Tuesday, March 28, 2017

QSFP28 Transceiver With MTP or LC Duplex Cables

Nowadays, QSFP28 transceiver is the mainstream of 100G optics market. So as to meet different 100G deployment needs, QSFP28 modules usually come in several standards such as QSFP28 PSM4, QSFP28 CWDM4, IR4, SR4 and LR4, etc . Compared with CXP and CFP 100G optical transceivers, QSFP28 optics are the smallest form factors that provide a high-density and high-speed solution for 100G networks. A previous article provide detailed information about what distance QSFP28 optics can support for 100GbE deployment. Today’s article will introduce 100G QSFP28 cabling solutions by the use of MTP/MPO cables and duplex LC cables.
QSFP28 modules offer four channels of high-speed differential signals with each data rates up to 28Gbps, and will meet 100 Gbps (4x25 Gbps) in the end. QSFP28 transceiver is available in 100GBASE-SR4, 100GBASE-LR4, PSM4 and CWDM4 standards. The interface of 100G QSFP28 transceivers includes MTP/MPO and LC duplex cables.
Cabling Solutions of QSFP28 MPO
100G QSFP28 100GBASE-SR4 and 100GBASE-PSM4 transceiver modules are the 100G transceiver modules that need to be connected with MTP/MPO interfaces. 100GBASE-SR4 QSFP28 complies with QSFP28 MSA and IEEE 802.3bm specifications. It can support a link length of 100 m. 100G PSM4 specification defines requirements for a point-to-point 100 Gbps link over eight single-mode fibers with a supporting distance of 500 m. Figure 1 shows the QSFP28 SR4 with MTP connector.
MTP/MPO fiber cable is commonly used to connect QSFP+ or QSFP28 transceivers with single-mode and multimode categories, which is specially designed for 40G/100G high-density data center cabling system. MTP/MPO fiber cables are usually terminated with 12-fiber, 24-fiber, 48-fiber MTP/MPO connectors. Single-mode MTP/MPO cable is able to carry signal over long distance while multimode is for short-reach application. QSFP28 mpo
  • 100GBASE-SR4 QSFP28 over Multimode MTP cable
100GBASE-SR4 QSFP28 works over a 12-fiber multimode MTP/MPO patch cable (four not used) for short-reach 100G connection. Figure 2 shows the direct connection between 100GBASE-SR4 QSFP28 modules by the use of Female to Female 12-Fibers OM4 trunk Cable.
  • 100GBASE-PSM4 QSFP28 Over Single-mode MTP Cable
Similar to 100GBASE-SR4 QSFP28, 100GBASE-PSM4 QSFP28 also requires 12-fiber MTP/MPO patch cable. But QSFP28 PSM4 matches with single-mode MTP/MPO fiber patch cable instead of the multimode MTP/MPO .patch cables.
100G QSFP28 Optics With Single-mode Duplex LC Interface
100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28 are the 100G modules designed for long-reach applications terminated with duplex LC interface. 100GBASE-CWDM4 QSFP28, as the name implies, it is a full duplex module with the use of CWDM technologies. It integrates transmit and receive path in one module. 4 lanes of optical signals (25 Gbps per lane) firstly are multiplexed into an LC duplex interfaces on the transmitting side. Then data streams are de-multiplexed by an integrated optical de-multiplexer and transformed to an electrical CAUI-4 output driver. QSFP28 CWDM4 can support a distance of 2 km over single-mode fibers. Figure 3 shows the interconnection of 100G QSFP28 LR4 module connected with MTP to LC breakout and MTP cassette to achieve a total 400G data rate transmission.
Cisco QSFP28 LR4 optics
100GBASE-LR4 QSFP28 is a 4x25Gbps transceiver module that can support link lengths up to 10 km. 100GBASE-LR4 QSFP28 also operates over single-mode fiber cable with duplex LC connector by multiplexing and de-multiplexing optical signals. Common single-mode duplex LC patch cable can meet the cabling requirement of these two transceivers. For high density data center, HD LC fiber patch cable is highly recommended as the push-pull tab is easy to remove and can save space.
With compact size and low power consumption, 100G QSFP28 modules are becoming the most popular 100G optics on the market. QSFP28 SR4 and QSFP28 PSM4 transceivers terminate with MTP/MPO interfaces, while QSFP28 LR4 and CWDM4 modules connect with LC duplex cables. Besides QSFP28 transceivers, there are QSFP28 DAC and AOC cable available for short-reach 100G connections.

