Some Comments on 802.11E Draft 2.0

IEEE P802.11
Wireless LANs

Some Comments on 802.11e Draft 2.0

Date:January 16, 2002

Author:Jin-Meng Ho

Texas Instruments

12500 TI Boulevard, MS 8649

Dallas, Texas 75243

Phone: 214-480-1994

Email:

Abstract

This document contains some comments prepared for LB #30 in the form of Word Comment, as well as some proposed editorial and techanical changes to IEEE 802.11e Draft 2.0 in the form of insertions, deletions, and modifications to the text of that draft. These changes are presented, using red color, on top of the changes, shown in blue color, of that draft with respect to IEEE Std 802.11-1999. Some figures may appear only in print layout view.

Draft Supplement to IEEE STANDARD Standard FORfor

Information technology -
Telecommunications and Iinformation Eexchange

Bbetween Ssystems -
LAN/MAN Local and metropolitan area networks –

Specific Rrequirements -
Part 11: Wireless LAN Medium Access Control (MAC) and pPhysical lLayer (PHY) specifications:
Medium Access Control (MAC) Enhancements for Quality of Service (QoS)

Introduction

[(This introduction is not part of IEEE P802.11de, Draft Supplement to IEEE STANDARD Standard FORfor Information Technology -
Telecommunications and Iinformation Eexchange Bbetween Ssystems - LAN/MAN Local and metropolitan area networks - Specific Rrequirements -
Part 11: Wireless LAN Medium Access Control (MAC) and pPhysical lLayer (PHY) specifications:
Medium Access Control (MAC) Enhancements for Quality of Service (QoS).)]

Participants

At the time this standard was submitted to Sponsor Ballotballoted, the 802.11 wWorking gGroup had the following membership:

Current Chair, Chair

This is an unapproved IEEE Standards Draft, subject to change.1

IEEE
Medium Access Control Enhancements for Quality of ServiceP802.11e/D1.42.0, October November 2001

The following persons were onmembers of the the balloting committee voted on this standard:

(To be provided by IEEE editor at time of publication.)

______

This is an unapproved IEEE Standards Draft, subject to change.1

IEEE
Medium Access Control Enhancements for Quality of ServiceP802.11e/D1.42.0, October November 2001

ContentsContents

Introduction

Contents

1.2Purpose

2.Normative references

3.Definitions

3.13coordination function

3.20distribution system (DS)

3.25extended service set (ESS)

3.52bridge portal (BP)

3.53contention free period (CFP)

3.54contention period (CP)

3.55controlled access phase (CAP)

3.56controlled contention

3.57differentiation

3.58fragmentation

3.59hybrid coordination function (HCF)

3.60hybrid coordinator (HC)

3.61link

3.62parameterized QoS

3.63prioritized QoS

3.64QoS access point (QAP)

3.65QoS basic service set (QBSS)

3.66QoS facility

3.67QoS station (QSTA)

3.68superframe

3.69traffic category (TC)

3.70traffic category identifier (TCID)

3.71traffic classification (TCLAS)

3.72traffic identifier (TID)

3.73traffic specification (TSPEC)

3.74traffic stream (TS)

3.75traffic stream identifier (TSID)

3.76transmission opportunity (TXOP)

3.77wireless station (WSTA)

4.Abbreviations and acronyms

5.General description

5.1.1.2The media impact the design......

5.1.1.4Interaction with other IEEE 802 layers......

5.2.2.2QBSS: The quality of service network......

5.2.4Integration with wired LANs......

5.3Logical service interfaces

5.3.1Station service (SS)......

5.3.2Distribution system service (DSS)......

5.4Overview of the services

5.4.1.2Integration......

5.4.2.1Mobility types......

5.4.2.2Association......

5.4.4Traffic differentiation and QoS support......

5.4.4.1Differentiation......

5.5Relationships between services

5.6Differences between ESS and IBSS LANs

5.7.1Data......

