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ISP Dual Queue Networking Deployment Recommendations
draft-livingood-low-latency-deployment-07

Document Type Active Internet-Draft (individual)
Author Jason Livingood
Last updated 2024-10-27 (Latest revision 2024-10-17)
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draft-livingood-low-latency-deployment-07
Independent Stream                                          J. Livingood
Internet-Draft                                                   Comcast
Intended status: Informational                           17 October 2024
Expires: 20 April 2025

          ISP Dual Queue Networking Deployment Recommendations
               draft-livingood-low-latency-deployment-07

Abstract

   The IETF's Transport Area Working Group (TSVWG) has finalized
   experimental RFCs for Low Latency, Low Loss, Scalable Throughput
   (L4S) and new Non-Queue-Building (NQB) per hop behavior.  These
   documents describe a new architecture and protocol for deploying low
   latency networking.  Since deployment decisions are left to
   implementers, this document explores the potential implications of
   those decisions and makes recommendations that can help drive
   adoption and acceptance of L4S and NQB.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 20 April 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  A Different Understanding of Application Needs  . . . . .   4
     1.2.  New Thinking on Low Latency Packet Processing . . . . . .   5
   2.  Key Low Latency Networking Concepts . . . . . . . . . . . . .   5
     2.1.  Prioritization: Same Best Effort Priority for All
           Traffic . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Throughput: Shared Across All Traffic . . . . . . . . . .   6
     2.3.  Access-Agnostic: Can Work on All Types of Network
           Technology  . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Recommendations for Application Developers  . . . . . . . . .   6
     3.1.  Delivery Infrastructure Needs for L4S . . . . . . . . . .   6
     3.2.  Delivery Infrastructure Needs for NQB . . . . . . . . . .   7
     3.3.  Don't Mark Non-Delay-Sensitive Traffic for L4S or NQB . .   7
     3.4.  Consider Application Needs in Choosing L4S vs. NQB  . . .   7
   4.  Recommended Deployment Decisions for ISPs . . . . . . . . . .   8
     4.1.  Application-Originated Marking vs. Middleboxes  . . . . .   8
       4.1.1.  Applications Mark Traffic, Not Middleboxes  . . . . .   9
       4.1.2.  Any Application Provider Can Mark Traffic - No Advance
               Permission  . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Interconnection Points (Provider Edge)  . . . . . . . . .  10
       4.2.1.  Allow ECN Across Domain (Peer) Boundaries . . . . . .  10
       4.2.2.  Allow DSCP-45 Across Domain (Peer) Boundaries . . . .  10
     4.3.  Inside the ISP Network (Core Network) . . . . . . . . . .  11
       4.3.1.  Avoid Internal Remarking of DSCP Values if
               Possible  . . . . . . . . . . . . . . . . . . . . . .  11
     4.4.  Last Mile Network (Access Network)  . . . . . . . . . . .  11
       4.4.1.  Consider Queue Protection . . . . . . . . . . . . . .  12
     4.5.  Customer Premise Equipment (Customer Edge)  . . . . . . .  12
       4.5.1.  Support a Variety of End User Equipment . . . . . . .  12
       4.5.2.  Pass Markings to Customer-Administered CPE  . . . . .  13
     4.6.  Inside the Home (Customer Local Area Network) . . . . . .  13
       4.6.1.  In Home Wi-Fi LAN Configuration . . . . . . . . . . .  13
       4.6.2.  Use Permissive Upstream NQB Queue Admission . . . . .  14
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   8.  Regulatory Considerations . . . . . . . . . . . . . . . . . .  15
   9.  Revision History  . . . . . . . . . . . . . . . . . . . . . .  15
   10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  16
   11. Informative References  . . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  20

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1.  Introduction

   The IETF's Transport Area Working Group (TSVWG) has finalized RFCs
   for Low Latency, Low Loss, Scalable Throughput (L4S) and Non-Queue-
   Building (NQB) per hop behavior [RFC9330] [RFC9331] [RFC9332]
   [I-D.ietf-tsvwg-l4sops] [I-D.ietf-tsvwg-nqb]
   [I-D.ietf-tsvwg-dscp-considerations].  These documents do a good job
   of describing a new architecture and protocol for deploying low
   latency networking.  But as is normal for many such standards,
   especially those in experimental status, certain deployment decisions
   are ultimately left to implementers.

   This document explores the potential implications of key deployment
   decisions and makes recommendations for those decisions that may help
   drive adoption.  In particular, there are best practices based on
   prior experience as a network operator that should be considered and
   there are network neutrality types of considerations as well.  These
   technologies are benign on their own, but the way they are
   operationally implemented can determine whether they are ultimately
   perceived positively and adopted by the broader Internet ecosystem.
   That is a key issue for low latency networking, because the more
   applications developers and edge platforms that adopt new packet
   marking for low latency traffic, then the greater the value to end
   users, so ensuring it is received well is key to driving strong
   initial adoption.

