Mapping Diffserv to IEEE 802.11
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Extracted elements (28)
DSCP passthrough is preferred over UP-to-DSCP mapping for upstream traffic because the 6→3→6-bit round-trip loses information (collapsing 12 differentiated service classes to 8), whereas passing the original DSCP preserves the full marking. Additionally, setting DSCP is far more accessible to application developers than setting 802.11 UP values.
High-Throughput Data (AF1x) is mapped to UP 0 rather than AC_BK because the 802.11 four-AC model has no corresponding fit; assigning to AC_BK would impose a lower-than-best-effort penalty on legitimate business traffic, while AC_BE at least provides parity with the standard class.
The default 'MSB' DSCP-to-UP mapping (3 high-order bits of DSCP → UP) is widely deployed but produces systematic conflicts with RFC 4594 recommendations: EF maps to AC_VI instead of AC_VO, CS3/Broadcast Video maps to AC_BE instead of AC_VI, CS2/OAM maps to AC_BK instead of AC_BE, and Low-Latency Data maps to AC_BK.
IEEE 802.11 cannot support true EF PHB or AF PHB services because its contention-based medium access (CSMA/CA) is non-deterministic: no access category can be guaranteed strict priority or assured minimum bandwidth over another.
RFC 7561 (based on GSMA IPX Guidelines) specifies DSCP-to-UP mappings that conflict with RFC 4594 and this document. The two plans cannot be normalized; they belong to separate Differentiated Services Domains, requiring codepoint translation at domain boundaries.
All unused or unauthorized DSCP codepoints are RECOMMENDED to be mapped to UP 0, both at the AP (downstream) and in the wireless endpoint OS (upstream), to prevent WLAN DoS via non-standard or unauthorized markings.
All wireless APs and wireless endpoint devices are RECOMMENDED to support fully configurable mappings between DSCP and UP, as well as the ability to mark both DSCP and UP independently.
Broadcast Video traffic marked CS3 is RECOMMENDED to be mapped to UP 4 (AC_VI) via a non-default mapping, since the default MSB mapping places CS3 in UP 3 (AC_BE), which is contrary to the video service intent.
EF DSCP MUST use a non-default mapping to UP 6 (Voice Access Category, AC_VO) rather than the default UP 5 (AC_VI), because the default MSB-based mapping places telephony traffic in the wrong access category.
High-Throughput Data (AF1x) is RECOMMENDED to be mapped to UP 0 (AC_BE) because there is no directly corresponding fit within the four-AC 802.11 model, and AC_BK would impose lower-than-best-effort treatment.
In AP-to-AP or infrastructure/mesh deployment models where network infrastructure is downstream, network control protocols are RECOMMENDED to be mapped to UP 7.
In Wi-Fi-at-the-edge deployment models where only client devices are downstream, CS6 and CS7 DSCP are RECOMMENDED to be mapped to UP 0 rather than their default UP 6/7, preventing WLAN DoS and IP network instability.
Low-Latency Data (AF2x) is RECOMMENDED to be mapped to UP 3 (AC_BE) rather than the default UP 2 (AC_BK), as AC_BK contradicts the foreground, user-interactive nature of this service class.
Network Control traffic marked CS6 is RECOMMENDED to be mapped to UP 7 (AC_VO) rather than the default UP 6, to distinguish it from data-plane voice traffic while still receiving high-priority service.
OAM traffic marked CS2 is RECOMMENDED to be mapped to UP 0 (AC_BE) rather than the default UP 2 (AC_BK), because AC_BK contradicts the intent in RFC 4594 for OAM traffic to receive at-least-best-effort service.
VOICE-ADMIT DSCP (44 decimal / 101100 binary, per RFC 5865) is RECOMMENDED to be mapped to UP 6, placing it in the Voice Access Category (AC_VO).
When the IEEE 802.11u QoS Map element is enabled, each of the eight UP values (0–7) are RECOMMENDED to be mapped to DSCP 0 as a baseline, with up to 21 provisioned exceptions per Section 4.3.
When upstream passthrough is required, Layer 3 DSCP markings are RECOMMENDED over Layer 2 UP markings, except for CS6 and CS7 which SHOULD NOT be passed through to the wired network unless explicitly configured by an administrator.
Wireless APs MUST NOT leverage Layer 2 IEEE 802.11 UP markings set by wireless hosts and subsequently perform a UP-to-DSCP mapping in the upstream direction, as IEEE 802.11 does not intend UP to influence wired IP QoS treatment.
Wireless APs treating the edge as a Diffserv boundary and explicitly marking DSCP in the upstream direction is RECOMMENDED over any form of UP-based mapping, as this is the most secure option.
Wireless client operating systems SHOULD map CS6 and CS7 DSCP to UP 0 and SHOULD re-mark such packets to DSCP 0, because CS6/CS7 are intended for network control and SHOULD NOT be sourced from wireless endpoint devices.
DSCP occupies the first 6 bits of the IPv4 TOS field and the IPv6 Traffic Class field; the remaining 2 bits carry ECN (RFC 3168). The common 'default' practice derives 802.11 UP by using the 3 most significant bits of the DSCP, and reverses it upstream by left-shifting UP by 3 bits.
IEEE 802.11 Access Categories achieve QoS differentiation through distinct AIFS values (AC_VO/AC_VI: 2 slot times; AC_BE: 3; AC_BK: 7) and CW ranges (AC_VO CWmin=3/CWmax=7; AC_VI 7/15; AC_BE/AC_BK 15/1023).
The IEEE 802.11u QoS Map Set element, transmitted from AP to non-AP station in association/re-association Response frames, communicates DSCP-to-UP mappings so wireless endpoints can align upstream markings with the AP's downstream configuration. It supports up to 21 explicit DSCP exceptions from eight UP-range associations.
User Priority (UP) is a 3-bit field in the IEEE 802.11 QoS Control frame header supporting eight values (0–7). Pairs of UP values map non-configurably to four Access Categories: AC_VO (UP 6,7), AC_VI (UP 4,5), AC_BE (UP 0,3), AC_BK (UP 1,2).
A traffic-conditioning policy should 'bleach' (re-mark to DSCP DF / UP 0) any packets from unauthorized users, applications, or endpoints. EF-marked flows should additionally be policed per RFC 2474 Section 7 and RFC 3246 Section 3.
IoT devices connected with little or no security capabilities can be leveraged for DDoS attacks amplified by QoS preferential treatment if their packet markings are trusted. It is generally NOT RECOMMENDED to pass through DSCP from unauthenticated or unauthorized devices.
Wireless clients can monopolize the shared 802.11 medium by flooding traffic marked to preferred UP values (4–7), causing WLAN DoS for voice and video classes. CS6 or CS7 floods are especially dangerous as they also starve wired-network routing-protocol queues, causing IP network instability.