Guralp Systems CD1.1 - Manual (Page 17)

Operator's Guide
A CD1.1 sender module can only transmit to a single Data
Consumer (DC). If there is a requirement to support multiple
DCs, multiple sender module instances are needed. Each can
send a different set of subframes, if required.
Because the multiplexer supports multiple senders, it is more
efficient for the multiplexer to store transmitted frames, rather
than the sender. This avoids having to store the same frame
multiple times. However, because the frame numbering of
outgoing frames is connection specific, the multiplexer cannot
know these numbers and it stores frames by time-stamp,
rather than by frame number. The sender keeps track of which
frame is which by storing a database of frame numbers against
timestamps. This database is consulted when the sender
receives an acknack frame, so that it can request the correct
frame from the multiplexer by time-stamp.
It also handles back-fill over extended periods of outage by
recording which times the system was down, and requesting
the data once the link is established again. Back-fill order is
configurable: it can either be “first-in, first-out” (FIFO) or “last-
in, first-out” (LIFO).
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