EDCF Access Categories
This document discusses the status and proposed enhancements for EDCF parameters as part of the 802.11e D1.3 draft. It addresses issues relating to priority parameters and their mappings to delivery priorities and traffic categories, highlighting the need for a redesigned concept of Access Categories (ACs). The proposal aims to simplify the mapping process, suggest the removal of confusing delivery priorities, and streamline the queue management for different traffic types in WLAN environments to enhance Quality of Service (QoS).
EDCF Access Categories
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Presentation Transcript
EDCF Access Categories Menzo Wentink, Intersil; Sunghyun Choi, Javier del Prado, Sai Shankar Philips Research USA; Atul Garg, Philips Semiconductors mwentink@intersil.com and sunghyun.choi@philips.com M.M. Wentink, Intersil & S. Choi, Philips
Introduction Priority, Priority Parameter, Delivery Priority, TCs, Queues and EDCF Parameters M.M. Wentink, Intersil & S. Choi, Philips
Status as of 802.11e/D1.3 (1) • Priority parameter = TC (from 0 to 15) • provided in the MA-UNIDATA.request • Priority (from 0 to 7) • extracted from the Priority Parameter • indirectly in the Delivery Priority of the TSPEC • Delivery Priority (from 0 to 7) • mapped from Priority using dot11PriorityMapping M.M. Wentink, Intersil & S. Choi, Philips
Status as of 802.11e/D1.3 (2) 16 Priority Parameters or TCs 8 Priorities 8 Delivery Priorities <= 8 Physical Queues EDCF Parameters (AIFS, CWmin,…) M1 M2 M3 M.M. Wentink, Intersil & S. Choi, Philips
Status as of 802.11e/D1.3 (2) • Mapping M1 using table dot11PriorityMapping • Mapping M2 not specified • Mapping M3 between access parameters (i.e., AIFS[i], Cwmin[i], PF[i]) and queues is currently problematic • this was noted earlier by Sunghyun Choi • see next slides! • more details about the problems can be found in submissions by Choi, et al. (01/534) and Wentink (01/541) • the solution outlined in this proposal supersedes the solutions in the above mentioned documents M.M. Wentink, Intersil & S. Choi, Philips
Problematic Descriptions in D1.3 • 9.1.3.1: • “An ESTA or EAP may implement fewer than 8 physical queues and shall provide a mapping from traffic categories and delivery priorities to the available queues by means of the dot11PriorityMapping table in the MAC MIB.” • 9.2.3.4: • “An ESTA that provides fewer than 8 output queues shall use the TxAIFS [TC] slot boundary for queue [i] where TC is the highest priority TC assigned to queue [i]. • What happens if an ESTA has only one queue? • All frames will be served using TC=7 AIFS !!! • This does not sound reasonable at all !!! M.M. Wentink, Intersil & S. Choi, Philips
Problematic Descriptions in D1.3 • 9.2.4: • The enumeration of implemented queues determines which access parameters should be used: “queue i uses CWmin[i]" • 9.2.3.4: • “An ESTA that provides fewer than 8 output queues shall use the TxAIFS [TC] slot boundary for queue [i] where TC is the highest priority TC assigned to queue [i]. • So which access parameters should be used for queue i when there are <8 queues? M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution (1) • Delete the concept of Delivery Priority • confusing with Priority • doesn’t appear to have any use in the draft • Introduce the concept of Access Category (AC) • an Access Category represents a single virtual DCF • Let 4 ACs be normative, for EAP and ESTA • in absence of certain types of traffic, the corresponding queue does not have to be implemented • i.e. no burden on dedicated application terminals, like phones • Note 4 ACs does not limit the number of queues to 4. M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution (2) • Simplify M1 and M2 into one unique mapping M0: • see tables on next slides Priority Access Category M0 • Let the QoS Parameter Set element contain 4 sets of access parameters • M3is now a trivial one-to-one mapping between access parameters and ACs M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution (3) 16 Priority Parameters or TCs 8 Priorities M0 4 ACs (↔ 4x EDCF parameters) M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution – M0 (I) • Priority to Access Category mapping, alt. I • according to 802.1D tables H.15, H.16 • introduces a ‘lower-than-best-effort’ AC bk = background sp = spare be = best effort ee = excellent effort vi = video cl = controlled load vo = voice nc = network control M.M. Wentink, Intersil & S. Choi, Philips
Proposed Solution – M0 (II) • Priority to Access Category mapping, alt. II • dedicated AC for voice, video • no ‘lower-than-beest-effort’ AC, but this does not exclude a ‘lower-than-best-effort’ priority. bk = background sp = spare be = best effort ee = excellent effort vi = video cl = controlled load vo = voice nc = network control M.M. Wentink, Intersil & S. Choi, Philips
