The Message Switch is a Server-Resident Application (SRA) which runs in a Freeway server. It implements a switching function which transfers all data received by a set of client application sessions to one or more other sessions. The Message Switch software uses Simpact's Data Link Interface (DLI to open and manage Freeway client sessions to transmit and receive data.
The following is a quick overview of how to use the Message Switch software:
Customize the provided configuration files to define the required client sessions for your Freeway environment, and to load and run the Message Switch.
Boot the Freeway server. The Message Switch automatically configures itself, uses DLI to attach to one or more ICP ports, and begins transferring data. (ICP boards, or Intelligent Communications Processor boards, are the Protogate hardware product which implement various data communications protocols for sending and receiving data on a WAN link.)
To communicate through the Message Switch, a client application can open a socket and send and receive data using the Freeway's IP address. Example programs are provided for testing purposes.
The following types of data can be exchanged through the Message Switch:
Loopback
Multicast (on Freeway platforms that support Multicast)
Unicast
WAN
The Message Switch offers an extremely flexible range of data-switching capabilities, all of which are available simply by modifying configuration files. For example, it is possible to use the Message Switch to translate data streams between different protocols, or between similar protocols with different characteristics (see Section A.3). Data streams can be replicated to multiple destinations (see Section A.4). Data streams from several sources can be combined into one (or more) destinations (see Section A.5). And the sources or destinations of any of these data streams can be WAN lines or IP unicast or multicast addresses, in any combination.
In addition, a Freeway which is running the Message Switch can be used by traditional DLI client application programs, in either Raw or Normal operation, and using either Simpact's DLI library or a simple socket interface (see Section A.6).
The Message Switch can greatly simplify the writing of client application programs which do not use Simpact's DLI library. For example, the Message Switch relieves the client application of the need to send and receive all the packets which are normally required to attach, bind, configure, and enable each data link. This is possible because the Message Switch does all the work necessary to bring up a link using data from its own configuration files (such as swdcfg).
After the Freeway and Message Switch are running, the client application program can simply open a socket and start sending and receiving data. For an example, see Section A.8 and the remarkably short program freeway/client/test/switch/apinull.c.