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Introduction to 10GbE/25GbE/40GbE/100GbE Fiber Optic Cabling

Introduction to 10GbE/25GbE/40GbE/100GbE Fiber Optic Cabling

Technology is changing rapidly. Just when you got used to Gigabit Ethernet speeds being a fast & reliable system, someone unveiled 10GbE, 25GbE, 40GbE or even 100GbE systems a few years later. The newer and higher performing iterations are indeed the great breakthrough for telecommunication industry, but also pose difficulty in choosing network migration path—10G to 40G to 100G, or to 25G to 50G to 100G. We have described 10G, 25G, 40G and 100G Ethernet technology before, now in this blog, we’d like to introduce the four fiber optic cabling, and compare two 100G migration paths.

Cost-effective 10GbE Fiber Optic Cabling

10 Gigabit Ethernet technology defined by IEEE 802.3ae-2002 standard, is matured nowadays. Just like the “old” Gigabit Ethernet, 10Gb network can be terminated with either copper or fiber cabling. 1000BASE-T standard usually uses the Cat5e cables as the transmission media, while 10GbE bandwidth requires high grade copper cables like Cat6/Cat6a/Cat7 cables to support 10Gbps data rate. For instance, 10G SFP+ 10GBASE-T transceiver modules utilize Ethernet copper cables (Cat6a/Cat7) for a link length of 30m. SFP+ direct attach cables (DAC) and active optical cables (AOC) are also regarded as the cost-effective solutions for 10G short-reach applications. Besides 10G copper cables, there are single-mode (OS2) and multimode fiber patch cables (OM3/OM4) applied to different 10GbE IEEE standards. For the detailed information about the 10G cabling options, please see the following table.

10G fiber optic cable

As to the 10G fiber optic transceivers, there are a series of optical form factors including the XENPAK, X2, XFP, SFP+. The former three 10GbE optical transceivers were released earlier than smaller 10G form factor—SFP+ module. However, owing to their larger footprint, they are not successful on the 10G hardware market. Furthermore, SFP+ optics, compliant with several IEEE standards (SR, LR, LRM, ER, ZR and 10GBASE-T…) wins the heart of 10G end-users.

Singe-lane Design Makes 25GbE Shine

When 25G Ethernet was developed to support a single-lane 25Gbps standard in 2014, it was treated as the “new” 10GbE technology but delivers 2.5 times more data. Compared to 40GbE that was based on 10GbE, 25GbE with one lane obviously improves the port density and cost requirement. 25GbE network can support both copper and fiber optic cables, seen in the below table.Similar to 10GbE networks, 25G Ethernet physical interface specification supports several 25Gbps capable form factors, including CFP/CFP2/CFP4, SFP28 (1×25 Gbps) and QSFP28 (4×25 Gbps), which is also used for 100GbE. SFP28 25GBASE-SR and 25GBASE-LR SFP28 are two popular 25GbE optical transceiver modules available on the market, the former supports up to 100m link length while the latter allows a maximum transmission distance of 10 km.

25G optical modules

The available optical switches of the market do not support direct 25GbE connections using an SFP28 direct attach copper (DAC) cable. It is recommended to use a breakout cable that allows four 25GbE ports to connect to a 100GbE QFSFP28 switch port. FS.COM SFP28 DAC cable lengths are limited to four meters (1m, 2m, 3m, 5m) for 25GbE. And if you prefer a longer length, the 25GbE active optic cable (AOC) solutions are good recommendations.

25G Optics SFP28 Type
All 25G SFP28 Ports 25GBASE-SR 50µm MMF / 70m
25GBASE-LR 9µm SMF / 10km
25GBASE-AOC Pre-terminated in 3, 5, 7, 10, 15, 20, 25, 30m lengths
25G Copper SFP28 Type Media/Reach
All 25G SFP28 Ports 25GBASE-CR Twinax / ‘Direct Attach’ Pre-terminated in 1m, 2m, 3m, 5m lengths


Fast & Reliable 40GbE Fiber Optic Cabling

Like the 10GbE fiber optic cabling, there are several IEEE standards of 40GbE transceiver in the whole evolution. 40G QSFP+ optical transceivers are the most commonly used optics for 40G network. So how to choose fiber optic cables for 40G optical transceivers? The following table will help you out.

