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Can I Use QSFP+ Optics on the QSFP28 Port?

100G Ethernet will have a larger share of network equipment market in 2017, according to Infonetics Research. But we can’t neglect the fact that 100G technology and relevant optics are still under development. Users who plan to layout 100G network for long-hual infrastructures usually met some problems. For example, currently, the qsfp28 optics on the market can only support up to 10 km (QSFP28 100GBASE-LR4) with WDM technology, which means you have to buy the extra expensive WDM devices. For applications beyond 10km, QSFP28 optical transceivers cannot reach it. Therefore, users have to use 40G QSFP+ optics on 100G switches. But here comes a problem, can I use the QSFP+ optics on the QSFP28 port of the 100G switch? If this is okay, can I use the QSFP28 modules on the QSFP+ port? This article discusses the feasibility of this solution and provides a foundational guidance of how to configure the 100G switches.

For Most Switches, QSFP+ Can Be Used on QSFP28 Port

As we all know that QSFP28 transceivers have the same form factor as the QSFP optical modules. The former has just 4 electrical lanes that can be used as a 4x10GbE, 4x25GbE, while the latter supports 40G ( 4x10G). So from all of this information, a QSFP28 module breaks out into either 4x25G or 4x10G lanes, which depends on the transceiver used. This is the same case with the SFP28 transceivers that accept SFP+ transceivers and run at the lower 10G speed.

QSFP+ can work on the QSFP28 ports

A 100G QSFP28 port can generally take either a QSFP+ or QSFP28 optics. If the QSFP28 optics support 25G lanes, then it can operate 4x25G breakout, 2x50G breakout or 1x100G (no breakout). The QSFP+ optic supports 10G lanes, so it can run 4x10GE or 1x40GE. If you use the QSFP transceivers in QSFP28 port, keep in mind that you have both single-mode and multimode (SR/LR) optical transceivers and twinax/AOC options that are available.

In all Cases, QSFP28 Optics Cannot Be Used on QSFP+ Port

SFP+ can’t auto-negotiate to support SFP module, similarly QSFP28 modules can not be used on the QSFP port, either. There is the rule about mixing optical transceivers with different speed—it basically comes down to the optic and the port, vice versa. Both ends of the two modules have to match and form factor needs to match as well. Additionally, port speed needs to be equal or greater than the optic used.

How to Configure 100G Switch

For those who are not familiar with how to do the port configuration, you can have a look at the following part.

  • How do you change 100G QSFP ports to support QSFP+ 40GbE transceivers?

Configure the desired speed as 40G:
(config)# interface Ethernet1/1
(config-if-Et1/1)# speed forced 40gfull

  • How do you change 100G QSFP ports to support 4x10GbE mode using a QSFP+ transceiver?

Configure the desired speed as 10G:
(config)# interface Ethernet1/1 – 4
(config-if-Et1/1-4)# speed forced 10000full

  • How do you change 100G QSFP ports from 100GbE mode to 4x25G mode?

Configure the desired speed as 25G:
(config)# interface Ethernet1/1 – 4
(config-if-Et1/1-4)# speed forced 25gfull

  • How do you change 100G QSFP ports back to the default mode?

Configure the port to default mode:
(config)# interface Ethernet1/1-4
(config-if-Et1/1)# no speed

Note that if you have no experience in port configuration, it is advisable for you to consult your switch vendor in advance.

Conclusion

To sum up, QSFP+ modules can be used on the QSFP28 ports, but QSFP28 transceivers cannot transmit 100Gbps on the QSFP+ port. When using the QSFP optics on the QSFP28 port, don’t forget to configure your switch (follow the above instructions). To make sure the smooth network transmission, you need to ensure the connectors on both ends are the same and no manufacturer compatibility issue exists.

Original source : http://www.chinacablesbuy.com/can-use-qsfp-optics-qsfp28-port.html

Guide to QSFP28 Transceivers for 100G Data Center Connectivity

Using standard transceivers and cables is the most straightforward way to upgrade to 100G traffic. However, there are several types of 100G optics (transceivers and cables) available on the market like the CFP, CFP2, CFP4 and QSFP28 fiber optic assemblies. QSFP28 transceivers offer the cost-optimized solutions for connecting 100G switches together in a rack or data center, which become very popular in the 100G connectivity. Today, we are going to introduce this smallest 100G form factor transceiver—QSFP28 to you.

QSFP28 Optical Transceivers

It is notable that QSFP28 transceiver not only have the same physical size as the QSFP+ used for 40G traffic, but the lowest power consumption among those that are capable of handling 100G traffic. The QSFP28 interconnect offers four channels of high-speed differential signals with data rates ranging from 25 Gbps up to potentially 40 Gbps, and will meet 100 Gbps Ethernet and 100 Gbps 4X InfiniBand Enhanced Data Rate (EDR) requirements. There are basically two types of QSFP28 transceivers seen in the below image.

qsfp28-sr4-vs-lr4

QSFP28-SR4 transceivers is specially designed to support connections of up to 100 meters over multimode fiber. This approach is similar to using AOC cables, but here it is possible to use structured cabling. They use more expensive non-standard MPO (multi push-on/pull-off cable) connectors which cancel out some of the cost savings of the transceiver. QSFP28-LR4 versions support connections up to 10km over single-mode fiber. They use standard LC connectors and the existing structured LC cabling.

For distances longer than 10km, there have also been some recent breakthroughs in transceivers with DWDM capabilities, most significantly the PAM4. To be effective, however, the DWDM QSFP28 PAM4 requires amplification for even very short distances, and for any distance over 5 or 6km, needs dispersion compensation. With this, it can handle data traffic up to 80km.

QSFP28 Cable Assemblies

Compared to the QSFP28 transceivers, QSFP28 cable (DAC or AOC cables) is the more convenient, low-cost method of connecting 100G equipment. And most importantly, using a single cable assembly removes many of the problems associated with dirty connectors. DAC is suitable for applications within 15m and AOC up to 70m. AOC cable assemblies provide similar performance to discrete transceivers and fiber cables. The following image shows a QSFP28 AOC (left) and QSFP28 DAC cables (right).

qsfp28-aoc-and-dac-cables

QSFP28 Application

No matter you choose to use the QSFP28 transceivers or cables, they are indeed the ideal solution for switch vendors who need to handle data that stays within the rack and the data center. QSFP28 offers the perfect fit for these scenarios. However, for the 100G longer distance, the CFP and CFP2 offer DWDM Coherent technology and enable multi-channel long distance connectivity of more than 1000km. One thing we can’t miss is that the CFP is too big to be used in an Ethernet switch in volume.

Even though a vendor chooses the smaller CFP2 or CFP4, the size and power are often unrealistically high. One solution is to offer CFP DWDM support for those few links where it’s required, but even there, the increase in power consumption and the decrease in available ports have an impact on the overall cost-effectiveness of the switch.

Conclusion

The QSFP28 fiber optic solution that offers the best of both worlds allows the user to get the full benefits of QSFP28 transceivers and cables in the datacom equipment, but also gets the advantages of high-speed traffic transportation between sites. FS.COM offers a variety of 100G modules, DACs and AOCs, as well as the cable assemblies and management hardware which can satisfy short or long reach applications. For more detailed information, please contact us directly.