   It is worth stating though that these decisions are not embedded in
   or inherent to L4S and NQB per se, but are decisions that can change
   depending upon differing technical, regulatory, business or other
   requirements.  Even two network operators with the same type of
   access technology and in the same market area may choose to implement
   in different ways.  Nevertheless, this document suggests that certain
   specific deployment decisions can help maximize the value of low
   latency networking to both users and network operators.

   The IETF documents on L4S and NQB also made clear that nearly all
   modern application types - from video conferencing to web browsing -
   can benefit from low latency networking.  In addition, the design of
   the protocols also make clear that applications developers are best
   positioned to understand the needs of their applications and to, by
   extension, express any such low latency needs via appropriate L4S or
   NQB packet marking.  Furthermore, unlike with bandwidth priority on a
   highly/fully utilized link, low latency networking can better balance
   the needs of different types of best effort flows (with some caveats
   - see Section 1.2).

   For additional background on latency and why latency matters so much
   to the Internet, please read [BITAG].

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1.1.  A Different Understanding of Application Needs

   In the course of working to improve the responsiveness of network
   protocols, the IETF concluded with their L4S and NQB work that there
   were fundamentally two types of Internet traffic and that these two
   major traffic types could benefit from having separate network
   processing queues in order to improve the way the Internet works for
   all applications, and especially for interactive applications.

   One of the two major traffic types is Queue Building (QB) - things
   like file downloads and backups that are designed utilize as much
   network capacity as possible but with which users are usually not
   interacting with in real-time.  The other was Non-Queue-Building
   (NQB) - such as DNS lookups, voice interaction with artificial
   intelligence (AI) assistants, video conferencing, gaming, and so on.
   NQB flows tend to be ones where the end user is sensitive to any
   delays.

   Thus, the IETF created specifications for how to use two different
   network processing queues.  The performance value of dual queue
   networking (simply "low latency networking" hereafter) has proven out
   in Comcast's dual queue networking field trial [Comcast].  That field
   trial lasted for over a year and was regularly reported on over time
   at several IETF TSVWG meetings [IETF-TSVWG-117] [IETF-TSVWG-118]
   [IETF-TSVWG-119] [IETF-TSVWG-120] and demonstrated that L4S and NQB
   can work deliver excellent responsiveness for a variety of
   applications - from video conferencing to cloud gaming, DNS and other
   applications.  It seems likely that this new capability will enable
   entirely new classes of applications to become possible, driving a
   wave of new Internet innovation, while also improving the
   applications people use today.

   +--------------------------------+---------------------------------+
   | May Benefit from L4S/NQB       | Classic Queue Building          |
   +--------------------------------+---------------------------------+
   | User interacting with screen   | Unattended background process   |
   +--------------------------------+---------------------------------+
   | Video conference, audio        | Cloud file backup, cloud file   |
   | conference, live event video   | restoration, game platform      |
   | stream, cloud document editing | update, operating system update |
   +--------------------------------+---------------------------------+

                   Table 1: Comparison of Traffic Types

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1.2.  New Thinking on Low Latency Packet Processing

   The Introduction says that unlike with bandwidth priority on a
   highly/fully utilized link, low latency networking can better balance
   the needs of different types of best effort flows.  But this bears a
   bit of further discussion to understand more fully.

   L4S does *not* provide low latency in the same way as previous
   technologies like DiffServ Quality of Service (QoS).  That prior QoS
   approach used packet prioritization, where it was possible to assign
   a higher relative priority to certain application traffic, such as
   Voice over IP (VoIP) telephony.  This approach could provide
   consistent and relatively low latency by assigning high priority to a
   partition of the capacity of a link, and then policing the rate of
   packets using that partition.  This traditional approach to QoS is
   hierarchical in nature.

   That QoS approach is to some extent predicated on an idea that
   network capacity is very limited and that links are often highly
   utilized.  But in today's Internet, it is increasingly the case that
   there is an abundance of capacity to end users (e.g., symmetric 1
   Gbps), which makes such traditional QoS approaches ineffective in
   delivering ever-lower latency.  This new low latency networking
   approach is not based on hierarchical QoS prioritization.  Rather, it
   is built upon conditional priority scheduling between its two queues
   that operate at best effort QoS priority.

2.  Key Low Latency Networking Concepts

   Before proceeding into deployment recommendations, it is important to
   first explore a few key concepts about low latency networking.  This
   is critical because in the past many networks have thought of only
   bandwidth and/or priority at the sole network attributes that could
   be adjusted in order to improve application or network quality.  The
   advent of low latency networking forces a re-examination of those old
   assumptions, as we take into account the profound impact that latency
   and jitter have on the quality of the end user experience.

