Issue link: https://www.e-digitaleditions.com/i/1386104
July/August/September 2021 I 15 FIGURE 8: 400G switch-to-switch use case using 8-fiber multimode configuration (10/40/100/200/400G) with 400GBASE-SR4.2 BiDi. FIGURE 9: 400G to 4x100G breakout use case with 8-fiber singlemode channel breakout configuration using 400GBASE-DR4/XDR4. FIGURE 10: 200G to 8x25G breakout use case with 24-fiber singlemode channel configuration with 2x100-PSM4 transceiver. For a multimode example, Figure 8 shows an 8-fiber channel for 400GBASE-SR4.2 bi-directional (BiDi) technology. This configuration uses 24-fiber OM4 trunk cabling with conversion cassettes, ensuring 100% utilization of all the fibers. These break out into 8-fiber array cords to the transceivers on both ends. This has become a fairly common approach and is essentially the same channel configuration that many have been using for 400GBASE-SR4 and 100GBASE-SR4. BREAKOUT USE CASES While there are many scenarios for breaking out channels, the following are currently the most common examples. When breaking 400 Gb/s down to four 100 Gb/s channels using 400GBASE-DR4 or 400G-XDR4 over singlemode, the configuration shown in Figure 9 breaks out to duplex LCs to QSFP28 modules at the server. The breakout in Figure 10 is used for a 200 Gb/s network introduced by Cisco. The channel uses 2x100-PSM4 transceivers at the switch that requires a 24-fiber MPO connection. This example retains the 24-fiber MPO backbone trunk cable and breaks out to eight 25 Gb/s SFP28 transceivers over duplex LC patch cords. This is an attractive option to lower the cost of 25 Gb/s lanes. Cisco also introduced the same option for multimode using 2x100-SR4 transceivers, which also converts a 24-fiber channel into 8 duplex fiber channels. QSFP-DD/OSFP 400G 400G-DR4/XDR4 8F MPO Array Cord QSFP-DD/OSFP 400G MPO-MPO Cassette MPO-MPO Cassette MPO-MPO Cassette MPO-LC Cassette MPO-LC Cassette 8F MPO Array Cord 8F MPO Array Cord Base24 MPO Trunk Base24 MPO Trunk Base24 MPO Trunk LC-LC Patch Cords LC-LC Patch Cords QSFP28 100G-DR SFP28 25G-LR 2X100-PSM4 Requires MPO24 24 MPO Array Cord MPO pass-thru