QSFP-DD Fibre Optic Transceiver Technology Overview

QSFP-DD

The QSFP-DD (Quad Small Form-factor Pluggable – Double Density) form-factor is used for 200G, 400G and 800G applications and is backward compatible with lower speed QSFP+, QSFP28, QSFP56 and QSFP112 technologies. This makes it a popular choice when upgrading existing infrastructures that already use QSFP modules as it does not require major hardware changes.

The “Double Density” means it supports double the of high speed electrical interfaces compared to previous models, allowing them to reach much higher data rates. They are fully compliant with IEEE802.3bs and QSFP-DD MSA standards.

QSFP-DD modules have the same physical dimensions as other QSFPs, but have an eight-lane internal electrical interface as opposed to four-lane. Additionally, the ASIC ports are doubled to accommodate existing interfaces such as CAUI-4. To allow for the extra row of contacts, the mechanical interface of QSFP-DD transceivers on the host board is slightly deeper than conventional QSFP devices.

To achieve 200G transmission, each channel targets 25Gbps through NRZ (Non Return to Zero) modulation. For 400G and 800G, PAM4 (Pulse Amplitude Modulation, 4-level) is used for speeds of 50Gbps, or 100Gbps per channel. PAM4 modulation combines two bits into each symbol with four amplitude levels, effectively doubling the potential data rate compared to NRZ. Visit our knowledge base to find out more about these modulation types.

Standards & Protocols

QSFP-DD MSA standards
IEEE802.3bs for 400GBASE-DR4, 400GBASE-FR8, and 400GBASE-LR8
IEEE P802.3cm for 400GBASE-SR8, 400GBASE-SR4.2
IEEE P802.3cn for 400GBASE-ER8
IEEE P802.3ct for 400GBASE-ZR
100G Lambda MSA for 400GBASE-FR4, 400GBASE-LR4
CWDM8 MSA for 400G-CWDM8-2, 400G-CWDM8-10

Features

Format	Reach	Media Type	Architecture	Wavelength
400GBASE-DR4	500m	SMF	4 x 100G PAM4	1300nm
400GBASE-FR8	2km	SMF	8 x 50G PAM4	WDM
400GBASE-LR8	10km	SMF	8 x 50G PAM4	WDM
400GBASE-SR8	100m	MMF	8 x 50G PAM4	850nm
400GBASE-SR4.2	100m	MMF	8 x 50G PAM4 BiDi	850/910nm
400GBASE-ER8	40km	SMF	8 x 50G PAM4	WDM
400GBASE-ZR	80km	SMF	Coherent	DWDM
400GBASE-FR4	2km	SMF	4 x 100G PAM4	CWDM
400GBASE-LR4	10km	SMF	4 x 100G PAM4	CWDM
400G-CWDM8-2	2km	SMF	8 x 50G	CWDM
400G-CWDM8-10	10km	SMF	8 x 50G	CWDM
800GBASE-SR8	50m	MMF	8 x 100G PAM4	850nm
800GBASE-DR4	500m	SMF	8 x 100G PAM4	1310nm
800GBASE-2DR4	500m	SMF	8 x 100G PAM4	1310nm
800GBASE-DR8	500m	SMF	8 x 100G PAM4	1310nm
800GBASE-FR4	2km	SMF	8 x 100G PAM4	CWDM
800GBASE-2FR4	2km	SMF	8 x 100G PAM4	CWDM
800GBASE-FR8	2km	SMF	8 x 100G PAM4	CWDM
800GBASE-2LR4	10km	SMF	8 x 100G PAM4	CWDM
800GBASE-LR8	10km	SMF	8 x 100G PAM4	1310nm
800GBASE-ZR	80km	SMF	Coherent	DWDM