Tag Archives: QSFP28

25G Switches: A Key Choice for Future Networks

25G switches are currently very popular with customers. ince its introduction in 2014, 25G Ethernet has existed for approximately five years. The market for 25G Ethernet has experienced many ups and downs over the years. If we compare the advanced methods of 10G-25G-100G and 10G-40G-100G, we will discover that customers seem to prefer 25G Ethernet because it appears to be more refined. Why go with 25GbE? How can the advantages of 25GbE be understood? The possibility of 25G switches will be discussed from various angles in this article.

The Development of 25G Ethernet

Due to virtualization and cloud computing, networks are now facing modern challenges requiring increased bandwidth. Even with the rapid development of 10G, the most important TOR switch in the data center has been difficult to meet the needs of existing network data. The standards for 100G and 40G were later endorsed by the IEEE. However, while 100G is relatively costly and difficult to implement, 40G is neither expensive nor efficient for cloud providers in terms of TOR switching.
IEEE 802.3 has developed a 25G Ethernet connection standard for the above situations. It facilitates the upgrade deployment of cloud-based database environment and enterprise environment, and also helps expand the 25G switch market. IEEE 100G Ethernet serves as the basis for 25G Ethernet, utilizing Ethernet’s single-lane 25Gbps connection and 4 x 25 Gbps lanes.

Why choose 25G Ethernet?

Due to the growth of Internet data, 25G switches are also designed with high-density ports to meet enterprise needs. So, compared with 10G or 40G networks, what breakthroughs does 25G Ethernet have at the technical level? Why will 25G Ethernet still be popular in the future.
Serializers and deserializers channels: A combination transceiver or circuit known as a SERIALIZER/DESERIALIZER (SERDES) is utilized for high-speed transmission, serial data conversion to an aligned interface, and other purposes. To connect one end point of the 25G Ethernet card to the other end point of the 25G Ethernet card, we only require one SERDES channel at 25Gbps.
25G Ethernet NICs: The popular Intel Xeon CPU provides 40 lanes of PCI Express 3.0 with a bandwidth of about 8Gbps per lane. We use a lane called PCI Express to connect the NIC to the CPU. A 25G Ethernet network card requires a single PCI Express 3.0×8 channel, and the usage efficiency is 25G2/(8G8)=78%. In terms of PCI Express lanes, the 25G network is more flexible and efficient than the 40G network.
Cost-effective cabling: SFP28 optical modules are used in 25G Ethernet switches and boards. Since they are single-lane links, they can be used with 10G Ethernet LC optics. You can save money and time by not having to change cables when you upgrade from 10G network to 25G network.
Benefits of 25G I/O switch: The most significant switch I/O representation and fabric capacity are provided by 25G Ethernet. The network bandwidth of 10G Ethernet has the potential to increase the network scale and profit of cloud companies by 2.5 times. 25G switches can also achieve network scalability and higher-density port applications through single-channel transmission.

Why Do We Need 25G Switches?

Switch Compatibility
Most of the available 25G switches are backward compatible because most of their supporting optical modules use SFP28. For 25G signal transmission, SFP28 is an improved version of SFP+. SFP+ transceivers can be connected to SFP28 ports since they have the same form factor. Fiber optic cabling in data centers can also be used with SFP28.
Therefore, re-architecting your data center with 25G Ethernet switches can save a lot of money and give you more flexibility to increase bandwidth during migration.
Port and System Density
25G technology is similar to 10G, but with 2.5 times higher performance. 25G technology significantly reduces power consumption and cost per gigabit, which means it requires 25G switches to provide higher port and system density. Using four 25 Gb/s data streams, for instance, a compact 100G path over copper or fiber optic cables is possible. Additionally, this method conserves energy and requires fewer TOR switches and cables, resulting in significant OpEx savings for data center operators.
Price and Performance
When price and performance are taken into consideration, 25G Ethernet is significantly less expensive per Gbit/s of bandwidth than 10G Ethernet. 25G switches or transceivers are priced very competitively on the market, only 30-40% more expensive than 10GbE, and this premium is expected to go down over time. In this case, 25G equipment needs to be deployed, such as 25G data center switches, 25G campus switches, etc.
The Crehan forecast below demonstrates that 25G is superior in both price and performance.
Figure 3: Price Comparison by Connection Speed

