ows: An Out of Frame event is declared when the receiver detects two or more framing-bit errors within a 3 millisecond period, or two or more errors out of five or less consecutive framing-bits. At this time, the framer enters the Out of Frame State, and starts searching for a correct framing pattern. The Out of Frame state ends when reframe occurs. Bipolar Violation (BPV) A bipolar violation occurs when two mark signals (ones) occur in sequence with the same polarity. DS1 signaling specifies that each mark must be the opposite polarity of the one preceding it. When two marks occur with the same polarity (when not part of a B8ZS substitution), this is considered an error. Excessive BPVs will put the station into alarm. BPVs are described in RFC 1232 as follows: A Bipolar Violation, for B8ZS-coded signals, is the occurrence of a received bipolar violation that is not part of a zero-substitution code. It also includes other error patterns such as: eight or more consecutive zeros and incorrect parity. Performance Monitoring CRC6 is the Cyclic Redundancy Check (6-bit) mechanism for error checking in ESF. This error is a result of ESF reporting data integrity problems. CRC6 events are not described in RFC 1232. Errored Seconds (ES) Errored Seconds (ES) is a counter showing the number of seconds in a 15-minute interval during which errors have occurred. This counter provides a quick way to see whether there are problems. It also offers an indication of how "dirty" a T1 might be. If the number is high, there is a consistent problem. If it is low, there is probably a short-term (possibly repetitive) or intermittent problem. Errored seconds are usually incremented when one or more errors occur in the span of one second. Errored seconds are described in RFC 1232 as follows: An Errored Second is a second with one or more Code Violation Error Events OR one or more Out of Frame events. In D4 and G.704 section 2.1.3.2 (eg, G.704 which does not implement the CRC), the presence of Bipolar Violations also triggers an Errored Seco