A Comparison between 40GBASE-SR4, LR4, CSR4, and CR4:

While choosing a QSFP+ optical transceiver, there is confusion for models of 40 Gigabit transceivers. Some models are significantly alike, just as 40GBASE-CSR4 and 40GBASE-SR4. How can we differentiate them? This article will distinguish the four most confusing 40 Gigabit QSFP+ modules and some constant complications.

A Description of 40GBASE-SR4:

We use 40GBASE-SR4 for a 40 Gigabit Ethernet network in short reach. Compliant to IEEE 802.3ba QSFP-40G-SR4 standard, QSFP+ SR4 fiber optics, with an MTP/MPO fiber optic ribbon connector, can transfer up to 100m above OM3 cable and 150m above OM4 wire apart.

The QSFP-40G-SR4 possesses independent receiver and transmitter sections with four equivalent fiber strands. When we use SR4 fiber optic in a 40 Gigabit link, we require all the eight fiber strands, and we also need the fiber optic cable with twelve fiber MPO/MTP connectors. Consequently, there are insignificant four fiber strands in every link.

A Description of 40GBASE-LR4:

Like 40GBASE-SR4, we also use 40GBASE-LR4 for 40 Gigabit Ethernet. Compliant to the IEEE 802.3ba QSFP-40G-LR4 standard, QSFP+ LR4 fiber optics, with an LC duplex connector can support long-range networks up to 10 kilometers over SMF. Utilizing the similar form factor as QSFP-40G-SR4, QSFP-40G-LR4 optical transceiver also provides four independent receive and transmit channels, with 10Gbps bandwidth for each one.

The 40G LR4 fiber optics need multiplex/de-multiplex fiber optic signals through Mux/De-mux inside to support four-channel signs over an SMF. You can point to the figure below for a complete working model of QSFP-40G-LR4.

A Description of 40GBASE-CSR4:

The base of 40GBASE-CSR4 is on the IEEE 802.3ba QSFP-40G-SR4 standard, and it is an extended form of 40GBASE-SR4 with a similar working concept. Moreover, each 10G lane of the QSFP-40G-CSR4 module is adaptable to the specifications of IEEE 10GBASE-SR. Having an MPO/MTP interface, 40GBASE-CSR4 supports an extensive 40 Gigabit transmission up to 300 meters over OM3 and 400 meters over OM4 apart.

A Description of 40GBASE-CR4:

40GBASE-CR4 is a copper cable, and it has terminated ends. It is dissimilar from the three 40 Gigabit modules mentioned in earlier parts. We recognize 40GBASE-CR4 as 40G QSFP+DAC; nevertheless, 40GBASE-LR4/SR4/CSR4 are fiber optic transceivers. QSFP-40G-CR4 can approach a transmission range up to 7m for passive direct attach cable and 10m for active direct attach cable types.

How to Choose between 40GBASE-SR4, LR4, CSR4, and CR4?

We have designed 40GBASE-LR4/SR4/CR4/CSR4 modules for 40 Gigabit Ethernet transmissions. You can confuse which module is best, and the answer will depend on the particular implementations and whether the optical transceivers performance can come up to your application. We have described the main dissimilarities between a QSFP+ cable and these three QSFP+ optical transceivers for your understanding.

Frequently Asked Questions Regarding 40GBASE-SR4/LR4:

Q: What are the differences between 40GBASE-SR4 and ISR4/EISR4?

ANS: 40GBASE-ISR is Huaweis brand name for the QSFP-40G-SR4 optical transceiver. The features of 40GBASE-EISR4 and 40GBASE-ISR4 are similar to 40GBASE-CSR4 and 40GBASE-SR4, respectively. Moreover, 40GBASE-EISR4, which also belongs to Huawei, signifies the QSFP-40G-CSR4 module.

Q: How can we distinguish 40GBASE-ER4 from 40GBASE-LR4?

ANS: Like QSFP-40G-LR4, we use 40GBASE-SR4 with an LC duplex connector for long-range transmission. Nevertheless, these two 40 Gigabit optical transceivers show dissimilarities in IEEE standard and transmission distance. Compliant with the IEEE 803.3bm QSFP-40G-ER4 standard, the connection distance of 40 GBASE-ER4 is up to 40 kilometers over the SMF cable.

Q: What are the differences between QSFP-40G-PLR4 and QSFP-40G-LR4?

ANS: We can also name QSFP-40G-PLR4 as QSFP-40G-LR4 PSM by a few IT peers in a simple way. The main differences between 40GBASE-PLR4 and 40GBASE-LR4 depend on their supported protocols and optical interface. The base of the 40GBASE-PLR4 module is on IEEE 802.3ae 10GBASE-LR4 standard, and it comes with an MPO/MTP connector. Nevertheless, the foundation of 40GBASE-LR4 is on IEEE 802.3ba 40GBASE-LR4 standard, and it comes with an LC duplex connector.

Q: What are the differences between 40GBASE-SR4 and AOC?

ANS: Just like the 40GABSE-SR4 optical transceiver, we use 40 Gigabit AOC for 40 Gigabit Ethernet implementations in a short distance. However, the difference is that the QSFP+ active optical cable is a pre-terminated fiber optic cable. The termination on one end is with 40GBASE QSFP+, and on the other end, the ending is with LC connector, SFP+ connector, etc. Usually, the connection range of 40G active optical cable is no farther than 100m.