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NCM Means High Performance Networking

NCM (Network Control Model) is one of the USB Implementers Forum's major stories for 2011.  Here are some detailed responses from MCCI CEO Terry Moore to a few questions about the NCM device class specification:

Q: Can you please give us a quick, high-level explanation of what the NCM specification is?

A: The Network Control Model (NCM) specification is a high-performance standard for connecting networking devices to PCs using USB.  Although it was designed specifically to support the needs of new 4G network standards (such as LTE and WiMax), it has substantial benefits when used for any kind of network traffic.

Q: What are the key features and benefits of the NCM specification?



NCM has two key features: First, it allows multiple Ethernet frames to be encapsulated in a single USB transfer...

This greatly reduces the overhead of processing high speed traffic, both on the embedded device and in the PC.  For LTE networks, the target downlink speed is about 100 megabits/second.  This translates to over 8,000 full-size Ethernet frames/second.  By combining multiple frames into a single transfer, we can greatly reduce the USB-level processing overhead (typically to less than 1,000 interrupts/second).



Secondly, the data formats were carefully chosen by industry experts to be optimal for use within wireless modems.  Such things as data alignment, padding, and transfer formats were chosen in such a way as to allow much less processing power to be used by the wireless modem for USB functionality than was possible with earlier specifications.   As a pleasing side-effect, we find that NCM implementations also take substantially less overhead on the PC as well.
 


Q: What's new with the NCM specification? What is the latest level of the spec?

A: After the first round of industry implementations had been completed, the NCM committee engaged in a substantial program of interoperabilty testing.  The experience arising from implementation and testing led us to issue errata to the NCM specification.  These errata were published earlier this month. The official version of the specification is "Revision 1.0 (Errata 1)", dated Nov 24, 2010.



Now the NCM committee has started a new work initiative, intended to lead to version 2.0 of the specification.  This initiative aims at two major enhancements.  First, the standard will be enhanced to transport IP packets directly as well as Ethernet frames.  This eliminates one level of encapsulation that is not needed for 4G networks.  Second, the committee is working on a common set of control operations, to allow NCM devices to be used more easily for "machine to machine" (M2M) or "Internet of Things" applications.

Q: What do you see as the future of this specification?



A: Based on the rapid adoption by the industry, it seems very likely that this will be one of the most important ways of connecting PCs to 4G networks.  Already, implementations are available for PCs from multiple vendors, and support has been incorporated into recent releases of Linux.  Our testing has revealed that the performance and interoperability goals have been met.  With development of NCM 2.0, and combined with HSIC USB, I think that the standard will be a leading candidate for the primary interconnect from wireless modems to embedded systems for M2M applications.



The group is also developing a test specification, which will serve as the base for future compliance tests.

Q:  Is the spec available for download?



A: The spec is available from the USB web site, on the published device class specifications page:  http://www.usb.org/developers/devclass_docs/NCM10_012011.zip