Understanding Backward Compatibility with QSFP-DD, QSFP28, QSFP+ and SFP+

For optical modules, backward compatibility is essential. The upkeep and operation of the network infrastructure are directly related. Future data center deployment will benefit tremendously from the flexibility of transceivers with backward compatibility. This page will serve as a helpful guide to backward compatibility. It covers popular transceiver types like QSFP-DD, QSFP28, QSFP+, and SFP+.

Backward Compatibility with SFP+

What is SFP+?

Optimized small form-factor pluggable, SPF+, is intended for 10G networking uses. Before 10G SFP+, the majority used 300Pin, XENPAK, X2, and XFP versions in 10G optical transceivers. Realizing the 10 Gbit/s data throughput in a relatively compact form factor—which is the same as SFP—is the most notable improvement of SFP+. In 2006, developers first made the SFP+ standard available. SFP+ optical modules have been widely used in the industry for over ten years due to their low cost and high density. 10G SFP+ is widely used in data centers nowadays. Applications for SFP+ transceivers include Ethernet, Fibre Channel, and InfiniBand. 10G BASE-SR, 10GBASE-LR, 10G BASE-T, 10G BiDi SFP+, and 10G SFP+ CWDM/DWDM are examples of typical SFP+ kinds.

Is SFP+ Backward Compatible with SFP?

Certainly right. SFP+ is backward compatible with SFP since it has precisely the same dimensions as SFP, but it offers substantially faster data speeds. With 1G SFP modules, SFP+ ports can function, albeit at 1Gbps rather than 10Gbps. In most cases, the data rate configuration is not automated; instead, you must manually set the port to 1G speed.

Is SFP+ Compatible with XENPAK or X2?

The answer is no, SFP+ is not compatible with XENPAK or X2. An XENPAK to SFP+ converter adapter or an X2 to SFP+ converter adapter is necessary if your SFP+ modules need to be connected to older equipment that has XENPAK ports or X2 ports.

Backward Compatibility with QSFP+

What is QSFP+?

Four 10 Gbit/s channels can allow data speeds of up to 40 Gbps with QSFP+ (Quad Small Form-factor Pluggable Plus). IEEE 802.3ba specifies QSFP+. This optical transceiver is slightly bigger than SFP+, but it offers the best density for 40 Gigabit Ethernet. LR4, ER4, and 40G QSFP+ SR4 are the most typical types of QSFP+ optical transceivers.

Is SFP+ and QSFP+ Compatible? How Can a QSFP+ Port be Converted to an SFP+ Port?

As a result of their dissimilar physical dimensions, QSFP+ and SFP+ are incompatible. Does this imply that there is a connection problem between the QSFP+ and SFP+ ports? No, there are several options available to convert a QSFP+ port to SFP+.​

Option 1: Using a QSFP to SFP+ breakout cable

To link to a 40G QSFP switch port on one end and to four 10G SFP+ ports on the other, utilizing QSFP to four SFP+ active optical breakout cables or QSFP to four SFP+ copper direct attach breakout cables (DAC). Both types of DAC and AOC breakout cables come pre-fitted with a QSFP+ transceiver at one end and four SFP+ transceivers at the opposite end. The AOC employs fiber lines, whereas the DAC uses copper wires. This is the primary distinction between both. For individuals who want short-distance connections, these breakout cables are ideal since they provide a very practical and affordable solution.

Option 2: Employing optical transceivers in conjunction with an MTP to LC breakout cable

One QSFP optical transceiver and four SFP+ transceivers are required for this setup, and they are connected via an MTP to LC 8 fiber breakout cable. The two endpoints of the optical transceivers select which of the MMF and SMF types of fiber breakout cables to use. Although it costs more, this option can give a far greater distance than the previous one.

Option 3: Adopting a QSFP to SFP+ adapter

Another cost-effective way to convert a QSFP+ to an SFP+ port is to use a QSFP to SFP+ adapter. It enables QSFP-only systems to have a 10 Gigabit Ethernet connectivity. You don't need to configure anything—just plug and play. The QSA adapter is compatible with all standard SFP+ optical transceivers. It also works with direct attached copper cables (DAC) and active optical cables (AOC). With this ingenious adapter, you can connect to a slower port on the other end of your network. Just use any SFP+ transceiver or cable you like.

Backward Compatibility with QSFP28

What is QSFP28?

With four channels that each allow 25 Gbit/s, QSFP28 is intended for 100G Ethernet and can handle data speeds of up to 100 Gbps. SFP and SFP+ are progressively being supplanted by 100G QSFP28 transceivers as the most widely used types of optical modules. PSM4, CWDM4, SR4, and LR4 are examples of typical 100G QSFP28 transceivers. Additionally common in short-range 100G applications such as QSFP28 DAC and AOC is QSFP28 to QSFP28 cable. 400G QSFP-DD SR8, DR4, FR4, LR4, and LR8 transceivers are common configurations. In addition, 200G QSFP-DD transceivers such as SR8, PSM8, and LR8 are available.

Is Backward Compatibility with QSFP Permitted by QSFP28?

Certainly right. QSFP28 and QSFP share the same dimensions and factors. Each QSFP and QSFP28 has four lanes. QSFP28 offers 25 Gbit/s per lane, while QSFP only permits 10 Gbit/s. QSFP28 and QSFP are backward compatible because of their comparable physical form factors and operational principles.

Backward Compatibility with QSFP-DD

What is QSFP-DD?

A new form factor termed QSFP-DD (Quad Small Form-factor Pluggable Double Density) is intended for the high-density 200G and 400G Ethernet protocols of the future generation. It meets with QSFP-DD MSA and IEEE802.3bs. As the name suggests, QSFP-DD offers an eight-lane electrical interface. It also has twice as many high-speed electrical connectors as its 4-lane QSFP28 and QSFP predecessors.

QSFP-DD provides data rates up to 200Gbps or 400Gbps based on various lane data rates and modulation technologies:

• 200Gbps: 8 lanes with NRZ modulation that provide 25 Gbps per lane

• 400Gbps: 8 lanes with PAM4 modulation that support 50Gbps per lane

  

Is Backward Compatibility Permitted with QSFP-DD? What Types of Factors Does it Permit?

Yes, of course. Based on the QSFP pluggable form factor, QSFP-DD was created. Its pinout is identical to that of the QSFP connector. Consequently, QSFP-DD preserves port density while quadrupling aggregate switch bandwidth.

Furthermore, 40G QSFP+, 100G QSFP28, and 200G QSFP56 are among the currently available QSFP form factor varieties with which QSFP-DD is backward compatible. This implies that the implementation of equipment incorporating QSFP-DD connectors will preserve backward compatibility, potentially enabling support for existing QSFP and QSFP28 modules. This gives end users more options and flexibility.

Conclusion

FS understands the importance of backward compatibility and is committed to providing comprehensive Internet data center solutions to meet the diverse needs of customers.

For those looking to leverage the benefits of SFP+, QSFP+, QSFP28, and QSFP-DD while ensuring seamless integration with existing infrastructure, FS offers various products and flexible solutions from optical transceivers to a range of DAC/AOC/AEC cables, which are not only cost-effective but also provide reliable performance. Furthermore, our professional technical team and testing laboratory can make sure that our products meet the highest standards of quality and service.

With our commitment to quality and customer satisfaction, FS is your trusted partner in navigating the complex world of optical module compatibility.