Common and Distinct Features of 100G LR4, CWDM4 and PSM4

Date 12/03/2021

100G CWDM4 vs 100G LR4 vs 100G PSM4, What are their common and distinct features? This post will tell from every aspect of their working principle, specification, technology, optical component, cable solution, cost, etc.

100G optical modules are popular in data centers with the rapid development of optical communications, such as the 5G network. There are many types of 100G transceivers, 100G QSFP28 SR4, LR4, CWDM4, PSM4, ER4, etc. Among them, 100G QSFP28 CWDM4, LR4, and PSM4 are three major products for medium-and-long range transmission for 100G high-speed interconnection. All of them are single-mode transceiver types. Then, what are the differences between CWDM4 vs LR4 vs PSM4? Which is the better choice for your 100G data center deployment? This article will tell.

Overviews of 100G CWDM4, LR4 and PSM4

What is 100G QSFP28 LR4 Optics?

LR4 stands for 4-channel long reach. QSFP28 LR4 100G transceiver designs for long-haul transmission distance in 100G optical interconnection. The distance of 100G LR4 can be as far as 10 kilometers over single-mode fiber with duplex LC connectors. It complies with the IEEE 802.3 100GBASE-LR4 standard.

What is 100G QSFP28 CWDM4 Optics?

CWDM4 stands for Coarse Wavelength Division Multiplexing 4-lane. Not as far as QSFP28 LR4 transmit distance, 100G CWDM4 reaches about 2 kilometers distance over single-mode fiber with duplex LC connectors, neither too long nor too short. It adopts WDM technology that enables 4 wavelengths of 25G signals multiplexed and demultiplexed in the device. It is compliant with CWDM4 MSA.

What is 100G QSFP28 PSM4 Optics?

PSM4 stands for Parallel Single Mode Quad. 100G QSFP28 PSM4 reaches about 500 meters distance over single-mode fiber with MTP/MPO connectors, whose transmission distance is the shortest among these three transceivers, but it is still longer than the 100m transmission distance of QSFP SR4. It complies with the 100G PSM4 MSA.

100G CWDM4 vs LR4 vs PSM4 Spec Comparison

100G LR4 spec vs 100G CWDM4 spec vs 100G PSM4 Spec

Transceiver	Wavelength(nm)	Cable	Connector	Max Distance	Power Consumption	Industry Standard
QSFP-100G-LR4-S	1295, 1300, 1304, 1309	SMF	Duplex LC	10km	4W	IEEE 802.3 100GBASE-LR4
QSFP-100G-CWDM4	1271, 1291, 1311, 1331	SMF	Duplex LC	2km	3.5W	CWDM4 MSA
QSFP-100G-PSM4	1310	SMF	MTP/MPO-12	500m	3.5W	100G PSM4 MSA

Common Features of QSFP28 LR4, QSFP28 CWDM4, and QSFP28 PSM4

Supports 100G Ethernet Connectivity

Firstly, QSFP28 LR4, QSF28 CWDM4 and QSFP28 PSM4 all support 100GBase Ethernet rate. They are able to be applied in various 100 Gigabit Ethernet connectivity situations like data centers, large-scale cloud, high-performance computing networks, enterprise core and distribution layers.

Features with QSFP28 Form Factor

Secondly, they feature the QSFP28 (Quad Small Form-Factor Pluggable) form factor, which is the smallest and most popular form factor of 100G. The development of 100G form factor has experienced from CFP, CFP2, CFP4 to QSFP28. The size of CFP4 is only a quarter of CFP, however, QSFP28 is even smaller than CFP4. Consequently, QSFP28 features a significant advantage of higher port density. Besides high-density, QSFP28 also features a lower power consumption than previously CFP form factors. The difference of QSFP28 vs CFP vs CFP2 vs CFP4 is shown in the below table.

Form Factor	CFP	CFP2	CFP4	QSFP28
Dimension(mm)	82 x 14 x 145	42 x 13 x 108	22 x 10 x 92	18 x 8.5 x 52
Power	< 25 W	< 12W	< 6W	< 4W

Work over Single-mode Fiber

Thirdly, 100G QSFP28 LR4, CWDM4 and PSM4 all connect with single-mode fiber to reach a distance of 10km, 2km, 500m respectively.

