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How the Frame Generator Works How Frames are Generated
14 Agilent 81250 ParBERT SONET/SDH Frame Generator, November 2002
See the following sections for more information:
• “SONET Section Overhead and SDH RS Overhead Details” on
page 18
This section describes how the section overhead is generated.
• “SONET Line Overhead and SDH MS Overhead Details” on page 17
This section describes how the line overhead and multiplexer
overhead are generated.
• “SONET Path Overhead and SDH HP Overhead Details” on page 16
This section describes how the path overhead is generated.
• “Payload Details” on page 15
The section describes how the payload is generated.
BIP Coding
The SONET specification calls for Bit Interleaved Parity (BIP) of error
monitoring. For the monitored section of signal, an error code is
defined so that all there is an even number of 1s in the X bits, counting
the monitored section and the error code. This is illustrated in the
following figure.
Figure 5 BIP-8 coding
To ensure that the signal is correctly transferred, the error code byte
of one frame is stored in a byte of the next frame. The receiver
compares the calculated parity with the byte stored in the next frame
to determine if the frame arrived correctly.
1 0 1 1 0 0 1 1
1 1 0 1 0 0 0 1
1 0 1 1 1 1 0 1
0 1 1 1 0 1 1 1
1 0 1 1 0 0 1 1
0 0 0 1 1 0 1 1
Error code
of frame
Even number
of 1s
X bits