2.1.  Prioritization: Same Best Effort Priority for All Traffic

   Low latency traffic to is not prioritized over other (best effort
   priority) "classic" Internet traffic.  That is the case over the ISP
   network and the broader internet, though it may not not necessarily
   be the case for a user's in-home Wi-Fi network due to the particulars
   of how the IEEE 802.11 wireless protocol [IEEE] functions at the
   current time - see [RFC8325]).  In addition, some user access points
   may prioritize certain traffic (such as gaming) and some traffic such
   as NQB may use the AC_VI Wi-Fi link layer queue [I-D.ietf-tsvwg-nqb].

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   This best effort approach stands in contrast to prior differential
   quality of service (QoS) approaches or to what has been discussed for
   5G network slicing [CDT-NN] [van-Schewick-1A] [van-Schewick-1B]
   [van-Schewick-2] [van-Schewick-3].

2.2.  Throughput: Shared Across All Traffic

   Low latency networking flows do not get access to greater throughput
   than "classic" flows.  Thus, a user's total provisioned or permitted
   throughput on an ISP access network link is shared between both
   classic and low latency queues.

2.3.  Access-Agnostic: Can Work on All Types of Network Technology

   Ultimately, the emergence of low latency networking represents a
   fundamental new network capability that applications can choose to
   utilize as their needs dictate.  It reflects a new ground truth about
   two fundamentally different types of application traffic and
   demonstrates that networks continue to evolve in exciting ways.  This
   new network capability can be implemented in a variety of network
   technologies.  For example in access network technologies this could
   be implemented in DOCSIS [LLD], 5G [Ericsson], PON [CTI], and many
   other types of networks.  Anywhere that a network bottleneck could
   occur may benefit from this technology.

3.  Recommendations for Application Developers

   Application developers need to add L4S or NQB packet marking to their
   application, which will often depend upon the capabilities of a
   device's operation system (OS) or a software development kit (SDK)
   [Apple] that the OS developer makes available.  In addition, the
   application server will also need to support the appropriate marking
   and, when L4S is used, to implement a responsive congestion
   controller.

3.1.  Delivery Infrastructure Needs for L4S

   Since L4S uses the Explicit Congestion Notification (ECN) field of
   the packet header, to ensure ECN works end-to-end, application
   developers need to be certain that their servers, datacenter routers,
   and any transit, cloud provider, or content delivery network (CDN)
   server involved in their application IS NOT altering or bleaching the
   ECN field.  For an application to use the L4S queue, they must mark
   their packets with the ECT(1) code point to signal L4S-capability or
   with the Congestion Experienced (CE) code point when appropriate.
   Coupled with client marking, if an application client or server
   detects CE marks, it should respond accordingly (e.g., by reducing
   the send rate), which typically means that the server must be running

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   a "responsive" congestion controller (i.e., is able to adjust rate
   based the presence or absence of CE marks for L4S traffic - such as
   DCTCP, TCP Prague, SCReAM, and BBRv2).  See Section 4.3 of [RFC9330]
   and Section 4.3 of [RFC9331] for more information about this.

3.2.  Delivery Infrastructure Needs for NQB

   Since NQB uses the DSCP-45 code point in the DiffServ part of the
   packet header, to ensure NQB works end-to-end, application developers
   need to be certain that their servers, datacenter routers, and any
   transit, cloud provider, or content delivery network (CDN) server
   involved in their application IS NOT altering or bleaching a DSCP-45
   mark.  One relative advantage of NQB is that the server does not need
   to run a special responsive congestion controller.  On the other
   hand, NQB is geared toward bandwidth-limited sparse flows rather than
   capacity-seeking flows, so it will depend on your application's
   needs.  In addition, it is common for networks to bleach or modify
   DSCP marks on ingress, which means that networks will need to change
   that packet handling policy for NQB to function on an end-to-end
   basis.  In contrast, it is far less common for the ECN field of the
   packet header to be modified.

3.3.  Don't Mark Non-Delay-Sensitive Traffic for L4S or NQB

   It may seem tempting to mark all traffic for L4S or NQB handling, but
   this will likely harm the experience of queue-building apps like file
   downloads.  Also, remember that the network priority for L4S and NQB
   is still best efforts and so there is not more bandwidth for L4S or
   NQB compared to classic traffic; they share the same bandwidth and
   best-efforts priority.  It is also possible that some flows from an
   application can benefit, while others will not.  For example, a video
   gaming service may benefit from using L4S or NQB for real-time
   controller inputs and gameplay, while major game software updates
   would best be left in the classic queue.

3.4.  Consider Application Needs in Choosing L4S vs. NQB

   Determine whether your application needs "sparse" flows or
   "congestion-controlled" (higher capacity) flows.  Sparse flows that
   are latency senstive should be marked as NQB (thus DSCP-45).  This
   may be things like DNS queries or VoIP media flows, where maximizing
   the bandwidth of the flow is not necesary.

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   Latency-sensitive flows that need more bandwidth are congestion
   controlled, and identified via ECN marking.  These types of
   applications are less limited by the application protocol itself
   (i.e., a small DNS query), which means the application quality can
   improve as more bandwidth is available - such as shifting a video
   stream or a video conference session from Standard Definition (SD) to
   4K quality.

