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For the NetDC system to function properly, data centers have to be able to exchange state information and request data between each other in an automated fashion. This can be achieved by establishing a protocol of formatted text that NetDC programs on either end of a connection can read and act on.

This protocol should allow for a message to identify itself as a formatted action item, indicate what data type the message relates to, and specify what kind of action or signal is to be acted on relating to that data type. In addition, it should have the capacity to encapsulate text data should larger volumes of information need to be interchanged.

This requirement is satisfied in the form of NetDC datagrams. This is a simple email message format that NetDC can read and act on to perform a variety of tasks. Sometimes the message triggers an action and sometimes data is exchanged. Datagrams are meant to be strictly software generated. User interfacing through datagrams may be performed under special circumstances but care must be taken to avoid errors when doing so.

A datagram first identifies itself through the subject line of the email message:

Subject: NETDC DATAGRAM

Following this, the body of the message will start with an action tag which triggers what is requested of the NetDC system. The template for the action tag is:

%%ACTION <CLASS>::<METHOD>

where <CLASS> indicates the type of data the message refers to and <METHOD> relates the action or trigger to be acted on that type of data. The CLASS will take the form names such as DATA, INV, or RESP. The METHOD names take on directives such as RCVOK, LOCALDONE, and RESEND.

Below is a sample datagram that is sent locally to notify the NetDC system that local processing of a DATA request is completed:

Subject: NETDC DATAGRAM

%%ACTION DATA::LOCALDONE
.HUB_ID NCEDC:Feb_25,22:07:30:17501
.NAME Bill_Mantle
.EMAIL bmantle@upthrust.seismolab.edu
.LABEL Sample_01
.DISPOSITION_USER
.DISPOSITION_HUB
.FILENAME /usr/local/processing/netdc/local_data.Feb_25.001
.END

What follows the ACTION title is a list of parameters that relates to the CLASS and METHOD of the message. For a given CLASS and METHOD, the receiving site will expect to see certain parameters in order to have enough information to carry out the desired action effectively. As you can see, the above example is telling NetDC that a particular user, Bill Mantle, has a file waiting for pickup called "local_data.Feb_25.001" in a local directory for the request identified by the HUB_ID. NetDC will grab the listed file and place it in Bill Mantle's request directory, followed by marking off the data as COMPLETE in the request checklist file. This is merely one example of datagram functionality in NetDC. Others datagrams will be illustrated throughout this manual.

For a complete specification of currently implemented datagrams, please consult Appendix A.

introduction •• overall concept •• request format •• request reception and delegation
datagrams •• local request processing •• inventory requests •• response requests
waveform requests •• product shipment •• installation and setup •• writing interface code
troubleshooting •• future implementations •• conclusion •• appendix A - summary of NetDC datagrams

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