User`s guide

Aironet Wireless Communications, Inc. 3-4 Confidential and Proprietary
specification. The format of each of the individual frame types is defined in section 7.2 of the IEEE
802.11 specification.
Frame
Control
Duration/
ID
FCSAddress 1 Address 2 Address 3
Sequence
Control
Frame
Body
MAC Header
2 2 6 6 6 2 0 - 2312 4
Address 4
6Octets:
Figure 3.3 - MAC Control Information
The 2 byte Frame Control field consists of the following sub-fields: Protocol Version, Type, Subtype, To
DS, From DS, More Fragments, Retry, Power Management, More Data, WEP and Order.
The Duration/ID field is 16 bits in length. The contents of the this field is as follows:
a) In Control Type frames of subtype PS-Poll, the Duration/ID field carries the association
identity (AID) of the station that transmitted the frame in the 14 least-significant bits, with
the 2 most-significant bits both set to 1. The value of the AID is in the range 1 - 2007.
b) In all other frames the Duration/ID field contains a duration value as defined for each frame
type in section 7.2 of the 802.11 specification. For frames transmitted during the contention
free period the duration field is set to 32768.
There are four address fields in the MAC frame format. These fields are used to indicate the BSSID,
source address, destination address, transmitting station address and receiving station address. Each
Address field contains a 48-bit address as defined in 5.2 of IEEE Std 802-1990.
The Sequence Control field is 16 bits in length and consists of two subfields, the Sequence Number and
the Fragment number.
The Frame Body is a variable length field and contains information specific to individual frame types and
subtypes. The minimum frame body is zero octets. The maximum length frame body is defined by the
maximum length (MSDU + ICV + IV); where ICV and IV are the WEP fields defined in section 8.2.5 of
the IEEE 802.11 specification.
The FCS field is a 32 bit field containing a 32-bit Cyclic Redundancy Check (CRC). The FCS is
calculated over all the fields of the MAC header and the frame body field.
Table 3.1 indicates all of the defined 802.11 frame types.