Class-based Contention Periods (CCP) for the 802.11n MAC

1. 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

2. 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

3. ECP Scheduling (Informative) Abel Dasylva, Nortel Networks

4. 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

5. 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

6. 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

7. 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

8. 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 • TA: 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. 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

16. Simulation results • Scenarios • Residential: UM 1 • Large entreprise: UM 4 • Hot spot: UM 6 Abel Dasylva, Nortel Networks

17. Conclusions Abel Dasylva, Nortel Networks