4.  Recommended Deployment Decisions for ISPs

   Like any network or system, a good deployment design and
   configuration matters and can be the difference between a well-
   functioning and accepted system and one that experiences problems and
   faces user and/or developer opposition.  In the context of deploying
   low latency networking in an ISP network, this document describes
   some recommendations that should help to ensure a deployment is
   resilient, well-accepted, and creates the environment for generating
   strong network effects.  Following these recommendations should help
   avoid barriers to adoption and help provide a strong foundation for
   growth.

   The first sections below will look at the end-to-end network path
   from when packets come into an ISP's network (provider edge), then
   what happens within the ISP's network core, how packets are delivered
   to customner premise equiment (CPE), and finally what may happen with
   the Local Area Network (LAN) in a home.

   This section will then conclude with key deployment decisions, which
   have both operational as well as technology policy implications.

4.1.  Application-Originated Marking vs. Middleboxes

   As noted in [Tussle] there has always been a tension in the end-to-
   end model between how much intelligence and processing takes place
   along the end-to-end path inside of a network and how much takes
   place at the end of the network in servers and/or end user client
   devices and software.  In this new approach to low latency
   networking, entry into a low latency queue depends upon marks in the
   packet header of a particular application flow.  In practice, this
   marking is best left to the application edge of the network, rather
   than it being a funcyion of a so-called middlebox.  As explored
   below, this is the most efficient, least prone to error or mis-
   classification, and is most acceptable from the standpoint of network
   neutrality regulation.

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4.1.1.  Applications Mark Traffic, Not Middleboxes

   The best approach is for applications to mark traffic to indicate
   their preference for the low latency queue, not the network making
   such a decision on its own.  This is for several reasons:

   *  According to the end-to-end principle, this function is best
      delegated to the edge of the network as an architectural best
      practice (the edge being the application in this case).

   *  Application marking maintains the loose coupling between the
      application and network layers, eliminating the need for close
      coordination between networks and application developers.

   *  Application developers know best whether their application is
      compatible with low latency networking and which aspects of their
      traffic flows will or will not benefit.

   *  Only the application (not the network) knows whether a scalable
      congestion control algorithm congestion control is being used on
      the application server.  Thus, only the developer and server
      administrator know if they are correctly responding to Congestion
      Experienced (CE) markings for L4S (see Section 4.1 of [RFC9331]).

   *  Application traffic is almost entirely encrypted, which makes it
      very difficult for networks to accurately determine application
      protocols and to further infer which flows will benefit from low
      latency and which flows may be harmed because they need to build a
      queue.  It is likely that false positives [Lotus] and false
      negatives will occur if network-based inference is used; all of
      which can be avoided simply by relying solely on application
      marking.

   *  The pace of innovation and iteration is necessarily faster-moving
      in the application edge at layer 7, rather than in the network at
      layer 3 (and below) - where there is greater standards stability
      and a lower rate of major changes.  As a result, the application
      layer is best suited to rapid experimentation and iteration.
      Network operators and equipment vendors trying to infer
      application needs will in comparison always be in a reactive mode,
      one step behind changes made in applications.

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4.1.2.  Any Application Provider Can Mark Traffic - No Advance
        Permission

   Any application provider should be able to mark their traffic for the
   low latency queue, with no restrictions other than standards
   compliance or other reasonable and openly documented technical
   guidelines.  This maintains the loose cross-layer coupling that is a
   key tenet of the Internet's architecture by eliminating the need for
   application providers and networks to coordinate and creates an
   environment of so-called "permissionless innovation".

4.2.  Interconnection Points (Provider Edge)

4.2.1.  Allow ECN Across Domain (Peer) Boundaries

   Traffic sent TO a peer network marked with ECT(1) or CE in the ECN
   header MUST pass to that peer without altering or removing the ECT(1)
   or CE marking (see exception below).  Traffic FROM peers marked with
   ECT(1) or CE in the ECN header MUST be allowed to enter the network
   without altering or removing the ECT(1) or CE marking (see exception
   below).  The only exception would be when a network element is CE-
   aware and able to add a CE mark to signal that it is experiencing
   congestion at that hop.

   This part - allowing unmodified ECN across the network - is likely to
   be easier than DSCP-45 for NQB (see next section), since it appears
   rare that networks modify the ECN header of packet flows.

4.2.2.  Allow DSCP-45 Across Domain (Peer) Boundaries

   Traffic sent TO a peer network marked with DSCP value 45 MUST pass to
   that peer without altering or removing the DSCP 45 marking (see
   exception below).  Traffic FROM peers marked with DSCP value 45 MUST
   be allowed to enter the network without altering or removing the DSCP
   45 marking (see exception below).  Peer marking exception: Some peer
   networks may use DSCP 45 for purposes other than NQB LL within their
   network.  In these cases, the peer using DSCP 45 for other purposes
   is responsible for remarking on ingress and egress from their
   network.  In all cases, traffic marked DSCP 45 must still be handled
   as best efforts - not a higher priority than other Internet traffic.

