QSFP-DD vs QSFP56 vs QSFP28 Optical Transceivers
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QSFP-DD vs QSFP56 vs QSFP28 Optical Transceivers
The advancement of 40G QSFP+ to 100G QSFP28 optical transceiver has created a major step for the 200G QSFP56 and 400G QSFP-DD optical transceivers.
In this newsletter, we shall discuss on the differences between QSFP-DD, QSFP56 and QSFP28.
Form Factor
Form Factor | QSFP-DD | QSFP56 | QSFP28 |
Data Rate | 400G/200G | 200G | 100G |
Lane count | 8 electrical | 4 electrical | 4 electrical |
Lane data rate | 25 / 50 Gbps | 50 Gbps | 25 Gbps |
Modulation type | NRZ / PAM4 | PAM4 | NRZ |
Power consumption | 12 W | 4 -7.5 W | < 3.5 W |
Connector types | CS / LC | LC / MPO / CS | LC / MPO |
Dimensions | 18.35 / 89.4 /8.5mm | 18.35 / 72.3 / 8.5mm | 18.35 / 72.3 / 8.5mm |
Data Rate
Data rate is the amount of data transmitted during over a network at a specific time.
QSFP-DD is Double-Density, which allows the maximum data rate of 200Gbps or 400Gbps:
- 8 channels modulated with NRZ of 25Gbps per channel results to 200Gbps
- 8 channels modulated with PAM4 of 50Gbps per channel results to 400Gbps
- 4 channels modulated with PAM4 of 100Gbps per channel results to 400Gbps
QSFP56:
- 4 channels modulated with PAM4 of 50Gbps per channel results to 200Gbps
QSFP28:
- 4 channels modulated with NRZ of 25Gbps per channel results to 100Gbps
Transceiver type | Modulation |
100G QSFP28 | NRZ |
200G QSFP56 | NRZ / PAM4 |
400G QSFP-DD | PAM4 |
Modulation Type
In every optical transceiver, it consists of an optical laser which emits light, and a modulator that manipulates the property of light. The transmission of the optical transceiver depends on the intensity of the light that is modulated.
For 1G, 10G and 25G SFP modules, the modulation technique used is non-return to zero (NRZ), and for longer distance transmissions, the host side is enabled with forward error correction (FEC). For higher data rates of 40G and 100G modules, 4 lanes of parallel signals of 10G and 25G NRZ are modulated respectively. The modulation at NRZ consists of 2 levels of binary code using low and high signal levels to represent 1 and 0. NRZ can only transmit 1 bit, i.e. a 0 or 1, of information per signal symbol period.
For higher speeds like 200G and beyond, PAM4 modulation is developed to achieve higher data rates. Pulse Amplitude Modulation 4 (PAM4) is a 4-level signal modulation format used to transmit signals. Each signal level represents 2 bits of logic information. With PAM4 modulation, information can be transmitted at twice shorter time.
Figure: PAM4 Modulation
Click here to read more about PAM4 modulation.
Power Consumption
Optical transceivers are active modules that consumes power from host equipment. A higher data rate optical transceiver will draw higher power from the host device, and results in higher temperature and larger heat dissipation component. Typical power consumption of optical transceiver for various form factor is shown in the table below:
Transceiver type | Power consumption |
100G QSFP28 | < 3.5 Watts |
200G QSFP56 | < 5 Watts |
400G QSFP-DD | < 12 Watts |
Connector Type
For every optical transceiver, there is an electrical connector that connects to the host equipment, and laser output which connects to optical fiber. QSFP28 and QSFP56 transceivers have a 38-pin electrical interface which connects to the host device, while the QSFP-DD as a double density module, has a double count of electrical pins – 76-pin. For a system designed with QSFP-DD port, it is backward compatible with QSFP56 and QSFP28 form factor transceivers. In other words, if you have a router with QSFP-DD port, you can plug in a QSFP-DD, QSFP56 or QSFP28 into the same port. However, you may want to check the product data sheet if it supports the QSFP56 or QSFP28 transceiver.
Figure: QSFP-DD with additional electrical pad
Dimension
QSFP-DD is a longer transceiver because of the extra electrical pads which makes it a double density transceiver. The typical dimension of the various modules is:
QSFP-DD: 18.35 x 89.4 x 8.5 (W x D x H) mm
QSFP56: 18.35 x 72.3 x 8.5 (W x D x H) mm
QSFP28: 18.35 x 72.3 x 8.5 (W x D x H) mm
Although QSFP56 and QSFP28 share the same size, the host switch must support the speed at the port where it is designed for. For example, a 100G port on the switch can activate a QSFP28 but not a QSFP56.
Type of Various Modules
Summary
QSFP28, QSFP56 and QSFP-DD transceivers differ in many ways. The most significant difference for the QSFP-DD transceiver is the double density form factor to support data rate of 400Gbps. The QSFP-DD unlocks the ability to achieve 400Gbps with PAM4 modulation. This modulation technique allows transmission in two times shorter time – or two times more information at the same time. With this principle QSFP-DD can achieve higher data rates.
Why Choose Starview Transceivers?
Starview sets the standard for reliability, performance, and support for transceiver modules. With our dedicated service, these transceivers are reprogrammable to work seamlessly with various networking equipment, eliminating error messages and alarms.
To learn more about Starview’s product lineup, explore our E-Catalog or contact us at sales@starviewtech.net. Embrace the power of data transmission with Starview.