The Extended Service Daemon (ESD) Protocol:

Communication between IGUANA modules is implemented with specific protocols, which were designed for the IGUANA gateway. One of these protocols is the ``ESD protocol'', which is dedicated to the communication between an Internet front-end and the ESD⁹².

The protocol is textual-based and stream-oriented, similar to the ``Simple Mail Transfer Protocol'' (SMTP) and consists of single line commands and according response messages, which may be basic (single line) and extended (multiple lines). Such a command/response sequence is shown in Listing 27 with the request in the first line and the response in the second.

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The addressing of a datapoint corresponds to the hierarchical addressing schema denoted above and is formatted as depicted in figure 42. An example address can be seen in listing 27.

Figure 42: Address Format in the ESD Protocol

The following commands are available in the ESD protocol:

READ:

This command retrieves the value of a datapoint in a requested encoding style. An example is given in Listing 28.

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WRITE:

The WRITE command writes a value to a datapoint in a specified encoding style. An example is given in Listing 29.

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DPINFO:

This command retrieves the properties of a datapoint. An example can be seen in Listing 27.

NODEINFO/ENODEINFO:

The Nodeinfo and Extended Nodeinfo commands can be used to retrieve the properties of a given fieldbus node.

Retrieving/Updating the Nodelist:

These commands can be used to retrieve a list of nodes that are connected to a fieldbus. Moreover, they can be used to update the list if nodes are disconnected or new nodes are connected to the fieldbus.

Commands regarding the event processor:

These commands can be used to create, delete or list events stored in the ESD.

Commands related to logging:

The logging commands are used to retrieve or clear logs associated to certain events.

Detailed information about the ESD protocol can be found in [LOB02].