building flow were to mark its packets as NQB, it versa). If a queue-building flow were to mark its packets as NQB, it
would be unlikely to receive a benefit by doing so, and it could would be unlikely to receive a benefit by doing so, and it could
experience excessive packet loss, excessive latency variation and/or experience excessive packet loss, excessive latency variation and/or
excessive out-of-order delivery (depending on the nature of the excessive out-of-order delivery (depending on the nature of the
traffic protection function). If a non-queue-building flow were to traffic protection function). If a non-queue-building flow were to
fail to mark its packets as NQB, it could suffer the latency and loss fail to mark its packets as NQB, it could suffer the latency and loss
typical of sharing a queue with capacity seeking traffic. typical of sharing a queue with capacity seeking traffic.
skipping to change at page 14, line 49 skipping to change at page 16, line 28
potential abuse on these WiFi links, but since these existing WiFi potential abuse on these WiFi links, but since these existing WiFi
networks already give one quarter of the DSCP space this same networks already give one quarter of the DSCP space this same
treatment, and further they give another quarter of the DSCP space treatment, and further they give another quarter of the DSCP space
even higher priority, the NQB DSCP does not seem to be of any greater even higher priority, the NQB DSCP does not seem to be of any greater
risk for abuse than these others. risk for abuse than these others.
The NQB signal is not integrity protected and could be flipped by an The NQB signal is not integrity protected and could be flipped by an
on-path attacker. This might negatively affect the QoS of the on-path attacker. This might negatively affect the QoS of the
tampered flow. tampered flow.
15. References 12. References
15.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
skipping to change at page 15, line 32 skipping to change at page 17, line 13
March 2017, <https://www.rfc-editor.org/info/rfc8085>. March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to [RFC8325] Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to
IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February
2018, <https://www.rfc-editor.org/info/rfc8325>. 2018, <https://www.rfc-editor.org/info/rfc8325>.
15.2. Informative References 12.2. Informative References
[Barik] Barik, R., Welzl, M., Elmokashfi, A., Dreibholz, T., and [Barik] Barik, R., Welzl, M., Elmokashfi, A., Dreibholz, T., and
S. Gjessing, "Can WebRTC QoS Work? A DSCP Measurement S. Gjessing, "Can WebRTC QoS Work? A DSCP Measurement
Study", ITC 30, September 2018. Study", ITC 30, September 2018.
[Custura] Custura, A., Venne, A., and G. Fairhurst, "Exploring DSCP [Custura] Custura, A., Venne, A., and G. Fairhurst, "Exploring DSCP
modification pathologies in mobile edge networks", TMA , modification pathologies in mobile edge networks", TMA ,
2017. 2017.
[I-D.briscoe-docsis-q-protection] [I-D.briscoe-docsis-q-protection]
Briscoe, B. and G. White, "Queue Protection to Preserve Briscoe, B. and G. White, "Queue Protection to Preserve
Low Latency", Work in Progress, Internet-Draft, draft- Low Latency", Work in Progress, Internet-Draft, draft-
briscoe-docsis-q-protection-00, 8 July 2019, briscoe-docsis-q-protection-00, 8 July 2019,
<http://www.ietf.org/internet-drafts/draft-briscoe-docsis- <https://datatracker.ietf.org/doc/html/draft-briscoe-
q-protection-00.txt>. docsis-q-protection-00>.
[I-D.ietf-tsvwg-aqm-dualq-coupled] [I-D.ietf-tsvwg-aqm-dualq-coupled]
Schepper, K., Briscoe, B., and G. White, "DualQ Coupled Schepper, K. D., Briscoe, B., and G. White, "DualQ Coupled
AQMs for Low Latency, Low Loss and Scalable Throughput AQMs for Low Latency, Low Loss and Scalable Throughput
(L4S)", Work in Progress, Internet-Draft, draft-ietf- (L4S)", Work in Progress, Internet-Draft, draft-ietf-
tsvwg-aqm-dualq-coupled-13, 15 November 2020, tsvwg-aqm-dualq-coupled-16, 7 July 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-aqm- <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
dualq-coupled-13.txt>. aqm-dualq-coupled-16>.
[I-D.ietf-tsvwg-dscp-considerations]
Custura, A., Fairhurst, G., and R. Secchi, "Considerations
for Assigning a new Recommended DiffServ Codepoint
(DSCP)", Work in Progress, Internet-Draft, draft-ietf-
tsvwg-dscp-considerations-00, 26 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
dscp-considerations-00>.
[I-D.ietf-tsvwg-ecn-l4s-id] [I-D.ietf-tsvwg-ecn-l4s-id]
Schepper, K. and B. Briscoe, "Identifying Modified Schepper, K. D. and B. Briscoe, "Explicit Congestion
Explicit Congestion Notification (ECN) Semantics for Notification (ECN) Protocol for Very Low Queuing Delay
Ultra-Low Queuing Delay (L4S)", Work in Progress, (L4S)", Work in Progress, Internet-Draft, draft-ietf-
Internet-Draft, draft-ietf-tsvwg-ecn-l4s-id-12, 15 tsvwg-ecn-l4s-id-19, 26 July 2021,
November 2020, <http://www.ietf.org/internet-drafts/draft- <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
ietf-tsvwg-ecn-l4s-id-12.txt>. ecn-l4s-id-19>.
