Tag Archives: 400G Network

400G OTN Technologies: Single-Carrier, Dual-Carrier and Quad-Carrier

In order to achieve 400G long-haul (LH) transmission, three 400G Optical Transport Network (OTN) technologies come into being to meet the needs: single-carrier 400G, dual-carrier 400G, and quad-carrier 400G. They differ from each other mainly in the number of wavelengths used for transmission. This post will reveal what they are and their respective pros and cons.

Single-Carrier for 400G OTN

Single-carrier 400G, or single-wavelength 400G, means there is 400G capacity on a single wavelength. The single-carrier 400G adopts high-order modulation formats such as PM-16QAM, PM-32QAM and PM-64QAM. Normally, a single-carrier for 400G optical transport network is used only in network access, metro, or DCI (Data Center Interconnection) transmission.

Figure 1: Single-Carrier for 400G OTN

Take PM-16QAM (Polarization-Multiplexed-16 Quadrature Amplitude Modulation) as an example. PM refers to a process where the 400G (448Gbit/s) optical signal is separated into two signals and modulated to transmit in two polarization directions – X and Y, which can cut the original signal rate in half (224Gbit/s). QAM is a process of separating the signals in X and Y to further reduce the rate. 16 stands for 4 bits, which means the signal in X and Y is respectively divided into 4 signals and the rate will accordingly decrease to 1/4 on the basis of the previous 224Gbit/s. By using PM-16QAM, the signal rate at this moment becomes 56G Baud (the rate of electrical processing).

Note: Because in current circuit technology, 100Gbit/s has approached the limit of the electronic bottleneck. If the Baud continues to increase, problems like signal loss, power dissipation, and electromagnetic interference will remain a hassle, which will, even if solved, require tremendous costs.

Figure 2: PM-16QAM

Pros of Single-Carrier for 400G Optical Transport Network

Compared with the multi-carriers scheme, single-carrier 400G is an easier wavelength allocation solution with simpler structure and smaller size that can provide easy network management and low power consumption.
With higher-order QAM, single-carrier for 400G OTN network can increase signal rates and spectrum efficiency, which will significantly expand network capacity and increase the number of users to support.
Also, with high system integration, it can connect the separate subsystems into a complete one and make them work in coordination with each other and achieve the best overall performance.

Cons of Single-Carrier for 400G Optical Transport Network

Since single-carrier for 400G OTN network adopts more advanced QAM, it requires a higher OSNR (Optical Signal Noise Ratio) and greatly reduces transmission distance (less than 200km). Also, single-carrier is more susceptible to laser phase noise and fiber nonlinear effects. Therefore, it is the best solution only for some specific applications that don’t require ultra long-haul transmission distance, but need large bandwidth capacity.

Dual-Carrier for 400G OTN

Dual-carrier 400G, also named dual-wavelength 400G, offers 400G capacity via two 200G wavelengths. The dual-carrier 400G system based on the 2× 200G super-channel scheme adopts lower-order modulation formats like PM-QPSK (Quadrature Phase Shift Keying, a symbol represents two bits, which means the rate is reduced to 1/2), PM-8QAM or PM-16QAM. Dual-carrier for 400G optical transport network is applied in more complex metro networks to achieve 400G long-haul transmission.

Figure 3: Dual-Carrier for 400G OTN

Pros of Dual-Carrier for 400G Optical Transport Network

The spectrum efficiency of dual-carrier 400G has increased by more than 165%, with relatively high system integration, small size, low power consumption. Dual-carrier 400G is regarded as the most commonly-used technology for 400G OTN.
The span of dual-carrier 400G is longer than single-carrier 400G, which can reach up to 500km for commercial use. When deployed with low-attenuation fiber optic cable and EDFA (Erbium Doped Fiber Amplifiers), dual-carrier for 400G OTN network can cover more than 1000km, which can basically satisfy the 400G long-haul transmission application.

