Hi Max and others, It seems, I faced similar problem while working on the libosmocoding. Despite the bursts_test in OsmoBTS always pass without any errors, when I merely moved some parts of GSM 05.03 code into a separate library, this test sometimes passes and fails on different machines... Thanks to tnt, who suggested me to use valgrind. Using this great tool and some tricks with memset(), I found, that the gsm0503_tch_burst_map() uses one uninitialized bit from the iB within the tch_hr_encode(). The same things happens in the tch_hr_decode(). I don't know, is it gsm0503_tch_hr_(de)interleave's bug or gsm0503_tch_burst_(un)map's one, we need to check GSM 05.03 specifications. With best regards, Vadim Yanitskiy.