40G modules

Besides the QSFP+ fiber transceivers and fiber optic cables, 40G DAC cables available in QSFP+ DAC cables and AOC cables enable short-reach options. For 40G cabling, QSFP+ to QSFP+ (40G to 40G) and QSFP+ to 4SFP+ (40G to 10G) breakout cables satisfy customers for various fiber types and reach requirements.

100GbE Fiber Optic Cabling For Future Proofing

With the price of 100G optics cutting down in 2017, 100GbE network is no longer out of customers’ reach. Telecom giants like Cisco, Arista, HPE launches series of 100G optical switches to meet the market demand. And for other 100G components like 100G optical transceivers, fiber patch cables, racks & enclosures, etc, those are ubiquitous on the market.

100G optical transceivers including the CFP, CFP2, CFP4, CXP and the most popular 100G QSFP28 optics in IEEE standards provide a great selection to the overall users.For 100G inter-rack connections, QSFP28 to QSF28 Direct Attach Copper (DAC) Cables and Active Optical Cables (AOC) as well as the QSFP28 to SFP28 breakout cables are the cost-effective solutions.

Path 1: 10G to 40G to 100G

Many of the largest data centers has already moved to 40GbE, which are constructed out of 4 parallel SerDes 10Gb/s links between the Ethernet chip and the QSFP pluggable. The short-reach QSFP interfaces (QSFP+ SR4 modules) use 4 pair of fiber between them, and the copper Direct Attach Cable (DAC) equivalent carry the same on several copper cables inside the big cable. Longer-reach QSFP interfaces (QSFP+ LR4 optics) put the 4 10Gb/t streams onto separate Wave Division Multiplexing (WDM) waves which can be carried over a single pair of fiber. This is part of the reason why QSFP optics are fairly expensive still, especially for longer distances.10GbE to 40GbE to 100GbESimilarly for the 100GbE interfaces that are available today, these are really constructed out of 10 parallel paths of 10Gb/t streams. 100G SR10 modules is the optical transceiver modules that support 10×10Gb/s modes. But neither the CXP SR10 modules or CFP 100G SR10 optics are not popular on the 100G hardware market owing to their larger form factors. Eventually, they need to utilize the smaller footprint 100G modules—QSFP28 transceiver, which is mentioned above as the optical transceivers that can be used in 25GbE and 100GbE.

Result: Although the migration path from 10G to 40G to 100G requires more ports and increases cost per bit, 40GbE between switches is expected to be remain and will not be affected in the near future.

Path 2: 25G to 100G—The Move From 10 Lanes to 4

The old transition path of Ethernet has increased by 10X in speed like the 10G to 40G to 100G. However, 25 Gbps over a single lane for server makes 100G migration be 4×25Gb/s mode.100-gbe-block-diagramUsing four-lane variants like QSFP28 is more economical in several ways:

  • The single-lane design makes four 25 Gbps lanes transceivers less expensive than ten 10Gbps lanes because the transceiver is simpler and less costly to manufacture.
  • The power required to run SFP28 transceivers is much less than required for a typical 10-lane transceiver, it is the same case as the cooling costs.
  • For fiber connections, moving from 10GbE to 40GbE may require an upgrade to four times the number of fibers (MPO), but a 25GbE connection does not because it is the same as 10GbE (single TX and single RX, not four each for TX and RX).
  • Moving from 10GbE to 40GbE typically requires a forklift upgrade to thicker, more expensive cables, but a 25GbE direct attach copper connection does not.

Result: There are few switches and NIC cards that directly support 25GbE. But the curve for 25GbE won’t fade away, rapid development and pre-standard 25GbE products coming soon!


This article introduces 10G/40G/100G fiber optic cabling, and make a clear comparison between the two paths to 100GbE. Customers prefer 4×25Gbps for the reasons: Less parallel paths, less fibers, less optics, less everything. For those who want to upgrade from 40G to 100G, appreciate the reliable performance of 40G with the potential to run across 2 parallel 25Ghz rather than 4 required today.

Several 100G DWDM Solutions for Arista 7500E Series

Several 100G DWDM Solutions for Arista 7500E Series

To keep up with the global demand for higher bandwidth, Arista has designated 7500E series switch to address 100G long-hual dense wavelength division multiplexing (DWDM) connectivity. Arista 100G interconnect solution combines Layer 2/Layer 3 switching, wire-speed encryption and coherent DWDM into a high-density line card for the Arista 7500E data centers. Along with the introduction of Arista 7500E series switches, this article will illustrate several 100G DWDM solutions for distance up to 80 km, 150 km and 3000 km as well.