Explore the Features of 25G Switches

With the landing of the 25G standard, its supporting equipment has also been launched in 2016, such as 25G SFP28 transceivers, DAC cables, 25G adapters, 25G switches, etc. According to application scenarios, 25G equipment is also divided into 25G data center switches and 25G campus switches, etc., and their respective performances will also have some differences.
The 25G Ethernet switch market is mainly dominated by some brand vendors, such as 25G Dell, Cisco, Juniper, Arista, and Mellanox switches. Generally, 25G 48-port switches are the most popular type. Most 25G switches today offer two types of 25GbE interface form factors: QSFP28, which can support 4x25Gbps, and SFP28, which can support 1x25Gbps.
For example, FS N8500-48B6C is a 25G Ethernet switch with 48 x 25Gb SFP28, with 8 x 100Gb QSFP28 ports, which can be used to build a data center network. Whether it is a TOR (Top of Rack) switch or a switch deploying a spine-leaf architecture, a 25G network switch is a good choice.
Figure 2: FS 25G Ethernet Switch N8500-48B6C
     ”Also Check- N8500-48B6C Switch


With the trend towards higher Ethernet bandwidth, the demand for 10G Ethernet has been declining. Regardless of market research, 25G inevitably looks like the ideal choice because it is cost-effective, offers high bandwidth and requires low power consumption. In this context, equipment such as 25G switches play an indispensable role.

Difference Between 100G-QSFP-PSM4, 100G-QSFP-SR4 and 100G-QSFP-LR4

QSFP28 fiber optic transceiver is becoming the preferred solution for 100G network. It has the same outside looking as the 40G QSFP+ transceiver. But it has a 4*25G electrical interfaces which can transmit optical signals up to 100G. The part numbers of the QSFP28 transceivers are usually market as 100G-QSFP-xx. Now there is a wide selection of 100G QSFP28 modules for 100G Ethernet link, including fiber optic transceiver and direct attached cable. Different part numbers of 100G modules are making customers confused. This post will introduce the differences between the three 100G QSFP28 modules: 100G-QSFP-PSM4, 100G-QSFP-SR4 and 100G-QSFP-LR4.


Transmission Mode

It is known that QSFP28 modules generally use four lanes to transmit 100G with each lane supporting 25G. Thus, the transmission method is just like 40G QSFP+ transceiver. 100G QSFP28 SR4, LR4 and PSM4 all use the 4*25 transmission mode. However, both the QSFP28 SR4 and QSFP28 PSM4 use a 12-fiber MTP interface which achieves dual-way 100G transmission over 8 fibers at the same time. QSFP28 LR4 uses a LC duplex fiber optic interface for 100G transmission on two directions at the same time. QSFP28 LR4 transmit optical signals over four different wavelengths around 1310nm with each wavelength carrying 25G optical signal. The wavelength ranges of the four lanes are as following:

  • 1294.53nm-1296.59nm
  • 1299.02nm-1301.09nm
  • 1303.54nm-1305.63nm
  • 1308.09nm-1310.19nm
Transmission Media and Distances

The three modules can support different transmission distances. 100G-SR4 QSFP28 module works over wavelength of 850nm and is used with 12-fiber MTP OM3 or OM4 multimode fiber cables for short transmission distances up to 100m. 100G-LR4 QSFP28 module is suggested to be used with single-mode fiber. It works over 1310nm wavelengths and can transmit 100G signals up to 2km. 100G-PSM4 QSFP28 is also used with 12-fiber MTP fiber cables but the fiber type is single-mode and the transmission distance is up to 500m.


Cabling Structure

The transmission mode of the fiber optic transceiver plays an important role during fiber cabling. 100G-QSFP-SR4 and 100G-QSFP-LR4 are invented for short distance transmission and long distance transmission separately. However, the have different cabling structure. The former requires a multi-fiber cabling structure based on 12-fiber MMF MTP interfaces. While 100G-QSFP-LR4 just required the traditional two-fiber SMF cabling structure. In this case, the conversion between multimode fiber to single-mode fiber would be complex as they used totally different cabling structure. Thus, 100G-QSFP-PSM4 is invented which runs over single-mode fiber, but uses the same cabling structure as 100G-QSFP-SR4. With 100G-QSFP-PSM4, the conversion between multimode and single-mode would save more without changing the existing fiber cabling structure.

