気の向くままの個人用メモ

The PCF mechanism is obsolete. Consequently, this subclause might be removed in a later revision of the standard.

PCFは時代遅れなので、将来的には削除されます。なので訳も適当です。

The PCF provides CF frame transfer. It is an option for an AP to be able to become the PC. A non-AP STA shall not become a PC. All STAs inherently obey the medium access rules of the PCF, because these rules are based on the DCF, and all STAs set their NAV at the beginning of each CFP. The operating characteristics of the PCF are such that all STAs are able to operate in the presence of a BSS in which a PC is operating, and, if associated with a point-coordinated BSS, are able to receive frames sent under PCF control. It is also an option for a STA to be able to respond to a CF-Poll received from a PC. A STA that is able to respond to CF-Polls is referred to as being CF-Pollable and may request to be polled by an active PC. CF-Pollable STAs and the PC do not use RTS/CTS in the CFP. When polled by the PC, a CF-Pollable STA may transmit only one MPDU, which might be sent to the PC but may have any destination, and may “piggyback” the acknowledgment of a frame received from the PC using particular data frame subtypes for this transmission. If the Data frame is not in turn acknowledged, the CF-Pollable STA shall not retransmit the frame unless it is polled again by the PC, or it decides to retransmit during the CP. If the addressed recipient of a CF transmission is not CF-Pollable, that STA acknowledges the transmission using the DCF acknowledgment rules, and the PC retains control of the medium. A PC may use CF frame transfer solely for delivery of frames to STAs, and never to poll CF-Pollable STAs.

PCFはCFフレームを送信する。APはオプションでPCになり、STAはPCになってはならない。すべてのSTAはPCFに従う。なぜなら、DCFに従い、各CFPの開始ではすべてのSTAはNAVにならないといけないからです。PCFの特徴はPC注はすべてのSTAが操作でき、PCF制御の下でフレーム受信ができるということです。CFPではRTS/CTSは使用しません。PC中はSTAは1つだけMPDUを送信します。データフレームにAckがなければ再送もしません。再送する場合はCP中になります。

A PC may perform a backoff on retransmission of an unacknowledged frame during the CFP. A PC that is maintaining a polling list may retry the unacknowledged frame the next time the particular AID is at the top of the polling list.

CFP中PCは再送のバックオフをします。ポーリングリストに従って特定のAIDにAckが来なかったフレームを再送します。

A PC may retransmit an unacknowledged frame during the CFP after a PIFS.

PCはPIFS後のCFPの間に再送します。

When more than one point-coordinated BSS is operating on the same PHY channel in overlapping space, the potential exists for collisions between PCF transfer activities by the independent PCs. The rules under which multiple, overlapping point-coordinated BSSs may coexist are presented in 10.4.4.3. As shown in Figure 10-1 (in 10.2), the PCF is built on top of the CSMA/CA-based DCF, by utilizing the access priority provisions provided by this scheme. An active PC shall be located at an AP, which restricts PCF operation to infrastructure networks. PCF is activated at a PC-capable AP by setting the CFPMaxDuration parameter in the CF Parameter Set of the MLME-START.request primitive to a nonzero value.

Data frames sent by, or in response to polling by, the PC during the CFP shall use the appropriate data subtypes based upon the following usage rules:

• Data +CF-Poll, Data +CF-Ack +CF-Poll, CF-Poll, and CF-Ack +CF-Poll shall be sent only by a PC.
• Data, Data +CF-Ack, Null Function, and CF-Ack may be sent by a PC or by any CF-Pollable STA.

ポーリング方式で送信します。

A STA receiving Data frames shall consider the frame body as the basis of a possible indication to LLC only if the frame is of subtype Data, Data +CF-Ack, Data +CF-Poll, or Data +CF-Ack +CF-Poll. A CF-Pollable STA shall interpret all subtype bits of received Data type frames that contain the BSSID of the current BSS for CF purposes, but shall not inspect the frame body unless the frame is of subtype Data, Data +CF-Ack, Data +CFPoll, or Data +CF-Ack +CF-Poll.