bittikoodauksen

Bittikoodaus, also known as bit encoding or bit stuffing, is a technique used in digital communication and data storage to ensure reliable transmission of data. The primary purpose of bittikoodaus is to prevent the occurrence of long sequences of identical bits, such as all zeros or all ones, which can cause synchronization issues for receivers.

In many digital systems, the clock signal is recovered from the data stream itself. If there are long strings of identical bits, the receiver's clock can drift, leading to errors in decoding the data. Bittikoodaus modifies the data stream by inserting special patterns or altering existing bits to guarantee a sufficient number of transitions (changes from 0 to 1 or 1 to 0) within a given period.

One common example of bittikoodaus is found in High-Level Data Link Control (HDLC) protocols. In HDLC, a flag sequence of 01111110 is used to delineate the start and end of a frame. To avoid confusion if this flag sequence accidentally appears within the data itself, a zero bit is inserted after every five consecutive one bits in the data stream. When the receiver encounters five consecutive one bits, it checks the next bit. If it's a zero, it removes it. If it's a one, it indicates the start of a flag sequence.

Another method, like Manchester encoding, achieves synchronization by ensuring that every bit period contains a transition. In Manchester encoding, a '1' might be represented by a high-to-low transition in the middle of the bit period, and a '0' by a low-to-high transition. This guarantees at least one transition per bit, regardless of the data pattern.

The specific method of bittikoodaus employed depends on the requirements of the communication system or storage medium, balancing the need for synchronization with the overhead introduced by the encoding process.