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With the large-scale deployment of 100G, the ultra 100G technology — 400G has gradually become a hot topic in the industry. There is no doubt that 400G will eventually be the next major Ethernet speed in the data centers. In fact, the world’s leading optical transceiver manufacturers have launched their own 400G optical transceiver modules such as 400G QSFP-DD, OSFP, CFP8 and COBO transceivers for 400G data transmission. This article will focus on the 400G QSFP-DD and CFP8 transceivers.

What Is 400G QSFP-DD Transceiver?

QSFP-DD refers to Quad Small Form-factor Pluggable Double Density. It is a new 400G transceiver designed with eight lanes that operate up to 25Gb/s NRZ modulation or 50Gb/s PAM4 modulation, providing solutions up to 200Gb/s or 400Gb/s aggregate. The term “Double-Density” refers to the doubling of the number of high-speed electrical interfaces that the module supports compared to the regular QSFP28 module. 400G QSFP-DD transceiver enables up to 14.4Tb/s aggregate bandwidth in a single switch slot. By quadrupling aggregate network switch bandwidth while maintaining port density, QSFP-DD can support continuing growth in network bandwidth demand and data center traffic.

What Is 400G CFP8 Transceiver?

CFP8 transceiver is the 400G form factor type specified by the CFP MSA (Multi-Source Agreements). It is the same size as the CFP2 transceiver but uses a new 16x25G electrical I/O connector. As for bandwidth density, it respectively supports eight times and four times the bandwidth density of CFP and CFP2 transceiver. Generally speaking, there are four types of CFP8 modules on the market— CFP8 FR8/LR8, CFP SR16, and CFP DR4. The interfaces of the four CFP8 transceivers are generally specified to allow for 8 x 50Gb/s, 16 x 25Gb/s, 4x100Gb/s modes, respectively.

CFP8 VS QSFP-DD: Which 400G Transceiver to Choose?

The upgrading path of the CFP series is CFP-CFP2-CFP4-CFP8, and QSFP-DD has also experienced hardware specifications from 1.0 to 4.0. These are all long-established form-factor series. Compared to the QSFP series, the CFP series seems to be less popular for obvious reasons — large size and high power consumption. Below we will detail the differences between CFP8 VS QSFP-DD.

CFP8 VS QSFP-DD: Form Factor

In general, the width, length, and thickness of QSFP-DD are 18.35mm, 89.4mm and 8.5mm, while those of CFP8 are 41.5mm, 107.5mm and 9.5mm. The size of CFP8 transceiver is larger than QSFP-DD, and the volume is more than three times that of QSFP-DD. However, since the CFP8 transceivers are applied for telecommunication applications, and the port density requirements are not as high as in the data center, so the size is acceptable.

CFP8 VS QSFP-DD: Bandwidth

The maximum bandwidth of CFP8 and QSFP-DD is 400Gb/s, but CFP8 only supports 400Gb/s (16x25G, 8x50G, 4x100G), while QSFP-DD supports both 200Gb/s (8x25G) and 400Gb/s (8x50G). Thus, QSFP-DD works better than CFP8 in the performance.

CFP8 VS QSFP-DD: Thermal Capacity and Power Consumption

QSFP-DD has a thermal capacity of 7 to 12 watts, while CFP8 allows up 24 watts power consumption. The larger the thermal capacity, the greater the power consumption that the optical transceiver can withstand. With the advancement of technology, some industry-leading manufacturers have been able to reduce the power consumption of optical modules far below the upper limit of thermal capacity specified by MSA, so the larger thermal capacity does not seem to be a real advantage. However, as we all know, the lower the power consumption, the better.

CFP8 VS QSFP-DD: Backwards Compatibility

There is not any mention of backward compatibility in the hardware specification of CFP8. In fact, the entire CFP series transceiver does not seem to be backward compatible. However, 400G QSFP-DD transceiver has the advantage of backward compatible with QSFP, QSFP+, and QSFP28, which provides flexibility for end users and system designers.

