RFlink is Nettech's transport protocol API for communication among the client and gateway libraries, which has been specifically optimized for wireless transmission. For example, when designing a TCP/IP application you have the option to choose User Datagram Protocol (UDP) or TCP sockets based on whether your application requires a reliable transport.

Frequently an application developer will choose UDP in a wireless environment for performance to reduce the high number of acknowledgements required by TCP, and subsequently rebuild logic to maintain reliability. A logical message with RFlink, on the other hand, already includes a relia ble mechanism and requires only a single confirmation packet. RFlink also has separate blocking and nonblocking calls, allowing the programmer to return control to the user rather than waiting for a response with a high latency.

We found tha t the API itself is relatively sim ple, consisting basically of open, close, send and receive. Nevertheless, these APIs are intended for developing mobile applications from the outset. They allow you to make the network layer appear transparent and obtain maximum performance from your application, but they do not directly support existing applications.

Standard APIs Most of the recent efforts in wireless middleware have been aimed at successfully enabling TCP/IP over wireless links. This is an attempt to support higher-level standard APIs. IBM's Advanced Radio communication on Tour (ARTour) fits into this category of middleware.

The primary techniques for accomplishing TCP/IP over wireless is through the use of protocol reduction, acknowledgement spoofing and data compression.

Switching wireless networks was as simple as exiting ARTour and selecting a different network icon. ARTour enables existing applications to run over the TCP/IP protocol, but as these latencies show, designing an application for wireless environments results in a better application.

IBM's approach to supporting standard APIs takes the low road--basically low-level device drivers and protocol modifications. The InstantRF Enter prise edition of Nettech's line, on the other hand, takes the high road by including Open Database Connectivity (ODBC) in the mix. Building on the core support layers, RFquery adds an ODBC server on the gateway and an ODBC driver on the client. Communication between the two is accomplished entirely with the RFlink transport protocol. This gives an ODBC application the benefit of improved performance while not stopping a query from returning large result sets.

Other API support packages are available. Ericcson's Ericsson Virtual Office (EVO), for example, supports both ODBC and Messaging API (MAPI).

Wireless Agents Web server agents for developing wireless applications recently have come into the picture and hold a tremendous amount of promise (see "Web Browsing: Choice of a Wireless Generation?," below right).