Cons of Dual-Carrier for 400G Optical Transport Network

Even with low-attenuation fiber optic cable and EDFA, dual-carrier 400G still fails to reach as long as quad-carrier 400G does, not suitable for ultra long-haul (ULH) transmission over 2000km.

Quad-Carrier for 400G OTN

Quad-carrier 400G refers to a solution that offers 400G capacity through four 100G wavelengths. It is achieved by constructing a 400G super-channel based on 100G PM-QPSK with four carriers, suitable for ultra long-haul (ULH) transmission over 2000km.

Figure 4: Quad-Carrier for 400G OTN

Pros of Quad-Carrier for 400G Optical Transport Network

Quad-carrier for 400G OTN network adopts the mature 100G transmission technology that has been widely-used for commercial purpose.
It can achieve ultra long-haul transmission of more than 2000km at relatively low cost.

Cons of Quad-Carrier for 400G Optical Transport Network

Quad-carrier 400G system makes sense only when spectrum compression technology is introduced to improve spectrum efficiency, and the 100G chip is upgraded to solve the problems of integration and power consumption. Otherwise, a 400G system built on the current 100G chip is essentially a 100G system.

Conclusion

In all, 400G long-haul transmission is mainly realized by single-carrier, dual-carrier and quad-carrier. Single-carrier for 400G OTN network can only cover a distance of less than 200km; dual-carrier for 400G OTN network is the ideal solution for MAN transmission (with PM-16QAM) and medium long-haul transmission (with PM-QPSK); quad-carrier for 400G OTN network has the same transmission distance as 100G and is appropriate for ULH transmission. As global data traffic keeps climbing, there is no end to bandwidth demands. While it may take time to transit to 400G, you can learn about What’s the Current and Future Trend of 400G Ethernet? to make preparations first.

Original Source: 400G OTN Technologies: Single-Carrier, Dual-Carrier and Quad-Carrier

How Much Do You Know About QSFP56?

Over the past years, there have emerged various optical module form factor types with the growth of new technology and high-speed interconnects, among which QSFP56, as a member of the QSFP family, is a solution for 200G applications. What‘s the difference between QSFP56 with other QSFP family form factors? Is QSFP56 the same as QSFP56-DD? If you are wondering about these questions, this article is for you.

Figure 1: Transceiver form factor

QSFP56—Form Factor of 200G Transceivers

To make clear what QSFP56 is, let’s take a look at the QSFP form factor first. Quad Small Form-Factor Pluggable (QSFP) was developed after SFP, which was originally designed to replace the single-channel SFPs with high-density optical modules. Due to the fact that it denotes four lanes for up to 4 wavelengths, it provides higher bandwidth capacity compared with the SFP modules.

Developed on the basis of QSFP, 40G QSFP+ arose and then 100G QSFP28 came into use for high-density applications. With the rising of data traffic in data centers and advanced network applications, the market is urgent to achieve higher-speed general availability. There is more addition to QSFP family form factors, such as 200G QSFP56 and 400G QSFP56-DD.

Figure 2：Types of QSFP form factor

As an evolution of the previous 40G QSFP+ and 100G QSFP28, Quad 50 Gigabits Small Form-factor Pluggable (QSFP56) is the one designed for 200G Ethernet. QSFP56 denotes 4 x 50 to 56Gb/s in a QSFP form factor. Sometimes it can also be referred to as 200G QSFP for sake of simplicity. QSFP56 optical modules are similar to QSFP ones in terms of size and form factor. Classified by distance, QSFP56 modules can be divided into QSFP56 CR, SR, DR, FR, LR, which enables different transmission distances over a single mode fiber (SMF) or multimode fiber (MMF).

Generally, two QSFP56 modules can be used with an SMF or MMF to realize a 200G link. QSFP56 AOC/DAC is also a way to realize a 200G link by connecting QSFP56 ports on two devices in a simplified linking process. For bridging 200G QSFP56 ports with other speeds, there are 200G QSFP56 to 2x100G QSFP28 breakout cables and 200G QSFP56 to 4x50G SFP56 breakout cables to achieve 2x100G or 4x50G connections.

