Guralp Systems CD1.1 - Manual (Page 9)

Operator's Guide
The multiplexor is responsible for responding to retransmission
requests arriving from external receivers via a data-out-cd11
instance. The subframe store is used to satisfy these requests.
An interactive logging tool is provided to allow the operator to
query and inspect the contents of the store.
One storage file is created per day. To limit the amount of
back-fill being stored, a directory cleaner task must be set up
to remove unwanted storage files.
2.1.1 Frame assembly time-outs
Two separate time-out parameters are used to control the
assembly of related subframes into frames: one for real-time
data and one for back-filled data.
In complex networks, data may arrive from a number of CD1.1
data producers (DPs) along diverse routes, each with different
transmission latencies. DPs may be added and removed at any
time and communications may be interrupted for short or long
periods. A dropped link or a decommissioned station should
not interrupt the flow of data from other stations. Because of
this, the frame assembly algorithm does not and, indeed,
cannot know how many subframes it should expect for any
given time-stamp. It is therefore necessary to use time-outs
when assembling subframes into frames.
As an example, let us consider a hypothetical array with three
remote sensor stations functioning as CD1.1 DPs, all of which
use ten-second subframes, and a central data consolidation
station. The transmission times of the three links to the central
station are, say, one, two and three seconds. The real-time
data time-out at the central station will be set to three seconds.
At some time, T
0
, each station begins assembling samples into
subframes and, at around T
0
+ 10 seconds, they all transmit
their completed subframes to the station. Each subframe is
labelled with the time-stamp of its first sample: T
0
.
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