Arista 7500E Series Switch & Line Card

Arista 7500E series is the second generation of 7500 series switch that delivers scalable and deterministic network performance for mission critical data centers, enterprise and HPC environments. Available in a compact 7RU (4-slot) or 11RU (8-slot), Arista 7500E offers over 30Tbps of total capacity for 1,152 ports of 10GbE, 288 ports of 40GbE and support for 96-port 100GbE with a broad choice of interface types that support flexible combinations of 10G, 40G and 100G modes on a single port.

The 7504 and 7508 are the two types of Arista 7500E series switches. The 7508 systems support 8 linecards, dual supervisor modules and 6 fabric modules to provide a full 30Tbps of capacity. The smaller 7504 systems share a common architecture with the 7508 with the primary difference being support for 4 linecards and 15Tbps of forwarding capacity. The most unique feature of this switch is that it can connect with 10G SFP+, 40G QSFP+, 100G QSFP28 and CFP2 modules.


Arista 7500E series line card for addressing 1/10G, 40G and 100G with full support for industry standard connections and comprehensive layer 2 and 3 features for flexible deployment choice. The line card delivers error-free performance up to 3000 km of fiber and consumes less than 140W per 100Gbps. Similar to any other Arista platform, the DWDM line card utilizes the single binary image of Arista’s extensible operating system (EOS). Line cards with CFP2 and QSFP support standard 100G for both single and multimode fiber for distance up to 40 km.

Why Need 100G DWDM Solution?

100G optical transceivers provide the most straightforward method to connect 100G traffic over long-hual applications. 100G optics like CFP and QSFP28 offer cost-optimized solutions for connecting 100G switches together in a rack or data center. Nevertheless, the small and cost-effective QSFP28 100G optics now can only handle connections over distances of less than 10 km. For example, QSFP28 LR4 is compliant with 100GBASE-LR4 standard that operates over duplex LC cables for a link length of 10 km.

As to the CFP form factors, coherent CFP modules is designed to support metro and long-hual DWDM applications. CFP 100GbASE-ER4 can support up to 40 km. However, owing to its large size and high power consumption, CFP transceivers are less popular on the market. If you want to use CFP optics for 100G deployment, keep in mind, CFP modules are too large to fit in the Ethernet switches and will significantly reduce port counts and increase power usage, making 100G switches poor performance in cost-effectiveness. Therefore, customers who want to upgrade 100G network can only cover a distance of 10 km, which is obviously insufficient for geographically separated data centers or metro infrastructures. Figure 2 shows the basics of DWDM system.


To realize 100G long-distance transmission, Arista 100G DWDM solution combines DWDM optics with a fully passive Mux/Demux system that can handle up to 3,000 km. Arista 100G DWDM solution is a 6 x 100G Coherent DWDM line card for the 7500E series with integrated wire-speed encryption and analog coherent CFP2 optical interfaces. Several use cases for the Arista 7500E Series DWDM card in multi-site data center networks exist. The following sections identify three use cases for Arista 7500E DWDM solutions.

Use Cases for Arista 7500E DWDM Solutions
  • Use Case 1—Less Than 80KM Dark Fiber Connection

For a typical metro link that is less than 80 km, Arista 7500E Series DWDM line cards can directly terminate a dark fiber connection providing a point-to-point connection between two locations.

DWDM solution for 80 km

Just as figure 3 shows, Arista DWDM solution is ideal for metro applications transmitting up to 9.6Tbps traffic without the need for any additional amplification.

  • Use Case 2—Greater Than 80 km But Less Than 150 km

When extending the distance beyond 80 km, there is a need to amplify the signal to offset heavy signal loss that occurred in the light signal when passing through fiber cables, patch panels and other optical devices. Under this circumstance, EDFA’s or Erbium Doped Fiber Attenuators are employed to give the aggregated wave a boost.

100G DWDM solution about 100 km

By using EDFAs (seen in Figure 4) to the transmit side of each end of the dark fiber link, the signal can be boosted to achieve distances of up to 150 km. Exact distances will be dependent on the number of patches, fiber splices and quality of the fiber.

