Diffserv to IEEE 802.11 Mapping
draft-ietf-tsvwg-ieee-802-11-09

Versions: (draft-szigeti-tsvwg-ieee-802-11)   00         Standards Track
          01 02 03 04 05 06 07 08 09                                    
Transport Working Group                                       T. Szigeti
Internet-Draft                                                  J. Henry
Intended status: Standards Track                           Cisco Systems
Expires: March 12, 2018                                         F. Baker
                                                       September 8, 2017


                    Diffserv to IEEE 802.11 Mapping
                    draft-ietf-tsvwg-ieee-802-11-07

Abstract

   As internet traffic is increasingly sourced-from and destined-to
   wireless endpoints, it is crucial that Quality of Service be aligned
   between wired and wireless networks; however, this is not always the
   case by default.  This document specifies a set Differentiated
   Services Code Point (DSCP) to IEEE 802.11 User Priority (UP) mappings
   to reconcile the marking recommendations offered by the IETF and the
   IEEE so as to maintain consistent QoS treatment between wired and
   IEEE 802.11 wireless networks.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 12, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   (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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Related work  . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Interaction with RFC 7561 . . . . . . . . . . . . . . . .   4
     1.3.  Applicability Statement . . . . . . . . . . . . . . . . .   4
     1.4.  Document Organization . . . . . . . . . . . . . . . . . .   5
     1.5.  Requirements Language . . . . . . . . . . . . . . . . . .   5
     1.6.  Terminology Used in this Document . . . . . . . . . . . .   6
   2.  Service Comparison and Default Interoperation of Diffserv and
       IEEE 802.11 . . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.1.  Diffserv Domain Boundaries  . . . . . . . . . . . . . . .   9
     2.2.  Default DSCP-to-UP Mappings and Conflicts . . . . . . . .  10
     2.3.  Default UP-to-DSCP Mappings and Conflicts . . . . . . . .  11
   3.  Wireless Device Marking and Mapping Capability
       Recommendations . . . . . . . . . . . . . . . . . . . . . . .  12
   4.  DSCP-to-UP Mapping Recommendations  . . . . . . . . . . . . .  13
     4.1.  Network Control Traffic . . . . . . . . . . . . . . . . .  13
       4.1.1.  Network Control Protocols . . . . . . . . . . . . . .  14
       4.1.2.  Operations Administration Management (OAM)  . . . . .  14
     4.2.  User Traffic  . . . . . . . . . . . . . . . . . . . . . .  15
       4.2.1.  Telephony . . . . . . . . . . . . . . . . . . . . . .  15
       4.2.2.  Signaling . . . . . . . . . . . . . . . . . . . . . .  15
       4.2.3.  Multimedia Conferencing . . . . . . . . . . . . . . .  16
       4.2.4.  Real-Time Interactive . . . . . . . . . . . . . . . .  16
       4.2.5.  Multimedia-Streaming  . . . . . . . . . . . . . . . .  17
       4.2.6.  Broadcast Video . . . . . . . . . . . . . . . . . . .  17
       4.2.7.  Low-Latency Data  . . . . . . . . . . . . . . . . . .  17
       4.2.8.  High-Throughput Data  . . . . . . . . . . . . . . . .  18
       4.2.9.  Standard Service Class  . . . . . . . . . . . . . . .  18
       4.2.10. Low-Priority Data . . . . . . . . . . . . . . . . . .  19
     4.3.  DSCP-to-UP Mapping Recommendations Summary  . . . . . . .  19
   5.  Upstream Mapping and Marking Recommendations  . . . . . . . .  20
     5.1.  Upstream DSCP-to-UP Mapping within the Wireless Client
           Operating System  . . . . . . . . . . . . . . . . . . . .  21
     5.2.  Upstream UP-to-DSCP Mapping at the Wireless Access Point   21
     5.3.  Upstream DSCP-Passthrough at the Wireless Access Point  .  22
     5.4.  Upstream DSCP Marking at the Wireless Access Point  . . .  23
   6.  Appendix: IEEE 802.11 QoS Overview  . . . . . . . . . . . . .  23
     6.1.  Distributed Coordination Function (DCF) . . . . . . . . .  23
       6.1.1.  Slot Time . . . . . . . . . . . . . . . . . . . . . .  24
       6.1.2.  Interframe Spaces . . . . . . . . . . . . . . . . . .  24
       6.1.3.  Contention Windows  . . . . . . . . . . . . . . . . .  25



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     6.2.  Hybrid Coordination Function (HCF)  . . . . . . . . . . .  26
       6.2.1.  User Priority (UP)  . . . . . . . . . . . . . . . . .  26
       6.2.2.  Access Category (AC)  . . . . . . . . . . . . . . . .  26
       6.2.3.  Arbitration Inter-Frame Space (AIFS)  . . . . . . . .  27
       6.2.4.  Access Category Contention Windows (CW) . . . . . . .  28
     6.3.  IEEE 802.11u QoS Map Set  . . . . . . . . . . . . . . . .  29
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
     8.1.  General QoS Security Recommendations  . . . . . . . . . .  30
     8.2.  WLAN QoS Security Recommendations . . . . . . . . . . . .  31
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  32
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     10.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35

1.  Introduction

   Wireless has become the preferred medium for endpoints connecting to
   business and private networks.  However, the wireless medium defined
   by IEEE 802.11 [IEEE.802.11-2016] presents several design challenges
   for ensuring end-to-end quality of service.  Some of these challenges
   relate to the nature of the IEEE 802.11 RF medium itself, being a
   half-duplex and shared medium, while other challenges relate to the
   fact that the IEEE 802.11 standard is not administered by the same
   standards body as IP networking standards.  While the IEEE has
   developed tools to enable QoS over wireless networks, little guidance
   exists on how to maintain consistency of QoS treatment between wired
   IP and wireless IEEE 802.11 networks.  The purpose of this document
   is to provide such guidance.

1.1.  Related work

   Several RFCs outline Diffserv QoS recommendations over IP networks,
   including:

   o  [RFC2474] specifies the Diffserv Codepoint Field.  This RFC also
      details Class Selectors, as well as the Default Forwarding (DF)
      treatment.

   o  [RFC2475] defines a Diffserv architecture

   o  [RFC3246] specifies the Expedited Forwarding (EF) Per-Hop Behavior
      (PHB)

   o  [RFC2597] specifies the Assured Forwarding (AF) PHB.




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   o  [RFC3662] specifies a Lower Effort Per-Domain Behavior (PDB)

   o  [RFC4594] presents Configuration Guidelines for Diffserv Service
      Classes

   o  [RFC5127] presents the Aggregation of Diffserv Service Classes

   o  [RFC5865] specifies a DSCP for Capacity Admitted Traffic

   Note: [RFC4594] is intended to be viewed as a framework for
   supporting Diffserv in any network, including wireless networks;
   thus, it describes different types of traffic expected in IP networks
   and provides guidance as to what DSCP marking(s) should be associated
   with each traffic type.  As such, this document draws heavily on
   [RFC4594], as well as [RFC5127], and [RFC8100].

   In turn, the relevant standard for wireless QoS is IEEE 802.11, which
   is being progressively updated; the current version of which (at the
   time of writing) is [IEEE.802.11-2016].

1.2.  Interaction with RFC 7561

   There is also a recommendation from the Global System for Mobile
   Communications Association (GSMA), specifically their Mapping Quality
   of Service (QoS) Procedures of Proxy Mobile IPv6 (PMIPv6) and WLAN
   [RFC7561] specification.  This GSMA specification was developed
   without reference to existing IETF specifications for various
   services, referenced in Section 1.1.  Thus, [RFC7561] conflicts with
   the overall Diffserv traffic-conditioning service plan, both in the
   services specified and the code points specified for them.  As such,
   these two plans cannot be normalized.  Rather, as discussed in
   [RFC2474] Section 2, the two domains (IEEE 802.11 and GSMA) are
   different Differentiated Services Domains separated by a
   Differentiated Services Boundary.  At that boundary, code points from
   one domain are translated to code points for the other, and maybe to
   Default (zero) if there is no corresponding service to translate to.

1.3.  Applicability Statement

   This document is applicable to the use of Differentiated Services
   that interconnect with IEEE 802.11 wireless LANs (referred to as Wi-
   Fi, throughout this document, for simplicity).  These guidelines are
   applicable whether the wireless access points (APs) are deployed in
   an autonomous manner, managed by (centralized or distributed) WLAN
   controllers or some hybrid deployment option.  This is because in all
   these cases, the wireless access point is the bridge between wired
   and wireless media.




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   This document applies to IP networks using WiFi infrastructure at the
   link layer.  Such networks typically include wired LANs with wireless
   access points at their edges, however, such networks can also include
   Wi-Fi backhaul, wireless mesh solutions or any other type of AP-to-AP
   wireless network that extends the wired network infrastructure.

