Dissimilarities between QSFP56-DD and QSFP28, QSFP+, QSFP56, CFP8, OSFP, COBO

The slightest form factor QSFP-DD for 400 Gigabit optical transceivers provides the industry's high-level bandwidth density. Being the popular fiber optic transceivers within 400 Gigabit excessive speed applications, we often compare QSFP-DD with modules like OSFP, COBO, CFP8, and QSFP56. This writing will describe them.

QSFP56-DD Wiki:

"Double Density" here stands for doubling the excessive-speed electric interfaces that the module favors more than the standard Quad Small Form Factor Pluggable module. QSFP-DD, which we can also call QSFP56-DD, means Quad Small Form Factor Pluggable Double Density, and it is thoroughly compliant with QSP56-DD MSA and IEEE 802.3bs standards. Each channel's data rate can extend to 25 Gigabytes via NRZ modulation technics, understanding 200 Gigabit network transmissions. Moreover, each channel's data rate can grow to 50 Gigabytes through the modulation technology of PAM4, attaining 400 Gigabit network communication, which is appropriate for cloud networks and high-performance cloud computing data centers.
We have given here the benefits of the form factor QSFP-DD:
●    Backward Compatibility: enabling the QSFP56-DD to favor the current QSFP modules (like QSFP56, QSFP28, QSFP+, etc.) and offering system designers and end-users flexibility.
●    Taking on the 2x1 collected desegregated connector/cage to favor the two-high and one-high cage connector method.
●    1XN Cage Pattern and SMT Connector: This design can facilitate thermal help for not less than 12W for one module. The high thermal decreases the demand for heat dissolution capabilities of optical transceiver, so decreasing some unessential expenses.
●    ASIC Design: promoting different rates of interface and thoroughly backward adaptable to QSFP28 and QSFP+ modules, so decreasing equipment development and port costs.

A Comparison between QSFP+, QSFP28, QSFP56, and QSFP-DD:

QSFP56-DD, QSFP28, QSFP56, and QSFP+ connect to the form factor QSFP. We have explained the differences in the given descriptions. However, how can we differentiate them?

Structure:

Regarding appearance, the length, thickness, and width of QSFP-DD are similar to QSFP56, QSFP28, and QSFP+. However, we have equipped the module QSFP56-DD with an eight-lane electric interface instead of a four-lane as we have doubled the different QSFP modules and QSFP-DD's ASIC ports to support current interfaces like CAUI-4. That's why QSFP-DD's mechanical interface upon the host system is moderately deep compared with other QSFP transceivers to adjust the extra contacts line.

Application and Bandwidth:

The QSFP56-DD modules can extend to 400 Gigabytes per second, whereas QSFP56, QSFP28, and QSFP+ can support 200Gbps/100Gbps/40Gbps, respectively. We use QSFP56-DD connectors in 400 Gigabit fiber optic modules, AOCs and DACs, and apply for 400 Gigabit data center connections. Moreover, we use QSFP56, QSFP28, QSFP+ modules, and DAC/AOC for 200G/100G/40G network links.

Backward Compatibility:

As discussed earlier, the QSFP-DD is backward adaptable to the earlier QSFP system optical transceiver modules. Moreover, its backward adaptability can evade the current equipment replacement upon the scale and efficiently decrease the cost of network upgrades. That is to say,  earlier form factor, we have technically upgraded the QSFP56-DD to support extended bandwidth.

A Comparison between OSFP, CFP28, COBO, and QSFP-DD:

The 400G form factors are CFP8/OSFP/COBO and QSFP56-DD. We have listed below the dissimilarities of them:

OSFP VS QSFP-DD:

OSFP is a new form factor having eight excessive speed electric lanes that can primarily support 400 Gigabytes (8x50 Gigabits) or extend to 800 Gigabytes. The form factor of OSFP is slightly profound and comprehensive compared with QSFP-DD. The length, thickness, and width of QSFP56-DD are 8.5mm, 89.4mm, and 18.35mm, and regarding OSFP are 13.0mm, 107.8mm, and 22.58 millimeters. However, it still favors 36 ports of OSFP per 1 Unit front panel, facilitating 14.4 Tb/s for 1 Unit.
Generally, QSFP-DD’s power consumption is 7-12 watts, whereas OSFP can extend from 12-15 watts. The function of the optical transceiver will be better if power consumption is lower. Contrary to QSFP-DD, OSFP is not backward compatible with QSFP+/QSFP28 because it possesses a massive size compared with QSFP+/QSFP28.

CFP8 VS QSFP-DD:

Featuring a form factor of 41.5 millimeters* 107.5millimeters*9.5millimeters, the module CFP8 provides high bandwidth compared with the current 100 Gigabit solutions. We have generally specified its electric interface to enable 8x50 Gigabytes and 16x25 Gigabytes mode. As CFP8'S size is large compared with QSFP-DD, CFP8's power consumption is higher compared with QSFP-DD. In the meantime, we can't use CFP28 on the ports of QSFP+/QSFP28. The highest bandwidth of QSFP-DD and CFP28 is 400 Gigabytes. However, CFP28 only favors the set-up of 8x50G or 16X25G, whereas QSFP-DD also favors both 200 Gigabytes (8x25G).

COBO VS QSFP-DD:

COBO means Consortium for on-Board Optics. We can install it to the equipment line card in controlled conditions. It has no support for hot-pluggable. Therefore, it is very problematic for modules COBO to maintain compared with QSFP-DD. Furthermore, the form factor COBO possesses two electric interfaces-sixteen lanes and eight-lane to encounter 2x400 Gigabit and 1X400 Gigabit transmission requirements.
The chart below manifests the marketing maturity of OSFP, QSFP-DD, COBO, and CFP28 form factors. The more the numbers are, the higher the form factors' maturity.

We can observe from the chart that the general rating of the form factors OSFP and QSFP-DD are significant compared with more form factors. Therefore, OSFP and QSFP-DD are more favorites for optical fiber manufacturers. In contrast, we can apply the former for telecommunications implementations, and the latter is appropriate for data center implementations.

Is QSFP-DD Desirable in 800GbE?

We will apply the 400 Gigabit optics widely. For the applications of data centers, QSFP-DD is appropriate compared with OSFP. With the growing pressure on the data center's internal bandwidth and the concentration within the data center's east-west network traffic, the time interval between the implementation of excessive speed fiber optic modules within the data center and the telecom market is constantly shortening. So, QSFP-DD will get the advantage from 400GbE and get involved in a reliable development prospect.

As 400 Gigabit becomes commercially achievable widely, we have set one-wave 100 Gigabit technology to mature, setting down the preparations for the advent of 800 Gigabit. In recent times, the QSFP56-DD MSA Association issued the first edition of QSFP56-DD 800 optical transceiver hardware particulars, which we dedicate to the continuance of the existing form-factor QSFP-DD to favor a one channel rate of about 100 Gigabytes per second eight-channel modern generation QSFP56-DD 800. It also signifies that 800 Gigabit may still take on the form factor QSFP-DD to bring significant values and advantages to Internet service suppliers.