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

2. General description of CCP
August 2004
doc.: IEEE /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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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

18. August 2004
Conclusions
Abel Dasylva, Nortel Networks