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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

400G ZR & ZR+ – New Generation of Solutions for Longer-reach Optical Communications

400G

400G ZR and ZR+ coherent pluggable optics have become new solutions for high-density networks with data rates from 100G to 400G featuring low power and small space. Let’s see how the latest generation of 400G ZR and 400G ZR+ optics extends the economic benefits to meet the requirements of network operators, maximizes fiber utilization, and reduces the cost of data transport.

400G ZR & ZR+: Definitions

What Is 400G ZR?

400G ZR coherent optical modules are compliant with the OIF-400ZR standard, ensuring industry-wide interoperability. They provide 400Gbps of optical bandwidth over a single optical wavelength using DWDM (dense wavelength division multiplexing) and higher-order modulation such as 16 QAM. Implemented predominantly in the QSFP-DD form factor, 400G ZR will serve the specific requirement for massively parallel data center interconnect of 400GbE with distances of 80-120km. To learn more about 400G transceivers: How Many 400G Transceiver Types Are in the Market?

Overview of 400G ZR+

ZR+ is a range of coherent pluggable solutions with line capacities up to 400Gbps and reaches well beyond 80km supporting various application requirements. The specific operational and performance requirements of different applications will determine what types of 400G ZR+ coherent plugs will be used in networks. Some applications will take advantage of interoperable, multi-vendor ecosystems defined by standards body or MSA specifications and others will rely on the maximum performance achievable in the constraints of a pluggable module package. Four categories of 400G ZR+ applications will be explained in the following part.

400G ZR & ZR+: Applications

400G ZR – Application Scenario

The arrival of 400G ZR modules has ushered in a new era of DWDM technology marked by open, standards based, and pluggable DWDM optics, enabling true IP-over-DWDM. 400G ZR is often applied for point-to-point DCI (up to 80km), making the task of interconnecting data centers as simple as connecting switches inside a data center (as shown below).

Figure 1: 400G ZR Applied in Single-span DCI

Four Primary Deployment Applications for 400G ZR+

Extended-reach P2P Packet

One definition of ZR+ is a straightforward extension of 400G ZR transcoded mappings of Ethernet with a higher performance FEC to support longer reaches. In this case, 400G ZR+ modules are narrowly defined as supporting a single-carrier 400Gbps optical line rate and transporting 400GbE, 2x 200GbE or 4x 100GbE client signals for point-to-point reaches (up to around 500km). This solution is specifically dedicated to packet transport applications and destined for router platforms.

Multi-span Metro OTN

Another definition of ZR+ is the inclusion of support for OTN, such as client mapping and multiplexing into FlexO interfaces. This coherent pluggable solution is intended to support the additional requirements of OTN networks, carry both Ethernet and OTN clients, and address transport in multi-span ROADM networks. This category of 400G ZR+ is required where demarcation is important to operators, and is destined primarily for multi-span metro ROADM networks.

Figure 2: 400G ZR+ Applied in Multi-span Metro OTN

Multi-span Metro Packet

The third definition of ZR+ is support for extended reach Ethernet or packet transcoded solution that is further optimized for critical performance such as latency. This 400G ZR+ coherent pluggable with high performance FEC and sophisticated coding algorithms supports the longest reach over 1000km multi-span metro packet transport.

Figure 3: 400G ZR+ Applied in Multi-span Metro Packet

Multi-span Metro Regional OTN

The fourth definition of ZR+ supports both Ethernet and OTN clients. This coherent pluggable also leverages high performance FEC and PCS, along with tunable optical filters and amplifiers for maximum reach. It supports a rich feature set of OTN network functions for deployment over both fixed and flex-grid line systems. This category of 400G ZR+ provides solutions with higher performance to address a much wider range of metro/regional packet networking requirements.

400G ZR & ZR+: What Makes Them Suitable for Longer-reach Transmission in Data Center?

Coherent Technology Adopted by 400G ZR & ZR+

Coherent technology uses the three degrees of freedom (amplitude, phase and polarization of light) to focus more data on the wave that is being transmitted. In this way, coherent optics can transport more data over a single fiber for greater distances using higher order modulation techniques, which results in better spectral efficiency. 400G ZR and ZR+ is a leap forward in the application of coherent technology. With higher-order modulation and DWDM unlocking high bandwidth, 400G ZR and ZR+ modules can reduce cost and complexity for high-level data center interconnects.

Importance of 400G ZR & ZR+

400G ZR and 400G ZR+ coherent pluggable optics take implementation challenges to the next level by adding some of the elements for high-performance solutions while pushing component design for low-power, pluggability, and modularity.

Conclusion

Although there are still many challenges to making 400G ZR and 400G ZR+ transceiver modules that fit into the small size and power budget of OSFP or QSFP-DD packages and also achieving interoperation as well the costs and volume targets. With 400Gbps high optical bandwidth and low power consumption, 400G ZR & ZR+ may very well be the new generation in longer-reach optical communications.

Original Source: 400G ZR & ZR+ – New Generation of Solutions for Longer-reach Optical Communications