The key value proposition of SWDM4 and 100 Gb BiDi is the utilization
of much lower cost, often already installed, duplex fiber cabling
and connectivity instead of parallel fiber cabling and connectivity.
IEEE P802.3db 100 Gb/s, 200 Gb/s,
and 400 Gb/s Short Reach Fiber Task Force
A task force has been formed to develop physical layer
specifications that will support a number of objectives,
including 100 Gb/s over 1 pair of MMF, 200 Gb/s over
2 pairs of MMF, and 400 Gb/s over 4 pairs of MMF, with
lengths up to at least 50 m. The key area of consideration
will be MMF/VCSEL-based solutions.
Large hyperscale and enterprise data centers
are considering a move away from top of rack (ToR)
switching, migrating to middle of row (MoR) or end
of row (EoR) switches as server counts in racks decrease,
driven by increasing power dissipation per server as server
speeds move to 100 Gb (Figure 20).25 Links over MMF will
evolve to 100 Gb/s PAM4 VCSELs in the 2021 timeframe.
They will initially target short-reach (30 m) server
interconnects in an 800GBASE-SR8-type application
(2 x 400G-BASE-SR4, since 800 Gb/s MAC rate is not
yet specified), offering eight-way breakout from one
800 Gb/s switch port (2 x 400 Gb/s) to eight 100 Gb/s
server ports.
There is also considerable interest on the part of some
hyperscale customers for switch-to-switch links up to 50+
meters. As manufacturing experience is gained, support
for longer reach 100 m switch-to-switch links will
become available.
The market need for 100Gb/s lanes is expected
to expand rapidly once 100 Gb/s server ports become
available and are rapidly deployed in hyperscale data
centers. These data centers can contain hundreds of
thousands of servers, so the availability of a low power,
low cost solution is crucial. When this requirement for
higher speed is combined with longer switch to server
links, traditional copper twinax and twisted-pair solutions
are no longer viable, thereby opening the door for new
low-cost optical solutions.
Breakout Use Case - Servers
FIGURE 20: Evolution from TOR switch architecture to MOR switch architecture.
62 I ICT TODAY
Today
TOR Tier 0/1
Future
Switch
ASIC
Switch
ASIC
25G 100G 20-
30m
3m
25G 100G
25G 100G
100G
50G (2x25G)
50G (2x25G)
Consortium/MSA
25G
Server Server
Server No Supporting SMF PMDs