draft-ietf-tsvwg-nqb-01.txt   draft-ietf-tsvwg-nqb-02.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: September 10, 2020 ARM Expires: March 26, 2021 ARM
March 9, 2020 September 22, 2020
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-01 draft-ietf-tsvwg-nqb-02
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 low latency and, when PHB is to provide a separate queue that enables low latency and, when
possible, low loss for application-limited traffic flows that would possible, low loss for application-limited traffic flows that would
ordinarily share a queue with capacity-seeking traffic. This PHB is ordinarily share a queue with capacity-seeking traffic. This PHB is
implemented without prioritization and without rate policing, making implemented without prioritization and without rate policing, making
it suitable for environments where the use of either these features it suitable for environments where the use of either these features
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This Internet-Draft will expire on September 10, 2020. This Internet-Draft will expire on March 26, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Overview: Non-Queue-Building Flows . . . . . . . . . . . . . 3 3. Overview: Non-Queue-Building Flows . . . . . . . . . . . . . 3
4. DSCP Marking of NQB Traffic . . . . . . . . . . . . . . . . . 4 4. DSCP Marking of NQB Traffic . . . . . . . . . . . . . . . . . 4
5. Non-Queue-Building PHB Requirements . . . . . . . . . . . . . 5 4.1. End-to-end usage and DSCP Re-marking . . . . . . . . . . 5
6. Relationship to L4S . . . . . . . . . . . . . . . . . . . . . 6 5. Non-Queue-Building PHB Requirements . . . . . . . . . . . . . 6
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. Impact on Higher Layer Protocols . . . . . . . . . . . . . . 7
7.1. DOCSIS Access Networks . . . . . . . . . . . . . . . . . 6 7. Relationship to L4S . . . . . . . . . . . . . . . . . . . . . 7
7.2. Mobile Networks . . . . . . . . . . . . . . . . . . . . . 6 8. Configuration and Management . . . . . . . . . . . . . . . . 8
7.3. WiFi Networks . . . . . . . . . . . . . . . . . . . . . . 7 9. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9.1. DOCSIS Access Networks . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 9.2. Mobile Networks . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9.3. WiFi Networks . . . . . . . . . . . . . . . . . . . . . . 9
11. Informative References . . . . . . . . . . . . . . . . . . . 9 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 10
13. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
This document defines a Differentiated Services (DS) per-hop behavior This document defines a Differentiated Services (DS) 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
is intended to enable networks to provide low latency and low loss is intended to enable networks to provide low latency and low loss
for traffic flows that are relatively low data rate and that do not for traffic flows that are relatively low data rate and that do not
themselves materially contribute to queueing delay and loss. Such themselves materially contribute to queueing delay and loss. Such
Non-Queue-Building flows (for example: interactive voice and video, Non-Queue-Building flows (for example: interactive voice and video,
gaming, machine to machine applications) are application limited gaming, machine to machine applications) are application limited
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There are many application flows that fall very neatly into one or There are many application flows that fall very neatly into one or
the other of these categories, but there are also application flows the other of these categories, but there are also application flows
that may be in a gray area in between (e.g. they are NQB on higher- that may be in a gray area in between (e.g. they are NQB on higher-
speed links, but QB on lower-speed links). speed links, but QB on lower-speed links).
If there is uncertainty as to whether an application's traffic aligns If there is uncertainty as to whether an application's traffic aligns
with the description of NQB behavior in the preceding section, the with the description of NQB behavior in the preceding section, the
application SHOULD NOT mark its traffic with the NQB DSCP. In such a application SHOULD NOT mark its traffic with the NQB DSCP. In such a
case, the application SHOULD instead implement a congestion control case, the application SHOULD instead implement a congestion control
mechanism, for example as described in [RFC8085]. mechanism, for example as described in [RFC8085] or
[I-D.ietf-tsvwg-ecn-l4s-id].
This document recommends a DSCP of 0x2A to identify packets of NQB This document recommends a DSCP of 42 (0x2A) to identify packets of
flows. (editor's note: this value is subject to change) NQB flows.
It is worthwhile to note that the NQB designation and marking is It is worthwhile to note that the NQB designation and marking is
intended to convey verifiable traffic behavior, not needs or wants. intended to convey verifiable traffic behavior, not needs or wants.