1.4.  Document Organization

   This document is organized as follows:

   o  Section 1 introduces the wired-to-wireless QoS challenge,
      references related work, outlines the organization of the
      document, and specifies both the requirements language and the
      terminology used in this document.

   o  Section 2 begins the discussion with a comparison of IETF Diffserv
      QoS and Wi-Fi QoS standards and highlights discrepancies between
      these that require reconciliation.

   o  Section 3 presents the marking and mapping capabilities that
      wireless access points and wireless endpoint devices are
      recommended to support.

   o  Section 4 presents DSCP-to-UP mapping recommendations for each of
      the [RFC4594] service classes, which are primarily applicable in
      the downstream (wired-to-wireless) direction.

   o  Section 5, in turn, considers upstream (wireless-to-wired) QoS
      options, their respective merits and recommendations.

   o  Section 6 (in the form of an Appendix) presents a brief overview
      of how QoS is achieved over IEEE 802.11 wireless networks, given
      the shared, half-duplex nature of the wireless medium.

   o  Section 7 on notes IANA considerations

   o  Section 8 presents security considerations relative to DSCP-to-UP,
      UP-to-DSCP mapping and remarking

1.5.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].







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1.6.  Terminology Used in this Document

   Key terminology used in this document includes:

      AC: Access Category.  A label for the common set of enhanced
      distributed channel access (EDCA) parameters that are used by a
      quality-of-service (QoS) station (STA) to contend for the channel
      in order to transmit medium access control (MAC) service data
      units (MSDUs) with certain priorities.  [IEEE.802.11-2016]
      Section 3.2.

      AIFS: Arbitration Interframe Space.  Interframe space used by QoS
      stations before transmission of data and other frame types defined
      by [IEEE.802.11-2016] Section 10.3.2.3.6.

      AP: Access Point.  An entity that contains one station (STA) and
      provides access to the distribution services, via the wireless
      medium (WM) for associated STAs.  An AP comprises a STA and a
      distribution system access function (DSAF) [IEEE.802.11-2016]
      Section 3.1.

      BSS: Basic Service Set. Informally, a wireless cell; formally, a
      set of stations that have successfully synchronized using the JOIN
      service primitives and one STA that has used the START primitive.
      Alternatively, a set of STAs that have used the START primitive
      specifying matching mesh profiles where the match of the mesh
      profiles has been verified via the scanning procedure.  Membership
      in a BSS does not imply that wireless communication with all other
      members of the BSS is possible.  Defined in [IEEE.802.11-2016]
      Section 3.1.

      Contention Window: See CW.

      CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance.
      A media access control method in which carrier sensing is used,
      but nodes attempt to avoid collisions by transmitting only when
      the channel is sensed to be "idle".  When these do transmit, nodes
      transmit their packet data in its entirety.

      CSMA/CD: Carrier Sense Multiple Access with Collision Detection.
      A media access control method (used most notably in early Ethernet
      technology) for local area networking.  It uses a carrier-sensing
      scheme in which a transmitting station detects collisions by
      sensing transmissions from other stations while transmitting a
      frame.  When this collision condition is detected, the station
      stops transmitting that frame, transmits a jam signal, and then
      waits for a random time interval before trying to resend the
      frame.



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      CW: Contention Window.  Limits a CWMin and CWMax, from which a
      random backoff is computed.

      CWMax: Contention Window Maximum.  The maximum value (in unit of
      Slot Time) that a contention window can take.

      CWMin: Contention Window Minimum.  The minimum value that a
      contention window can take.

      DCF: Distributed Coordinated Function.  A class of coordination
      function where the same coordination function logic is active in
      every station (STA) in the basic service set (BSS) whenever the
      network is in operation.

      DIFS: Distributed (Coordination Function) Interframe Space.  A
      unit of time during which the medium has to be detected as idle
      before a station should attempt to send frames, as per
      [IEEE.802.11-2016] Section 10.3.2.3.5.

      DSCP: Differentiated Service Code Point [RFC2474] and [RFC2475].
      The DSCP is carried in the first 6 bits of the IPv4 and IPv6 Type
      of Service (TOS) Byte (the remaining 2 bits are used for IP
      Explicit Congestion Notification [RFC3168]).

      HCF: Hybrid Coordination Function A coordination function that
      combines and enhances aspects of the contention based and
      contention free access methods to provide quality-of-service (QoS)
      stations (STAs) with prioritized and parameterized QoS access to
      the wireless medium (WM), while continuing to support non-QoS STAs
      for best-effort transfer.  [IEEE.802.11-2016] Section 3.1.

      IFS: Interframe Space.  Period of silence between transmissions
      over 802.11 networks.  [IEEE.802.11-2016] describes several types
      of Interframe Spaces.

      Random Backoff Timer: A pseudorandom integer period of time (in
      units of Slot Time) over the interval (0,CW), where CWmin is-less-
      than-or-equal-to CW, which in turn is less-than-or-equal-to CWMax.
      Stations desiring to initiate transfer of data frames and-or
      Management frames using the DCF shall invoke the carrier sense
      mechanism to determine the busy-or-idle state of the medium.  If
      the medium is busy, the STA shall defer until the medium is
      determined to be idle without interruption for a period of time
      equal to DIFS when the last frame detected on the medium was
      received correctly, or after the medium is determined to be idle
      without interruption for a period of time equal to EIFS when the
      last frame detected on the medium was not received correctly.
      After this DIFS or EIFS medium idle time, the STA shall then



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      generate a random backoff period for an additional deferral time
      before transmitting.  [IEEE.802.11-2016] Section 10.3.3.

      RF: Radio Frequency.

      SIFS: Short Interframe Space.  An IFS used before transmission of
      specific frames as defined in [IEEE.802.11-2016]
      Section 10.3.2.3.3.

      Slot Time: A unit of time used to count time intervals in 802.11
      networks, and defined in [IEEE.802.11-2016] Section 10.3.2.13.

      Trust: From a QoS-perspective, trust refers to the accepting of
      the QoS markings of a packet by a network device.  Trust is
      typically extended at Layer 3 (by accepting the DSCP), but may
      also be extended at lower layers, such as at Layer 2 by accepting
      User Priority markings.  For example, if an access point is
      configured to trust DSCP markings and it receives a packet marked
      EF, then it would treat the packet with the Expedite Forwarding
      PHB and propagate the EF marking value (DSCP 46) as it transmits
      the packet.  Alternatively, if a network device is configured to
      operate in an untrusted manner, then it would remark packets as
      these entered the device, typically to DF (or to a different
      marking value at the network administrator's preference).  Note:
      The terms "trusted" and "untrusted" are used extensively in
      [RFC4594].

      UP: User Priority.  A value associated with a medium access
      control (MAC) service data unit (MSDU) that indicates how the MSDU
      is to be handled.  The UP is assigned to an MSDU in the layers
      above the MAC [IEEE.802.11-2016] Section 3.1.  The UP defines a
      level of priority for the associated frame, on a scale of 0 to 7.

      Wi-Fi: An interoperability certification defined by the Wi-Fi
      Alliance.  However, this term is commonly used, including in the
      present document, to be the equivalent of IEEE 802.11.

2.  Service Comparison and Default Interoperation of Diffserv and IEEE
    802.11

   (Section 6 provides a brief overview of IEEE 802.11 QoS.)

   The following comparisons between IEEE 802.11 and Diffserv services
   should be noted:

   o  [IEEE.802.11-2016] does not support an EF PHB service [RFC3246],
      as it is not possible to assure that a given access category will




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      be serviced with strict priority over another (due to the random
      element within the contention process)

   o  [IEEE.802.11-2016] does not support an AF PHB service [RFC2597],
      again because it is not possible to assure that a given access
      category will be serviced with a minimum amount of assured
      bandwidth (due to the non-deterministic nature of the contention
      process)

   o  [IEEE.802.11-2016] loosely supports a [RFC2474] Default Forwarding
      service via the Best Effort Access Category (AC_BE)

   o  [IEEE.802.11-2016] loosely supports a [RFC3662] Lower Effort PDB
      service via the Background Access Category (AC_BK)

   As such, these high-level considerations should be kept in mind when
   mapping from Diffserv to [IEEE.802.11-2016] (and vice-versa);
   however, access points may or may not always be positioned at
   Diffserv domain boundaries, as will be discussed next.

2.1.  Diffserv Domain Boundaries

   It is important to recognize that the wired-to-wireless edge may or
   may not function as an edge of a Diffserv domain or a domain
   boundary.

   In most commonly-deployed WLAN models, the wireless access point
   represents not only the edge of the Diffserv domain, but also the
   edge of the network infrastructure itself.  As such, only client
   endpoint devices (and no network infrastructure devices) are
   downstream from the access points in these deployment models.  Note:
   security considerations and recommendations for hardening such Wifi-
   at-the-edge deployment models are detailed in Section 8; these
   recommendations include mapping network control protocols (which are
   not used downstream from the AP in this deployment model) to UP 0.

