Specifies the pattern to be sent during a loopback test. allZeroes(1) is most often used to verify B8ZS line encoding. allOnes(2) is most often used to measure signal power. oneZeroOne(3) alternates ones and zeroes. It is most often used to test bridge taps. oneIn5(4) is the pattern '00001', to send a remote loopback request. oneIn8(5) is the pattern '00000001', used to test repeater timing recovery. threeIn24(6) is 21 zeroes followed by 3 ones, used to test the ones density tolerance in AMI coded lines. qrs(7) is a quasi-random signal approximating live data. It is also available in repeating patterns of 511 or 2047 bits. none means no pattern; used for response.