Also, it is important that incentives are aligned correctly, i.e. Also, it is important that incentives are aligned correctly, i.e.
that there is a benefit to the application in marking its packets that there is a benefit to the application in marking its packets
correctly, and no benefit to an application in intentionally correctly, and no benefit to an application in intentionally
mismarking its traffic. Thus, a useful property of nodes that mismarking its traffic. Thus, a useful property of nodes that
support separate queues for NQB and QB flows would be that for NQB support separate queues for NQB and QB flows would be that for NQB
flows, the NQB queue provides better performance than the QB queue; flows, the NQB queue provides better performance than the QB queue;
and for QB flows, the QB queue provides better performance than the and for QB flows, the QB queue provides better performance than the
NQB queue. By adhering to these principles, there is no incentive NQB queue. By adhering to these principles, there is no incentive
for senders to mismark their traffic as NQB, and further, any for senders to mismark their traffic as NQB, and further, any
mismarking can be identified by the network. mismarking can be identified by the network.
In contrast to the existing standard DSCPs, which are typically only 4.1. End-to-end usage and DSCP Re-marking
meaningful within a DiffServ Domain (e.g. an AS or an enterprise
network), this DSCP is expected to be used end-to-end across the In contrast to the existing standard DSCPs, many of which are
Internet. Some network operators typically bleach (zero out) the typically only meaningful within a DiffServ Domain (e.g. an AS or an
DiffServ field on ingress into their network [Custura], and in some enterprise network), this DSCP is expected to be used end-to-end
cases apply their own DSCP for internal usage. Networks that support across the Internet. Some network operators typically bleach (zero
the NQB PHB SHOULD preserve the NQB DSCP when forwarding via an out) the DiffServ field on ingress into their network
interconnect from or to another network. [Custura][Barik], and in some cases apply their own DSCP for internal
usage. Networks that support the NQB PHB SHOULD preserve the NQB
DSCP when forwarding via an interconnect from or to another network.
Bleaching the NQB DSCP is not expected to cause harm to default
traffic, but it will severely limit the ability to provide NQB
treatment end-to-end.
Reports on existing deployments of DSCP manipulation [Custura][Barik]
categorize the remarking behaviors into the following six policies:
bleach all traffic (set DSCP to zero), set the top three bits (the
former Precedence bits) on all traffic to 0b000, 0b001, or 0b010, set
the low three bits on all traffic to 0b000, or remark all traffic to
a particular (non-zero) DSCP value. There were no observations
reported in which traffic was marked 42 by any of these policies.
Thus it appears that these remarking policies would be unlikely to
result in QB traffic being marked as NQB. 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 be indistinguishable
from some subset (possibly all) of other traffic. In the policies
where all traffic is remarked using the same (zero or non-zero) DSCP,
the ability for a subsequent network hop to differentiate NQB traffic
via DSCP would clearly be lost entirely. In the policies where the
top three bits are overwritten, NQB would receive the same marking as
AF41, AF31, AF21, AF11 (as well as the currently unassigned DSCPs 2,
50, 58), with all of these codepoints getting mapped to DSCP=2, AF11
or AF21 (depending on the overwrite value used). Since the
recommended usage of the standardized codepoints in that list include
high throughput data for store and forward applications (and it is
impossible to predict what future use would be assigned to the
currently unassigned values) it would seem inadvisable for a node to
attempt to treat all such traffic as if it were NQB marked. For the
policy in which the low three bits are set to 0b000, the NQB value
would be mapped to CS5 and would be indistinguishable from CS5, VA,
EF (and the unassigned DSCPs 41, 43, 45). Traffic marked using the
existing standardized DSCPs in this list are likely to share the same
general properties as NQB traffic (non capacity-seeking, very low
data rate or relatively low and consistent data rate). Furthermore,
as this remarking policy results in an overt enforcement of the IP
Precedence compatibility configuration discussed in [RFC4594]
Section 1.5.4, and to the extent that this compatibility is
maintained in the future, any future recommended usages of the
currently unassigned DSCPs in that list would be likely to similarly
be somewhat compatible with NQB treatment. Here there may be an
opportunity for a node to provide the NQB PHB or the CS5 PHB and
retain some of the benefits of NQB marking. As a result, nodes
supporting the NQB PHB MAY additionally classify CS5 marked traffic
into the NQB queue.