QSFP56 vs QSFP28 vs QSFP+

Seen from their industry names, QSFP56, QSFP28 and QSFP+ are very similar in that they share the same QSFP form factor as their postfix shows, and they have the same size as each other. However, their data center and connectivity capabilities are different. Below is a table listing the basic parameters of QSFP56, QSFP28, and QSFP+.

Industry name	Year	original meaning	Number of Electric Lanes	Number of Optical Lanes	Bit Rate/Lane	Modulation	Line Rates
QSFP+	2013	Quad Small Form-factor Pluggable Plus	4	4	10Gbps	NRZ	40G
QSFP28	2016	Quad Small Form-factor Pluggable 28	4	4	25Gbps	NRZ	100G
QSFP56	2017	Quad 50 Gigabits Small Form-factor Pluggable	4	4	50Gbps	PAM4	200G

From the comparison chart, it can be distinctly seen that compared with QSFP+ and QSFP28, the QSFP56 form factor performs a higher network speed as 200G QSFP supporting 4×50G channels. While QSFP+ is an evolution of QSFP to support 4×10G channels carrying 10G Ethernet, 10G fiber channel or QDR InfiniBand. It introduced the concept of multiplexing four lanes to increase the bandwidth, capable of handling 40Gbps line rates at 10GBaud NRZ per lane. QSFP28 supports 4×25G channels and contains 4-lane optical transmitter and 4-lane optical receiver as QSFP+ does.

The most significant change from QSFP+ and QSFP28 to QSFP56 is that QSFP56 made the change from NRZ encoding to PAM4 encoding. Though QSFP56 still uses 4 lanes as QSFP28, the modulation is doubled to 50G per channel, which enables more data on existing fiber, accordingly, more suitable for hyper-scale data center networks.

Shift from QSFP56 to QSFP56-DD (400G QSFP-DD)

With data centers undergoing rapid growth, the rising demand for data volume is pushing network components to support higher bandwidth and higher density. The latest iteration of optical module form factor is from QSFP56 to QSFP56-DD, which is also called 400G QSFP-DD. DD here refers to double density, representing reaching 400G (with 50G PAM4) by doubling data lanes of QSFP56, from 4 lanes to 8 lanes.

Though QSFP56-DD has the double density, its size is similar to QSFP56. 400G QSFP56-DD port is backward compatible with the QSFP transceiver which means as long as the switch supports, QSFP56 can work on the QSFP56-DD port. When using a QSFP56 module in an QSFP56-DD port, this port will be configured for a data rate of 200G, instead of 400G.

The QSFP56-DD form factor is now recognized by the 400G market as the 400G form factor that gets the most concern. Despite that nowadays 400G Ethernet is seen as a futureproofing solution for the next-generation data center, there is still a need for 200G QSFP56 for some organizations deploying 200G Ethernet.

Article Source

https://community.fs.com/blog/introduction-to-qsfp56-form-factor.html

https://community.fs.com/blog/differences-between-qsfp-dd-and-qsfp-qsfp28-qsfp56-osfp-cfp8-cobo.html

https://community.fs.com/blog/400g-qsfp-dd-transceiver-types-overview.html

Differences Between QSFP-DD and QSFP+ / QSFP28 / QSFP56 / OSFP / CFP8 / COBO

QSFP-DD, as the smallest form factor for 400G transceivers, offers industry’s highest bandwidth density while leveraging the backward compatibility to lower-speed QSFP pluggable modules and cables, making it popular among the fiber optic manufacturers. As the newest hot type of optical transceivers in 400G high-speed applications, QSFP-DD is often compared with other modules such as QSFP56, OSFP, CFP8, and COBO. So what are the differences among these optical modules? This post will illustrate them thoroughly.

