<\/p>\n
<\/p>\n
What Is QSFP28? (Quick Technical Foundation)<\/strong><\/h2>\nThe 4\u00d725G NRZ Architecture<\/strong><\/h3>\nQSFP28, or Quad Small Form-factor Pluggable 28, is the industry-standard form factor for 100 Gigabit Ethernet. It uses four electrical lanes to deliver a total throughput of 103.1 Gbps, with each lane operating at 25.78 Gbps.<\/p>\n
This 4\u00d725G design is what separates QSFP28\u00a0from its 40G predecessor, QSFP+. While the physical dimensions are identical, the electrical signaling and optical architectures are fundamentally different. For a deeper comparison, see our\u00a0QSFP28<\/u>\u00a0vs QSFP+ guide<\/u><\/a>.<\/p>\n <\/p>\n
Form Factor and Power Specifications<\/strong><\/h3>\nThe QSFP28\u00a0modules have the dimension of 18.35 millimeters wide and 72.4 millimeters long. They support hot-pluggable insertion and removal, enabling network upgrades without powering down switches. Commercial-grade modules operate from 0\u00b0C to 70\u00b0C, while industrial models are designed for carrier deployments.<\/p>\n
Power consumption varies significantly. QSFP28\u00a0DAC cables may consume less than 1.5 W, while ER4 or ZR4 modules can draw up to 5.5 W. On a high-density 1U switch, this difference matters when every port is populated.<\/p>\n
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MSA and IEEE Standards Compliance<\/strong><\/h3>\nMost QSFP28\u00a0modules comply with the QSFP28\u00a0MSA and IEEE 802.3bm standards, ensuring compatibility across Cisco, Arista, Juniper, NVIDIA, and other leading networking platforms. Always refer to your specific switch firmware release notes for module validation.<\/p>\n
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QSFP28\u00a0Module Types by Application<\/strong><\/h2>\n <\/p>\n
![\"QSFP28](\"https:\/\/ascentoptics.com\/blog\/wp-content\/uploads\/2026\/04\/QSFP28\u7c7b\u578b.png\")
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QSFP28\u00a0SR4: The Data Center Workhorse (MMF, 100 m)<\/strong><\/h3>\nThe QSFP28\u00a0SR4<\/a> is the most common 100G\u00a0module for intra-data center data connections. It uses four 850 nm VCSEL-based lasers over multimode fiber and terminates with an MPO-12 connector (eight active fibers: four TX, four RX).<\/p>\nSR4 supports reaches of 70 m over OM3 fiber and 100 m over OM4 fiber. Some long-reach variants (eSR4) can extend to approximately 150 m over OM4\/OM5. These modules are the default choice for top-of-rack to end-of-row or leaf-to-spine connections within the same data center hall.<\/p>\n
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QSFP28\u00a0PSM4: Parallel Single-Mode Alternative (SMF, 500 m\u20132 km)<\/strong><\/h3>\nQSFP28\u00a0PSM4<\/a> uses four parallel 1310 nm DML lasers and eight strands of single-mode fiber with an MPO-12 connector (same as SR4). It supports a standard reach of 500 m, with some variants extending to 2 km.<\/p>\nQSFP28\u00a0PSM4 uses four parallel 1310 nm DML lasers and eight strands of single-mode fiber with an MPO-12 connector (same as SR4). It supports a standard reach of 500 m, with some variants extending to 2 km.<\/p>\n
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QSFP28\u00a0LR4: The 10 km Enterprise Standard (SMF, LC)<\/strong><\/h3>\nQSFP28\u00a0LR4<\/a> uses LAN-WDM technology to multiplex four 25G lanes onto a single pair of LC duplex fibers. It operates with wavelengths between 1295\u20131310 nm and supports up to 10 km over single-mode fiber.<\/p>\nLR4 is widely used for campus backbones, metro-enterprise networks, and data center interconnects where buildings are separated by several kilometers. It employs EML lasers, offering stable long-reach performance at a higher price point than SR4.<\/p>\n
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QSFP28\u00a0CWDM4: The Cost-Optimized Sweet Spot (SMF, 2 km)<\/strong><\/h3>\nQSFP28\u00a0CWDM4<\/a> combines four uncooled CWDM wavelengths (1271, 1291, 1311, and 1331 nm) over a single LC duplex single-mode fiber pair. The MSA specification guarantees a 2 km reach.<\/p>\nCWDM4 sits between PSM4 and LR4 in terms of performance and price. It is the most cost-effective choice for links between 500 m and 2 km, delivering significant fiber savings compared to PSM4.<\/p>\n
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QSFP28\u00a0ER4: Extended Reach for Metro Networks (SMF, 40 km)<\/strong><\/h3>\nBuilding on the LR4 architecture with higher-power EML lasers and APD receivers, QSFP28\u00a0ER4 extends the reach to 40 km. It is ideal for carrier aggregation, regional metro rings, and long-haul data center interconnects.<\/p>\n
