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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 TransceiversStandardsMax Cable DistanceConnectorMediaTemperature Range
400G QSFP-DD SR8QSFP-DD MSA Compliant70m OM3/100m OM4MTP/MPO-16MMF0 to 70°C
400G QSFP-DD DR4QSFP-DD MSA, IEEE 802.3bs500mMTP/MPO-12SMF0 to 70°C
400G QSFP-DD XDR4/DR4+QSFP-DD MSA2kmMTP/MPO-12SMF0 to 70°C
400G QSFP-DD FR4QSFP-DD MSA2kmLC DuplexSMF0 to 70°C
400G QSFP-DD 2FR4QSFP-DD MSA, IEEE 802.3bs2kmCSSMF0 to 70°C
400G QSFP-DD LR4QSFP-DD MSA Compliant10kmLC DuplexSMF0 to 70°C
400G QSFP-DD LR8QSFP-DD MSA Compliant10kmLC DuplexSMF0 to 70°C
400G QSFP-DD ER8QSFP-DD MSA Compliant40kmLC DuplexSMF0 to 70°C
400G OSFP SR8IEEE P802.3cm; IEEE 802.3cd100mMTP/MPO-16MMF0 to 70°C
400G OSFP DR4IEEE 802.3bs500mMTP/MPO-12SMF0 to 70°C
4000G OSFP XDR4/DR4+/2kmMTP/MPO-12SMF0 to 70°C
400G OSFP FR4100G lambda MSA2kmLC DuplexSMF0 to 70°C
400G OSFP 2FR4IEEE 802.3bs2kmCSSMF0 to 70°C
400G OSFP LR4100G lambda MSA10kmLC DuplexSMF0 to 70°C
QSFP-DD CablesCatagoryProduct DescriptionReachTemperature RangePower Consumption
400G QSFP-DD DACQSFP-DD to QSFP-DD DACwith each 400G QSFP-DD using 8x 50G PAM4 electrical lanesno more than 3m0 to 70°C<1.5W
400G QSFP-DD Breakout DACQSFP-DD to 2x 200G QSFP56 DACwith each 200G QSFP56 using 4x 50G PAM4 electrical lanesno more than 3m0 to 70°C<0.1W
QSFP-DD to 4x 100G QSFPs DACwith each 100G QSFPs using 2x 50G PAM4 electrical lanesno more than 3m0 to 70°C<0.1W
QSFP-DD to 8x 50G SFP56 DACwith each 50G SFP56 using 1x 50G PAM4 electrical laneno more than 3m0 to 80°C<0.1W
400G QSFP-DD AOCQSFP-DD to QSFP-DD AOCwith each 400G QSFP-DD using 8x 50G PAM4 electrical lanes70m (OM3) or 100m (OM4)0 to 70°C<10W
400G QSFP-DD Breakout AOCQSFP-DD to 2x 200G QSFP56 AOCwith each 200G QSFP56 using 4X 50G PAM4 electrical lane70m (OM3) or 100m (OM4)0 to 70°C/
QSFP-DD to 8x 50G SFP56 AOCwith each 50G SFP56 using 1x 50G PAM4 electrical lane70m (OM3) or 100m (OM4)0 to 70°C/
400G OSFP DACOSFP to OSFP DACwith each 400G OSFP using 8x 50G PAM4 electrical lanesno more than 3m0 to 70°C<0.5W
400G OSFP Breakout DACOSFP to 2x 200G QSFP56 DACwith each 200G QSFP56 using 4x 50G PAM4 electrical lanesno more than 3m0 to 70°C/
OSFP to 4x100G QSFPs DACwith each 100G QSFPs using 2x 50G PAM4 electrical lanesno more than 3m0 to 70°C/
OSFP to 8x 50G SFP56 DACwith each 50G SFP56 using 1x 50G PAM4 electrical laneno more than 3m//
400G OSFP AOCOSFP to OSFP AOCwith each 400G OSFP using 8x 50G PAM4 electrical lanes70m (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 Transceiver400G QSFP-DD400G OSFPCFP8
Application ScenarioData centerData center & telecomTelecom
Size18.35mm× 89.4mm× 8.5mm22.58mm× 107.8mm× 13mm40mm× 102mm× 9.5mm
Max Power Consumption12W15W24W
Backward Compatibility with QSFP28YesThrough adapterNo
Electrical signaling (Gbps)8× 50G
Switch Port Density (1RU)363616
Media TypeMMF & SMF
Hot PluggableYes
Thermal ManagementIndirectDirectIndirect
Support 800GNoYesNo

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
400G to 4x 100G
  • QSFP-DD-XDR4 to 4x 100G-QSFP-FR over 2km SMF
400G to 4x 100G
  • QSFP-DD-LR4 to 4x 100G-QSFP-LR over 10km SMF
400G to 4x 100G
  • OSFP-400G-2FR4 to 2x QSFP-100G-CWDM4 over 2km SMF
400G to 4x 100G

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

Related Articles:

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

400G OSFP Transceiver Types Overview

SFP Connector vs SFP+ Connector vs SFP28 Connector

SFP (Small Form-factor Pluggable) module connector with various data speed rate is one of the major optical transceivers used for data communication. With ever-increasing demand for faster speed and higher density, the SFP connectors have experienced several generations of update for the signal speed capability as well as port density, from the original SFP to SFP+ and then to the new SFP28 type. The compatibility of these connecting ports is the pain point for many subscribers in data communication transmission. So what’s the similarities and differences between them and are these module connectors compatible with each other when plugged into switches? SFP28 vs SFP+ vs SFP connector, which one should you choose? This paper will give you the answer.

