XRT75VL00D datasheet(59/92 Pages) EXAR

59 / 92 page

XRT75VL00D

REV. 1.0.3

E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

In general, the role/purpose of the POH bytes is to fulfill the following functions.

• To support error detection within the STS-1 SPE

• To support the transmission of various alarm conditions such as RDI-P (Path - Remote Defect Indicator) and

REI-P (Path - Remote Error Indicator)

• To support the transmission and reception of "Path Trace" Messages

The role of the POH bytes is beyond the scope of this data sheet and will not be discussed any further.

9.2.1.2

Mapping DS3 data into an STS-1 SPE

Now that we have defined the STS-1 SPE, we can now describe how a DS3 signal is mapped into an STS-1

SPE. As mentioned above, the STS-1 SPE is basically an 87 byte column x 9 row structure of data. The very

first byte column (e.g., in all 9 bytes) consists of the POH (Path Overhead) bytes. All of the remaining bytes

within the STS-1 SPE is simply referred to as "user" or "payload" data because this is the portion of the STS-1

signal that is used to transport "user data" from one end of the SONET network to the other. Telcordia GR-253-

CORE specifies the approach that one must use to asynchronously map DS3 data into an STS-1 SPE. In

short, this approach is presented below in Figure 36.

FIGURE 35. ILLUSTRATION OF THE BYTE STRUCTURE OF THE STS-1 SPE

Payload (or User) Data

86 Bytes

1 Byte

87 Bytes

9 Rows

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