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.
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:
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 Range400G QSFP-DD SR8QSFP-DD MSA Compliant70m OM3/100m OM4MTP/MPO-16MMF0 to 70°C400G QSFP-DD DR4QSFP-DD MSA, IEEE 802.3bs500mMTP/MPO-12SMF0 to 70°C400G QSFP-DD XDR4/DR4+QSFP-DD MSA2kmMTP/MPO-12SMF0 to 70°C400G QSFP-DD FR4QSFP-DD MSA2kmLC DuplexSMF0 to 70°C400G QSFP-DD 2FR4QSFP-DD MSA, IEEE 802.3bs2kmCSSMF0 to 70°C400G QSFP-DD LR4QSFP-DD MSA Compliant10kmLC DuplexSMF0 to 70°C400G QSFP-DD LR8QSFP-DD MSA Compliant10kmLC DuplexSMF0 to 70°C400G QSFP-DD ER8QSFP-DD MSA Compliant40kmLC DuplexSMF0 to 70°C400G OSFP SR8IEEE P802.3cm; IEEE 802.3cd100mMTP/MPO-16MMF0 to 70°C400G OSFP DR4IEEE 802.3bs500mMTP/MPO-12SMF0 to 70°C4000G OSFP XDR4/DR4+/2kmMTP/MPO-12SMF0 to 70°C400G OSFP FR4100G lambda MSA2kmLC DuplexSMF0 to 70°C400G OSFP 2FR4IEEE 802.3bs2kmCSSMF0 to 70°C400G OSFP LR4100G lambda MSA10kmLC DuplexSMF0 to 70°C QSFP-DD CablesCatagoryProduct DescriptionReachTemperature RangePower Consumption400G QSFP-DD DACQSFP-DD to QSFP-DD DACwith each 400G QSFP-DD using 8x 50G PAM4 electrical lanesno more than 3m0 to 70°C<1.5W400G 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<0.1WQSFP-DD to 4x 100G QSFPs DACwith each 100G QSFPs using 2x 50G PAM4 electrical lanesno more than 3m0 to 70°C<0.1WQSFP-DD to 8x 50G SFP56 DACwith each 50G SFP56 using 1x 50G PAM4 electrical laneno more than 3m0 to 80°C<0.1W400G 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<10W400G 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<0.5W400G 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<9.5WQ5: 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:
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 OSFPCFP8Application ScenarioData centerData center & telecomTelecomSize18.35mm× 89.4mm× 8.5mm22.58mm× 107.8mm× 13mm40mm× 102mm× 9.5mmMax Power Consumption12W15W24WBackward Compatibility with QSFP28YesThrough adapterNoElectrical signaling (Gbps)8× 50GSwitch Port Density (1RU)363616Media TypeMMF & SMFHot PluggableYesThermal ManagementIndirectDirectIndirectSupport 800GNoYesNoFor 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).
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:
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
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