Q:

What does it stand for in bit operations?

What do those lines of code stand for?
payloadType = header[1] & 127;
sequenceNumber = unsigned_int(header[3]) + 256*unsigned_int(header[2]);
timeStamp = unsigned_int(header[7])
               + unsigned_int(header[6])
               + 65536*unsigned_int(header[5])
               + 16777216*unsigned_int(header[4]);

Where header is a byte[12] and the method unisigned_int is this:
private int unsigned_int(byte b) {
    if(b >= 0) {
        return b;
    }
    else {
        return 256 + b;
    }
}

Thank you for answering!

A:

 payloadType = header[1] & 127;

Strip the sign bit off header 1 / get bottom 7 bits
sequenceNumber = unsigned_int(header[3]) + 256*unsigned_int(header[2]);

extract a 16 bit value from the header
 timeStamp = unsigned_int(header[7])
           + unsigned_int(header[6])
           + 65536*unsigned_int(header[5])
           + 16777216*unsigned_int(header[4]);

extract a 32 bit value from the header. With the bug as observed by Mark Byers.
private int unsigned_int(byte b) {
     if(b >= 0) {
         return b;
     }
     else {
         return 256 + b;
     }
}

convert an integer from -128 to 127 (i.e. a byte) into a 8 bit unsigned int represented as an integer. Equivalent to
 return b & 255

