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2.1.3
Fault Tolerant Redundant Ring
With the architecture of Figure 4, all modems are arranged along a dual fiber ring, starting with the
master controller modem (operating in Master Fault Tolerant mode), looping through an indeterminate
number of local terminal modems (operating in Local Fault Tolerant mode), and terminating back into
the second set of optical ports of the master controller modem, completing the ring.
In this architecture the master modem transmits data in both directions around the ring and receives
its own signal. The ring is terminated at the master modem. In other words, the data is not repeated
by the master modem, but ends there instead.
Each local modem in the ring transmits its input data in both directions, receives from both directions,
and re-times and retransmits the data received by the optical receivers in both directions. Each local
modem, receiving data from the master from both directions around the ring, will select the data that
arrives first and output that signal on the RS232 port (RD). If the transmission is interrupted in that
direction, the modem will automatically select the data from the other direction. The master modem
also receives data from both directions from each of the local modems, and selects the first arriving
data in the same manner.
Using the expansion port on any of the local modems, the network can be branched outin anydirection
using a non-fault tolerant daisy chain. Unlimited daisy chain branches may be connected to the fault
tolerant ring.
2.2 Modes of Operation
To set up a modem into one of its four operating modes, the user selects one of four combinations for
switch sections 1 and 2 of the MODE dipswitch.
These four modes are characterized by the specific signal routing within the modem and the availability
of the various operational features such as the expansion port, anti-streaming and fiber activity CTS
inhibit. Figures 4 show the signal routing within the modem and the available operational features for
each of these four modes. The following sections include a detailed description of each mode and
Figure 4.
2.2.1
Master Daisy Chain Mode In this mode a TD input to the data port is transmitted out via the TX2/RX2
optical port and out the expansion port as RD in RS232 format. With the INDICATORS
mode switch in the up position, a TD input will cause the TX1, TX2 and RD indicators to illuminate.
Conversely, an optical input via the TX2/RX2 optical port or an RS232 level input via the expansion port
will be output via the DB25 port as RD.
In this mode, priority select is notused. This mode is normallyused in a network withnumerousmodems
in local daisy chain mode, where the master can actat the head of two separate daisy chains (ormore,
if the expansion port is used).
Summary of Contents for 9525AY
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Page 8: ...8 FIGURE 1 9525AY DIMENSIONS ...
Page 10: ...10 FIGURE 3 MULTIPLE DAISY CHAIN TRUNKS WITH ONE MASTER CONTROLLER ...
Page 12: ...12 FIGURE 4 FAULT TOLERANT RING WITH DAISY CHAIN BRANCHES ...
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