400G Transceiver Test – How Does It Ensure the Quality of Optical Modules?

Posted on June 27, 2022 by Admin
400G

Higher bandwidth requirements are enhancing the need for 400G optical modules in the large data center interconnections. And a series of tests is significant to ensure the high quality of the 400G transceivers. This article will introduce the 400G transceiver test from three aspects: challenges, key items, and opportunities.

Challenges of 400G Transceiver Test

The electrical interfaces of 400G transceivers use either 16× 28Gb/s with NRZ (non-return to zero) modulation or the newer 4 or 8× 56Gb/s with PAM4 (4-level pulse amplitude) modulation. Higher speeds and the utilization of PAM4 do bring great improvements but also result in high complexity at the physical layer, causing signal transmission errors easily and bringing challenges for optical module vendors.

High Complexity at the Physical Layer

On the physical appearance layer, the high-speed interfaces of 400G optical modules include more electrical input/output interfaces, optical input/output interfaces, and other power and low-speed management interfaces. And all the performance of these interfaces should be made to a complaint of 400G standards. As the size of 400G transceivers is similar to the existing 100G transceivers, the integration of those interfaces needs more sophisticated manufacturing technology.

Signal Transmission Errors

The higher lane speed in 400G electrical interfaces means more noise (also called signal-to-noise ratio) in signal transmission, causing an increased bit error rate (BER), which in turn affects the signal quality. Therefore, corresponding performance tests should be taken to ensure the quality of 400G modules.

Development & Manufacturing Test Costs

The complex 400G transceiver test also brings new challenges for the optical module vendors. To ensure the transceiver quality for users, vendors have to attach great importance to the transceiver test equipment and R&D technical. They should ensure that the new products can support 400G upgrade while dampening associated development and manufacturing test costs that may hamper competitive pricing models.

Key Items in 400G Transceiver Test

For transceiver vendors, product quality testing is fundamental to building reliable connections with customers. Let’s have a look at the key items in the 400G transceiver test. For more detailed information, please visit the 400G QSFP-DD Transceivers Test Program.

ER Performance and Optical Power Level Tests

ER (extinction ratio), the optical power logarithms ratio when the laser outputs the high level and low level after electric signals are modulated to optical signals, is an important and the most difficult indicator to measure the performance of 400G optical transceivers. The ER test can show whether a laser works at the best bias point and within the optimal modulation efficiency range. OMA (outer optical modulation amplitude) can measure the power differences when the transceiver laser turns on and off, testing 400G transceivers’ performance in another aspect. Both the ER and the average power can be measured by mainstream optical oscilloscopes.

Optical Spectrum Test

The optical spectrum test is mainly divided into three parts: center wavelength, side mode suppression ratio (SMSR), and spectrum width of the 400G transceivers. All of these three parameters are essential for keeping a high-quality transmission and performance of the modules. The larger the value of the side mode suppression ratio, the better the performance of the laser of the module. Watch the following video to see how FS tests the optical spectrum for 400G QSFP-DD transceivers.https://www.youtube.com/embed/xMwbi85Hlig?rel=0&showinfo=0&enablejsapi=1&origin=https%3A%2F%2Fcommunity.fs.com

Forwarding Performance Tests

400G transceiver has a more complicated integration compared with the existing QSFP28 and QSFP+ modules, which puts higher requirements for the test of its forwarding performance. RFC 2544 defines the following baseline performance test indicator for networks and devices: throughput, delay, and packet loss rate. In this test procedure, the electrical and optical interfaces will be tested and make sure the signal quality they transmitted and received will not get distortion.

Eye Diagram Test

Different from the single eye diagram of NRZ modulation in 100G optical transceivers, the PAM4 eye diagram has three eyes. And PAM4 doubles the bit bearing efficiency compared with NRZ, but it still has noise, linearity, and sensitivity problems. IEEE proposes using PRBS13Q to test the PAM4 optical eye diagram. The main test indicators are eye height and width. By checking the eye height and width in the test result, users can tell if the signal linearity quality of the 400G transceiver is good or not.

