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How to Access WAN Protocol Data from an IP Network

There are many ways to access WAN protocol data from an IP network. Each method has its advantages and disadvantages. These advantages and disadvantages generally reflect a tradeoff between simplicity and capability, with some methods being simpler to implement and other methods providing increased capabilities.

The following list describes some of the methods of accessing WAN data from an IP network, listed in order from the simplest to the most complex. For the purpose of these descriptions, the term "server" refers to a Freeway system (or to the machine to which the WAN protocol data lines are attached) and the term "client" refers to another machine which requires access to the WAN data (the client could also be a program running directly within a Freeway, but would still connect to the Freeway server daemon with a socket interface). The "Message Switch" is an optional software component which runs in the Freeway.

 
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  1. Freeway, Off-the-Shelf Protocol, and Message Switch configured for data only

    A Freeway can be configured to use the Message Switch software to automatically configure protocol lines statically, with pre-canned specifications, and then to transfer data between TCP/IP or UDP/IP datastreams and the WAN protocol lines. For example, if you have bisynchronous protocol WAN lines running at 9600 bits/second, and all you need to do is to send and receive data to/from those WAN lines, then the Freeway/Message Switch could be configured to receive the data from those WAN lines and send it to your IP network as TCP or UDP packets, destined to a specific IP port and address (or if UDP, to the broadcast address). It could also receive TCP or UDP packets from or to various IP ports, and send those packets to specified WAN lines.

    This is the simplest method to implement in the client. Depending on the destination or source of data required by the client, this method requires either no programming whatsoever, or minimal socket-level programming (to create a program to send and receive the IP data streams). For comparison with the other methods, a socket-level program to send and receive IP data (and therefore WAN data) might take only 50 to 100 lines of C code.

  2. Freeway, Off-the-Shelf Protocol, and Message Switch configured for control information and data

    The Message Switch can also be configured to pass control information as a 32-byte header at the beginning of each data packet on the IP network. This allows simple socket-level client application programs to be written which can send commands to, and retrieve status information from, the WAN protocol lines. An example of this would be a client which wants to start or stop a WAN link; the previously-described "data only" client could not start or stop a WAN link (because that type of client can only send or receive WAN data), but a "control information and data" client can start or stop a WAN link, or even change the WAN parameters.

    Implementing this method is slightly more complex than the previous (data-only) method. For example, a socket-level program to send and receive IP data and WAN control information might take approximately 150 lines of C code.

  3. Freeway, Off-the-Shelf Protocol (no Message Switch); Normal-Mode Protocol

    A Freeway can be configured without the Message Switch to simply download the protocol code into the ICP board(s), but not to configure any of the protocol parameters (datarate, electrical interface, etc.); that job is left for the client application program to perform.

    This method requires that a program be written on the client machine to connect to the Freeway and send commands to configure the WAN protocol lines (to set the datarate, etc.). For many of Protogate's off-the-shelf protocols, Protogate provides source code for a DLI/TSI library, which can be linked with your client program to aid in making the connection to the Freeway and in configuring the protocol(s). That DLI/TSI code contains instructions which are specifically-designed to aid in writing client programs for certain protocols. The protocols which are supported by the DLI/TSI library are called "Normal-Mode" protocols, and those which are unsupported are called "Raw-Mode" protocols. This method assumes that a Normal-Mode protocol is used and the client program is written to take advantage of the full DLI/TSI capabilities.

    Implementation of this method is moderately complex, because of the client application program that must be written. This client program must not only connect to the Freeway via the LAN, but must also send commands to configure the Freeway and the protocol, and handle all of the various packet types which the Freeway might send to it. Because in the Normal-Mode much of this code is in the DLI/TSI library, a typical Normal-Mode client application program might take approximately 2000 lines of C code. Configuration of the WAN links is performed by code inside the DLI/TSI library based on an easy-to-edit ASCII DLI configuration file, which can be changed without any need to also change the client program.

  4. Freeway, Off-the-Shelf Protocol (no Message Switch); Raw-Mode Protocol

    This is similar to the previous method, but the client application program accesses the Freeway and protocol in Raw-Mode, either by choice or because the DLI/TSI does not support Normal-Mode for the protocol in use.

    Implementation of this method is even more complex than the previous (Normal-Mode) method, because of the additional work that the client application program must perform. This client program must not only connect to the Freeway via the LAN, but must also send commands to configure the Freeway and the protocol, and handle all of the various packet types which the Freeway might send to it. Because in Raw-Mode the DLI/TSI provides less help in performing these tasks (and therefore the client program must itself include code to accomplish these tasks), a typical Raw-Mode client application program might take approximately 3000 lines of C code.

  5. Embedded ICP board, Off-the-Shelf Protocol; Raw-Mode Protocol

    Inside all Freeway systems which handle WAN links are one or more ICP boards. Each ICP board contains several serial WAN ports -- but it also contains a CPU and RAM; and the Freeway downloads a file into each ICP board which contains instructions for that ICP's CPU to execute to implement the lowest levels of the protocol (the bit level and the character level). A separate CPU in the Freeway implements the higher levels of the WAN protocol (at the block-of-characters level) and drives the LAN (IP network).

