Class-based Contention Periods (CCP) for the 802.11n MAC August 2004 doc.: IEEE 802.11-02/xxxr0 August 2004 Class-based Contention Periods (CCP) for the 802.11n MAC A. Dasylva, Z. Yao, D.Y. Montuno, W. Chen, M. Ouellette, J. Aweya Nortel Networks Abel Dasylva, Nortel Networks Abel Dasylva, Nortel Networks

General description of CCP August 2004 doc.: IEEE 802.11-02/xxxr0 August 2004 General description of CCP Two types of contention periods Explicit CPs (ECPs) allocated by the 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 AP grants access to the channel access function after a Qos negotiation phase Abel Dasylva, Nortel Networks Abel Dasylva, Nortel Networks

ECP Scheduling (Informative) August 2004 doc.: IEEE 802.11-02/xxxr0 August 2004 ECP Scheduling (Informative) Abel Dasylva, Nortel Networks Abel Dasylva, Nortel Networks

Control frames/ ECP-Start frame August 2004 Control frames/ ECP-Start frame A frame sent by the 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 Abel Dasylva, Nortel Networks

Control frames/ ECP-End frame August 2004 Control frames/ ECP-End frame A frame sent by the AP to end an ECP Fields: RA: set to the broadcast group address Duration: frame duration Abel Dasylva, Nortel Networks

Control frames/ ECP-End+ECP-Start frame August 2004 Control frames/ ECP-End+ECP-Start frame A frame sent by the 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 Abel Dasylva, Nortel Networks

Control frames/ ECP-Access Req. frame August 2004 Control frames/ ECP-Access Req. frame A frame sent by a QSTA to the AP to request access to ECPs of one or more types Fields: Duration: frame duration TA: address of the requesting QSTA 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 Abel Dasylva, Nortel Networks

Control frames/ ECP-Access Req. ACK. frame August 2004 Control frames/ ECP-Access Req. ACK. frame A frame sent by a QSTA to the AP to acknowledge the receipt of an ECP-access request Fields: Duration: frame duration RA: address of the requesting QSTA Request number: request number assigned by the QAP Abel Dasylva, Nortel Networks

Control frames/ ECP-Access Resp. frame August 2004 Control frames/ ECP-Access Resp. frame A frame sent the AP to a requesting QSTA in response to an ECP access request access Fields: Duration: frame duration RA: address of the requesting QSTA ECP type n: n-th ECP type for which access is requested Resp n: admission decision for ECP n Abel Dasylva, Nortel Networks

Mgmt frames/ ECP capability element August 2004 Mgmt frames/ ECP capability element Information element advertising ECP capability by the QAP or QSTAs Fields: ECP capability: bit indicating whether the QAP is able to allocate ECPs, or QSTAs are able to interpret ECP frames ECP length: maximum ECP length Num. ECP types: the number of ECP types that are supported by the QAP Abel Dasylva, Nortel Networks

Mgmt frames/ ECP parameter element August 2004 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 negoiation (1) AC mask: ACs that are allowed to contend for channel access Abel Dasylva, Nortel Networks

MAC sublayer functional description 1/2 August 2004 MAC sublayer functional description 1/2 ECP allocation and scheduling The QAP 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 set in the ECP length filed of the CP capability element An ECP-Start or ECP-End+ECP-Start frame may be allocated A SIFS interval after the completion of a CFP or ECP A SIFS interval after the transmission of a frame in LCPs Channel access during ECPs Essentially EDCA rules with minor modifications: A frame exchange sequence intiated 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 Abel Dasylva, Nortel Networks

MAC sublayer functional description 2/2 August 2004 MAC sublayer functional description 2/2 Channel access during LCPs All QSTAs may contend according to EDCA rules The HCCA function may allocate polled TXOPs Interaction with the power save feature Consider a QSTA emerging from power-save mode This QSTA may not have knowledge of the current CFP/ECP/LCP The QSTA 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 QSTA 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 Abel Dasylva, Nortel Networks

MAC sublayer Mgmt/ ECP capability August 2004 MAC sublayer Mgmt/ ECP capability ECP capability information: included by the QAP 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 QAP 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 Abel Dasylva, Nortel Networks

MAC sublayer Mgmt/ IBSS operation August 2004 MAC sublayer Mgmt/ IBSS operation Currently not supported with ECPs. Abel Dasylva, Nortel Networks

MAC sublayer mgmt/ Coexistence with legacy STAs August 2004 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 interfer with ECP traffic Channel access within LCPs: all STAs including legacy ones may contend accroding to EDCA No conflict with HCCA Abel Dasylva, Nortel Networks

Simulation results Scenarios Residential: UM 1 Large entreprise: UM 4 August 2004 Simulation results Scenarios Residential: UM 1 Large entreprise: UM 4 Hot spot: UM 6 Abel Dasylva, Nortel Networks

August 2004 Conclusions Abel Dasylva, Nortel Networks