Comparison of waveforms and eye diagrams between NRZ and PAM4 signals.png

The following video shows how FS tests 400G QSFP-DD-SR8 transceivers’ eye pattern with Anritsu MP2110A All-in-One BERT and Sampling Oscilloscope to ensure the QSFP-DD transceivers’ signal quality.https://www.youtube.com/embed/DlfMLDy6VmY?rel=0&showinfo=0&enablejsapi=1&origin=https%3A%2F%2Fcommunity.fs.com

Jitter Test

The jitter test is mainly designed for the output jitter of transmitters and jitter tolerance of receivers. The jitter includes random jitter and deterministic jitter. Because deterministic jitter is predictable when compared to random jitter, you can design your transmitter and receiver to eliminate it. In a real test environment, the jitter test is operated together with the eye diagram test to check the 400G transmitter and receiver performance.

Bit Error Rate Test in Real Working Condition

In this testing procedure, 400G optical transceivers will be plugged into the 400G switches to test their working performance, BER, and error tolerance ability in a real environment. As mentioned above, the higher BER in 400G optical transceiver lanes leads to transmission problems in most 400G links. Therefore, FEC (forward error correction) technology is applied to improve signal transmission quality. FEC provides a way to send and receive data in extremely noisy signaling environments, making error-free data transmissions in 400G link as possible. How FS tests the BER of 400G QSFP-DD modules is displayed in the following video to ensure the stability and reliability of the transmission.https://www.youtube.com/embed/KJ7eWECtZ54?rel=0&showinfo=0&enablejsapi=1&origin=https%3A%2F%2Fcommunity.fs.com

Temperature Test

Each 400G transceiver module comes with a vendor-defined operating temperature range. If the temperature exceeds or beyond the normal temperature range, then the modules will fail to perform well or even won’t operate normally, and even lead to delays or network breakdowns. So the temperature test is also essential for the transmission performance of transceivers. This is to guarantee the reliability of these high-speed 400G transceivers used within the high-speed communication network and data centers. The video below shows how FS tests its 400G QSFP-DD modules at different temperatures.https://www.youtube.com/embed/CgwfapEcU2o?rel=0&showinfo=0&enablejsapi=1&origin=https%3A%2F%2Fcommunity.fs.com

Opportunities in 400G Transceiver Test

Driven by 5G, artificial intelligence (AI), virtual reality (VR), Internet of Things (IoT), and autonomous vehicles, though multiple technical transceiver test issues are needed to be resolved, the booming trend of the 400G Ethernet market cannot stop. Lots of manufacturers and test solution providers have promoted their own 400G product solutions to the market. Under this situation, for some smaller optical module vendors, the 400G transceiver test is one of the key points they should consider, because how to improve the quality of the 400G products and supply speed will determine how much profit they get from the 400G market. Know more about What’s the Current and Future Trend of 400G Ethernet? to prepare for the coming fast-speed era.

Original Source: 400G Transceiver Test – How Does It Ensure the Quality of Optical Modules?

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100G NIC: An Irresistible Trend in Next-Generation 400G Data Center

Posted on June 27, 2022 by Admin

NIC, short for network interface card, which can be called network interface controller, network adapter or LAN adapter, allows a networking device to communicate with other networking devices. Without NIC, networking can hardly be done. There are NICs with different types and speeds, such as wireless and wired NIC, from 10G to 100G. Among them, 100G NIC, as a product appearing in recent years, hasn’t taken a large market share yet. This post gives a description of 100G NIC and the trends in NIC as follows.

What Is 100G NIC?