In practice, many ER4 solutions require host-side FEC to achieve the full 40 km reach. Without FEC, a more realistic distance is around 30 km. Always confirm that your switch platform supports FEC before deploying ER4.<\/p>\n
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QSFP28\u00a0ZR4: Long-Haul DCI (SMF, 80 km)<\/strong><\/h3>\nQSFP28\u00a0ZR4<\/a> extends LAN-WDM reach to 80 km or more and sits at the high end of the cost spectrum. It is used in telecom core networks and extended-distance data center interconnects.<\/p>\nZR4 modules require FEC and very clean single-mode fiber with minimal dispersion. They are rarely used in typical enterprise data centers except for specific inter-city connectivity needs.<\/p>\n
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Emerging Single-Lambda QSFP28\u00a0Module<\/a> Types<\/strong><\/h2>\nAs 100G deployments continue to scale in hyperscale and AI environments, single-lambda QSFP28\u00a0modules have emerged as a simplified and cost-effective alternative to traditional multi-wavelength designs. Unlike SR4, PSM4, CWDM4, or LR4, which use four separate optical lanes or wavelengths, single-lambda modules transmit the full 100G signal over one optical wavelength using PAM4 modulation. This architecture dramatically reduces fiber count, simplifies cabling, lowers inventory complexity, and eases future upgrades.<\/p>\n
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DR1: Replacing SR4\/PSM4 at 500 m<\/strong><\/h3>\nDR1 transmits 100G using a single wavelength (PAM4) over one fiber. It completely eliminates the need for the eight-fiber parallel pairs required by PSM4 and significantly simplifies cabling compared to SR4\u2019s MPO-12 setup. With only a duplex LC or single MPO connector, DR1 is ideal for short-reach single-mode links up to 500 m.<\/p>\n
It offers lower fiber usage, reduced patch-panel density, and easier installation while maintaining the same performance level as traditional parallel optics \u2014 making it a popular choice for new greenfield data centers and AI clusters.<\/p>\n
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FR1: The CWDM4 Alternative at 2 km<\/strong><\/h3>\nQSFP28\u00a0FR1 is a cost-effective single-lambda PAM4 module that reaches 2 km over single-mode fiber. It serves as a direct, simpler alternative to CWDM4 by using just one wavelength instead of four. This reduces optical complexity, lowers module cost, and minimizes the risk of wavelength-specific issues.<\/p>\n
However, because it carries the entire 100G payload on a single lane, FR1 is more demanding on link budget and requires higher-quality, low-loss single-mode fiber. It performs best in modern, well-maintained fiber plants.<\/p>\n
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LR1: Simplifying 10 km Links<\/strong><\/h3>\nLR1 provides a single-lambda option for 10 km links using a 1310 nm PAM4 signal and a standard duplex LC connector. It achieves the same reach as LR4 but with far simpler optics \u2014 no need for wavelength multiplexing or multiple lasers. This results in lower power consumption, reduced thermal load, easier spares management, and lower overall operational overhead compared to multi-wavelength LR4.<\/p>\n
LR1 is rapidly gaining traction in cloud providers and large-scale enterprise campuses seeking to streamline their 100G deployments.<\/p>\n
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When to Consider Single-Lambda Modules<\/strong><\/h3>\nIn hyperscale data centers, AI clusters, or networks equipped with clean and well-documented fiber infrastructure, single-lambda modules are the best choice. However, they are not as good if there is an older fiber network or for those mixed vendor environments where proven spurious will be a criteria.<\/p>\n
When to Consider Single-Lambda Modules<\/p>\n
Single-lambda modules (DR1, FR1, LR1) are ideal for hyperscale data centers, AI training clusters, or any network with clean, well-documented, high-quality single-mode fiber infrastructure. They excel where fiber count, cabling simplicity, and long-term operational efficiency are priorities.<\/p>\n
However, they are less suitable for older fiber plants, mixed-vendor environments, or deployments where maximum link margin and proven multi-wavelength stability are critical. In such cases, traditional CWDM4 or LR4 modules often remain the safer, more compatible choice.<\/p>\n
