The PCIe TLP (Transaction Layer Packet) payload size determines the amount of data transmitted within each data packet to/from the Host (CPU) system/chipset and the PCIe device connected to it, for e.g. a PCIe switch or PCIe endpoint. The Maximum Payload Size (MPS) is determined by the BIOS/software, each device on the PCIe link reports the MPS it supports and the software typically configures the active MPS to the highest common value – for example if one device reports a supported MPS of 256B and the other device report supported MPS of 512B then the software shall typically configure the MPS to 256B but it can configure it to a lower value. This process is called “link training”. The default setting (found in the Mellanox INI file) for Mellanox ConnectX-3 ICs, and hence ConnectX-3 based HCAs (Host Card Adapters), is 256B. This is the value that Mellanox’s ConnectX-3 (PCIe endpoint) device “advertises” during the link training process. So, even if the CPU or PCIe switch connected to the ConnectX-3 device supports a larger MPS, this is the highest value the software can configure. Mellanox firmware currently supports 128B, 256B and 512B max payload size with future support for 1KB, 2KB and 4KB.