NIC is installed on a computer and used for communicating over a network with another computer, server or other network devices. It comes in many different forms but there are two main different types of NIC: wired NIC and wireless NIC. Wireless NICs use wireless technologies to access the network, while wired NICs use DAC cable or transceiver and fiber patch cable. The most popular wired LAN technology is Ethernet. In terms of its application field, it can be divided into computer NIC card and server NIC card. For client computers, one NIC is needed in most cases. However, for servers, it makes sense to use more than one NIC to meet the demand for handling more network traffic. Generally, one NIC has one network interface, but there are still some server NICs that have two or more interfaces built in a single card.

100G NIC

Figure 1: FS 100G NIC

With the expanding of data center from 10G to 100G, 25G server NIC has gained a firm foothold in the NIC market. In the meantime, the growth in demand for bandwidth is driving data center to higher bandwidth, 200G/400G and 100G transceivers have been widespread, which paves the way for 100G server.

How to Select 100G NIC?

How to choose the best 100G NIC from all the vendors? If you are stuck in this puzzle, see the following section listing recommendations and considerations to consider.

Connector

Connector types like RJ45, LC, FC, SC are commonly used connectors on NIC. You should check the connector type supported by NIC. Today many networks are only using RJ45, so it may be not that hard to choose the NIC for the right connector type as it has been in the past. Even so, some network may utilize a different interface such as coax. Therefore, check if the card you are planning to buy supports this connection before purchasing.

Bus Type

PCI is a hardware bus used for adding internal components to the computer. There are three main PCI bus types used by servers and workstations now: PCI, PCI-X and PCI-E. Among them, PCI is the most conventional one. It has a fixed width of 32 bits and can handle only 5 devices at a time. PCI-X is a higher upgraded version, providing more bandwidth. With the emergence of PCI-E, PCI-X cards are gradually replaced. PCI-E is a serial connection so that devices no longer share bandwidth like they do on a normal bus. Besides, there are different physical sizes of PCI-E card in the market: x16, x8, x4, and x1. Before purchasing a 100G NIC, it is necessary to make sure which PCI version and slot width can be compatible with your current equipment and network environment.

Hot swappable

There are some NICs that can be installed and removed without shutting down the system, which helps minimize downtime by allowing faulty devices to be replaced immediately. While you are choosing your 100G NIC, be sure to check if it supports hot swapping.

Trends in NIC

NICs were commonly used in desktop computers in the 1990s and early 2000s. Up to now, it has been widely used in servers and workstations with different types and rates. With the popularization of wireless networking and WiFi, wireless NICs gradually grows in popularity. However, wired cards are still popular for relatively immobile network devices owing to the reliable connections.NICs have been upgrading for years. As data centers are expanding at an unprecedented pace and driving the need for higher bandwidth between the server and switches, networking is moving from 10G to 25G and even 100G. Companies like Intel and Mellanox have launched their 100G NIC in succession.

During the upgrading from 10G to 100G in data centers, 25G server connectivity popularized for 100G migration can be realized by 4 strands of 25G. 25G NIC is still the mainstream. However, considering the fact that the overall bandwidth for data centers grows quickly and hardware upgrade cycles for data centers occur every two years, the ethernet speed can be faster than we expect. 400G data center is just on the horizon. It stands a good chance that 100G NIC will play an integral role in next-generation 400G networking.

Meanwhile, the need of 100G NIC will drive the demand for other network devices as well. For instance, 100G transceiver, the device between NIC and network, is bound to pervade. Now 100G transceivers are provided by many brands with different types such as CXP, CFP, QSFP28 transceivers,etc. FS supplies a full series of compatible 100G QSFP28 and CFP transceivers that can be matched with the major brand of 100G Ethernet NIC, such as Mellanox and Intel.

Conclusion

Nowadays with the hyping of the next generation cellular technology, 5G, the higher bandwidth is needed for data flow, which paves the way for 100G NIC. On the occasion, 100G transceivers and 400G network switches will be in great need. We believe that the new era of 5G networks will see the popularization of 100G NIC and change towards a new era of network performance.

Article Source: 100G NIC: An Irresistible Trend in Next-Generation 400G Data Center

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400G QSFP Transceiver Types and Fiber Connections

How Many 400G Transceiver Types Are in the Market?