   Alternatively, in other deployment models, such as Wi-Fi backhaul,
   wireless mesh infrastructures, wireless AP-to-AP deployments, or in
   cases where a Wi-Fi link connects to a device providing service via
   another technology (e.g.  Wi-Fi to Bluetooth or Zigbee router), the
   wireless access point extends the network infrastructure and thus,
   typically, the Diffserv domain.  In such deployments, both client
   devices and infrastructure devices may be expected downstream from
   the access points, and as such network control protocols are
   recommended to be mapped to UP 7 in this deployment model, as is
   discussed in Section 4.1.1.





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   Thus, as can be seen from these two examples, the QoS treatment of
   packets at the access point will depend on the position of the AP in
   the network infrastructure and on the WLAN deployment model.

   However, regardless of the access point being at the Diffserv
   boundary or not, Diffserv to [IEEE.802.11-2016] (and vice-versa)
   marking-specific incompatibilities exist that must be reconciled, as
   will be discussed next.

2.2.  Default DSCP-to-UP Mappings and Conflicts

   While no explicit guidance is offered in mapping (6-Bit) Layer 3 DSCP
   values to (3-Bit) Layer 2 markings (such as IEEE 802.1D, 802.1p or
   802.11e), a common practice in the networking industry is to map
   these by what we will refer to as 'Default DSCP-to-UP Mapping' (for
   lack of a better term), wherein the 3 Most Significant Bits (MSB) of
   the DSCP are used as the corresponding L2 markings.

   Note: There are mappings provided in [IEEE.802.11-2016] Annex V
   Tables V-1 and V2, but it bears mentioning that these mappings are
   provided as examples (as opposed to explicit recommendations).
   Furthermore, some of these mappings do not align with the intent and
   recommendations expressed in [RFC4594], as will be discussed in this
   and the following section (Section 2.3).

   However, when this default DSCP-to-UP mapping method is applied to
   packets marked per [RFC4594] recommendations and destined to 802.11
   WLAN clients, it will yield a number of inconsistent QoS mappings,
   specifically:

   o  Voice (EF-101110) will be mapped to UP 5 (101), and treated in the
      Video Access Category (AC_VI), rather than the Voice Access
      Category (AC_VO), for which it is intended

   o  Multimedia Streaming (AF3-011xx0) will be mapped to UP3 (011) and
      treated in the Best Effort Access Category (AC_BE), rather than
      the Video Access Category (AC_VI), for which it is intended

   o  Broadcast Video (CS3-011000) will be mapped to UP3 (011) and
      treated in the Best Effort Access Category (AC_BE), rather than
      the Video Access Category (AC_VI), for which it is intended

   o  OAM traffic (CS2-010000) will be mapped to UP 2 (010) and treated
      in the Background Access Category (AC_BK), which is not the intent
      expressed in [RFC4594] for this service class

   It should also be noted that while [IEEE.802.11-2016] defines an
   intended use for each access category through the AC naming



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   convention (for example, UP 6 and UP 7 belong to AC_VO, the Voice
   Access Category), [IEEE.802.11-2016] does not:

   o  define how upper layer markings (such as DSCP) should map to UPs
      (and hence to ACs)

   o  define how UPs should translate to other medium Layer 2 QoS
      markings

   o  strictly restrict each access category to applications reflected
      in the AC name

2.3.  Default UP-to-DSCP Mappings and Conflicts

   In the opposite direction of flow (the upstream direction, that is,
   from wireless-to-wired), many APs use what we will refer to as
   'Default UP-to-DSCP Mapping' (for lack of a better term), wherein
   DSCP values are derived from UP values by multiplying the UP values
   by 8 (i.e. shifting the 3 UP bits to the left and adding three
   additional zeros to generate a DSCP value).  This derived DSCP value
   is then used for QoS treatment between the wireless access point and
   the nearest classification and marking policy enforcement point
   (which may be the centralized wireless LAN controller, relatively
   deep within the network).  Alternatively, in the case where there is
   no other classification and marking policy enforcement point, then
   this derived DSCP value will be used on the remainder of the Internet
   path.

   It goes without saying that when 6 bits of marking granularity are
   derived from 3, then information is lost in translation.  Servicing
   differentiation cannot be made for 12 classes of traffic (as
   recommended in [RFC4594]), but for only 8 (with one of these classes
   being reserved for future use (i.e.  UP 7 which maps to DSCP CS7).

   Such default upstream mapping can also yield several inconsistencies
   with [RFC4594], including:

   o  Mapping UP 6 ([RFC4594] Voice) to CS6, which [RFC4594] recommends
      for Network Control

   o  Mapping UP 4 ([RFC4594] Multimedia Conferencing and/or Real-Time
      Interactive) to CS4, thus losing the ability to differentiate
      between these two distinct service classes, as recommended in
      [RFC4594] Sections 4.3 and 4.4

   o  Mapping UP 3 ([RFC4594] Multimedia Streaming and/or Broadcast
      Video) to CS3, thus losing the ability to differentiate between




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      these two distinct service classes, as recommended in [RFC4594]
      Sections 4.5 and 4.6

   o  Mapping UP 2 ([RFC4594] Low-Latency Data and/or OAM) to CS2, thus
      losing the ability to differentiate between these two distinct
      service classes, as recommended in [RFC4594] Sections 4.7 and 3.3,
      and possibly overwhelming the queues provisioned for OAM (which is
      typically lower in capacity [being network control traffic], as
      compared to Low-Latency Data queues [being user traffic])

   o  Mapping UP 1 ([RFC4594] High-Throughput Data and/or Low-Priority
      Data) to CS1, thus losing the ability to differentiate between
      these two distinct service classes, as recommended in [RFC4594]
      Sections 4.8 and 4.10, and causing legitimate business-relevant
      High-Throughput Data to receive a [RFC3662] Lower Effort PDB, for
      which it is not intended

   The following sections address these limitations and concerns in
   order to reconcile [RFC4594] and [IEEE.802.11-2016].  First
   downstream (wired-to-wireless) DSCP-to-UP mappings will be aligned
   and then upstream (wireless-to-wired) models will be addressed.

3.  Wireless Device Marking and Mapping Capability Recommendations

   This document assumes and RECOMMENDS that all wireless access points
   (as the bridges between wired-and-wireless networks) support the
   ability to:

   o  mark DSCP, per Diffserv standards

   o  mark UP, per the [IEEE.802.11-2016] standard

   o  support fully-configurable mappings between DSCP and UP

   o  process DSCP markings set by wireless endpoint devices

   This document further assumes and RECOMMENDS that all wireless
   endpoint devices support the ability to:

   o  mark DSCP, per Diffserv standards

   o  mark UP, per the [IEEE.802.11-2016] standard

   o  support fully-configurable mappings between DSCP (set by
      applications in software) and UP (set by the operating system and/
      or wireless network interface hardware drivers)





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   Having made the assumptions and recommendations above, it bears
   mentioning while the mappings presented in this document are
   RECOMMENDED to replace the current common default practices (as
   discussed in Section 2.2 and Section 2.3), these mapping
   recommendations are not expected to fit every last deployment model,
   and as such MAY be overridden by network administrators, as needed.

4.  DSCP-to-UP Mapping Recommendations

   The following section specifies downstream (wired-to-wireless)
   mappings between [RFC4594] Configuration Guidelines for Diffserv
   Service Classes and [IEEE.802.11-2016].  As such, this section draws
   heavily from [RFC4594], including service class definitions and
   recommendations.

   This section assumes [IEEE.802.11-2016] wireless access points and/or
   WLAN controllers that support customizable, non-default DSCP-to-UP
   mapping schemes.

   This section also assumes that [IEEE.802.11-2016] access points and
   endpoint devices differentiate UP markings with corresponding queuing
   and dequeuing treatments.  To illustrate, [IEEE.802.11-2016] displays
   a reference implementation model in Figure 10-24 which depicts four
   transmit queues, one per access category.  In practical
   implementations, however, it is common for WLAN network equipment
   vendors to implement dedicated transmit queues on a per-UP (versus a
   per access category) basis, which are then dequeued into their
   associated access category in a preferred (or even in a strict
   priority manner).  For example, it is common for vendors to dequeue
   UP 5 ahead of UP 4 to the hardware performing the EDCA function
   (EDCAF) for the Video Access Category (AC_VI).  As such, Signaling
   traffic (marked UP 5, per the recommendations made in Section 4.2.2)
   may benefit from such a treatment versus other video flows in the
   same access category which are marked to UP 4 (in addition to a
   preferred treatment over flows in the Best Effort and Background
   access categories).

4.1.  Network Control Traffic

   Network control traffic is defined as packet flows that are essential
   for stable operation of the administered network [RFC4594] Section 3.
   Network control traffic is different from user application control
   (signaling) that may be generated by some applications or services.
   Network control traffic MAY be split into two service classes:

   o  Network Control, and

   o  Operations Administration and Management (OAM)



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4.1.1.  Network Control Protocols

   The Network Control service class is used for transmitting packets
   between network devices (e.g. routers) that require control (routing)
   information to be exchanged between nodes within the administrative
   domain, as well as across a peering point between different
   administrative domains.