Thursday, March 23, 2017

10GBASE-T SFP+ Copper Transceiver Module – Innovative But Controversial

The past few years have seen the broad adoption of 10Gbps connectivity at network edge equipment. SFP+ optics including SFP+ fiber devices and SFP+ direct attach copper (DAC) cables, dominates the 10Gbps connectivity solution in the core or spine due to the longer link lengths and higher aggregated data bandwidth, however, 10GBASE-T cable (Cat 6a/7) is proven to be unbeaten for its lower cost, ease of installation and reliable performance for 10Gbps edge network with a link length of 100 m. In order to get most of your cat6a cabling, last year HPE and some other vendors launched a 10GBASE-T SFP+ transceiver module, which claimed to give equipment designers and data center professionals a new option in architecting their network solution. This article will provide detailed information about the innovative but controversial SFP+ 10GBASE-T copper module from a positive point of view.
SFP+ 10GBASE-T Copper Transceiver—RJ45 connector, 30 m, 2.5 W
SFP+ 10GBASE-T copper transceiver is specifically designed for high-speed communication links that require 10 gigabit Ethernet over Cat 6a/7 cable with a link limit of 30 m. Compared with standard SFP+ SR/LR fiber optics, the added benefit is that it uses standard-based technology with the familiar RJ45 connector and provides backward compatibility with legacy networks.
SFP+ 10GBASE-T module usage
SFP+ 10GBASE-T transceiver, compliant with MSA standard, is the first transceiver that offers 10GbE communication over copper. Seen from the above image, you can directly plug the 10GBASE-T SFP+ module into SFP+ port of the NIC or switch. The power usage and heat generated for 10GBASE-T is 4-8 watts, but SFP+ 10GBASE-T copper transceiver consumes 2.5 watts. Obviously, the specification of SFP+ copper module has been optimized to save more than 0.5 W per port when compared to an embedded 10GBASE-T RJ45 port for link distances up to 30m.
Nowadays SFP+ 10GBASE-T transceiver, owing to the compatible issue with switches, is not offered by many vendors. However, from a network equipment designer’s perspective, 10G SFP+ copper modules will become popular in the near future.
The Innovative Points of SFP+ 10GBASE-T Transceiver Module
It is true that Cat 6/Cat6a cabling can provide limited support of 10GBASE-T in some environments, but the reality is that there are several compelling reasons to specify SFP+ 10GBASE-T copper modules in a new 10 Gbps-ready data center.
  • Smaller Form Factor: Interoperable with any SFP+ cage and connector system
  • Reliability: The RJ45 connector interface is rock solid. No surprises when deployed in your data center
  • Reach: Up to 30 m over Cat 6a UTP cable, sufficient for all network access use cases
  • Innovation: Hot-pluggable with a managed soft-start
  • Performance: Full PHY presentation, which means nothing is missing
  • Cost: Pay-as-you-grow model that performs for today and scales for tomorrow
The Controversial Points of SFP+ Copper Module
Q1: Vendors thought that it would never be possible to create a 10Gb copper transceiver as SFP+ specification use less power than 10GBASE-T requires. But theoretically, SFP+ 10GBASE-T copper module indeed reduces the power consumption of more than 0.5 watts.
Note that SFP+ 10GBASE-T transceiver module meets the SFP+ spec, but it is not meeting 10GBASE-T official spec.
Q2: With the cheap SFP+ DAC Twinax and reliable SFP+ fiber optics available for 10Gbps application, why should people use the SFP+ copper modules?
In terms of application, some server NICs and gears don’t work well with DAC twinax. In this case, instead of replacing all your copper devices into the fiber cabling, you’d better stick to the copper-based network. The following part displays two scenarios of 10G connectivity by using SFP+ copper modules.
Scenario 1: Use Case Between Server and Storage Appliance
Scenario 2: Use Case Between Edge Switches
Scenrio 2 network-upgrade-to-10G
From the technical point of view, 10G SFP+ copper twinax cable and 10G SFP+ modules share some differences in power consumption, latency, linking length and cost.
The power usage, latency and heat generated for 10GBASE-T is 4-8 watts, which is considerably higher than using DAC twinax or fiber optics (nearly 1 watt). SFP+ 10GBASE-T copper module, however, uses 2.5 watts (max). Furthermore, SFP+ DAC cables (both passive and active) can only support up to 10 m, but the SFP+ 10GBASE-T transceiver connected with cat6a cables can cover a distance of 30 m.
The low-cost of twinax DAC makes it a better choice for performance in ToR deployments. With 10m twinax you can usually cover up to 3-adjecent racks. While the existing SFP+ 10GBASE-T transceivers usually charge even higher than the regular SFP+ fiber optics. Besides, you should factor in the power and cooler requirement overhead that 10GBASE-T optics brings with it.
Q3: Is it reliable to use SFP+ 10GBASE-T modules in your network?
So far, customers still feel skeptical about this product. Many professionals said that technically it could work, but it is not supported for most of the switches.
Final Words
Data center managers are taking the advantages of the convenience and flexibility provided by deploying 10 Gbps technology over twisted-pair copper cabling and leveraging their investment in installed copper infrastructure. To have a great interoperability between existing fiber switches and those with 10G copper ports, 10G copper SFP+ is introduced. However, owing to the unsolved compatible issues and limited usage, customers nowadays still choose to use DAC Twinax or SFP+ fiber optics for 10Gbps connectivity. We believe, in the incoming future, all the problems will be solved.

