Optelecom 9522A Installation And Operation Manual page 17

Local Daisy Chain (LDC) Mode
In this mode, there is a specific "upstream" and "downstream" data direction, because data is only transmitted
to or from the master rather than in both directions as on a ring. Specifically, the TX1/RX1 port communicates
upstream with the master controller and the TX2/RX2 port communicates downstream with the next modem
on the daisy chain. The local daisy chain mode is not fault tolerant. A break in the chain will cut off the
modems farther downstream from the break. Optical data received from the master via TX1/RX1 is retimed,
retransmitted downstream via the TX2/RX2 port, and output from the Primary data port (RD) and from the
Secondary data port (TDE). Optical anti-streaming on the TX1/RX1 port is disabled because it would serve no
purpose. Optical data received from the next modem downstream via the TX2/RX2 port is retimed and
retransmitted upstream to the master controller via the TX1/RX1 port. Data input to the Primary data port (TD)
and data input from the Secondary data port (TDE) are ORed with the data from the TX2/RX2 port to be
transmitted back to the master via the TX1/RX1 port. Anti-streaming is an option on the TX2/RX2 port in this
mode.
Master Fault Tolerant (MFT) Mode
In this mode the Primary data port is configured as a Master port and the Secondary port is configured as a
Local port. Data input to the Primary data port (TD) is transmitted out via the optical ports and output from
the Secondary data port (RD). Data input to the Secondary data port (TDE) will be output from the Primary
port (RD), but will not enter the optical network. Conversely, an optical input via the TX2/RX2 optical port or
data input via the Secondary port (TDE) will be output via the Primary port (RD). In this mode, since optical
signals will normally arrive via both optical ports skewed slightly by time of arrival, the Priority Select circuitry
is employed to choose only the first arriving data. In this mode neither Optical nor Electrical side anti-
streaming may be employed. Also, the automatic ring break detection circuit is enabled when operating in this
mode.
Local Fault Tolerant (LFT) Mode
This mode is used for all the local modems serving the many terminals around a fault tolerant dual fiber
counter-rotating ring and for modems in the trunks between dual masters. In this mode optical data received
via both optical ports is selected based on the earliest arrival (see Priority Select section), and routed to the
RD output of the Primary data port and the RDE output of the Secondary data port. Optical data received via
TX1/RX1 is retimed and retransmitted via TX2/RX2. Optical data received via TX2/RX2 is retimed and
retransmitted via TX1/RX1. Data input via either the Primary data port (TD) or the Secondary data port (TDE)
is ORed and transmitted via both the TX1/RX1 and TX2/RX2 optical ports.
17