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The link layer check of telegram format B is performed on a maximum of 128 bytes, including the CRC field. Telegrams with a length of up to 128 bytes, including CRC and L field, contain a single CRC field covering both the first and the second block. Telegrams with a length between 131 bytes and 256 bytes (maximum length) contain two CRC fields, with the second CRC field covering the optional block. The format of the different blocks in the telegram is defined below.