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4.3.  Inside the ISP Network (Core Network)

   Within an ISP network, packets will typically traverse edge routers,
   backbone routers, and regional/local routers before being send into a
   last-mile access network to which end users are connected.  In the
   case of ECN, there are unlikely to be any issues in these hops, as
   ECN appears to pass end-to-end across most networks.  Nevertheless,
   it is important to check network policies and router configurations
   to confirm this and to validate it via packet captures at an end user
   CPE.

   Ensuring support for NQB via DSCP-45 may be more challenging, as
   network operators typically have unique uses of various DSCP marks
   within their network, such as to differentiate residential internet
   traffic from commercial internet, transit, voice services, management
   traffic, and so on.  If DSCP-45 is already used, then a network
   policy will need to be created and deployed that will transform
   ingress packets at the peer edge marked as DSCP-45 to some internal-
   use value, then back again to DSCP-45 when packets hit the end user
   CPE.  Then the reverse must be done for egress packets, changing
   DSCP-45 marks from CPE to the internal-use value and then at the
   peering edge back to DSCP-45.  There will also need to be a policy to
   transform DSCP marks from the internal-use value back to DSCP-45 at
   the CPE for cases when a flow is peer-to-peer, meaning directly
   between two end users on a given ISP network.

4.3.1.  Avoid Internal Remarking of DSCP Values if Possible

   If possible, for operational simplicity, a network should try to
   maintain the use of DSCP 45 on an end-to-end basis without remarking
   in their interior network hops.  This may not be possible in all
   networks, because some may already use DSCP 45 for some private
   internal reason.  In such cases, packets must obviously be remarked
   to and from DSCP 45 at the customer edge (CPE) and network ingress/
   egress to other networks.  But if DSCP 45 is not used internally, it
   is far simpler for network operations and troubleshooting to preserve
   that mark on an end to end basis.

4.4.  Last Mile Network (Access Network)

   There are two hops of interest in the last mile access network.  One
   will be a point of user aggregation, such as a Cable Modem
   Termination System (CMTS) or Optical Line Terminal (OLT).  The second
   is at the user location, such as a Cable Modem (CM) or Optical
   Network Unit (ONU), both of which are example of CPE.

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4.4.1.  Consider Queue Protection

   The specifications in [I-D.ietf-tsvwg-nqb] describe a concept of
   Traffic Protection, also known as a Queue Protection Function
   [I-D.briscoe-docsis-q-protection] or simply Queue Protection.  The
   document says that Traffic Protection is optional and may not be
   needed in certain networks.  In the case of an ISP deploying low
   latency networking with two queues, an ISP should consider deploying
   such a network function to at least detect mismarking (if not
   necessarily to correct mismarking).  This may be implemented, for
   example, in end user CPE, last mile network equipment, and/or
   elsewhere in the ISP network - or closely monitors network statistics
   and user feedback for any indication of widespread low latency packet
   mismarking by applications.

   Queue Protection can be implemented any place that there are two
   queues for low latency networking.  For example, for downstream
   traffic, this would be in the aggregation device (i.e., CMTS, OLT)
   and in the upstream direction in the CPE (i.e., CM or ONU).

4.5.  Customer Premise Equipment (Customer Edge)

   In most residential internet services, there are typically two
   equipment modes.  One is very simple CPE that hands off from the
   ISP's access network (i.e., DSL, 5G, DOCSIS, PON) and provides the
   customer with an Ethernet interface and IP address(es).  The customer
   then connects their own router and wireless access point (often
   integrated into the router, typically referred to as a "wireless
   gateway" or "wireless router").  The other model is more typical,
   which is that the CPE integrates a link layer termination function
   (i.e., Cable Modem, 5G radio, or Optical Network Unit) as well as a
   wireless gateway.

   Not all ISP networks support both of these models; sometimes only a
   wireless gateway is available.  Even in this case, some users "double
   NAT" and install their own router and wireless access point(s) to get
   whatever functionality and control over their home network that they
   desire.  The cases explored below are commonplace but may not apply
   to all networks.

4.5.1.  Support a Variety of End User Equipment

   To create the best foundation for growth, both customer-owned and
   ISP-administered Customer Premises Equipment (CPE) should be
   supported (assuming that is typical and technically feasible in a
   particular type of access network), when applicable.  In mobile
   networks, where a user device connects directly to the network, this
   may be easier as it simply depends upon operating system software in

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   that end user device.  In fixed networks, there is usually CPE that
   demarcates between the ISP network and the user's home LAN.  The
   software running on those CPE devices will also need to support low
   latency networking, as well as software in other ISP network devices
   where CPE connections are aggregated.  The more CPE devices that are
   enabled, the greater the pool of potential users, and thus the
   broader adoption would be, positively driving network effects.

