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The QSFP28 optical transceiver, also known as the 100G transceiver, is an important component of 100G networks and is mainly used in 100G Ethernet and EDR InfiniBand applications. Its core feature is to use of four 25 Gbit/s channels (with NRZ modulation) for parallel transmission to achieve a 100G Ethernet transmission rate, achieving an excellent balance between power consumption, port density, and cost.
Simply put, QSFP28 optical transceivers are mainly used in network environments that require high density, high speed, and distances ranging from 100 meters to 80 kilometers. Its core positioning is the physical layer cornerstone of data centers and metropolitan area networks in the 100G era. Specifically, it can be summarized into the following four typical application scenarios:
1. Within the data center (core and largest usage)
This is where QSFP28 optical transceiver has the highest usage. Here, it mainly solves the high-speed interconnection between servers and switches.
- Server to TOR (top of rack) switch: usually several meters to tens of meters away, mainly using DAC direct copper cable (with the lowest power consumption) or AOC active optical cable.
- TOR switch to EOR (end of row)/MOR (middle of row) switch: The distance is between tens to 100 m, mainly using QSFP28 SR4 modules (with multimode fiber cables), with low cost and low power consumption.
- Spine Leaf Interconnection: The Mainstream Architecture of Modern Data Centers. The distance between leaf switches and spine switches is usually between 100 m and 2 km.
- Within 500 m: Choose QSFP28 PSM4 optical transceiver (requires 8 core MPO connector).
- Within 2 km: Choose QSFP28 CWDM4 transceiver (the most popular choice, using only 2-core fiber, with moderate cost).
- 10-20 km: Choose QSFP28 LR4/LR1 (used to connect different data center parks within the same city).
2. Campus network and metropolitan area network
QSFP28 optical transceivers are used to connect buildings or nodes within the same company or institution that are slightly farther apart.
- Campus/Enterprise Park: Connect the core switches of different teaching and office buildings, usually within a distance of 2 to 10 km. 100GBE LR4 is standard selection, utilizing existing single mode optical fibers.s
- Metropolitan aggregation layer: Telecom operators aggregate multiple access points to the core node, with a distance of 10-40 km. The QSFP28 ER4 module 40 km is a common solution.
3. Telecom operator backbone network and DCI (Data Center Interconnection)
When the distance between data centers is far (tens to hundreds of kilometers), more powerful technology is needed.
- Long distance transmission: When the distance exceeds 40 km, standard NRZ modulation modules (such as ER4) are not sufficient. At this point, 100G QSFP28 ZR4 or coherent optical modules (such as CFP2-DCO, some also use QSFP28 packaging) will be used, utilizing coherent technology and EDFA fiber amplifiers to achieve relay free transmission for 80 km or even hundreds of km. This is mainly used for DCI of operator backbone networks or large cloud vendors.
4. High performance computing and special industries
- Supercomputing Center: Connecting computing nodes and storage nodes, requiring extremely low latency and high bandwidth. QSFP28 100GBASE SR4 and 100GBASE AOC are very common.
- Financial trading: Connecting exchanges and data centers, extremely sensitive to latency and jitter. We often use 100G LR4 with single-mode fiber or special low latency modules.
- Video/Broadcasting: Used for long-distance transmission of 4K/8K uncompressed video signals, requiring stable and high bandwidth optical links.
How to choose the right QSFP28 optical transceiver?
You can quickly determine which QSFP28 you need based on distance and environment:
| Transmission distance | Application | QSFP28 optical transceiver types | Characteristics |
| <5m | Same cabinet in the computer room | QSFP28 DAC cable | cheapest and most energy-efficient |
| 5 – 100 m | Within the same floor | SR4 + multimode fiber patch cable | high cost-effectiveness |
| 100 -500 m | Different floors or adjacent buildings | PSM4 | requiring more fiber optic resources |
| AOC | convenient, but slightly expensive | ||
| 500 -2 km | Different buildings within the park | CWDM4 | the most popular solution, using only two optical fibers |
| 2 – 10 km | within the same city | LR4 | standard metropolitan area scheme |
| 10 – 40 km | urban core or suburban data center | ER4 | FEC needs to be enabled |
| 40 – 80 km and above | Different cities | ZR or coherent optical module | the most complex solution |
Conclusion
From above explanation, you will know that if you want to find one QSFP28 optical transceiver to fit your equipment, please make clear of the specific connection distance, fiber type (existing or newly installed), and equipment brand information, then you can know which transceiver module solution is more suitable.
- Internally connected switches in data centers, commonly using SR4/CWDM4;
- Connecting buildings between parks and urban areas, LR4 is commonly used;
- Cross city long-distance transmission, using ZR or coherent modules.