Sunday, March 19, 2017

Will Single-mode Fiber Work Over Multimode SFP Transceiver?

Network installers usually come across a situation that device you have in your network does not always fit and work perfectly with the fiber. They plan to make a cable plant based on the multimode cabling, but owing to the link limitation or other reasons, they have to connect multimode equipment with single-mode devices. Is it feasible? Or put it more specifically, can I use the multimode SFP over single-mode fibers or vice versa? This article will give you a detailed illustration about the feasibility of the solutions, and introduce two relevant devices (mode conditioning cable and multimode to single-mode fiber media converter).
Single-mode Fiber Over Multimode SFP—You Can If You Are Lucky
This is the question that has been asked so many time, but no one can give the exact answer—yes or no. Hence, let’s illustrate it in details.
Most people think single-mode and multimode fibers are not interchangable because of the wave length of the laser and core size of the fiber. Single-mode fiber (MMF) uses a laser as a light source (the light beam is very concentrated), while multimode fiber (MMF) uses an LED to generate the signal. This would require two significantly different devices to generate the signal.
The core sizes are drastically different between SMF and MMF. SMF is 9 micron and multimode is 62.5 or 50 micron. If users try to mix the single-mode and multimode cabling in the same network, they might have trouble dealing with the two different types of signal.
However, it is possible to interconnect two devices using SMF interfaces at one end and MMF receiver at the other end. Keep in mind that it depends on the devices, so you can if you are lucky. When plugging LC single-mode duplex fibers on the multimode fiber transceiver (1000GBASE-SX) in the network, you will find the link came up (the light on the switch turns green). Therefore, the multimode fiber transceiver connected by the single-mode fibers works for short-reach application. The following image is the real screenshot of the single-mode fibers inserting into the 1000BASE-SX SFP.
real screenshot of inserting single-mode fiber over multimode fiber transceivers
While it should be stressed that the link is not reliable and it only works for particular brand devices with a very short link length. Many sophisticated vendors like Huawei, Alcatel or Cisco do not support it. Nevertheless, owing to the differential mode delay (DMD) effect, signal loss of this connection is not acceptable, either.
To sum up, this might be feasible but not advisable. If you need to make a connection between single-mode and multimode interfaces, you’d better use the intermediate switch that is able to convert the signals between single-mode and multimode fibers. The following part will introduce two solutions that might be helpful for the multimode and single-mode conversion.
Solution 1: MCP Cable—Single-mode In and Multimode Out
As to the multimode fiber with single-mode SFPs, most people mention the mode conditioning patch (MCP) cables. The MCP cable is launched to support 1000BASE-LX optics over multimode cable plant. The mode conditioning cables allow customers to successfully run Gigabit Ethernet over our multimode cable using single-mode fiber transceivers, Cisco 1000BASE-LX/LH SFP is the special type of transceiver that can both support single-mode and multimode fibers. The image below displays the difference between standard SC multimode patch cable and SC mode conditioning patch cable.
comparison between standard SC multimode fiber patch cable and SC MCP cable
