1 frame = 6480 bits = 810 bytes

Frame 1

Frame 2

• • •

Frame 8000

-SONET transmits 8000 frames/sec-

-SONET transmits 8000 frames/sec-

Fig. 10.16. Frame format STS-1 signal.

Each STS-1 frame is made up of 9 rows and 90 columns bytes. Thus the frame size is 9 x 90 = 810 bytes or 810 octets or 810 x 8 bits = 6480 bits. A frame is 125 | sec in duration, corresponding to the 8 kHz voice sample. This gives the STS—1data rate 51.84 Mbps (i.e. 8000 frames/sec = 8000 x 6480 bits/sec = 51.84 Mbps).

The upper three rows of the first three columns are used for section overhead (SOH). The lower six rows of first three columns are used for line overhead (LOH). This first three columns of the frame are used as a transport overhead. Column 4 to 90 are used for SPE. of 87, columns of SPE, one column is used for path overhead POH (usually the first column). The path load modules end-to-end tracking information. The STS-1 frame is transmitted left to right, top to bottom.

Section over head (SOH). It contains information about frame synchronization (informing the destination of an incoming frame), carries information about OAM, handles frame alignment, and separates data from voice. SOH contains 9 bytes of the transport overhead accessed, generated and processed by section terminating equipment.

Fig. 10.17 (a) shows the section overhead.

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