Recording in a Networked World
At the heart of many networked Flight Test Instrumentation systems is a Network Recorder. The high data rates up to Gigabit speeds achievable in networked FTI systems put increased demands on the Network Recorder to support ever faster read and write rates. However, thanks to the developments in CompactFlash and SATA technologies, such recording rates are achievable. The primary challenge is to ensure that the recorder is designed to overcome any bottlenecks writing to and reading from the memory media whilst also optimizing memory capacity usage and minimizing data loss on power outages.
The key to the performance and success of meeting high data rate recording speeds, particularly for Gigabit environments, is the format in which the data is recorded. Utilizing a simple lightweight network-centric recording file format, such as Packet CAPture (PCAP), vastly reduces the per-packet processing overhead so as to enable fast writing to the recording media. For given applications there may be multiple recorders dedicated to recording certain subsets of data, for example, there may be a dedicated video recorder, a dedicated PCM over IP (PCMoIP) recorder, and another recorder used for all other data. To satisfy requirement the recorder uses filters to enable the user to configure and control what is recorded.
Although recording is the primary function of the Network Recorder, it is also necessary to design the recorder for fast retrieval of the data from the media supporting read-after and read-while write functionality particularly as FTI networks move towards higher data rates and the SATA SSDs support ever increasing recording capacities. Given that the recorder may have Terabytes of data recorded over months of testing, the challenge of data mining from the recorder is not trivial. First, there is the data mining requesting protocols that are used to allow the user to specify their read-after or read-while write data mining requirements. Once the recorder has parsed the data mining request, the recorder must then retrieve the data in question. One solution is to use indexing techniques to provide fast internal memory address pointers to key locations, events, and times on the recording media.