 equivalent to no more than 29 errored seconds during a 2-hr, one-way (loopback) test (Ref. 11). 6.12.3.3 Error Performance from a CCITT Perspective. The CCITT cornerstone for error performance is Rec. G.821 (Ref. 12). Here error performance objectives are based on a 64-kbps circuit-switched connection used for voice traffic or as a "bearer circuit" for data traffic. The CCITT error performance parameters are defined as follows (CCITT Rec. G.821): "The percentage of averaging periods each of time interval (0) during which the bit error rate (BER) exceeds a threshold value. The percentage is assessed over a much longer time interval T(L)." A suggested interval for T(L) is 1 month. It should be noted that total time (L) is broken down into two parts: 1. Time that the connection is available 2. Time that the connection is unavailable The following BERs and intervals are used in CCITT Rec. G.821 in the statement of objectives (Ref. 12): A BER of less than 1 x 10-6 for T(0) = 1 min A BER of less than 1 X 10 for T(0) = 1 sec Zero errors for T(0)=1sec Table 6.6 provides CCITT error performance objectives. 6.12.3.4 Jitter. Jitter was discussed in Section 6.9.2, where we stated that it was major digital transmission impairment. We also stated that jitter magnitude is a function of the number of regenerative repeaters there are in tandem. Guidelines on jitter objectives may be found in Ref. 15. 6.12.3.5 Slips 6.12.3.5.1 From a Bellcore Perspective. Slips, as a major digital network impairment, are explained in Section 6.12.2.1. When stratum-3 slip conditions are trouble-free, the 21 This is a long-term average over many days. Due to day-to-day variation, the number of burst errored seconds occurring on a particular day may be greater than the average. DIGITAL NETWORKS Table 6.6 CCITT Error Performance Objectives for International ISDN Connections Performance Classification Objective a Degraded minutes ,b Fewer than 10% of 1-min intervals to have a bit error ratio worse than 1 X 10-6 d b Severely errored seconds Fewer than 