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QSFP28\u00a0Cable Options (DAC and AOC)<\/strong><\/h2>\n <\/p>\n
![\"QSFP28](\"https:\/\/ascentoptics.com\/blog\/wp-content\/uploads\/2026\/04\/Breakout\u67b6\u6784.png\")
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QSFP28\u00a0DAC: Lowest-Cost In-Rack Connectivity<\/strong><\/h3>\nA Direct Attach Copper (DAC) cable is a passive or active twinax copper assembly with QSFP28\u00a0connectors on both ends. It offers the cheapest and lowest-power 100G connection available.<\/p>\n
Passive DACs are typically used up to 3 m; active DACs can reach 5 m or more. They are best for in-rack switch-to-switch or GPU-to-switch applications where distance is limited.<\/p>\n
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QSFP28\u00a0AOC: Flexible Intra-Data-Center Links<\/strong><\/h3>\nAOC encodes the optical transceivers’ data directly onto each end of the cable. They are lightweight and more flexible than DACs which makes it easier to deal with them.<\/p>\n
Thirty meters is usually the shortest length to which QSFP28\u00a0AOCs can extend. Typically, these AOCs are employed for execution of data center row-to-row connection, AI\/HPC clustering, and any hard-copy variance.<\/p>\n
Active Optical Cables (AOC) integrate optical transceivers directly into the cable ends. They are lighter and more flexible than DACs.<\/p>\n
QSFP28\u00a0AOCs typically extend up to 30 m or more and are commonly used for row-to-row connections, AI\/HPC clustering, and any deployment where flexibility is important.<\/p>\n
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Breakout Cables: 100G to 4\u00d725G Fan-Out<\/strong><\/h3>\nQSFP28\u00a0breakout cables divide 100G ports into four 25G SFP28 links. This fan-out pattern is one of the most common server access architectures in modern data centers.<\/p>\n
Breakout cables come in both DAC and AOC variants. A QSFP28-to-4\u00d7SFP28 DAC is typically used for in-rack server connections, while the AOC version extends to end-of-row deployments.<\/p>\n
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QSFP28 Module Types Selection Decision Matrix<\/strong><\/h2>\nSelecting the right QSFP28 module is not just about transmission distance\u2014it requires balancing fiber infrastructure, cost efficiency, power consumption, and future scalability. The following decision matrix provides a quick reference, while the guidelines below help you make a more informed and practical choice.<\/p>\n
QSFP28, or Quad Small Form-factor Pluggable 28, is the industry-standard form factor for 100 Gigabit Ethernet. It uses four electrical lanes to deliver a total throughput of 103.1 Gbps, with each lane operating at 25.78 Gbps.<\/p>\n
This 4\u00d725G design is what separates QSFP28\u00a0from its 40G predecessor, QSFP+. While the physical dimensions are identical, the electrical signaling and optical architectures are fundamentally different. For a deeper comparison, see our\u00a0QSFP28<\/u>\u00a0vs QSFP+ guide<\/u><\/a>.<\/p>\n <\/p>\n The QSFP28\u00a0modules have the dimension of 18.35 millimeters wide and 72.4 millimeters long. They support hot-pluggable insertion and removal, enabling network upgrades without powering down switches. Commercial-grade modules operate from 0\u00b0C to 70\u00b0C, while industrial models are designed for carrier deployments.<\/p>\n Power consumption varies significantly. QSFP28\u00a0DAC cables may consume less than 1.5 W, while ER4 or ZR4 modules can draw up to 5.5 W. On a high-density 1U switch, this difference matters when every port is populated.<\/p>\n <\/p>\n Most QSFP28\u00a0modules comply with the QSFP28\u00a0MSA and IEEE 802.3bm standards, ensuring compatibility across Cisco, Arista, Juniper, NVIDIA, and other leading networking platforms. Always refer to your specific switch firmware release notes for module validation.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n The QSFP28\u00a0SR4<\/a> is the most common 100G\u00a0module for intra-data center data connections. It uses four 850 nm VCSEL-based lasers over multimode fiber and terminates with an MPO-12 connector (eight active fibers: four TX, four RX).<\/p>\n SR4 supports reaches of 70 m over OM3 fiber and 100 m over OM4 fiber. Some long-reach variants (eSR4) can extend to approximately 150 m over OM4\/OM5. These modules are the default choice for top-of-rack to end-of-row or leaf-to-spine connections within the same data center hall.