Distinct Features of 100G CWDM4 vs 100G LR4

The arrival of 100G CWDM4 made up for link distance vacancies between QSFP 100G SR4 and LR4. What are the differences between CWDM4 vs LR4? The below post will tell.

CWDM4 vs LR4: Transmission Distance Comparison

The biggest difference between CWDM4 and LR4 is the supported link distance. Although both of the two transceivers support 100G data links over duplex LC single-mode fiber, the transmission distance of 100G CWDM4 reaches 2km while 100G LR4 is able to reach 10km. Although the transmission distance of CWDM4 is not as far as LR4, It provides an indispensable and cost-effective choice for the diverse lengths of optical links.

CWDM4 vs LR4: Working Principle and Optical Component Comparison

100G CWDM4 complies with CWDM4 MSA, which defines the block diagram, specifications, optical parameters of the transceiver. 100G CWDM4 transceiver has the features of four optical transmitters, four optical receivers, a wavelength division multiplexer, and demultiplexer. It uses four-lane center wavelengths of 1271nm, 1291nm, 1311nm, and 1331nm to realize 100G optical communication, each of which transmits 25G data rate. Based on WDM technology, the CWDM4 module enables the four-lane wavelengths multiplexing to one single-mode fiber. The working diagram is shown below.

The working principle of 100G LR4 is similar to CWDM4, it also adopts WDM technology. The difference is LR4 uses the four-lane wavelengths of 1295nm, 1300nm, 1304nm, and 1309nm. Besides, as QSFP28 100G operates at a long transmission link length up to 10km, it generally uses EML laser while 100G CWDM4 uses DML laser. Because EML laser is more costly than DML, here comes the below price differences between the two transceivers.

QSFP28 100G CWDM4 Working Diagram

QSFP28 100G LR4 Working Diagram

CWDM4 vs LR4: Price Comparison

Typically, the price of CWDM4 is less than half of LR4. It can be confirmed from the collected the price of the two transceivers from three 3rd-party optics manufacturers in the market as below.

CWDM4 vs LR4: Price of QSFPTEK, FS, Edgeoptic

Manufacturer	QSFPTEK	FS.COM	Edgeoptic
QSFP-100G-CWDM4	$109	$189	$151.07
QSFP-100G-LR4-S	$239	$499	$397.40

CWDM4 vs LR4: FEC Function

As the optical link needs to operate at a BER (Bit Error Ratio) of 5x10^-5, CWDM4 is required to be applied in the link that supports FEC (Forward error correction) function to ensure a reliable system operation, while the LR4 does not employ the use of FEC.

Distinct Features of 100G PSM4 vs 100G CWDM4

Both 100G PSM4 and CWDM4 are designed for middle/ short-range 100G high-speed communication. Then, what are the differences between PSM4 vs CWDM4?

Working Principle

Different from CWDM4 adopting WDM technology to multiplex four different wavelength lanes of signals to one single-mode fiber, 100G PSM4 carries 100G signal over 4 parallel lanes of 1310nm link without multiplexing and demultiplexing. Each lane supports a 25Gbps data rate. The working diagram of 100G PSM4 is shown below.

QSFP28 100G PSM4 Working Diagram

100G PSM4 Cable Solution vs 100G CWDM4 Cable Solution

What cable does PSM4 work with? As structured with an MTP/MPO connector, the PSM4 transceiver works with MTP to MTP single-mode fiber or MTP to 4 LC single-mode fiber to connect four 25G LR transceivers in a 4x25G connectivity link. As for 100G CWDM4, because of structuring with a duplex LC connector, it operates with duplex LC single-mode fiber in 100G links.

PSM4 Cable vs CWDM4 Cable

Technology and Optical Component

100G CWDM4 adopts WDM technology and uses four CWDM DML lasers, which generally use distributed feedback structure for stable operation of direct modulation. And 100G PSM4 adopts a new Silicon Photonics technology. which enables 100G data rate transmission per second.

Conclusion

QSFP28 100G LR4, psm4, and cwdm4 optics provide solutions towards your diverse optical link lengths. Which one is better generally depends on your demand link length, link power consumption, optical cable structure, budget, etc. QSFPTEK provides a wide range of original brands (Cisco, Juniper, Arista, Intel, Mellanox, Huawei, etc) compatible 100G optical modules and cables including QSFP28 100G SR4, LR4, CWDM4, PSM4, etc, each of which rigorously tested before leaving the factory. Welcome to inquire at sales@qsfptek.com.