Example: NASA Deep Space Network Network packet

1 example: nasa deep space network

1.1 ccsds packet definition
1.2 telecom processing notes
1.3 handling data loss

example: nasa deep space network

the consultative committee space data systems (ccsds) packet telemetry standard defines protocol used transmission of spacecraft instrument data on deep-space channel. under standard, image or other data sent spacecraft instrument transmitted using 1 or more packets.

ccsds packet definition

a packet block of data length can vary between successive packets, ranging 7 65,542 bytes, including packet header.

packetized data transmitted via frames, fixed-length data blocks. size of frame, including frame header , control information, can range 2048 bytes.
packet sizes fixed during development phase.

because packet lengths variable frame lengths fixed, packet boundaries not coincide frame boundaries.

telecom processing notes

data in frame typically protected channel errors error-correcting codes.

even when channel errors exceed correction capability of error-correcting code, presence of errors detected error-correcting code or separate error-detecting code.
frames uncorrectable errors detected marked undecodable , typically deleted.

handling data loss

deleted undecodable whole frames principal type of data loss affects compressed data sets. in general, there little gain attempting use compressed data frame marked undecodable.

when errors present in frame, bits of subband pixels decoded before first bit error remain intact, subsequent decoded bits in segment corrupted; single bit error disruptive many bit errors.
furthermore, compressed data protected powerful, long-blocklength error-correcting codes, types of codes yield substantial fractions of bit errors throughout frames undecodable.

thus, frames detected errors unusable if not deleted frame processor.

this data loss can compensated following mechanisms.

if erroneous frame escapes detection, decompressor blindly use frame data if reliable, whereas in case of detected erroneous frames, decompressor can base reconstruction on incomplete, not misleading, data.
however, extremely rare erroneous frame go undetected.
for frames coded ccsds reed–solomon code, fewer 1 in 40,000 erroneous frames can escape detection.
all frames not employing reed–solomon code use cyclic redundancy check (crc) error-detecting code, has undetected frame-error rate of less 1 in 32,000.