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What’s the Current and Future Trend of 400G Ethernet?

Posted on June 27, 2022 by Admin
400G

According to the leading Cloud Service Providers (CSPs) and various networking forecast reports, 400G Ethernet will emerge as the leading technology since 2020. IDC (International Data Corporation) and Cignal Ai have also proved the similar situation. In short, 400G Ethernet will replace 100G and 200G deployments in a faster way than 100G did to the previous Ethernet.

New Technology Adoption Rates.jpg
Faster 400G Ethernet Trend Than Previous Ethernet.jpg

The Rise of 400G Ethernet

The factors affecting the development of 400G are mainly application-driven and technology-driven. The application drivers include 5G high-speed transmission, market requirements for data centers, cloud computing, and high-definition video transmission. Technology drivers include development of technologies in the market and product standardization.

Application-Driven Factors

  • 5G Accelerates 400G Ethernet: An analysis from Cisco points out that 5G technology needs edge computing architecture, which brings cloud resources—compute, storage and networking—closer to applications, devices and users. While, the edge computing needs more bandwidth, support for more devices on the network, and greater security to protect and manage the data. For example, a 4G radio system can support up to only 2,000 active devices in a square kilometer, while 5G could support up to 100,000 active devices in the same range. With 400G technology offering more bandwidth, more devices and applications could be supported in 5G.
ITEMS4G LTE5G
Average Data Rate25 Mb/s100 Mb/s
Peak Data Rate150 Mb/s10,000 Mb/s
Latency50 ms1 ms
Connection Density2,000 Per Square Kilometer100,000 Per Square Kilometer
  • Data Center & Cloud Computing Requirements: A research from Cisco indicates that cloud-based data centers will take over 92% of the next-generation data center workload while the traditional data centers will take over less than 8% after 2021. These objective requirements for higher data rates drive 400G development greatly. It is estimated that 400G will be the prevailing speed in switch chips and network platforms in the coming years.
  • High-Definition Video Transmission Needs: Basically all forms of Internet applications are moving towards video. It is estimated that more than 80% of the traffic is video. Video is a very important platform for everyone to interact in the future, especially real-time video streaming, such as multi-party video conferences. High-definition videos (such as 4K videos) need more bandwidth and less latency compared with the previous normal ones featuring lower definition.

Technology-Driven Factors

400G technology was originally known as IEEE 802.3bs and was officially approved in December,  2017. It regulates new standards including Forward Error Correction (FEC) to improve error performance. Abide by these standards, early 400G network elements have successfully completed trials and initial deployment. At present, some brand 400G switches have been put into use such as Cisco 400G Nexus, Arista 400G 7060X4 Series, Mellanox Spectrum-2, FS 400G switch, etc. 400G connection scheme is also blooming such as 400G DAC and 400G transceivers (400G QSFP-DD transceiver, 400G OSFP transceiver, 400G CFP8 transceiver, etc.), of which 400G QSFP-DD is becoming the leading form factor for its high density and low power consumption. As 400G Ethernet grows faster to standardization, commercialization and scale, soon 400G product system will be gradually perfect and more 400G products will appear in return.

Influences of 400G Ethernet

400G Optics Promotes 25G and 100G Markets While Reduces 200G Market Share

Compared to the 10G Ethernet, 25G Ethernet gains more popularity in the whole optical transmission industry because 25Gbps and 50Gbps per channel technology provide the basic standards for existing 100G (4x 25Gbps), the coming 400G (8x 50Gbps) and the future 800G network. Therefore, the rapid development of 400G Ethernet will promote the 25G and 100G markets to a certain extent in turn. Similarly, the quick appearance of 400G applications implicates that 200G is a flash in the pan.

