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25GE Solution for Data Center Interconnection

Number of visits: Date:2018-3-29 09:53


After over 40 years' development, Ethernet has achieved the goals that its creator wants to. Just like its name, Ethernet exists everywhere, becoming the ubiquitous media in the information society.

These years, with the rapid development of Internet, cloud computing and cloud data, the construction of IT infrastructure data center has promoted fast. In the Ethernet of Data Center, a new upgrading is also prepared, in which 25G Ethernet is very popular.

Let's look at the change on the ports of data center device first, as it shown in the below picture:

1. Background of 25G Ethernet Technology

For the needs of Ethernet, it's mainly out of consideration for energy-saving and cost. Fields related to data center includes the development of cloud and Leaf/Spine matrix type network structure. With the further improvement of server performance and the upgrading of data center from leaf-to-spine connection to 100 Gbps, the upgrading of server from 10 Gbps to 25 Gbps/50 Gbps is with more practical significance. Because 10G Ethernet usually can't meet the needs, and the 100G is too expensive, the birth of 25G and 50G Ethernet rightly makes up for the shortages of them. In addition, the channel tech of 25 Gbps and 50 Gbps will be the basis of 100Gbps (four 25 Gbps) and 400Gbps (eight 50 Gbps) Ethernet in the future. So companies in this field generally hope to use the transmission rate of 25G to replace 10Gbps's.

2. Technical Advantages of 25G Ethernet

Compared with 40 GE, 25 GE has strengthened in cost for its single channel. 40G needs multi-channel due to its use of 10G tech. For 25G Ethernet, its essential advantage is that many parts have been developed earlier, because 100G is the combination of four 25 Gbps. Therefore, their components can be produced largely to lead to the falling of cost. By the SFP connector with 4 channels(QSFP), 100 G can be divided into four 25 Gbps, and 40 G is able to be divided into four 10 G. Therefore, multi-speed Ethernet products are developed and applied.

Using same copper fiber cables with low cost can get quicker performance and higher cardinal number. The rule stipulates that by using the single exchanger/NIC SerDes, the bandwidth provided by 25G Ethernet link path is equal to 2.5 times of the one offered by the 10Gbps link path of 2 pairs of biax copper cables and FP+ DAC. By using two channels of exchangers/NIC SerDes operating at 25 Gbps, 50G Ethernet link path can provide more 25% bandwidth than 40 G. In addition, compared with the present QSFP+DAC cabling, only 4 biax copper cables are used according to the reference standards. When the speed rate of every channel is 25 Gbps, the exchanger and NIC chips' working speed will be quicker, and their power dissipation is relatively little higher. However, after the bandwidth is standardized, the advantages in cost and power dissipation will be more apparent.

Compared with 40 GE, connection with TOR exchanger, 25 GE can support higher server density in the rack.

Table 6. Why to Select 25GbE-Comparision

Characteristic/Need 10GbE 25GbE 40GbE 100GbE
Quantity of PCle Gen3 Channels at each port 2 4 8 16
PCle Cen3 Bandwidth Utilization Rate 62.5% 78% 62.5% 78%
Clock Rate 10.31Ghz 25.78Ghz 10.31Ghz 25.78Ghz
Serdes Channel Single Single Four Four
Server/TOR 3:1 Overload Ratio 48 48 24 Future
Connector SFP+ SFP28 QSFP QSFP28
DAC Wiring Thin 4-wire Thin 4-wire Bulkier 16-wire Bulkier 16-wire
Cable Material Cost Low Low High High
Transit to 10GbE more easily   Yes No  

For the density of ports, compared with the connection of present 10G and 40G Ethernet, 25G and 50G Ethernet link path, defined by 25G Ethernet Union, can make the performance of serializer/ SerDes' s channel and biax copper cables raised by 2.5 times, which can reduce over 50% of rack-level network cost about bandwidth per unit, obviously improving the profit and loss level of MSDC manufacturers. Besides, the performance of this standard can also broaden the network scale, usually called base number. Compared with 40G Ethernet server connecting to TOR, it can support higher density in the rack.

3. Introduction on Gigalight 25G Series Product Lines

To follow the steps of the next generation of 25GE data centers, Gigalight has self-developed 25G series products in recent two years, including 25G SFP28 SR, 25G SFP28 LR, and 25G SFP28 AOC/DAC. Advanced technology, reliable quality and competitive cost fully reflect Gigalight's strengths and determinations on the layout of 25G data center. Product line is as below:

Gigalight Product No Working Speed Rate Packaging Form Type Working Distance
GPP-PC250-XXXC 25GE SFP28 DAC Copper Cable 5m
GSS-MDO250-XXXC 25GE SFP28 AOC Multimode 850nm 100m(OM4)
GPP-85250-SRC 25GE SFP28 Optical Module Optical Fiber 850nm 100m(OM4)
GPP-85250-LRC 25GE SFP28 Optical Module Optical Fiber 1310nm 10km
25G SFP28(AOC)Checker N/A N/A N/A N/A

3.1. Technical Decryption of Gigalight 25G Series Products

25G product lines consist of 25G fiber and 25G copper products. The former includes AOC, series of optical modules and the latter is mainly used for DAC in super-short distance (5m) interconnection. Mature COB tech, independently-developed hot pressing welding technique, automatic coupling equipment and process ensure the availability of bulk production.