    It is possible to purchase individual ICP boards and protocols, and install them into your own computer running NT, Solaris, or VMS. You must then install an ICP-board driver into your operating system, and write an application program which uses driver-level calls to download the protocol to the ICP board and then to read and write control information and data from and to the WAN links on the ICP board. For some operating systems Protogate offers a "DLITE" library which provides a bit of help, but the DLITE library does not contain nearly as much functionality as the true DLI/TSI library (but the DLI/TSI library only supports interfacing to a Freeway).

    Implementation of the embedded board method is even more complex than the "Freeway, Raw-Mode protocol" method, because of the driver-level interface, because the client application must download the protocol code to the ICP board, and because of the lack of Normal-Mode DLI features in the DLITE library.

  6. Freeway or Embedded ICP board, Custom Protocol

    For the greatest level of control (at the greatest cost in difficulty of implementation), any of the previously-described Freeway or embedded WAN-access methods can also be configured to use a custom protocol, which might be custom-written either by Protogate (to your specifications) or by yourself.

    This requires not only that a client program be written (as in the "Freeway, Off-the-Shelf Protocol" method above) but also that the custom protocol code be developed (written, cross-compiled, tested, and debugged) to run on the ICP board.

    Developing a custom protocol requires a great deal of work (it generally takes several engineer-weeks to develop even the simplest protocol code), but allows the most possible flexibility. Writing the protocol code yourself means that you have control even down to the bit level on your WAN protocol lines. If you need this level of customization and want to write your own protocol, Protogate offers the sourcecode for a representative protocol as part of a "protocol toolkit", to help get you started.


The previous list includes most of the WAN access methods, but if none of those methods satisfy your needs completely, there are two more possibilities: use of a Server Resident Application (SRA) and use of Message Switch "Programmable Endpoints". An SRA can be used with any of the Freeway methods described above. Programmable Endpoints can be used with either of the Message Switch methods described above.

SRA

The Freeway system is programmable and includes a full set of native development tools. You can use those tools to develop an application program which runs on the Freeway itself. If that application program is written to use sockets or the DLI/TSI library to connect to a Freeway daemon (running either in the same Freeway, or another Freeway connected via an IP network), then we call it an SRA (Server Resident Application).

An SRA can utilize all the features of the Freeway, just as any client application can, but because it runs in the Freeway it can perform extra work before the data leaves the Freeway; it can thus make the Freeway into a self-contained data processing system, rather than simply a data-transferring system. For example, an SRA could be written to capture data from several WAN lines and output a report (to the console, to a socket, or any to other output device) when those datastreams differ.

SRAs can be as simple or as complex to write as any other Freeway client application. They can be written to use the socket-level Message Switch interface or the DLI/TSI interface, in either Normal-Mode or Raw-Mode. In fact, all of the client application programs described in the first 4 methods above can run directly on a Freeway as an SRA: the socket-level program to send and receive IP data, the socket-level program to send and receive IP data and WAN control information, the Normal-Mode client program, and the Raw-Mode client program will all run on a Freeway.

Message Switch Programmable Endpoints

The Message Switch software which runs on the Freeway can be configured to transfer data from a set of inputs to one or more sets of outputs. From the Message Switch's point of view, these inputs and outputs are simply "endpoints"; the Message Switch takes data from each endpoint and sends it to one or more other endpoints. These endpoints can be WAN links, UDP or TCP sockets, or other devices (hard disks files, etc.). Another type of endpoint supported by the Message Switch is called "Programmable Endpoints".

Programmable Endpoints are separate programs, running on the Freeway, which have their Standard Input and Standard Output connected to the Message Switch. When the Message Switch is configured to use a Programmable Endpoint, it forks a separate process running the Programmable Endpoint program, with data pipes set up to connect that process to the Message Switch. Whenever the Message Switch sends data to that endpoint, the Programmable Endpoint process will receive it on stdin, and whenever the Programmable Endpoint process sends data to stdout, the Message Switch will be able to read it from that endpoint.

Because the Programmable-Endpoint program is a simple stdin-stdout program, it can be easy to create, but because it has access to all of the features of the Freeway it can have great power. For example, a program to compress WAN-link data can be written in about 250 lines of C code, and another program to send WAN-link data to an FTP server can be written in even fewer lines.

The last program described above is a good example of the power and flexibility of the Freeway when running the Message Switch with Programmable Endpoints. When configured this way, the Freeway will take all of the data on all desired WAN links and write it into a set of files on an FTP server; and it will begin doing so automatically, as soon as it is powered up, with no intervention necessary by any person or other machine.


Our Recommendations

We recommend that you use the simplest method which still provides all the capabilities you need. In general, use of a Freeway is much simpler than use of embedded ICP boards, and requires less effort on the client's part. See our list describing the advantages of using Freeway versus embedded boards.

When choosing a WAN-access method, it is also important to remember that most of the methods described above can be used in combination with each other. Use of one method does not preclude the simultaneous use of other methods. For example, a single Freeway with several WAN lines could be running the Message Switch and also several different SRAs, and could be accessed simultaneously by different client programs, some socket-level (data-only and data-and-control) and some DLI/TSI (Normal-Mode and Raw-Mode).


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