400G Technology Is Expected to Reduce Overall Network Operation and Maintenance Costs

  • For access, metro, and data center interconnection scenarios, where short transmission distance and higher bandwidth are required, fiber resources are relatively scarce. The single-carrier 400G technology can provide the largest transmission bandwidth and the highest spectral efficiency with the simplest configuration, which effectively reduces transmission costs.
  • In the backbone and some more complex metropolitan area networks, where the transmission distance is longer with more network nodes, the requirements for transmission performance are more stringent. Under such circumstances, dual-carrier technology (2x 200G) and an optimized algorithm could work together to compress the channel spacing. This can not only improve the spectral efficiency by 30% (close to the level of a single-carrier 400G technology), but also extend the transmission distance of 400G Ethernet to several thousand kilometers, helping operators quickly deploy 400G backbone networks with minimum bandwidth resources.
  • 400G solution can also increase the single fiber capacity by 40% and reduce power consumption by 40%, thereby greatly improving network performance and reducing network operation and maintenance costs.

Opportunities for 400G Ethernet Vendors and Users

Many suppliers hype their 400G products to get ahead of the curve. Actually, few vendors have the real supply capacity and the quality of most 400G products supplied can’t be assured. To win from the fierce market competition, vendors should pay more attention to improving product quality and strong supply capability. And this is indubitably beneficial to users, who can get better products and services with relatively lower prices.

Impact of 400G Optics on Cabling and Connectivity

In the multimode installed base, the biggest difference between 100G and 400G modules is the increase in total number of fibers. For single mode transmission system, most of the duplex LC and MPO-based architecture that is deployed at 100G should serve for 400G. For parallel or multi-fiber transmission, transceivers like 400GBASE-SR4.2 operating with short wavelength division multiplexing (SWDM) at four wavelengths provide longer distances over OM5 fiber than OM4 or OM3. And OM5 wideband multimode fiber (WBMMF) will allow use of SWDM technology to transmit multiple signals (wavelengths) on one fiber. This indicates that OM5 fiber and SWDM technologies will continue to offer improved support on 400G Ethernet.

Are You Ready for 400G Ethernet?

400G Ethernet is an inevitable trend in current networking market. Driven by various market demands and technologies, it has come more rapidly than any previous technology. And it also has many significant effects, such as reducing the market share of 200G and saving transmission costs to a certain extent. There are already some mature 400G optics products in the market, such as 400G QSFP-DD transceivers, 400G DACs, as well as 400G DAC breakout cables. And 400G technology is no doubt going to be more and more advanced to promote the developments of 400G Ethernet and 400G applications.

Original Source: What’s the Current and Future Trend of 400G Ethernet?

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How FS 400G MTP/MPO Cables Enable Efficient Connectivity

Posted on June 27, 2022 by Admin
400G

The demand for 400G transmission rates by major data centers and telecom carrier continues to grow and cabling solutions are constantly being updated. In order to achieve 400G data rates and save cabling costs, breakthroughs, higher connection density, and simplified network design approaches must be considered, so 400G MTP/MPO cables are becoming more and more common. FS offers MTP/MPO cabling solutions to meet the needs of high-performance 400G networks. This article will describe specific cabling application scenarios.

A Glance at FS 400G MTP/MPO Cables and Transceivers

MTP/MPO cables with multi-core connector are used for optical transceiver connection. There are 4 different types of application scenarios for 400G MTP/MPO cables.

Common MTP/MPO patch cables include 8-fiber, 12-core, and 16-core. 8-core or 12-core MTP/MPO single-mode fiber patch cable is usually used to complete the direct connection of two 400G-DR4 optical transceivers. 16-core MTP/MPO fiber patch cable can be used to connect 400G-SR8 optical transceivers to 200G QSFP56 SR4 optical transceivers, and can also be used to connect 400G-8x50G to 400G-4x100G transceivers. The 8-core MTP to 4-core LC duplex fiber patch cable is used to connect the 400G-DR4 optical transceiver with a 100G-DR optical transceiver.