4.5.2.  Pass Markings to Customer-Administered CPE

   In some cases, dual queue networking and associated packet marking is
   supported up to the ISP's demarcation point - such as in a cable
   modem.  It is recommended that packet markings should pass from such
   a demarcation point to any attached customer-administered CPE, such
   as a router or wireless access point.  That enables a customer-
   administered router to implement dual queue networking, rather that
   it only being possible with ISP-administered CPE.

4.6.  Inside the Home (Customer Local Area Network)

   As noted above with the mention of an integrated wireless gateway,
   and is most common, the CPE and router/wireless network gear may be
   integrated into a single CPE device.  Even though these are
   functionally in one piece of hardware, we can think of the wide area
   network interface and local area network as functionally separate for
   purposes of this analysis.

4.6.1.  In Home Wi-Fi LAN Configuration

   As noted above with respect to prioritization of packets in the ISP
   network, all packets should be handled with the same best effort
   priority in the ISP access network and on the internet.  However, in
   a user's home Wi-Fi (wireless) local area network (WLAN), this is
   more complicated, because there is not a precise mapping between IETF
   packet marking and IEEE 802.11 marking, explored in [RFC8325].  In
   short, today's 802.11 specifications enable a Wi-Fi network to have
   multiple queues, using different "User Priority" and "Access
   Category" values.  At the current time, these queues are AC_BK
   (Background), AC_BE (Best Effort), AC_VI (Video), and AC_VO (Voice).

   As explored in [I-D.ietf-tsvwg-nqb], packets in the low latency queue
   may be expected to be marked for the best effort (AC_BE) or video
   (AC_VI) wireless queue.  For additional context, please refer to
   Section 8.1 of [I-D.ietf-tsvwg-nqb].  In some situations, such as a
   user-owned wireless access point or CPE, it may not be possible for
   the user to select which wireless queue is used.  In cases where the
   CPE is ISP-administered, selecting a specific wireless queue may be
   possible - though it is not yet clear what the best practice may be

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   for this selection until ISPs and application developers have more
   experience with low latency networking.  As of the writing of this
   document, it appears that the AC_VI queue may be used for the low
   latency queue in some networks - and that many latency-sensitive
   applications are already marking their WLAN traffic for AC_VI and
   AC_VO.

4.6.2.  Use Permissive Upstream NQB Queue Admission

   Since the IETF's NQB specification is only recently completed, many
   applications that have been using other DSCP marks for their latency-
   sensitive flows have not yet shifted to adopt DSCP-45.  One example
   is the Microsoft Xbox platform [Microsoft], which is using DSCP-46.
   So in the relatively short-term, ISPs may find it beneficial to their
   customers to use a more permissive upstream NQB admission policy,
   allowing DSCP-40, 45, 46, and 56 admission into the low latency
   queue.  It may take a year or more after the NQB DSCP assignment is
   made by IANA for developers to shift to DSCP-45, given other items in
   their development backlog and their software release schedule.

5.  Acknowledgements

   Thanks to Bob Briscoe, Mat Ford, Vidhi Goel, Eliot Lear, Sebastian
   Moeller, Sebnem Ozer, Jim Rampley, Dan Rice, Greg Skinner, Greg
   White, and Yiannis Yiakoumis for their review and feedback on this
   document.

6.  IANA Considerations

   RFC Editor: Please remove this section before publication.

   This memo includes no requests to or actions for IANA.

7.  Security Considerations

   The key security consideration pertains to Queue Protection.  As the
   current time, it is recommended that implementers utilize Queue
   Protection, to ensure that any traffic that is incorrectly marked for
   low latency can be detected and remarked for the classic queue.  The
   necessity of Queue Protection remains something of a debate, with
   some firmly believing it is necessary but others believing that it is
   not needed.  The latter view is that application developers have a
   natural incentive to correctly mark their traffic, because to do
   otherwise would worsen the quality of experience (QoE) for their
   users.  In that line of thinking, if a developer mismarks, they and/
   or their users will notice and they will fix that error.  However, it
   is also conceivable that malicious software could be operating on a
   user's device or home network and that malicious software could try

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   to send some much traffic to the low latency queue that the queue or
   both queues become unusable.  This is quite similar to other
   "traditional" denial of servce (DoS) attacks, so it does not
   necessarily seems unique to low latency networking.  But due to the
   possibility of this occuring, and low latency networking being such a
   new approach, it seems prudent to implement Queue Protection.

8.  Regulatory Considerations

   Network Neutrality (a.k.a.  Net Neutrality) can mean a variety of
   things within a country, as well as between different countries,
   based on different opinions, market structures, business practices,
   laws, and regulations.  Generally speaking, In the context of the
   United States' market, it has come to mean that Internet Service
   Providers (ISPs) should not block, throttle, or deprioritize lawful
   application traffic, and should not engage in paid prioritization,
   among other things.  Net Neutrality concerns can sometimes affect the
   deployment of new technologies by ISPs, so they should carefully
   consider regulatory issues when making deployment decisions.

