XRT75L03D Datasheet, PDF (101/134 Pages) Exar Corporation – THREE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

áç
XRT75L03D
THREE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER REV. 1.0.0
FIGURE 35. ILLUSTRATION OF THE BYTE STRUCTURE OF THE STS-1 SPE
1 Byte
J1
B3
C2
G1
9 Rows
F2
H4
Z3
Z4
Z5
87 Bytes
86 Bytes
Payload (or User) Data
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.
96