ica- tions channel that operates at 192 kbits/s, which provides an OAM&P capability between section terminating equipment. Line Overhead Bytes The line overhead consists of six rows, each con- taining 3 bytes, for a total of 18 bytes per STS-1 frame. The first row in the section overhead, which is row 4 in Figure 6.7, contains the previous- ly described H1, H2, and H3 bytes. The first byte in the second row of the line overhead section, which is shown as row 5 in Figure 6.7, is the B2 byte. This byte functions in essen- tially the same way as the B1 byte; however, it provides an error perfor- mance monitoring capability at the line layer instead of the section layer. Continuing on the second row of the line overhead section, the B2 byte is followed by the K1 and K2 bytes. The K1 and K2 bytes provide the capa- bility to rearrange a SONET ring as well as to detect the alarm indication signal (AIS) and the remote detection indication (RDI) signal. These 2 bytes are referred to as the automatic protection switching (APS) bytes. Fiber in the WAN The third through fifth rows in the line overhead area, which equate to rows 6 through 8 in Figure 6.7, contain the bytes labeled D4 through D12. These nine bytes provide a 576-kbit/s data transmission rate for OAM&P use. The last row in the line overhead area contains 3 bytes labeled S1, M0, and E1. The S1 byte represents a synchronization status byte. Four bits in this byte (bits 5 through 8) are used to transport the synchronization status of the network element. The following byte, which is labeled MO, represents a line remote error indication (REI) byte. If a receiver receives a corrupted signal, it will set the MO byte to indicate the occurrence of this situation. Last but not least, the E2 byte represents the last or final line overhead byte. This byte provides a voice channel that can be used by technicians and represents a 64-kbit/s order wire byte. As this is a voice PCM channel, this byte is ignored as it passes through regenerators. Path Overhead Bytes In concludin