networkArm
The network arm goes out to the server specified in the network source, and retrieves all the networks, stations sites, and channels that server knows about that pass the subsetters contained in the arm. It then runs those successful items through the processors, all the while keeping the network status items abreast of the process. If a source is not given, it defaults to the FDSN Station web service at the IRIS DMC.
Example
<networkArm/>
Places this can be found
sod contains this directly