Then, in this situation, you can run successfully from a single-mode fiber transceiver over multimode fiber with the use of MCP cables, but the distance will not exceed the link specification for multimode transceivers. Otherwise, there will be much signal loss in the cable run.
In general, if you want to run multimode fiber optic cable over 1000BASE-LX SFPs, you can use the mode conditioning cable. However, mode conditioning patch cords are required for link distances greater than 984 feet (300 meters). For distance less than 300 m, please omit the mode conditioning patch cords (although there is no problem using it on short links).
Solution 2: Fiber to Fiber Media Converter—Conversion Between Multimode and Single-mode Fibers
As noted before, mode conditioning cables, to some extent, can realize the connection between single-mode to multimode, but you can not say that you can convert single-mode to multimode or vice versa. Mode conversion between multimode and single-mode fibers often requires fiber to fiber media converters or the single-mode to multimode fiber converter.
In the above diagram, two Ethernet switches equipped with multimode fiber ports are connected utilizing a pair of fiber-to-fiber converters which convert the multimode fiber to single-mode and enable network connectivity across the distance between Gigabit switches.
It doesn't really make much sense to use the single-mode fiber transceivers with multimode fibers in your network or vice versa, although the link will come up. Like I said above, you can if you are lucky connect. MCP cables and fiber to fiber converter are the two available options for single-mode and multimode connection. If you bought the wrong fiber optic cables, just replace it into the right one. Fiber optic cables and optical transceivers modules nowadays are very cheap. You won’t need to risk of mixing them in the same network.

Thursday, March 16, 2017

Comparing Three Fiber Optical Transceiver Manufacturers – Monoprice, Fluxlight & Fiberstore

If you search reliable fiber optic transceiver module manufacturers on Google, you will get thousands of results in a few seconds. But, where should you get the high-quality and low-price fiber optic transceiver modules? Monoprice, Fluxlight and Fiberstore as the representative of reputable optical transceiver manufacturers, are frequently recommended by many users. Are their fiber optic transceiver module worth any penny you spend? This article will decode these three companies and provide a vivid comparison between their fiber optic transceivers.

Monoprice—A Reliable Cable Supplier
Founded in 2002, monoprice used to be famous as a leading cable manufacturer, but now it develops to allow customers pulling together the whole computer system. Monoprice has built a stellar reputation for product excellence and customer services. The following are the screenshots of monoprice’s feedback. “The great part of monoprice is that we allow our customers to do things they want to do with price far below what competitors charge” says by the CEO of monoprice.

monoprice feedback
monoprice feedback 2

According to monoprice, they offer over 6,500 high-quality, affordable electronics and accessories to professionals and consumers worldwide. Cables such as the HDMI cables, networking patch cables, bulk networking cables are offered in variable standards and different cable length. As for the fiber transceivers, they recently do not offer many types of fiber optic transceivers. Their existing compatible fiber transceivers are from Ironlink. For example, the Ironlink Cisco SFP-10G-SR from monoprice is the Cisco Compatible 10GBase-SR SFP+.