   The RECOMMENDED DSCP marking for Network Control is CS6, per
   [RFC4594] Section 3.2; additionally, CS7 DSCP value SHOULD be
   reserved for future use, potentially for future routing or control
   protocols, again, per [RFC4594] Section 3.2.

   By default (as described in Section 2.2), packets marked DSCP CS7
   will be mapped to UP 7 and serviced within the Voice Access Category
   (AC_VO).  This represents the RECOMMENDED mapping for CS7, that is,
   packets marked to CS7 DSCP are RECOMMENDED to be mapped to UP 7.

   However, by default (as described in Section 2.2), packets marked
   DSCP CS6 will be mapped to UP 6 and serviced within the Voice Access
   Category (AC_VO); such mapping and servicing is a contradiction to
   the intent expressed in [RFC4594] Section 3.2.  As such, it is
   RECOMMENDED to map Network Control traffic marked CS6 to UP 7 (per
   [IEEE.802.11-2016] Section 10.2.4.2, Table 10-1), thereby admitting
   it to the Voice Access Category (AC_VO), albeit with a marking
   distinguishing it from (data-plane) voice traffic.

   It should be noted that encapsulated routing protocols for
   encapsulated or overlay networks (e.g., VPN, NVO3) are not network
   control traffic for any physical network at the AP, and hence SHOULD
   NOT be marked with CS6 in the first place.

   Addtionally, and as previously noted, the Security Considerations
   section (Section 8) contains additional recommendations for hardening
   Wifi-at-the-edge deployment models, where, for example, network
   control protocols are not expected to be sent nor recevied between
   APs and downstream endpoint client devices.

4.1.2.  Operations Administration Management (OAM)

   The OAM (Operations, Administration, and Management) service class is
   RECOMMENDED for OAM&P (Operations, Administration, and Management and
   Provisioning).  The RECOMMENDED DSCP marking for OAM is CS2, per
   [RFC4594] Section 3.3.

   By default (as described in Section 2.2), packets marked DSCP CS2
   will be mapped to UP 2 and serviced with the Background Access
   Category (AC_BK).  Such servicing is a contradiction to the intent



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   expressed in [RFC4594] Section 3.3.  As such, it is RECOMMENDED that
   a non-default mapping be applied to OAM traffic, such that CS2 DSCP
   is mapped to UP 0, thereby admitting it to the Best Effort Access
   Category (AC_BE).

4.2.  User Traffic

   User traffic is defined as packet flows between different users or
   subscribers.  It is the traffic that is sent to or from end-terminals
   and that supports a very wide variety of applications and services
   [RFC4594] Section 4.

   Network administrators can categorize their applications according to
   the type of behavior that they require and MAY choose to support all
   or a subset of the defined service classes.

4.2.1.  Telephony

   The Telephony service class is RECOMMENDED for applications that
   require real-time, very low delay, very low jitter, and very low
   packet loss for relatively constant-rate traffic sources (inelastic
   traffic sources).  This service class SHOULD be used for IP telephony
   service.  The fundamental service offered to traffic in the Telephony
   service class is minimum jitter, delay, and packet loss service up to
   a specified upper bound.  The RECOMMENDED DSCP marking for Telephony
   is EF ([RFC4594] Section 4.1).

   Traffic marked to DSCP EF will map by default (as described in
   Section 2.2) to UP 5, and thus to the Video Access Category (AC_VI),
   rather than to the Voice Access Category (AC_VO), for which it is
   intended.  Therefore, a non-default DSCP-to-UP mapping is
   RECOMMENDED, such that EF DSCP is mapped to UP 6, thereby admitting
   it into the Voice Access Category (AC_VO).

   Similarly, the [RFC5865] VOICE-ADMIT DSCP (44/101100) is RECOMMENDED
   to be mapped to UP 6, thereby admitting it also into the Voice Access
   Category (AC_VO).

4.2.2.  Signaling

   The Signaling service class is RECOMMENDED for delay-sensitive
   client-server (e.g. traditional telephony) and peer-to-peer
   application signaling.  Telephony signaling includes signaling
   between IP phone and soft-switch, soft-client and soft-switch, and
   media gateway and soft-switch as well as peer-to-peer using various
   protocols.  This service class is intended to be used for control of
   sessions and applications.  The RECOMMENDED DSCP marking for
   Signaling is CS5 ([RFC4594] Section 4.2).



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   While Signaling is RECOMMENDED to receive a superior level of service
   relative to the default class (i.e.  AC_BE), it does not require the
   highest level of service (i.e.  AC_VO).  This leaves only the Video
   Access Category (AC_VI), which it will map to by default (as
   described in Section 2.2).  Therefore it is RECOMMENDED to map
   Signaling traffic marked CS5 DSCP to UP 5, thereby admitting it to
   the Video Access Category (AC_VI).

   Note: Signaling traffic is not control plane traffic from the
   perspective of the network (but rather is data plane traffic); as
   such, it does not merit provisioning in the Network Control service
   class (marked CS6 and mapped to UP 6).  However, Signaling traffic is
   control-plane traffic from the perspective of the voice/video
   telephony overlay-infrastructure.  As such, Signaling should be
   treated with preferential servicing vs. other data plane flows.  One
   way this may be achieved in certain WLAN deployments is by mapping
   Signaling traffic marked CS5 to UP 5 (as recommended above and
   following the EDCAF treatment logic described in Section 4.

4.2.3.  Multimedia Conferencing

   The Multimedia Conferencing service class is RECOMMENDED for
   applications that require real-time service for rate-adaptive
   traffic.  The RECOMMENDED DSCP markings for Multimedia Conferencing
   are AF41, AF42 and AF43 ([RFC4594] Section 4.3).

   The primary media type typically carried within the Multimedia
   Conferencing service class is video; as such, it is RECOMMENDED to
   map this class into the Video Access Category, which it does by
   default (as described in Section 2.2).  Specifically, it is
   RECOMMENDED to map AF41, AF42 and AF43 to UP 4, thereby admitting
   Multimedia Conferencing into the Video Access Category (AC_VI).

4.2.4.  Real-Time Interactive

   The Real-Time Interactive service class is RECOMMENDED for
   applications that require low loss and jitter and very low delay for
   variable rate inelastic traffic sources.  Such applications may
   include inelastic video-conferencing applications, but may also
   include gaming applications (as pointed out in [RFC4594] Sections 2.1
   through 2.3, and Section 4.4).  The RECOMMENDED DSCP marking for
   Real-Time Interactive traffic is CS4 ([RFC4594] Section 4.4).

   The primary media type typically carried within the Real-Time
   Interactive service class is video; as such, it is RECOMMENDED to map
   this class into the Video Access Category, which it does by default
   (as described in Section 2.2).  Specifically, it is RECOMMENDED to




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   map CS4 to UP 4, thereby admitting Real-Time Interactive traffic into
   the Video Access Category (AC_VI).

4.2.5.  Multimedia-Streaming

   The Multimedia Streaming service class is RECOMMENDED for
   applications that require near-real-time packet forwarding of
   variable rate elastic traffic sources.  Typically these flows are
   unidirectional.  The RECOMMENDED DSCP markings for Multimedia
   Streaming are AF31, AF32 and AF33 ([RFC4594] Section 4.5).

   The primary media type typically carried within the Multimedia
   Streaming service class is video; as such, it is RECOMMENDED to map
   this class into the Video Access Category, which it will by default
   (as described in Section 2.2).  Specifically, it is RECOMMENDED to
   map AF31, AF32 and AF33 to UP 4, thereby admitting Multimedia
   Streaming into the Video Access Category (AC_VI).

4.2.6.  Broadcast Video

   The Broadcast Video service class is RECOMMENDED for applications
   that require near-real-time packet forwarding with very low packet
   loss of constant rate and variable rate inelastic traffic sources.
   Typically these flows are unidirectional.  The RECOMMENDED DSCP
   marking for Broadcast Video is CS3 ([RFC4594] Section 4.6).

   As directly implied by the name, the primary media type typically
   carried within the Broadcast Video service class is video; as such,
   it is RECOMMENDED to map this class into the Video Access Category;
   however, by default (as described in Section 2.2), this service class
   will map to UP 3, and thus the Best Effort Access Category (AC_BE).
   Therefore, a non-default mapping is RECOMMENDED, such that CS4 maps
   to UP 4, thereby admitting Broadcast Video into the Video Access
   Category (AC_VI).

4.2.7.  Low-Latency Data

   The Low-Latency Data service class is RECOMMENDED for elastic and
   time-sensitive data applications, often of a transactional nature,
   where a user is waiting for a response via the network in order to
   continue with a task at hand.  As such, these flows are considered
   foreground traffic, with delays or drops to such traffic directly
   impacting user-productivity.  The RECOMMENDED DSCP markings for Low-
   Latency Data are AF21, AF22 and AF23 ([RFC4594] Section 4.7).