QSFP-DD Wiki

QSFP-DD (also called QSFP56-DD) stands for Quad Small Form Factor Pluggable Double Density, which is fully compliant with IEEE802.3bs and QSFP-DD MSA standards. The “double density” means the doubling of the number of high-speed electrical interfaces that the module supports compared with a standard QSFP28 module. The data rate of each channel can reach 25Gb/s through NRZ modulation technology, realizing 200G network transmission. Also, the data rate of each channel can reach 50Gb/s by the PAM4 modulation technology, achieving 400G network transmission, which is suitable for high-performance computing data center and cloud network. For more information about PAM4 modulation technology, please visit: PAM4: Learn 400G Ethernet From Here.

The advantages of QSFP-DD form factor are as follows:

Backward compatibility: allowing the QSFP-DD to support existing QSFP modules (such as QSFP+, QSFP28, QSFP56, etc.) and provide flexibility for end-users and system designers.
Adopting the 2×1 stacked integrated cage/connector to support the one-high cage connector and two-high stack cage connector system.
SMT connector and 1xN cage design: this kind of design can enable thermal support of at least 12W per module. The higher thermal reduces the requirement for heat dissipation capabilities of transceivers, thus reducing some unnecessary costs.
ASIC design: supporting multiple interface rates and fully backward compatible with QSFP+ and QSFP28 modules, thus reducing port and equipment deployment costs.

QSFP-DD vs QSFP+/QSFP28/QSFP56

QSFP-DD, QSFP+, QSFP28 and QSFP56 belong to the QSFP form factor, but what are the differences among them? The differences are explained in the following descriptions.

Structure

In terms of the appearance, the width, length and thickness of the QSFP-DD are the same as QSFP+, QSFP28 and QSFP56. But the QSFP-DD module is equipped with an 8-lane electrical interface rather than a 4-lane like other QSFP modules and the ASIC ports of QSFP-DD are doubled to support existing interfaces such as CAUI-4. Therefore, the mechanical interface of QSFP-DD on the host board is slightly deeper than that of the other QSFP system transceivers to accommodate the extra row of contacts.

Bandwidth & Application

The QSFP-DD modules can support 400Gbps while QSFP+/QSFP28/QSFP56 can only reach 40Gbps/100Gbps/200Gbps respectively. Therefore, QSFP-DD connectors are used in 400G optical modules, DACs and AOCs, and applied for the 400G data center interconnections. And QSFP+/QSFP28/QSFP56 modules and DAC/AOC are used for 40G/100G/200G networks. interconnection.

Backward Compatibility

As mentioned above, the QSFP-DD can be backward compatible with the previous QSFP system transceiver modules. In other words, based on the previous form factor, the QSFP-DD has been technically upgraded to support increased bandwidth. And its backward compatibility can avoid existing equipment replacement on the scale and effectively reduce the network upgrade cost.

Form Factor	QSFP-DD	QSFP56	QSFP28	QSFP+
Released Year	2016	2018	2016	2010
Number of Electrical Interface Lanes	8	4	4	4
Single Channel Rate	25Gbps/50Gbps	50Gbps	25Gbps	10Gbps
Modulation Technology	NRZ/PAM4	PAM4	NRZ	NRZ
Backward Compatibility	QSFP+/QSFP28/QSFP56	QSFP+/QSFP28	QSFP+	/

QSFP-DD vs OSFP/CFP8/COBO

QSFP-DD (QSFP56-DD) and OSFP/CFP8/COBO are the form factors of 400G optics on the market, the differences of them are listed below:

QSFP-DD vs OSFP

OSFP is a new pluggable form factor with eight high speed electrical lanes that will initially support 400Gb/s (8x50G) or reach up to 800Gb/s. The width, length and thickness of QSFP-DD are 18.35mm, 89.4mm and 8.5mm, while those of OSFP are 22.58mm, 107.8mm and 13.0mm. It is obvious that the OSFP form factor is slightly wider and deeper than the QSFP-DD, but it still supports 36 OSFP ports per 1U front panel, enabling 14.4Tb/s per 1U.