   As it is envisioned in the design of the IETF's new low latency
   networking protocols, the addition of a low latency packet processing
   queue at a network link is merely a second packet queue and does not
   mean that this queue is hierarchically prioritized or that it has
   more capacity.  As a result, low latency networking appears to pose
   no new Net Neutrality issues.  However, it is important for ISPs to
   keep these risks in mind as they make deployment design decisions.

   One key aspect of low latencty networking is that it operates, from
   the perspective of an ISP's deployment, is application-agnostic.  The
   ISP creates a second network queue on key network links, but does not
   decide on their own what applications can use this queue.  Rather,
   they add the queue and packet flows are sent to that queue based on
   packet marking set by application developers.  This approach is far
   superior to older approaches, which caused significant Net Neutrality
   risks [Lotus], that used middleboxes to attempt to infer applications
   based on observing packet flows on ISP network links.

9.  Revision History

   RFC Editor: Please remove this section before publication.

   v00: First draft

   v01: Incorporate comments from 1st version after IETF-115

   v02: Incorporate feedback from the TSVWG mailing list

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   v03: Final feedback from TSVWG and prep for sending to ISE

   v04: Refresh expiration before major revision

   v05: Changes from Greg Skinner and Eliot Lear

   v06: More changes from Eliot Lear

   v07: More changes from Eliot Lear

10.  Open Issues

   RFC Editor: Please remove this section before publication.

   - Open issues are being tracked in a GitHub repository for this
   document at https://github.com/jlivingood/IETF-L4S-Deployment/issues

11.  Informative References

   [RFC8325]  Szigeti, T., Henry, J., and F. Baker, "Mapping Diffserv to
              IEEE 802.11", RFC 8325, DOI 10.17487/RFC8325, February
              2018, <https://www.rfc-editor.org/info/rfc8325>.

   [RFC9330]  Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G.
              White, "Low Latency, Low Loss, and Scalable Throughput
              (L4S) Internet Service: Architecture", RFC 9330,
              DOI 10.17487/RFC9330, January 2023,
              <https://www.rfc-editor.org/info/rfc9330>.

   [RFC9331]  De Schepper, K. and B. Briscoe, Ed., "The Explicit
              Congestion Notification (ECN) Protocol for Low Latency,
              Low Loss, and Scalable Throughput (L4S)", RFC 9331,
              DOI 10.17487/RFC9331, January 2023,
              <https://www.rfc-editor.org/info/rfc9331>.

   [RFC9332]  De Schepper, K., Briscoe, B., Ed., and G. White, "Dual-
              Queue Coupled Active Queue Management (AQM) for Low
              Latency, Low Loss, and Scalable Throughput (L4S)",
              RFC 9332, DOI 10.17487/RFC9332, January 2023,
              <https://www.rfc-editor.org/info/rfc9332>.

   [I-D.ietf-tsvwg-l4sops]
              White, G., "Operational Guidance on Coexistence with
              Classic ECN during L4S Deployment", Work in Progress,
              Internet-Draft, draft-ietf-tsvwg-l4sops-06, 17 March 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
              l4sops-06>.

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   [I-D.ietf-tsvwg-nqb]
              White, G., Fossati, T., and R. Geib, "A Non-Queue-Building
              Per-Hop Behavior (NQB PHB) for Differentiated Services",
              Work in Progress, Internet-Draft, draft-ietf-tsvwg-nqb-25,
              31 August 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-tsvwg-nqb-25>.

   [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-13, 3 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
              dscp-considerations-13>.

   [I-D.briscoe-docsis-q-protection]
              Briscoe, B. and G. White, "The DOCSIS(r) Queue Protection
              Algorithm to Preserve Low Latency", Work in Progress,
              Internet-Draft, draft-briscoe-docsis-q-protection-07, 23
              November 2023, <https://datatracker.ietf.org/doc/html/
              draft-briscoe-docsis-q-protection-07>.

   [BITAG]    Broadband Internet Technical Advisory Group, "Latency
              Explained", 10 January 2022,
              <https://bitag.org/documents/BITAG_latency_explained.pdf>.

   [Lotus]    Eckerseley, P., von Lohmann, F., and S. Schoen, "Packet
              Forgery By ISPs: A Report on the Comcast Affair", 28
              November 2007, <https://www.eff.org/wp/packet-forgery-
              isps-report-comcast-affair>.

   [IETF-114-Slides]
              White, G., "First L4S Interop Event @ IETF Hackathon", 25
              July 2022,
              <https://datatracker.ietf.org/meeting/114/materials/
              slides-114-tsvwg-update-on-l4s-work-in-ietf-114-hackathon-
              00.pdf>.

   [LLD]      White, G., Sundaresan, K., and B. Briscoe, "Low Latency
              DOCSIS: Technology Overview", February 2019,
              <https://cablela.bs/low-latency-docsis-technology-
              overview-february-2019>.