   By default (as described in Section 2.2), Low-Latency Data will map
   to UP 2 and thus to the Background Access Category (AC_BK), which is
   contrary to the intent expressed in [RFC4594].



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   In line with the assumption made in Section 4, mapping Low-Latency
   Data to UP 3 may allow such to receive a superior level of service
   via transmit queues servicing the EDCAF hardware for the Best Effort
   Access Category (AC_BE).  Therefore it is RECOMMENDED to map Low-
   Latency Data traffic marked AF2x DSCP to UP 3, thereby admitting it
   to the Best Effort Access Category (AC_BE).

4.2.8.  High-Throughput Data

   The High-Throughput Data service class is RECOMMENDED for elastic
   applications that require timely packet forwarding of variable rate
   traffic sources and, more specifically, is configured to provide
   efficient, yet constrained (when necessary) throughput for TCP
   longer-lived flows.  These flows are typically non-user-interactive.
   Per [RFC4594]-Section 4.8, it can be assumed that this class will
   consume any available bandwidth and that packets traversing congested
   links may experience higher queuing delays or packet loss.  It is
   also assumed that this traffic is elastic and responds dynamically to
   packet loss.  The RECOMMENDED DSCP markings for High-Throughput Data
   are AF11, AF12 and AF13 ([RFC4594] Section 4.8).

   By default (as described in Section 2.2), High-Throughput Data will
   map to UP 1 and thus to the Background Access Category (AC_BK), which
   is contrary to the intent expressed in [RFC4594].

   Unfortunately, there really is no corresponding fit for the High-
   Throughput Data service class within the constrained 4 Access
   Category [IEEE.802.11-2016] model.  If the High-Throughput Data
   service class is assigned to the Best Effort Access Category (AC_BE),
   then it would contend with Low-Latency Data (while [RFC4594]
   recommends a distinction in servicing between these service classes)
   as well as with the default service class; alternatively, if it is
   assigned to the Background Access Category (AC_BK), then it would
   receive a less-then-best-effort service and contend with Low-Priority
   Data (as discussed in Section 4.2.10).

   As such, since there is no directly corresponding fit for the High-
   Throughout Data service class within the [IEEE.802.11-2016] model, it
   is generally RECOMMENDED to map High-Throughput Data to UP 0, thereby
   admitting it to the Best Effort Access Category (AC_BE).

4.2.9.  Standard Service Class

   The Standard service class is RECOMMENDED for traffic that has not
   been classified into one of the other supported forwarding service
   classes in the Diffserv network domain.  This service class provides
   the Internet's "best-effort" forwarding behavior.  The RECOMMENDED




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   DSCP marking for the Standard Service Class is DF.  ([RFC4594]
   Section 4.9)

   The Standard Service Class loosely corresponds to the
   [IEEE.802.11-2016] Best Effort Access Category (AC_BE) and therefore
   it is RECOMMENDED to map Standard Service Class traffic marked DF
   DSCP to UP 0, thereby admitting it to the Best Effort Access Category
   (AC_BE).  This happens to correspond to the default mapping (as
   described in Section 2.2).

4.2.10.  Low-Priority Data

   The Low-Priority Data service class serves applications that the user
   is willing to accept without service assurances.  This service class
   is specified in [RFC3662] and [I-D.ietf-tsvwg-le-phb].

   The Low-Priority Data service class loosely corresponds to the
   [IEEE.802.11-2016] Background Access Category (AC_BK) and therefore
   it is RECOMMENDED to map Low-Priority Data traffic marked CS1 DSCP to
   UP 1, thereby admitting it to the Background Access Category (AC_BK).
   This happens to correspond to the default mapping (as described in
   Section 2.2).

4.3.  DSCP-to-UP Mapping Recommendations Summary

   Figure 1 summarizes the [RFC4594] DSCP marking recommendations mapped
   to [IEEE.802.11-2016] UP and access categories applied in the
   downstream direction (i.e. from wired-to-wireless networks).


   +------------------------------------------------------------------+
   | IETF Diffserv | PHB  |Reference|         IEEE 802.11              |
   | Service Class |      |   RFC   |User Priority|  Access Category   |
   |===============+======+=========+=============+====================|
   |               |      |         |     7       |    AC_VO (Voice)   |
   |Network Control| CS7  | RFC2474 |            OR                    |
   |(reserved for  |      |         |     0       | AC_BE (Best Effort)|
   | future use)   |      |         |See Security Considerations-Sec.8 |
   +---------------+------+---------+-------------+--------------------+
   |               |      |         |     7       |    AC_VO (Voice)   |
   |Network Control| CS6  | RFC2474 |            OR                    |
   |               |      |         |     0       | AC_BE (Best Effort)|
   |               |      |         |See Security Considerations-Sec.8 |
   +---------------+------+---------+-------------+--------------------+
   |   Telephony   |  EF  | RFC3246 |     6       |    AC_VO (Voice)   |
   +---------------+------+---------+-------------+--------------------+
   |  VOICE-ADMIT  |  VA  | RFC5865 |     6       |    AC_VO (Voice)   |
   |               |      |         |             |                    |



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   +---------------+------+---------+-------------+--------------------+
   |   Signaling   | CS5  | RFC2474 |     5       |    AC_VI (Video)   |
   +---------------+------+---------+-------------+--------------------+
   |   Multimedia  | AF41 |         |             |                    |
   | Conferencing  | AF42 | RFC2597 |     4       |    AC_VI (Video)   |
   |               | AF43 |         |             |                    |
   +---------------+------+---------+-------------+--------------------+
   |   Real-Time   | CS4  | RFC2474 |     4       |    AC_VI (Video)   |
   |  Interactive  |      |         |             |                    |
   +---------------+------+---------+-------------+--------------------+
   |  Multimedia   | AF31 |         |             |                    |
   |  Streaming    | AF32 | RFC2597 |     4       |    AC_VI (Video)   |
   |               | AF33 |         |             |                    |
   +---------------+------+---------+-------------+--------------------+
   |Broadcast Video| CS3  | RFC2474 |     4       |    AC_VI (Video)   |
   +---------------+------+---------+-------------+--------------------+
   |    Low-       | AF21 |         |             |                    |
   |    Latency    | AF22 | RFC2597 |     3       | AC_BE (Best Effort)|
   |    Data       | AF23 |         |             |                    |
   +---------------+------+---------+-------------+--------------------+
   |     OAM       | CS2  | RFC2474 |     0       | AC_BE (Best Effort)|
   +---------------+------+---------+-------------+--------------------+
   |    High-      | AF11 |         |             |                    |
   |  Throughput   | AF12 | RFC2597 |     0       | AC_BE (Best Effort)|
   |    Data       | AF13 |         |             |                    |
   +---------------+------+---------+-------------+--------------------+
   |   Standard    | DF   | RFC2474 |     0       | AC_BE (Best Effort)|
   +---------------+------+---------+-------------+--------------------+
   | Low-Priority  | CS1  | RFC3662 |     1       | AC_BK (Background) |
   |     Data      |      |         |             |                    |
   +-------------------------------------------------------------------+

   Note: All unusued codepoints are recommended to be mapped to UP 0
   (See Security Considerations Section - Section 8)


   Figure 1: Summary of Downstream DSCP to IEEE 802.11 UP and AC Mapping
                              Recommendations

5.  Upstream Mapping and Marking Recommendations

   In the upstream direction (i.e. wireless-to-wired), there are three
   types of mapping that may be implemented:

   o  DSCP-to-UP mapping within the wireless client operating system,
      and

   o  UP-to-DSCP mapping at the wireless access point, or



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   o  DSCP-Passthrough at the wireless access point (effectively a 1:1
      DSCP-to-DSCP mapping)

   As an alternative to the latter two options, the network
   administrator MAY choose to use the wireless-to-wired edge as a
   Diffserv boundary and explicitly set (or reset) DSCP markings
   according to administrative policy, thus making the wireless edge a
   Diffserv policy enforcement point.  This is RECOMMENDED whenever
   supported.

   Each of these options will now be considered.

5.1.  Upstream DSCP-to-UP Mapping within the Wireless Client Operating
      System

   Some operating systems on wireless client devices utilize a similar
   default DSCP-to-UP mapping scheme as described in Section 2.2.  As
   such, this can lead to the same conflicts as described in that
   section, but in the upstream direction.

   Therefore, to improve on these default mappings, and to achieve
   parity and consistency with downstream QoS, it is RECOMMENDED that
   wireless client operating systems utilize instead the same DSCP-to-UP
   mapping recommendations presented in Section 4, with the explicit
   RECOMMENDATION that packets requesting a marking of CS6 or CS7 DSCP
   SHOULD be mapped to UP 0 (and not to UP 7).  Furthermore, in such
   cases the wireless client operating system SHOULD remark such packets
   to DSCP 0.  This is because CS6 and CS7 DSCP, as well as UP 7
   markings, are intended for network control protocols and these SHOULD
   NOT be sourced from wireless client endpoint devices.  This
   recommendation is detailed in the Security Considerations section
   (Section 8).

