Break Out Cable with 40G CWDM Mux


Modern 40Gbps based Ethernet switches allow the configuration of each 40Gbps switch port to act as if it was not one port but four individual 10Gbps ports. A 40Gbps switch can therefore, provide an extremely high packaging density of (virtual) 10Gbps ports.

However, mechanically the 40Gbps port remains a single port which is typically in accordance to the QSFP+ MSA. Regardless if the port is configured as a 40Gbps or 4 pieces of 10Gbps port, the only usable transceivers will be either 40GBase-SR4, -CSR4, -LR4 or -ER4 versions.

At present, only the short reach multi-mode fiber version transceivers provide four duplex fiber connections and the long reach single-mode LR4 /ER4 QSFP+ transceivers feature one duplex fiber port.

Therefore the 40Gbps split into four 10Gbps streams cannot be realized for LR or ER optics by simply configuring the switch, but also the transceiver outputs must be physically broken down from one duplex fiber into four duplex fibers.

40Gbps LR4/ER4 Optics Break Out  

Table 1 40G QSFP+ Transceivers and break out options

Because of the overwhelming growth in data traffic, today the datacenters are migrating towards higher density 40Gbps Ethernet uplink connections. While the default mode of operation for a 40GbE switch is the native 40Gbps mode with its front panel ports configured accordingly, the 40GbE switch can also be operated in a 10GbE mode. In such a mode, the single switch port acts like four individual 10Gbps interfaces. The transceivers available for such are the 40GBase-SR4, -CSR4, -LR4 or ER4 as shown in Table 1.

The SR and CSR optics have multimode output with MTP connections which can be easily broken down to four duplex LC connectors with the widely available MTP to LC break out cables. However, the 40GBase-LR/ER4 QSFP supports 40Gbps transmissions over duplex fibers with four wavelengths. The duplex fibers are used for bi-directional transmission. Therefore splitting 40GBase-LR/ER4 QSFP to 4 individual duplex SMF fibers to route them to 4 separate 10Gig transceivers cannot be realized by simple optical rerouting. The transceiver outputs must be physically broken down from one duplex fiber into four duplex fibers such that each of the wavelengths is transmitted in four different fibers, ref. Figure 1.

With the aid of the COLOR Cube, CUBO boasts to be the first to solve such an issue. A COLOR Cube is simply a multiplexer/de-multiplexer which splits the four wavelengths in a single fiber to 10Gbps signal in four different fibers. Two break-out variants are possible in the form of a cable or a box as shown in the figure. The break-out cable solution has a single COLOR Cube with LC connectors while the box solution has eight COLOR Cubes fitted into a 19” unit with LC connectors.

These solutions are optimized according to the application and density of connections. Both of these solutions provide a cost-effective way to connect within racks and across adjacent racks when the native 40GbE is not needed but multiple CWDM 10GbE interfaces between two switches are desired.

Figure 1 Break Out Options
(a) Cable
(b) Box