0.2% of 1-s intervals to have a bit error ratio worse than 1 X 10-3 C Errored seconds Fewer than 8% of 1-s intervals to have any errors (equivalent to 92% error-free seconds) The terms degraded minutes, severely errored seconds, and errored seconds are used as a convenient and concise performance objective "identifier." Their usage is not intended to imply the acceptability, or otherwise, of this level of performance. The 1-min intervals mentioned in the table and in the notes are derived by removing unavailable time and severely errored seconds from the total time and then consecutively grouping the remaining seconds into blocks of 60. The basic 1-sec intervals are derived from a fixed time pattern. 'The time interval T(L), over which the percentages are to be assessed, has not been specified since the period may depend on the application. A period of the order of any one month is suggested as a reference. For practical reasons, at 64 kbps, a minute containing four errors (equivalent to an error ratio of 1.04 X 10-6) is not considered degraded. However, this does not imply relaxation of the error ratio objective of 1 X 10-6. Source: CCITT Rec. G.821 (Ref. 12). nominal clock slip rate is 0. If there is trouble with the primary reference, a maximum of one slip on any trunk will result from a switched reference or any other rearrangement. If there is a loss of all references, the maximum slip rate is 255 slips the first day for any trunk. This occurs when the stratum-3 clocks drift a maximum of 0.37 parts per million from their reference frequency (Ref. 13). 6.12.3.5.2 From a CCITT Perspective. With plesiochronous operation, the number of slips on international links will be governed by the sizes of buffer stores and the accuracies and stabilities of the interconnecting national clocks. 22 The end-to-end performance should satisfy the service requirements for telephone and nontelephone services on a 64-kbps digital connection in an ISDN. The slip rate objectives for an international end-to-end connection are specif