SR8-vs-DR4-vs-DR8.jpg

Figure 1: SR8-vs-DR4-vs-DR8

FS 400G MTP/MPO Cabling Solutions for Typical 400G Network Applications

As the network upgrades and data centers migrate to 400G rates, how to transition from existing 50G/100G/200G devices to 400G, here are FS MTP/MPO cabling solutions.

400G-400G Direct Connection

500m span with 8-fiber/12-fiber MTP/MPO cable

400G short and medium distance direct connection usually consists of 8-core/12-core MTP patch cable with 400G-DR4 OSFP/QSFP-DD modules. The term “DR4″—”DR” stands for 500m reach using single-mode fiber and “4” implies there are 4 x 100 Gbps optical channels. Since one optical channel requires two fibers, an 8-fiber or a 12-core MTP/MPO cable can be used for the 400G-DR4 module to achieve direct connection. In the 8-fiber MTP cabling, the fiber utilization is 100%, while in the 12-core MTP cabling, four fibers remain unused. Take 400G QSFP-DD module as an example, the following picture is presenting the MTP cabling for 400G DR4 direct connection.

400G-400G Direct Connection Scenario 1.jpg

Figure 2: 400G-400G Direct Connection Scenario 1

PRODUCTSDESCRIPTION
400G DR4 QSFP-DDGeneric Compatible 400G DR4 QSFP-DD PAM4 1310nm 500m DOM Transceiver Module
MTP®-12 (Female) 12 Fibers OS2 Single ModeOS2 Single Mode Elite Trunk Cable, 12 Fibers, Type B, Plenum (OFNP)

100m span with 16-fiber MTP/MPO cable

The 400G-SR8 transceivers require the use of a 16-core MTP cable. The term “SR8” – “SR” stands for a distance of 100 meters using multimode fiber, and “8” implies there exist 8 optical channels with each operating at 50Gbps. In this direct connection, the 16-core MTP cable has 100% fiber utilization. The primary adopters of these 400G-SR8 fiber transceivers are expected to be certain hyperscale cloud service providers in North America and China.

400G-400G Direct Connection Scenario 2.jpg

Figure 3: 400G-400G Direct Connection Scenario 2

PRODUCTSDESCRIPTION
400GBASE-SR8 QSFP-DDGeneric Compatible 400GBASE-SR8 QSFP-DD PAM4 850nm 100m DOM Transceiver Module
MTP®-16 APC (Female) OM4 CableOM4 Multimode Elite Trunk Cable, 16 Fibers, Plenum (OFNP), Magenta, 850/1300nm

400G-2x200G Direct Connection

100m span with 16-fiber MTP conversion cable

In the backbone and some more complex metropolitan area networks, the dual-carrier technology (2x200G) will be adopted to compress the channel spacing compared to a single-carrier 400G technology. Extending the transmission distance and improving the spectral efficiency, 400G-2x200G direct connection can help to deploy 400G backbone networks with minimum bandwidth resources.

In this case, 16-core MTP conversion cables terminated with MTP/MPO connectors on both ends are needed. With this type of cable, one 400G OFSP/QSFP-DD module and two 200G QSFP56 modules can be directly connected.

400G-2x200G Direct Connection Scenario.jpg

Figure 4: 400G-2x200G Direct Connection Scenario 3

PRODUCTSDESCRIPTION
400GBASE-SR8 QSFP-DDGeneric Compatible 400GBASE-SR8 QSFP-DD PAM4 850nm 100m DOM Transceiver Module
200GBASE-SR4 QSFP56FS for Mellanox MMA1T00-VS Compatible 200GBASE-SR4 QSFP56 850nm 100m DOM Transceiver Module
MTP®-16 APC (Female) OM4 CableOM4 Multimode Elite Trunk Cable, 16 Fibers, Plenum (OFNP), Magenta, 850/1300nm

400G-4x100G Direct Connection

500m span with 8-fiber MTP/MPO trunk cable and 4-LC duplex patch cable

In the 400G to 4x100G migration scenario, an 8-core MTP-LC cassette that packaged in the fiber rackmount enclosure is adopted to realize the transmission from MTP to LC, and then an 8-core MTP/MPO trunk and 4-LC duplex patch cables are used to connect at both ports.

