IEEE 802.11 MAC Enhancements for Quality of Service

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IEEE 802.11 MAC Enhancements for Quality of
Service

• IEEE Std 802.11e

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Characteristics of IEEE 802.11e

• The major enhancement of 802.11e
• Traffic differentiation
• Enhanced DCF (contention-based)
• EDCF

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MAC Architecture
IEEE 802.11 MAC Architecture
IEEE 802.11e MAC Architecture

• DCF A contention-base access for 802.11.
• PCF An option to support contention-free access
  in 802.11.
• Hybrid Coordination Function (HCF) IEEE 802.11
  Task Group E (TGe) proposes HCF to provide QoS
  for real-time applications.

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HCF - Introduction

• HCF combines functions from the DCF and PCF with
  enhanced QoS-specific mechanisms.
• HCF consists of
• Enhance DCF (EDCF) for contention-based access
• Controlled Access (HCCA) for contention-free
  access

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EDCF Traffic Category

• The EDCF provides differentiated access to the WM
  for 8 priorities, identical to IEEE 802.1D
  priority tag, for non-AP STAs.
• Priorities are numbered from 0 (the lowest
  priority) to 7 (the highest priority).
• The set of MSDUs with the same priority is refer
  to a Traffic Category (TC).

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EDCF Access Category (1/5)

• EDCF defines access category (AC) mechanism to
  support the priority mechanism at QSTAs.
• An AC is an enhanced variant of the DCF which
  contends for transmission opportunity (TXOP)
  using the set of parameters such as CWminAC,
  CWmaxAC, AIFSAC, etc.

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EDCF Access Category (2/5)IFS (Inter Frame
Spacing)
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EDCA
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EDCF Access Category (3/5)

• The parameter set is specified in the EDCA
  parameter set element of beacon frames.
• Default QoS parameter set

video
voice
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EDCF Access Category (4/5)Queues

• An QSTA has four ACs.
• Collision between ACs within a QSTA is called
  internal collision. Collisions will be resolved
  internally (giving to higher-priority queues).

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EDCF Access Category (5/5)

• The mapping from 8 priories to 4 ACs is

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Summary

• A new EDCF block
• Use of different IFS in traffic categories for
  QoS support