Optical Modules for 25 Gigabit Ethernet

Although the widely acknowledged Ethernet speed upgrading path was 10G-40G-100G, web-scale data centers and cloud based services need servers with above 10GbE capability and cost sensitive for nearer-term deployment. It indicates that the latest path for server connection will be 10G-25G-100G with potential for future upgrading to 400G. But why 25G? Because moving from 10G to 40G is a big jump and it turns out that the incremental cost of 25G silicon over 10G is not that great. This new 25 Gigabit Ethernet standard will require improved cables and transceiver modules capable of handling this additional bandwidth. It is just under this circumstance that QSFP28 and SFP28 for 25 Gigabit Ethernet are promoted.

25GbE Ethernet—An Emerging Standard

25 Gigabit Ethernet (25GbE) has passed the first hurdle in the IEEE standards body with a successful Call for Interest (CFI) in July, 2014. It is a proposed standard for Ethernet connectivity that will benefit cloud and enterprise data center environments. 25GbE leverages technology defined for 100 Gigabit Ethernet implemented as four 25-Gbit/s lanes (IEEE 802.3bj) running on four fibers or copper pairs.

Significant Performance Benefits—25G Over 40G

The value of 25GbE technology is clear in comparison to the existing 40GbE standard. Obviously, 25GbE technology provides greater port density and a lower cost per unit of bandwidth for rack server connectivity. For applications that demand substantially higher throughputs to the endpoint, there exists 50GbE—using only two lanes instead of four—as a superior alternative to 40GbE in both link performance and physical lane efficiency.

The proposed 25GbE standard delivers 2.5 times more performance per SerDes lane using twinax copper wire than that available over existing 10G and 40G connections. A 50GbE link using two switch/NIC SerDes lanes running at 25 Gb/s each delivers 25% more bandwidth than a 40GbE link while needing just half the number (four) of twinax copper pairs. Therefore, a 25GbE link using a single switch/NIC SerDes lane provides 2.5 times the bandwidth of a 10GbE link over the same number of twinax copper pairs are used in today’s SFP+ direct-attach copper (DAC) cables.

Maybe the most outstanding benefit of 25GbE technology to data-center operators is maximizing bandwidth and port density within the space constraints of a small 1U front panel. It also leverages single-lane 25Gb/s physical layer technology developed to support 100GbE.

Cloud Will Drive to QSFP28 and SFP28

QSFP28 is used for 4x25GE and SFP28 is used for a single 25GE port. SFP28 module, based on the SFP+ form-factor, supports the emerging 25G Ethernet standard. It enables error-free transmission of 25Gb/s over 100m of OM4 multi-mode fiber and a new generation of high-density 25 Gigabit Ethernet switches and network interface cards, facilitating server connectivity in data centers, and a conventional and cost-effective upgrade path for enterprises deploying 10 Gigabit Ethernet links today in the ubiquitous SFP+ form factor. The QSFP28 (25G quad small form-factor pluggable) transceiver and interconnect cable is a high-density, high-speed product solution designed for applications in the data center and networking markets. The interconnect offers four channels of high-speed signals with data rates ranging from 25 Gbps up to potentially 40 Gbps, and will meet 100 Gbps Ethernet (4x25 Gbps) and 100 Gbps 4X InfiniBand Enhanced Data Rate (EDR) requirements. The following shows a QSFP28-SR4 module and a 10GBASE-SR SFP+ module (MA-SFP-10GB-SR).

Conclusion

The dominant next-generation server connection speed is going to be 25G as it providing a cost competitive longer reach option for mainstream customers. FS.COM has already introduced cost-effective QSFP28 modules, QSFP28 to QSFP28 cable as well as SFP28 cable. With advanced OEM technology and strict cost control, we can help you save more than 30%~50% off on the cost of the QSFP28 modules.

The Deployment of 25 Gigabit Ethernet in Data Center

Although 10 GbE (Gigabit Ethernet) to 40/100 GbE migration has been widely recognized as the Ethernet speed upgrading path, users still keep pursuing a better solution to replace the existing “10GbE-40GbE-100GbE” path. Companies like Google, Microsoft, Arista, and Mellanox are pushing the development of a 25 Gigabit Ethernet standard for top-of-tack server networking. Some may question the need for this technology, but they will soon see the benefits. New deployments, such as 10GbE—25GbE—100GbE or 10GbE—25GbE—50GbE—100GbE are announced to better serve the data center and cloud network. Thus, what is 25 GbE and why is it in demand?