Generally, the power consumption of QSFP-DD is 7-12W, while the OSFP can reach 12-15W. The lower the power consumption, the better the performance of the transceiver. Unlike the QSFP-DD, OSFP can’t be backward compatible with QSFP+/QSFP28 since it has a larger size than that of QSFP+/QSFP28.

QSFP-DD vs CFP8

Featuring a 41.5mm*107.5mm*9.5mm form factor, the CFP8 module delivers four times more bandwidth than existing 100G solutions. Its electrical interface has been generally specified to allow for 16×25 Gb/s and 8×50 Gb/s mode. Since the size of CFP8 is almost three times larger than that of QSFP-DD, the power consumption of CFP8 is much higher than QSFP-DD. Meanwhile, the CFP8 can’t be used on QSFP+/QSFP28 ports. The maximum bandwidth of CFP8 and QSFP-DD is 400Gb/s, but CFP8 only supports in the form of 16x25G or 8x50G while QSFP-DD also supports both 200Gb/s (8x25G).

QSFP-DD vs COBO

COBO stands for Consortium for On-Board Optics, it can be installed internally to the line-card equipment in a controlled environment, which lacks flexibility. And it doesn’t support hot-pluggable, so it is more difficult for COBO modules to maintain than QSFP-DD. Additionally, the COBO form factor has two electrical interfaces——one eight lane and the other sixteen lane to meet both 1x400G and 2x400G transmission requirements.

The following chart shows the market maturity of the QSFP-DD, OSFP, CFP8 and COBO form factors. The larger the numbers, the higher the market maturity of these form factors.

Performance	CFP8	OSFP	QSFP-DD	COBO
Volume	1	2	3	4
Power Consumption	3	2	1	4
Cost	1	3	4	2
Maturity	4	3	2	1
Compatibility	3	2	4	1
Difficulty for Operation & Maintenance	2	3	4	1
Overall Ratings	14	15	18	13

We can see from the table that the overall rating of QSFP-DD and OSFP form factors are higher than other form factors. So the QSFP-DD and OSFP are more popular with fiber optic manufacturers. While the former is suitable for data center applications and the latter often applied for telecommunications applications. For more types of 400G transceivers, please refer to How Many 400G Transceiver Types Are in the Market? for more detailed information.

Will QSFP-DD Be Popular in 800G Ethernet?

The QSFP-DD (QSFP56-DD) is more suitable for data center applications than OSFP. With the concentration of east-west traffic in the data center and the increasing pressure on the internal bandwidth of the data center, the time gap between the application of high-speed optical modules in the telecom market and the data center market is gradually shortening. The 400G optics will be applied widely. That is, QSFP-DD will benefit from the 400G Ethernet and ushered in a good development prospect.

As 400G becomes commercially available on a large scale, single-wave 100G technology is set to mature, laying the groundwork for the arrival of 800G. Recently, the QSFP-DD800 Multi-Source Agreement (MSA) organization released the first version of the QSFP-DD800 transceiver hardware specification, which is dedicated to the continuation of the current QSFP-DD form factor to support a single channel rate of 100Gbps 8-channel new generation QSFP-DD800. This also means that 800G might still adopt the QSFP-DD form factor to bring greater advantages and values for Internet service providers.

Article Source:

https://community.fs.com/blog/differences-between-qsfp-dd-and-qsfp-qsfp28-qsfp56-osfp-cfp8-cobo.html

https://community.fs.com/blog/400g-ethernet-400g-transceiver.html

https://community.fs.com/blog/400g-qsfp-dd-transceiver-types-overview.html

FAQs on 400G Transceivers and Cables

400G transceivers and cables play a vital role in the process of constructing a 400G network system. Then, what is a 400G transceiver? What are the applications of QSFP-DD cables? Find answers here.

FAQs on 400G Transceivers and Cables Definition and Types

Q1: What is a 400G transceiver?

A1: 400G transceivers are optical modules that are mainly used for photoelectric conversion with a transmission rate of 400Gbps. 400G transceivers can be classified into two categories according to the applications: client-side transceivers for interconnections between the metro networks and the optical backbone, and line-side transceivers for transmission distances of 80km or even longer.

