QSFP28 transceiver is designed for 100G speeds and using the 4×25 wiring specification. Now, technology of QSFP28 is relatively matured. With the movement to reduce costs, the QSFP28 transceiver become increasing popular in the market. Similar to 40G QSFP+ that is implemented using four 10Gbps lanes, the QSFP28 uses four 25Gbps lanes with parallel technology, eliminating the costly gearbox found in the other version of 100G transceiver like CFP, CFP2, and the CPAK. Additionally, the QSFP28 transceiver has an upgraded electrical interface to support signaling up to 28Gbps signals, yet keeps all of the physical dimensions of its predecessor.
Two basic versions of QSFP28 transceiver are 100GBASE-SR4 QSFP28 transceiver and 100GBASE-LR4 QSFP28 transceiver that are respectively used for multimode (MMF) and single-mode (SMF) 100G applications.
The QSFP28 makes deploying 100GbE (or beyond) networks as easy as 10GbE networks, having a strong ability to increase density, decrease power consumption, and decreases price per bit.
There are limitations of the other versions of 100G transceiver. For example, in the first generation of 100GbE switches and routers, the smaller CXP form factor was used for cabling and the CFP or CFP2 was used for transceivers. This forced huge equipment design sacrifices. A switch with CXP ports couldn’t be used in a data center with single-mode fiber (SMF). A router using CFP2 or CPAK ports had bandwidth limited by the 8-10 ports that could fit on the front panel.
QSFP28 solves these issues because it supports both cables and transceivers. With QSFP28, a one rack-unit switch can accommodate up to 36 QSFP ports. Many more varieties of transceivers and cables can plug into these ports. The cables can be either copper direct attach cables (DACs) or active optical cables (AOCs).
What’s more, the QSFP28 transceiver can use either VCSELs (useful for shorter distances on MMF) or silicon photonics (for longer distances on SMF). Silicon photonics enables QSFP28 transceiver to support any data center reach up to 10 kilometers, and provides a high degree of integration. Silicon photonics is low power; even WDM (Wavelength Division Multiplexing) designs can fit within the 3.5W maximum of QSFP.
According to the current market trends, the QSFP28 has great market prospect. And the coming generations of high-bandwidth switches, routers, and adapters will all feature QSFP28 ports to better adapt the 100G (or beyond) network demands.