5.7.2Association......

5.7.3Reassociation......

6.MAC service definition

6.1.1Asynchronous data service......

6.1.1.1.QoS support......

6.1.3MSDU ordering......

7.Frame formats

7.1MAC frame formats

7.1.1Conventions......

7.1.2General frame format......

7.1.3.1Frame Control field......

7.1.3.2Duration/ID field......

7.1.3.5QoS Control field......

7.1.3.6TAID field......

7.1.3.7Frame Body field......

7.1.3.8FCS field......

7.2.1.1Request To Send (RTS) frame format......

7.2.1.2Clear To Send (CTS) frame format......

7.2.1.3Acknowledgement (ACK) frame format......

7.2.1.4Power Save Poll (PS-Poll) frame format......

7.2.1.5CF-End frame format......

7.2.1.6CF-End + CF-Ack frame format......

7.2.1.7 Burst Acknowledgement (BurstAck) frame format......

7.2.1.9Contention Control (CC) frame format......

7.2.1.10Reservation Request (RR) frame format......

7.2.2Data frames......

7.2.3Management frames......

7.2.3.1Beacon frame format......

7.2.3.4Association Request frame format......

7.2.3.5Association Response frame format......

7.2.3.6Reassociation Request frame format......

7.2.3.7Reassociation Response frame format......

7.2.3.8Probe Request frame format......

7.2.3.9Probe Response frame format......

7.2.3.10Action frame format......

7.3.1.4Capability Information field......

7.3.1.7Reason Code field......

7.3.1.9Status Code field......

7.3.2Information elements......

7.3.2.13QBSS Load element......

7.3.2.14HCF Contention Parameter Set element......

7.3.2.15Traffic Specification (TSPEC) element......

7.3.2.16Error Statistics element......

7.3.2.17Extended Capability element......

7.3.2.18Traffic Classification (TCLAS) Element......

7.4QoS management actions

7.4.1Add TS QoS Action frame format......

7.4.2Del TS QoS Action frame format......

7.5MAC-Level FEC and FEC frame formats

7.6Frame usage guidelines

9.MAC sublayer functional description

9.1MAC architecture

9.1.1Distributed coordination function (DCF)......

9.1.3Hybrid coordination function (HCF)......

9.1.3.1HCF contention-based channel access (EDCF)......

9.1.3.2HCF controlled channel access......

9.1.4Coexistence of DCF, PCF and HCF......

9.1.6MAC data service......

9.2.3Inter frame space (IFS)......

9.2.3.4Arbitration IFS (AIFS)......

9.2.4Random backoff time......

9.2.5.1Basic Access......

9.2.5.2Backoff Procedure

9.2.5.3Recovery Procedures and Retransmit Limits......

9.2.5.4Setting and resetting the NAV......

9.2.10DCF timing relations......

9.10HCF controlled access

9.10.1HCF controlled access procedure......

9.10.1.1CAP generation......

9.10.1.2Recovery from the absence of an expected reception......

9.10.1.3CFP generation by the HC......

9.10.2TXOP structure and timing......

9.10.2.1NAV operation during a CAP......

9.10.3HCF transfer rules......

9.10.3.1TXOP requests......

9.10.3.2Use of RTS/CTS......

9.10.3.3 Burst transmission and acknowledgment......

9.10.4Controlled contention......

9.10.4.1CC Transmission......

9.10.4.2CCI response procedure......

9.10.4.3CCI feedback procedure......

9.10.4.4CCI generation by HC......

9.10.6HCF frame exchange sequences......

10.Layer management

10.3.2Scan......

10.3.2.1MLME-SCAN.request......

10.3.2.2MLME-SCAN.confirm......

10.3.6.1MLME-ASSOCIATE.request......

10.3.7.1MLME-REASSOCIATE.request......

10.3.10.1MLME-START.request......

10.3.11 QoS management action......

10.3.11.1MLME-ADDTS.request......