What Is 25 GbE?

25GbE (25 Gigabit Ethernet) is a proposed standard for Ethernet connectivity in a data center environment. An industry consortium (25G Ethernet Consortium) was formed in July 2014 to support the specification of single-lane 25Gb Ethernet technology, because the proposed 25 GbE standard will use the same physical silicon from a single 25 Gbit/s lane. This simplifies the process with just minor changes for forward error correction and lane alignment, and it reduces the cost when compared to 40 GbE.

Why Is 25 GbE in Demand?

As is known to all, in the high-density data center, using multiple 10 GbE would require twice as many Ethernet switches with their associated space, power, and cooling costs. Deploying 25GbE networks enables organizations to significantly decrease capital and operating expenses by reducing the required number of switches and cables to solve these issues, compared to 10GbE and 40GbE (4×10 GbE) technology. Additionally, fewer network components also reduce ongoing management and maintenance costs.

For instance, if we use the 10GbE—40GbE—100GbE path, we will have 10 GbE single, 40 GbE quads and 100 GbE ten lanes in production. But when we turn to 25 GbE, we just need 25 GbE single, 50 GbE dual and 100 GbE quads in production. Obviously, 25GbE enables us to have 2.5X the performance of 10Gb Ethernet, making it a cost-effective upgrade to the 10GbE infrastructure. While compared to 40GbE, which is actually four 10GbE lanes, 25GbE is delivered across a single lane which provides greater switch port density and network scalability. Moreover, using multiple 25GbE lanes, it is easy to upgrade of 50GbE and 100GbE networks. It is a cost-effective solution for datacenter upgrade and cloud-scale network expansion. This is why 25 GbE is favoured and highly recommended by those famous consortium.

SFP28 & QSFP28 Assemblies

The SFP28 (25G Small Form-Factor Pluggable) and QSFP28 (25G Quad Small Form-Factor Pluggable) transceivers and interconnect cables are high-density, high-speed product solution designed for 25GbE and 100GbE applications in the telecommunications, data center and cloud-scale networks. The emergence of these two form-factors pluggable certainly reflect the trend in the industry to aggressively bring 100GE density up and costs down.

Based on the SFP+ MSA form-factor, SFP28 assembly solution enables a new generation of high-density 25G Ethernet switches and NIC cards, facilitating server connectivity in data centers, and a conventional and cost-effective upgrade path for enterprises deploying 10G Ethernet links today in the ubiquitous SFP+ form factor.

QSFP28 transceiver, as a new type of 100G transceivers, 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 (4×25 Gbps) and 100 Gbps 4X InfiniBand Enhanced Data Rate (EDR) requirements. According to IEEE 802.3bm, the 100GBASE-SR4 QSFP28 is designed for multimode application and support maximum link length of 100 m over OM4 Fiber. The 100G QSFP28 LR4 module is designed for single-mode application which support maximum link length of 10 km over SMF. QSFP28 has the same footprint and faceplate density as QSFP+ and is just slightly smaller than CFP4. Theoretically, QSFP28 seems to have the density advantage over CFP4, but CFP4’s higher maximum power consumption gives it the advantage on longer reach optical distances. As the two main types of 100GbE transceivers, each of them has its own merits. Only time will tell how this all plays out.

Conclusion

Through the above analysis, we can see that, 25 GbE solution is more suitable for the high-density data center. But at present, for long distance transmission, the existing 40/100GbE solution—QSFP/QSFP+ and CFP family (CFP, CFP2, CFP4) seems to be better. FS.COM offers a comprehensive solution of fiber optic transceivers and cable assemblies. For data center, we offer a full product line of basic transceiver optics, such as 1000BASE-SX, 1000BASE-LX/LH SFPs, 10GBASE-LR SFP+ etc. We also offer high-density interconnection solution by launching whole series of 40GBASE QSFP+ optics and 100GBASE-LR4 CFP2 and CFP4 optics as well as the cable assemblies.