With the increasing demand for high broadband from private cloud, public cloud data center and service providers, 25G and 100G have been widely used, and 200G/400G optical devices will be produced and shipped from 2019.So far, most server vendors have started to offer 25G fiber optic network CARDS as an I/O(input/output) option for servers, and Ethernet signal transmission rates have increased from an earlier 10G to 25G, 100G or more.While 1G, 10G, and 40G currently dominate the Ethernet port market, the future demand for 25G and 100G will be stronger than ever because high bandwidth is undeniably driving data centers toward greater scalability and flexibility.

1. Why is 25Gb coming to the data center?

Data centers are expanding at an unprecedented rate, driving the demand for higher bandwidth for connections between servers and switches. To meet this trend, the access network has been gradually upgraded from 10gb to 25gb, which provides high-density, low-cost and low-power solutions for connections between servers and ToR switches.

The development of 25G

Since 25gb was introduced in 2014, Google, Microsoft, Arista networks, broadcom and Mellanox have been pushing for the 25gb Ethernet standard, with the intention of implementing 25gb set-top server networks.As the popularity of 25G continues to rise, 25G is rapidly spreading in the market. In the future, 25G will provide a comprehensive solution for the connection between server and switch.The figure below shows the key milestones for 25gb Ethernet from 2014 to 2018.

2, From the existing network upgrade way to talk about the advantages of 25G

Before the release of 25G Ethernet standard, 10g-40g was generally adopted for the network upgrade of data centers such as enterprises and operators. With the official release of 25G Ethernet standard, 25g-100g network upgrade gained more applications with the advantages of low cost, low power consumption and high density, which promoted the rapid development of 100G Ethernet.Let's take a look at what the difference is between 10G/25G/40G and which upgrade is better.

25G provides higher performance bandwidth than 10G

In the current data center, the network connection between the server and the switch is generally chosen between 10gb and 25gb.Compared to 10G, 25G is based on 10G package and chip technology, providing higher bandwidth and performance.The appearance of 25G enables the data center to be based on the existing network architecture, without any cable interconnection, and to support the transmission of higher speed (more than 10G), meeting the demand of higher bandwidth for the future network, making the network upgrade more convenient and easy.The cabling infrastructure required for 25G and 10G transmission is basically the same, which can effectively avoid expensive costs and rewiring complexity, and make the network upgrade more convenient.

In addition, 25G is similar to 10G, with single channel SerDes(Serlializer and Deserializer) and backward compatibility, which significantly reduces power consumption and costs and helps data center operators save capital and operating expenses.

What speed will we get if we plug a 25G SFP28 light module into a 10G SFP+ port?

Theoretically, the 25G SFP28 optical module is backward compatible with 10G SFP+ port with a speed up to 10Gb/s. However, this mode of use may not be suitable for all brand switches and optical modules and is generally not recommended due to the limitations of fiber network card and switch port.

Compared with 40G, 25G is more suitable for high-density demand

25G enables interoperability between the Ethernet specifications of the server network adapter (NIC) and the switch, providing greater port density and lower unit costs for rack server bandwidth connections.Compared to 40G, it provides a higher port density to maximize the I/O performance and switching power of the switch.In terms of the number of connected switches, since 25G is single-channel (1 25G port) and 40G is four-channel (4 10G ports), 25G has more connected switches.In addition, compared with the existing 10G and 40G, the transmission performance of 25G and 50G is improved by 2.5 times.

For large, high-end enterprises, the port density of the server largely determines the cost of wiring and switch infrastructure throughout the system, so the cost of upgrading from 25G to 100G is relatively low compared to 40G.When 25g-100g network is upgraded, the switch port is fully utilized and the cost of bandwidth is effectively reduced.

It has been upgraded to 40G network, is it necessary to deploy 25G network?

25G devices are expensive compared to 40G devices, so is it necessary to deploy 25G networks after upgrading to 40G networks?Due to the reasonable cost of 25G channels, 25G is definitely an important path to upgrade from 10G to 100G or higher in the future.If you need to increase the baud rate (signal transfer rate) or are planning to upgrade your network to a higher speed (100G/200G/400G), you must deploy a 25G network.

3. View the prospect of 25G from the future 100G/200G/400G data center

At present, 25G servers and 100G switches can be seen everywhere in the super-large data centers, which gradually replace the 10G servers and 40G switches. This network upgrade has increased the throughput of the whole system by 2.5 times, and reduced the incremental cost of equipment.As the Ethernet industry continues to innovate and lay the foundation for higher rate research and development, the 25g-100g upgrade model has become an important path for data centers.

25G offers more possibilities for 50G

As is known to all, 25G can provide 2.5 times of bandwidth with only one channel compared with 10G, and 50G can provide 1.25 times of bandwidth with only one channel compared with 40G in the future. Currently, 50G has been proposed as the basis for upgrading 100G/200G/400G network, but it still needs some time to implement 50G Ethernet standard.

25G will provide more possibilities for 50G, and since 50G Ethernet can be implemented on two 25G channels, it will be an alternative to the current 40G using four 10G channels, reducing the network equipment cost of the data center by reducing channel deflection.In the future, the network upgrade path may evolve from the traditional 10g-40g-100g to 10g-25g-50g-100g.In any case, upgrading a data center over multiple 25G channels to a 50G or 100G network will be simpler and cheaper.

25G lays the foundation for the 200G/400G network upgrade

The 25G/50G/100G network architecture is more flexible and is often used as a solution for large data centers, paving the way for later 200G/400G upgrades.At present, high-end enterprises and large data centers are turning to this, effectively promoting the implementation of large data centers and the interconnection between data centers.More and more suppliers are working on 200G/400G optical devices, and some of these products have been successfully put into use.The implementation of 100G Ethernet is based on the development of 25G/50G, just as the future 200G/400G network upgrade will be based on 100G.The following table lists the paths to upgrade from 25G/50G/100G to 200G/400G.