Conclusion

After introducing and comparing QSFP-DD and CFP8, we find that QSFP-DD has unparalleled advantages in 400G applications. It is expected that when the world’s leading hyper-scale data centers begin to deploy 400G, QSFP-DD will become the mainstream form-factor of 400G optical transceivers. It is undeniable that QSFP-DD transceiver is the best choice for your network.

Original Source:

400 Gigabit Ethernet was planned to be released in December this year. It is designed to meet IEEE P802.3bs Task Force standard and to apply to both metro and long-haul networks. The 400GbE operates over 100 m of multimode fiber, 500 m of singlemode fiber, 2 km of SMF, and 10 km of SMF. 400G CDFP and CFP8 are two form factors of 400G Ethernet technology. This article would give a introduction to 400G CDFP and CFP8 modules and make a comparison between them.

Introduction to 400G CDFP Module

The CDFP is short for 400 (CD in Roman numerals) Form factor Pluggable, which is designed to provide a low cost, high density 400 Gigabit Ethernet solution. It features as front panel, hot-pluggable, 16 channel and 400 Gbps module. CDFP will be a short reach module, which enables 4 Terabit line cards. From the perspective of interface, it is very similar to the QSFP and CXP modules. CDFP developers have targeted using the developing IEEE802.3bs specification for Ethernet 400GBaseSR, 400GBaseLR.

5 meter direct attach cables

100 meter multimode fiber

500 meter parallel singlemode fiber

2 kilometers of duplex singlemode fiber

Figure2: 400G CDFP Module

Information About 400G CFP8 Module

Following CFP2 and CFP4 naming, CFP8 module was proposed in the year 2015. CFP8 is a new form factor which is still under development by members of the CFP multisource agreement (MSA). The form factor of CFP8 is amounting to CFP2, but it supports 4 × 100G and 400G, for example, 4×CFP2’s 1×100G. The CFP8 uses a new 16 × 25G electrical I/O connector. The CFP8’s interface has been generally specified to allow for 16 × 25 Gb/s and 8 × 50 Gb/s mode. From the point of bandwidth density, the CFP8 module is eight times larger than the CFP module and four times larger than the CFP2 module.

Figure3: 400G CFP8 module operation

Example IEEE specifications supported by CFP8:

400GBASE-SR16 parallel MMF (16x25G NRZ)

400GBASE-FR8/LR8 duplex SMF (8x50G PAM4 WDM)

400GBASE-DR4 parallel SMF (4x100G PAM4)

CDAUI-16, CDAUI-8

Figure4: Form factors of CFP modules

Among all the specifications on the above, 400GBaseDR4 is the most revolutionary one. 400GBaseDR4 uses 4x100G parallel SMF PAM4 signaling technology. This technology is also aimed at fitting in the CFP4 21.5-mm width module size, while using 12 (SMF) fibers within a 1×12 MPO optical connector and the host board electrical 56-pin edge connector.

Low power consumption is also a distinctive feature of CFP8. Active optical modules have been widely deployed in the process of data transmission, but some of them or some copper applications really cost a lot and consumes much power. CFP8 module uses internal mid-board optical or electrical interconnect flyovers and bulkhead MPO or MXC connectors to connect the switch. This reduces power consumption to a great extent.

400G CFDP Vs. CFP8

—Form factor

CDFP was proposed earlier than CFP8, it has larger form factor than CFP8.

—Supported fiber type

CDFP supports passive and active copper cable, active optical cable and multimode fiber while CFP8 supports singlemode and multimode fiber.

—Transmission distance

CFP8 modules support longer data link distance compared with CDFP modules.

—Applications

The CDFP modules provide a very versatile solution for data center interconnects. CFP8 would be used in high-density 4x100GbE fan-out applications, such as datacom applications or in ITU-T for telecom applications.

Conclusion