  • Use Case 3—Greater Than 150 km But Less Than 3,000 km

Arista 7500E DWDM solutions can also cover the distance of greater than 150 km but less than 3000 km. Employing further EDFAs at a spacing of approximately 80 km along the fiber route allows the length of a connection to be extended to over 3,000 km. As shown below, EDFAs are used on both paths to boost the signal.

DWDM solution for 3000 km

Supported Optics for Arista 7500E Series

All Arista 10G SFP+ transceivers, with the exception of LRM, are supported on the Arista 7500E SFP+ ports.

Interface Type SFP+ ports
10GBASE-CR 0.5m-5m
10GBASE-AOC 3m-30m
10GBASE-SRL 100m (OM3) / 150m (OM4)
SFP-10G-SR 300m (OM3) /400m (OM4)
SFP-10G-LRL 1km
SFP-10G-LR 10km
SFP-10G-ER 40km
SFP-10G-ZR100 100km
100Mb TX, 1GbE SX/LX/TX Yes

The 40G QSFP+ transceivers and cables allow for 4x10G mode support with the use of fiber breakout cables, MTP to LC cassettes, or QSFP to SFP+ cables. See the below table for details on the latest supported 40G transceivers.

Interface Type QSFP+ ports
40GBASE-CR4 0.5m-5m
40GBASE-AOC 3m-100m
QSFP-40G-UNIV 150m (OM3) / 150m (OM4), 500m (SM)
QSFP-40G-SRBD 100m (OM3) /150m (OM4)
QSFP-40G-SR4 100m (OM3) / 150m (OM4)
QSFP-40G-XSR4 300m (OM3) / 400m (OM4)
QSFP-40G-PLRL4 1km (1km 4x10G LR/LRL)
QSFP-40G-PLR4 10km (10km 4x10G LR/LRL)
QSFP-40G-LRL4 1km
QSFP-40G-LR4 10km
QSFP-40G-ER4 40km

100G QSFP28 and CFP2 Optics

Interface Type 100G CFP2 Ports 100G QSFP Ports
100GBASE-XSR10 300m OM3 / 400m OM4 Parallel MMF
100GBASE-SR4 100m OM3 / 150m OM4 Parallel MMF
100GBASE-LR4 10km SM Duplex 10km SM Duplex
100GBASE-LRL4 2km SM Duplex
100GBASE-ER4 40km SM Duplex
100GBASE-CWDM4 2km SM duplex
100GBASE-PSM4 500m SM Parallel
100GBASE-AOC 3m to 30m
100GBASE-CR4 1m to 3m

Arista 7500E DWDM solution works in conjunction with passive Optical Mux/Demux devices and in-line amplifiers to support additional bandwidth and extended reaches. Arista 7500E DWDM solution can directly reach up to 80 km without requiring in-line amplification, which is ideal for metro applications. With an Optical Signal to Noise ratio (OSNR) of 11.6dB, it can be used effectively for point to point long-haul applications up to 3,000kms with in-line amplifiers and multiplexers.

What’s the Difference Between 100G CLR4 and CWDM4?

What’s the Difference Between 100G CLR4 and CWDM4?

Since the existing 100G Ethernet links with QSFP28 SR4 or LR4 are either too short or too expensive, 100G modules that can cover this enormous middle ground between 100m and 10km are expected to come to the market. 100G CLR4 and CWDM4 are two types of 100G interface to deliver distance up to 2km over duplex single-mode fiber. As CLR4 and CWDM4 are similar, so what’s the difference between them?

CLR4 Alliance

100G CLR4 is a new, open, multi-vendor 100G optics specification created by 100G CLR4 Alliance who consists of end-customers, system companies, and optical companies. It is a low-power, cost-effective, 100G-CWDM solution that routes four 25Gbps optical transmissions down a single-mode fiber for reaches of up to 2km. CLR4 Alliance is designed to address market requirements of large data center customers. CLR4 specification supports FEC (Forward Error Correction) and non-FEC applications.

Clause & Players

CLR4 Alliance—Altera, Arista, Aurrion, Brocade, Ciena, ColorChip, Dell, ebay, Fabrinet, Fujitsu, Hewllett-Packard, Huawei, Intel, Juniper Networks, Kaiam, MACOM, Materials Magic, NeoPhotonics, Netronome, Oclaro, Oplink, Oracle, SAE Magnetics, Semtech, Skorpios, Source Photonics, TE Connectivity, VMware, 3ality Technica.