5. Non-Queue-Building PHB Requirements 5. Non-Queue-Building PHB 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 the queue used for queue-building building traffic separate from the queue used for queue-building
traffic. traffic.
NQB traffic SHOULD NOT be rate limited or rate policed separately NQB traffic, in aggregate, SHOULD NOT be rate limited or rate policed
from queue-building traffic of equivalent importance. separately from queue-building traffic of equivalent importance.
The NQB queue SHOULD be given equal priority compared to queue- The NQB queue SHOULD be given equal priority compared to queue-
building traffic of equivalent importance. The node SHOULD provide a building traffic of equivalent importance. The node SHOULD provide a
scheduler that allows QB and NQB traffic of equivalent importance to scheduler that allows QB and NQB traffic of equivalent importance to
share the link in a fair manner, e.g. a deficit round-robin scheduler share the link in a fair manner, e.g. a deficit round-robin scheduler
with equal weights. with equal weights.
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=0x00) as QB traffic having equivalent importance to the NQB (DSCP=0) as QB traffic having equivalent importance to the NQB marked
marked traffic. traffic. A node supporting the NQB DSCP MUST support the ability to
configure the classification criteria that are used to identify QB
and NQB traffic having 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. than the buffer provided for QB traffic. It is expected that most QB
traffic is optimized to make use of a relatively deep buffer (e.g. on
the order of tens or hundreds of ms) in nodes where support for the
NQB PHB is advantageous (i.e. bottleneck nodes). Providing a
similarly deep buffer for the NQB queue would be at cross purposes to
providing very low queueing delay, and would erode the incentives for
QB traffic to be marked correctly.
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 (editor's note: SHOULD vs MUST is TBD) support a "traffic SHOULD support a "traffic protection" function that can identify QB
protection" function that can identify QB flows that are mismarked as flows that are mismarked as NQB, and reclassify those flows/packets
NQB, and reclassify those flows/packets to the QB queue. Such a to the QB queue. Such a function SHOULD be implemented in an
function SHOULD be implemented in an objective and verifiable manner, objective and verifiable manner, basing its decisions upon the
basing its decisions upon the behavior of the flow rather than on behavior of the flow rather than on application-layer constructs.
application-layer constructs. One example algorithm can be found in One example algorithm can be found in
[I-D.briscoe-docsis-q-protection]. [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. Similarly, flow queueing
systems obviate the need for an explicit 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. Relationship to L4S 6. Impact on Higher Layer Protocols
Network elements that support the NQB PHB and that support traffic
protection as discussed in the previous section introduce the
possibility that flows classified into the NQB queue could experience
out of order delivery. This is particularly true if the traffic
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
queue to form in this bottleneck link could see some of its packets
forwarded by the NQB queue, and some of them redirected to the QB
queue. Depending on the queueing latency and scheduling within the
network element, this 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 that out of order delivery will be
experienced.
7. Relationship to L4S
Traffic flows marked with the NQB DSCP as described in this draft are 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 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- result being that NQB traffic and L4S traffic can share the low-
latency queue in an L4S dual-queue node latency queue in an L4S dual-queue node
[I-D.ietf-tsvwg-aqm-dualq-coupled]. [I-D.ietf-tsvwg-aqm-dualq-coupled]. Compliance with the DualQ
coupled AQM requirements is considered sufficient to enable fair
allocation of bandwidth between the QB and NQB queues.
7. Use Cases 8. Configuration and Management
7.1. DOCSIS Access Networks As required above, nodes supporting the NQB PHB provide for the
configuration of classifiers that can be used to differentiate
between QB and NQB traffic of equivalent importance. The default for
such classifiers is recommended to be the assigned NQB DSCP (to
identify NQB traffic) and the Default (0) DSCP (to identify QB
traffic).
9. Use Cases
9.1. 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 shaping bandwidth with MUST be configured to share the service's rate shaping bandwidth with
the queue for QB traffic. the queue for QB traffic.