[I-D.ietf-tsvwg-l4s-arch] [I-D.ietf-tsvwg-l4s-arch]
Briscoe, B., Schepper, K., Bagnulo, M., and G. White, "Low Briscoe, B., Schepper, K. D., Bagnulo, M., and G. White,
Latency, Low Loss, Scalable Throughput (L4S) Internet "Low Latency, Low Loss, Scalable Throughput (L4S) Internet
Service: Architecture", Work in Progress, Internet-Draft, Service: Architecture", Work in Progress, Internet-Draft,
draft-ietf-tsvwg-l4s-arch-08, 15 November 2020, draft-ietf-tsvwg-l4s-arch-10, 1 July 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-tsvwg-l4s- <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
arch-08.txt>. l4s-arch-10>.
[IEEE802-11] [IEEE802-11]
IEEE-SA, "IEEE 802.11-2020", IEEE 802, December 2020, IEEE-SA, "IEEE 802.11-2020", IEEE 802, December 2020,
<https://standards.ieee.org/standard/802_11-2020.html>. <https://standards.ieee.org/standard/802_11-2020.html>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>. <https://www.rfc-editor.org/info/rfc2475>.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", RFC 3551, July Video Conferences with Minimal Control", STD 65, RFC 3551,
2003, <https://www.rfc-editor.org/info/rfc3551>. DOI 10.17487/RFC3551, July 2003,
<https://www.rfc-editor.org/info/rfc3551>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for Diffserv Service Classes", RFC 4594, Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006, DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>. <https://www.rfc-editor.org/info/rfc4594>.
[RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of [RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of
Diffserv Service Classes", RFC 5127, DOI 10.17487/RFC5127, Diffserv Service Classes", RFC 5127, DOI 10.17487/RFC5127,
February 2008, <https://www.rfc-editor.org/info/rfc5127>. February 2008, <https://www.rfc-editor.org/info/rfc5127>.
[RFC7893] Stein, Y(J)., Black, D., and B. Briscoe, "Pseudowire [RFC7893] Stein, Y(J)., Black, D., and B. Briscoe, "Pseudowire
Congestion Considerations", RFC 7893, June 2016, Congestion Considerations", RFC 7893,
DOI 10.17487/RFC7893, June 2016,
<https://www.rfc-editor.org/info/rfc7893>. <https://www.rfc-editor.org/info/rfc7893>.
[RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White, [RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White,
"Proportional Integral Controller Enhanced (PIE): A "Proportional Integral Controller Enhanced (PIE): A
Lightweight Control Scheme to Address the Bufferbloat Lightweight Control Scheme to Address the Bufferbloat
Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017, Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017,
<https://www.rfc-editor.org/info/rfc8033>. <https://www.rfc-editor.org/info/rfc8033>.
[RFC8034] White, G. and R. Pan, "Active Queue Management (AQM) Based [RFC8034] White, G. and R. Pan, "Active Queue Management (AQM) Based
on Proportional Integral Controller Enhanced PIE) for on Proportional Integral Controller Enhanced PIE) for
Data-Over-Cable Service Interface Specifications (DOCSIS) Data-Over-Cable Service Interface Specifications (DOCSIS)
Cable Modems", RFC 8034, DOI 10.17487/RFC8034, February Cable Modems", RFC 8034, DOI 10.17487/RFC8034, February
2017, <https://www.rfc-editor.org/info/rfc8034>. 2017, <https://www.rfc-editor.org/info/rfc8034>.
[RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control: [RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control:
Circuit Breakers for Unicast RTP Sessions", RFC 8083, Circuit Breakers for Unicast RTP Sessions", RFC 8083,
March 2017, <https://www.rfc-editor.org/info/rfc8083>. DOI 10.17487/RFC8083, March 2017,
<https://www.rfc-editor.org/info/rfc8083>.
[RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection [RFC8100] Geib, R., Ed. and D. Black, "Diffserv-Interconnection
Classes and Practice", RFC 8100, DOI 10.17487/RFC8100, Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
March 2017, <https://www.rfc-editor.org/info/rfc8100>. March 2017, <https://www.rfc-editor.org/info/rfc8100>.
[RFC8289] Nichols, K., Jacobson, V., McGregor, A., Ed., and J. [RFC8289] Nichols, K., Jacobson, V., McGregor, A., Ed., and J.
Iyengar, Ed., "Controlled Delay Active Queue Management", Iyengar, Ed., "Controlled Delay Active Queue Management",
RFC 8289, DOI 10.17487/RFC8289, January 2018, RFC 8289, DOI 10.17487/RFC8289, January 2018,
<https://www.rfc-editor.org/info/rfc8289>. <https://www.rfc-editor.org/info/rfc8289>.