3.1.1. COB process is mature and reliable, completely meeting the requirements of low cost and high-efficiency production of optical fiber products.

Gigalight self-developed COB tech platform and critical optical engine design are mature and reliable. High-precision SMT, reliable gold wire bonding with accurate optical design and coupling design ensure that the optical module has the advantages of low power consumption, low cost and high reliability, etc.

3.1.2. Self-developed DAC laser stripping technique and visual hot pressing welding process.

Laser stripping machine uses for manual transfer, artificial upper and lower material laser stripping, and non-contact processing have no damage to the product, no tool wear. High-speed cutting without sawtooth provides high production efficiency and support 30AWG~26AWG cable insulation leather cutting. It's also available with other kinds of wire diameters processing such as LVDS, MINI SAS, USB3.0, and TYPE C series.

Gigalight self-developed hot pressing welding equipment is used for 30AWG~26AWG 25G&100G DAC welding with high-accuracy camera which is fully compatible with the pressure welding process and timely correction of welding abnormalities to ensure the welding quality. Meanwhile, it is suitable for all kinds of cables and connector/ PCB welding, widely used in USB2.0&3.0, TYPE C, HDMI, H-SPEED, FFC, FPC and other products with high welding quality, high welding precision and the smallest welding PITCH which can reach 0.3 mm.

3.2. The Quality of Gigalight 25G Series Products

Gigalight owns strict quality test platform and test system. Not only 25G series product pass reliability testing, but also 25G DAC products pass rigorous S-parameter testing. A series of measures ensure the reliable product quality.

3.2.1. Gigalight 25G fiber and copper series products pass test in reliability.

Module Qualification Test Results:

Description Sample Size Result
Mechanical Integrity Mechanical Shock 11 All Pass
Vibration 11 All Pass
Endurance Accelerated Aging (High Temp) 11 All Pass
Thermal Shock 11 All Pass
Temperature Cycling 11 All Pass
Damp Heat (Humidity Aging) 11 All Pass
Low Temperature Storage 11 All Pass
High Temperature Storage 11 All Pass

3.2.2. Gigalight owns self-developed DAC test platform, and 25G DAC products pass rigorous S-parameter testing.

Gigalight self-developed automatic test system eliminates the cumbersome operation, a key to complete all the parameters of the test such as impedance, insertion loss, COM parameters, etc. greatly improving the test efficiency and the reliability of test results.

Test Result Summary:

1 SDD11 Return Loss Pass
2 SCC11 Common Mode Return Loss Pass
3 SDD22 Return Loss Pass
4 SCC22 Common Mode Return Loss Pass
5 SCD11 Return Loss Pass
6 SCD22 Return Loss Pass
7 Insertion Loss Pass
8 SCD21 Conversion-Insertion Loss Pass
9 Connector Impedance Pass
10 Connector Impedance(Far End) Pass
11 Channel Operating Margin Pass

3.3. Advantages of Gigalight 25G Series Products' Cost

The most critical cost assurance for products and markets entering 25 G and above comes from supply chain support and yield. Since 2011, Gigalight has been offering DAC and AOC products, which is living in the leading position and has a great performance in Date Center field.

DAC: Automatic production and commissioning are key factors in DAC costs. From the BOOM list, the DAC product cost is clear, and the processing is the primary cost. Over the course of two years, Gigalight successfully developed a complete set of production processes, and overcame the comprehensive evaluation parameters: COM parameters. The automatic processing ensures that the price of 1 meter 25G DAC can be less than $ 15.

AOC: Gigalight delivers no less than 300,000 AOC products over the world every year which accumulate quality reliability and rich production experience as well as get strong support from global supply chain. Now Gigalight AOC can completely pass double 85 environment reliability tests which is numbered in industry. Low cost, low consumption and high quality are the features of Gigalight AOC products. At present, Gigalight 25G AOC 1m product sales price is around $70.


Since Standards about TOR exchanger was put forward by ODCC group, lead by BAT, last year, 25 G has been the next goal of data center. It's predicted that data center focusing on 25 G will be deployed by Bat on a large scare, after the Scorpio 3.0 Plan is pushed out in 2017. In addition, the needs of network products about data center will be raised quickly. The age of 25 G is coming! Undoubtedly, the technology, quality and price advantages of 25G series products will bring much development and opportunity for Gigalight in the current and future 25G market.

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