Stm-Rr Frame Structure (Sub Stm-1); Administrative Unit; Tributary Units And Their Structure - Siemens SRA 4 User Manual

1 - PRELIMINARY INFORMATION
1.4.1.6
Fig. 1.7
1.4.1.7
1.4.1.8
1-18

STM-RR frame structure (Sub STM-1)

Fig. 1.7 shows the frame structure of an STM-RR signal. A frame comprises 9 lines,
each one containing 96 bytes. Each byte consists of 8 bits. the transmitted capacity is
equal to 55,296 Mbit/s.
STM-RR frame structure
9
3
RSOH
1 AU3 PTR
5
MSOH
AU-3 Administrative unit
The 21x2 or 34 Mbit/s plesiochrone interface maps the payload in an AU-3; an AU-3 only
is inserted in the STM-RR frame.
The STM-1 synchronous interface comprises an input section and an output section.
The input section receives an STM-1 structure (standard AU-4), converts the AU-4
mapping in 3xAU-3 and only one, out of the three AU-3, is transmitted to the modulator.
The output section receives from demodulator the STM-RR frame AU-3 mapped,
convert if in AU-4 by inserting all "1" in the two missing TUG-3
Then, it returns an STM-1 frame with an useful payload of 1/3 of the capacity.

Tributary units and their structure

The container of the VC-4 can be loaded either with a single signal, such as in the case
of a 140 Mbit/s tributary, or with various signals with lower transport capacity, called
tributary units (TU). These units contain a field (payload), which is divided in address
time cells where the payload signal to be transported can be loaded, together with a
pointer which indicates the starting point.
As shown in Fig. 1.1, the ETSI scheme foresees three types of tributary units: TU-3,
TU-2, and TU-12.
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SRA 4 - 6/7/8/10/11/13 GHz (WB ODU) - UMN
911-381/02C0000 - Issue 3, July 2004
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