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Doc.: IEEE 802.11-04/879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 1 Class-based Contention Periods (CCP) for the 802.11n MAC A. Dasylva,

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Presentation on theme: "Doc.: IEEE 802.11-04/879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 1 Class-based Contention Periods (CCP) for the 802.11n MAC A. Dasylva,"— Presentation transcript:

1 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 1 Class-based Contention Periods (CCP) for the n MAC A. Dasylva, Z. Yao, D.Y. Montuno, W. Chen, M. Ouellette, J. Aweya, and K. Felske Nortel Networks

2 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 2 Acronyms HC: Hybrid Coordinator CP: Contention Period CFP: Contention Free Period CCP: Class-based Contention Periods ECP: Explicit Contention Period. A type of CP explicitly allocated by the HC and where a subset of the ACs may contend. It starts and ends with specific control frames LCP: Legacy Contention Period. A traditional CP. STA: Station. Unless mentioned other wise an STA indicates a legacy STA (with or without QoS support) HT STA: High Throughput STA, an STA supporting the new features described in this document and other n features. HT AP: High Throughput AP, an AP supporting the features described in this document and other n features.

3 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 3 General description of CCP Two types of contention periods –Explicit CPs (ECPs) allocated by the HT AP –Legacy CPs (LCPs) In each ECP a subset of ACs contend according to EDCA rules ECPs are delimited by –ECP-Start –ECP-End or –ECP-Start+ECP-end frames Two access modes for ECPs –Default mode: a channel access function can access the channel within an ECP if its AC is allowed in the ECP –QoS negotiation mode: the HT AP grants access to the channel access function after a QoS negotiation phase

4 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 4 Motivation for CCP The need for a simple and effective QoS provisioning mechanism EDCA does not provide good isolation of real time traffic from UDP best effort traffic The complexity and polling overhead (especially the associated preamble+PLCP overhead) of HCCA The difficulty of accurate QoS provisioning with EDCA Solution CCP: blend features of HCCA and EDCA –Centralized allocation and scheduling of ECPs –Distributed channel access within ECPs –QoS provided by the proper selection of ECP lengths and scheduling

5 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 5 ECP Scheduling (Informative)

6 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 6 Control frames/ ECP-Start frame A frame sent by the HT AP to initiate a new ECP Fields: –RA: set to the broadcast group address –ECP type: 1 byte field giving the ECP type. Each ECP type maps to a subset of ACs. –Duration: this field is set to the length of the ECP

7 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 7 Control frames/ ECP-End frame A frame sent by the HT AP to end an ECP Fields: –RA: set to the broadcast group address –Duration: frame duration

8 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 8 Control frames/ ECP-End+ECP-Start frame A frame sent by the HT AP to end the current ECP and start the next ECP Fields: –RA: set to the broadcast group address –Duration: duration of the ECP –ECP type: type of the next ECP

9 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 9 Control frames/ ECP-Access Req. frame A frame sent by a HT STA to the AP to request access to ECPs of one or more types Fields: –Duration: frame duration –TA: address of the requesting HT STA –ECP type n: n-th ECP type for which access is requested –TSPEC n: TSPEC of the traffic to be transmitted in ECPs of type n

10 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 10 Control frames/ ECP-Access Req. ACK. frame A frame sent by an HT AP to an HT STA to acknowledge the receipt of an ECP-access request frame Fields: –Duration: frame duration –RA: address of the requesting HT STA –Request number: request number assigned by the HT AP

11 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 11 Control frames/ ECP-Access Resp. frame A frame sent by the HT AP to a requesting HT STA in response to an ECP access request access Fields: –Duration: frame duration –RA: address of the requesting HT STA –ECP type n: n-th ECP type for which access is requested –Resp n: admission decision for ECP n

12 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 12 Mgmt frames/ ECP capability element Information element advertising ECP capability by the HT AP or HT STAs Fields: –ECP capability: bit indicating whether the HT AP is able to allocate ECPs, or HT STAs are able to interpret ECP frames –ECP length: maximum ECP length –Num. ECP types: the number of ECP types that are supported by the HT AP

13 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 13 Mgmt frames/ ECP parameter element An information element giving the parameters of an ECP type Fields: –ECP type: type of the ECP between 0 and 255 –Mode: access mode for the ECP type, i.e. default (0) or through QoS negotiation (1) –AC mask: ACs that are allowed to contend for channel access

14 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 14 MAC sublayer functional description 1/5 ECP allocation and scheduling –The HT AP allocates ECPs by sending ECP-Start or ECP- Start+ECP-End frames –The duration of a new ECP is set in the duration field of the corresponding ECP-Start, or ECP-Start + ECP-End frame –The length of an ECP cannot exceed the value of MAX_ECP_LENGTH (larger than the CFP length) set in the ECP length field of the ECP capability element –An ECP-Start or ECP-End+ECP-Start frame may be allocated A PIFS interval after the completion of a CFP or ECP A PIFS interval after the transmission of a frame in LCPs Channel access during ECPs –Essentially EDCA rules with minor modifications: –A frame exchange sequence initiated within an ECP must complete within that ECP –A TXOP obtained within an ECP must complete within the ECP –The HCCA function cannot obtained polled TXOPs within an ECP

15 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 15 MAC sublayer functional description 2/5 Channel access during LCPs –All HT STAs may contend according to EDCA rules –The HCCA function may allocate polled TXOPs Interaction with the power save feature –Consider a HT STA emerging from power-save mode –This HT STA may not have knowledge of the current CFP/ECP/LCP –The HT STA resets an ECP-length timer with the value MAX_ECP_LENGTH and waits for of the following events to occur: The timer expires: then the HT STA concludes that it is within an LCP, and the states of the channel access functions are set accordingly A CFP-End, ECP-Start, ECP-End or ECP-Start+ECP-End frame is received and the states of the channel access functions may be properly set

16 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 16 MAC sublayer functional description 3/5 Support of frame aggregation ( class-based frame aggregation) : it is possible to transmit aggregate frames within ECPs subject to the following limitations: –For an ECP with no required QoS negotiation: only frames of ACs allowed within the ECP may form an aggregate –For an ECP with required QoS negotiation: only frames from channel access functions of the allowed ACs that have been granted access to the ECP type by the HC

17 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 17 MAC sublayer functional description 4/5 ECP allocation examples

18 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 18 MAC sublayer functional description 5/5 ECP allocation examples

19 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 19 MAC sublayer Mgmt/ ECP capability ECP capability information: included by the HT AP in association or re- association messages with the following info –Whether ECPs are supported –The maximum ECP length (MAX_ECP_LENGTH) –The number of supported ECP types ECP parameters: included by the HT AP in association or re- association messages with the following info for each ECP type –The mode: default or through QoS negotiation –AC mask: allowed ACs

20 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 20 MAC sublayer Mgmt/ IBSS operation Currently not supported with CCP

21 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 21 MAC sublayer mgmt/ Coexistence with legacy STAs Legacy STAs: STAs not able to interpret ECP control frames Channel access within ECPs: the setting of the duration field in ECP- Start, and Ecp-Start+ECP-End frames ensure that legacy STAs do not interfere with ECP traffic Channel access within LCPs: all STAs including legacy ones may contend according to EDCA No conflict with HCCA

22 doc.: IEEE /879r3 Submission August 2004 Abel Dasylva, Nortel NetworksSlide 22 Conclusion A simple framework for effective QoS provisioning A wide variety of bandwidth allocation and QoS policies supported Full back compatibility with /802.11e The requirement for admission control to ensure QoS within real time ECPs (beyond the scope of this work)


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