About IrLAP Frame Format
IrLAP defines the format of the frames sent and received on the infrared media. Each IrLAP frame consists of the following elements:
One or more Beginning of Frame (BOF) flags that mark the beginning of the frame. The size of the BOF member varies in length depending on the speed as described in Receiver Synchronization.
An address (A) member that identifies the secondary connection address. The address member is 8 bits. The address member specifies the address of a device that belongs to a particular IrDA miniport driver. This IrDA miniport driver transmits or receives the frame that contains this address through this device. For more information about the address member, see Address Member.
A control (C) member that specifies the function of the particular frame. The control member is eight bits.
An optional information (I) member that contains the information data. The information member is an integral number of octets.
A frame check sequence (FCS) member that allows the receiving station to check the transmission accuracy of the frame. The FCS member is either 16 or 32 bits, depending on the speed.
An end of frame (EOF) flag that signals the end of the frame. The size of the EOF member varies depending on the speed.
The following example of an IrLAP frame shows the order of the elements that are described preceding.
BOF |
A |
C |
I |
FCS |
EOF |
The coding of packets and BOF, EOF, and FCS members varies depending on the operating speed of the infrared media. Complete documentation about physical frames can be found in the publication Infrared Data Association Serial Infrared Physical Layer Link Specification, available from IrDA. A brief summary of the differences in coding schemes is provided in IrDA Miniport Driver Packet Coding Schemes.