For TOR switch design, take an 8 TB/s bandwidth Switch ASIC supporting 56 G PAM4 as an example, the number of Serdes is 160 Lanes, and the hardware design can be designed as 48 downlink DSFP interfaces and 8 uplinks QSFP-DD The DSFP interface is connected to the cabinet server, and the uplink QSFP-DD is connected to the spine switch of the data center. DSFP hardware design is introduced in the first section. Usually, when a 1U switch is designed with 48 100G and 8 400G interfaces, the number of ports is large, and the space size is a big problem. If 100G uses QSFP28, the space will not be able to accommodate so many ports. At this time, the DSFP port has its unique advantages, because its cage size is compatible with SFP28, and the opening size of QSFP-DD is the same as that of QSFP28, so in In terms of organizational size, it can use the same structural components as the 48 × 25G (SFP28) + 8 × 100G (QSFP28) TOR switches commonly used in data centers. From this point of view, DSFP is a very good choice for 48×100G+8×400G TOR applications. DSFP is mainly used for 100G interface communication, and the main scenario of application in the data center is mainly the interconnection between the Smart NIC card of the server and the network TOR switch.
1) 100G interface
The interface is mainly 100G (2×50G PAM4). On the TOR switch, the DSFP interface is configured as a dual Lane single port, and the port speed is 100G. Also on the side of the server such as the Smart NIC, DSFP is also configured as a dual-lane 100G interface. Usually AOC or DAC can be interconnected through optical modules in the whole rack.
2) 50G interface
It is mainly used in 50G scenarios. The TOR switch is configured as two ports, and each port uses a 56G Lane. This mode is the usual Breakout mode. Usually the network card of the peer server also uses DSFP Breakout mode, using DAC and TOR for interconnection.
3) 25G interface
This application is to configure DSFP as two ports in TOR, and each port uses a 25G Lane. This application is to reduce the Serdes rate of Switch from 50G to 25G. In this case, you can use a 1-to-2 BreakoutDAC or AOC cable, that is, one TOR DSFP port is connected to two SFP28 ports on the server NIC side. Such usage is usually that the SFP28 port of the server network card remains unchanged, and the DSFP of the TOR switch is used to expand the interface capacity of the SFP28. For example, for the same 25G NRZ Serdes switching chip, 48 SFP28 can be synthesized into 24 DSFP ports, saving Half the space, or use the same space to double the interface capacity.