Q2: What are QSFP-DD cables?

A2: QSFP-DD cables contain two forms: one is a form of high-speed cable with QSFP-DD connectors on either end, transmitting and receiving 400Gbps data over a thin twinax cable or a fiber optic cable, and the other is a form of breakout cable that can split one 400G signal into 2x 200G, 4x 100G, or 8x 50G, enabling interconnection within a rack or between adjacent racks.

Q3: What are the 400G transceivers packaging forms?

A3: There are mainly the following six packaging forms of 400G optical modules:

QSFP-DD: 400G QSFP-DD (Quad Small Form Factor Pluggable-Double Density) is an expansion of QSFP, adding one row to the original 4-channel interface to 8 channels, running at 50Gb/s each, for a total bandwidth of 400Gb/s.
OSFP: OSFP (Octal Small Formfactor Pluggable, Octal means 8) is a new interface standard and is not compatible with the existing photoelectric interface. The size of 400G OSFP modules is slightly larger than that of 400G QSFP-DD.
CFP8: CFP8 is an expansion of CFP4, with 8 channels and a correspondingly larger size.
COBO: COBO (Consortium for On-Board Optics) means that all optical components are placed on the PCB. COBO is with good heat-dissipation and small-size. However, since it is not hot-swappable, once a module fails, it will be troublesome to repair.
CWDM8: CWDM 8 is an extension of CWDM4 with four new center wavelengths (1351/1371/1391/1411 nm). The wavelength range becomes wider and the number of lasers is doubled.
CDFP: CDFP was born earlier, and there are three editions of the specification. CD stands for 400 (Roman numerals). With 16 channels, the size of CDFP is relatively large.

Q4: What 400G transceivers and QSFP-DD cables are available on the market?

A4: The two tables below show the main types of 400G transceivers and cables on the market:

400G Transceivers	Standards	Max Cable Distance	Connector	Media	Temperature Range
400G QSFP-DD SR8	QSFP-DD MSA Compliant	70m OM3/100m OM4	MTP/MPO-16	MMF	0 to 70°C
400G QSFP-DD DR4	QSFP-DD MSA, IEEE 802.3bs	500m	MTP/MPO-12	SMF	0 to 70°C
400G QSFP-DD XDR4/DR4+	QSFP-DD MSA	2km	MTP/MPO-12	SMF	0 to 70°C
400G QSFP-DD FR4	QSFP-DD MSA	2km	LC Duplex	SMF	0 to 70°C
400G QSFP-DD 2FR4	QSFP-DD MSA, IEEE 802.3bs	2km	CS	SMF	0 to 70°C
400G QSFP-DD LR4	QSFP-DD MSA Compliant	10km	LC Duplex	SMF	0 to 70°C
400G QSFP-DD LR8	QSFP-DD MSA Compliant	10km	LC Duplex	SMF	0 to 70°C
400G QSFP-DD ER8	QSFP-DD MSA Compliant	40km	LC Duplex	SMF	0 to 70°C
400G OSFP SR8	IEEE P802.3cm; IEEE 802.3cd	100m	MTP/MPO-16	MMF	0 to 70°C
400G OSFP DR4	IEEE 802.3bs	500m	MTP/MPO-12	SMF	0 to 70°C
4000G OSFP XDR4/DR4+	/	2km	MTP/MPO-12	SMF	0 to 70°C
400G OSFP FR4	100G lambda MSA	2km	LC Duplex	SMF	0 to 70°C
400G OSFP 2FR4	IEEE 802.3bs	2km	CS	SMF	0 to 70°C
400G OSFP LR4	100G lambda MSA	10km	LC Duplex	SMF	0 to 70°C