Fluxlight, established in 2003, manufactures and sells optical products for use in communication fields. Products like optical transceivers, media converters, jumper cables, and patch cables are welcomed by users. FluxLight only offers brand-new, top-quality optical interconnect products that are guaranteed to be compatible with vendors like Cisco, 3com, Dell, D-Link, Extreme, Juniper, HP, and Finisar.

Fiberstore—A Cost-effective Optical Transceiver Manufacturer
Founded in 2009, Fiberstore (FS.COM) gradually becomes a leading company devoting to research & development, and offer fiber connectivity network solutions for carriers, ISPs, content providers and networks. With a few years of development and accumulation, Fiberstore have owned a whole series of optical communication products including the WDM equipment, transceivers, fiber optic assemblies, racks & enclosures, bulk fiber cables, enterprise network and so on.

Their wholesale fiber optic transceiver products are offered at the lowest price and fully compatible with the original devices. They assured to every customers that every fiber transceiver offered by Fiberstore before shipping has to go through strict test to assure 100% compatibility and high performance.

Fiber Optic Transceivers From Monoprice, Fluxlight and Fiberstore
Monoprice, Fluxlight and Fiberstore are offering several types of fiber optic transceivers. Where should I get the fiber transceivers? The following part will draw a brief comparison between them from the aspects of price, selection, and reputation.
Price is the number one factor that people would take into account. We can’t list all the products from their website and compare them here. So let’s take the 10G SFP+ modules as an example, the Ironlink Cisco SFP-10G-SR from monoprice is sold at $136.75. Fluxlight SFP-10G-SR is only $54.00. The price of Cisco compatible SFP-10G-SR from FS.COM is $16.00.

fiber optic tranceiver price

In the above image, Ironlink Cisco SFP-10G-LR from monoprice is $315.00. SFP-10G-LR from Fluxlight is $134.00. However, Fiberstore Cisco SFP-10G-LR is $34.00. Note that the above price do not include the delivery fees. You need to consult with salesmen about your final payment.

  • Products Options
Both Fiberstore and Fluxlight offers a full range of fiber optic transceivers that are fully compatible with many brands. While monoprice, nowadays do not have many selections of optical modules. But if you need HDMI, Video or power cables, you can definitely have a look at their website.

  • Reputation—Fiberstore Wins
Fiberstore is known as the cost-effective optical transceiver manufacturer that offers high-quality and low price compatible products. Monoprice is mostly recommended for its patch cables. If you don’t buy it, you can have a look at the following screenshots.

fiberstore feedback
monoprice feedback 2

Can I order any branded fiber optic transceivers? Or should I buy the cheap OEM optical modules? Customers often ask about the similar questions when selecting reliable optical transceivers. This article compares the fiber optics from Monoprice, Fluxlight and Fiberstore. I bet readers must know how to make their choices.

