(a) (b)
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).
January/February 2019 I55
150%
125%
100%
750%
50%
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
150%
125%
100%
750%
50%
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%
Transceiver Cost Cable/Connectivity Cost
0%
400G-FR4 (CWDM4)
Relative TCO of 400G Links
400GBASE-DR4 (PSM4)
25%
Transceiver Cost Cable/Connectivity Cost
300%
250%
200%
150%
100%
0%
Duplex-LC at 100G MPO at 100G
Combined cost of 100G and
400G links
50%
No Change in Architecture for 400G
Change in Architecture for 400G
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.