NCM for LTE and MirrorLink




The USB CDC Network Control Model (NCM) sets the networking performance standard for high-speed, next-gen mobile devices.

As network operators prepare to roll out LTE and WiMax communications networks, handset designers are turning to networked communications models to outperform yesterday's modem-based data communications. Although there are configurations in which a full-speed USB device may need little more than MCCI's CDC Ethernet USB class drivers, LTE radios deliver content at a rate of 75-100 Mbps. For this kind of throughput, full-speed devices and full-speed technologies are not optimal. Similarly, when implementing MirrorLink to connect smart phones to cars, throughputs of 100 to 200 Mbps are needed in order to satisfy the users with quick response and smooth updates of the display.

For high-speed devices, turn to MCCI for seamless, high-quality, high-throughput NCM functionality. MCCI was the primary contributor to and technical editor of the CDC NCM specification; our implementations are the fastest in the industry.

MCCI offers NCM device protocol implementations in several forms.

  • An NCM protocol implementation is offered as part of the MCCI USB DataPump, using the "Abstract NIC protocol".
  • Operating-system-specific NCM protocol implementations are also available from MCCI. We offer support for Linux and Windows CE.

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At the most basic level, modem-based products are throughput-restricted because the modem protocol CDC ACM (Abstract Control Model) uses PPP-encapsulated IP frames to communicate with the host PC. CDC NCM eliminates the overhead of CDC ACM and maximizes data flow to the handset.

Once the switch from a modem architecture to a network architecture is made, the problem of frequent interrupts must be addressed because CDC Ethernet and CDC ECM transfer only a single frame per USB transfer. Every time a USB transfer finishes, the processor must stop what it is doing and service the interrupt. This is very costly in terms of performance and battery life. CDC NCM includes many Ethernet frames within a single USB transfer, thus reducing the interrupt burden substantially.

Further improvements brought by NCM:

  • A standard way of imposing structure on the raw USB pipe data stream has been defined, so that Ethernet frames don't have to begin or end on packet boundaries.
  • Highly efficient DMA (Direct Memory Access) is used to move data directly from the USB transfer buffers into the final application buffer, web browser, etc.
  • Cache handling and interrupt loading are optimized across all standards for mobile platforms and communications. This makes CDC NCM a good remedy in situations where excessive control plane activity results in unstable connections.

MCCI's experience with NCM implementations began before the specification was completed. MCCI developed the Experimental NCM (ENCM) specification, which was used as the basis for the final NCM specification. MCCI's NCM device implementation is used in the MCCI Catena 2210, which was selected as the reference test device by the Car Connectivity Consorutium for testing MirrorLink USB host implementations.