SDH Hierarchy

Before the advent of SDH, the hierarchy of digital signal multiplexer to America / Canada, Japan and Europe differ as stated in Table 1. With the SDH hierarchy becomes uniform as shown in Figure 1.
 

Tabel 1. Hirarki sinyal digital di Amerika, Jepang dan Eropa

Level hirarki ke:	Amerika/kanada (Mbps)	Jepang (Mbps)	Eropa (Mbps)
1 2 3 4 5	1,544 6,312 44,736 274,176 -	1,544 6,312 32,064 97,728 397,200	2,048 2,442 34,368 139,264 560,840

Dari Gambar 1 tersebut terlihat bahwa pada level atau tingkat yang paling tinggi, SDH transport network is a network nx STM-1 (nx 155 Mbps).

STM-1 (Synchronous Transport Module) is a synchronous transport module level-1. A single frame of STM-1 is expressed by a matrix consisting of nine rows and 270 columns. These frames are formed of 2430 bytes, each byte consists of 8 bits. STM-1 frame contains two parts, the SOH (Section Overhead) and the VC (Virtual Container) which is its payload. Figure 2 states STM-1 frame structure, Figure 3 states the structure of his VC,sedang Gambar 4 menyatakan alokasi byte pada SOH.
SOH provides information between the two LTE (Line Terminating Equipment) of frame alignment, monitoring the BER (Bit Error Rate) and the transfer of information between the two LTE and so on. While the VC is used for transporting signals its tributary (individual input signals are fed to the multiplexer) through a pathway. Each VC consists of a POH (Path Overhead) and a
Container. POH seperti tercantum dalam Gambar 2 carry information between the points and disasembly asembly as parity checks, labeling channels, alarm monitoring, and performance monitoring. A container carrying tributary signals, is a pointer showing the location of the first bit her on the VC.