CHAPTER 3: INSTALLATION DIRECT INPUT AND OUTPUT COMMUNICATIONSB90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-253Figure 3-22: Direct input and output single-channel connectionIRC modules with protocol C37.94 and G.703 are designed for back-to-back communication connections, so the ringconfiguration shown in the previous figure does not apply. To establish inter-relay communication in more than two URs,you need to have two channel IRC module and enable DIRECT I/O CHANNEL CROSSOVER function in all relays, as shown inthe next figure. This configuration can be expanded to 16 URs, and this configuration does not provide redundancy ringsince both channels are made into single ring by the channel crossover function. As per the figure Typical PinInterconnection between Two G.703 Interfaces later in this chapter, the clock is supplied typically by multiplexer (MUX) andall URs are in Loop Timing Mode. If there is no MUX, then UR1 and UR3 can be in Internal Timing Mode and UR2 and UR4can be in Loop Timing Mode. That is, connected channels must have opposite timing modes.Figure 3-23: Ring configuration for C37.94 module (concept also applies to G.703)The interconnection for dual-channel type 7 communications modules is shown as follows. Two-channel modules allow fora redundant ring configuration. That is, two rings can be created to provide an additional independent data path. Therequired connections are: UR1-Tx1 to UR2-Rx1, UR2-Tx1 to UR3-Rx1, UR3-Tx1 to UR4-Rx1, and UR4-Tx1 to UR1-Rx1 for thefirst ring; and UR1-Tx2 to UR4-Rx2, UR4-Tx2 to UR3-Rx2, UR3-Tx2 to UR2-Rx2, and UR2-Tx2 to UR1-Rx2 for the second ring.