The 400G-4x100G architecture uses four optical modules with 100Gbps wavelengths. However, the current 100G technology is based on a 4x25G design and unable to scale to 400G. 100Gbps per channel can be achieved using PAM4 technology and then aggregated to achieve an overall 400Gbps speed with 4x100G. MTP/MPO cables allow splitting 400G bandwidth into multiple 100G or 40G data streams.

400G-4x100G Direct Connection Scenario.jpg

Figure 5: 400G-4x100G Direct Connection Scenario 4

PRODUCTSDESCRIPTION
400G DR4 QSFP-DDGeneric Compatible 400G DR4 QSFP-DD PAM4 1310nm 500m DOM Transceiver Module
100GBASE-DR QSFP28 Single LambdaGeneric Compatible 100GBASE-DR QSFP28 Single Lambda 1310nm 500m DOM Transceiver Module
MTP® Female to 4 LC UPC Duplex 8 FibersMTP Type B Plenum (OFNP) OS2 9/125 Single Mode Elite Breakout Cable 1310/1550nm
FHD MTP®-8 Cassette to 4x LC Duplex (Blue)8 Fibers OS2 Single Mode, Universal Polarity, MTP® to 4x LC Duplex (Blue), 0.35dB max
Customized 8-144 Fibers MTP®-12OS2 Single Mode Elite Breakout Cable
FHD 144 Fibers (LC) EnclosureFHD High Density 1U Rack Mount Enclosure Unloaded, Tool-less Removable Top Cover, Holds up to 4x FHD Cassettes or Panels

400G-8x50G Direct Connection

500m span with 16-fiber MTP conversion cable and LC duplex patch cable

The rapid growth of 400G has contributed in part to the less popular 50G market, and MTP/MPO cables provide the technology to scale 50GbE to accommodate 400G (8x50G) network. For this scenario example, the MTP cassette is in the middle to connect the 16-core MTP conversion cable and the LC duplex patch cords together to realize the 400G-8x50G direct connection. Eight 50G lanes can support the optical link of 40Gbps aggregation via PAN modulation.

400G-8x50G Direct Connection Scenario.jpg

Figure 6: 400G-8x50G Direct Connection Scenario 5

PRODUCTSDESCRIPTION
400G DR4 QSFP-DDGeneric Compatible 400G DR4 QSFP-DD PAM4 1310nm 500m DOM Transceiver Module
MTP®-16 APC (Female) OM4 CableOM4 Multimode Elite Trunk Cable, 16 Fibers, Plenum (OFNP), Magenta, 850/1300nm
FHD MTP®-24 Cassette to 12x LC Duplex (Aqua)24 Fibers OM4 Multimode, Type A, MTP® to 12x LC Duplex (Aqua), 0.35dB max
MTP®-16 APC (Female) to 8 LC UPC Duplex CableOM4 Multimode Elite Breakout Cable, 16 Fibers, Plenum (OFNP), Magenta,850/1300nm
FHD 144 Fibers (LC) EnclosureFHD High Density 1U Rack Mount Enclosure Unloaded, Tool-less Removable Top Cover, Holds up to 4x FHD Cassettes or Panels

Scaling to FS 400G MTP/MPO Cabling System for 400G Networks

400G is increasingly becoming ubiquitous in many high-performance and high-density networking environments. 400G MTP/MPO cables have been widely used as cabling solutions for 400G network transmission rates due to their unique cabling simplicity and cost reduction benefits. FS offers a wide range of related 400G MTP/MPO cabling products and solutions to smoothly achieve high-speed data transmission.

