As the arrival of 40G Ethernet, many enterprise users have to think about how to migrate their network to a 40G network with full use of the current 10G network infrastructure. Specifically, when new 40G switches with QSFP+ ports are added in, how to directly connect them with your existing 10GbE devices (like switches and servers) with SFP+ ports is the top thing you need to consider. In this post, three widely used migration solutions to directly convert a port from QSFP+ to SFP+ will be shared for your references.
The first method to directly convert QSFP+ to SFP+ port is using the QSFP+ breakout cable. QSFP+ breakout cables now can be found in DAC (direct attach cable) and AOC (active optical cable) types. Mostly, both two types are pre-terminated with a QSFP+ transceiver on one end and four SFP+ transceivers on the other end, which are known as QSFP+ to SFP+ breakout cables. In addition, another type of AOC breakout cable, QSFP+ to 4x duplex LC AOC cable, having QSFP+ on one end but duplex LC fiber cables on the other, can also convert a port from QSFP+ to SFP+ when used with additional SFP+ transceivers.
No matter what type you choose, all these QSFP+ breakout cables can split a 40G connectivity into 4x10G channels (just like the following figure shown), while you connect them with a QSFP+ switch on the one end and several 10G devices (up to four) containing SFP+ ports on the other end.
The second way to convert QSFP+ to SFP+ port is using MTP/MPO to LC breakout cable. This solution is similar to the prior solution but without the transceiver pre-terminated on each end. With an MTP/MPO connector on one side, MPO/MTP 8-fiber assembly is often equipped with four LC duplex connectors on the other side. To realize the conversion from 40G to 10G, you need to add one QSFP+ transceiver with MTP/MPO interface and four SFP+ modules with duplex LC interfaces for each MTP/MPO to LC breakout cable. As the figure is shown below, you just need to plug the cables into the matching 10G or 40G transceivers and then insert these transceivers into QSFP+ port or SFP+ ports.
Another way to directly convert QSFP+ to SFP+ port is via the help of a 10G type of the QSA (quad small form-factor pluggable adapter): CVR-QSFP-SFP10G. Built-in a QSFP+ form factor with a cage for SFP+ module at the back, this QSFP+ to SFP+ adapter enables smooth connectivity between devices that use 40G QSFP+ port and 10G SFP+ port. To have a 10G connection, you can insert an SFP+ module into a QSFP+ to SFP+ adapter and then connect this CVR-QSFP-SFP10G adapter to a QSFP+ port. In that connection, the QSFP+ to SFP+ adapter will act as an interface of an SFP+ module.
Up to now, we have explored three direct ways to convert a port from QSFP+ to SFP+ port. However, in data centers or other high-density cablings, network migration is a complex process. Sometimes, inter-connect connectivity also needs to be used. But how to make your selection about those methods, you can take the following factors into considerations.
To migrate a QSFP+ port to SFP+ port, the transmission distance should be the prior thing to be checked. Based on that, you can decide to use what type of transceiver and connectivity. Usually, the inter-connect type, with a combined use of 40G MTP/MPO trunk cables and 8-fiber cable assemblies like figure 4 shown, will be more suitable for long-distance transmission. Even for the direct connection, the QSFP+ to 4xSFP+ AOC/DAC cable is limited for a short-reach distance compared with the other two types.
Although fiber optic cable is becoming more and more popular, copper cable is still used for 40G-to-10G transmission in some cases. With its own feature, the copper cable can only be used for short-distance transmission within several meters. Since copper cable is much cheaper than optical cable, the copper solution from QSFP+ to SFP+ port like DAC QSFP+ breakout cable can be chosen in a short-reach distance transmission.
In a high-density network, there could be hundreds or thousands of QSFP+ ports and SFP+ ports needed to realize 40G-to-10G connectivity. Cable assemblies like QSFP+ breakout cable with pre-terminated transceivers will be more suitable than QSFP+ to SFP+ QSA adapter and other inter-connect methods in saving space and simplifying the network maintenance.
Last but not least, the whole cost is one of the most crucial factors for choosing a way to convert QSFP+ to SFP+ port. You need to take all the above factors together to pick the most cost-effective solution. For example, if your 40G-to-10G connections are taken in a short-distance within 7 meters, the 40G QSFP+ to 4x10G SFP+ DAC cables, with pre-terminated QSFP+ module and four SFP+ modules will be the most economical solution than any other combinations.
With a trend for higher network speed, it will be a normal state for enterprise networks and data centers to have multi-speed coexist. Grasping the solution to connect a lower speed port with a higher speed port, like converting QSFP+ to SFP+ port, matters a lot for your network performance improvement.
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