Issue link: https://www.e-digitaleditions.com/i/1066130
January/February 2019 I 55 the PSM4 architecture are slightly cheaper than their CWDM counterpart. This is mainly due to the 3x increase in transceiver cost compared to 100 Gb. At 400 Gb, the Duplex-LC based transceiver consumes close to 90% of the spend, whereas the PSM4 based links still have a 60% -40% distribution between cost of optics and cable/ connectivity. If a data center infrastructure is built only for a specific speed, then for 100 Gb, CWDM4 is the cost-effective choice; for 400 Gb, the PSM4 version. For a 100 Gb to 400 Gb migration scenario with re-use of existing infrastructure in mind, there are two possible options. In the first option, the optics and cabling infrastructure is kept the same for both 100 Gb and 400 Gb. In the second option, an architecture change is implemented where the optical architectures are not the same at 100 Gb and 400 Gb. In the first option, the cost of migration from 100 Gb to 400 Gb is only from additional transceivers, since no new cabling/ connectivity is required (as long as the existing 100 Gb cabling infrastructure meets the power budget and reflectance requirements for 400 Gb). In the latter scenario where the migration is based on change in architecture, additional cost from cabling and connectivity may incur on top of the added cost of new optical transceivers. For example, when a migration from CWDM4 to PSM4 is considered, there is additional cabling/connectivity cost that is incurred due to increased fiber count for the PSM4 architecture; whereas in the opposite case, where a PSM4 to CWDM4 migration is considered, additional connectivity to convert from MPO to Duplex-LC will be required. Taking everything into account while considering a specific design as per Table 2, the overall cost of ownership of both 100 Gb and 400 Gb combined was calculated for different migration scenarios as shown in Figure 5. If a 100 Gb- CWDM4 link costs $1, migrating to 400 Gb-FR4 would incur an additional cost of around $1.40, and the total cost of a 100 Gb and 0% 100G-CWDM4 Relative TCO of 100G Links 100G-PSM4 25% 50% 750% 100% 125% 150% Transceiver Cost Cable/Connectivity Cost 0% 400G-FR4 (CWDM4) Relative TCO of 400G Links 400GBASE-DR4 (PSM4) 25% 50% 750% 100% 125% 150% Transceiver Cost Cable/Connectivity Cost 0% Duplex-LC at 100G MPO at 100G Combined cost of 100G and 400G links 50% 100% 150% 200% 250% 300% No Change in Architecture for 400G Change in Architecture for 400G FIGURE 4: (a) Total link cost of 100 Gb options relative to 100 Gb-CWDM4. (b) Total link cost of 400 Gb options relative to 400 Gb-FR4 (CWDM4). FIGURE 5: Consolidated cost of 100 Gb and 400 Gb, relative to the cost of only 100 Gb-CWDM4 links with and without change in architecture during speed migration. (a) (b)