<\/p>\n <\/p>\n QSFP28\u00a0PSM4<\/a> uses four parallel 1310 nm DML lasers and eight strands of single-mode fiber with an MPO-12 connector (same as SR4). It supports a standard reach of 500 m, with some variants extending to 2 km.<\/p>\n QSFP28\u00a0PSM4 uses four parallel 1310 nm DML lasers and eight strands of single-mode fiber with an MPO-12 connector (same as SR4). It supports a standard reach of 500 m, with some variants extending to 2 km.<\/p>\n <\/p>\n QSFP28\u00a0LR4<\/a> uses LAN-WDM technology to multiplex four 25G lanes onto a single pair of LC duplex fibers. It operates with wavelengths between 1295\u20131310 nm and supports up to 10 km over single-mode fiber.<\/p>\n LR4 is widely used for campus backbones, metro-enterprise networks, and data center interconnects where buildings are separated by several kilometers. It employs EML lasers, offering stable long-reach performance at a higher price point than SR4.<\/p>\n <\/p>\n QSFP28\u00a0CWDM4<\/a> combines four uncooled CWDM wavelengths (1271, 1291, 1311, and 1331 nm) over a single LC duplex single-mode fiber pair. The MSA specification guarantees a 2 km reach.<\/p>\n CWDM4 sits between PSM4 and LR4 in terms of performance and price. It is the most cost-effective choice for links between 500 m and 2 km, delivering significant fiber savings compared to PSM4.<\/p>\n <\/p>\n Building on the LR4 architecture with higher-power EML lasers and APD receivers, QSFP28\u00a0ER4 extends the reach to 40 km. It is ideal for carrier aggregation, regional metro rings, and long-haul data center interconnects.<\/p>\n In practice, many ER4 solutions require host-side FEC to achieve the full 40 km reach. Without FEC, a more realistic distance is around 30 km. Always confirm that your switch platform supports FEC before deploying ER4.<\/p>\n <\/p>\n QSFP28\u00a0ZR4<\/a> extends LAN-WDM reach to 80 km or more and sits at the high end of the cost spectrum. It is used in telecom core networks and extended-distance data center interconnects.<\/p>\n ZR4 modules require FEC and very clean single-mode fiber with minimal dispersion. They are rarely used in typical enterprise data centers except for specific inter-city connectivity needs.<\/p>\n <\/p>\n <\/p>\n As 100G deployments continue to scale in hyperscale and AI environments, single-lambda QSFP28\u00a0modules have emerged as a simplified and cost-effective alternative to traditional multi-wavelength designs. Unlike SR4, PSM4, CWDM4, or LR4, which use four separate optical lanes or wavelengths, single-lambda modules transmit the full 100G signal over one optical wavelength using PAM4 modulation. This architecture dramatically reduces fiber count, simplifies cabling, lowers inventory complexity, and eases future upgrades.<\/p>\n <\/p>\n DR1 transmits 100G using a single wavelength (PAM4) over one fiber. It completely eliminates the need for the eight-fiber parallel pairs required by PSM4 and significantly simplifies cabling compared to SR4\u2019s MPO-12 setup. With only a duplex LC or single MPO connector, DR1 is ideal for short-reach single-mode links up to 500 m.<\/p>\n It offers lower fiber usage, reduced patch-panel density, and easier installation while maintaining the same performance level as traditional parallel optics \u2014 making it a popular choice for new greenfield data centers and AI clusters.<\/p>\n <\/p>\n QSFP28\u00a0FR1 is a cost-effective single-lambda PAM4 module that reaches 2 km over single-mode fiber. It serves as a direct, simpler alternative to CWDM4 by using just one wavelength instead of four. This reduces optical complexity, lowers module cost, and minimizes the risk of wavelength-specific issues.<\/p>\n However, because it carries the entire 100G payload on a single lane, FR1 is more demanding on link budget and requires higher-quality, low-loss single-mode fiber. It performs best in modern, well-maintained fiber plants.<\/p>\n <\/p>\n LR1 provides a single-lambda option for 10 km links using a 1310 nm PAM4 signal and a standard duplex LC connector. It achieves the same reach as LR4 but with far simpler optics \u2014 no need for wavelength multiplexing or multiple lasers. This results in lower power consumption, reduced thermal load, easier spares management, and lower overall operational overhead compared to multi-wavelength LR4.