QSFP-DD Cables	Catagory	Product Description	Reach	Temperature Range	Power Consumption
400G QSFP-DD DAC	QSFP-DD to QSFP-DD DAC	with each 400G QSFP-DD using 8x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	<1.5W
400G QSFP-DD Breakout DAC	QSFP-DD to 2x 200G QSFP56 DAC	with each 200G QSFP56 using 4x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	<0.1W
QSFP-DD to 4x 100G QSFPs DAC	with each 100G QSFPs using 2x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	<0.1W
QSFP-DD to 8x 50G SFP56 DAC	with each 50G SFP56 using 1x 50G PAM4 electrical lane	no more than 3m	0 to 80°C	<0.1W
400G QSFP-DD AOC	QSFP-DD to QSFP-DD AOC	with each 400G QSFP-DD using 8x 50G PAM4 electrical lanes	70m (OM3) or 100m (OM4)	0 to 70°C	<10W
400G QSFP-DD Breakout AOC	QSFP-DD to 2x 200G QSFP56 AOC	with each 200G QSFP56 using 4X 50G PAM4 electrical lane	70m (OM3) or 100m (OM4)	0 to 70°C	/
QSFP-DD to 8x 50G SFP56 AOC	with each 50G SFP56 using 1x 50G PAM4 electrical lane	70m (OM3) or 100m (OM4)	0 to 70°C	/
400G OSFP DAC	OSFP to OSFP DAC	with each 400G OSFP using 8x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	<0.5W
400G OSFP Breakout DAC	OSFP to 2x 200G QSFP56 DAC	with each 200G QSFP56 using 4x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	/
OSFP to 4x100G QSFPs DAC	with each 100G QSFPs using 2x 50G PAM4 electrical lanes	no more than 3m	0 to 70°C	/
OSFP to 8x 50G SFP56 DAC	with each 50G SFP56 using 1x 50G PAM4 electrical lane	no more than 3m	/	/
400G OSFP AOC	OSFP to OSFP AOC	with each 400G OSFP using 8x 50G PAM4 electrical lanes	70m (OM3) or 100m (OM4)	0 to 70°C	<9.5W

Q5: What do the suffixes “SR8, DR4 / XDR4, FR4 / LR4 and 2FR4” mean in 400G transceivers?

A5: The letters refer to reach, and the number refers to the number of optical channels:

SR8: SR refers to 100m over MMF. Each of the 8 optical channels from an SR8 module is carried on separate fibers, resulting in a total of 16 fibers (8 Tx and 8 Rx).
DR4 / XDR4: DR / XDR refer to 500m / 2km over SMF. Each of the 4 optical channels is carried on separate fibers, resulting in a total of 4 pairs of fibers.
FR4 / LR4: FR4 / LR4 refer to 2km / 10km over SMF. All 4 optical channels from an FR4 / LR4 are multiplexed onto one fiber pair, resulting in a total of 2 fibers (1 Tx and 1 Rx).
2FR4: 2FR4 refers to 2 x 200G-FR4 links with 2km over SMF. Each of the 200G FR4 links has 4 optical channels, multiplexed onto one fiber pair (1 Tx and 1 Rx per 200G link). A 2FR4 has 2 of these links, resulting in a total of 4 fibers, and a total of 8 optical channels.

FAQs on 400G Transceivers and Cables Applications

Q1: What are the benefits of moving to 400G technology?

A1: 400G technology can increase the throughput of data and maximize the bandwidth and port density of the data centers. With only 1/4 the number of optical fiber links, connectors, and patch panels when using 100G platforms for the same aggregate bandwidth, 400G optics can also reduce operating expenses. With these benefits, 400G transceivers and QSFP-DD cables can provide ideal solutions for data centers and high-performance computing environments.

Q2: What are the applications of QSFP-DD cables?

A2: QSFP-DD cables are mainly used for short-distance 400G Ethernet connectivity in the data centers, and 400G to 2x 200G / 4x 100G / 8x 50G Ethernet applications.

Q3: 400G QSFP-DD vs 400G OSFP/CFP8: What are the differences?

A3: The table below includes detailed comparisons for the three main form factors of 400G transceivers.

