Downloaded from https://www.everyspec.com ADS-79D-HDBK L.5.4 Data Transmission. Data corruption and loss may occur during transmission; therefore, the design should incorporate the necessary precautions to ensure data integrity during aircraft onboard and off-board data transmittal. This, for example, will range from EMI shielding of cables used to transmit analog data to procedures for ensuring the integrity of digital information transmitted over a data bus. Digital transmission procedures will range from the use of embedded checksums to the use of error correcting codes for recovering corrupted data.
Check-sum digital hash signatures can be generated using accepted algorithms such as MD5, CRC, SHA-1, etc. Unrecoverable data lost in the course of transmission may be resolved with protocols such as automatic re-transmission and transmit/receive handshaking. Built-in Windows OS testing utilities for file comparisons include the DOS commands: fc, comp, cksum, diff, shasum, and dir for byte comparisons as common data integrity checks. In addition to physical ‗line noise‘, other possible transmission errors include factors affecting completeness of TCP/IP session errors 404 (string to long), 403 (missing data), and time-outs for large files particularly.
Data chunking and compression are one way to reduce time-out errors. Common checks for transmission errors include header checksums, end-of-file (EOF) markers and byte-alignment checks as described in checksum algorithms. L.5.5 Data Storage. Data corruption and loss may occur during storage; therefore, the design should incorporate the necessary precautions to ensure data integrity during aircraft onboard and off-board storage. Typical corruption scenarios include unsafe partitioning of storage media or use of multiple-version dissimilar software. Built-in Windows OS testing utilities for file comparisons include the DOS commands:
fc, comp, cksum, diff, shasum, and dir for byte comparisons as common data integrity checks. In addition, the design should incorporate proper database administration (DBA) procedures and policies to ensure stored data integrity. These procedures should include the use of routine system-wide data backups performed by the database administrator to prevent catastrophic data loss. Many different techniques have been developed to optimize the backup procedure. These include optimizations for dealing with open files and live data sources as well as compression, encryption, backup file rotation and de-duplication, among others.
An incremental backup copies everything that has changed since the last backup (full, differential or incremental). While magnetic tape has long been the most commonly used backup media, hard disks including RAID configurations, optical storage and geographically distributed remote storage are also flexible options for managing data recovery. It should be noted that while data backup is one of the most valuable integrity tools, it has limitations related to cost (hardware, software, and labor), performance (particularly for encryption, compression and indexing) and bandwidth-limited network transfers.
Also, the database administrator should perform routine maintenance using a set of database consistency check (DBCC) queries. These queries will include relational integrity checks that identify and fix orphaned records, confirm known record counts within tables, and identify and resolve the existence of multiple primary keys within damaged tables. 230