User`s guide

Aironet Wireless Communications, Inc. 7-35 Confidential and Proprietary
if (bap0_setup(rid, 0) != SUCCESS) return ERROR;
bap0_write(pBuf, len);
// ---now commit the rid data
return PC4500_accessrid(rid, 0x100|CMD_ACCESS);
}
Frame Info Descriptor
A Frame Information Descriptor (FID) is used to pass transmit and receive packets to and from the
PC4500/4800. FIDs are passed to the host in the RxFid, TxAllocFid and TxComplFid registers. The
FID is then accessed (read/written) using the BAP registers. The BAP registers consist of a Selector,
Offset, Data registers. Details on using these registers is described in Memory (RID/FID) Access.
The FID consists of the following sections:
Control header
802.11 header
Gap for Protocol Encapsulation changes
802.3 header (may be disabled)
Packet Payload.
The control header contains fields for selecting transmission options, and for reporting status of receive
and transmit packets. When a transmit FID is allocated, the Control Header will be initialized to all
zeros.
The 802.11 header allows for transmitting and receiving of 802.11 packets. Station drivers typically
won’t use the 802.11 header, since they only receive data packets. Instead, station drivers will use the
802.3 header and allow the PC4500/4800 to build the 802.11 transmission header. Similarly for receive
packets, rather than having to interpret the 802.11 header, the station drivers will look at the 802.3 header
that has been provided by the PC4500/4800. For receive packets, the 802.11 header is always available
even if the 802.3 header is provided.
Access point hosts are required to interpret the 802.11 header since they must handle non-data packets
(e.g. 802.11 management packets). Access point hosts will typically disable the 802.3 header for
efficiency.
The PC4500/4800 provides for two style of hosts: ethernet and LLC. An ethernet style host is one which
expects an ether-type field at the beginning of the packet payload. An LLC style host expects 802.2
(LLC) to be the first protocol in the payload. For an LLC host, the PC4500/4800 will transmit and
receive packet payloads without modification.
Since 802.11 is an 802 network, the payloads require 802.2/LLC as the first protocol in the packet
payload. Ethernet packets must be reencapsulated using RFC1042 or 802.1H, to be sent on 802.11. For
LLC/802.2 hosts, the packet payloads are sent and received without any modifications. For ethernet
hosts, the transmit and receive payloads are modified using the encapsulation rules that were configured.
The Protocol Gap field allows for adding and stripping these protocol modifications. The offsets shown
for fields after the "gap" reflect a gap length of zero bytes. The offsets shown can be used to access the
fields shown. The PC4500/4800 will adjust the access to the correct location. However, if reading
through the gap, the host must skip past the appropriate number of locations.
Note, when a transmit FID is allocated, the Control header will be initialized to all zeros by the firmware,
all other fields will contain uninitialized data.