Protocols

Belcarra USBLAN supports industry-standard USB networking protocol families and automatically matches the protocol offered by the attached device. For system integration maps, see the Host Driver Architecture and device-side USB Framework Architecture.

• CDC-NCM
• CDC-EEM
• CDC-ECM
• RNDIS

Multi-frame transfer behavior

EEM, NCM, and RNDIS support aggregation of multiple network frames in a single USB transfer. This generally improves bus utilization and throughput compared with single-frame transfer patterns.

• ECM transfer size behavior is fixed.
• EEM does not prescribe fixed transfer sizes and requires proper transfer termination behavior.
• NCM and RNDIS allow negotiated/configurable operating behavior during setup and control exchange.

Protocol notes

CDC-ECM

ECM is an early standardized USB networking model. It uses notification behavior and interface control semantics that are broadly compatible with existing host networking stacks.

CDC-EEM

EEM simplifies parts of configuration and allows multiple Ethernet frames in one USB transfer. Throughput gains depend on correct frame aggregation support on both host and device implementations.

CDC-NCM

NCM is a successor model to ECM for higher efficiency, with frame encapsulation designed for multi-frame transfer and additional device requests for capability/configuration control.

RNDIS

RNDIS remains widely used in production systems and is supported in USBLAN alongside CDC protocol options for interoperability flexibility.

Integration guidance

• Select one protocol strategy per product line where possible to minimize support complexity.
• Validate host and gadget/device behavior under sustained transfer and reconnect cycles.
• Document protocol-specific limits in your OEM integration notes and release documentation.