hronous Transfer Mode (ATM) and High Level Data Link Control (HDLC). The process of contiguous concatenation allows larger bandwidth containers to be created by simply summing the bandwidth of X smaller Concatenation Contiguous Concatenated Payloads > 10 Gbit/s 9.6 Gbit/s 10 Gbit/s AUG-64 AU-4-64c VC-4-64c C-4-64c STM-64 2.4 Gbit/s 2.5 Gbit/s AUG-16 AU-4-16c VC-4-16c C-4-16c STM-16 622 Mbit/s 600 Mbit/s AU-4-4c AUG-4 VC-4-4c C-4-4c STM-4 140 Mbit/s 155 Mbit/s STM-1 AUG-1 Interfaces 34 Mbit/s TUG-3 44 Mbit/s 6 Mbit/s TUG-2 2 Mbit/s Pointer processing TU-12 VC-12 Multiplexing Aligning 1.5 Mbit/s Mapping TU-11 VC-11 Fig. 11.1 SDH extended multiplex structures allowing contiguous concatenation. X.260 X + 1 X.261 C-4-Xc C-4-Xc Overhead (X = 4, 16, 64, 256) Bytes (X = 4, 16, 64, 256) 125 us 125 us C-4-Xc VC-4-Xc Fig. 11.2 Contiguous-concatenation frame structure for VC-4-Xc. containers (C-n); the result is a contiguous concatenated payload container referred to as a C-n-Xc. ITU-T recommendation G.707 has defined X to be limited to orders of four (i.e., X = 4, 16, 64, 256) (see Figure 11.1). For the transport of a C-n-Xc between two endpoints, the intermediate network elements in the transport network must not split the concatenated container into smaller pieces. Each network element must therefore have concatenated payload functionality. Figure 11.2 illustrates the frame structure of a contiguous payload container, VC-4-Xc, in a typical SDH matrix format. The repeated frame every 125 us consists of nine rows and X X 261 columns in which each cell contains a single byte. The VC-4-Xc is constructed by byte-interleaving (v.) the X individual VC-4s such that the columns containing the Chapter 11 Next Generation Synchronous Digital Hierarchy STM-16 0: A to D: 8 X VC-4 B to E: 8 X VC-4 t=T: A to D: Release 2 X VC-4 B to E: Release 3 X VC-4 Five Available VC-4s, But Unusable t=T2: C to F: Request a VC-4-4c ("stranded") for Concatenated FAIL! Bandwidth Requests Fig. 11.3 Example of a fragmentation problem with contiguous conca