10.3.11.2MLME-ADDTS.confirm......

10.3.11.3MLME-ADDTS.indication......

10.3.11.4MLME-ADDTS.response......

10.3.11.5MLME-DELTS.request......

10.3.11.6MLME-DELTS.confirm......

10.3.11.7MLME-DELTS.indication......

10.3.11.8MLME-DELTS.response......

10.3.12.1MLME-WMSTATUS.request......

10.3.12.2MLME-WMSTATUS.confirm......

11.MAC subayer management entity

Annex D

This is an unapproved IEEE Standards Draft, subject to change.1

IEEE
Medium Access Control Enhancements for Quality of ServiceP802.11e/D1.42.0, October November 2001

Draft Supplement to IEEE STANDARD Standard FORfor

Information technology -
Telecommunications and Iinformation Eexchange

Bbetween Ssystems -
LAN/MAN Local and metropolitan area networks –

Specific Rrequirements -
Part 11: Wireless LAN Medium Access Control (MAC) and pPhysical lLayer (PHY) specifications:
Medium Access Control (MAC) Enhancements for Quality of Service (QoS)

[This supplement is based on the current edition of IEEE Std 802.11, 1999 Edition and the 802.11a, 802.11b and 802.11d supplements]

EDITORIAL NOTE—The editing instructions contained in this supplement define how to merge the material contained herein into the existing base standard to form the new comprehensive standard as created by the addition of IEEE Std 802.11-19992002.

The editing instructions are shown in bold italic. Three editing instructions are used: change, delete, and insert. Change is used to make small corrections in existing text or tables. The editing instruction specifies the location of the change and describes what is being changed either by using strikethrough (to remove old material) or underscore (to add new material). Delete removes existing material. Insert adds new material with-out disturbing the existing material. Insertions may require renumbering. If so, renumbering instructions are given in the editing instruction. Editorial notes will not be carried over into future editions.

1.2Purpose

Insert the following text at the end of 1.2, as part of the indented list:

- Defines the MAC procedures to support LAN applications with Quality of Service (QoS) requirements, including the transport of voice, audio and video over IEEE 802.11 wireless LANs.

2.Normative references

Insert the following two citations at the appropriate locations in clause 2:

ISO/IEC 15802-3: 1998, Information Technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Common specifications – Part 3: Media Access Control (MAC) Bridges.

IEEE Std 802.1Q-1998, IEEE Standards for Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks.

3.Definitions

Change the definition of coordination function in 3.13 as follows:

3.13coordination function

The logical function which determines when a station operating within a Bbasic Sservice Sset (BSS) is permitted to transmit and may be able to receive protocol data units (PDUs) via the wireless medium (WM). The CF coordination funciton within a BSS may have one point coordination function (PCF) and will shall have one distributed coordination function (DCF). The CF coordination function within a QoS basic service set (QBSS)will shall have one hybrid coordination function (HCF).

Change the definition of distribution system in 3.20, and insert the informative note, as follows:

3.20distribution system (DS)

A system used to interconnect a set of basic service sets (BSSs) and portals to create an extended service set (ESS).

NOTE: This correction, and the correction of ESS below, are needed because of a conflict in IEEE Std 802.11-1999 between these definitions and the text clause 5.4.1.2, which states "Messages which are distributed to a portal cause the DS to invoke the integration function (conceptually after the distribution service). The Integration function is responsible for accomplishing whatever is needed to deliver a message from the DSM to the integrated LAN media (including any required media or address space translations)." Clause 5.4.1.2 is correct; whereas the existing definitions, which place the integrated LAN within the DS/ESS, are incorrect. If an integrated IEEE 802.3 LAN (or any other LAN that does not signal user priority) were connected directly to the DS/ESS, then QoS traffic from a device on the integrated LAN to an 802.11 station associated in the ESS would not transit a portal, hence there would be no opportunity to regenerate the priority value needed to identify the 802.11 QoS traffic category.