<\/p>\n LR1 is rapidly gaining traction in cloud providers and large-scale enterprise campuses seeking to streamline their 100G deployments.<\/p>\n <\/p>\n In hyperscale data centers, AI clusters, or networks equipped with clean and well-documented fiber infrastructure, single-lambda modules are the best choice. However, they are not as good if there is an older fiber network or for those mixed vendor environments where proven spurious will be a criteria.<\/p>\n When to Consider Single-Lambda Modules<\/p>\n Single-lambda modules (DR1, FR1, LR1) are ideal for hyperscale data centers, AI training clusters, or any network with clean, well-documented, high-quality single-mode fiber infrastructure. They excel where fiber count, cabling simplicity, and long-term operational efficiency are priorities.<\/p>\n However, they are less suitable for older fiber plants, mixed-vendor environments, or deployments where maximum link margin and proven multi-wavelength stability are critical. In such cases, traditional CWDM4 or LR4 modules often remain the safer, more compatible choice.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n A Direct Attach Copper (DAC) cable is a passive or active twinax copper assembly with QSFP28\u00a0connectors on both ends. It offers the cheapest and lowest-power 100G connection available.<\/p>\n Passive DACs are typically used up to 3 m; active DACs can reach 5 m or more. They are best for in-rack switch-to-switch or GPU-to-switch applications where distance is limited.<\/p>\n <\/p>\n AOC encodes the optical transceivers’ data directly onto each end of the cable. They are lightweight and more flexible than DACs which makes it easier to deal with them.<\/p>\n Thirty meters is usually the shortest length to which QSFP28\u00a0AOCs can extend. Typically, these AOCs are employed for execution of data center row-to-row connection, AI\/HPC clustering, and any hard-copy variance.<\/p>\n Active Optical Cables (AOC) integrate optical transceivers directly into the cable ends. They are lighter and more flexible than DACs.<\/p>\n QSFP28\u00a0AOCs typically extend up to 30 m or more and are commonly used for row-to-row connections, AI\/HPC clustering, and any deployment where flexibility is important.<\/p>\n <\/p>\n QSFP28\u00a0breakout cables divide 100G ports into four 25G SFP28 links. This fan-out pattern is one of the most common server access architectures in modern data centers.<\/p>\n Breakout cables come in both DAC and AOC variants. A QSFP28-to-4\u00d7SFP28 DAC is typically used for in-rack server connections, while the AOC version extends to end-of-row deployments.<\/p>\n <\/p>\n <\/p>\n Selecting the right QSFP28 module is not just about transmission distance\u2014it requires balancing fiber infrastructure, cost efficiency, power consumption, and future scalability. The following decision matrix provides a quick reference, while the guidelines below help you make a more informed and practical choice.<\/p>\nForm Factor and Power Specifications<\/strong><\/h3>\n
MSA and IEEE Standards Compliance<\/strong><\/h3>\n
QSFP28\u00a0Module Types by Application<\/strong><\/h2>\n
<\/p>\nQSFP28\u00a0SR4: The Data Center Workhorse (MMF, 100 m)<\/strong><\/h3>\n
QSFP28\u00a0PSM4: Parallel Single-Mode Alternative (SMF, 500 m\u20132 km)<\/strong><\/h3>\n
QSFP28\u00a0LR4: The 10 km Enterprise Standard (SMF, LC)<\/strong><\/h3>\n
QSFP28\u00a0CWDM4: The Cost-Optimized Sweet Spot (SMF, 2 km)<\/strong><\/h3>\n
QSFP28\u00a0ER4: Extended Reach for Metro Networks (SMF, 40 km)<\/strong><\/h3>\n
QSFP28\u00a0ZR4: Long-Haul DCI (SMF, 80 km)<\/strong><\/h3>\n
Emerging Single-Lambda QSFP28\u00a0Module<\/a> Types<\/strong><\/h2>\n
DR1: Replacing SR4\/PSM4 at 500 m<\/strong><\/h3>\n
FR1: The CWDM4 Alternative at 2 km<\/strong><\/h3>\n
LR1: Simplifying 10 km Links<\/strong><\/h3>\n
When to Consider Single-Lambda Modules<\/strong><\/h3>\n
QSFP28\u00a0Cable Options (DAC and AOC)<\/strong><\/h2>\n
<\/p>\nQSFP28\u00a0DAC: Lowest-Cost In-Rack Connectivity<\/strong><\/h3>\n
QSFP28\u00a0AOC: Flexible Intra-Data-Center Links<\/strong><\/h3>\n
Breakout Cables: 100G to 4\u00d725G Fan-Out<\/strong><\/h3>\n
QSFP28 Module Types Selection Decision Matrix<\/strong><\/h2>\n
![\"QSFP28](\"https:\/\/ascentoptics.com\/blog\/wp-content\/uploads\/2026\/04\/Selection.png\")
<\/p>\n![\"100G](\"https:\/\/ascentoptics.com\/blog\/wp-content\/uploads\/2026\/04\/Gemini_Generated_Image_2cwjnt2cwjnt2cwj.png\")
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