QSFP-DDs: The Benefits and Realities

The March of Time

There was once a time when T1 speeds of 1.544 Mbps were considered a blazing uplink and a 10Mb half-duplex LAN got the job done. However, time and technology do not stand still and 200Gbps and 400Gbps links are in production networks now around the globe. These link speeds are moving from the “wishlist” column into the “requirement” column in many expansion plans. If you find yourself asking the question, “Do I need connections this fast in my network?”, the answer typically is, “Yes!” or “ I will be sooner or later”.

The Road to 400G

There are competing formats of pluggable transceivers supporting rates beyond 100G, the most prominent are OSFP and QSFP-DD. OSFP is Octal Small Formfactor Pluggable. While it has some things going for it, it’s not really had the popularity predicted when it first came out.

The dominant format is the QSFP-DD and is also the result of the SFP form factor development. The QSFPs incorporate four SFP data lanes which makes QSFP to SFP breakouts easy.

QSFP-DD transceivers are a new format, but their ports have legacy support for the QSFP form factor as well! Essentially, they are two QSFPs engineered to fit into a single package. When you slot a QSFP-DD transceiver, the contacts push further into the connector to make the additional contacts. The shallower insertion depth of legacy QSFPs only reach the initial row of contacts.

The QSFP-DD standard supports multiple signaling rates. The QSFP28-DD can support 200Gb, based in 8 data lanes at 25Gbps, while the QSFP56-DD supports 400G links with 8 data lanes of 50Gbps.

The Need for Speed

Enough with the history lesson! You may be wondering if you can use 200G and 400G links in your network. The answer? Maybe. And if not now, you certainly will in the future. Not all switches, routers, and other network fixtures have the appropriate internal sockets and data lanes to support QSFP-DD so stepping up to faster link speeds might not be instantly possible. However, network equipment has a finite relevant lifespan so next time you need to plan an upgrade, make sure that the QSFP-DD support is covered by whatever you choose.  A great advantage to using QSFP-DDs as part of your growth strategy is being able to still use all your QSFP form-factor based transceivers.

Those Are Some Large Eggs in That Basket

Moving to such high-speed links is inevitable but should be implemented cautiously. Obviously, losing 400G of capacity due to a single fiber break could be devastating. By best practice, you have to plan for redundant links with redundant paths in case of disaster. And the longer the fiber run the greater its vulnerability. While the lack of extended reach QSFP-DD transceivers on the market today precludes some use cases, transitioning equipment purchases for QSFP-DD compatibility is a must because there are ways that your network can be improved using what’s available right now.

What Will Push You to 200G and 400G? 

If you’re supplying access to users, developers, a sales team, or other local agents you know that they always need more bandwidth.  Installing QSFP28-DD SR8s in your distribution network will let you break a 200G link out into 8 25G lanes with 100m range for flexible deployment of access switches that manage bottlenecks. QSFP56-DD SR8s are similar but with 50G per lanes you have 400G capacity.

• Datacenter TLC 

100 meters is enough for some applications but as datacenters grow, sometimes it’s just not enough. QSFP56-DD DR4 uses an MPO12 connector for breaking out 400G into 4x100G over distances of 500m (up to 2km with DR4+). QSFP56-DD DR4 400G transceivers connecting to 4 QSFP28 FR 100G transceivers is an excellent way to distribute bandwidth around your datacenter, building, or even campus.

QSFP28-DD CWDM4-CS breaks out a 200G connection to two 100G QSFP28-CWDM4. This is especially attractive if you’re network center is using CWDM4 for its existing distribution.

• Network Interconnects 

When it comes time to upgrade the link between two networks, the QSFP56-FR4 and QSFP56-LR4 are 400G options that use standard duplex single mode fibers. For high-speed interconnects requiring 2km to 10km, this is the way to go. When you consider the expense and commitment of adding additional fiber runs to add additional 100G links between facilities, the cost of 400G is the better investment.

It’s Eventual.

In the end, even if you don’t need to add the bandwidth now, if you have cause to conduct network upgrades, you should make QSFP-DD support a must have when shopping. With the variety of QSFP28-DD and QSFP56-DD options available making the right choices for your existing fiber infrastructure and bandwidth needs can be intimidating.

The experts at Integra Optics can take the guess work out of your design solution, no matter what platforms you are using.