OSI是一套规范的总称，包含了很多具体的协议标准，用于方便不同的系统之间互操作。OSI是ISO和ITU-U这两个组织定义的。

其中最有名的就是OSI参考模型，将网络分成不同Layer层次，并且为不同的Layer制定了相应的N多协议规范。

图示如下：

图 1.1. OSI参考模型以及不同层所对应的协议

对应的物理层和数据链路层，OSI所支持的介质访问协议包括：

而80211协议，只涉及最底层的，物理层和数据链路层。

下图是802.11和OSI模型的对应关系：

图 1.2. 802.11和OSI模型

对应的物理层方面，可能用到.FH/DS/IR/CCK/OFDM等技术，这部分后面会有详细解释。

NIC

Frame Types

http://www.wi-fiplanet.com/tutorials/article.php/1447501

Management Frames：

Control Frames

Data Frames

PLME

On the other hand PLME stands for Physical Layer Management Entity.

http://www.wi-fiplanet.com/tutorials/article.php/1492071/80211-Beacons-Revealed.htm

http://www.pulsewan.com/data101/802_11_b_basics.htm

Another MAC-layer problem specific to wireless is the ?hidden node? issue, in which two stations on opposite sides of an access point can both ?hear? activity from an access point, but not from each other, usually due to distance or an obstruction. To solve this problem, 802.11 specifies an optional Request to Send/Clear to Send (RTS/CTS) protocol at the MAC layer. When this feature is in use, a sending station transmits an RTS and waits for the access point to reply with a CTS. Since all stations in the network can hear the access point, the CTS causes them to delay any intended transmissions, allowing the sending station to transmit and receive a packet acknowledgment without any chance of collision. Since RTS/CTS adds additional overhead to the network by temporarily reserving the medium, it is typically used only on the largest-sized packets, for which retransmission would be expensive from a bandwidth standpoint.

http://www.pulsewan.com/data101/802_11_b_basics.htm

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) works as follows.

A station wishing to transmit senses the air, and, if no activity is detected, the station waits an additional, randomly selected period of time and then transmits if the medium is still free. If the packet is received intact, the receiving station issues an ACK frame that, once successfully received by the sender, completes the process. If the ACK frame is not detected by the sending station, either because the original data packet was not received intact or the ACK was not received intact, a collision is assumed to have occurred and the data packet is transmitted again after waiting another random amount of time.