100G CWDM4-fs


The CWDM4 MSA (Multi-Source Agreement) targets a common specification for low-cost 100G optical interfaces that run up to 2 km in data center applications. The MSA uses CWDM technology with 4 lanes of 25 Gbps optically multiplexed onto and demultiplexed from duplex single-mode fiber. CWDM4 MSA targets the broad data center 100G interconnects that support FEC applications.

Clause & Players

CWDM4 MSA—Avago Technologies, Brocade, ColorChip, Finisar, HiLight Semiconductor, Hitachi Metals, II-IV Inc, JDSU, Juniper Networks, Kaiam, Mitsubishi Electric, NeoPhotonics, Oclaro, Oplink, SiFotonics, Skorpios, Sumitomo Electric.

100G CLR4 vs CWDM4

As mentioned above, the specifications of the CLR4 and CWDM4 are very similar. Both include FEC, not in the module but as part of the system design, but whereas FEC is fundamental to the CWDM4, it is optional with the CLR4. The 100G CLR4 specification is fully interoperable with the 100G CWDM4 specification for links using FEC. But as FEC only as an option for CLR4, the CLR4 Alliance’s interface avoids the delay associated with FEC, so that it is more suitable to use in applications such as high-frequency trading where latency is an issue. The following table shows us some details about CLR4 vs CWDM4:

Interface Form Factor Wavelength Fiber Span FEC Support
100G CLR4 QSFP28 1310nm window, 20nm spacing Duplex single-mode fiber (with LC connector) Up to 2 km FEC and non-FEC



100G CLR4 and CWDM4 meet the demands on 2km span of large data center. They are similar enough to be interoperable—the CLR4 is fully interoperable with the CWDM4 for links using FEC. FS.COM offers 100GBASE-CWDM4 QSFP28 modules with large stock at very affordable price. For more information, please visit or contact


QSFP28 PSM4 and CWDM4 in Data Center 100G Ethernet

QSFP28 PSM4 and CWDM4 in Data Center 100G Ethernet

QSFP28 is considered as the main form factor for 100G Ethernet in data center. And in order to satisfy different applications, various of 100G interfaces are developed. 100GBASE-PSM4 and 100GBASE-CWDM4 are two non-IEEE defined interface among them which are expected to be an alternative for data center 100G Ethernet. Today, I’d like to talk something about them.

Why We Need PSM4 and CWDM4?

As we know, the most basic 100G interfaces used today are 100GBASE-SR4 and 100GBASE-LR4 which are defined by IEEE. However, there is a problem with them that reaches are either too short for practical application in data center or too long and costly. In fact, for data center operators, a 100G QSFP28 transceiver that is with 2km or 500m max reach is better. Thus, MSA (Multi-Source Agreement) strategy to bring a mid-reach solutions to the market. And 100G QSFP28 modules with PSM4 and CWDM4 interface are the products in this revolution. They are much less expensive than the 10km, 100GBASE-LR4 module, and support longer distance than 100GBASE-SR4 QSFP28.

QSFP28 PSM4 or QSFP28 CWDM4, Which Is Better?

Defined by the 100G PSM4 MSA, 100GBASE-PSM4 QSFP28 transceiver is a transceiver with parallel technology. It uses four lanes of parallel ribbon fiber delivering serialized data at a rate of 25 Gbps per lane (See the picture below). The light source of PSM4 optic module is a single uncooled distributed feedback (DFB) laser operating at 1310nm. PSM4 transceiver doesn’t need a MUX/DEMUX for each laser but it does need either a directly modulated DFB laser (DML) or an external modulator for each fiber. A PSM4 QSFP28 module supports link lengths of up to 500 meters over single-mode fiber with 12 fiber MTP/MPO connectors.



CWDM4 as opposed to PSM4 optics, uses only one optical fiber compared to four fibers for PSM4. Thus, the CWDM network is more cost-effective than a PSM4 network as a result of cable costs alone. CWDM4 module uses an optical multiplexer and de-multiplexer, operating around 1310nm with CWDM technology, as shown in the following picture. However, the high component count drives the cost of CWDM4 modules. Thus, on transceiver cost alone, CWDM4 is more expensive than PSM4.


