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SFP-DD – Next Generation SFP Module to Support 100G

Recently, a group of industry suppliers gathered to form a new transceiver module form-factor or Multi-Source Agreement (MSA). The agreement aims to foster the development of the next generation of SFP form-factor used in DAC and AOC cabling as well as optical transceivers. Mellanox often leads these sorts of technology developments and is a founding member of the SFP-DD MSA, as well as both QSFP-DD and OSFP MSAs.

While all the specs are not final yet, it’s called the SFP-DD or Small Form-factor Pluggable – Double Density. The “double density” refers to offering two rows of electrical pins enabling two-channels instead of the traditional one-channel in an SFP architecture – the smallest industry standard form-factor available today for data center systems.

New designs offer improved EMI and thermal management and will enable 50G and 100G PAM4 signaling in each channel for 100G and 200G support and up to 3.5 Watts of thermal dissipation; the same as the current QSFP28 which is about 2.5 times larger than the SFP-DD.

Bottom line:

First products on the market will likely be based on 50G PAM4 signaling and will feature two channels, offering 100G in SFP-DD form-factor. These new switches and network adapter configurations will enable increased bandwidth switch plate density, essentially doubling today’s current density.

This advancement will enable 100G (2x50G PAM4) in a tiny SFP port and 50G and 100G links to servers and storage in the smallest MSA available, with the highest number of 100G front-panel pluggable ports in a Top-of-Rack switch.  Eventually, two channels of 100G PAM4 will enable 200G per SFP-DD device.
 

Maintaining Popular Breakout Cabling to Servers

With the advent of new 8-channel form factors such as QSFP-DD, OSFP and COBO, a new 2-channel form factor was needed to enable 4-to-1 breakouts for servers and storage.

These time-tested data center Top-of-Rack breakout or splitter cable configurations can be maintained going forward to 400G with the SFP-DD in both copper DAC and AOC cables enabling supporting 10G, 25G, 50G, 100G and eventually 200G to the server such as:

• 40G QSFP+ -to-Quad 10G SFP+
• 100G QSFP28-to-Quad 25G SFP28
• 100G QSFP28-to-Dual 50G QSFP28
• 400G QSFP-DD-to-Quad 100G SFP-DD
• 400G QSFP-DD-to-Dual 200G SFP-DD

Servers today typically support one or two CPUs per server but are heading towards supporting four and eight CPUs per server in the future, with additional DRAM and FLASH on board and PCIe Gen4 at 16GT/s requiring more server uplink bandwidth.  Today, 10G and 25G uplinks are popular and some hyperscale companies also require 50G uplinks. At four and eight CPUs per server, 100G and 200G uplinks will be required.

Mellanox recently introduced two new 100G AOCs breakout cables that feature 100G-to-Quad 25G SFP28 and 100G-to-Dual 50G QSFP28. They are also available in copper DAC cabling. These breakout configurations can also be made using transceivers and splitter passive fiber cables if optical connectors are needed to detach fibers from the transceivers.

Similarly, new QSFP-DD and SFP-DD breakout cables will be available in the future to support new 50G PAM4-based switches and network adapters.

The SFP-DD new form-factors tie with Mellanox’s recent 200GbE Spectrum-2 switch IC announcement which is based on 50G PAM4 signaling and points to future 200G and 400G switch, network adapter, cable and transceiver developments from Mellanox.

Poised to Support the Next 5-10 years

By doubling the number of lanes, and at the same time doubling the number of bits per clock sent with PAM4 modulation, the SFP-DD bandwidth can transfer 100G versus the SFP28 at 25G. This translates into or four times the bandwidth of SFP28. In the future, the SFP-DD MSA goal is to support 100G PAM4 modulation enabling 200G (2x100G) per SFP-DD package which translates to eight times the current SFP28 bandwidth in the same physical space.

Referenece:

http://www.mellanox.com/blog/2017/07/sfp-dd-next-generation-sfp-module-support-100g/