100G CFP2-ACO and Inphi’s 100G PAM4 modules are in use; long-distance data center interconnect and long-haul transmission are cheaper now, and single-wavelength 100G standard will further reduce fiber and cost. 100G technologies are making progress in an inspiring way.
A Call for 100G Revolution
Currently most data centers rely on 10GbE and 40GbE, and these technologies work well for some time. Most people have no issue with 10G or 40G and they felt these speeds are more than enough. But issue becomes apparent when looking at it from the data center aspect. The traffic growth of Enterprise networks and service providers is demanding for more efficient and cost-effective technologies to deal with higher bandwidth. This is why 100G is mentioned more frequently in these days, especially in DCI and 100G DWDM networks. 100G technologies are called for a network transmission revolution.
What’s Happening in 100G Technology?
On Jan. 22, 2016, the Optical Internetworking Forum published the Implementation Agreement (IA) document for CFP2-ACO module. On Mar. 22, 2016, Inphi Corp. (a specialist in this area) announced the industry’s first 100G PAM4 QSFP28 form factor for 80km DWDM DCI. Almost at the same time, AppliedMicro demonstrated world’s first 100G PAM4 single-wavelength solution at the OFC. Then on Mar. 8, 2017, members of SWDM MSA group, consisting of companies like Finisar, Commscope, etc., released the specifications for 100G SWDM4 module that works over multimode fiber.
100G CFP2-ACO and PAM4 Are Real, 100G SWDM4 Is Near
CFP2-ACO belongs to the 100G coherent DWDM family. It has no digital signal processor (DSP) in the package but relies on the Host board/card, so the total power consumption (less than 12 W) of the module will not exceed power designation of the CFP2 form factor. Instead it has analog optical components and full C-band tunable laser on the module.
The CFP2-ACO module, along with existing CFP-DCO and in-development CFP2-DCO, mainly serves for 100G long-distance data center interconnect/metro and 100G long-haul applications. Transceiver manufacturers like Finisar have been supplying some of these 100G DWDM coherent CFPs.
Inphi 100G PAM4
Inphi’s 100G QSFP28 PAM4 module combines a pair of 50Gbps wavelengths to create the 100Gbps transmission.
Figure 2: 2x50G PAM4 block diagram.
The most significant breakthrough for this QSFP28 module is that it fills the gap in the DCI within a distance of 80 km of each other. Previously there was no 100G DWDM in QSFP28 form factor available, and sub 80km DCI was mainly relied on 10G DWDM. As the Cloud data centers are moving to adopt 100G to meet their switching and routing requirements, the high-density, low-latency and low power DWDM links are on demand. Inphi 100G PAM4 module is exactly such a QSFP28 form factor for this purpose, and Inphi will supply Microsoft this module.
However, the dual laser PAM4 (2x50G) is not the most optimized 100G solution. The best solution is the single laser 100G PAM4 technology, for its lower power dissipation, higher reliability and lower cost especially in large-scale deployment. As for the single-wavelength 100G transceiver, we can believe that it is not far away for single-wavelength 100G PAM4 technology to develop into the most desirable QSFP28 100G transceiver for DCI.
100G technology on the multimode side also kept up with the advance. The SWDM MSA specifications gave detailed information (see some in figures below) about the 100G SWDM4 module, including the module block diagram, the power dissipation, and the color code, etc. After reading the optical specifications for the 100G SWDM4 module, it is not hard to know that transceiver manufacturers will soon make it real. At that time, short-reach 100G transmission will use only two fibers (now is 8 or 20 fibers) and it will be a significant reduction on fiber count and space.
The latest advances of 100G technologies do not necessarily mean old ones will all be displaced, because all these old and new technologies are designed for different applications. Already existing 100G technologies and devices are still important in their places. Old 100G technologies are categorized by different standards, and there are different form factors in MSA supporting these 100G physical layer (PHY).
Table 3: Already existing 100G technologies.
Gigabit Per Lane
Twinax copper cable, 7 m
Mulitmode fiber, 850 nm, 100 m over OM3, 150 m over OM4
The difference in application is mainly due to their supported distances. In the whole, these 100G standard transceivers and DAC/ AOC cable assemblies are typically used for distances less than 40 km, together with future 100G SWDM4 module. When combined with DWDM technology, these modules can also support longer distances. 100G PAM4 is typically for distances between 40 km and 80 km. And coherent CFP/CFP2 DWDM optical transceivers are for 100G metro/DCI connectivity more than 80 km or a long-haul link more than 1000 km.
Figure 5: Typical application distances for different 100G devices.
Note: There’s a simple way to move to 100G if you do not bother to change your present infrastructure. That is by using 100G transponder/muxponder.
100G transponder/ muxponder is a device that aggregates multiple lower rate services onto a 100G DWDM link typically for long-distance transmission. The 100G muxponder can multiplex multiprotocol and multi-rate services instead of only one type, such as 8GFC, 10GbE LAN/SAN, 40GbE LAN, OTU2, STM64/OC-192, etc. The benefit of using 100G transponder/muxponder is that a redesign of the network is not required. The muxponder/transponder uses an existing wavelength in the DWDM network. In comparison with other solutions, the 100G muxponder saves considerable space and costs for space and energy.
Follow the Path of 100G When You Can!
If you still think that you can stay well at 10Gbps or even 100/1000Mbps, you’re deemed to be out of the Gigabit game. 100G is rapidly growing in major data centers and will soon take up a large amount of the network traffic. Technologies like 100G PAM4 and 100G coherent CFPs will enrich your communication with the world more, and in a smoother and easier way.
PAM4 = Pulse Amplitude Modulation
SWDM = Shortwave Wavelength Division Multiplexing
DCI = Data Center Interconnect
OFC = Optical Fiber Communication Conference and Exposition
QSFP28 = Quad small form-factor pluggable 28
CFP = C-form factor pluggable
CFP2, CFP4 = Next generations of CFP
DCO = Digital Coherent Optic
ACO = Analog Coherent Optic
DWDM = Dense wavelength division multiplexing
CXP = 120Gbps 12 lanes small form-factor pluggable
CPAK = Cisco’s proprietary 100 Gigabit Ethernet pluggable transceiver modules
DAC =Direct Attach Copper Cable
AOC = Active Optical Cable
MSA = Multi-source Agreements
RS-FEC = Reed Solomon Forward Error Correction
DP-QPSK = Dual Polarization Quadrature Phase Shift Keying
FC = Fibre Channel
LAN = Local area network
SAN = Storage Area Network
STM64/OC-192 = A variant of standard 10GbE, with transmission speeds up to 9.510912Gbit/s.