In the past decade, 10g and 40g technologies have occupied the majority of the Ethernet market. However, with the demand of users for high bandwidth and the development of special applications, 25g / 50g / 100g technologies have attracted more and more attention of users. They gradually stand out in network deployment by providing effective paths for high-speed. This paper will focus on 25g / 50g / 100g technology and the relationship among them.
25g Technology
The main advantage of 25g is using SerDes technology, which is a mainstream time division multiplexing (TDM), point-to-point (P2P) serial communication technology. It can make full use of the channel capacity of transmission media, reduce the number of transmission channels and device pins to the greatest extent, so as to improve the signal transmission rate and greatly reduce the communication cost.
At present, most components used in switches are running SerDes with a clock rate of about 10GHz, which can provide 10Gbps transmission rate between different components. In recent years, due to the rapid development of SerDes technology, the clock rate of 25ghz SerDes has become one of the economically feasible choices, which leads to the cost and benefit differences between 10g and 40g and 25g. For example:
10g vs 25g - also a SerDes channel, the throughput provided by 25g is 2.5 times higher than that provided by 10g. When the 10G network is upgraded to 25g, the 25g sfp28 optical module can use the LC jumper used in the wiring of 10G network without rewiring, so the cost can be effectively saved.
40g vs 25g - 40g adopts four 10Gbps fiber channels (SerDes with clock rate of 12.5ghz), while 25g adopts SerDes single channel, so 25g can provide higher port density. At the same time, as most 40g qsfp + optical modules on the market need to be used with MTP / MPO jumpers, 10g-40g will inevitably increase the cable cost.
50g Technology
With the maturity of 25g technology and users' requirements for higher speed, the industry has strong expectations for 50g. In 2018, IEEE launched the 50g Ethernet standard with the same architecture as 400g / 200g Ethernet standard. The standard adopts pam4 technology, which can effectively improve the bandwidth utilization efficiency and become the next solution for high-speed connection between servers and data centers. Because 50g can reuse 25g components in the existing 100g network, it can effectively reduce the cost. At the same time, the cost of 50g is half that of 40g, but its performance is improved by 25%.
Since pam4 technology maps pairs of bits into a single symbol, the total baud rate of each 50gbit / s channel is 26.5625 gbaud. 50gbaud pam4 can provide 100g transmission rate through 1 * 2 * 50 gbaud architecture (only one laser is needed), which means that the transmission rate can be increased from 10Gbps to 100gbps with one laser, which is a ten fold increase. Compared with the early NRZ technology, pam4 technology can provide higher transmission efficiency at a lower cost, so it is widely used in high-speed signal interconnection.
100g Technology
100g Ethernet was officially released in 2010. In order to meet the requirements of high speed, long distance and some special scenarios, the standard has been changed widely. Due to the continuous optimization of standards, the unification of technical solutions, the development of industrial chain and the higher transmission rate and longer transmission distance (using DWDM Technology), 100g is gradually replacing 40g.
PMD | 40G | 100G |
Multimode fiber Less than 100m (OM3) | 40GBASE-SR4 | 100GBASE-SR10 |
Single mode fiber More than 10 km | 40GBASE-LR4 | 10GBASE-LR4 |
Single mode fiber More than 40 km | 100GBASE-ER4 | |
Single mode fiber No specification | No specification |
It is especially suitable for high-speed transmission of single wavelength DWDM. Among them, the coherent CFP DWDM optical module is especially suitable for 100g man or data center interconnection (DCI) up to 80km or ultra long links with transmission distance over 1000km. In addition, in the case of multi rate and multi protocol network (such as 10g / 40g / 100g Ethernet protocol and rate), the use of 100g DWDM multiplexer can effectively avoid the redesign and planning of network architecture. It can directly combine signals of different protocols and different rates into a single wavelength up to 100g for transmission, providing a flexible and cost-effective solution.
What is the relationship between 25g / 50g / 100g?
Now 25g / 50g / 100g is widely used in cloud data center, and if the three together, 10g-25g-50g-100g network upgrade can be realized. Before the emergence of 25g and 50g, 100g network upgrade was realized by 10g-40g-100g, but this method is low efficiency and expensive. In contrast, 25g is the most cost-effective solution to upgrade to 100g. If 25g is used for 100g network upgrade, it can be implemented through 4 * 25g or 2 * 50g SerDes channel with ridge leaf architecture. In this way, 25g can be upgraded based on the existing cabling infrastructure with its compatibility, providing higher transmission efficiency and performance while saving CAPEX and OPEX. In a word, 25g-50g-100g network upgrade path can reduce the unit bandwidth cost by making full use of switch port function, and lay the foundation for 200g and 400g network upgrade.
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