Tag Archives: QSFP28

Can I Use the QSFP+ Optics on 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 transceiver. 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.

100G Optical Transceivers Links: PSM4 vs CWDM4

In the past few years, 100G optical transceivers are become more popular and widely used than before. The most common 100G optical transceivers we use today are CFP, CFP2, CFP4 and QSFP28, especially the QSFP28. Besides 100G optical transceivers links (-SR10, SR4, -LR4) defined by IEEE standard, Multi-Source Agreement (MSA) also defines two 100G optical transceivers links: PSM4 and CWDM4. Both PSM4 and CWDM4 architectures take the 100GE signal and carry it over 4 separate channels. So, what’s the difference between them? PSM4 vs CWDM4–difference between them will be introduced in this blog.

The 100G PSM4 Specification defines requirements for a point-to-point 100 Gb/s link over eight single mode fibers (4 transmit and 4 receive) up to at least 500 m, each transmitting at 25Gbps. Four identical and independent lanes are used for each signal direction (as shown in figure below). Therefore, two transceivers communicate usually over 8-fiber MTP/MPO single mode patch cords. PSM4 is limited to 500 m. At present, PSM4 links are usually used in 100G QSFP28 optical transceivers.

100G Optical Transceivers Links PSM4

Similar to PSM4, CWDM4 also uses 4 x 25 Gbps to achieve 100 Gbps. But unlike PSM4, CWDM4 uses an optical multiplexer and de-multiplexer to reduce the number of fibers to 2 (as shown in figure below). Therefore, we only need to use a duplex single mode fibers to connect two 100G CWDM4 optical transceivers modules. CWDM4 is limited to 2 km. At present, CWDM4 links are used in both 100G CFP4 or the QSFP28 optical transceivers.

100G Optical Transceivers Links CWDM4

100G Optical Transceivers Links: PSM4 vs CWDM4
A summary table comparing the key differences between CWDM4 and PSM4 is shown below. From an optical transceiver module structure viewpoint, PSM4 can be more cost effective because it uses a single uncooled CW laser which splits its output power into four integrated silicon modulators. However, from an infrastructure viewpoint, PSM4 would be more expensive when the link distance is long, mainly due to the fact that PSM4 uses 8 optical single-mode-fibers while CWDM4 uses only 2 optical single-mode-fibers.

100G Optical Transceivers Links PSM4 vs CWDM4
When considering the above two factors, a total cost comparison can be qualitatively shown in the figure below. As can be seen in the figure, PSM4 starts with a lower cost due to its lower transceiver cost, but as the link distance increases, its total cost climbs up very fast due to the fact that it uses 8 optical fibers.

100G links PSM4 vs CWDM4

Different companies have different opinions on what the link distance is at the crossing point, and what the transceiver cost difference is at zero distance. But based on the specifications of PSM4 MSA, the technology has to be limited to 500 meters, which can actually cover the majority of today’s data center needs. FS.COM provides both 100G PSM4 QSFP28 ($ 750.00) and 100G CWDM4 QSFP28 ($ 1350.00) optical transceivers for your options.

QSFP+ and QSFP28 Transceivers Cabling Solutions

The short range 40-Gigabit Ethernet QSFP+ and 100-Gigabit Ethernet QSFP28 transceivers that are widely used in today’s data center use 12-fiber patch cables with female MPO connectors. The fiber can be either OM3 or OM4. The long range QSFP+ and QSFP28 transceiver use single-mode fiber patch cables with duplex LC connectors. This article may introduce the cabling solutions for QSFP+ and QSFP28 transceiver to you.

QSFP+ and QSFP28 Transceiver Types
In terms of 40G QSFP+ transceivers, from short range to long range, they are available in 5 common types. The minimum transmission distance is 100m, and the max transmission distance is 40km. 100G QSFP28 transceivers are commonly avaiable in 100GBASE-SR4 and 100GBASE-LR4 two types. Detailed QSFP+ and QSFP28 transceiver specifications are displayed in following tables.

