ive stuff: invert 5 D-bits Positive stuff: invert 5-Ibits Figure 19.10 STS payload pointer (H1, H2) coding. ADVANCED BROADBAND DIGITAL TRANSPORT FORMATS Section Section Section Section Sonet Sonet signals Multiplexer Demultiplexer signals Terminal Regenerator Regenerator Regenerator Terminal Sonet Assembly Cross-section Disassembly Figure 19.11 SONET section, line and path definitions. An orderwire for network operator communications between path equipment (octet F2). Facilities to support and maintain the transport of the SPE between adjacent nodes are provided by the line and section overhead. These two overhead groups share the first three columns of the STS-1 frame (see Figure 19.1). The SOH occupies the top three rows (total of 9 octets) and the LOH occupies the bottom 6 rows (18 octets). The line overhead functions include: Payload pointer (octets H1, H2, and H3) (each STS-1 in an STS-N frame has its own payload pointer). Automatic protection switching control (octets K1 and K2). BIP parity check (octet B2). 576-kbps data channel (octets D4 through D12). Express orderwire (octet E2). A section is defined in Figure 19.11. Among the section overhead functions are: Frame alignment pattern (octets A1, A2). STS-1 identification (octet C1): a binary number corresponding to the order of appearance in the STS-N frame, which can be used in the framing and deinter-leaving process to determine the position of other signals. BIP-8 parity check (octet B1): section error monitoring. Data communications channel (octets D1, D2, and D3). Local orderwire channel (octet E1). User channel (octet F1). 19.2.2.7 The SPE Assembly/Disassembly Process. Payload mapping is the pro- cess of assembling a tributary signal into an SPE. It is fundamental to SONET operation. The payload capacity provided for each individual tributary signal is always slightly greater than that required by the tributary signal. The mapping process, in essence, is to synchronize the tributary signal with the payload capacity. This is achieved by adding stuffi