100G QSFP28 Transceiver Data Rate Interface Fiber Type Transmission
Wavelengths Cabling Structure
100G-QSFP-SR4 4*25G MTP MMF 70m (OM3);
100m (OM4)
850nm 12-Fiber MTP
100G-QSFP-LR4 4*25G LC SMF 2km 1310nm LC Duplex
100G-QSFP-PSM4 4*25G MTP SMF 500m 1310nm 12-Fiber MTP

The above table listed the basic information of the three modules for your referent. 100G-QSFP-SR4 are suitable for short distance transmission over OM3 or OM4 fiber using 12-MTP fiber cabling system. 100G-QSFP-PSM4 also has a 12-fiber MTP interface but it can support a transmission distance up to 500m over SMF. 100G-QSFP-LR4 is suitable for long transmission distance up to 2km over two single-mode fibers.

Related Article: 40G vs 100G: Which One Is Worth the Investment?

Double Density QSFP (QSFP-DD) Is Coming

Recently the building of QSFP-DD (Multi Source Agreement) Group has excited optical communication industry. This group, including 13 members which are all the leading vendors in the industry, like Cisco, Brocade and Finisar, aims to create a upgraded version of QSFP transceiver, which is called QSFP-DD ( double density QSFP) and will be able to support 200G/400G Ethernet.


The QSFP-DD is similar to the current QSFP. But there are many differences between the current QSFP. The reason why the new transceiver is called “double density” is related to the current 100G QSFP28 transceivers. The “double density” means the doubling of the number of high-speed electrical interfaces that the module supports compare to regular QSFP28 module.

QSFP-DD transceiver


We can understand the QSFP-DD better by comparing it with the current 100G QSFP28 module. QSFP28 transceiver is a four-channel transceiver which is able to transmit and receive 100G per second simultaneously. With the advantages of high speed and low power, QSFP28 transceiver is becoming more popular than other 100G transceivers like CFP2 and CFP4. The 100G QSFP28 transceiver is implemented with four lanes with each supporting data rate of 25G.

The working principle of QSFP-DD is similar with 100G QSFP28 transceiver. The QSFP-DD MSA group will increase the lane to eight. There will be a row of contacts providing for an eight lane electrical interface in QSFP-DD. If modulated by NEZ, each lane of the QSFP-DD can support data rate up to 25G, thus, it can support a total data rate of 200G. If modulated by PAM4, it can support data rate up to 400G with each lane supporting data rate of 50G. The MSA group also announced that the QSFP-DD can enable up to 14.4Tbps aggregate bandwidth in a single switch slot, which can definitely satisfy the increasing need for higher bandwidth.

Another great feature of QSFP-DD is that its system will be backwards compatible, allowing them to support existing QSFP modules and provide flexibility for end users and system designer. This means the data center could save a considerable sum of money in the future upgrading.

Future and Present

The appearance of QSFP28 transceiver has changed the regular development road map of Ethernet. The regular upgrade road is 10G to 40G and then 100G. While the QSFP28 transceiver has changed it from 25G directly to 100G. The road map of this QSFP-DD is also drawing our attention. It is predicted that it will become a useful family of modules for the industry with application at greater than 400G. Meanwhile, there is no efforts underway to define these new speeds but it is expected that QSFP-DD will have a roadmap that supports.

qsfp28 transceiver

Any way, no matter where the QSFP-DD lead our Ethernet to, it is good news for our future networking system. The creating of this new module will still need some time. For now, many data centers are considering about upgrading their data center with 100G QSFP28 transceivers. And there are a variety of switches which support QSFP28 interfaces on the market. However, 100G QSFP28 transceiver is still not cheap in the current market. For example, the price of a 100GBASE-SR4 QSFP28 transceiver is generally more than $2000.00. However, in FS.COM, supported by OEM, the price is much more favorable. A 100GBASE-SR4 QSFP28 transceiver only cost $650.00 in FS.COM. The following chart is detailed information of 100G QSFP28 transceivers in FS.COM.

FS P/N Form Type Data Rate Wavelength Max Cable Distance Interface Cable Type DOM Support
100G QSFP28-SR4 QSFP28 103.1 Gbps 850 nm 100 m MPO (MTP12) MMF Yes
100G QSFP28-LR4 QSFP28 103.1 Gbps 1310 nm 10 km LC Duplex SMF Yes

For more details, please contact us at sales@fs.com or visit FS.COM.

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