Thursday, March 9, 2017

Multimode Fiber Cabling Upgrade From 10GBASE-SR, 40GBASE-SR4 to 100GBASE-SR10

Telecom industry is in the best times in that new products and technologies keeping coming out, which greatly facilitate people’s daily lives. From the 10GbE, 40GbE to the 100GbE, users can be benefited from the varieties of Gigabit Ethernet applications. Pluggable from factor (SFP+, QSFP+, CFP) used in different Gigabit Ethernet that can support the multimode fibers (MM) leads to lower costs and low power consumption. By comparison of single-mode modules, MM optical transceivers enables a single build standard for short-reach connection in data centers. Today’s article will briefly illustrate the multimode cabling upgrade in 10G, 40G and 100G Ethernet.
According to wikipedia, there are similarities and differences between three standards. Let’s have a quick overview of it.
  • 10GBASE-SR
10GBASE-SR (short range) is a port type for multi-mode fiber (OM3 and OM4) and uses 850 nm lasers. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD in Clause 52. It delivers serialized data at a line rate of 10.3125 Gbit/s. The 10GBASE-SR transmitter is implemented with a VCSEL which is low cost and low power. 10GBASE-SR delivers the lowest cost, lowest power and smallest form factor optical modules with a link length of 300m over OM3, and 400M over OM4.
  • 40GBASE-SR4
40GBASE-SR4 is a port type for multimode fiber and uses 850 nm lasers. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 82 and its Physical Medium Dependent PMD in Clause 86. It uses four lanes of multimode fiber delivering serialized data at a rate of 10.3125 Gbit/s per lane. 40GBASE-SR4 has a reach of 100 m on OM3 and 150m on OM4.
  • 100GBASE-SR10
The IEEE P802.3ba Task Force developed a single architecture capable of supporting both 40bE and 100GbE. 100GBASE-SR10, which is defined as 10 wavelengths across 10 parallel fiber paths at 10Gbps on multimode fiber (operating at 850 nm). Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 86 (802.3ba). It uses ten lanes of multimode fiber delivering serialized data at a rate of 10.3125 Gbit/s per lane. 40GBASE-SR4 has a reach of 100 m on OM3 and 150m on OM4.
40 GbE links are re-used in this diagram, and require additional MTP/MTP trunk to complete channel, fibers 1 and 12 go dark.
10GBASE-SR, 40GBASE-SR4, 100GBASE-SR10 in Different From Factors
10GBASE-SR optical transceivers uses 10G SFP+ form factor with duplex LC connector. The range of this module depends on the type of multimode used. It generally supports a link length of 26 meters on standard Fiber Distributed Data Interface (FDDI)-grade multimode fiber and can also support link length up to 400 meters over OM4 multimode fiber. The following image shows the simplest solution between two Cisco switches by using the 10GBASE-SR SFP module optics.
10GBASE SR solution
40GBASE-SR4 optical transceiver is QSFP+ form factor, primarily enabling high-bandwidth 40GbE optical links over 12-fiber parallel fiber terminated with MPO/MTP multifiber female connectors. In general, it can support link lengths of 100 and 150 meters, respectively on OM3 and OM4 multimode fibers. In addition, using 12-fiber MPO/MTP to 6 duplex LC or 8-fiber MPO/MTP to 4 duplex LC breakout cable, the 40GBASE-SR4 interface can be divided into four 10GBASE-SR interfaces.
  • 100GBASE-SR10 CFP
CFP is the typical representative form factor of 100GBASE-SR10. The 10GBASE-SR10 CFP uses 24-fiber MPO/MTP optical interface, enabling high-bandwidth 100GbE links over 24-fiber ribbon cables terminated with MPO/MTP-24 connectors. Alternatively, 2 x 12-fiber MPO connector interface can be used where one connector is used for Receive while the other for Transmit. The 100GBASE-SR10 CFP can supports link lengths of 100 meters and 150 meters respectively on laser-optimized OM3 and OM4 multifiber cables. Additionally, it can be used in 10 x 10GbE mode along with ribbon to duplex fiber breakout cables for connectivity to ten 10GBASE-SR optical interfaces.
This article concludes the features of multimode cabling upgrade from 10G to 100G. multimode modules together with its lower price tag and low power consumption, are compelling to overall users. FS.COM, as a reliable china optical transceiver module manufacturer offers a full range of hot-selling fiber optics like SFP, SFP+, QSFP+, QSFP28 and CFP modules. They comes in different standards and full compatible with major brand. If you are interested, please visit our site.

Thursday, March 2, 2017

Can I Use the 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.
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.