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   [Ericsson] Willars, P., Wittenmark, E., Ronkainen, H., Johansson, I.,
              Strand, J., Ledl, D., and D. Schnieders, "Enabling time-
              critical applications over 5G with rate adaptation", May
              2021, <https://www.ericsson.com/49bc82/assets/local/
              reports-papers/white-papers/26052021-enabling-time-
              critical-applications-over-5g-with-rate-adaptation-
              whitepaper.pdf>.

   [CTI]      International Telecommunications Union - Telecommunication
              Standardization Sector (ITU-T), "Optical line termination
              capabilities for supporting cooperative dynamic bandwidth
              assignment", Series G: Transmission Systems and Media,
              Digital Systems and Networks Supplement 71, April 2021,
              <https://www.itu.int/rec/T-REC-G.Sup71-202104-I>.

   [IEEE]     IEEE Computer Society (IEEE), "Part 11: Wireless LAN
              Medium Access Control (MAC) and Physical Layer (PHY)
              Specifications", DOI 10.1109/IEEESTD.2021.9363693, IEEE
              Standard for Information Technology--Telecommunications
              and Information Exchange between Systems - Local and
              Metropolitan Area Networks--Specific
              Requirements 802.11-2020, 26 February 2021,
              <https://ieeexplore.ieee.org/document/9363693>.

   [Microsoft]
              Microsoft, "Quality of service (QoS) packet tagging on
              Xbox consoles", 19 August 2022,
              <https://learn.microsoft.com/en-
              us/gaming/gdk/_content/gc/networking/overviews/qos-packet-
              tagging>.

   [Comcast]  Comcast, "Comcast Kicks Off Industry's First Low Latency
              DOCSIS Field Trials", 16 June 2023,
              <https://corporate.comcast.com/stories/comcast-kicks-off-
              industrys-first-low-latency-docsis-field-trials>.

   [IETF-TSVWG-120]
              Livingood, J., "TSVWG Meeting at IETF-120", 26 July 2024,
              <https://datatracker.ietf.org/doc/slides-120-tsvwg-52-
              comcasts-l4s-nqb-field-trials/>.

   [IETF-TSVWG-119]
              Livingood, J., "TSVWG Meeting at IETF-119", 18 March 2024,
              <https://datatracker.ietf.org/doc/slides-119-tsvwg-sessa-
              41-comcasts-l4s-nqb-field-trials/>.

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   [IETF-TSVWG-118]
              Livingood, J., "TSVWG Meeting at IETF-118", 18 November
              2023, <https://datatracker.ietf.org/doc/slides-118-tsvwg-
              sessa-61-l4s-experience/>.

   [IETF-TSVWG-117]
              Livingood, J., "TSVWG Meeting at IETF-117", 27 July 2023,
              <https://datatracker.ietf.org/doc/slides-118-tsvwg-sessa-
              61-l4s-experience/>.

   [CDT-NN]   Doty, N. and M. Knodel, "Slicing the Network: Maintaining
              Neutrality, Protecting Privacy, and Promoting Competition.
              A technical and policy overview with recommendations for
              operators and regulators.", April 2023,
              <https://arxiv.org/pdf/2308.05829>.

   [van-Schewick-1A]
              van Schewick, B., Jordan, S., Open Technology Institute at
              New America, and Public Knowledge, "FCC Ex Parte In the
              matter of Safeguarding and Securing the Open Internet, WC
              Docket No. 23-320", 20 March 2024,
              <https://www.fcc.gov/ecfs/document/103120890811342/1>.

   [van-Schewick-1B]
              van Schewick, B., Jordan, S., Open Technology Institute at
              New America, and Public Knowledge, "Net Neutrality & Non-
              BIAS Data Services", 20 March 2024,
              <https://www.fcc.gov/ecfs/document/10323701322790/2>.

   [van-Schewick-2]
              van Schewick, B., "Net Neutrality & 5G Network Slicing", 3
              April 2024, <https://law.stanford.edu/wp-
              content/uploads/2024/08/van-Schewick-2024-5G-Network-
              Slicing-and-Net-Neutrality-Shetler-Steffen1.pdf>.

   [van-Schewick-3]
              van Schewick, B., "Network Slicing and Net Neutrality: No
              Throttling Rule", 18 April 2024,
              <https://law.stanford.edu/wp-content/uploads/2024/08/van-
              Schewick-2024-5G-Network-Slicing-and-No-Throttling-Rule-
              20240418.pdf>.

   [Apple]    Apple, "Testing and Debugging L4S in Your App",
              <https://developer.apple.com/documentation/network/
              testing-and-debugging-l4s-in-your-app>.

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   [Tussle]   Clark, D., Wroclawski, J., Sollins, K., and R. Braden,
              "Tussle in Cyberspace: Defining Tomorrow's Internets", 19
              August 2002,
              <https://dl.acm.org/doi/10.1145/633025.633059>.

Author's Address

   Jason Livingood
   Comcast
   Philadelphia, PA
   United States of America
   Email: jason_livingood@comcast.com

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