Transceiver Type Interface Standard Connector Type Fiber Type
QSFP+ 40GBASE-SR4 Female MTP/MPO, key up 12-fiber multi-mode fiber (MMF) (OM3 or OM4)
QSFP+ 40GBASE-PLRL4 Female MTP/MPO, key up 12-fiber single-mode fiber (SMF) 1km
QSFP+ 40GBASE-PLR4 Female MTP/MPO, key up 12-fiber SMF 10km
QSFP+ 40GBASE-LR4 LC duplex SMF 10km
QSFP+ 40GBASE-ER4 LC duplex SMF 40km
QSFP28 100GBASE-SR4 Female MTP/MPO, key up 12-fiber MMF (OM3 or OM4)
QSFP28 100GBASE-LR4 LC duplex SMF 10km

12-Fiber Patch Cables with MTP Connectors
12-fiber patch cables with MTP connectors can be used to connect two transceivers of the same type—40GBASE-SR4-to-40GBASESR4 or 100GBASE-SR4-to-100GBASE-SR4. You can also connect 4x10GBASE-LR transceivers such as 40GBASE-PLRL4 and 40GBASE-PLR4 using patch cables—4x10GBASE-LR-to-4x10GBASE-LR—instead of breaking the signal out into four separate signals. Ensure that you order cables with the correct polarity. The MTP connectors on the 12-fiber cables should be key up (sometimes referred to as latch up, Type B, or Method B). If you are using patch panels between two QSFP+ or QSFP28 transceivers, ensure that the proper polarity is maintained through the cable plant.

12-Fiber MTP Patch Cables

12-Fiber MPO Patch Cables

12-Fiber Breakout Cables with MTP-LC Duplex Connectors
12-fiber breakout cables with MTP-LC duplex connectors can be used to connect a 4x10GBASE-LR or 4x10GBASE-SR transceiver to four separate 10GBASE-LR or 10GBASE-SR SFP+ transceivers. The breakout cable is constructed out of a 12-ribbon fiber-optic cable. The breakout cable splits from a single cable with an MTP connector on one end, into 4 cable pairs with 4 LC duplex connectors on the opposite end.



LC Duplex Patch Cables
Single-mode patch cables with LC duplex connectors can be used to connect two transceivers of the same type—40GBASE-LR4-to-40GBASE-LR4 or 100GBASE-LR4-to100GBASE-LR4. The SMF patch cable is one fiber pair with two LC duplex connectors at opposite ends.

LC Duplex Patch Cables

25G SFP28 Cable: The Most Economical Option for ToR Server Connection

25 Gigabit Ethernet is proposed standard for Ethernet connectivity in a data center environment, developed by IEEE 802.3 task force P802.3by. The IEEE 802.3bj standard then uses technology defined for 100 Gigabit Ethernet implemented as four 25-Gbit/s lanes. These standards define:

  • a single-lane 25 Gbit/s 25GBASE-KR PHY for printed circuit backplanes
  • a single-lane 25 Gbit/s 25GBASE-CR-S PHY for 3 m twin-ax cables (in-rack)
  • a single-lane 25 Gbit/s 25GBASE-CR-L PHY for 5 m twin-ax cables (inter-rack)
  • a single-lane 25 Gbit/s 25GBASE-SR PHY for 100 m OM4 or 70 m OM3 multi-mode optical fiber

What’s 25G SFP28 Cable?
According to the above standards, the IEEE CFI is now focused on the SFP28 and QSFP28 direct attach copper twin-ax cables (DACs). SFP28 DAC refers to the 25G DAC cable using the SFP+ form factor, and QSFP28 DAC refers to the 100G DAC cable using the QSFP+ form factor. The maximum transmission distance of these cables is 5 meters.

There are two SFP28 DAC cable types: 25G SFP28 to SFP28 DAC and 100G QSFP28 to four SFP28 breakout DAC. The SFP28 to SFP28 passive copper cable is a high speed, cost-effective 25Gbp/s Ethernet connectivity solution designed to meet the growing needs for higher bandwidth in data centers. The QSFP28 to four SFP28 breakout DAC is used to connect 100G switches to four 25 Gigabit in cabinet or adjacent cabinet servers. Compared to 40G using four 10G lanes and 100G using 10 10G lanes, the 25G SFP28 DAC provides the low-cost copper server connection for Top of Rack (ToR) switches.

To more directly illustrate effectiveness of SFP28 to SFP28 DAC cable and QSFP28 to four SFP28 breakout DAC cable, let’s see a series of pictures displayed below:

