USBLAN and Gadget EEM

The CDC EEM protocol allows multiple network frames to be aggregated into a single CDC-EEM USB Bulk transfer. This allows for higher bus utilization and higher overall network throughput than the more commonly used CDC ECM (Ethernet Control Model) and Microsoft’s proprietary RNDIS protocols.

The CDC-EEM protocol also supports a streaming mode where the sender can send reasonably large CDC-EEM transfers even when the receiver does not know what the maximum size transfer is. This is achieved by ensuring that the CDC-EEM sender always terminates a CDC-EEM transfer with a short or Zero Length packet. The Belcarra USBLAN driver supports both frame aggregation and streaming with the CDC-EEM protocol.