As we know, there are a variety of QSFP transceivers that have the ability to support 40G Ethernet network with higher capacity and transmission data rate, such as: QSFP-40G-SR4, QSFP-40G-CSR4, QSFP-40G-LR4, QSFP-40G-PLR4, etc. In 40G long distance transmission, there is no doubt that OSFP+ transceivers with duplex LC interface like QSFP-40G-LR4 and QSFP-40G-PLR4 have a high performance. However, for 40G short distance transmission, both QSFP-40G-SR4 and QSFP-40G-CSR4 transceivers are designed complicatedly, requiring 12-fiber MTP/MPO connectors and 12 fibers, which are extremely different from the traditional 10G transceivers. Hence, the cabling infrastructure for the migration from 10G to 40G Ethernet network in short transmission should be changed greatly, which may cost a lot.
Taking the cost into consideration, experts come up with the BiDi technology and design QSFP bi-directional transceiver for 40G short transmission. By using QSFP BiDi technology, 40G Ethernet network can be deployed with the same infrastructure as 10G Ethernet network, thereby a cost saving will be made.
40G QSFP BiDi transceiver can be also called 40G QSFP bi-directional transceiver, firstly published by Cisco. It is able to transmit 40G signals over duplex multimode fiber optic cables with LC connectors, instead of multi-fibers with MTP/MPO connectors in the traditional 40G QSFP parallel transceiver, which addresses the challenges of cabling infrastructure. In general, there are a pair of duplex MMF cables with duplex LC connectors in one 40G QSFP BiDi transceiver. Each cable offers a 20G channel to transmit and receive 20G signals simultaneously with different wavelengths, achieving a complete 40G data transmission. For better understanding, here offers its working principle in the following figure.
When designing 40G Ethernet network with BiDi technology within a given row of cabinets, a Type A-to-B standard LC duplex patch cord is suggested to directly connect two 40G BiDi transceivers. As shown in the following figure, the Type A-to-B standard LC duplex patch cord consists of a blue fiber linked with connector position A on one side and connector position B on the opposite side, and an orange fiber linked in the same way, defined in TIA-568-C.3. This reverse fiber positioning allows a signal to be directed from the transmit position on one end of the network to the receive position on the other end of the network.
How can an interconnect cabling be deployed for 40G BiDi transceiver? As shown in the following figure, we can learn an example of an interconnect link between two bidirectional ports installed in a switch, which includes an MTP-based trunk, MTP-LC cassette modules and LC jumpers. In this interconnect link, both of the LC jumpers connect from the structured cabling patch panel to the electronics ports.
There are a lot of advantages by using interconnect cabling for 40G QSFP BiDi transceiver. Firstly, MMF MTP assembly in this interconnect cabling would provide more scalability to accommodate future data rates. Secondly, if you want to do a migration for your network in future, it can be done simply by changing the patch panels on each end of the link, instead of disrupting the cabling infrastructure. What should be pay attention to is that deployment of more permanent links should be taken into consideration when structured cabling is being designing.
Other than interconnect cabling, there are two independent structured cabling links that connect two switches in a centralized cross-connect cabling. Here offers an example of the cross-connect cabling approach for 40G BiDi transceiver in the following figure for your reference.
This cross-connect cabling is featured with the most flexible network configuration. That is to say, the electronic devices can be installed in various locations throughout the data center, with structured cabling links between the cross-connect location and designated zone cabinets. If you want to install a new equipment in the link, you just need patch cords to make the connection from the equipment to the patch panels.
When making the migration from 10G to 40G Ethernet network in short distance transmission, 40G QSFP BiDi transceiver would be the first choice that requires no changes in the cabling infrastructure. Hence, the cost and required time to deploy 40G Ethernet network could be reduced dramatically. There is no doubt that 40G QSFP BiDi transceiver will eventually displace the traditional 40G QSFP transceiver in a fast and cost-efficient manner.
Fiber Optic Communication 