Issue
139 February 2002
What
Good is IrD, Eh?
Part
2: Wireless Communication
byJeff
Bachiochi
IrLAP/IrLMP
Services
Table 1 shows
the IrLAP services available to the IrLMP layer. These
services have multiple service primitives. The primitives
imply direction of data flow as shown in Figure 2.
| Table
1—The IrLAP layer offers these services to the
IrLMP layer. Each service incorporates its own set
of primatives, which imply the direction of data flow. |
 |
| Figure 2—IrDA service
primatives (request, indication, response, and confirm)
are illustrated here to show primary and secondary
communications. |
The IrLAP must
translate between these services and one or more frames
of data transferred between devices within range via the
IrPHY layer. These translations take place as procedures
defining the behavior of the IrLAP layer during each phase
of the procedure. Figure 3 shows the logical flow of these
service procedures.
 |
| Figure 3—The IrLAP
performs a direct, logical progression through the
two modes of its state machine. |
There are two
modes of operation, operational and nonoperational. Nonoperational,
or Normal Disconnect mode (NDM), takes place before or
after an actual connection is made. All discovery and
address conflict resolution is handled in NDM. Normal
Response mode (NRM) takes place after a device is connected.
Primary and secondary roles must be determined prior to
initiation of NRM. The primary station has responsibility
for controlling the link, issuing commands, and granting
permission to transmit. The secondary station takes orders
from the primary and transmits only when given explicit
permission to do so.