The following table shows a summary of comparison between PSM4 and CWDM4.

Optical Transmitter Four integrated sillicon photonic modulators and one distributed-feedback laser Four CWDM directly-modulated lasers
Four-wavelength CWDM Multiplexer No Needed Needed
Connector MPO connector with eight fibers Duplex LC connector
Fiber Parallel Ribbon SMF (8 Fibers) Duplex SMF
Reach 500 meters 2 kilometers


Will They Be Popular in 2017?

As early as two years ago, LightCounting had expected the PSM4 and a merged CWDM offering to find strong market traction. Though in 2016, QSFP28 SR4 has still accounted for a large proportion of the market share (about 80%), the prospect of PSM4 and CWDM4 is expected to stay robust. Many transceiver vendors have introduced the PSM4 and CWDM4 QSFP28 modules to their 100G product list. In addition, according to the fibeReality (consulting and market research firm specializing in the telecommunications and data communications optical industry), the price of 100G QSFP PSM4 and CWDM4 will drop to a historic low. Now we have to see how PSM4 and CWDM4 play in 2017. Talking about your opinion in the comments section.



100 Gigabit Ethernet is popular in data center optics market this year. We have discussed much about 100G optics in the previous articles. In this blog, we are going to make a comparison between the two main physical layer standards for short reach interconnection—100GBASE-SR10 (CFP) and 100GBASE-SR4 (QSFP28 SR4) from several aspects.

Transceiver Form Factors Comparison

CFP is the typical representative form factor of 100GBASE-SR10. It is specified by a MSA (Multi-Source Agreement) between competing manufacturers. The CFP was designed after the SFP (Small Form-Factor Pluggable) interface, but is significantly larger to support 100 Gbps, using 10 x 10Gbps lanes.

QSFP28 is the latest 100G form factor. QSFP28 utilizes four 25G electrical lanes each to support the latest 100/50/25G transceivers and interconnects. Thus, it is the representative form factor of 100GBASE-SR4.


Result: QSFP28 form factor is more popular than CFP now, according to the surge shipment of QSFP28 optics.

Size Comparison

Transceivers with 100GBASE-SR4 and 100GBASE-SR10 interface respectively correspond to QSFP28 and CFP. Thus they have a significant difference in size. See the picture below, CFP is much larger than QSFP28. Obviousely, CFP is not much suitable for high density applications. In contrast, QSFP28 increases front-panel density and decrease power and price per bit.


Result: As high density is becoming one of the trends of data center, QSFP28 (100GBASE-SR4) is much more suitable to meet this demand than CFP (100GBASE-SR10).

Electrical and Optical Lanes Diagram

The following diagram shows the basic principles of 100GBASE-SR4 and 100GBASE-SR10:



Result: 100GBASE-SR4 has higher speed per channel with less channels so that it can decrease the port density.

Cables & Connectors Options

Both 100GBASE-SR4 and 100GBASE-SR10 optics use laser optimized multimode fiber (OM3/OM4) for transmission. But 100GBASE-SR4 optics (such as Cisco 100G-QSFP28-SR4) uses a 12-fiber standard QSFP MPO/MTP cable for connectivity (4 Tx and 4 Rx, each lane providing 25 Gbps of throughput) while 100GBASE-SR10 optics use a 2×12-fiber or 24-fiber strand MPO/MTP cable for connectivity (10 Tx and 10 Rx, each lane providing 10 Gbps of throughput).


Because optics with 100GBASE-SR4 and 100GBASE-SR10 interface can be respectively breakout to 4×25 Gbps and 10×10 Gbps, it is easy to upgrade from 25GbE/10 GbE to 100 GbE using MPO/MTP to LC harness cable.

Result: 100GBASE-SR4 uses 12-fiber MPO/MTP while 100GBASE-SR10 uses two 12-fiber or one 24-fiber MPO/MTP. For 100G point-to-point interconnection, the 100GBASE-SR4 is more cost-effective. For network migration, 100GBASE-SR4 is also better since it has less breakout legs which greatly reduce the cost of cable management.


100GBASE-SR4 offers layout advantages to the host board implementer and substantial cable plant fiber count reduction while being competitive with 100GBASE-SR10 in cost and power consumption.