7.2. Mobile Networks 9.2. Mobile Networks
Historically, mobile networks have been configured to bundle all Historically, mobile networks have been configured to bundle all
flows to and from the Internet into a single "default" EPS bearer flows to and from the Internet into a single "default" EPS bearer
whose buffering characteristics are not compatible with low-latency whose buffering characteristics are not compatible with low-latency
traffic. The established behaviour is rooted partly in the desire to traffic. The established behaviour is rooted partly in the desire to
prioritise operators' voice services over competing over-the-top prioritise operators' voice services over competing over-the-top
services and partly in the fact that the addition of bearers was services and partly in the fact that the addition of bearers was
prohibitive due to expense. Of late, said consideration seems to prohibitive due to expense. Of late, said consideration seems to
have lost momentum (e.g., with the rise in Multi-RAB (Radio Access have lost momentum (e.g., with the rise in Multi-RAB (Radio Access
Bearer) devices) and the incentives might now be aligned towards Bearer) devices) and the incentives might now be aligned towards
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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 be routed through the default EPS bearer. SHOULD be routed through the default EPS bearer.
7.3. WiFi Networks 9.3. WiFi Networks
WiFi networking equipment compliant with 802.11e generally supports WiFi networking equipment compliant with 802.11e generally supports
either four or eight transmit queues and four sets of associated either four or eight transmit queues and four sets of associated
Enhanced Multimedia Distributed Control Access (EDCA) parameters Enhanced Multimedia Distributed Control Access (EDCA) parameters
(corresponding to the four WiFi Multimedia (WMM) Access Categories) (corresponding to the four WiFi Multimedia (WMM) Access Categories)
that are used to enable differentiated media access characteristics. that are used to enable differentiated media access characteristics.
Implementations typically utilize the IP DSCP field to select a Implementations typically utilize the IP DSCP field to select a
transmit queue, but should be considered as Non-Differentiated transmit queue, but should be considered as Non-Differentiated
Services-Compliant Nodes as described in Section 4 of [RFC2475] Services-Compliant Nodes as described in Section 4 of [RFC2475]
because this transmit queue selection is a local implementation because this transmit queue selection is a local implementation
characteristic that is not part of a consistently operated DiffServ characteristic that is not part of a consistently operated DiffServ
domain or region. As a result this document discusses domain or region. As a result this document discusses
interoperability with WiFi networks, as opposed to PHB compliance. interoperability with WiFi networks, as opposed to PHB compliance.
As discussed in [RFC8325], most existing WiFi implementations use a As discussed in [RFC8325], most existing WiFi implementations use a
default DSCP to User Priority mapping that utilizes the most default DSCP to User Priority mapping that utilizes the most
significant three bits of the DiffServ Field to select "User significant three bits of the DiffServ Field to select "User
Priority" which is then mapped to the four WMM Access Categories. In Priority" which is then mapped to the four WMM Access Categories. In
order to increase the likelihood that NQB traffic is provided a order to increase the likelihood that NQB traffic is provided a
separate queue from QB traffic in existing WiFi equipment, the 0x2A separate queue from QB traffic in existing WiFi equipment, the 42
codepoint is preferred for NQB. This would map NQB to UP_5 which is codepoint is preferred for NQB. This would map NQB to UP_5 which is
in the "Video" Access Category. Similarly, systems that utilize in the "Video" Access Category. Similarly, systems that utilize
[RFC8325], SHOULD map the NQB codepoint to UP_5 in the "Video" Access [RFC8325], SHOULD map the NQB codepoint to UP_5 in the "Video" Access
Category. Category.
While the DSCP to User Priority mapping can enable WiFi systems to While the DSCP to User Priority mapping can enable WiFi systems to
support the NQB PHB requirement for segregated queuing, many support the NQB PHB requirement for segregated queuing, many
currently deployed WiFi systems may not be capable of supporting the currently deployed WiFi systems may not be capable of supporting the
remaining NQB PHB requirements in Section 5. This is discussed remaining NQB PHB requirements in Section 5. This is discussed
further below. further below.
skipping to change at page 8, line 25 skipping to change at page 10, line 25
As an additional safeguard, and to prevent the inadvertent As an additional safeguard, and to prevent the inadvertent
introduction of problematic traffic into unmanaged WiFi networks, introduction of problematic traffic into unmanaged WiFi networks,
network equipment that is intended to deliver traffic into unmanaged network equipment that is intended to deliver traffic into unmanaged
WiFi networks (e.g. an access network gateway for a residential ISP) WiFi networks (e.g. an access network gateway for a residential ISP)
MUST by default remap the NQB DSCP to Default. Such equipment MUST MUST by default remap the NQB DSCP to Default. 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.