5.2.  Upstream UP-to-DSCP Mapping at the Wireless Access Point

   UP-to-DSCP mapping generates a DSCP value for the IP packet (either
   an unencapsulated IP packet or an IP packet encapsulated within a
   tunneling protocol such as CAPWAP - and destined towards a wireless
   LAN controller for decapsulation and forwarding) from the Layer 2
   [IEEE.802.11-2016] UP marking.  This is typically done in the manner
   described in Section 2.3.

   It should be noted that any explicit remarking policy to be performed
   on such a packet only takes place at the nearest classification and
   marking policy enforcement point, which may be:

   o  At the wireless access point




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   o  At the wired network switch port

   o  At the wireless LAN controller

   As such, UP-to-DSCP mapping allows for wireless L2 markings to affect
   the QoS treatment of a packet over the wired IP network (that is,
   until the packet reaches the nearest classification and marking
   policy enforcement point).

   It should be further noted that nowhere in the [IEEE.802.11-2016]
   specifications is there an intent expressed for UP markings to be
   used to influence QoS treatment over wired IP networks.  Furthermore,
   [RFC2474], [RFC2475] and [RFC8100] all allow for the host to set DSCP
   markings for end-to-end QoS treatment over IP networks.  Therefore,
   it is NOT RECOMMENDED that wireless access points leverage Layer 2
   [IEEE.802.11-2016] UP markings as set by wireless hosts and
   subsequently perform a UP-to-DSCP mapping in the upstream direction,
   but rather, if wireless host markings are to be leveraged (as per
   business requirements, technical constraints and administrative
   policies), then it is RECOMMENDED to pass through the Layer 3 DSCP
   markings set by these wireless hosts instead, as is discussed in the
   next section.

5.3.  Upstream DSCP-Passthrough at the Wireless Access Point

   It is generally NOT RECOMMENDED to pass through DSCP markings from
   unauthenticated and unauthorized devices, as these are typically
   considered untrusted sources.

   When business requirements and/or technical constraints and/or
   administrative policies require QoS markings to be passed through at
   the wireless edge, then it is RECOMMENDED to pass through Layer 3
   DSCP markings (over Layer 2 [IEEE.802.11-2016] UP markings) in the
   upstream direction, with the exception of CS6 and CS7 (as will be
   discussed further), for the following reasons:

   o  [RFC2474], [RFC2475] and [RFC8100] all allow for hosts to set DSCP
      markings to achieve an end-to-end differentiated service

   o  [IEEE.802.11-2016] does not specify that UP markings are to be
      used to affect QoS treatment over wired IP networks

   o  Most present wireless device operating systems generate UP values
      by the same method as described in Section 2.2 (i.e. by using the
      3 MSB of the encapsulated 6-bit DSCP); then, at the access point,
      these 3-bit markings are converted back into DSCP values,
      typically in the default manner described in Section 2.3; as such,
      information is lost in the translation from a 6-bit marking to a



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      3-bit marking (which is then subsequently translated back to a
      6-bit marking); passing through the original (encapsulated) DSCP
      marking prevents such loss of information

   o  A practical implementation benefit is also realized by passing
      through the DSCP set by wireless client devices, as enabling
      applications to mark DSCP is much more prevalent and accessible to
      programmers of applications running on wireless device platforms,
      vis-a-vis trying to explicitly set UP values, which requires
      special hooks into the wireless device operating system and/or
      hardware device drivers, many of which do not support such
      functionality

   CS6 and CS7 are exceptions to this pass through recommendation
   because wireless hosts SHOULD NOT use them (see Section 5.1) and
   traffic with those two markings poses a threat to operation of the
   wired network (see Section 8.2).  CS6 and CS7 SHOULD NOT be passed
   through to the wired network in the upstream direction unless the
   access point has been specifically configured to do that by a network
   administrator or operator.

5.4.  Upstream DSCP Marking at the Wireless Access Point

   An alternative option to mapping is for the administrator to treat
   the wireless edge as the edge of the Diffserv domain and explicitly
   set (or reset) DSCP markings in the upstream direction according to
   administrative policy.  This option is RECOMMENDED over mapping, as
   this typically is the most secure solution, as the network
   administrator directly enforces the Diffserv policy across the IP
   network (versus an application developer and/or the wireless endpoint
   device operating system developer, who may be functioning completely
   independently of the network administrator).

6.  Appendix: IEEE 802.11 QoS Overview

   QoS is enabled on wireless networks by means of the Hybrid
   Coordination Function (HCF).  To give better context to the
   enhancements in HCF that enable QoS, it may be helpful to begin with
   a review of the original Distributed Coordination Function (DCF).

6.1.  Distributed Coordination Function (DCF)

   As has been noted, the Wi-Fi medium is a shared medium, with each
   station-including the wireless access point-contending for the medium
   on equal terms.  As such, it shares the same challenge as any other
   shared medium in requiring a mechanism to prevent (or avoid)
   collisions which can occur when two (or more) stations attempt
   simultaneous transmission.



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   The IEEE Ethernet working group solved this challenge by implementing
   a Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
   mechanism that could detect collisions over the shared physical cable
   (as collisions could be detected as reflected energy pulses over the
   physical wire).  Once a collision was detected, then a pre-defined
   set of rules was invoked that required stations to back off and wait
   random periods of time before re-attempting transmission.  While
   CSMA/CD improved the usage of Ethernet as a shared medium, it should
   be noted the ultimate solution to solving Ethernet collisions was the
   advance of switching technologies, which treated each Ethernet cable
   as a dedicated collision domain.

   However, unlike Ethernet (which uses physical cables), collisions
   cannot be directly detected over the wireless medium, as RF energy is
   radiated over the air and colliding bursts are not necessarily
   reflected back to the transmitting stations.  Therefore, a different
   mechanism is required for this medium.

   As such, the IEEE modified the CSMA/CD mechanism to adapt it to
   wireless networks to provide Carrier Sense Multiple Access/Collision
   Avoidance (CSMA/CA).  The original CSMA/CA mechanism used in IEEE
   802.11 was the Distributed Coordination Function.  DCF is a timer-
   based system that leverages three key sets of timers, the slot time,
   interframe spaces and contention windows.

6.1.1.  Slot Time

   The slot time is the basic unit of time measure for both DCF and HCF,
   on which all other timers are based.  The slot time duration varies
   with the different generations of data-rates and performances
   described by the [IEEE.802.11-2016] standard.  For example, the
   [IEEE.802.11-2016] standard specifies the slot time to be 20 us
   ([IEEE.802.11-2016] Table 15-5) for legacy implementations (such as
   IEEE 802.11b, supporting 1, 2, 5.5 and 11 Mbps data rates), while
   newer implementations (including IEEE 802.11g, 802.11a, 802.11n and
   802.11ac, supporting data rates from 6.5 Mbps to over 2 Gbps per
   spatial stream) define a shorter slot time of 9 us
   ([IEEE.802.11-2016], Section 17.4.4, Table 17-21).

6.1.2.  Interframe Spaces

   The time interval between frames that are transmitted over the air is
   called the Interframe Space (IFS).  Several IFS are defined in
   [IEEE.802.11-2016], with the two most relevant to DCF being the Short
   Interframe Space (SIFS) and the DCF Interframe Space (DIFS).

   The SIFS is the amount of time in microseconds required for a
   wireless interface to process a received RF signal and its associated



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   [IEEE.802.11-2016] frame and to generate a response frame.  Like slot
   times, the SIFS can vary according to the performance implementation
   of the [IEEE.802.11-2016] standard.  The SIFS for IEEE 802.11a,
   802.11n and 802.11ac (in 5 GHz) is 16 us ([IEEE.802.11-2016],
   Section 17.4.4, Table 17-21).

   Additionally, a station must sense the status of the wireless medium
   before transmitting.  If it finds that the medium is continuously
   idle for the duration of a DIFS, then it is permitted to attempt
   transmission of a frame (after waiting an additional random backoff
   period, as will be discussed in the next section).  If the channel is
   found busy during the DIFS interval, the station must defer its
   transmission until the medium is found idle for the duration of a
   DIFS interval.  The DIFS is calculated as:

      DIFS = SIFS + (2 * Slot time)

   However, if all stations waited only a fixed amount of time before
   attempting transmission then collisions would be frequent.  To offset
   this, each station must wait, not only a fixed amount of time (the
   DIFS), but also a random amount of time (the random backoff) prior to
   transmission.  The range of the generated random backoff timer is
   bounded by the Contention Window.

6.1.3.  Contention Windows

   Contention windows bound the range of the generated random backoff
   timer that each station must wait (in addition to the DIFS) before
   attempting transmission.  The initial range is set between 0 and the
   Contention Window minimum value (CWmin), inclusive.  The CWmin for
   DCF (in 5 GHz) is specified as 15 slot times ([IEEE.802.11-2016],
   Section 17.4.4, Table 17-21).

