XRT75R12D_07 Datasheet, PDF (96/133 Pages) Exar Corporation – TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET

XRT75R12D
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER REV. 1.0.3
FIGURE 40. THE BYTE-FORMAT OF THE TOH WITHIN AN STS-1 FRAME
9 Rows
3 Byte Columns
87 Byte Columns
AA11 AA22 CC11
BB11 EE11 FF11
DD11 DD22 DD33
HH11 HH22 HH33
BB22 KK11 KK22
DD44 DD55 DD66
DD77 DD88 DD99
DD1100 DD1111 DD1122
SS11 MM00 EE22
EEnnvveellooppeeCCaappaacciittyy
BByytteess
The TOH Bytes
In general, the role/purpose of the TOH bytes is to fulfill the following functions.
• To support STS-1 Frame Synchronization
• To support Error Detection within the STS-1 frame
• To support the transmission of various alarm conditions such as RDI-L (Line - Remote Defect Indicator) and
REI-L (Line - Remote Error Indicator)
• To support the Transmission and Reception of "Section Trace" Messages
• To support the Transmission and Reception of OAM&P Messages via the DCC Bytes (Data Communication
Channel bytes - D1 through D12 byte)
The roles of most of the TOH bytes is beyond the scope of this Data Sheet and will not be discussed any
further. However, there are a three TOH bytes that are important from the stand-point of this data sheet, and
will discussed in considerable detail throughout this document. These are the H1 and H2 (e.g., the SPE
Pointer) bytes and the H3 (e.g., the Pointer Action) byte.
Figure 41 presents an illustration of the Byte-Format of the TOH within an STS-1 Frame, with the H1, H2 and
H3 bytes highlighted.
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