8. Acknowledgements 10. Acknowledgements
Thanks to Bob Briscoe, Greg Skinner, Toke Hoeiland-Joergensen, Luca Thanks to Bob Briscoe, Greg Skinner, Toke Hoeiland-Joergensen, Luca
Muscariello, David Black, Sebastian Moeller, Ruediger Geib, Jerome Muscariello, David Black, Sebastian Moeller, Ruediger Geib, Jerome
Henry, Steven Blake, Jonathan Morton, Roland Bless, Kevin Smith, Henry, Steven Blake, Jonathan Morton, Roland Bless, Kevin Smith,
Martin Dolly, and Kyle Rose for their review comments. Martin Dolly, and Kyle Rose for their review comments.
9. IANA Considerations 11. IANA Considerations
This draft proposes the registration of a standardized DSCP = 0x2A to This document assigns the Differentiated Services Field Codepoint
denote Non-Queue-Building behavior. (DSCP) 42 ('0b101010', 0x2A) from the "Differentiated Services Field
Codepoints (DSCP)" registry (https://www.iana.org/assignments/dscp-
registry/) ("DSCP Pool 1 Codepoints", Codepoint Space xxxxx0,
Standards Action) to denote Non-Queue-Building behavior.
10. Security Considerations 12. Security Considerations
There is no incentive for an application to mismark its packets as There is no incentive for an application to mismark its packets as
NQB (or vice versa). If a queue-building flow were to mark its NQB (or vice versa). If a queue-building flow were to mark its
packets as NQB, it could experience excessive packet loss (in the packets as NQB, it could experience excessive packet loss (in the
case that traffic protection is not supported by a node) or it could case that traffic protection is not supported by a node) or it could
receive no benefit (in the case that traffic protection is receive no benefit (in the case that traffic protection is
supported). If a non-queue-building flow were to fail to mark its supported). If a non-queue-building flow were to fail to mark its
packets as NQB, it could suffer the latency and loss typical of packets as NQB, it could suffer the latency and loss typical of
sharing a queue with capacity seeking traffic. sharing a queue with capacity seeking traffic.
In order to preserve low latency performance for NQB traffic,
networks that support the NQB PHB will need to ensure that mechanisms
are in place to prevent malicious NQB-marked traffic from causing
excessive queue delays. This document recommends the implementation
of a traffic protection mechanism to achieve this goal, but
recognizes that other options may be more desirable in certain
situations.
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.
11. Informative References 13. Informative References
[Barik] Barik, R., Welzl, M., Elmokashfi, A., Dreibholz, T., and
S. Gjessing, "Can WebRTC QoS Work? A DSCP Measurement
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", draft-briscoe-docsis-q-protection-00 (work Low Latency", draft-briscoe-docsis-q-protection-00 (work
in progress), July 2019. in progress), July 2019.
[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., 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)", draft-ietf-tsvwg-aqm-dualq-coupled-10 (work in (L4S)", draft-ietf-tsvwg-aqm-dualq-coupled-12 (work in
progress), July 2019. progress), July 2020.
[I-D.ietf-tsvwg-ecn-l4s-id]
Schepper, K. and B. Briscoe, "Identifying Modified
Explicit Congestion Notification (ECN) Semantics for
Ultra-Low Queuing Delay (L4S)", draft-ietf-tsvwg-ecn-l4s-
id-10 (work in progress), March 2020.
[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., Bagnulo, M., and G. White, "Low
Latency, Low Loss, Scalable Throughput (L4S) Internet Latency, Low Loss, Scalable Throughput (L4S) Internet
Service: Architecture", draft-ietf-tsvwg-l4s-arch-05 (work Service: Architecture", draft-ietf-tsvwg-l4s-arch-06 (work
in progress), February 2020. in progress), March 2020.
[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>.
[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>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
[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
 End of changes. 27 change blocks. 
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