CRC-based framing
CRC-based framing is a kind of frame synchronization used in Asynchronous Transfer Mode (ATM) and other similar protocols.
The concept of CRC-based framing was developed by StrataCom, Inc. in order to improve the efficiency of a pre-standard Asynchronous Transfer Mode (ATM) link protocol. This technology was ultimately used in the principal link protocols of ATM itself and was one of the most significant developments of StrataCom. An advanced version of CRC-based framing was used in the ITU-T SG15 G.7041 Generic Framing Procedure (GFP), which itself is used in several packet link protocols.
The method of CRC-Based framing re-uses the header cyclic redundancy check (CRC), which is present in ATM and other similar protocols, to provide framing on the link with no additional overhead. In ATM, this field is known as the Header Error Control/Check (HEC) field. It consists of the remainder of the division of the 32 bits of the header (taken as the coefficients of a polynomial over the field with two elements) by the polynomial . The pattern 01010101 is XORed with the 8-bit remainder before being inserted in the last octet of the header.
Constantly checked as data is transmitted, this scheme is able to correct single-bit errors and detect many multiple-bit errors. For a tutorial and an example of computing the CRC see mathematics of cyclic redundancy checks.
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