[RFC8290] Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys,
J., and E. Dumazet, "The Flow Queue CoDel Packet Scheduler
and Active Queue Management Algorithm", RFC 8290,
DOI 10.17487/RFC8290, January 2018,
<https://www.rfc-editor.org/info/rfc8290>.
[SA-5G] 3GPP, "System Architecture for 5G", TS 23.501, 2019. [SA-5G] 3GPP, "System Architecture for 5G", TS 23.501, 2019.
Appendix A. DSCP Remarking Pathologies Appendix A. DSCP Remarking Pathologies
Some network operators typically bleach (zero out) the Diffserv field Some network operators typically bleach (zero out) the Diffserv field
on ingress into their network [Custura][Barik], and in some cases on ingress into their network
apply their own DSCP for internal usage. Bleaching the NQB DSCP is [I-D.ietf-tsvwg-dscp-considerations][Custura][Barik], and in some
not expected to cause harm to default traffic, but it will severely cases apply their own DSCP for internal usage. Bleaching the NQB
limit the ability to provide NQB treatment end-to-end. Reports on DSCP is not expected to cause harm to default traffic, but it will
existing deployments of DSCP manipulation [Custura][Barik] categorize severely limit the ability to provide NQB treatment end-to-end.
the re-marking behaviors into the following six policies: bleach all Reports on existing deployments of DSCP manipulation [Custura][Barik]
traffic (set DSCP to zero), set the top three bits (the former categorize the re-marking behaviors into the following six policies:
Precedence bits) on all traffic to 0b000, 0b001, or 0b010, set the bleach all traffic (set DSCP to zero), set the top three bits (the
low three bits on all traffic to 0b000, or remark all traffic to a former Precedence bits) on all traffic to 0b000, 0b001, or 0b010, set
particular (non-zero) DSCP value. the low three bits on all traffic to 0b000, or remark all traffic to
a particular (non-zero) DSCP value.
Regarding the DSCP values of 5 & 45, there were no observations of Regarding the DSCP values of 5 & 45, there were no observations of
DSCP manipulation reported in which traffic was marked 5 or 45 by any DSCP manipulation reported in which traffic was marked 5 or 45 by any
of these policies. Thus it appears that these re-marking policies of these policies. Thus it appears that these re-marking policies
would be unlikely to result in QB traffic being marked as NQB (45). would be unlikely to result in QB traffic being marked as NQB (45).
In terms of the fate of NQB-marked traffic that is subjected to one In terms of the fate of NQB-marked traffic that is subjected to one
of these policies, the result would be that NQB marked traffic would of these policies, the result would be that NQB marked traffic would
be indistinguishable from some subset (possibly all) of other be indistinguishable from some subset (possibly all) of other
traffic. In the policies where all traffic is remarked using the traffic. In the policies where all traffic is remarked using the
same (zero or non-zero) DSCP, the ability for a subsequent network same (zero or non-zero) DSCP, the ability for a subsequent network
skipping to change at page 18, line 30 skipping to change at page 20, line 26
CS5, VA, EF (and the unassigned DSCPs 41, 42, 43). Traffic marked CS5, VA, EF (and the unassigned DSCPs 41, 42, 43). Traffic marked
using the existing standardized DSCPs in this list are likely to using the existing standardized DSCPs in this list are likely to
share the same general properties as NQB traffic (non capacity- share the same general properties as NQB traffic (non capacity-
seeking, very low data rate or relatively low and consistent data seeking, very low data rate or relatively low and consistent data
rate). Similarly, any future recommended usage for DSCPs 41, 42, 43 rate). Similarly, any future recommended usage for DSCPs 41, 42, 43
would likely be somewhat compatible with NQB treatment, assuming that would likely be somewhat compatible with NQB treatment, assuming that
IP Precedence compatibility (see Section 1.5.4 of [RFC4594]) is IP Precedence compatibility (see Section 1.5.4 of [RFC4594]) is
maintained in the future. Here there may be an opportunity for a maintained in the future. Here there may be an opportunity for a
node to provide the NQB PHB or the CS5 PHB to CS5-marked traffic and node to provide the NQB PHB or the CS5 PHB to CS5-marked traffic and
retain some of the benefits of NQB marking. This could be another retain some of the benefits of NQB marking. This could be another
motivation to (as discussed in Section 5.2) classify CS5-marked motivation to (as discussed in Section 4.2) classify CS5-marked
traffic into NQB queue. For this same re-marking policy, the NQB (5) traffic into NQB queue. For this same re-marking policy, the NQB (5)
value would be mapped to CS0/default and would be indistinguishable value would be mapped to CS0/default and would be indistinguishable
from CS0, LE (and the unassigned DSCPs 2,3,4,6,7). In this case, NQB from CS0, LE (and the unassigned DSCPs 2,3,4,6,7). In this case, NQB
traffic is likely to be given default treatment in all subsequent traffic is likely to be given default treatment in all subsequent
nodes, which would eliminate the ability to provide NQB treatment in nodes, which would eliminate the ability to provide NQB treatment in
those nodes, but would be relatively harmless otherwise. those nodes, but would be relatively harmless otherwise.
Authors' Addresses Authors' Addresses
Greg White Greg White
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