Existing 10G Topology
Today’s volume topology for web-scale data centers

  • 48 servers/ToR
  • 3:1 oversubscription
  • Uses low-cost, thin 4-wire SFP+ DAC cable

sfp+ to sfp+ DAC

40G Topology
High-performance, low volume topology

  • Uses bulkier 16-wire QSFP+ DAC cable
  • Max. 24 servers/ToR with 3:1 oversubscription
  • Will transition to 100G

qsfp+ to qsfp+ dac

25G Direct Connect
Same topology as 10G

  • 48 servers/ToR
  • 3:1 oversubscription w/ 100G uplinks, non-blocking w/ 400G
  • Uses 4-wire SFP28 DAC cable

sfp28 to sfp28 dac

Existing 4x10G Topology
Commonly used topology in web-scale data centers

  • Permits non-blocking 10G mesh
  • 40G ports used as 4x10G with QSFP+ to SFP+ breakout cable
  • Same server network interface card (NIC) as 10G

qsfp+ to 4 sfp+ dac

4x25G Breakout
Same topology as 4x10G

  • Permits non-blocking 25G mesh
  • 100G ports used as 4x25G with QSFP28 to SFP28 break-out cable
  • Same server network interface card (NIC) as 25G direct connect

qsfp28 to 4 sfp28 dac

High Density 25G
Increased port switch port density

  • 64 servers in non-blocking architecture
  • 96 servers in a 3:1 oversubscription
  • 24-port 400G ToR
  • 192 servers in non-blocking architecture

100G qsfp28 to 4 sfp28 dac

100G Optical Transceivers Will Be More Popular in 2016

According to a newly published report by Dell’Oro Group, the worldwide service provider core router market is expected to reach $3.4 billion in revenue in 2020 as 100G port shipments spur growth. There is a significant increase in deployments of 100G ports, driven by the continuous increase in IP traffic as well as the availability of higher capacity line cards in 2015. Besides, pricing declined significantly in 2015 for 100G as there was a mix shift in the types of routers on which 100G ports were installed. Furthermore, the availability of advanced optics in CFP2 and CPAK has pushed down pricing on 100G. Therefore, we expect 100G optical transceivers will be more and more popular in 2016.

100G Optical Transceiver Modules: from CFP to QSFP28
At present market, the 100G optical transceiver module include CXP, CFP, CFP2, CPAK, CFP4 and QSFP28. Among them, QSFP28 demonstrates its great superiority and will lead to denser optics and further price reductions. The QSFP28 increases front-panel density by 250% over QSFP+. The increase in panel density is even more dramatic when compared to some of the other 100G transceiver module: 450% versus the CFP2 and 360% versus the CPAK. In addition, the surge of QSFP28 shipments will be one of the factors to change the market from 40G to 100G, according to the report of IHS. QSFP28 is fast becoming the universal data center form factor.

100G Optical Transceiver Module

100G Optical Transceiver Module Is Much Cheaper Than Before
The cost for transceiver modules which keep adding up over time is one of the main considerations of the whole projects. In other word, the cost of the devices and components may influence the enthusiasm of network upgrade. But, in 2016, the 100G transceivers will be more affordable. On one hand, the cheap 100G silicon reaches production and the technology become mature. On the other hand, the adoption of widespread use of the 100G devices, and the vast increases in Internet traffic are core to change in the communications infrastructure markets. This reduction in pricing will lead to 100 GE selling at a price per bit transmitted below that of 10 GE in the 2018 time frame.

100G Optical Transceiver Module Is More Widely Used
Previously, 100G was primarily installed on high-end core routers and now more are being installed on relatively lower-priced edge routers, which pricing declined significantly reduces the price of 100G optical transceiver. In 2016, the global data center construction market will keep growing which means that the 100G optics application will be more wider. Geographically, North America, Europe and Asia-Pacific (mainly China) are the main market for 100G transceiver with their increasing demand for deployment of 100G equipment.

Fiberstore 100G Optical transceiver Solution
In 2015, FS.COM constantly improves the product line of fiber optic transceivers. For 100G optics, we introduced the 100GBASE-LR4 CFP2 and CFP4 modules as well as the 100GBASE-SR4 and 100GBASE-LR4 QSFP28 modules. With our serious cost control, the prices of all our 100G optics are much more affordable than the similar products in the market. Furthermore, with the mature coding technology, they can be compatible with many major brands.

FS Part Number Product Photo Description
CFP-LR4-100G CFP-LR4-100G 100GBASE-LR4 CFP 1310nm 10km Transceiver for SMF
CFP2-LR4-100G CFP2-LR4-100G 100GBASE-LR4 CFP2 1310nm 10km Transceiver for SMF
CFP4-LR4-100G CFP4-LR4-100G 100GBASE-LR4 CFP4 1310nm 10km Transceiver for SMF
QSFP28-SR4-100G QSFP28-SR4-100G 100GBASE-SR4 QSFP28 850nm 100m Transceiver for MMF
QSFP28-LR4-100G QSFP28-LR4-100G 100GBASE-LR4 QSFP28 1310nm 10km Transceiver for SMF