Guralp Systems CMG-DM24 - Manual (Page 109)

Operator's guide
A client should continue issuing GCFSEND packets periodically while
it still wants to be sent data. If a client does not issue a GCFSEND
packet for a long period, the server will stop sending data to it.
If the server has active clients when it shuts down, it sends a packet
containing the string GCFNOSV to all of the clients.
Data packets
Once the client has sent a GCFSEND packet, the server will start
sending it GCF blocks, each in a single UDP packet. There are two
formats used, “Version 31” and “Version 40”.
Version 31 data packets
1024 octets – The GCF block as described above.
1 octet – The version number (decimal 31)
1 octet – The length of the following string, in octets
32 octets – A string describing the source of the data, padded to length
32 with zeros. The string takes the form STREAM-
ID/COMxx/HOSTNAME where COMxx is the name of the serial port
(COM1, etc.) and STREAM-ID is as in the GCF block (see above)
2 octets – The sequence number, in the byte order specified below
(same as for data)
1 octet – A code for the byte order, 1 = big-endian (default), 2 = little-
endian
Version 40 data packets
1024 octets – The GCF block.
1 octet – The version number (decimal 40)
1 octet – A code for the byte order, as above
2 octets – The sequence number, in the byte order specified
1 octet – The length of the following string, in octets
48 octets – A string describing the data source, as above but padded to
length 48 with zeros.
October 2009 109