What Is SFP Connector?

Specified by a multi-source agreement (MSA), SFP connector was first introduced in early 2000 and designed to replace the previous gigabit interface converter (GBIC) connector in fiber optic and Ethernet high-speed networking systems. Based on the IEEE 802.3, SFF-8472 protocol specification, SFP module connectors has the ability to handle up to 4.25Gb/s with greater port density than the GBIC, which is why SFP is also known as mini GBIC. This allowed it to quickly become the connector of choice for system administrators who liked the idea of being able to significantly increase their output per rack. The SFP connectors can support Gigabit Ethernet, Fibre Channel, Synchronous Optical Network (SONET) and other communication standards.

What Is SFP+ Connector?

To cater the need for faster transmission speed, the SFP+ (or SFP10) was introduced in 2006, as an extension of the SFP connector. Based on IEEE802.3ae, SFF-8431, and SFF-8432 protocol specifications, the SFP+ is designed to support data rates up to 10Gb/s. Compared with its predecessor SFP, the newly SFP+ can support Fibre Channel, 10GbE, SONET, OTN, and other communication standards. The SFP+ is similar in size to the SFP connector. And the primary difference between an SFP and a SFP+ is their transmission speed. It is noticeable that SFP/SFP+ are both copper and optical.

SFP28

SFP28 Connector–The Third Generation of SFP Connector

As the third generation of SFP interconnect systems, the SFP28 (Small Form-Factor Pluggable 28) is designed for 25G performance specified by the IEEE 802.3by. The SFP28 connector delivers increased bandwidth, superior impedance control with less crosstalk compared to the SFP10. SFP28 can be sorted into SFP28 SFP-25G-SR and SFP-25G-LR. The former is designed to transfer data over short distance (up to 100m over MMF) while the latter is suitable for long distance transmission (up to 10 km over SMF). Utilizing 25GbE SFP28 leads to a single-lane connection similar to existing 10GbE technology, however it can deliver 2.5 times more data, which enables network bandwidth to be cost-effectively scaled in support of next-generation server and storage solutions.

Are the SFP, SFP+ and SFP28 Products Backward Compatible?

In most cases the connector and cable assembly are all backward compatible – an SFP+ connector is a direct replacement for an SFP connector to ensure simple upgrade to customer systems. As these are standard products, the cable assembly will also be compatible between the systems – an SFP copper cable assembly can be inserted to an SFP+ cage and mate with a SFP+ connector on the board.

Then how about the new SFP28 product? Since transceivers with various SFP connector types have become an important constituent of data communication network, compatibility issue of SFP28 and SFP+ is controversial among many subscribers. Here is a typical topic from Reddit, and it says like “For a project we’re looking to purchase some nexus 93180YC-EX ToRs for 25Gb+ down to the compute nodes. Cisco states that the downlink 25Gb ports are also 10Gb capable, but one can only really assume that means that the port is compatible with SFP+ optics too. Cisco’s SFP+ compatibility matrix appears to support that claim, however just curious if any of you have any SFP28 experience yet to confirm?”

The answer is definitely “yes”. SFP28 adopts the same form factor as SFP+, just running at 25 Gb/s instead of 10Gb/s, which offers better performance and higher speed. Besides, the pinouts of SFP28 and SFP+ connectors are mating compatible. Therefore, SFP28 connector is backwards compatible with SFP+ ports. That is to say, an SFP28 can be plugged into an SFP+ port and vice versa, but plugging an SFP+ into an SFP28 port would not get you 25Gb/s data rates.

Conclusion

SFP28 vs SFP+ vs SFP connector? Have you made clear which one to choose? Whether choosing SFP or SFP+ depends on your switch types. If your switch port only supports 1G, you can only choose the 1000BASE SFP (eg.MGBSX1). If it is a 10G switch, it depends on the speed and distance you require. When choosing between SFP28 and SFP+, it all depends on the transmission data rates you need. The SFP28 aims to build 25GbE networks that enables equipment designers to significantly reduce the required number of switches and cables. Thus when considering reduced facility costs related to space, power and cooling, the SFP28 would be the optimal choice for you.

Related articles: FS.COM QSFP28 Optical Modules Solution

                             SFP Compatibility Guide and How to Use a Compatible SFP Module?