What’s the Difference Between 40GBASE-SR4 vs. 40GBASE-SR BiDi

With the development of data centers, 10G Ethernet has gradually been unable to meet the needs of data transmission, and a large part of data centers are trying to shift to 10Gbps at the access layer and 40Gbps at the aggregation layer. And to convert your existing infrastructure to 40G, you’ll probably need 40GBASE-SR4 and 40GBASE-SR BiDi. This article will compare the 40GBASE-SR4 cabling solution and 40GBASE-SR BiDi cabling solution in detail, and provide you with some suggestions for building a data center by comparing these two solutions

What is a 40GBASE-SR4 QSFP+ Transceiver?

40GBASE-SR4 QSFP+ optical module, generally used for short-distance data transmission, where SR stands for short-reach, this optical module uses QSFP appearance, it is designed to use independent transmitter and receiver, each receiver has four independent parallel fibers. The maximum transmission distance of 40GBASE-SR4 is 150m over OM4. In the 40G network transmission connection, the optical link needs to use 8 optical fibers strands and should be equipped with a 12-core MPO connector.

The vast majority of data centers use a 10G connection in the fiber infrastructure at the aggregation layer, which results in the direct connection of LC to LC MMF between devices is allowed. In another case, LC to LC fiber can connect devices connect to patch panels. The typical duplex LC optical fiber cannot be directly used for 40G connection by 40G switch.

What is a 40GBASE-SR BiDi QSFP+ Transceiver?

QSFP BiDi optical modules are first designed by cisco, 40G QSFP SR-BD is designed with LC connector, it can transmit full-duplex 40G traffic over one duplex MMF cable. This module solves the trouble of replacing optical fiber infrastructure in many data centers. QSFP BiDi only needs a bunch of MMF cables to build a 40G connection. This optical module is backward compatible with the same infrastructure as 10GBASE-SR. IT technicians can complete the upgrade to 40G Ethernet Connection without adding other fibers.

QSFP BiDi is also a transceiver used for short-distance optical data transmission, it transmits 40Gbps Ethernet over duplex OM3 or OM4 MMF cable. Its maximum transmission distance is 100m via OM3, 150m via OM4. There are two independent optical modules inside the transmission channel, the rate of each transmission channel is 20Gbps, and the aggregation is 40Gbps data rate. The following figure shows the working principle of QSFP BiDi.

Different Cabling System Between 40GBASE-SR4 vs 40GBASE-SR BiDi

The data center will use the structured cabling system to build the network, which can provide sufficient flexibility and scalability to the cabling infrastructure system. Structured cabling can connect the switch to a patch panel, and also connect the device to another patch panel for remote equipment, which needs to be routed through cables. The following sections of the article will introduce two different connections solution.

40G Cabling System with QSFP SR4 Transceivers

In this solution, we need the following equipment: 12 Fibers 10G OM4 Multimode 12 Strands MTP Female 0.35dB Trunk Cable, 12 Fibers 10G OM4 Multimode 12 Strands MTP Male 0.35dB Trunk Cable, 48 Ports 1U Rackmount Fiber Enclosure, loaded with 4 FAPs 12x MTP Key-up/Key-down.

Figure 2: QSFP SR4 Transceivers Connection

40G Cabling System with QSFP SR BiDi Transceivers

In this solution, we need the following equipment: 5M LC UPC to LC UPC Duplex 2.0mm PVC(OFNR) 10G OM4 Fiber Optic Patch Cable, 12 Fibers 10G OM4 LC Duplex 12 Strands MTP Male 0.35dB Standard LGX Cassette, 24 Fibers 10G OM4 12 Strands MTP Trunk Cable 3.0mm LSZH/Rise.

Figure 3: QSFP SR-BiDi Transceivers Connection


Through the introduction of this article, the difference between QSFP+ 40G SR4 and QSFP+ 40G BiDi is described. At the same time, we mentioned how to build these two different 40G Ethernet connections. If you need to upgrade your data center network to a 40G Ethernet network, please contact QSFPTEK, which is a company specializing in the production of high-quality, cost-effective optical fiber products, providing you with a series of products including optical modules like QSFP+ 40G SR4 and QSFP+ 40G BiDi. If you need a detailed quotation, please contact QSFPTEK customer service via sales@qsfptek.com.

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