   However, it is possible that two (or more) stations happen to pick
   the exact same random value within this range.  If this happens then
   a collision may occur.  At this point, the stations effectively begin
   the process again, waiting a DIFS and generate a new random backoff
   value.  However, a key difference is that for this subsequent
   attempt, the Contention Window approximatively doubles in size (thus
   exponentially increasing the range of the random value).  This
   process repeats as often as necessary if collisions continue to
   occur, until the maximum Contention Window size (CWmax) is reached.
   The CWmax for DCF is specified as 1023 slot times
   ([IEEE.802.11-2016], Section 17.4.4, Table 17-21).

   At this point, transmission attempts may still continue (until some
   other pre-defined limit is reached), but the Contention Window sizes
   are fixed at the CWmax value.



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   Incidentally it may be observed that a significant amount of jitter
   can be introduced by this contention process for wireless
   transmission access.  For example, the incremental transmission delay
   of 1023 slot times (CWmax) using 9 us slot times may be as high as 9
   ms of jitter per attempt.  And, as previously noted, multiple
   attempts can be made at CWmax.

6.2.  Hybrid Coordination Function (HCF)

   Therefore, as can be seen from the preceding description of DCF,
   there is no preferential treatment of one station over another when
   contending for the shared wireless media; nor is there any
   preferential treatment of one type of traffic over another during the
   same contention process.  To support the latter requirement, the IEEE
   enhanced DCF in 2005 to support QoS, specifying HCF in IEEE 802.11,
   which was integrated into the main IEEE 802.11 standard in 2007.

6.2.1.  User Priority (UP)

   One of the key changes to the [IEEE.802.11-2016] frame format is the
   inclusion of a QoS Control field, with 3 bits dedicated for QoS
   markings.  These bits are referred to the User Priority (UP) bits and
   these support eight distinct marking values: 0-7, inclusive.

   While such markings allow for frame differentiation, these alone do
   not directly affect over-the-air treatment.  Rather it is the non-
   configurable and standard-specified mapping of UP markings to
   [IEEE.802.11-2016] Access Categories (AC) that generate
   differentiated treatment over wireless media.

6.2.2.  Access Category (AC)

   Pairs of UP values are mapped to four defined access categories that
   correspondingly specify different treatments of frames over the air.
   These access categories (in order of relative priority from the top
   down) and their corresponding UP mappings are shown in Figure 2
   (adapted from [IEEE.802.11-2016], Section 10.2.4.2, Table 10-1).














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                +-----------------------------------------+
                |   User    |   Access   | Designative    |
                | Priority  |  Category  | (informative)  |
                |===========+============+================|
                |     7     |    AC_VO   |     Voice      |
                +-----------+------------+----------------+
                |     6     |    AC_VO   |     Voice      |
                +-----------+------------+----------------+
                |     5     |    AC_VI   |     Video      |
                +-----------+------------+----------------+
                |     4     |    AC_VI   |     Video      |
                +-----------+------------+----------------+
                |     3     |    AC_BE   |   Best Effort  |
                +-----------+------------+----------------+
                |     0     |    AC_BE   |   Best Effort  |
                +-----------+------------+----------------+
                |     2     |    AC_BK   |   Background   |
                +-----------+------------+----------------+
                |     1     |    AC_BK   |   Background   |
                +-----------------------------------------+


    Figure 2: IEEE 802.11 Access Categories and User Priority Mappings

   The manner in which these four access categories achieve
   differentiated service over-the-air is primarily by tuning the fixed
   and random timers that stations have to wait before sending their
   respective types of traffic, as will be discussed next.

6.2.3.  Arbitration Inter-Frame Space (AIFS)

   As previously mentioned, each station must wait a fixed amount of
   time to ensure the medium is idle before attempting transmission.
   With DCF, the DIFS is constant for all types of traffic.  However,
   with [IEEE.802.11-2016] the fixed amount of time that a station has
   to wait will depend on the access category and is referred to as an
   Arbitration Interframe Space (AIFS).  AIFS are defined in slot times
   and the AIFS per access category are shown in Figure 3 (adapted from
   [IEEE.802.11-2016], Section 9.4.2.29, Table 9-137).












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               +------------------------------------------+
               |   Access   | Designative    |   AIFS     |
               |  Category  | (informative)  |(slot times)|
               |===========+=================+============|
               |   AC_VO   |     Voice       |     2      |
               +-----------+-----------------+------------+
               |   AC_VI   |     Video       |     2      |
               +-----------+-----------------+------------+
               |   AC_BE   |   Best Effort   |     3      |
               +-----------+-----------------+------------+
               |   AC_BK   |   Background    |     7      |
               +-----------+-----------------+------------+


        Figure 3: Arbitration Interframe Spaces by Access Category

6.2.4.  Access Category Contention Windows (CW)

   Not only is the fixed amount of time that a station has to wait
   skewed according to [IEEE.802.11-2016] access category, but so are
   the relative sizes of the Contention Windows that bound the random
   backoff timers, as shown in Figure 4 (adapted from
   [IEEE.802.11-2016], Section 9.4.2.29, Table 9-137).


         +-------------------------------------------------------+
         |   Access   | Designative    |   CWmin    |   CWmax    |
         |  Category  | (informative)  |(slot times)|(slot times)|
         |===========+=================+============|============|
         |   AC_VO   |     Voice       |     3      |     7      |
         +-----------+-----------------+------------+------------+
         |   AC_VI   |     Video       |     7      |     15     |
         +-----------+-----------------+------------+------------+
         |   AC_BE   |   Best Effort   |     15     |    1023    |
         +-----------+-----------------+------------+------------+
         |   AC_BK   |   Background    |     15     |    1023    |
         +-----------+-----------------+------------+------------+


           Figure 4: Contention Window Sizes by Access Category

   When the fixed and randomly generated timers are added together on a
   per access category basis, then traffic assigned to the Voice Access
   Category (i.e. traffic marked to UP 6 or 7) will receive a
   statistically superior service relative to traffic assigned to the
   Video Access Category (i.e. traffic marked UP 5 and 4), which, in
   turn, will receive a statistically superior service relative to
   traffic assigned to the Best Effort Access Category traffic (i.e.



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   traffic marked UP 3 and 0), which finally will receive a
   statistically superior service relative to traffic assigned to the
   Background Access Category traffic (i.e. traffic marked to UP 2 and
   1).

6.3.  IEEE 802.11u QoS Map Set

   IEEE 802.11u [IEEE.802-11u.2011] is an addendum that has now been
   included within the main [IEEE.802.11-2016] standard, and which
   includes, among other enhancements, a mechanism by which wireless
   access points can communicate DSCP to/from UP mappings that have been
   configured on the wired IP network.  Specifically, a QoS Map Set
   information element (described in [IEEE.802.11-2016] Section 9.4.2.95
   and commonly referred to as the QoS Map element) is transmitted from
   an AP to a wireless endpoint device in an association / re-
   association Response frame (or within a special QoS Map Configure
   frame).

   The purpose of the QoS Map element is to provide the mapping of
   higher layer Quality of Service constructs (i.e.  DSCP) to User
   Priorities.  One intended effect of receiving such a map is for the
   wireless endpoint device (that supports this function and is
   administratively configured to enable it) to perform corresponding
   DSCP-to-UP mapping within the device (i.e. between applications and
   the operating system / wireless network interface hardware drivers)
   to align with what the APs are mapping in the downstream direction,
   so as to achieve consistent end-to-end QoS in both directions.

   The QoS Map element includes two key components:

   1) each of the eight UP values (0-7) are associated with a range of
   DSCP values, and

   2) (up to 21) exceptions from these range-based DSCP to/from UP
   mapping associations may be optionally and explicitly specified.

   In line with the recommendations put forward in this document, the
   following recommendations apply when the QoS Map element is enabled:

   1) each of the eight UP values (0-7) are RECOMMENDED to be mapped to
   DSCP 0 (as a baseline, so as to meet the recommendation made in
   Section 8.2

   2) (up to 21) exceptions from this baseline mapping are RECOMMENDED
   to be made in line with Section 4.3, to correspond to the Diffserv
   Codepoints that are in use over the IP network.





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   It is important to note that the QoS Map element is intended to be
   transmitted from a wireless access point to a non-AP station.  As
   such, the model where this element is used is that of a network where
   the AP is the edge of the Diffserv domain.  Networks where the AP
   extends the Diffserv domain by connecting other APs and
   infrastructure devices through the IEEE 802.11 medium are not
   included in the cases covered by the presence of the QoS Map element,
   and therefore are not included in the present recommendation.

7.  IANA Considerations

   This memo asks the IANA for no new parameters.

8.  Security Considerations

   The recommendations in this document concern widely-deployed wired
   and wireless network functionality, and for that reason do not
   present additional security concerns that do not already exist in
   these networks.  In fact, several of the recommendations made in this
   document serve to protect wired and wireless networks from potential
   abuse, as is discussed further in this section.

