Home WTI User's Guides
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1. Introduction
2. Binary Block Read Mode and Structure
2.1. Compressed Binary Block Read Sequence
2.2. Compressed Binary Block Structure
2.2.1. Data Block Structure
2.2.2. Record String Structure
3. Compression Decompression Methods
3.1. Table Decompression
3.1.1. Nibble Positioning
3.1.2. Record String Format
3.1.2.1. Data Decompression Considerations
3.1.3. Table Decompression Example
3.2. Space Compression
4. DLE Stuffing
5. The Cyclic Redundancy Check Option
5.1. Calculation
6. Other Binary Read Commands
6.1. Continuous Binary Block Read
6.2. Send Binary Information Block
7. Customer Service
PollCat NetLink B

3.1.2. Record String Format

 

Compressed call records are always stored in "Record Strings", using whole numbers of bytes. This means there is always an even number of nibbles in the compressed data string. If an odd number of nibbles is used to represent the original call record, the left over nibble (the MSN of the last byte) is ignored.

Each Record String is made up of a three byte Record Header and a number of data bytes (see Section 2.2.2). The three byte header contains information needed to decompress the data string. The Record Header is discussed again here to clarify the decompression process.

1                     Offset Byte: A binary count of the number of bytes in the Record String, including the Record Header. It can therefore be used as an offset to the next record or as a count (Offset -3) of the number of bytes following the header used to represent the original data.

2                     Mode Byte: Certain bits in this byte are used to determine if data has been table or space compressed (see Section 2.2.2). If bit two is not set, then the data was not table compressed and the bytes following the record header are the original data bytes (with possible exception of space compressed characters which are explained in Section 3.2).

3                     Character Count Byte: This byte contains the number of characters in the data string before either space or table compression. In other words, this byte is a binary count of the number of characters in the original record as it was received, plus the time/data stamp characters if the option was enabled at storage time.