Monthly Archives: April 2017

Can 40GBASE-LR4 Be Used for 4x10G?

We know that 40GBASE-SR4 QSFP+ transceiver can be used for 4x10G SFP+ connections, because it offers 4 independent transmit and receive channels, each capable of 10G operation for an aggregate data rate of 40G over 100 meters of OM3 MMF or 150 meters of OM4 MMF. However, for 40GBASE-LR4 QSFP+ transceiver, it is commonly utilized over long transmission distance of SMF in 40G network applications. Can 40GBASE-LR4 be used for 4x10G? The answer depends and this article will focus on this question.

40GBASE-LR4 CWDM QSFP+ Transceiver Cannot Be Used for 4x10G

The 40GBASE-LR4 CWDM QSFP+ transceiver, such as QSFP-40GE-LR4, is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. It contains a duplex LC connector for the optical interface. The maximum transmission distance of the transceiver is 10km over SMF. In the transmit side, the transceiver converts 4 inputs channels of 10G electrical data to 4 CWDM optical signals by a driven 4-wavelength distributed feedback (DFB) laser array, and then multiplexes them into a single channel for 40G optical transmission, propagating out of the transmitter module from the SMF. Reversely, the receiver side accepts the 40G CWDM optical signals input, and demultiplexes it into 4 individual 10G channels with different wavelengths. Each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA). Therefore, 40GBASE-LR4 CWDM QSFP+ transceiver cannot be used for 4x10G. It cannot be split into 4x10G, because it uses 4 wavelengths on a pair of single-mode fiber with LC duplex connector, and does not allow itself to split into 4 pairs without substantial complexity to split out the wavelengths.

Working Principle of 40GBASE-LR4 CWDM QSFP+ Transceiver

40GBASE-LR4 PSM QSFP+ Transceiver Can Be Used for 4x10G

The 40GBASE-LR4 PSM QSFP+ transceiver is a parallel single-mode optical transceiver with an MTP/MPO fiber ribbon connector. It also offers 4 independent transmit and receive channels, each capable of 10G operation for an aggregate data rate of 40G on 10km of single-mode fiber. The transmitter side accepts electrical input signals compatible with common mode logic (CML) levels. All input data signals are differential and internally terminated. The receiver side converts parallel optical input signals via a photo detector array into parallel electrical output signals. That’s to say, the parallel optical signals are transmitted parallelly through 8 single mode fibers. As a result, 40GBASE-LR4 PSM QSFP+ transceiver can be used for 4x10G, because it uses parallel (ribbon) fiber with MTP/MPO connector, which allows the creation of 4 fiber pairs.

Working Principle of 40GBASE-LR4 PSM QSFP+ Transceiver

Note: From an optical transceiver module structure viewpoint, PSM uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. Therefore, it allows for splitting into 4x10G (single-mode).

Conclusion

In a world, the answer of question “Can 40GBASE-LR4 be used for 4x10G?” depends. The 40GBASE-LR4 CWDM QSFP+ transceiver cannot be split into 4x10G, while for 40GBASE-LR4 PSM QSFP+ transceiver, it cab be used for 4x10G. To put it simply, 40G QSFP+ transceiver which is with MTP/MPO interface can be used for 4x10G connections, otherwise, it can only support 40G link. The 40G QSFP+ transceivers mentioned above can be found in FS.COM, if you want to know more details, please visit our site.

MTP Connectivity — Low-loss Multifiber Connectivity

It is not difficult to understand that MTP connectivity is widely applied in 40G and 100G network applications because it is a multifiber connectivity, which can meet the demand for high-density cabling. As a matter of fact, there is another key advantage of MTP connectivity, that is low-loss. With the length and type of the fiber cable, number of connectors and splices all contributing to the link loss, there is no doubt that insertion loss is inevitable during the cabling process. Therefore, cabling solution with low-loss will be preferred by data center managers, who are now regarding optical insertion loss budgets as one of the top concerns. But what contributes to low-loss in MTP connectivity? This post will show you the answer.

Low-loss Connector

Typical MPO/MTP fiber connector, which is used for 40 and 100 GbE deployments, has insertion loss values that range from 0.3 dB to 0.5 dB. In addition, MPO/MTP connector is structured with MT ferrule which has low insertion loss and can provide accurate fiber alignment. Take 12 fiber MPO connector and 24 fiber MPO connector for example, with low-loss ferrules, the insertion loss of both two type of connectors can be rated at 0.35 dB maximum. Reading this, you may ask shouldn’t the result be that higher fiber count will lead to higher insertion loss? The answer is no. Because when using proper polishing techniques, 24-fiber MPO/MTP terminations can meet the same performance levels as 12-fiber MPO/MTP assemblies.

Low-loss Cable

We know that OM3 and OM4 fibers used in MTP connectivity utilize 850 nm source, and IEEE 40GBASE-SR4 and 100GBASE-SR10 standards for 40 and 100 GbE over multimode fiber have more stringent loss requirements for these two types of fibers, which lowers the overall channel loss. As shown in the following table, as speeds have increased from 1 Gb/s to 40 and 100 Gb/s, maximum channel distance and loss has decreased significantly. For OM3 fiber cabling, the 40 and 100 GbE standards allows for a channel distance of 100 meters with a maximum channel loss of 1.9 dB, including a maximum connector loss of 1.5 dB; for OM4 fiber cabling, the distance is increased to 150 meters but with a maximum channel loss of 1.5 dB, including a maximum connector loss of 1.0 dB.

channel loss of OM3 and OM4 fibers

Note: Current TIA and ISO standards require a minimum of OM3 fiber, while TIA recommends the use of OM4 due to its longer transmission capabilities. In fact, the 100GBASE-SR4 standard that uses eight fibers (four for transmitting and four for receiving) at 25 Gb/s is anticipated to be supported by OM4 fiber to 100 meters, but to only 70 meters using OM3.

Conclusion

In today’s large virtualized server environments with high speed 40 and 100 gigabit Ethernet (GbE) backbone switch-to-switch deployments for networking and storage area networks (SANs), staying within the loss budget is essential for ensuring that optical data signals can be properly transmitted from one switch to another without high bit error rates and performance degradation. MTP connectivity, based on low-loss MPO/MTP connector, OM3 and OM4 fibers, is able to reduce the insertion loss to a minimum, which makes this low-loss multifiber connectivity take its place on the market. FS.COM provides high-quality MTP assemblies, such as MTP/MPO fanout cable, MTP MPO trunk cable, MTP cassette and so on. If you want to know more details, please visit our site.