 Optional Protocol Stack IrDA's optional protocol stack (Figure 10-13) offers applications a number of new services and emulations of legacy services, the most important of which are described below. LM-IAS The link management information access service (LM-IAS) provides a database to enable applications to discover devices and to access device-specific information, in essence a "yellow pages" of devices and the services they can provide. All services or applications available via an incoming connection must have an entry in the LM-IAS database, which can be queried to obtain information about these services, for example the current load experienced by a network resource or the attributes of a serial link emulation. Wireless PAN Standards Tiny-TP Tiny-TP is an intermediate protocol layer that provides a simple transport protocol to control flow on IrLMP connections. It also provides a segmentation and re-assembly service to prevent deadlock situations that can occur as a result of limited device buffer space. Tiny-TP controls flow by adding a single "credit" byte of overhead to each transmitted frame. A receiving device can use this credit when one of its applications need to transmit an LMP frame back to the other device. This simple system is similar to the flow control mechanism used in Bluetooth's RFCOMM protocol, described above, and ensures that communication is not interrupted by a device running out of buffer space. IrCOMM IrCOMM emulates legacy serial (or parallel) port connections for applications such as printing. When installed, IrCOMM creates a virtual port which appears to the host computer or applications as if it were a standard serial or parallel port connection. IrCOMM includes emulation of a number of legacy interfaces including RS232 and Centronics LPT. IrOBEX IrOBEX is an optional application layer protocol that is designed to enable applications to exchange a wide variety of arbitrary data objects such as files, electronic business cards and digital images. It defines the Information IrLAN I