Change the definition of extended service set in 3.25 as follows:

3.25extended service set (ESS)

A set of one or more interconnected basic service sets (BSSs) or QoS basic service sets (QBSSs) and portals that appears as a single BSS or QBSS to the logical link control sublayer at any station associated with one of those BSSs or QBSSs.

Insert the following new definitions at the appropriate locations in clause 3, renumbering as necessary:

3.52bridge portal (BP)

Anenhanced QoS station (ESTAQSTA) within in a QoS basic service set (QBSS) that is not the enhanced QoS access point (EAPQAP) for the QBSS, but which includes a portal that is functionally equivalent to an IEEE 802.1D MAC bridge or IEEE 802.1Q VLAN bridge. Bridge portals can be used to provide multiple links to the infrastructure within a single QBSS, as well as to provide the sole infrastructure link in cases where the site for physical connection to the infrastructure is a poor location for operation of the EAPQAP or its co-located hybrid coordinator (HC).

3.53contention free burst (CFB)[J. Ho: 1]

A transmission opportunity (TXOP) during which an enhanced station (ESTAQSTA) may transfer a plurality of MPDUs, retaining control of the WM by using short inter-frame spaces (SIFS) and the virtual carrier sense mechanism (NAV) so that the entire burst appears to be a single instance of WM activity to contending stations. The use of CFB transfers may increase the aggregate data throughput within a given basic service area (BSA), but may also cause an increase of latency and/or latency variation (jitter) for all traffic being transferred within the same BSA.

3.5453contention free period (CFP)

A time period during operation of a basic service set (BSS) or a QoS basic service set (QBSS) when a point coordination function (PCF) or hybrid coordination function (HCF) is active, and the right to transmit is assigned to stations by a point coordinator (PC) or hybrid coordinator (HC), allowing frame exchanges to occur without intra-BSS contention for the wireless medium (WM) or under controlled contention.

3.5554contention period (CP)

A time period during operation of a basic service set (BSS) when a distributed coordination function (DCF) or hybrid coordination function (HCF) is active, and the right to transmit is either determined locally as stations with pending transfers contend for the WM using a carrier sense multiple access algorithm with collision avoidance (CSMA/CA), or is assigned to enhanced QoS stations (ESTAQSTAs) by the a hybrid coordinator (HC) thus allowing frame exchanges between QoS stations (QSTAs) to occur without intra-BSS contention for the wireless medium (WM) or under controlled contention.

3.5655controlled access periodphase (CAP[J. Ho: 2])

A set of sequential frame exchange sequences, with no embedded interframe spaces longer than PIFS, starting with a transmission by the HC, and potentially including one or more CFBs transmitted by WSTAs that receive QoS (+)CF-Polls from the HC.A time period during operation of a QoS basic service set (QBSS) in the contention period (CP) when a hybrid coordination function (HCF) controlled access method is used, and the right to transmit is assigned to QoS stations (QSTAs) by a hybrid coordinator (HC) thus allowing frame exchanges between QSTAs to occur without intra-BSS contention for the wireless medium (WM) or under controlled contention.

3.5756controlled contention

A contention-based multiple access scheme that may be used by enhanced QoS stations (ESTAQSTAs) to send reservation request frames into time intervals specified by a hybrid coordinator (HC) to request transmission opportunities (TXOPs) from the hybrid coordinator (HC), without incurring the overhead of periodic polling nor the highly variable delays of DCF-based contention in a busy QBSS. Each instance of controlled contention occurs solely among a subset of ESTAQSTAs that need to send reservation requests and which meet criteria defined by the HC. Controlled contention takes place during a controlled contention interval (CCI) whose starting time and duration are determined by the HC.

3.57differentiation

The service that, by using the QoS facility, differentiates medium access control (MAC) service data units (MSDUs) in their transfer between peer MAC entities to support prioritized and parameterized QoS.