Original Source: How FS 400G MTP/MPO Cables Enable Efficient Connectivity

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NRZ vs. PAM4 Modulation Techniques

Posted on June 27, 2022 by Admin

The leading trends such as cloud computing and big data drive the exponential traffic growth and the rise of 400G Ethernet. Data center networks are facing a larger bandwidth demand, and innovative technologies are required for infrastructure to meet shifting demands. Currently, there are two different signal modulation techniques examined for next-generation Ethernet: non-return to zero (NRZ), and pulse-amplitude modulation 4-level (PAM4). This article will take you through these two modulation techniques and compare them to find the optimal choice for 400G Ethernet.

NRZ and PAM4 Basics

NRZ is a modulation technique using two signal levels to represent the 1/0 information of a digital logic signal. Logic 0 is a negative voltage, and Logic 1 is a positive voltage. One bit of logic information can be transmitted or received within each clock period. The baud rate, or the speed at which a symbol can change, equals the bit rate for NRZ signals.

NRZ
NRZ

PAM4 is a technology that uses four different signal levels for signal transmission and each symbol period represents 2 bits of logic information (0, 1, 2, 3). To achieve that, the waveform has 4 different levels, carrying 2 bits: 00, 01, 10 or 11, as shown below. With two bits per symbol, the baud rate is half the bit rate.

PAM4
PAM4

Comparison of NRZ vs. PAM4

Bit Rate

A transmission with NRZ mechanism will have the same baud rate and bitrate because one symbol can carry one bit. 28Gbps (gigabit per second) bitrate is equivalent to 28GBdps (gigabaud per second) baud rate. While, because PAM4 carries 2 bits per symbol, 56Gbps PAM4 will have a line transmission at 28GBdps. Therefore, PAM4 doubles the bit rate for a given baud rate over NRZ, bringing higher efficiency for high-speed optical transmission such as 400G. To be more specific, a 400 Gbps Ethernet interface can be realized with eight lanes at 50Gbps or four lanes at 100Gbps using PAM4 modulation.

Signal Loss

PAM4 allows twice as much information to be transmitted per symbol cycle as NRZ. Therefore, at the same bitrate, PAM4 only has half the baud rate, also called symbol rate, of the NRZ signal, so the signal loss caused by the transmission channel in PAM4 signaling is greatly reduced. This key advantage of PAM4 allows the use of existing channels and interconnects at higher bit rates without doubling the baud rate and increasing the channel loss.

Signal-to-noise Ratio (SNR) and Bit Error Rate (BER)

According to the following figure, the eye height for PAM4 is 1/3 of that for NRZ, causing the PAM4 to increase SNR (Signal-Noise Ratio) by -9.54 dB (Link Budget Penalty), which impacts the signal quality and introduces additional constraints in high-speed signaling. The 33% smaller vertical eye opening makes PAM4 signaling more sensitive to noise, resulting in a higher bit error rate. However, PAM4 was made possible because of forward-error correction (FEC) that can help link system to achieve the desired BER.

NRZ vs. PAM4
NRZ vs. PAM4

Power Consumption

Reducing BER in a PAM4 channel requires equalization at the Rx end and pre-compensation at the Tx end, which both consume extra power than the NRZ link for a given clock rate. This means PAM4 transceivers generate more heat at each end of the link. However, the new state-of-the-art silicon photonics (SiPh) platform can effectively reduce energy consumption and can be used in 400G transceivers. For example, FS silicon photonics 400G transceiver combines SiPh chips and PAM4 signaling, making it a cost-effective and lower power consumption solution for 400G data center.

Shift from NRZ to PAM4 for 400G Ethernet

With massive data transmitted across the globe, many organizations pose their quest for migration towards 400G. Initially, 16× 25G baud rate NRZ is used for 400G Ethernet, such as 400G-SR16, but the link loss and size of the scheme can not meet the demands of 400G Ethernet. Whereas PAM4 enables higher bit rates at half the baud rate, designers can continue to use existing channels at potential 400G Ethernet data rates. As a result, PAM4 has overtaken NRZ as the preferred modulation method for electrical or optical signal transmission in 400G optical modules.

Article Source: NRZ vs. PAM4 Modulation Techniques

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