A blocking probability of B = 0.01 is the quality of service (QoS) objective. With judicious use of alternative routing, a blocking probability of 0.005 might be expected. 6.12.3.2 Error Performance from a Telcordia Perspective Definitions BER The BER is the ratio of the number of bits in error to the total number of bits transmitted during a measurement period. Errored Seconds (ES) An errored second is any 1-sec interval containing at least one error. Burst Errored Seconds A burst errored second is any errored second containing at least 100 errors. 1. The BER at the interface levels DSX-1, DSX-1C, DSX-2, and DSX-3 shall be less than 2 X 10-10. excluding all burst errored seconds in the measurement period. During a burst errored second, neither the number of bit errors nor number of bits is counted. This requirement applies in a normal operating environment, and it shall be met by every channel in each protection switching section. 20 DSX means digital system cross-connect. 6.12 DIGITAL NETWORK 2. The frequency of burst errored seconds, other than those caused by protection switching induced by hard equipment failures, shall average no more than four per day at each of the interface levels DSX-1, DSX-1C, DSX-2, and DSX-3. 21 This requirement applies in a normal operating environment and must be met by every channel in each protection switching system. 3. For systems interfacing at the DS1 level, the long-term percentage of errored sec- onds (measured at the DS1 rate) shall not exceed 0.04%. This is equivalent to 99.96% error-free seconds (EFS). This requirement applies in a normal operating environment and is also an acceptance criterion. It is equivalent to no more than 10 errored seconds during a 7-hr, one-way (loopback) test. 4. For systems interfacing at the DS3 level, the long-term percentage of errored seconds (measured at the DS3 rate) shall not exceed 0.4%. This is equivalent to 99.6% error- free seconds. This requirement applies in a normal operating environment and is also an acceptance criterion. It is