Optelecom 9525A, Installation And Operation Manual

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2.2.2 Local Daisy Chain Mode
In this mode, there is a specific "upstream" and "downstream" data direction. Specifically, the TX1 and
RX1 ports communicate upstream with the master controller and the TX2 and RX2 ports communicate
downstream with the next modem on the daisy chain. The local daisy chain mode is not fault tolerant.
Optical data received from the master via RX1 is re-timed, retransmitted downstream via the TX2 port
and output as RD on the data port. Anti-streaming on the RX1 port is disabled because it would serve
no purpose. Optical data received from the next modem downstream via the RX2 port is re-timed and
retransmitted upstream to the master controller via the TX1 port. Data received via the expansion port
input TDE from a modem feeding a branch, and from the TD input of the data port are ORed with the
data from the RX2 port to be transmitted back to the master via the TX1 port.
Antistreaming is an option on the RX2 port in this mode when operating in RS232 data mode.
2.2.3 Master Fault Tolerant Mode
This mode is virtually the same as the master daisy chain mode explained in Section 2.2 with these
exceptions: Because this is a fault tolerant mode, data will normally be received via both optical ports,
skewed slightly in time of arrival. Therefore, in this mode the priority select circuitry is employed to
choose only the data that arrives first. Secondly, the expansion port is not available in this mode.
2.2.4 Local Fault Tolerant Mode
This mode is used for all the local modems serving the many terminals around a fault tolerant dual
fiber counter-rotating ring. In this mode optical data received via both optical ports is selected based
on the earliest arrival (see Priority Select, Section 2.1.4), and routed to the RD output of the data port
and the RD output of the expansion port.
Optical data received via RX1 is retransmitted via TX2. Optical data received via RX2 is retransmitted
via TX1. These functions serve to regenerate and repeat data traveling both directions on the dual
optical ring. Data input via either TD on the RS232 port or TDE on the expansion port is ORed and
transmitted in both directions on the dual fiber ring.
2.3 Operational Features and Considerations
In addition to the signal routing that characterize each mode of operation (Section 2.2) the following
features of operation are incorporated as either basic indispensable functions or as performance
enhancements.
2.3.1 Electrical Side (Data Input) Anti-Streaming (RS232 mode only)
The electrical side anti-streaming feature, when enabled, limits the time that a terminal unit may
transmit data with a single request-to-send (RTS) enable. This feature is designed to prevent a
terminal unit from monopolizing the network if a terminal unit fails in a mode causing continuous
transmission. When the RTS input is set high (TRUE), the RS232 side anti-streaming counter is armed.
When data transmission begins, the timer begins, allowing the terminal to transmit data for a period of
time up to the time-out limit. When the terminal unit stops transmitting it must immediately set the
RTS low, (FALSE), resetting the timer. If the terminal continues to transmit data to the modem past
the timeout period, transmission from the modem will cease, the CTS will go Low, the FAULT indicator
will illuminate, and the alarm dry contact relay will activate.