SDH signal hierarchy
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This section describes the basics of the SDH hierarchy.
STM-1 Frame
The SDH signal hierarchy is based on a basic “building block” frame called the
Synchronous Transport Module 1 (STM-1), as shown in “SDH STM-1 frame” (p. A-5).
The STM-1 frame has a rate of 8000 frames per second and a duration of 125
microseconds
The STM-1 frame consists of 270 columns and 9 rows.
Each cell in the matrix represents an 8-bit byte.
Transmitting Signals
The STM-1 frame (STM = Synchronous Transport Module) is transmitted serially
starting from the left with row 1 column 1 through column 270, then row 2 column 1
through 270, continuing on, row-by-row, until all 2430 bytes (9x270) of the STM-1
frame have been transmitted. Because each STM-1 frame consists of 2430 bytes and
each byte has 8 bits, the frame contains 19440 bits a frame. There are 8000 STM-1
frames a second, at the STM-1 signal rate of 155.520.000 (19440 x 8000) kbit/s.
Three higher bit rates are also defined:
• 622.080 Mbit/s (STM-4)
• 2488.320 Mbit/s (STM-16)
• 9953.280 Mbit/s (STM-64)
• 39813.120 Mbit/s (STM-256)
The bit rates of the higher order hierarchy levels are integer multiples of the STM-1
transmission rate.
An SDH overview
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A-4
Alcatel-Lucent - Proprietary
See notice on first page
365-312-801R7.2
Issue 3, May 2007
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