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V D IF

VLBI Data Interchange Format
Alan Whitney, Chris Phillips, Sekido Mamoru, Mark Kettenis


Scope


VDIF is intended as a VLBI data interchange format usable for both real-time e-VLBI and non-real time data file formats Data are assumed to be uniformly time sampled.




Requirements










Data is self-identifying via time tag and data identification. Data may be discontinuous in time. Data may be single-channel or multichannel. Data may be single bit or multi-bit. The number of channels should be flexible (not necessarily 2n. Minimize conversion for different data transfer techniques. Suitable for data rates up to 100Gbit/s.


Data Frames (1)










Each frame has a 16-byte header followed by a data array of userspecified length. Data frame length for a single "stream" is constant for a particular scan. Data frame length should be a multiple of 8 bytes. Data frames per second must be an integer. Data frame cannot "cross" second boundary.


Data Frames (2)
Two choices: Data array contains bits for a single c hannel
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Multiple channels in different "streams" Preferred for new equipment/apps.

Data array contains bits for multiple channels
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Multiple channels in a single "stream" Avoid corner turning for legacy equipment


Data Frames (3)


Layout still under discussion: Time (seconds since 00UT 1 Jan 1990) Stream ID Invalid marker Frame # within second # channels Bits/sample Frame length Station ID (two letter code)