400G Transceiver	400G QSFP-DD	400G OSFP	CFP8
Application Scenario	Data center	Data center & telecom	Telecom
Size	18.35mm× 89.4mm× 8.5mm	22.58mm× 107.8mm× 13mm	40mm× 102mm× 9.5mm
Max Power Consumption	12W	15W	24W
Backward Compatibility with QSFP28	Yes	Through adapter	No
Electrical signaling (Gbps)	8× 50G
Switch Port Density (1RU)	36	36	16
Media Type	MMF & SMF
Hot Pluggable	Yes
Thermal Management	Indirect	Direct	Indirect
Support 800G	No	Yes	No

For more details about the differences, please refer to the blog: Differences Between QSFP-DD and QSFP+/QSFP28/QSFP56/OSFP/CFP8/COBO

Q4: What does it mean when an electrical or optical channel is PAM4 or NRZ in 400G transceivers?

A4: NRZ is a modulation technique that has two voltage levels to represent logic 0 and logic 1. PAM4 uses four voltage levels to represent four combinations of two bits logic-11, 10, 01, and 00. PAM4 signal can transmit twice faster than the traditional NRZ signal.

When a signal is referred to as “25G NRZ”, it means the signal is carrying data at 25 Gbps with NRZ modulation. When a signal is referred to as “50G PAM4”, or “100G PAM4”, it means the signal is carrying data at 50 Gbps, or 100 Gbps, respectively, using PAM4 modulation. The electrical connector interface of 400G transceivers is always 8x 50Gb/s PAM4 (for a total of 400Gb/s).

FAQs on Using 400G Transceivers and Cables in Data Centers

Q1: Can I plug an OSFP module into a 400G QSFP-DD port, or a QSFP-DD module into an OSFP port?

A1: No. OSFP and QSFP-DD are two physically distinct form factors. If you have an OSFP system, then 400G OSFP optics must be used. If you have a QSFP-DD system, then 400G QSFP-DD optics must be used.

Q2: Can a QSFP module be plugged into a 400G QSFP-DD port?

A2: Yes. A QSFP (40G or 100G) module can be inserted into a QSFP-DD port as QSFP-DD is backward compatible with QSFP modules. When using a QSFP module in a 400G QSFP-DD port, the QSFP-DD port must be configured for a data rate of 100G (or 40G).

Q3: Is it possible with a 400G OSFP on one end of a 400G link, and a 400G QSFP-DD on the other end?

A3: Yes. OSFP and QSFP-DD describe the physical form factors of the modules. As long as the Ethernet media types are the same (i.e. both ends of the link are 400G-DR4, or 400G-FR4 etc.), 400G OSFP and 400G QSFP-DD modules will interoperate with each other.

Q4: How can I break out a 400G port and connect to 100G QSFP ports on existing platforms?

A4: There are several ways to break out a 400G port to 100G QSFP ports:

QSFP-DD-DR4 to 4x 100G-QSFP-DR over 500m SMF

QSFP-DD-XDR4 to 4x 100G-QSFP-FR over 2km SMF

QSFP-DD-LR4 to 4x 100G-QSFP-LR over 10km SMF

OSFP-400G-2FR4 to 2x QSFP-100G-CWDM4 over 2km SMF

Apart from the 400G transceivers mentioned above, 400G to 4x 100G breakout cables can also be used.

Article Source: FAQs on 400G Transceivers and Cables

400G Transceiver, DAC, or AOC: How to Choose?

400G OSFP Transceiver Types Overview

Infographic – Types of 400G Transceivers

With the tremendous requirement for high bandwidth in 5G, loT and cloud data center, the focus on 400G Ethernet has been lasting for several years. As the key hardware devices for optical network interconnection, 400G transceivers have also become the mainstream of the industry. The following is a brief introduction to the types of 400G transceivers.

https://community.fs.com/blog/infographic-types-of-400g-transceivers.html

https://community.fs.com/blog/400g-transceiver-dac-or-aoc-how-to-choose.html

https://community.fs.com/blog/faqs-about-fs-400g-transceivers.html

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