8.1.  General QoS Security Recommendations

   It may be possible for a wired or wireless device (which could be
   either a host or a network device) to mark packets (or map packet
   markings) in a manner that interferes with or degrades existing QoS
   policies.  Such marking or mapping may be done intentionally or
   unintentionally by developers and/or users and/or administrators of
   such devices.

   To illustrate: A gaming application designed to run on a smart-phone
   or tablet may request that all its packets be marked DSCP EF and/or
   UP 6.  However, if the traffic from such an application is forwarded
   without change over a business network, then this could interfere
   with QoS policies intended to provide priority services for business
   voice applications.

   To mitigate such scenarios it is RECOMMENDED to implement general QoS
   security measures, including:

      Setting a traffic conditioning policy reflective of business
      objectives and policy, such that traffic from authorized users
      and/or applications and/or endpoints will be accepted by the
      network; otherwise packet markings will be "bleached" (i.e.
      remarked to DSCP DF and/or UP 0).  Additionally, Section 5.3 made
      it clear that it is generally NOT RECOMMENDED to pass through DSCP
      markings from unauthorized and/or unauthenticated devices, as



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      these are typically considered untrusted sources.  This is
      especially relevant for IoT deployments, where tens-of-billions of
      devices that may have little or no security are being connected to
      IP networks.

      Policing EF marked packet flows, as detailed in [RFC2474]
      Section 7 and [RFC3246] Section 3.

   In addition to these general QoS security recommendations, WLAN-
   specific QoS security recommendations can serve to further mitigate
   attacks and potential network abuse.

8.2.  WLAN QoS Security Recommendations

   The wireless LAN presents a unique DoS attack vector, as endpoint
   devices contend for the shared media on a completely egalitarian
   basis with the network (as represented by the AP).  This means that
   any wireless client could potentially monopolize the air by sending
   packets marked to preferred UP values (i.e.  UP values 4-7) in the
   upstream direction.  Similarly, airtime could be monopolized if
   excessive amounts of downstream traffic were marked/mapped to these
   same preferred UP values.  As such, the ability to mark/map to these
   preferred UP values (of UP 4-7) should be controlled.

   If such marking/mapping were not controlled, then, for example, a
   malicious user could cause WLAN DoS by flooding traffic marked CS7
   DSCP downstream.  This codepoint would map by default (as described
   in Section 2.2) to UP 7 and would be assigned to the Voice Access
   Category (AC_VO).  Such a flood could cause Denial-of-Service to not
   only wireless voice applications, but also to all other traffic
   classes.  Similarly, an uninformed application developer may request
   all traffic from his/her application to be marked CS7 or CS6,
   thinking this would acheive in the best overall servicing oftheir
   application traffic, while not realizing that such a marking (if
   honored by the client operating system) could cause not only WLAN
   DoS, but also IP network instability, as the traffic marked CS7 or
   CS6 finds its way into queues intended for servicing (relatively low-
   bandwidth) network control protocols, potentially starving legitimate
   network control protocols in the process.

   Therefore, to mitigate such an attack, it is RECOMMENDED that all
   packets marked to Diffserv Codepoints not in use over the wireless
   network be mapped to UP 0; this recommendation applies both at the
   access point (in the downstream direction) and within the wireless
   endpoint device operating system (in the upstream direction).

   Such a policy of mapping unused codepoints to UP 0 would also prevent
   an attack where non-standard codepoints were used to cause WLAN DoS.



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   Consider the case where codepoints are mapped to UP values using a
   range function (e.g.  DSCP values 48-55 all map to UP 6), then an
   attacker could flood packets marked, for example to DSCP 49, in
   either the upstream or downstream direction over the WLAN, causing
   DoS to all other traffic classes in the process.

   In the majority of WLAN deployments, the AP represents not only the
   edge of the Diffserv domain, but also the edge of the network
   infrastructure itself; that is, only wireless client endpoint devices
   are downstream from the AP.  In such a deployment model, CS6 and CS7
   also fall into the category of codepoints that are not in use over
   the wireless LAN (since only wireless endpoint client devices are
   downstream from the AP in this model and these devices do not
   [legitimately] participate in network control protocol exchanges).
   As such, it is RECOMMENDED that CS6 and CS7 DSCP be mapped to UP 0 in
   these Wifi-at-the-edge deployment models.  Otherwise, it would be
   easy for a malicious application developer, or even an inadvertently
   poorly-programmed IoT device, to cause WLAN DoS and even wired IP
   network instability by flooding traffic marked CS6 DSCP, which would
   by default (as described in Section 2.2) be mapped to UP 6, causing
   all other traffic classes on the WLAN to be starved, as well
   hijacking queues on the wired IP network that are intended for the
   servicing of routing protocols.  To this point, it was also
   recommended in Section 5.1 that packets requesting a marking of CS6
   or CS7 DSCP SHOULD be remarked to DSCP 0 and mapped to UP 0 by the
   wireless client operating system.

   Finally, it should be noted that the recommendations put forward in
   this document are not intended to address all attack vectors
   leveraging QoS marking abuse.  Mechanisms that may further help
   mitigate security risks include strong device- and/or user-
   authentication, access-control, rate limiting, control-plane
   policing, encryption and other techniques; however, the
   implementation recommendations for such mechanisms are beyond the
   scope of this document to address in detail.  Suffice it to say that
   the security of the devices and networks implementing QoS, including
   QoS mapping between wired and wireless networks, SHOULD be considered
   in actual deployments.

9.  Acknowledgements

   The authors wish to thank David Black, Gorry Fairhurst, Ruediger
   Geib, Vincent Roca, Brian Carpenter, David Blake, Cullen Jennings,
   David Benham and the TSVWG.

   The authors also acknowledge a great many inputs, notably from David
   Kloper, Mark Montanez, Glen Lavers, Michael Fingleton, Sarav




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   Radhakrishnan, Karthik Dakshinamoorthy, Simone Arena, Ranga Marathe,
   Ramachandra Murthy and many others.

10.  References

10.1.  Normative References

   [IEEE.802.11-2016]
              "Information technology - Telecommunications and
              information exchange between systems - Local and
              metropolitan area networks - Specific requirements - Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) specifications", IEEE Standard 802.11, 2016,
              <https://standards.ieee.org/findstds/
              standard/802.11-2016.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2597]  Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597,
              DOI 10.17487/RFC2597, June 1999,
              <https://www.rfc-editor.org/info/rfc2597>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <https://www.rfc-editor.org/info/rfc3168>.

   [RFC3246]  Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
              J., Courtney, W., Davari, S., Firoiu, V., and D.
              Stiliadis, "An Expedited Forwarding PHB (Per-Hop
              Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002,
              <https://www.rfc-editor.org/info/rfc3246>.

   [RFC3662]  Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
              Per-Domain Behavior (PDB) for Differentiated Services",
              RFC 3662, DOI 10.17487/RFC3662, December 2003,
              <https://www.rfc-editor.org/info/rfc3662>.




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   [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>.

   [RFC5865]  Baker, F., Polk, J., and M. Dolly, "A Differentiated
              Services Code Point (DSCP) for Capacity-Admitted Traffic",
              RFC 5865, DOI 10.17487/RFC5865, May 2010,
              <https://www.rfc-editor.org/info/rfc5865>.

10.2.  Informative References

   [I-D.ietf-tsvwg-le-phb]
              Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)",
              draft-ietf-tsvwg-le-phb-02 (work in progress), June 2017.

   [IEEE.802-11u.2011]
              "Information technology - Telecommunications and
              information exchange between systems - Local and
              metropolitan area networks - Specific requirements - Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) specifications", IEEE Standard 802.11, 2011,
              <http://standards.ieee.org/getieee802/
              download/802.11u-2011.pdf>.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <https://www.rfc-editor.org/info/rfc2475>.

   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of
              Diffserv Service Classes", RFC 5127, DOI 10.17487/RFC5127,
              February 2008, <https://www.rfc-editor.org/info/rfc5127>.

   [RFC7561]  Kaippallimalil, J., Pazhyannur, R., and P. Yegani,
              "Mapping Quality of Service (QoS) Procedures of Proxy
              Mobile IPv6 (PMIPv6) and WLAN", RFC 7561,
              DOI 10.17487/RFC7561, June 2015,
              <https://www.rfc-editor.org/info/rfc7561>.

   [RFC8100]  Geib, R., Ed. and D. Black, "Diffserv-Interconnection
              Classes and Practice", RFC 8100, DOI 10.17487/RFC8100,
              March 2017, <https://www.rfc-editor.org/info/rfc8100>.








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Internet-Draft        DSCP Mapping for IEEE 802.11        September 2017


Appendix A.  Change Log

   Initial Version:  July 2015

Authors' Addresses

   Tim Szigeti
   Cisco Systems
   Vancouver, British Columbia  V6K 3L4
   Canada

   Email: szigeti@cisco.com


   Jerome Henry
   Cisco Systems
   Research Triangle Park, North Carolina  27709
   USA

   Email: jerhenry@cisco.com


   Fred Baker
   Santa Barbara, California  93117
   USA

   Email: FredBaker.IETF@gmail.com
























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