Migrating to 400G? Choosing the Right Option

As customers deploy 400G connectivity, they are transitioning from 25/100G connectivity to 100/400G connectivity for the different tiers of the network. Before making a decision, you should carefully consider your technical needs and budget with these parameters in mind:

• Reach: the distance you need to transmit data
• Power Consumption
• Flexibility – bending ratio. This is particularly important in tight spaces
• Cost

Let us look at network transition at the different tiers.

ToR to Server/storage

Most customers use DAC (Direct Attach Copper) cables to connect a ToR to servers/storage as they are very cost-effective. We expect that to continue. Some customers may augment DAC with AOC (Active Optical Cables) to extend beyond 3m reach of 400G DAC cables.

Between ToR & Leaf

For 100G, most customers use AOC, SR4, BiDi or PSM4. We expect 100G-AOC customers to use 400G-AOC for up to 30m connectivity. We expect 100G-SR4 & 100G-BiDi customers to use 400G-SR8 and 400G-BiDi for up to 100m connectivity. We expect 100G-PSM4 customers to deploy 400G-DR4 to 400G-DR4 or 400G-DR4 to 4x100G-DR1 connectivity.

Between Leaf & Spine and Spine & DCI

For 100G, most customers use PSM4 or CWDM4. We expect them to move to 400G-DR4 for up to 500m and to 400G-FR4 or 400G-2FR4 for up to 2km connectivity. We expect 400G-DR4 volumes to be high, as it is being used in multiple tiers of a data center, where the number of switches is high.

Inter-DC Connectivity

For 100G, most customers use CWDM4, LR4 or Coherent optics depending on distance requirements. They will likely move to 400G-FR4, 400G-LR8/LR4 or 400G-ZR/ZR+ Coherent optics, depending on reach requirements. Customers often use MACsec on these links for privacy and security reasons.