3.5758enhanced access point (EAPQAP)

An access point (AP) that implements the access point functionality required for the QoS facility. An EAPQAP differentiates among 8 traffic categories within the traffic to/from each associated ESTAQSTA, provides at least 4 transmit queues for differing priorities or other categories of QoS traffic, and supports the hybrid coordination function (HCF).

Editor's Remark: In the TGi draft the acronym "EAP" is used for Extensible Authentication Protocol. It is likely that TGe will need to adopt a different acronym, because the meaning ascribed to EAP by TGi is consistent with prior security-related use in IETF RFC 2284 and the 802.1X drafts. Several people have suggested that TGe replace the QoS-related instances of "EAP" with "QAP" along with a corresponding replacement of "ESTA" with "QSTA."

3.5859enhanced station (ESTAQSTA)

An IEEE 802.11 station (STA) that implements the QoS facility and hybrid coordination function (HCF) as specified herein, and includes an IEEE 802.11-conformant physical (PHY) interface to the wireless medium (WM).

3.596058fragmentation

The process of partitioning a MAC service data unit (MSDU) or MAC management protocol data unit (MMPDU) into a sequence of smaller MAC protocol data units (MPDUs) prior to transmission in order to increase the probability of successful transfer across the WM and/or in order to use available transmission opportunity (TXOP) duration limits efficiently in cases where the remaining TXOP duration is shorter than the time required to transmit the entire pending MSDU. The process of recombining a set of fragment MPDUs into an MSDU or MMPDU is known as defragmentation.

3.606159hybrid coordination function (HCF[J. Ho: 3])

A coordination function that combines, and enhances, aspects of the distributed coordination function (DCF) and the point coordination function (PCF)contention-based and polling-based access methods to provide QoS stations (QoS STAs) withthe selective handling of MSDUs requiredprioritized and parameterized QoS access to the wireless medium (WM)for the QoS facility, while continuing to support non-QoS stations (STAs) for best-effort traffic transer. The HCF is upward compatible from bothwith the distributed coordination funciton(DCF) and may optionally contain the point coordination function (PCF),;and allowsit supportsenhanced stations (ESTAQSTAs) to use a uniform set of frame formats and exchange sequences that QoS stations (QSTAs) may use during both the contention period (CP) and the contention free period (CFP).

NOTE: For historical reasons, the contention-based channel access mechanism of the HCF is referred to as the "EDCF." Despite the presence of "CF" in its name, the EDCF is part of the HCF and is not a separate coordination function.

3.616260hybrid coordinator (HC)

A type of point coordinator, defined as part ofthe QoS facility, that implements the QoS facility andframe exchange sequences and MSDU handling rules defined bythe hybrid coordination function (HCF) to manage and control access to the wireless medium (WM) for both QoS and non-QoS traffic transfer in a QoS basic service set (QBSS) . The HC operates during both the contention period (CP) and contention free period (CFP). The HC performs bandwidth management including the allocation of TXOPs to ESTAQSTAs and the initiation of controlled contention intervals. An HC is typically collocated with anEAPQAP.

3.626361link

In relation to any IEEE 802.11 MAC entity, a logical unilateral path used to exchange MSDUs with a peer entity, includingbetween peer entities in a basic service set (BSS) or QoS basic service set (QBSS), with one or more traversals of the wireless medium (WM)and zero or more traversals of non-wireless distribution system media.

3.62parameterized QoS

A quality of service (QoS) expressed in terms of specific or quantitative values of QoS parameters, such as data rate, delay bound, and jitter bound, that are expected to be met within the MAC data service in the transfer of data frames between peer QoS stations (QSTAs) in a QoS basic service set (QBSS). Due to the nature of the wireless medium (WM), such QoS parameter values may not be met in the transfer of data frames. Parameterized QoS applies to traffic streams (TSs) only, with the QoS parameters provided by a traffic specification (TSPEC) designated for the TS.